Auburn University Digital Library
|
small (250x250 max)
medium (500x500 max)
Large
Extra Large
large ( > 500x500)
Full Resolution
|
|
! [ LJ 7' ' / ./fJ g 7-ll (2. .. : l / Ji-lt- ~ },...------..,.,...,, l /:~ , ~ > ~.:- \ t 4'•, \ . 9 -· - ..--...., i ~;:-0 '- Auburn University Libraries 1111111 lllll lllll lllll ll/11l l/1111111II IIII IIIII IIIII IIII II/II IIIII /IIIII IIII III 3 1 706 025 85049 1 File D 52.83/38 AIR SERVICE INFORMATION CIRCULAR (AEROSTATION ) Vol. I ( . CONDENSATION OF WATER FROM ENGINE EXHAUST FOR AIRSHIP BALLASTING By Mr. Robert F. Kohr Bureau of Standards Washington, D. C. WASHINGTON GOVERNMENT PRINTING OFFICE 1924 CERTIFICATE: By direction of the Secretary of War the matter contained herein is published as administrative information and is required for the proper transaction of the public business. (n) V ·CONDENSATION OF WATER FROM ENGINE EXHAUST FOR AIRSHIP BALLASTING PART !.- GENERAL INTRODUCTION The maintenance of a constant total lift in lighterthan- air craft falls naturally into two distinct divisions: (1) Recovery of ballast as the consumption of fuel tends to lighten the ship. (2) Control of the temperature and thus the density of the lifting gas in order to compensate for changes of lift due to changes of atmospheric density or superheating of the lifting gas by solar radiation upon the envelope. The problem is of great significance when helium - is us~d as a lifting gas. It is generally conceded by those familiar with the operation of airships that valving of lifting gas must be nearly eliminated before a gas so rare and expensive as helium can be adopted for general use. Inasmuch as the known worlct supply of helium is largely found in this country, it constitutes a national monopoly for military use, and its conservation is therefore imperative. In long flights both phases of the ballasting problem assume considerable importance, but, of the two, the ballast recovery appears to be the more vital. Although the development of both projects was for a time carried on along parallel lines, · it was thought advisable to postpone all work on temperature control until ballast recovery reached a point where satisfactory apparatus was available. This paper, therefore, deals only with the work on ·ballast recovery apparatus. The desirability of making up ballast during flight at a ra.te equivalent by weight to the fuel consumption has been realized since the beginning of airship navigation. A number of means of maintaining equilibr~um have been proposed, including the absorption of water vapor from the air by hygroscopic substances, compression of the lifting gas into rigid containers, and condensation of the water vapor which forms a part of the engine exhaust gas. The first of these proposals seems impracticable on account of the small quantity of water vapor present in the air under · ordinary flying conditions (about 0.0005 pound per cubic foot) and the immense exposed area which would be required. The second method is eliminated by the great weight of compressing machinery and high-pressure gas containers. The recovery of water of combustion from engine exhaust gas by cooling and condensation, however, is feasible as a method for the solution o( the problem. When the usual gasoline fuel is .used , about 1.4 pounds of water vapor is formed for each pound of fuel burned. This affords an ample margin for inefficiency in the process of cooling the gas and separating the entrained moisture, so that extreme refinements are unnecessary. PREVIOUS WORK The recovery of water ballast from engine exhaust gas is the subject of a publication of the (British) Advisory Committee for Aeronautics, by Guy Barr, elated September, 1915. This report discusses the principles involved and describes the operation of experimental apparatus installed on No. 1 Naval Airship. The apparatus embodied a water-cooled muffler at the engine and a single air-cooled pipe of 4-inch diameter, about 400 feet long. Separation of entrained moisture at the end of this pipe was accomplished by making the cooled gas bubble through water. The engine served by this apparatus had an output of 180-200 horsepower. The test quoted lasted 35 minutes and yielded water in the amoimt of 52.2 per cent of the weight of the fuel burned. During this period there was a marked increase of temperature, both in the exhaust gas and the cooling water, indicating a decrease in the per cent recovery with further operation. In view of the crude apparatus used, the result might well be regarded as having given promise of future success. When the work described in this paper was initiated at the Bureau of Standards, the Navy Department was testing an experimental water-recovery apparatus developed by Mr. H. S. McDewell, engineer in charge of the Aeronautic Engine Laboratory. The Navy Department, through Mr. McDewell, was kind enough to give every possible assistance to this bureau in determining the lines which might most profitably be fo llowed in further work. The Navy apparatus embodied a length of about 50 feet of 5-inch finned sheet-iron pipe, for initial air cooling, from which the exhaust gas passed to a jet condenser, and thence through a baffle type separator to the atmosphere. From the separator and the jet condenser the water drained through settling basins to radiators, and was then p11mped back through the condenser jets. The excess water, representing the recovery from the exhaust gas, was drained to buckets and weighed. This apparatus produced, 11nder favorable conditions (cold weather), 1.2 pounds of water per pound of fuel burned . Mr. McDewell must be credited with haviJ1g ( 1) -...-- -- • I demonstrated the entire feasibility of collecting exhaust water in sufficient quantities to fully compensate for the increased lift due to fuel consumption . The apparatus used in this work was constructed with little regard for weight and as a result, was far too heavy to be used on an airship. Mr. McDewell estimated that, by exercising the greatest care in design, the weight of such an apparatus could be reduced to about 6 pounds per brake horsepower. SUMMARY OF WORK AT THE BUREAU OF STANDARDS It is to be noted that both the systems already outlined involve t he use of both water and direct air cooling. The same general scheme was at first followed by the Bureau of Standards in laying out a proposed experimental design . 2 This first design differ ed only in detail from the Navy apparatus already described . The settling basins were replaced by a centrifugal separator and the whole apparatus was made as compact as possible. Computations based on this arrangement indicated that the apparatus, exclusive of radiators and cooling water, could be built within weight limits of about 2 pounds per brake horsepower. While collecting preliminary data necessary to design such an apparatus within acceptable weight limits, a critical analysis was made of the fundamentals entering this heat transfer problem. The primary requirement to be met was that all the heat abstracted from the engine exhaust must be delivered fairly promptly to the air through which the ship moves. No large heat reservoirs could be used, nor did the cooling problem offer any similarity to that of a marine or stationary gas engine, where an unlimited quantity of cold water is available. The cycle is parallel to t he cooling of a motor car or aviation engine, where, if water is used to take heat from the engine, it must in t urn give tip all this heat to the air, and return to its original temperature before again abstracting heat from the engine. In such cases, a water system, as opposed to direct' transfer of heat from t he hot body to the air, is introduced solely for the p urpose of utilizing much more effectiv ely some factors concerned in the heat transfer process. Unless t here is such a compensating featme, no ju t ification for the extra weight and inconven ience of the water syst em exists. The present problem seems to differ from that of an engine cylind er, in that there seems to be no reason why, in the direct transfer of heat from the hot gas to the air, every unit of cooling surface and every degree of temperature head can not be used to maximum advantage. Accordingly, the information regarding a ircraft radiators, obtained in several years of work upon this subj ect at the Bureau was brought to bear upon t he question of securing the most effective direct heat exchanger to take heat from a hot gas and deliver it to a stream of air. By the time the proposed design and weight estimate for a water-cooling syst em were available, the invest igation of the direct air cooling method was well under way and seemed to give promise of somewhat lower weights. The jet condenser system was held up pending the completion of the preliminary air-cooled design, and was then definitely abandoned in favor of the latter which showed a designed weight of about 1.5 pounds per brake horsepower, complete, in addition to avoiding t he mechanical complications of water cooling and handling apparatus. While t he detai led d esign of the test apparatus was being carried forward, it was thought advisable to check the theory involved by a laboratory test of a sma ll section similar to the proposed full -size apparatus. With this end in Yiew a wind tunnel of 9 inches sq uare section was constructed, served by a centrifugal blower fan driven by a small automobile engine which also furni sh ed the exhaust gas . A condenser was made up of standard 1-inch iron pipe, with three 20-foot banks of t hree pipes in parallel, having return bends connecting the successive banks. This was installed in the tunnel and connected at one end to the engine exhaust manifold, and at t he other to a small baffie type separator . Measurements were made of gasoline consumpt ion, exhaust water collected, air velocity and temperature, and final exhaust temperature. The resvlts were found to closely check those expected from theoretical considerations, and the work of construction of the •fullsize units was begun without further delay. The full air-cooled system allows of extensive use of aluminum in the form of thin seamless t ubes and cast headers. The design and detailed description of t he two condensers built are discussed in Part III. In general, the method is to pass the exhaust gas at high velocity through parallel lengths of about 60 feet of 1-inch aluminum tube, the outer surface of which is swept by air at a rate determined by the flying speed of the ship. For convenience, the 60 feet is arranged in three banks connected by return headers, so that the overall length is about 21 feet. To handle the quant. ity of exhaust gas produced by the two 150-horsepower engines to be used , with due consideration for the desired velocities and back pressures, there are 50 -such cooling t ubes in parallel. The who]e ·unit presents t he appearance of 150 parallel 1-inch tubes in one bank whose overall length is 21 feet. Both Models I and II have t his general form, although t hey differ considerabl, v in details of construction and arrangement of the hot and cold banks of t ubes. Both of t hese units are intended for suspension between the envelope and car on Class C and D airships of the original design, and a re normally slanted about 6° downward to t he rear to assist in draining the tubes of condensed water as well as to provide some cross flow of air between them, t hus avoiding the loss of effi ciency clue to heated a ir coming from a hot tube and striking a cooler tube fart her along. In each case a baffle type separator is provided to collect the entrained moisture from the gaseous produ cts leaving the condenser. The first of these condensers, Model I, was set up for a ground test early in NoYember, 1921, using a stock 400-horsepower Liberty engine to provide both the exhaust gas and air stream. The propeller used was furni shed by the Engineering Division, Air Service, and a calibration had shown that. it would absorb 307 horsepower at 1,600 revolutions per min.ute. /' ' 3 The complete set-up is shown in Figure 1, from which The endurance run was begun on March 11, 1922, it will be seen that the suspension of t he condensing and was terminated at the end of 90 hours, April 3, unit is taken care of by six diagonal cables from the because of failure of the engine. It was thought that supporting posts, simulating as closely as possible the the endurance of t he condenser had been sufficiently proposed installation on an a irship. It may be men- demonstrated. The r esults are indicated in a later tioned here that the apparatus shown, without sus- I section of the paper. FIG. 1 pensions, separator , or exhaust conducting pipe, weighed just 400 pounds. When installed on a ship the total loss of lift would probably not exceed 450 pounds. The results of t his test showed the performance of the apparatus to be satisfactory, and it was decided that an endurance test of 100 hours should be run to ascertain the effects of continued vibration and After the completion of the endurance test the ap- . paratus was taken down and packed for shipment to Langley Field. Another Liberty engine was set up and the Model II condenser swung in place for an endurance test. It was thought that 50 hours would be enough to show up any distinct weakness of construction, and would allow of a considerable saving of Fw. 2 possible carbon deposition. ,vhile no pro v1s10n was made to secu re a uniform ai r blast over the condenser, thus permitting of securing suffi cient p hysical data to check the theory of its design, it nevertheless seemed advisable to make such meaurements of temperature as could be easily secured. Accordingly, another setup was made in which were incorporated a number of thermocouples at various points in the exhaust gas stream as well as the necessary weighing apparatus for gasoline and collected water . ~ ------------- - - - - - - - - - money and t ime as well as avoiding many of t he delays incident to engine trouble. The Model I condenser was shipped to Langley Field early in the spring (1922) and authorization was secured for the use of Airship D- 3 for two months in order to carry on flight tests. The work of installation was begun about July 21 and t he first fligh t was made on the morning of August 17. The condenser is shown in position on the a irship in Figures 2 and 3, which were taken just prior to the 4 FIG. 3 initial flight. A comparison of size with the whole some heat from the surfaces of the warmer second half. ship, car, engines, etc., may be had in Figure 2. Figure The schematic diagram, Figure 4, illustrates the flow. 3 shows some of the detail looking from the left side. The detailed arrangement of tubes and return The separator is mounted at the upper left in Figure 3 headers is shown in the photograph, Figure 5, in on the side opposite the observer. which the exhaust enters at the upper left while the During the first flight the exhaust piping developed air flow is from right to left. faults and water leaks were discovered at the first It wiU be noted from the photograph of component drains from the condenser. These were repaired the parts, Figure 6, that an attempt \Yas made to streamnext clay, and the ship was again flown on the afternoon of August 18. No further mechanical trouble appeared and, after one short flight on the morning of August 19, the ship was flown to Aberdeen Proving Grounds, where further flight work was conducted. The D- 3, equipped with the Model I condenser, was flown for a total of 53 hours, and during the greater portion of that time the apparatus was found to func6AS 6-4S 0(.ITJ.l=T -~E~NT~NII=NCE= =;=» ~l:= ======7~~ -~ FIG. 4 tion satisfactorily. A detailed account of the results line both the headers and header manifolds in order lo appears in another section of this paper. DESCRIPTION OF CONDENSERS !Ji the Model I condenser the tubes are arranged so that two-thirds of the total cooling area is in counterflow; that is, having the direction of flow of the exhaust gas opposite to the flow of the air stream. In addition, if the unit be considered as two halves, front and rear, the forward half is the cooler one, thus providing a secondary overall counterflow effect, since the air passing over the fir st half will still be cool enough to abstract secure the best possible conditions of air flow around the castings and between the tubes, as well as to keep down the head resistance of the apparatus as a whole. The result is shown in the encl view, Figure 7, lookiPg in the direction of the air stream. The Model II condenser, figures 8, 9, and 10, differs from the Model I chiefly in respect to arrangement of tubing and type of header. The flow of ' exhaust gas and air is two-thirds counterflow as in the case of Model I, but no attempt was made to secure a corresponding over-all counterflow effect. The schematic 1 5 FIG. 5 F 1G. 6. - l. Tube. 2. B ender manifold. 3. End heade r. 4. Return header. FIG. 7 G FIG. 8 FIG.) FIG.LO diagram, Figure 11, indicates the direction of gas and air flow. The construction is somewhat similar to that of Model I , a lthough t he headers are of an entirely different type. The same ma terials are employed, with the exception of the first 10-foot section which, in this case, is of Benedict nickel, a commercial a lloy containing 16- 18 per cent nickel, balance copper. This material is used to avoid warping of the tubes due to the high temperat ures in t his section. GAS l:Nr/1'ANCI: ::>) -~~~~=~(i~A?- OUTL~T F IG. ll In Figure 10 it will be observed that in the middle layer of the upper bank many of the tubes have taken a decided permanent set. This is due to the poor gas distribution between the tlll'ee layers of the bank in question. The exha ust gas tends to flow through the central layer on acco~mt of the more direct path as opposed to the elbow nipples of the outer tubes. For this reason the center tubes are hotter, and their expansion greater, with the r esult that they fail as long columns. These tubes are of aluminum. It is noted that some of the upper tubes at the far end (Benedict nickel) are also bent. This, however, is a result of accidental mechanical stresses and not of any temperature effect . The number of parallel tubes per bank in this condenser is 50, and ea ch bank is composed of two 10-foot lengths, end to end, so that a total of 3,000 feet of tubing is used. For better mechanical stiffness and strength the aluminum t ubing used has a wall thickness of 0.022 inch in st ead of 0.016 inch. This is the thinnest walled tube made as a stock product by manufacturers of aluminum and is far cheaper than the thinner material used in Model I. The Benedict nickel,' which is very easily worked, was drawn to. a thickness of 0.010- 0.012 inch , making it about 40 per cent heavier than the 0.022 inch aluminum tube. The actual weights per foot are as follows : Pound 0.010- 0.012-inch Benedict nickel_ __ ___ ___ ____ 0. 1208 0.022-inch aluminum __ __________ ____ ______ _ 0. 0857 This makes the total weight of tubing 274.6 pounds, which is about 50 per cent higher than that of Model I. The increase in tube weight, however, is offset by a decrease in the casting weight, to such an extent that the Model II condenser is only about 9. per cent heavier than Model I. The actual weights without suspensions, exhaust pipe connections, or separators 7 linear expansion, and a header design providing good gas distribution, the added weight of Benedict nickel tubing would not be justifiable. The importance of the separators for the collection of entrained moisture can not be overemphasized. No matter how low a temperature is reached in cooling the exhaust gases, much of the water condensed remains in the form of ~pray and is carried along by the gases until the separator is reached. In the absence of such a device this represents a loss of about 50 per cent of the water condensed. Since the functioning of the separators is the same for both condensers, only the Model II will be described in detail. This separator was bolted up directly to the exit elbow shown in Figure 9 and extended back under the condenser, where its free end was supported by wires extending diagonally upward between the tubes to the header casting above. The separator is shown in some detail in Figures 12 and 13. Its action depends upon the drops of water being thrown against the baffles shown in Figure 12 and guided by the small vertical gutters to holes punched through the bottom to a fal se bottom, from which the collected water is drained to the ballast tanks. The exhaust gas enters at the upper right, Figur~ 13, passes between the baffles, and escapes at the left. It will be observed that there is a lip on the outlet end to prevent t he separated water washing along the bottom past the holes and so escaping with the gas. The separator is built of tinn_ed sheet iron, and is soldered together. This material was selected purely because of its availability and the ease with which it can be worked. Some noncorrosive material .such as aluminum or a copper-nickel alloy might be a decided improvement. The Model I separator, differing only in outer shape, may be seen at the upper right, Figure 5, and upper left, Figure 7. TEST RESULTS The results of the 90-hour ground test of the Model I condenser are shown graphically on Fignre 14. A summary of the results follows : Average air speed entering condenser __ 48 m. p. h. Average air temperature ________ _____ 1.5° C. Total weight fuel used ________ _____ ___ 15, 075 lb. Total weight water collected ___ _______ 13, 943 lb. ·water collected 2 _ _ _ _ _ _ _ _ _ ______ _____ 92. 5 per cent The recovery is somewhat low, but t his is not inherently a fault of the condenser. , Trouble was experienced during the test, with misfiring of the engine, cracked exhaust ducts, small water leaks at drain conare as follows: Pounds nections and thermocouple bushings, ,and clogged Model!_ _____ ______ _______ ___ ____ ______ _____ 400 drain pipes. Inprovements in construction should Model IL ____ _________ __ ___ ___ ____ ____ __ ____ 434 obviate these difficulties and materially increase the It is proba ble t hat wi th exhaust pipe connections of ample flexibility, freely moving slip joints to t ake up 1 Benedict nickel is a copper nickel alloy used largely in the manu· facture of plumbing fixtures on account of its noncorrosive character. It is easily worked and has a bigber tensile strength tban aluminum. 96997- 24t--2 recovery. 2 The water recoverable, water condensed, and water collected, when expressed as per cent, are based upon the weight of the gasoline or other fuel burned. Thus, a recovery or collection or 100 per cent exactly compensates for the weight of fu el burned. I 8 42-'' Fir.. 12 'Ten roi,vs or bo/'rles equa//y spaced as shown-end prov/ded wir.17 f "r/aps ,ror so/den~ T() rop and bofron1 o.f" veparalor . .5ee baf'f'!e A-A/ far details I ==)_ .3" ~ P/),e collp/1~ .solderec/lo raise bot/on, ror clra/n connect/on. FrG. 13.-Moctel II separator elevat ion 60 ~ ~ i:: ~ \] 40 ~ ~ ~ c:s I "~' 20 K ~ ~ ~ 0 60 1-0 zo 0 .90/loul? f:NOURANCC li'uN- Mooa I CoNocNSCR OK£. Tr-P.t: FIG. 14 . I ( I ~I ,' 10 !n ·conducting this test it was intended that a ·"helium heater," for regulating the temperature of the lifting gas, should be tested at the same time. This apparatus was connected into the exhaust line by a bypass valve which allowed of passing the exhaust gas at will through the heater or direct to the condenser. The valve plate was of brass, clamped to a steel operating stem by set screws. Shortly after completion of 50 hours of operation the set screws loosened, dropping the valve to the position necessary to cut in the heater. As the valve was very inaccessible, and inasmuch as the test was for the purpose of demonstrating the mechanical strength of the condenser unit, the run was continued under the new conditions. The point at which the helium heater was cut in is readily observed on the chart, Figure 14, from which it will be seen that the change came during the fiftysecond hour of operation. For this reason the recovery header. The tubes were in a similar condition, with the addition of white corrosion spots at frequent intervals. These spots were not deep and gave no indication that trouble might be expected from this source. It will be noted also in Figure 15 that the machined surfaces of the nipples show no signs of exhaust-gas leakage. With regard to carbon formation it should be noted here that the engines used, both in this test and in the 50-hour test of Model II, were equipped with the Navy type oil scraper pistons which were known to materially reduce the oil consumption. It would seem that every effort should be made to minimize oil consumption when exhaust-water-recovery apparatus is to be employed. Some of the castings used in the construction of the Model I condenser had been found porous and were plugged with aluminum solder in order to stand the FIG. 15 and fuel consumption have also been computed separately for the first 50 hours of the run. The results follow : Average air temperature ______ ______ __ 16.5° C. Total gasoline burned _________________ 8,126 lbs. Total water collected _________________ 7,662 lbs. Water collected __ __ ___ ________ _____ __ 94.4 per cent. These results indicate that the decrease of the exhaustgas temperature at the entrance to the condenser was more than offset by the increase in the losses, already mentioned, during the last 40 hours of the run. The carbon or soot in the water collected took the form of a light foamy scum or a mushy sludge. The latter gave some trouble by clogging drain tubes wherever a contraction or shoulder allowed an accumulation to build up. Substitution of large,' smooth drains should prove an effective remedy. The deposit of carbon in the tubes and castings of the condenser proper proved to be practically negligible . . A light soot accumulated during periods devoted to warming up the engine under idling conditions, but immediately upon opening the throttle this soot was blown out through the separator with the appearance of dense black smoke. After completion of the 90-hour run one of the header castings and the adjacent tubes were sawed into sections in order to permit examination of the carbon deposit. Figure 15 shows parts of this sectioned leakage test. This solder melted and oozed from the pores of the exhaust entrance header manifold during the preliminary ground test but the leakage of gas was thought to be so small as not to warrant replacement. In the light of this experience, however, it would be well to specify that castings for this purpose be required to stand a leakage test without repair of any kind. No mechanical failure of any kind occurred in the Model I unit during all test work to which it was subjected, and the structural design is therefore concluded to be sound, although it is realized that many modifications may prove desirable in laying out apparatus for service use. · Ground test of the Model II condenser is charted in Figure 16. Summarized results follow: Average air speed entering condenser_ ___ 35 m. p. h. Average air temperature_______________ 20° C. Total weight fuel used __ _____ _____ ____ 8,195 lbs. Total weight water collected ___ __ ______ 5,324 lbs. Water collected ___ ____ ____ ______ _____ 65.0percent. The postponement of this test for several months resu1ted in serious rusting of the flexible leads from the exhaust manifolds of the engine to the exhaust pipe line to the condenser, and as a consequence the resumption of test work was marked by persistent occurrence of breaks in the flexible piping with attendant leakage of exhaust gas. Trouble was also en- 60 (j ~ ~w c~s I ~;::s R.zo ~ ~ ~ 0 50 fiouR ENOURANCc RuN MoocL ll CoNOcNSCR PARKCR 'lYPc FJG.15 UJ 20 0 ... 12 countered wi th clogging of t he drain from the separator, owing to rust and sed iment deposits which would not be expected during continuous or semicontinuous operation. In Figure 16 the line of water condensed is obtained by referring poin ts from t he line of final exhaust temperature to l<' igure 21 , assuming the mixture ratio to have been 15 : 1. It will be noted that the line of water condensed is at least in the same general range as that of water collected during the few runs made in August, whereas with the runs of October these lines at once diverge so that there is an average difference of perhaps 20 per cent. This is believed to result from exh aust-gas leaks and \Yaste of water clue· to persistent stoppage or the separator drain. This stoppage causes the falsjl bottom of the separator to fill and overflow , so that the water separated by t he baffles from the· issuing exhaust gas can not drain off and is swept out by t he gas. The only mechan ical failure \Yas occasioned by .differential expansion of the entrance header elbol\· and the header bolted to it. The entrance elbow casting was, of course, hotter t han the header proper, and the upper fl ange of the elbow warped ·upward, pulling off the lugs of t he corrcsponcli11g flange of the header. This occurred early in t he test and \Yas remedied by passing a bolt through the elbo1Y castiug, thu~ drawing down the upper edge and holdiug it permanently in place. The bolt may be seen in Figure 8. A condensed log of the flight tests of i\Iodel I condenser is shown in Table 1. Totals and averages follow: Air temperature ____ _____ ___ __ ____ ___ -22° C. Total weight fu el burned ___ ___ _______ 2,799 lbs. Total weight water collected ______ __ __ 2,170 lbs. Water collect ed ____ ___ _ _____ _____ ___ 79.4 per cent. In rn.aking up t he separator drain from whate.ver ma t erials and fittings were a,·a ilable, a shoulder was left at the p oint of connection of the drain pipe and separator, and this resulted in the loss of a co nsiderable qua ntity of wa ter, clue to clogging of the drain by carbon. 01\"ing to lack of data as regards engine power and final exhaust temperature, a nd to the variation in air speed , no comparison can be made between the t heoretical and act ual res ults on this test. It is t hough t, hO\,·ever, that the leakage of exhaust water due to stoppage of the separator drain and sticking of t he ballast dumping valve may easily account for the difference in " ·eight between the water collected and the fuel burned. It is to be noted that condensers designed for a:n air temperature of 15° C. can not be expected to condense sufficient water to completcl_,. compensate for t he weight of fuel burned when higher t emperatures are encou ntered, as in summer flying. Figure 17 indicates the variation of water condensed with change of a ir t emperature based on the design of the Model II condenser. In computing the points for this curYe, all other conditi ons are assumed as constant. In the flight test , as in t he ground test of t he same apparatus, no t ro'uble of anr kind was experienced with the condenser proper . Some difficulties were encountered \\·ith a ccessories, such as exhaust piping and drain tnbes, but these parts were of a makeshift nature and should give no trouble in a service unit whose parts are well designed and constructed. It is worthy of comment that the installation of the Model I condenser on the D- 3 produced no appreciable decrease in the ship's flying speed at a given propeller speed. Th.is was contrary to expectations but may be readily credit ed when t he immense projected fron tal area of t he ship is taken into account. TABLE 1.- S ummary of flight tests on Nlodel I condenser '"l'ime Fligbt No. \ -- Hrs_:_1;\l: L --·--·-·--· - ·- · •) ___ ____ ____ ___ _ _ 3 __ _____________ _ 4_ - . - -· -----·---· 56 •_._ _·_-_- -_-_-_-__-_-_-_·_· -_-_ _ 7 - - • ---- - ---· - ·-- 8 . -- · ---- - ----· - - 910- _·-__·-_-__-_-_-_- ·__--_· ·__· ·_ 11 . _. -------- - - -- -- -- 12 ___ - ----- - --- - - 3 j ~I 2 3 4 13 18 52 47 9 2.J 59 18 11 1 0 0 :1 I I 13_ __ _____ ____ ___ 4 I o :\lean ___________ '. ------!------ 1 This rnlue not included. Mean air temperature o C. 20. 5 24. J 23. 5 24. 4 20. 5 22. 7 21. 5 18. 5 24. 5 22. 3 Air speed M . p. h. 39 37 46 34 38 44 48 Altitude Feet 1, 000 1,000 800 900 I. 000 950 J, 250 800 50 900 Engine R. p . m . 900 J. 100 1, 000 I , 200 J,000 900 1, 100 900 900 J, 100 J. 200 Water Pounds 206 254 210 212 232. 5 227 180 278 371 G r Water I aso inc collected Pou'rirls 24 2. 5 3:31 285 332 266 302 260. 5 309. 5 4il Per cent 84. 9 76. 7 73. 7 1 63.8 87. 3 75. 2 69.1 89.S T otaL _.. 2. 1 70. 5 2, 799. 5 78. 8 79.4 Remarks "Separator dra iu clogged. Gasoline record uncertain. \Yater spilled in draining. \\' ater leaked through emergenry release v?Jve. Release valve stuck-water lost. Flight abandoned due to oil leak on left . motor. Mean . )i°OTE .- Six preliminary flights were made (total time 12 hours, 46 minutes) in order to eliminate minor mecbaoical defects. The average water collected for these flights was 72.4 pe,r cent . 13 JO -10 70 80 9 0 / 00 //0 /20 · % CoNOEN,5AT/ON FIG. Ji CONCLUSIONS Al1 hough no claim is made for the present general design as repre~eniing the ultimate form of ballast recovery apparatus-, the feasibility of condeusation of water from the engine exhaust as a means of compensating for the increased lift, due to the loss of the fuel burned, has been demonstrated. The weight of the apparatus is not excessiYe and can be wholly rompe11satecl for IJ.v a correspoucling decrease in the \Yeight of the water ballast usually carried. Owing to the large frontal area of an airship, the head r('sistance of a condenser of the type thus far used represeuts such a small portion of the whole as to be nearly negligible. Condensers of the general t_vpe of Models I and II, ha\·ing no moving parts, require little attention and eompare favorably, as regards fly ing li fe , with most aircraft engines 1101T in service use. In cold weather, 1\·ith a couclensat iou in excess of the fuel equilibrium requirements, the exhaust ,rnter may also be used to at least partly compensalc for the change in l ift clue to ('hanging barometric pressure or temperature of the lifting gas. Although some assumptions used in the design work a,ppear to be only rough approximations, none of the test results seem to indicate any great error within the range of conditions thus far encountered. ... PART II- THEORY In reviewing the theory involved in the process of obtaining water from the engine exhaust gas, it may be well, in order to avoid confusion, to first discuss ·the nomenclature used. Reference is made to the chart, Figure 18, in which ordinates represent weights of the quantities indicated. The fuel burned is, of course, the basis upon which the other quantities are determined. The total water ! W'ATEH e1VreRIN6 W'ITH AIH i , perature itself, it at once becomes apparent that the recoverable water is the total minus the vapor necessary to saturate the gaseo us exhau8t products at a ir temperature. The designed recovery is, of cou rse, limited by the recoverable water as determined by an assumed air temperature. It may be arbitrarily placed at any value less than that of the recoverable water, but would not ordinarily be less than the fuel burned. ~ ,.... ·, ~ ~ q~ ~ ~ ! ~ ~ " ~ ~ ~ ~ ~ - R ~ ~ ~ ~ l ~ ~~ Q: ~ "' ....., ~ 8 ~ a\ j ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ V , FIG. 18 in the exhaust gas is the sum of the water of combustion and the moisture entering with the carburetor a ir. This quantity depends upon the kind of fuel and to a small extent upon the mixture ratio. When using gasoline there is present more than 1.4 pounds of water for every pound of fu el burned . Since the amount of water lost as vapor depends upon the exhaust-gas final temperature, and since, in an air-cooled system, the limit of cooling is the air tern- Since the designed r ecovery is based upon a designed final exhaust ·temperature, it is evident that error in design assumptions or changes in flying speed or air temperature will change this final temperature and therefore the water actually condensed. The water condensed may be either greater or less t han the designed ·recovery, but is represented as showing a loss. In the collection of t he water condensed , leaks of any kind, as well as faulty separation of entrained moisture, (14) will lower the quantity actually available as ballast. The water collected is therefore a lmost certain to be less than that actually condensed. Any of the quantities shown, when expressed as per cent, are based upon the weight of fuel burned. The design of the condensing a pparatus is dependent upon a large number of variables 'which may best be taken up as they appear. It is at once apparent that the \\·ater condensed is dependent upon exhaust-gas composition and its fina l temperature. The first of these is readily determined when the chemical composition of the fuel, ratio of air .ss 15 The air composition is approximately oxygen 23 per c.ent and nitrogen 77 per cent by weight. The air temperature was assumed to be 15° C. lower than that of the exhaust products leaving .the condenser. It is obvious that the exhaust gas wiU never be cooled to the temperature of the air. The relative humidity was assumed as 60 per cent, which is an approximate average for all parts of this country for the whole year for altitudes less than 5,000 feet. As a basis of comparison of the different fuels their chemically correct air-fuel ratios were used. ff'o /0 eo 30 'fo SO 60 70 80 90 100 110 !ZO / 30 /40 ISO 7o CCWOf NMTION FIG. 19 to fu el, and relative humidity and temperature of t he air are known . The fina l exhaust temperature; howe, ·er, is a fun ction of the length, d iameter, spacing and number of condenser tubes, mass flow, and initial tempera. tu re of exhaust gas, and the velocity and temperat ure of the air flowing past the tubes. Taking first the effect of different fuels, Figure 19 ,;hows t he water condensed in per cent by weight of the fuel burned, plotted against the final exhaust temperature, for a number of liqu id fuels. In order to arrive at the curves shown it was necessarv to make assumptions for carbureter air composit io1:, temperature and humidity , and n1ixture ratio, or pounds air per pound fuel. 96997-24t--q The condensed water per pound of fuel is, of course, the water of combustion plus the moistme entering with the air, minus the water issuing as vapor with the cooled exhaust products. It may be well to follow through the computation with one of the fue'.s involved. Taking pentane as an example, we have from its composition (C5H 12) the hydrogen and carbon content per pound 0.167 and 0.833 pound, respectively (see Table 2). Then from the combining proportion of hydrogen and oxygen (1: 8) the water of combustion will be nine times th!;! wei~ht of the hydrogen, or 1.500 pounds. 16 TABLE 2.- Combustion data for liquid fuels assuming correct mixtiire ratio for complete combustion Content per pound of fuel Product per pound of fu el Air content Ratio Exhaust Molecular molecular gas Fuel 1-----~---1----.----1---- ---1 Mixture ratio weight we,gt~t weight of au per exhaust molecular pound A ir factor Hz C 02 H,O co, 0 2 ;;~';!\ of fuel --- ---- --- -------- --- - ------ ----- Hexane C,Ht< ---- -- --- --Pentane C,H12------- ---Dodecane C12H20 - - ---- - -- Alcohol C,H,OH _____ ___ _ Beuzol C,H, ____________ _ 'l'oluol C,Hs--------------1 XEtyhleorl CCs,HHI1O0-0- _-_-_-_-_- -__-_-_-_--_-_ 0.163 I . 167 .153 . ] 30 .077 . 087 . 094 . 135 0. 837 . 833 . 847 . 522 . 348 . 923 . 913 . 906 . 649 ---.216- 1 1. 467 3. 07 3. 54 l. 500 3. 05 3. 55 l. 375 3. J05 3. 48 l. 173 l. 915 2. 08 . 692 3. 38 3. 08 . 782 3. 35 3. 13 . 850 3. 32 3.17 l. 215 2. 38 2. 394 11. 86 15. 4 30. 28 0. 952 14. 93 14. 2:3 ll. 89 15.44 30. 28 . 952 14. 94 14. 24 11. 66 15.14 30. 28 . 952 14. 76 14. 07 6. 96 9.04 30. 39 . 958 8. 875 8. 42 10. 32 13.4 30.72 . 939 13. 70 12. 87 10. 49 13. 62 I 30. 68 . 940 13. 84 13. 02 10. 62 13. 79 30. 65 . 941 13. 94 13.12 8. 68 11. 27 30. 40 . 949 11. 06 10. 50 Similarly, we know that the relation of the carbon The total exhaust gas weight, exclusive of water, per d . "d t b . 44 b . . pound of fuel is t he sum of the carbon dioxide and 10x1 e o car on 1s 12, . nngmg the carbon dioxide nitrogen present, or 44 produced to 12 X 0.833 or 3.050 pounds . The oxygen 3.050 + 11.890 = 14.940 pounds r equired for combustion is then the difference between the weight of t he fuel and t hat of t he products of combustion, l.500 +3.050-1.00 =3.550 pounds Since the air is 77 per cent nitrogen by weight, the nitrogen content of the exhaust gas will be ;~ X3.550 =U.890 pounds. and the total weight of a ir per pound of fuel \\·ill be the sum of the oxygen and nitrogen, or 3.500 +11.890=15.440 pounds. Expressed as a ratio of weight, t his is the correct com-_ bining air-fuel ratio. The weight of water vapor which will be taken up by a pound of dry gas at any temperat ure is proport ional to the specific volume of the gas or inversely proportional to its densit y . · For convenience, t he molecular weight is substituted for density. For air, the molecular weight is 100 77 + 23 = 28.84 28 32 where 28 and 32 are the molecular weights of nitrogen and oxygen, respectively. Similarly, the molecular weight of the exhaust gas products, exclusive of water, is 3.050+11.890 3.050 + 11.890 =30.28. 44 28 From this we obtain t he ratio of molecular weights, and hence of the densities of air and exhaust gas 28.84 = 0 952 30.28 · which is also the in verse ratio of specific volumes, and hence the direct ratio of specific volumes of exhaust gas to air. and th·e product of this with t he ratio above gives the a ir factor shown in the last column of Ta ble 2 14.940 X0.952 = 14.240. Since the air factor is the product of t he rat io of specific volumes of exhaust gas and air and t he weight of the exhaust gas (other than water vapor) per pound of fuel burned, t he vapor content of the exhaust products leaving the condenser may be readily obtained by multiplying this factor by the weight of water necessary to saturate a p ound of dry a ir at the same temperature aud pressure. A physical r epresentation of the air factor is the number of pounds of dry air which would be saturated by the quantity of water leaving the apparatus with the other exhaust products from 1 p ound of fu el, · at t he same temperature and pressure. For a constant fuel composition and mixture ratio the air factor does not change. Referring now to Table 3, the first line is the temperature of the exhaust gases issuing from the condenser. T he second line is the moisture content of 1 pound of dry air saturated, at this temperature and atmospheric pressure (Goodenough's tables). These values mult iplied by t he air factor from Table 2 give the water content of the outgoing gases per pound of fuel in each case. The a ir temperatures in Table 4 are shown as 15° C. lower than those of the final exhaust in Table 3, complying with .the assumption made. To ascertain the moisture entering with the air for each pound of fuel it is only necessary to multiply the water per pound of a ir saturated by 0.60 (assumed relative humidity) and again multiply by the mixture ratio. To find the water condensed (Table 5) at any temperature considered, t he water co ntent of tll°e enteriug air (Table 4) is added to the water of combustion (Table 2) and the water content of the exhaust -gas at the corresponding temperature is subtracted from this sum. The curves in Figure 17 are plotted from values recorded in Table 5. 17 TABLE 3.- Pounds of waler vapor leaving with exhaust gases per pound of Juel. Relative humidity, 100 per cent Exhaust temperature, °C 10 15 w I 25 w u ~ ~ - w ~ c. 00764 0. 01068 o. 01476 1 0. ~2017 0. 02729 0. 03662 0. 04899 0. 0654 0. 0873 0. 1156 Pounds moisture per pound saturated air_ _______ __ _____ _ 0. 00542 -----------1------------------------- ------ ---- - - ------ Hexane ___ __ __ _____ __________ _ Pentane ____ __________________ _ Dodecane ___ _______ ______ ----- Alcohol __ - - - - - ------------ ___ _ Benzol __ -- ---- - - - - - --- _______ _ ToluoJ ___ ___ ___ ______________ _ Xylol _______ _________________ _ Ether -- - - --- -------------··-·- . 0772 . 0772 . 0762 . 0456 . 0697 . 0706 . 0711 . 0569 .1087 .1088 .1074 .0644 .0984 .0995 .1002 .0803 . 1522 . 1523 .lW5 . 0901 . 1370 .1392 . 1403 . 11 22 .W85 .W87 . 2062 .1242 .1 886 . Hl09 . 1923 . 15W . 2872 . 2874 . 2838 . 1699 . 2596 . 2627 . 2647 . 2117 . 3913 . 3918 . 3868 . 2297 . 3540 . 3580 . 3608 . 2918 . 5210 . 5215 . 51W . 3080 . 4712 .4764 . 4800 . 3847 . 6974 . 6977 . 6890 . 4125 . 6305 . 6378 . 6432 . 5147 . 9315 . 9321 . 9210 . 5510 . 8324 . 8524 . 8585 . 6872 1. 240 1. 2415 1. 2265 . 7345 L 122 L 1350 L 1435 . 9168 l. 645 1. 647 1.627 . 974 1. 487 L 506 L 517 L 214 TABLE 4.- Po1mds waler vapor entering with air per pound of fuel. Relative humidity , 60 per cent Air temperature, 0 0 - 10 -5 0 10 15 20 25 30 35 40 -----------,---------------- ----- ------- ----- P ounds moistme per pound saturated air _______________ O. 001643 O. 002553 O. 003782 0. 00542 · 0. 00764 0. 01068 0. 01476 O. OW17 O. 02729 0. 03662 0. 04899 ---- ·~1- - ---- Hexane ____ ______ _____________ . 0152 . 0236 .0350 . OWl .0706 .0987 .1364 .186.1 . 25W . 3383 . 4527 Pentane___ ___ __ _______________ . 0152 . 0237 . 0350 . OW2 . 0708 0990 . 1367 . 1868 . 2528 . 3392 . 4539 Dodecane_ ______ ______________ . 0149 . 0232 . 0344 . 0493 . 0694 ·I . 0971 .1341 .1833 . 2480 . 3327 . 4453 Alcohol __ _____ __ ______________ . 0089 . 0139 . 0205 . 0294 . 0414 I . 0579 . 080l . 1094 .1480 . 1986 . 26,57 ,Benzo]__ ___ ___________________ . 0132 . OW5 . 0304 . 0436 . 0614 . 0859 . 1186 . 1621 . 2193 . 2944 . 393~ roluoL ___ ____________________ . 0134 . 0209 . 0309 . 0443 . 0624. . 087a - . 1206 .1648 . 2230 . 2992 . 4003 XyloL ______________________ __ . 0136 . 02ll . 0313 . 0449 . 0632 . 0884 .1222 .1669 . 2258 . 3031 . 4054 E ther_ ___ ___ ________ __________ . 0111 . 0173 . 0256 . 0366 . 0516 . 0722 . 0998 .1363 . 1845 . 2476 . 33 11 I TABLE 5.-Pouncls waler condensed per pound of f uel, assuming complete.combustion. Relative humidity, 60 per cent Exhaust tempera- Water II ___tu _,·e, oc_ __, _ _g _~_~z_otn- --5--·- -10-- _ _ 15 _ __2_0 _ __:__ __3_0 ___3_ 5 __4_ 0 ___45 _ 1__:__ __55 _ _ Hexane ___________ _ Pentane ______ ___ __ Dodecane ____ _____ Alcohol__ ______ ___ _ _ BenzoL ____ __ _____ _ 'l'oluoL ____ _______ _ Xylol. _ ---------- -Ether __ - - - - - - ---- -- 1. 467 1. 500 1. 375 l. 173 . 692 . 782 . SW l. 215 1 I. 405 I. 438 l. 314 l. 136 .636 . 725 . 792 1.169 I. 382 L 415 1. 291 1.122 . 614 . 703 . 769 1. 152 1. 350 1. 383 1. 259 l. 103 . 585 . 674 . 741 L 128 1. 309 1. 342 1. 218 I. 078 . 547 . 635 . 703 I. 097 At the lowest assumed temperature the water of combustion from · pentane is 1.50 pounds (Ta ble 2). Adding to this the water entering with the air (Ta ble 4) we have 1.500+ 0.015= 1.515 pounds Subtracting the water lost as vapor with the exha ust gas leaving the appa ratus we have 1.515 - 0.077= 1.438 pounds which is the water conden.sed . Since it is improbable that any fu el having exactly the composition of one of those shown in Figure 19 will ever be actually put into service use, thfa figme is supplemented by Figure 20, showing the final t emperature to which the exhaust gas must be cooled in order to condense 1 p ound of water per pound of any hydrocarbon fuel within the range of fuel composition apt to be encountered. This curve was derived by plotting the points at which the curves of Figure 19 cross the 100 per cent condensation line. In order to secure the points for the lower end of the curve, fuels having lower h ydrogen content than t he gasoline group were assumed. To find the required final t emperat ure for 100 per cent condensation from any blend of hydrocarbon fuels it is only necessary to k now the h ydrogen content of the mixt ure. The lower limit of the curve I. 250 I. 283 1. 161 1. 044 . 494 . 582 . 649 1. 055 1.174 1.W7 l.085 l. 001 . 424 . 511 . 578 . 995 I. 082 l. 115 . 994 . 945 . 339 .426 . 492 . 930 0. 956 . 989 . 869 . 870 . 224 . 309 . 374 . 837 0. 788 1 0. 565 . 821 . 598 . 307 . 702 1 . 481 . 193 770 . 637 . 465 . 079 - - -- - --- -- 0. 275 .153 - --- - - -- -- - - -------- . 217 1 .010 . 712 . 546 . 332 of Figure 20 represents a fuel blend of about 41 per cent benzol with a gasoline of 15 per cent hydrogen content. All the curves shown thus far are based on the theoretical combining mixture ratios of air to fuel, which correspond to extremely lean carburetor settings and give the economy so vitally important in the operation of airships. Some multi-cylinder engines are unable to operate on mixtures quite as lean as those shown, but since the leaner mixtures are less advantageous as regards water recovery, the curves are based on the worst expected condition and are on the safe side. The effect of mixture ratio upon water condensed at various temperatLires is shown in Figure 21. These curves were computed in the same way as those of Figure 19, as represented by the computation sheets, Tables 6, 7, 8, and 9. The fuel in this case was assumed to be gasoline having a 15 per cent hydrogen content, which closely approximates the fuel now in service use. The final temperatures required for 100 per cent condensation (1 pound of water per pound of fuel) using this fuel and the indicated mixture ratios, are shown in Figure 22, which is obtained. by plotting the points where the curves of Figure 21 cross the 100 per cent line. • <· ... .18 I ~ n ff / M ~ ~ 2 ~ ~ - Z ~ 3 38 'f'O /7/VAL CXHAU.5T ffMPC:RATURe- °C FIG. 20 so / O zo ~o -fO so 60 7o ~o 9o 100 110 120 /30 #O ,so % Cb.lYL7CIY..l4T/ON FJG. 21 19 Since the humidity is uncontrolled, it may be that for special cases some figure other t han the average one of 60 per cent may be applied. The curves of Figure 23 indicate the limits of t he humidity range between zero a 1Jd 100 per cent when using gasoline having a 15 per cent hydrogen content with a 13 : 1 ai rfu el ratio. The data for t hese curves (Table 10) are largely obtained from the mixture ratio computations . ~ Jix ture ratio ~ fu el Oxygen in air TABLE 6 Exhaust gas content \ Moleru- Weightof Oxygen l\1Iole9u- lar we_ight exhaust in air ,----~--~----,tar weight ra~10 gas per less 1.2 of ex- air pound CO2 N 2 Oz lrn.ust gas exhaust of fuel Air factor -------·--- - --------·I---- - - - - - --- ---------------- -------- 12_ 13 ___ _____ __ ____ _____ _______ _____ _____ ____ _____ ____ _ 14 ____ ___ ___ ___ . ----- -- - · _ --- - - - ------- --- -- - - - - -- IA __ ---- - --- - ---- - - - -- - -- - - --- - ----- - - - - - - -- -- - ---- - 16 ___ ____ ____ ______ _____ __ - - --- --- - - - - - - - - - -- - - --- -- Gasoline assumed l5 per cent hydrogen. Water produced= .15X9= l. 35 #/# fuel. Necessc1ry oxygen= I. 35-. 15= 1. 2 pound~. ::VIolecular weigh t of ai r =28. R4 . . \ ir assumed 2.1 per eent oxygen, 77 per ct>nt nit.ru~en. 2. 76 2. ll9 :1. 22 3. 45 3. 68 l. 56 l. 79 2. 02 2. 25 2. 48 2.14 2. 46 ' 2. 78 3. 09 3. 11 9. 24 29. 7 0.972 10. 01 30. 18 . 956 10. 78 30. 27 . 953 JI. 55 30. 32 . 952 12. 32 0. 22 30. 25 1 . 954 TABLE 7.-Poirnds Wlller vapor losl wilh saluralecl exhcwsl gases per pownd of gasoline 11. 38 11. 05 12. 47 11. 91 13. 56 12. 91 14. 64 13. 93 15. 65 14. 92 Exhaust temperature, °C. 5 ; IO 1;; . 20 I 25 30 :!5 40 · 45 50 55 :lloist ure per ~y~nct saturated O 00542 1 o 00764 O 0 1068 o 01476 I O 02017 O 02729 0. o:l662 0 04899 0 065.J O 0873 0. 1156 1'.lixture ratio: I--- - --------1-------------------------------- . 12 __________ ___ ____ ___ . 060 084 118 163 .223 302 405 542 .723 .965 1 278 13 ___ _________________ .065 .091 . 127 . 176 .240 . 326 .436 .584 .779 1.039 J. 377 . !4 . . ------- - -------- - - - - - -- . 070 . 099 . 13~ . 190 . 260 . 352 . 47;3 . 633 . 845 1.1 27 I. 492 15 ______ _______ ______ .07f5 .106 . 149 .206 .281 .380 .5 10 .683 .912 1.215 J. 612. ]6 _ _ _ _ _ _ _ ___ __ _ ____ ______ __ .081 .114 . 159 . . 220 .301 .407 .546 .730 . 977 1.301 1.727 TABLE 8. - Pounds waler vavor entering with air per pound of gasoline. Relative lwmidily, 60 per cent Air lemperatore, °C. - 10 -5 o 5 :o 15 20 25 30 35 I 40 --- - - - - - --·--- - - !- :lloisture per pound satu rated 1 _ 001643 air . 002553 . 003782 I • 00542 . 00764 . 01068 . 01476 . 02017 . 02729 . 03662 . 04899 Mixfte ratio: ______________ _ \ 13. ____ _____ ______ -·--- - -- 14 . ___ _____ __ ___ _____ __ -- - - :t :::::::::::::::::::::::\ . 012 . 014 . 015 . 016 . om 1 . 018 . 020 . 021 . 023 . 024 I . C27 . o:io . 032 . 0:34 . 036 . 039 . 042 . 046 . 049 . 052 . 055 . 060 . 064 . 069 . 073 . 077 . 083 . 090 . 096 . 103 . 106 .. 1l 2145 1 . 133 . 142 . 145 . 157 . 169 . 181 . 194 .196 . 213 . 230 . 246 262 1 . 263 . 286 . 307 . 329 . 351 . 353 . 382 . 411 . 441 . 470 TABLE 9.-Poimds waler condensed per poimd of gasoline. Relative humidity, 60 per cent 1vl ixture rat io: . 12 ____________________ ___ _ 1143 ______________ _-_--__-_-_- _-_- _- -_-_-_-__-_- -__- -_ 15 _ ______ ______ ___ ___ ____ _ ]6 ____ ___ __ __ _______ _____ __ . 10 15 I 20 25 30 1 35 I 40 45 50 I 55 J. 302 J. 284 I. 259 1 I. 226 1.182 I. 125 , l. 05 L . 953 . 823 ---.:-----: 1. 298 1. 219 1. 2s:i I 1. 216 1. 170 1. 101 1. 029 . 923 . 784 . 597 . 35., I. 294 I. 272 I. 244 I. 206 I. 154 J. 088 I. 001 . 886 . 735 . 530 . 269 1. 290 1. 251 1. 235 1 1. 193 1. 138 1. oori o. 013 . 848 I . 684 . 464 . 1,0 J. 285 J. 260 J. 227 L 182 I. 122 J. 046 0. 946 . 814 . 635 . 400 . 093 I l 'iual exhaust temperature, °C. TABLI,; 10.- Pounds water condensed per po·und of gasoline wilh dry and 8alti-rnled air, mixliire ralio, 13:1; ga:;oline, 15 per cenl hydrogen Final exhaust temperature, °C. 10 15 20 25 30 35 40 45 50 55 Air temperature, °C. -10 -5 10 15 20 25 30 35 40 Water entering with sat urated air __ -- -- - - ---- - - - --- --- -- -- - Water lost with exhaust gas __ . 024 . 033 . 049 . 070 . 099 . 139 . 192 . 262 . 355 . 476 . 637 .065 .091 .127 . 176 . 240 . 326 . 436 . 584 . 779 I. 039 1. 377 Water condensed: Air saturated __ ____ _ l. 309 l. 292 J. 272 l. 244 I. 209 I. 163 I. 106 1.028 . 926 . 787 . 610 Air dry ______ ______ __ ____ I. 285 1.259 I. 223 I. 174 I. J 10 I. 024 . 9JA . 766 . 571 . 311 96997-24-....J4 • 20 /6 /. JO 31 :JZ 33 J,f- 3S ~6 :57 38 J9 -?O "11 42 43 -? riNAL .C%/7AUST «MPeli'ATURe - °C FIG. 22 So l $0 ~1.; "' ~10 K ~ ~.15 ~~ 3o .... ':> :i ~ZS ~ l(J 20 "I' . ~ ;:,- /0 "o / 0 2o Jo 0 .,.0 60 70 6'0 0 /00 / / 0 /ZO /30 /. 0 /~O % C'ONDEIV.SATION F IG. 23 21 The effect of humidity upon the final temperature I The equations are developed from the simple as- '.rnce~sary for 100 ~er cent water condensed is shown j s.u~ption th~t . in a given len~th of pipe for equi- 111 Figure 24. This figure was obtamed by plottmg a hbnum cond1twns, the heat given up by t he passing series of curves similar to those of Figure 21 for several exhaust gas is equal to that taken up by the pipe wall, conditions of humidity, and picking off the points of which is equal to that dissipated by the pipe wall and intersection with the 100 per cent condensing line as equal in turn to that taken up by the external air before. stream. These conditions give three equations in The points plotted on Figure 23 represent a verage four variables, of which one is readily eliminated, values of the water collected in the endurance t est of giving a pair of simultaneous differential equations to Model I condenser. It will be noted that most of express 0, the t emperature ,of the exhaust gas, and cf,, these points lie within the range indicated. Any the t emperature of the air st.ream, as fun ctions of x, /. 90 /0 0 ZS JO 3~ ,f-O .P.~ 17/VAL fYltAUST TCMPfRATURc- °C FIG. 24 leakage of exhaust gas or condensed water would-tend I t he coordinate along the pipe to lower the apparent condensation, so that the as- ' direction of exhaust gas flow. sumption of 100 per cent separation is felt to be cor - simultaneous equations is length, posit ive in the The solut ion of these r ect within reasonable limits. It is _obvious from the foregoing p aragraphs and curves tha t it is a relatively simple matt er to determine a desirable fin al exhaust temperature, ha ving ass_umed the kind of fuel, mixture ratio, a ir temperature, and relative humidit y . From t h is point on the task is so to select a nd arrange the cooling system as to a rrive at the desired final t emperature. The equations for heat transfer which are the basis of the design of the exhaust cooling syst em ha ve been derived under the following assumptions : (a) The t emperature of the pipe surfaces is the same inside and out at any given point in the length of t he pipe and is of course uniform around the circumference; (b) the a ir flowing over the external pipe surface is of temperat ure, density, pressure, and humidity characterizing normal atmospheric conditions, and the velocity of this air is uniform and perfectly turbulent. O =AeN +B (1) (2) Where N =-p -qh+qc ( H1 + H1 ) X . qh qC h C e = base of natural logarithms. p = perimet er of pipe - cm. q" = coeffici ent of surface heat transfer between exhaust gas and pipe wall -cal/secX°C. Xcm2• q0 = t he same coefficient, air st ream and pipe wall, cal/secX°C. X cm2• Hb = heat capacity of the mass of exhaust gas which passes any point in a unit time-cal/°C.Xsec. H0 =heat capacity of the mass of air stream - cal/°C.Xsec. 22 A and B a re constants of integration . To eliminate these constants the following end ditions are applied: For co unterflow of e),haust gas aed air-fJ =T.} </> =lb when x = 0. fJ=1\} </> =l. when x_· L. And for parallel flow-fJ= T • } w:rnn .c = 0. </> =l. o--T b }w hen x = L. </> =lb . Where T,.=initial exhaust temperature, °C. Tb =final exhaust temperature, °C. l,. = initial air temperature, °C. lb =final air temperature, °C. L =length of pipe, cm. con- The res ulting equations arranged in the form most convenient for design work are : For counter flow- (3) And for parallel flow- (4) The terms Hh and H 0 are obtained from the relation in which Mh mass flow of ·exhaust in one tube, g/sec Ci, = specific heat, at constant pressure of exhaust i\1 0 = mass flow of air around or.e tube, g/sec C0 = specific heat of air. The terms qh and q0 are obtained from the Lanchester- Stanton relation 1, 2. q = c"M [ o.0765 Cvf D) 0 ·" 5 + 0.0009 J (5) in ,,·hich C" specific heat at co nstant pressure μ viscosity, c. g. s. units ~I mass flow, g/sec X cm2 D = diameter of t11 be, cm In " ·orking to,Yard a satisfactory heat dissipating apparat us t he first determination 11ecessary is the total rate of mass flow of exhaust gas coming from the engin e. This \\·ill , of course, be the product of the brake horsepower, the fuel economy, expr~ssed in p ounds per brake horsep ower-hour, and the weight of mixture taken by the ellgine per pound of fuel , ·giving the mass flo"· in pounds per hour. From consideration of equations 3 and 4, for maximum efficiency of heat transfer, it is desirable that the velocities in side and outside of the tube be somewhere near the same. Hence having a known flying speed 1 Great Britain Committee for Aeronautics, Tech. Rep. 1912-13, p. 45. ' B. S. Tech. P aper No. 211, page 320. it is an easy matter to set this equal to the mean velocity of flow inside the pipe, and from the mean density over the temperature range within the pipes compute the mass flow. There is no point in folJowing through this process in this paper. Suffice it to say that for an air speed of 45 miles per hour the desirable mass flow inside the pipes works out to be 0.017 pound per second per square inch of cross sectional area (1.195 g/sec. X cm2), provided the temperature of the exhaust gas lies in the neighborhood of 650° C. at the hot end and 32° at the cold end. This figure (0.017) may be increased or decreased in proportion to the air speed, but since little gain is to be expected from any but broad approximations in this respect, it is probably as well to use this mass flow as a constant when working ,Yith airships having the cruising speeds of any now in serv ice or likely to be fo r some time to come. The selection· of the most advantageous size of tubes, must of necessity be a compromise between heat transfer efficiency and mechanical consid eratioH s. The effectiveness of the apparatus will be found (equation 5) to be increased as the d iameter of the t ubes is . decreased, whereas the smaller the t ubes, t he greater will be the exhaust back press ure and liability· to clogging, and the less the mechanical strength of the tubes both as self-supporting beams and as long columns. An indication of the relative resistance to flow wit h increase or decrease of pipe sizes may easily be ol::tained, but for the purposes of this work it is safe to let the limiting factor in redu cing tube diameter l;e the mechanical strength necessary in a structure of the type contemplated. Soon after the beginnillg of design " ·ork on the full ai r-cooled type of " ·ater recovery apparatus a tube of 1 inch diameter ,,·as assumed and the strength of thin tube of this size was computed. This choice of dimensions has, since been vindicated by the ground and fl ying tests, ~ince tubes of this diameter and the thinnest walls commercially obtainable have proven amply strong, while the back pressure is nearJ~, at the allowable limit. In the theory and design sections of this paper, therefore , only tubing of circular section, 1 inch in diameter, is considered . Having the assumed tube size, t he known total mass flow, and adYantageous mass flow per unit area, the total number of tubes and mass flow per tube is easily computed. In solving equation 5 for q, the mass flow of ai r i\l is determined by the air dcnsit.v, flying speed, nnd spacing and munber of the tubes, " ·bile D has a Yalue a lso determi11ed by t he tube spacing. The diameter of a circle equivalent in area to the space include:l by four tubes was used as an approximat ion. D=-J4:B-d2 in which D=equivalent diameter used in equation 5. d=diameter of tube. ~} =vertical and transverse spacing of tubes, respectiyely. 23 The specific heat of the exhaust gas is approximately constant for the range from 600° C. down to 53°, the temperature at which condensation starts. Assuming t he gas 90 per cent air, with Cp=0.24 and 10 per cent. steam, with Cμ=0.45, the equivalent C11 is 0.26. For the range below 53°, the effective specific heat is very high due to the latent heat of condensation. This was approx imately determined by computing the total heat of 1 gram of the gas mixture at frequent temperatu re intervals below 53° and finding the rate of change of total heat "·ith temperature. This rate of change was taken as the effective specific heat with a mean value of 2.83 in the range 53° to 45° and 1.92 in the range 45° to 35° or 2.20 for the ent ire range 53° to 35° . The figure 45° C. for the exhaust temperature at the end of the second condenser bank \Yas secured b~· successive approximations, and is used only to determine the effective specific heats over the ranges indicated. These values were. checked by a more rigorous mathematical determination which can well be omitted here. The viscosity of the gas changes considerably with ten:iperature but an average value of μ over the range 600° to 50° was taken as 2.4 X 10-, c. g. s. units, t he viscosity of air at 150° C. For the range below 53° it was assumed the effect of the condensing vapor was negligible and the value 2.0 X 10-, c. g. s. units, for the viscosity of air ,Yas used . For the air flowing outside t he tubesμ = l.8.5 X 10-•. Thus we have constant values for the variables in equation (5) so that qb and q0 an'cl consequently qh+q" . qh qc may be taken as constant for each range above and below the condensation point. For a t hree-bank condenser of the general form of Model II it is impossible to directly compute the necessary L on account of the changing functions of t he variables during parallel and counterflow as ·well as t he change of CP with temperature of the e·xhaust gas. The most convenient method is to assume an over-all length for the condenser and work through using the equations given. It is of course necessary to measure or assume the temperature of the exhaust gas received by the condenser, as well as the air temperature. It will be found that there will be left two variables in each case, but that one of them can be eliminated by solving simultaneo11 sl_1· the eq uation expressing t he fact that the heat lost by the exhaust is equal to the heat taken up by the air Design computations will be taken up and examples given in another section of this paper. Inasmuch as the heat to be abstracted from t he exhaust gas varies 1Yith change in composition of the fu el this total heat has been computed for th ree fuels, gasoline and two half-and-half mixtures of gasoline with benzol and alcohol, r espectively. These latter represent two classes of nondetonating fuel P!L rt icula rly suited to the requirements of h igh compression engines. The change in total heat thus computed is equivalent to the heat abstracted in a constant pressure process between 650° C. and 32° C. The ex haust gas is assumed to have been cooled to 650° C. by the piping from the engines. Under these conditions, assuming each fu el burned with a chemically correct mixture rad io, t he heat abstracted is as follows : B. t. u. Gasoline __ _______ ______ ___________________ 5,226 Gasoline-benzoL ___________________________ 4, 564 Gasolin e-alcohol_ ___ ______ . __ __________ _____ 4, 2211 By using Figures 19 and 21 it will be found tliat at the fi nal temperature of 32° C. the water condensed from these three fu els will be 103.0 per cent, 71.3 per cent, and 98.0 per cent, respectively. Owing to the differnnee in mixture ratio, the same engine would burn about 25 per cent more of the alcohol mixture, so that the heat to be abstracted would be brought to about the same figure as that for gasoline alone. For 100 per cent condensation the exhaust from this mixture must be cooled to 30° C. The benzol blend, while having a low exhaust heat value, must be brought below 0° C. before 100 per cent condensation can be obtained. It is indicated, t herefore, that blending of antiknock fuels for airship engines, especially for mixtures containing large proportions of the antiknocking component, should be accomplished b~· the use of alcohol rather than benzol. It is to be noted that exhaust water produced b? the combustion of commercial benzol is very apt to contain sulph ur compounds having a corrosive action on some of t he metal parts of the condensing apparatus. PART III- DESIGN AND CONSTRUCTION For_purposes of illustration the design of a condenser for a class " D " airship is taken up, assuming Maximum B. H. P. equals 300. Fuel equa ls aviation gasoline. Cruising speed equa ls 45 miles per ho ur. Mixt ure ratio equals 15 :1. Referring now to Figure 21, the 15 :1 mixture ratio curve crosses t he 100 per cent condensation line at a temperature of 33.5° C. This is the final temperature to which t he exhaust gas must be cooled. The total mass flow, based on the assumption of 0.50 pound fuel per brake horsepower hour, is 0.50X (15.0 + 1.0) X 300 =2,400 lb ./hr. For a sp eed of 45 miles per hour, a mass flow of exhaust gas of 0.017 pound per second per square inch cross-sectiona l area is about right (see p. 22). Assuming round t ubes of 1 inch diameter (p. 22) t he cross-sectional area of each is -i square inch. The mass flow per tube is 0.017X-i =0.0133 lb. /sec. =6.0 g/sec. The total mass flow is 2,400 3,6oo=0.667 lb./sec. Hence, the n umber of tubes necessary is The r ise in temperatu re of the cooling air must be kept small if the final temperature of the cooled exha ust is to be low. The mass flow of a ir, t herefore, must be much greater than that of the exhaust gas. For this reason the spacing of the Model II condenser was chosen as 2~-inch center to center of t11bes in both directions. The cross-sectional a rea of the a ir Rpare under this co ndit ion is 2~ X2X-i'=4.277 sq . in. per t.1 1be. The mass fl ow of a ir is pVA=Mc in whi ch-p= density = 0.754 lb ./cu. ft. (750 mm. Hg. 15° C.). V =velocity =45 m . p. h. =66 ft. /sec. A= cross-sectional area= 4.277 sq. in . = 0.0297 sq. ft. M0 =0.0754 X66 X0.0297=0.148 lb. /sec. =67 g/scc. From page 23- C0 =0.24. Ch =0.26 above 53° C. Ch =2.83 between 53° C. and 45° C. C1, = 1.92 between 45° C. and 35° C. H ence H c=Mc Cc=67X0.24 = 16.08 and Hh=6X0.26=1.56 above 53° C. = 6 X 2.83 = 17 .0 between 53° C. and 45° C. =6Xl.92=11.5 between 45° C. and 35° C. The t hree values of Hh apply , r espectively, to the first, and first part of the second section , t he last part of the second, and all of the third sect ion, in a t hreebank condenser, since these general temperature ranges prevail as noted. Small departures from the indicated temperature ranges will not affect the values of Hh to an appreciable extent, so that they may with reasonable accuracy be considered as constants. Let us consider the condenser as d ivided into four sectons of which 1 is the first bank, 2 is the first part of t he second , 3 the last part of t he second , and 4 the whole of the third bank. Then, since t he first bank is in counterflow, t he function of H 0 and H h is HI - H1 , h C while the sign changes to plus for the second bank and back again to minus for the third. Calling this fun ct ion of H 0 and Rh, H0 we may compute the following values: Section 1 2 3 4 Ho 0. 580 . 703 . 121 . 0247 The coefficients of heat transfer qh and q0 for t his size pipe and spacing and the corresponding mass flow of gas and air per unit area are computed from equation (5). From pages 22, 23, and 24 the values Cv, M, μ , and D are as follows: c. ______ ____ _________ _______ ____ _ M sec.; cm2 ---- - --- - - -- ----- - -~- D \,t~:-~~'.~s_:: :::::::::::::::::: Exhaust gas above 53° C. 0. 26 L 19 2. 4X l0-' 2. 54 Exhaust gas below 53° C. 2. 2 1.19 2.0X JQ-! 2.54 S11bstituting t hese values in equation (5) qh = 0.0012 above 53° C. q1, =0.0090 below 53° C. g. = 0.0014. Outside air. 0. 24 2. 43 J. 85X l H 5. 93 Hence the values of qh+q. for t he sections numbered 1 to qh qc 4 above are as follows, Q0 representing the fun ction of q1, and q0 : Section Q. 1 and 2 0. 000647 3 and 4 0. 001211 .(24) 25 We may now combine all the fun ctions of q1, , q0 , H1,, H0 , and pin a single list of constants by multiplying together H0 , Q0 , and p. Call t his constant K . The res ults follow: Section K 1 0. 00299 2 0. 00362 3 0. 001169 4 0. OOOZJ9 With t he, above values equat ions 3 and 4 take t i1e fo rm T - t log. - • - "= KL for counterflow Tb- t, and T -t log0 T: - l:= KL for parallel fl ow. For Ta, t he initial exha ust temperat ure at ent rance to t he condenser, 650° C. may well be taken . This approximates t he melting p oint of aluminum. For t,., t he ini t ia l a ir temperature, 15° C. is probably a fairly high fi gure. With t hese assumpt ions only two temperatures and t he length remain to be determined . T he only way to arrive at the desired temperature of 33.5° C. for Tb is to assume a length and apply t he equations for each section, finding t he final T., for t he last section. The length of t he condeuser may t hen be increased or decreased according as t he final t emperature of exhaust is too high or too low. For t his purpose an effective over-a ll leugth of 20 feet has been assumed , making a total length of 60 feet in t hree banks, of which t he second is parallel flow. Keeping to t he same designa ti on of t he four sections involved in t he calculation , we ha ve for section 1 L =20 ft. =610 cm. T . =650° C . . t. = 15° C. K =0.00299 log. i:·= ~:=KL =0.00299 X610 = 1.824 = log. 6.20 650-tb=6 20 T1, -15 · tb = 650- 6.20 T b+93.0 =734.0-6.20 1\ . Simultan eously (T 0 -T1,) H1, = (t1,-t,) H e or Therefore (650 -1\) 1.56 = (tb - 15) 16.08 lb =15 + 63.1-0.09711\ = 78.1-0.0971 1\ . 743.0 -6.201\ = 78.1 - 0.09711\, 6.103 1\ = 664 .9 Tb= 108.9° C. T he condit ions at section 2 are thus determined: T . =108.9°C. t. =l5°C. Tb = 53° C. K =0.00362. Since parallel flow now prevails, the main equation becomes T -t log. T • t"=KL = 0.00362L 1,- b log. 10 ;/_~b 15 =0.00362L 93.9 . L log. 53 -l" =0.00362 a nd al ·o (T . - 1\) l:-Ii, = (l0 -t") He (108.9 -53) 1.56 = (t1, -15) 16.08 ti,= 15+1 1 /0 6 8 (108.9-53) =15+5.42 =20.42 sustituting above for tb 93.9 L 93.9 log. 53 _ 20_42 = O. 00362 = log.32.58 loge 2.88 = 1.058 1.058 L=_00362=292 cm. The le11gth for section 3 will be the d iffe rence bebrnen 610 and 292 centimeters. The condit ions at this section are then Ta=5:{° C. t. =20.42 L=610-292=31S cm. K =0.0011 69. T he fl u,,· is still parallel as in sectiuu 2 so t hat l T.-t, YL ug. 1\-tb = "- 53-20.42 loge T t 0.001169X318 =.3717 =loge 1.-!50 b - b 32.58 = l -! -o T.,-tb . ::, t" = rI\ -22.46. Simultaueously (Ta - T.,) H11 (t., -l,) H0 (53 - 1\) 17 = (lb -20.42) 16.08 l1, =20.42 +56 - 1.056rl\ Droppiug t., rl\-22.46 = 76.-!2 - 1.056T., 1.056 T., =98.88 Tb =48.1° C. The condit ions for section 4 arc now determined ati T.=48.1 t. = 15° C. L,;610 cm. E =0.000239 Tlic flu,,· i~ 110 ,,· changed again tu counterflow so t hat T ,. -tb 1-1, loge rr -t = \. b a loge 4-T8. 1 -lt' b= 0.000239X 6 10 = 0 .1 4 5,s b- ;J = loge 1.157 tb =48.1 -1.1571\ + 17 .35 =65.-!5 - 1.157Tb 26 Simultaneously Heuce (1'. -T,,J H11 = (t1,-t.)Hc (48. 1 -'1\) ll.5 =(t,,- 15) 16.08 tb = 15 +34.4-0.716T,, =49.4 - 0.7161\ 65.45-l.157T" =±9.J -0.716T,, 0.4411\ = 16.05 Tb =36.4° C. This temperature is some1d1at higher t lian that required for 100 per cent condensation under the 14 zz 10 ra /6 14 ~ "~' fl ~ ~ ~ /0 i:: ~ ~ 8 " " 4- ,l 0 -z --+ 17 flO It may be found advisable on account of drainage to cha nge t he position so t hat the long dimension of cross-section is vert ical, as if, for example, it were p laced agaiust the side wall of the car of a D or C class ship. It is by no means certain t hat the use of the same number of t ubes in each bank is desirable for t he best condit ion of heat exchange. It is suggested that valuable data m ight be made available by a mathematical comparison of t he present type exemplified by Model II, and one in which the number of tubes in the CoNoJ<"NSE"R L,rNr;rH-/'iu:r F1G. 25 assumed condit ions, but tl1e d ifference is no greater than the probable error in lhe as8111ned values used in comput ing the heat trausfer. The fact that the cool ing surface of the cast aluminum headers has not been taken iuto consideration a lso makes probable a somewhat better performance than that indicated by t he computations. It is not assumed that a three-bank condenser of t he same type as Models I and II is the ultimate solution of the p roblem of exhaust heat transfer. ,vhen t he construction and arrangement of the a irship permit, it may be possible to secure better res ul ts by using fewer banks and a greater overall length or vice versa. first bank is increased by one-third or one-half and the number in the last bank co rrespondingly deereased. This would give a more uniform velocity of exhaust gas and might on this account increase t he overall efficiency of the unit. For the p urpose of designing apparatus similar to the two condensers already b uilt, t he computations have been worked out between wide limits of a ir speed, condenser length, and initial exhaust temperature. The final temperature of the exhaust necessary for 100 per cent condensation was taken as 32° C., which allows a ma rgin of safety of 1.5° C. The curves a re shown on Figure 25, which requires little explanation. 27 Assuming the same conditions used in the design computations just preceding, that is, an entrance exhaust gas temperature of 650° C., air temperature 15° and air speed 45 miles per hour, the required length is readily determined. It is only necessary to project the horizontal line of 15° air temperature to its intersection with the second curve of the lowest group and then to read the required length 011 the scale at the bottom of the sheet. The value thus obtained is approximately 25 feet, which is somewhat longer than the value computed. It is to be remembered that the final exhaust temperature in this case (32°) is some 5° lower than that computed for the 20-foot condenser, and that the cooling over the ra11ge of temperature covered by this difference is extremely ineffective, owing to the small temperature head between the exhaust gas a11d the cooling air stream. CONSTRUCTION-MODEL I The parts of the Model I condenser are few in kind if not in number, and the machine work necessary is not excessive after the necessary tools and fix tures are at hand. The materials used are a commercially pure aluminum for the tubes, and F lynite, 3 a light alumi11um alloy, for the castings. The aluminum tubes used are seamless, 1 inch in outside diamet er, and have a wall 0.016 inch thick. The manufacture of these tubes is a process susceptible of being held within close limits and 'no trouble whatever was experienced with variation i11 diameter. The weight of the tubing as it comes from the mill is 0.0591 pound per foot. There are 51 parallel tubes in each of the three banks of this unit, of which two require a tubing length of 20 feet and the other 20 feet 10 inches. This gives an aggregate of 3,102.5 feet and a total weight of 183.4 pounds for the tubing alone. The principal castings are those used as return bends and entrance and exit headers. The pattern was made with removable lugs and flanges, thereby serving for four different castings as indicated in Figure 26. The use of the lugs for anchorage of horizontal and vertical tie rods is best illustrated by Figures 5 and 7. The castings made with the flange in place were sawed t hrough with a narrow milling cutter, thus provjding wi th one operation two entrance or exit headers provided \Yith flanges having a finished surface for reception of ~ gasket when attached to the header manifold, as indicated in Figure 6. The only other castings are the three-hole tube connectors, Figure 27, and the header manifold 8hown in Figures 28 and 29. The former serves the purpose of joining the fore and aft tubes of the lowest bank of the condenser, while the latter distributes the exhaust gas from the line to the individual headers at the entering encl, and collects it again at the exit for conveyance into the separator. The problem of joining the tubes with the headers was the subject of much consideration before the 3 F lynite is a copper-a.Juminum alloy containing about 10 per cent copper, balance aluminum . It closely corresponds to alloy No. 2 as . described under Specification for A)uminum Alloy Castings, International Aircraft Standards, 3 N 11; October, 1917. method used was tried and found to be satisfactory . This joint is made by forcing the thin tube into a hole whose sides a re first parallel and then tapered until a shoulder is reached. Details of the holes into which the tubes are pushed are shown in Figure 30. A leakage test of a joint thus made was conducted ~s follows: A 10-foot tube was driven into one of the nipples of a return bend header casting (Figure 6), using a mixture of litharge and glycerine as a cement. The other holes of the casting were plugged with corks, and the whole assembly filled with water and left with the tube extending upward for a period of 24 hours. No leakage was discoverable. On attempting to remove the tube from the nipple, it was found necessary to drive the header off the tube by means of a heavy hammer. The process of machining the header nipples and three-hole connectors for r eception of the tubes is relatively simple, but req uires care and can not be hurried greatly with the tools thus far developed. The header casting or tube connector is first clamped to a fixture on the bed of a vertical spindle mill with the nipples pointing straight up. A rough boring tool is then carried right through the nipple, leaving it approximately the diameter of the inside of the tube. This tool is removed and a finishing cut is made with a piloted reamer which leaves a 1-inch hole having parallel sides for a distance of one-half inch and tapering 0.006 inch in the next three-eighths inch, ending in a shoulder at a depth of seven-eighths inch. The headers used to connect the tubes with the header ma nifold a re machined for reception of the tubes before being cut through the flange. The assembly is accomplished by driving the headers on the tubes after first smearing a t hin mixture of litharge and glycerin _in the holes. The condenser is first built up in sections as shown in Figure 31, and 17 of these are bolted together with -A--in ch chrome vanadium st_eel rods. Short pieces of aluminum tube strung on the rods keep the headers properly spaced. The entrance and exit headers are then secured to the machined face of the header manifold with filli ster head machine screws. An asbestos gasket in terposed between headers and manifold sec ures gas tightness at t his point. The vertical tie rods a lready mentiouecl are made up of !--inch stock in order to provide s ufficien t flexibility to allow for differential expansion clue to temperature differences between the upper and lower sect. ions. The front and rear upper banks are mechanically connected by stiff steel straps strung on the transverse tie rods between the headers as shown at A in Figure 32. The collect ion of condensed water is taken care of by drains from the low poi nts as shown in Figure 5. The drain at t he extreme left is made up of i -inch copper t ubes running from fittings screwed into the header castings to a i -inch iron pipe which conducts the collected water to the ballast tank. The other drain from the condenser proper is shown in Figure .5 emerging from the center of the apparatus. On account of limited space, short tee fittings are screwed into these headers, and these are connected straight UN/Yclf'.f"AL #EA.t?Elf' ...9LUN'/NU/V C..4S77NG :28 @-MT/r fi8NG'E ~ . ONLY - EST. W6"T I. 7 LL?. ~ Jf'/T# fl..4/VoE JI '/ Lu'6J#" - E.f'T. Jf/67. 1. ll L#. @-JWT# LU6S"C" IJ&Y-/Vt1 /Z/W6"E- EfT. H'6'T. !.S LO: ~WITH L.t/GfLl"(-C"-/V,?/ZA/Vtf'E-EfT.M,T. /.GL§. WALL TH/0<,'NEff Tt? BE ,;/TIYRL/t?UT#EA',tJER, PATTERNJ' Ft?R fiAIVuc :4" ,LUo ,r~ z-·= ,fY J'E-TE,/ fl' PETACIYABLE F.-.V #E,9,tJE,(! P,9T?cR,V. FIG. 2C t--t--+;,-,--.., :-··_ ------- . 3.--' >---------+-1 / --+------< c;: I I I t-.!<0 I - j__j_J..:::fj~f - -I I---+--_,__.,___;_.,, I • . I I I 1. -r1 > ,1cu I.- +--'-f--'-t-,--i-~ 'ri--t-Jro -+---+-+--41<-H--J-¥-,~ I I I 1 1 I 1 1 I I I ..l,..4-~- /0 - S/9 CIJ/1//JE/YSER Tv'L?E CIJ/Y/VEC!TOR 17- fiLt//JI//Vt//11 C/ISTI/VG (LY/V/TE) SVP£RS£0E~ /0-4~ I( /4I' 0 . I " I " --~~~12~~--+-+I~ 7 " 8 /" i--+--1--11----+---+-++---+-s 4- -+- - _L__---+-'-- F IG. 27 ~ ~. +-+-+-t-i - ~ r ";' :~ j~H~111T~~+hrl~-~~-~-~-=~-=-~-~-=~-~~-~-~-~-~~~~~-~-~-~~-~-~-~-=-~---------------- f ~ ---,---.i:=:r---3[- --t----t--,-.t--,f ------.A ----- ,9 - -I~.. . r--- , , , ~TT ·-- -ti -"- -..,-- ,·---~ T - ..J- -.&.--•L-.J-l t 1, - ----- ----+--------------1 ------ --- ----------- FlG. 28 -- ---------- --~-- I ...! B "'1 .. ,'9 l' CIQ1~ .r _____ ,,, ----,/1 ----;· _,. .r _,. ! ·(-~ ! _._ --: rT ,--1-n--1- l -'-- u_.J __ ._ _ _..__..__ ;> 111, --+.. ------ --:~rl - - -- - ---- - /r'E/?OER M/JIY/FULP r'f'L'U/>r//VU/'? C"'9S'T//VG 8,1 ------- -?~ - __ ___.:_::.i'llll!alllli1111--tt---tt--__JL-- 7:;J- ._. ------+----+------- 7" G# #-~------f---t---~ • -1~~~~ :::j::j::=-:::-=J:t==t==,,~ F IG. 29 32 ~~ Tapered /rom / 'to.99,I.~ B in this len_gth. :Shoulder eQ'uc1! to tube w«/1 th/ckne.ss . De TAILS or= UN1VE.1?0"'1L /J'e;4DE-/? TY.P.c-1-A ScEO!r'AWIN6JX-!O-I FIG. 3:) F IG . 31 t hrough by short alumin um tu bes, t hus bringing all t he collected wa t er out to one point from which it d rains to t he t an k . The other d rain is from t he false bott om of t he baffl e-type sepa rator Rh own a t upper ri gh t in Figure 5. In orrler to counteract a nY t endency of the tubes to creep out of t he headers, a nd to t ake care of t he poss ible end t hrust d ue to explosions of unburned gas in t he condenser , ~o. 22 steel p iano wires wi t l1 t urnbuckles were strnng between and paral lel to the tubes, ty ing t h.e headers together and t ru ssing t he stru cture d iago na lly in the vert ical pl a ne in o rder to gua rd aga inst st resses imposed b.,· un equal tension of support ing cables . These wires may be seen in Figure 7, and are indica t ed by t he lines BC, CD, E F , a nd GR in F igure 32. MODEL II The castings of the Model II conde nser a rc of t he same mater ial (F lyn ite) as t hose of Model I. Figures 33 and 34 show the deta il of t he ma in header casting, nsed for both en t rance a nd exit a nd return bends. The header cover , Figures ·35 and 36, is 1he return bend used to co nnect a dj acen t banks. The e ntrance und ex it elbows a rc idcnt icul, a nrl a re i11u strated b)' F igure 37. The condenser tube suppor t s, Figure 38, serve to connect I he 10-foot lengt hs of t ubing in ea ch bunk. T he joints between t u bes and headers a re made as in t he Model I conde nser b.v pressing the t ubes into t he tapered h oles in t he header nipples and t he bushings of t he tube supports. _GAS /=4-ow /="HOM .E'N6I NS- ·17 ,v,,w.s 17 lf'OWJ' 17 N'OW'J" 10.ts'' - ----10..!. 5'· -------- ~ ----- 10~0" ==- F IG. 32 ~ ; - e { I I m--f ----- ' I --4-- e 4-· i f.--- 1 - - -- e.f - + COVE!f r/lCE 5eCTIOIV T/1/W t 11-/i FIG. 33 --,- I B +-------------- 7/" __ .J.._ _______ -'-----'---------/1.f:" --------------< L__l~~~=---\j/,,- =--~~:tj-~~-- ,:~.1T.p.-.-- ~' -_--}-:::: ~.,~i/,,' ::::::_-_-_-_ \-:]<?."~ ----- -'.~. j-?:.,;I ~',c::_~ :;. ,' -------~ ... -j-_, l, I( ·,' ,'- . ·------·, , ! . i ! l :7 '1 - - r---------, I I r, ---1-- 1 I I 1 : l I I I I I I I I I I 1 1 I I ·I ----'LL! ___ ul ___ ...LL _ __J1.J_ _ _J_.__ __ -11.L_ __ __Llc___:._ I __J 1tJF -I EJ ,, I 5/DE VIEW if SeCTION" T/1rW . i.. 3-5 Fra . 34 36 ~ lttl. I I I I I I~ --" .\J" I I - I J~ ~ 1,1 \J I I ,~ I I " \ I ·J+ --~ \ I I I .,~ I \ I I I ") I \ I ' I I \ I I I I I I \ I I I ~ I \ .1 .... ,1, I \ I I ~ I \ I I I I I \ I I I -i- \ ~ I I I '- ~ ,__ \ ,J, I I t0-~ CS) I _ll@- \ € -k- I I I I \~ ,,,,\t I I I I ,-1.- 4~ I I, 111 I I I A_!_ I ,~ I \~ I 1:~ ~/I I ' -+-1 I - -- I I .,,..:::,::~ I ---~ ~I I I- - I /,::, / I I I I ' ~ ~ / / I I I ~ I I I / / ' ~ v/m I I I I 111 -++ \ I I I ., ., I - 11'1 I I I I\ : I I s ~ ,, I -1--9-- li I -~B- ] \\ I I I "" : ,j ,, I I I ,, _.,,_;::;,, I I - r--- j I ,v I I '*--,~,. I JI; lr~' I I ( ~\ I I ~ I 1 ' r I I -~+ ~ I I i I I I {~ D "" I I · I I I ~ 1 I I I I I I I I I I I I I I I I I I I I I I I-I ' ' 'Z" ' l ' I _a __ '_., I I i I I_,, J I ~ I ,- -- I I I I ~·- _2 _ _ H I ~ I I I I --1!::f._ H-I I I I I I '3i: I I I I I I I I Ei -- 1- ~ -- __ J ___ I I I I 19* : ,_ ,_ I I - I -- I - \~ ) ,, 164- ,, ~) V. I #E..-1'£'.?ER COVER ( ,,e~TP ~/V $£NP} ~/ l ~ / -/1".LV ,.A,1"'/NP,¥ c ,,..,...,..r/NG ~ -~/ ..... / £.s-7". ff'E/ G /rT- L .i' -~~ I '---\_-~~ 1 17HJW Tl/JC£, !:U[Q J( l)I J;,r ,.,~,i BlJRfJ ll or SONOAR!)S . - • W46'HfiY010N. 0 . O SO l <( /"QU.r/.~ =-'"'"'"" H.,,.,j ulY. lit ! CO..-V.OE/VS~,E' ,~""-'*" 111•,u "1·1-ZI 14 -?-ll ?·l·Z,/ l S(CT. 1 IHE-9Db~~ff~-""- ,/,1'-,!-,Z FIG. J5 I I I I I I I I I I I I I I I I I I I I I I I I I / / / · / I I / / / / 37 --- ----- £NP VIEW SECT!O!Y / / / I / / / ,,, .... / SECTICN 8-8 IJIA# TH(IEO llfOIE ,.... -Z-Z/ -,--,.z1 .,£er. 1 F IG. 36 B,,C,,A,U ..F R.I. ,.r.t.. , .u-~-?# Jr1 -=:-:=:=:-.-=::-==:=-:-=-=-=-=:-=-=:-=-::-=----j~+ rh+-~ -------------- -~L-- '- --+----- ----- --------- - - --1' -- ---r---....,.'--------- ~ ~ i\_ \ 1, -- --- - - - -------:-..'}'.'.....l~,,:.....- . ~ i-----,. - --:r ~ - " r --- ---------------------i:f---~----i;~· -=-::..:::..:=-::::-=:-==-=-==:============j~~ , . \ t' : I : I I ' I I r , , . -., . I 38 ~ r ,Ly;;,-;;;,-::=:=-=-===·' ' ' 1 .lf"'" I ._.-;;;•, .... ._ I I I --------'_'_, :,::,, ;::.~I -#--f/•- -'1\ ~--.Ji:. ..J..,.~ - - -----'---- --- \1 \._ j [l-..:1 ,. ... ;, :!'.~ i \. 'J!_E'!_:-:-==t='="-='"9 l' IG. 37 -- -- .h'E/9P~~ ELL -A'L.V.H/NM"f' e,,,.s-r/NG F.S-T. ff/E/6"Hr 8 L8. ) £ ,,7 --- BUREAU OF STANDARDS · •• WM.HINOTON I ,I' I I I I I I I I I I j f1' I ~ 1-.: l------~~- I I I L-- ~--.J r-- L-..J, : I I I I ' • I I I I ,...______.., f----+-L'-- - 1 - _J (~1--·: -· I I ''I '' I I I I I L - -- -.J r'-- - -', I l.- - - _ , f- --', I' ~Emf? _sec~ VB"E ..S-L/r",C,O~T -/?Lb'/1:V/VV/>? C"h'.S-T/A/G" EST. ,.-VC/Gh'r- .w!f?. F IG. as 2. '' ' '' I I I ' I I I I '-- _.,, ',-- -4 ;'- - _,. ;'-- '' I I ' ...S-/ D. R~WlfiO IUHII ,/X-L'·,f ' 40 The assembly of this condenser is as follows : Fifty tubes are pushed by hand into the nipples of one header, while a grid or frame near the center of their length keeps the tubes properly spaced. A tube support is then placed against the projecting tube ends, and each tube is withdrawn a slight amount from its position in the header so that it just enters t he corresponding hole in the central tube support. The header and support are then backed up by 6- inch st eel H beams connected by six long !-inch steel rods having nuts for forcing the header and support together. These nuts are taken up until no further movement of the tubes into the nipples can be detected. The beam back of the tube snpport is then removed, more tubes inserted on this side, and the process repeated with another header on the end. It was found that simply extending the rods through from end to end of the two sections would not serve to force on the second header because of the tendency of the whole bank to buckle. For this reason steel bars were inserted between the tubes back of the centra\ tube support and the rods were threaded into them thus leaving the first end unstressed during the as~ sembly of the second. To keep the headers from moving off the tube ends, five 11-gauge spring steel wires were run straight through each section from end to end and secured to eye-bolts passing through bosses between the tubes on the face of the headers. These bolts were drawn up with nuts inside the headers before installing the header covers. The assembly proved to be so stiff t hat the addition of diagonal braces was unnecessary. Differential expansion is taken care of by slipjoints between the banks as indicated by Figure 39. An attempt was made in this condenser to drain all the water condensed in the tubes through the two bosses which may be seen at the bottom of the header bends at the rear end,· Figure 8. It was found that the greater part of the water condensed in the first two sections swept past these drain holes and collected in the lower tubes and elbows or was swept on and out into the separator, overloading the separator drain and causing a considerable loss of water. Sheet metal gutters inside the header casting and leading to the drain hoies remedied the condition only to a slight extent and these drains were finally replaced by a series of tubes attached by fittings to the lowest elbows on the rear lower header. The fi t tings may be seen at the bottom of Figure 8. Operation with the new drains proved fairly satisfactory, although from inspection of the drainage systems of Models I and II it will be seen that the form er has the better chance since the last drains are only 10 feet from the outlet end and hence are in a position to t ake care of the water C'omlensed in the first fi ve-sixths of the condenser. SUGGESTIONS It has been thought advisable to assemble some of t he general points bearing on furt her work. These apply, of course, only to apparatus of the same general type as that exemplified by Models I and II. Probably the most obvious fault of either condenser has been clogging of separator drains. It is of the utmost importance that these be made Jarge and smooth with no shoulders or contractions of any kind whicl; might catch and retain any clogging ma terial. It would doubtless be advisable to make these drains of a diameter of not less t.han ! inch. A noncorrosive ma terial, such as Benedict nickel or Mone! metal could readily be drawn thin and light for this purp~se and should serve admirably for making joints. In laying out a separator it is well to keep toward the lower limit of gas velocity. The limiting values a re about 900 and 500 feet per minute, but 600 should prove an acceptable figure. Below 500 feet per minute the velocity is too low to throw out the water, while above 900 the drops deposited on the baffles are again torn off and return to the gas stream. In assembling a condenser care must be taken to avoid stressing any tube so highly tha t it is distorted at the entrance to the header nipple. Such a distortion is a_ weak point which is apt to crack in service, just as a kmked wire is weakened. The wires used to connect adjacent headers must be designed with regard not only to strength but to elasticity, since the linear expansion of the t ubes is enough to stress them severely as long columns if this is not taken care of by stretching of the wires. It is quite possible that rearrangement of the tubes in order to decrease the velocity in the first section and increase it in the last section would result not only in decreased back pressure but also in increased effici~ncy of heat transfer with a corresponding decrease in weight. If a condenser of the type of Model II could be so mounted that the long dimension of cross section were vertical it might simplify the draining problem to some extent since only four drain connections would be necessary on the lowest nipples of the second and last section. The greatest care must be employed in coupling the condenser to the engine of an airship in order to avoid transmission of the engine vibration s, as · well as to eliminate excessive stresses on the flexible connections. It is al so essential that a condenser be mounted so that only the end where the exhaust enters is rigidly anchored to the car in a fore-and-aft direct ion. The other end must be free to allow over-all expa nsion of t he unit. The most promising fi eld for decreasing the weight of condensers of this t ype appears to be r educt.ion of t he w~ight of the h eaders . Castings can· doubtless be designed which will weigh fa r less t han t hose used and the possibility of building up headers of Rheet ~1.ock should be worth investigating. 'T 111:THOC OF CONNECtlN& CONOl':NSl:R BI/IYJf~ FIG. 39 0 T DETIIILS OF CONDENSER 1tAwrw• NO. .SUP-JOINTS .JK·/O-f
Click tabs to swap between content that is broken into logical sections.
Title | Condensation of water from engine exhaust for airship ballasting |
Author | Kohr, Robert F. |
Date Issued | 1924-05-01 |
Series Information | Air Service information circular (Aviation) ; v. 1, no. 44 |
Description | The maintenance of a constant total lift in lighter-than-air craft falls naturally into two distinct divisions: (1) Recovery of ballast as the consumption of fuel tends to lighten the ship. (2) Control of the temperature and thus the density of the lifting gas in order to compensate for changes of lift due to changes of atmospheric density or superheating of the lifting gas by solar radiation upon the envelope. the recovery of water of combustion from engine exhaust gas by cooling and condensation is feasible as a method for solution of the first problem. This report discusses the principles involved and describes the operation of experimental apparatus installed on No. 1 Naval Airship. |
Subject Terms | Airships; Military airships; Ballast water; Exhaust systems; Condensation; Condensers (Vapors and gases) |
Report Publisher | Washington, D.C. : Chief of Air Service |
File Name | asic044_ocr.pdf |
Document Type | Text |
File Format | |
File Size | 28.5 Mb |
Document Source | Auburn University Libraries. Government Documents. |
Digital Publisher | Auburn University Libraries |
Rights | This document is the property of the Auburn University Libraries and is intended for non-commercial use. Users of the document are asked to acknowledge the Auburn University Libraries. |
Submitted By | Coates, Midge |
OCR Transcript | ! [ LJ 7' ' / ./fJ g 7-ll (2. .. : l / Ji-lt- ~ },...------..,.,...,, l /:~ , ~ > ~.:- \ t 4'•, \ . 9 -· - ..--...., i ~;:-0 '- Auburn University Libraries 1111111 lllll lllll lllll ll/11l l/1111111II IIII IIIII IIIII IIII II/II IIIII /IIIII IIII III 3 1 706 025 85049 1 File D 52.83/38 AIR SERVICE INFORMATION CIRCULAR (AEROSTATION ) Vol. I ( . CONDENSATION OF WATER FROM ENGINE EXHAUST FOR AIRSHIP BALLASTING By Mr. Robert F. Kohr Bureau of Standards Washington, D. C. WASHINGTON GOVERNMENT PRINTING OFFICE 1924 CERTIFICATE: By direction of the Secretary of War the matter contained herein is published as administrative information and is required for the proper transaction of the public business. (n) V ·CONDENSATION OF WATER FROM ENGINE EXHAUST FOR AIRSHIP BALLASTING PART !.- GENERAL INTRODUCTION The maintenance of a constant total lift in lighterthan- air craft falls naturally into two distinct divisions: (1) Recovery of ballast as the consumption of fuel tends to lighten the ship. (2) Control of the temperature and thus the density of the lifting gas in order to compensate for changes of lift due to changes of atmospheric density or superheating of the lifting gas by solar radiation upon the envelope. The problem is of great significance when helium - is us~d as a lifting gas. It is generally conceded by those familiar with the operation of airships that valving of lifting gas must be nearly eliminated before a gas so rare and expensive as helium can be adopted for general use. Inasmuch as the known worlct supply of helium is largely found in this country, it constitutes a national monopoly for military use, and its conservation is therefore imperative. In long flights both phases of the ballasting problem assume considerable importance, but, of the two, the ballast recovery appears to be the more vital. Although the development of both projects was for a time carried on along parallel lines, · it was thought advisable to postpone all work on temperature control until ballast recovery reached a point where satisfactory apparatus was available. This paper, therefore, deals only with the work on ·ballast recovery apparatus. The desirability of making up ballast during flight at a ra.te equivalent by weight to the fuel consumption has been realized since the beginning of airship navigation. A number of means of maintaining equilibr~um have been proposed, including the absorption of water vapor from the air by hygroscopic substances, compression of the lifting gas into rigid containers, and condensation of the water vapor which forms a part of the engine exhaust gas. The first of these proposals seems impracticable on account of the small quantity of water vapor present in the air under · ordinary flying conditions (about 0.0005 pound per cubic foot) and the immense exposed area which would be required. The second method is eliminated by the great weight of compressing machinery and high-pressure gas containers. The recovery of water of combustion from engine exhaust gas by cooling and condensation, however, is feasible as a method for the solution o( the problem. When the usual gasoline fuel is .used , about 1.4 pounds of water vapor is formed for each pound of fuel burned. This affords an ample margin for inefficiency in the process of cooling the gas and separating the entrained moisture, so that extreme refinements are unnecessary. PREVIOUS WORK The recovery of water ballast from engine exhaust gas is the subject of a publication of the (British) Advisory Committee for Aeronautics, by Guy Barr, elated September, 1915. This report discusses the principles involved and describes the operation of experimental apparatus installed on No. 1 Naval Airship. The apparatus embodied a water-cooled muffler at the engine and a single air-cooled pipe of 4-inch diameter, about 400 feet long. Separation of entrained moisture at the end of this pipe was accomplished by making the cooled gas bubble through water. The engine served by this apparatus had an output of 180-200 horsepower. The test quoted lasted 35 minutes and yielded water in the amoimt of 52.2 per cent of the weight of the fuel burned. During this period there was a marked increase of temperature, both in the exhaust gas and the cooling water, indicating a decrease in the per cent recovery with further operation. In view of the crude apparatus used, the result might well be regarded as having given promise of future success. When the work described in this paper was initiated at the Bureau of Standards, the Navy Department was testing an experimental water-recovery apparatus developed by Mr. H. S. McDewell, engineer in charge of the Aeronautic Engine Laboratory. The Navy Department, through Mr. McDewell, was kind enough to give every possible assistance to this bureau in determining the lines which might most profitably be fo llowed in further work. The Navy apparatus embodied a length of about 50 feet of 5-inch finned sheet-iron pipe, for initial air cooling, from which the exhaust gas passed to a jet condenser, and thence through a baffle type separator to the atmosphere. From the separator and the jet condenser the water drained through settling basins to radiators, and was then p11mped back through the condenser jets. The excess water, representing the recovery from the exhaust gas, was drained to buckets and weighed. This apparatus produced, 11nder favorable conditions (cold weather), 1.2 pounds of water per pound of fuel burned . Mr. McDewell must be credited with haviJ1g ( 1) -...-- -- • I demonstrated the entire feasibility of collecting exhaust water in sufficient quantities to fully compensate for the increased lift due to fuel consumption . The apparatus used in this work was constructed with little regard for weight and as a result, was far too heavy to be used on an airship. Mr. McDewell estimated that, by exercising the greatest care in design, the weight of such an apparatus could be reduced to about 6 pounds per brake horsepower. SUMMARY OF WORK AT THE BUREAU OF STANDARDS It is to be noted that both the systems already outlined involve t he use of both water and direct air cooling. The same general scheme was at first followed by the Bureau of Standards in laying out a proposed experimental design . 2 This first design differ ed only in detail from the Navy apparatus already described . The settling basins were replaced by a centrifugal separator and the whole apparatus was made as compact as possible. Computations based on this arrangement indicated that the apparatus, exclusive of radiators and cooling water, could be built within weight limits of about 2 pounds per brake horsepower. While collecting preliminary data necessary to design such an apparatus within acceptable weight limits, a critical analysis was made of the fundamentals entering this heat transfer problem. The primary requirement to be met was that all the heat abstracted from the engine exhaust must be delivered fairly promptly to the air through which the ship moves. No large heat reservoirs could be used, nor did the cooling problem offer any similarity to that of a marine or stationary gas engine, where an unlimited quantity of cold water is available. The cycle is parallel to t he cooling of a motor car or aviation engine, where, if water is used to take heat from the engine, it must in t urn give tip all this heat to the air, and return to its original temperature before again abstracting heat from the engine. In such cases, a water system, as opposed to direct' transfer of heat from t he hot body to the air, is introduced solely for the p urpose of utilizing much more effectiv ely some factors concerned in the heat transfer process. Unless t here is such a compensating featme, no ju t ification for the extra weight and inconven ience of the water syst em exists. The present problem seems to differ from that of an engine cylind er, in that there seems to be no reason why, in the direct transfer of heat from the hot gas to the air, every unit of cooling surface and every degree of temperature head can not be used to maximum advantage. Accordingly, the information regarding a ircraft radiators, obtained in several years of work upon this subj ect at the Bureau was brought to bear upon t he question of securing the most effective direct heat exchanger to take heat from a hot gas and deliver it to a stream of air. By the time the proposed design and weight estimate for a water-cooling syst em were available, the invest igation of the direct air cooling method was well under way and seemed to give promise of somewhat lower weights. The jet condenser system was held up pending the completion of the preliminary air-cooled design, and was then definitely abandoned in favor of the latter which showed a designed weight of about 1.5 pounds per brake horsepower, complete, in addition to avoiding t he mechanical complications of water cooling and handling apparatus. While t he detai led d esign of the test apparatus was being carried forward, it was thought advisable to check the theory involved by a laboratory test of a sma ll section similar to the proposed full -size apparatus. With this end in Yiew a wind tunnel of 9 inches sq uare section was constructed, served by a centrifugal blower fan driven by a small automobile engine which also furni sh ed the exhaust gas . A condenser was made up of standard 1-inch iron pipe, with three 20-foot banks of t hree pipes in parallel, having return bends connecting the successive banks. This was installed in the tunnel and connected at one end to the engine exhaust manifold, and at t he other to a small baffie type separator . Measurements were made of gasoline consumpt ion, exhaust water collected, air velocity and temperature, and final exhaust temperature. The resvlts were found to closely check those expected from theoretical considerations, and the work of construction of the •fullsize units was begun without further delay. The full air-cooled system allows of extensive use of aluminum in the form of thin seamless t ubes and cast headers. The design and detailed description of t he two condensers built are discussed in Part III. In general, the method is to pass the exhaust gas at high velocity through parallel lengths of about 60 feet of 1-inch aluminum tube, the outer surface of which is swept by air at a rate determined by the flying speed of the ship. For convenience, the 60 feet is arranged in three banks connected by return headers, so that the overall length is about 21 feet. To handle the quant. ity of exhaust gas produced by the two 150-horsepower engines to be used , with due consideration for the desired velocities and back pressures, there are 50 -such cooling t ubes in parallel. The who]e ·unit presents t he appearance of 150 parallel 1-inch tubes in one bank whose overall length is 21 feet. Both Models I and II have t his general form, although t hey differ considerabl, v in details of construction and arrangement of the hot and cold banks of t ubes. Both of t hese units are intended for suspension between the envelope and car on Class C and D airships of the original design, and a re normally slanted about 6° downward to t he rear to assist in draining the tubes of condensed water as well as to provide some cross flow of air between them, t hus avoiding the loss of effi ciency clue to heated a ir coming from a hot tube and striking a cooler tube fart her along. In each case a baffle type separator is provided to collect the entrained moisture from the gaseous produ cts leaving the condenser. The first of these condensers, Model I, was set up for a ground test early in NoYember, 1921, using a stock 400-horsepower Liberty engine to provide both the exhaust gas and air stream. The propeller used was furni shed by the Engineering Division, Air Service, and a calibration had shown that. it would absorb 307 horsepower at 1,600 revolutions per min.ute. /' ' 3 The complete set-up is shown in Figure 1, from which The endurance run was begun on March 11, 1922, it will be seen that the suspension of t he condensing and was terminated at the end of 90 hours, April 3, unit is taken care of by six diagonal cables from the because of failure of the engine. It was thought that supporting posts, simulating as closely as possible the the endurance of t he condenser had been sufficiently proposed installation on an a irship. It may be men- demonstrated. The r esults are indicated in a later tioned here that the apparatus shown, without sus- I section of the paper. FIG. 1 pensions, separator , or exhaust conducting pipe, weighed just 400 pounds. When installed on a ship the total loss of lift would probably not exceed 450 pounds. The results of t his test showed the performance of the apparatus to be satisfactory, and it was decided that an endurance test of 100 hours should be run to ascertain the effects of continued vibration and After the completion of the endurance test the ap- . paratus was taken down and packed for shipment to Langley Field. Another Liberty engine was set up and the Model II condenser swung in place for an endurance test. It was thought that 50 hours would be enough to show up any distinct weakness of construction, and would allow of a considerable saving of Fw. 2 possible carbon deposition. ,vhile no pro v1s10n was made to secu re a uniform ai r blast over the condenser, thus permitting of securing suffi cient p hysical data to check the theory of its design, it nevertheless seemed advisable to make such meaurements of temperature as could be easily secured. Accordingly, another setup was made in which were incorporated a number of thermocouples at various points in the exhaust gas stream as well as the necessary weighing apparatus for gasoline and collected water . ~ ------------- - - - - - - - - - money and t ime as well as avoiding many of t he delays incident to engine trouble. The Model I condenser was shipped to Langley Field early in the spring (1922) and authorization was secured for the use of Airship D- 3 for two months in order to carry on flight tests. The work of installation was begun about July 21 and t he first fligh t was made on the morning of August 17. The condenser is shown in position on the a irship in Figures 2 and 3, which were taken just prior to the 4 FIG. 3 initial flight. A comparison of size with the whole some heat from the surfaces of the warmer second half. ship, car, engines, etc., may be had in Figure 2. Figure The schematic diagram, Figure 4, illustrates the flow. 3 shows some of the detail looking from the left side. The detailed arrangement of tubes and return The separator is mounted at the upper left in Figure 3 headers is shown in the photograph, Figure 5, in on the side opposite the observer. which the exhaust enters at the upper left while the During the first flight the exhaust piping developed air flow is from right to left. faults and water leaks were discovered at the first It wiU be noted from the photograph of component drains from the condenser. These were repaired the parts, Figure 6, that an attempt \Yas made to streamnext clay, and the ship was again flown on the afternoon of August 18. No further mechanical trouble appeared and, after one short flight on the morning of August 19, the ship was flown to Aberdeen Proving Grounds, where further flight work was conducted. The D- 3, equipped with the Model I condenser, was flown for a total of 53 hours, and during the greater portion of that time the apparatus was found to func6AS 6-4S 0(.ITJ.l=T -~E~NT~NII=NCE= =;=» ~l:= ======7~~ -~ FIG. 4 tion satisfactorily. A detailed account of the results line both the headers and header manifolds in order lo appears in another section of this paper. DESCRIPTION OF CONDENSERS !Ji the Model I condenser the tubes are arranged so that two-thirds of the total cooling area is in counterflow; that is, having the direction of flow of the exhaust gas opposite to the flow of the air stream. In addition, if the unit be considered as two halves, front and rear, the forward half is the cooler one, thus providing a secondary overall counterflow effect, since the air passing over the fir st half will still be cool enough to abstract secure the best possible conditions of air flow around the castings and between the tubes, as well as to keep down the head resistance of the apparatus as a whole. The result is shown in the encl view, Figure 7, lookiPg in the direction of the air stream. The Model II condenser, figures 8, 9, and 10, differs from the Model I chiefly in respect to arrangement of tubing and type of header. The flow of ' exhaust gas and air is two-thirds counterflow as in the case of Model I, but no attempt was made to secure a corresponding over-all counterflow effect. The schematic 1 5 FIG. 5 F 1G. 6. - l. Tube. 2. B ender manifold. 3. End heade r. 4. Return header. FIG. 7 G FIG. 8 FIG.) FIG.LO diagram, Figure 11, indicates the direction of gas and air flow. The construction is somewhat similar to that of Model I , a lthough t he headers are of an entirely different type. The same ma terials are employed, with the exception of the first 10-foot section which, in this case, is of Benedict nickel, a commercial a lloy containing 16- 18 per cent nickel, balance copper. This material is used to avoid warping of the tubes due to the high temperat ures in t his section. GAS l:Nr/1'ANCI: ::>) -~~~~=~(i~A?- OUTL~T F IG. ll In Figure 10 it will be observed that in the middle layer of the upper bank many of the tubes have taken a decided permanent set. This is due to the poor gas distribution between the tlll'ee layers of the bank in question. The exha ust gas tends to flow through the central layer on acco~mt of the more direct path as opposed to the elbow nipples of the outer tubes. For this reason the center tubes are hotter, and their expansion greater, with the r esult that they fail as long columns. These tubes are of aluminum. It is noted that some of the upper tubes at the far end (Benedict nickel) are also bent. This, however, is a result of accidental mechanical stresses and not of any temperature effect . The number of parallel tubes per bank in this condenser is 50, and ea ch bank is composed of two 10-foot lengths, end to end, so that a total of 3,000 feet of tubing is used. For better mechanical stiffness and strength the aluminum t ubing used has a wall thickness of 0.022 inch in st ead of 0.016 inch. This is the thinnest walled tube made as a stock product by manufacturers of aluminum and is far cheaper than the thinner material used in Model I. The Benedict nickel,' which is very easily worked, was drawn to. a thickness of 0.010- 0.012 inch , making it about 40 per cent heavier than the 0.022 inch aluminum tube. The actual weights per foot are as follows : Pound 0.010- 0.012-inch Benedict nickel_ __ ___ ___ ____ 0. 1208 0.022-inch aluminum __ __________ ____ ______ _ 0. 0857 This makes the total weight of tubing 274.6 pounds, which is about 50 per cent higher than that of Model I. The increase in tube weight, however, is offset by a decrease in the casting weight, to such an extent that the Model II condenser is only about 9. per cent heavier than Model I. The actual weights without suspensions, exhaust pipe connections, or separators 7 linear expansion, and a header design providing good gas distribution, the added weight of Benedict nickel tubing would not be justifiable. The importance of the separators for the collection of entrained moisture can not be overemphasized. No matter how low a temperature is reached in cooling the exhaust gases, much of the water condensed remains in the form of ~pray and is carried along by the gases until the separator is reached. In the absence of such a device this represents a loss of about 50 per cent of the water condensed. Since the functioning of the separators is the same for both condensers, only the Model II will be described in detail. This separator was bolted up directly to the exit elbow shown in Figure 9 and extended back under the condenser, where its free end was supported by wires extending diagonally upward between the tubes to the header casting above. The separator is shown in some detail in Figures 12 and 13. Its action depends upon the drops of water being thrown against the baffles shown in Figure 12 and guided by the small vertical gutters to holes punched through the bottom to a fal se bottom, from which the collected water is drained to the ballast tanks. The exhaust gas enters at the upper right, Figur~ 13, passes between the baffles, and escapes at the left. It will be observed that there is a lip on the outlet end to prevent t he separated water washing along the bottom past the holes and so escaping with the gas. The separator is built of tinn_ed sheet iron, and is soldered together. This material was selected purely because of its availability and the ease with which it can be worked. Some noncorrosive material .such as aluminum or a copper-nickel alloy might be a decided improvement. The Model I separator, differing only in outer shape, may be seen at the upper right, Figure 5, and upper left, Figure 7. TEST RESULTS The results of the 90-hour ground test of the Model I condenser are shown graphically on Fignre 14. A summary of the results follows : Average air speed entering condenser __ 48 m. p. h. Average air temperature ________ _____ 1.5° C. Total weight fuel used ________ _____ ___ 15, 075 lb. Total weight water collected ___ _______ 13, 943 lb. ·water collected 2 _ _ _ _ _ _ _ _ _ ______ _____ 92. 5 per cent The recovery is somewhat low, but t his is not inherently a fault of the condenser. , Trouble was experienced during the test, with misfiring of the engine, cracked exhaust ducts, small water leaks at drain conare as follows: Pounds nections and thermocouple bushings, ,and clogged Model!_ _____ ______ _______ ___ ____ ______ _____ 400 drain pipes. Inprovements in construction should Model IL ____ _________ __ ___ ___ ____ ____ __ ____ 434 obviate these difficulties and materially increase the It is proba ble t hat wi th exhaust pipe connections of ample flexibility, freely moving slip joints to t ake up 1 Benedict nickel is a copper nickel alloy used largely in the manu· facture of plumbing fixtures on account of its noncorrosive character. It is easily worked and has a bigber tensile strength tban aluminum. 96997- 24t--2 recovery. 2 The water recoverable, water condensed, and water collected, when expressed as per cent, are based upon the weight of the gasoline or other fuel burned. Thus, a recovery or collection or 100 per cent exactly compensates for the weight of fu el burned. I 8 42-'' Fir.. 12 'Ten roi,vs or bo/'rles equa//y spaced as shown-end prov/ded wir.17 f "r/aps ,ror so/den~ T() rop and bofron1 o.f" veparalor . .5ee baf'f'!e A-A/ far details I ==)_ .3" ~ P/),e collp/1~ .solderec/lo raise bot/on, ror clra/n connect/on. FrG. 13.-Moctel II separator elevat ion 60 ~ ~ i:: ~ \] 40 ~ ~ ~ c:s I "~' 20 K ~ ~ ~ 0 60 1-0 zo 0 .90/loul? f:NOURANCC li'uN- Mooa I CoNocNSCR OK£. Tr-P.t: FIG. 14 . I ( I ~I ,' 10 !n ·conducting this test it was intended that a ·"helium heater," for regulating the temperature of the lifting gas, should be tested at the same time. This apparatus was connected into the exhaust line by a bypass valve which allowed of passing the exhaust gas at will through the heater or direct to the condenser. The valve plate was of brass, clamped to a steel operating stem by set screws. Shortly after completion of 50 hours of operation the set screws loosened, dropping the valve to the position necessary to cut in the heater. As the valve was very inaccessible, and inasmuch as the test was for the purpose of demonstrating the mechanical strength of the condenser unit, the run was continued under the new conditions. The point at which the helium heater was cut in is readily observed on the chart, Figure 14, from which it will be seen that the change came during the fiftysecond hour of operation. For this reason the recovery header. The tubes were in a similar condition, with the addition of white corrosion spots at frequent intervals. These spots were not deep and gave no indication that trouble might be expected from this source. It will be noted also in Figure 15 that the machined surfaces of the nipples show no signs of exhaust-gas leakage. With regard to carbon formation it should be noted here that the engines used, both in this test and in the 50-hour test of Model II, were equipped with the Navy type oil scraper pistons which were known to materially reduce the oil consumption. It would seem that every effort should be made to minimize oil consumption when exhaust-water-recovery apparatus is to be employed. Some of the castings used in the construction of the Model I condenser had been found porous and were plugged with aluminum solder in order to stand the FIG. 15 and fuel consumption have also been computed separately for the first 50 hours of the run. The results follow : Average air temperature ______ ______ __ 16.5° C. Total gasoline burned _________________ 8,126 lbs. Total water collected _________________ 7,662 lbs. Water collected __ __ ___ ________ _____ __ 94.4 per cent. These results indicate that the decrease of the exhaustgas temperature at the entrance to the condenser was more than offset by the increase in the losses, already mentioned, during the last 40 hours of the run. The carbon or soot in the water collected took the form of a light foamy scum or a mushy sludge. The latter gave some trouble by clogging drain tubes wherever a contraction or shoulder allowed an accumulation to build up. Substitution of large,' smooth drains should prove an effective remedy. The deposit of carbon in the tubes and castings of the condenser proper proved to be practically negligible . . A light soot accumulated during periods devoted to warming up the engine under idling conditions, but immediately upon opening the throttle this soot was blown out through the separator with the appearance of dense black smoke. After completion of the 90-hour run one of the header castings and the adjacent tubes were sawed into sections in order to permit examination of the carbon deposit. Figure 15 shows parts of this sectioned leakage test. This solder melted and oozed from the pores of the exhaust entrance header manifold during the preliminary ground test but the leakage of gas was thought to be so small as not to warrant replacement. In the light of this experience, however, it would be well to specify that castings for this purpose be required to stand a leakage test without repair of any kind. No mechanical failure of any kind occurred in the Model I unit during all test work to which it was subjected, and the structural design is therefore concluded to be sound, although it is realized that many modifications may prove desirable in laying out apparatus for service use. · Ground test of the Model II condenser is charted in Figure 16. Summarized results follow: Average air speed entering condenser_ ___ 35 m. p. h. Average air temperature_______________ 20° C. Total weight fuel used __ _____ _____ ____ 8,195 lbs. Total weight water collected ___ __ ______ 5,324 lbs. Water collected ___ ____ ____ ______ _____ 65.0percent. The postponement of this test for several months resu1ted in serious rusting of the flexible leads from the exhaust manifolds of the engine to the exhaust pipe line to the condenser, and as a consequence the resumption of test work was marked by persistent occurrence of breaks in the flexible piping with attendant leakage of exhaust gas. Trouble was also en- 60 (j ~ ~w c~s I ~;::s R.zo ~ ~ ~ 0 50 fiouR ENOURANCc RuN MoocL ll CoNOcNSCR PARKCR 'lYPc FJG.15 UJ 20 0 ... 12 countered wi th clogging of t he drain from the separator, owing to rust and sed iment deposits which would not be expected during continuous or semicontinuous operation. In Figure 16 the line of water condensed is obtained by referring poin ts from t he line of final exhaust temperature to l<' igure 21 , assuming the mixture ratio to have been 15 : 1. It will be noted that the line of water condensed is at least in the same general range as that of water collected during the few runs made in August, whereas with the runs of October these lines at once diverge so that there is an average difference of perhaps 20 per cent. This is believed to result from exh aust-gas leaks and \Yaste of water clue· to persistent stoppage or the separator drain. This stoppage causes the falsjl bottom of the separator to fill and overflow , so that the water separated by t he baffles from the· issuing exhaust gas can not drain off and is swept out by t he gas. The only mechan ical failure \Yas occasioned by .differential expansion of the entrance header elbol\· and the header bolted to it. The entrance elbow casting was, of course, hotter t han the header proper, and the upper fl ange of the elbow warped ·upward, pulling off the lugs of t he corrcsponcli11g flange of the header. This occurred early in t he test and \Yas remedied by passing a bolt through the elbo1Y castiug, thu~ drawing down the upper edge and holdiug it permanently in place. The bolt may be seen in Figure 8. A condensed log of the flight tests of i\Iodel I condenser is shown in Table 1. Totals and averages follow: Air temperature ____ _____ ___ __ ____ ___ -22° C. Total weight fu el burned ___ ___ _______ 2,799 lbs. Total weight water collected ______ __ __ 2,170 lbs. Water collect ed ____ ___ _ _____ _____ ___ 79.4 per cent. In rn.aking up t he separator drain from whate.ver ma t erials and fittings were a,·a ilable, a shoulder was left at the p oint of connection of the drain pipe and separator, and this resulted in the loss of a co nsiderable qua ntity of wa ter, clue to clogging of the drain by carbon. 01\"ing to lack of data as regards engine power and final exhaust temperature, a nd to the variation in air speed , no comparison can be made between the t heoretical and act ual res ults on this test. It is t hough t, hO\,·ever, that the leakage of exhaust water due to stoppage of the separator drain and sticking of t he ballast dumping valve may easily account for the difference in " ·eight between the water collected and the fuel burned. It is to be noted that condensers designed for a:n air temperature of 15° C. can not be expected to condense sufficient water to completcl_,. compensate for t he weight of fuel burned when higher t emperatures are encou ntered, as in summer flying. Figure 17 indicates the variation of water condensed with change of a ir t emperature based on the design of the Model II condenser. In computing the points for this curYe, all other conditi ons are assumed as constant. In the flight test , as in t he ground test of t he same apparatus, no t ro'uble of anr kind was experienced with the condenser proper . Some difficulties were encountered \\·ith a ccessories, such as exhaust piping and drain tnbes, but these parts were of a makeshift nature and should give no trouble in a service unit whose parts are well designed and constructed. It is worthy of comment that the installation of the Model I condenser on the D- 3 produced no appreciable decrease in the ship's flying speed at a given propeller speed. Th.is was contrary to expectations but may be readily credit ed when t he immense projected fron tal area of t he ship is taken into account. TABLE 1.- S ummary of flight tests on Nlodel I condenser '"l'ime Fligbt No. \ -- Hrs_:_1;\l: L --·--·-·--· - ·- · •) ___ ____ ____ ___ _ _ 3 __ _____________ _ 4_ - . - -· -----·---· 56 •_._ _·_-_- -_-_-_-__-_-_-_·_· -_-_ _ 7 - - • ---- - ---· - ·-- 8 . -- · ---- - ----· - - 910- _·-__·-_-__-_-_-_- ·__--_· ·__· ·_ 11 . _. -------- - - -- -- -- 12 ___ - ----- - --- - - 3 j ~I 2 3 4 13 18 52 47 9 2.J 59 18 11 1 0 0 :1 I I 13_ __ _____ ____ ___ 4 I o :\lean ___________ '. ------!------ 1 This rnlue not included. Mean air temperature o C. 20. 5 24. J 23. 5 24. 4 20. 5 22. 7 21. 5 18. 5 24. 5 22. 3 Air speed M . p. h. 39 37 46 34 38 44 48 Altitude Feet 1, 000 1,000 800 900 I. 000 950 J, 250 800 50 900 Engine R. p . m . 900 J. 100 1, 000 I , 200 J,000 900 1, 100 900 900 J, 100 J. 200 Water Pounds 206 254 210 212 232. 5 227 180 278 371 G r Water I aso inc collected Pou'rirls 24 2. 5 3:31 285 332 266 302 260. 5 309. 5 4il Per cent 84. 9 76. 7 73. 7 1 63.8 87. 3 75. 2 69.1 89.S T otaL _.. 2. 1 70. 5 2, 799. 5 78. 8 79.4 Remarks "Separator dra iu clogged. Gasoline record uncertain. \Yater spilled in draining. \\' ater leaked through emergenry release v?Jve. Release valve stuck-water lost. Flight abandoned due to oil leak on left . motor. Mean . )i°OTE .- Six preliminary flights were made (total time 12 hours, 46 minutes) in order to eliminate minor mecbaoical defects. The average water collected for these flights was 72.4 pe,r cent . 13 JO -10 70 80 9 0 / 00 //0 /20 · % CoNOEN,5AT/ON FIG. Ji CONCLUSIONS Al1 hough no claim is made for the present general design as repre~eniing the ultimate form of ballast recovery apparatus-, the feasibility of condeusation of water from the engine exhaust as a means of compensating for the increased lift, due to the loss of the fuel burned, has been demonstrated. The weight of the apparatus is not excessiYe and can be wholly rompe11satecl for IJ.v a correspoucling decrease in the \Yeight of the water ballast usually carried. Owing to the large frontal area of an airship, the head r('sistance of a condenser of the type thus far used represeuts such a small portion of the whole as to be nearly negligible. Condensers of the general t_vpe of Models I and II, ha\·ing no moving parts, require little attention and eompare favorably, as regards fly ing li fe , with most aircraft engines 1101T in service use. In cold weather, 1\·ith a couclensat iou in excess of the fuel equilibrium requirements, the exhaust ,rnter may also be used to at least partly compensalc for the change in l ift clue to ('hanging barometric pressure or temperature of the lifting gas. Although some assumptions used in the design work a,ppear to be only rough approximations, none of the test results seem to indicate any great error within the range of conditions thus far encountered. ... PART II- THEORY In reviewing the theory involved in the process of obtaining water from the engine exhaust gas, it may be well, in order to avoid confusion, to first discuss ·the nomenclature used. Reference is made to the chart, Figure 18, in which ordinates represent weights of the quantities indicated. The fuel burned is, of course, the basis upon which the other quantities are determined. The total water ! W'ATEH e1VreRIN6 W'ITH AIH i , perature itself, it at once becomes apparent that the recoverable water is the total minus the vapor necessary to saturate the gaseo us exhau8t products at a ir temperature. The designed recovery is, of cou rse, limited by the recoverable water as determined by an assumed air temperature. It may be arbitrarily placed at any value less than that of the recoverable water, but would not ordinarily be less than the fuel burned. ~ ,.... ·, ~ ~ q~ ~ ~ ! ~ ~ " ~ ~ ~ ~ ~ - R ~ ~ ~ ~ l ~ ~~ Q: ~ "' ....., ~ 8 ~ a\ j ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ V , FIG. 18 in the exhaust gas is the sum of the water of combustion and the moisture entering with the carburetor a ir. This quantity depends upon the kind of fuel and to a small extent upon the mixture ratio. When using gasoline there is present more than 1.4 pounds of water for every pound of fu el burned . Since the amount of water lost as vapor depends upon the exhaust-gas final temperature, and since, in an air-cooled system, the limit of cooling is the air tern- Since the designed r ecovery is based upon a designed final exhaust ·temperature, it is evident that error in design assumptions or changes in flying speed or air temperature will change this final temperature and therefore the water actually condensed. The water condensed may be either greater or less t han the designed ·recovery, but is represented as showing a loss. In the collection of t he water condensed , leaks of any kind, as well as faulty separation of entrained moisture, (14) will lower the quantity actually available as ballast. The water collected is therefore a lmost certain to be less than that actually condensed. Any of the quantities shown, when expressed as per cent, are based upon the weight of fuel burned. The design of the condensing a pparatus is dependent upon a large number of variables 'which may best be taken up as they appear. It is at once apparent that the \\·ater condensed is dependent upon exhaust-gas composition and its fina l temperature. The first of these is readily determined when the chemical composition of the fuel, ratio of air .ss 15 The air composition is approximately oxygen 23 per c.ent and nitrogen 77 per cent by weight. The air temperature was assumed to be 15° C. lower than that of the exhaust products leaving .the condenser. It is obvious that the exhaust gas wiU never be cooled to the temperature of the air. The relative humidity was assumed as 60 per cent, which is an approximate average for all parts of this country for the whole year for altitudes less than 5,000 feet. As a basis of comparison of the different fuels their chemically correct air-fuel ratios were used. ff'o /0 eo 30 'fo SO 60 70 80 90 100 110 !ZO / 30 /40 ISO 7o CCWOf NMTION FIG. 19 to fu el, and relative humidity and temperature of t he air are known . The fina l exhaust temperature; howe, ·er, is a fun ction of the length, d iameter, spacing and number of condenser tubes, mass flow, and initial tempera. tu re of exhaust gas, and the velocity and temperat ure of the air flowing past the tubes. Taking first the effect of different fuels, Figure 19 ,;hows t he water condensed in per cent by weight of the fuel burned, plotted against the final exhaust temperature, for a number of liqu id fuels. In order to arrive at the curves shown it was necessarv to make assumptions for carbureter air composit io1:, temperature and humidity , and n1ixture ratio, or pounds air per pound fuel. 96997-24t--q The condensed water per pound of fuel is, of course, the water of combustion plus the moistme entering with the air, minus the water issuing as vapor with the cooled exhaust products. It may be well to follow through the computation with one of the fue'.s involved. Taking pentane as an example, we have from its composition (C5H 12) the hydrogen and carbon content per pound 0.167 and 0.833 pound, respectively (see Table 2). Then from the combining proportion of hydrogen and oxygen (1: 8) the water of combustion will be nine times th!;! wei~ht of the hydrogen, or 1.500 pounds. 16 TABLE 2.- Combustion data for liquid fuels assuming correct mixtiire ratio for complete combustion Content per pound of fuel Product per pound of fu el Air content Ratio Exhaust Molecular molecular gas Fuel 1-----~---1----.----1---- ---1 Mixture ratio weight we,gt~t weight of au per exhaust molecular pound A ir factor Hz C 02 H,O co, 0 2 ;;~';!\ of fuel --- ---- --- -------- --- - ------ ----- Hexane C,Ht< ---- -- --- --Pentane C,H12------- ---Dodecane C12H20 - - ---- - -- Alcohol C,H,OH _____ ___ _ Beuzol C,H, ____________ _ 'l'oluol C,Hs--------------1 XEtyhleorl CCs,HHI1O0-0- _-_-_-_-_- -__-_-_-_--_-_ 0.163 I . 167 .153 . ] 30 .077 . 087 . 094 . 135 0. 837 . 833 . 847 . 522 . 348 . 923 . 913 . 906 . 649 ---.216- 1 1. 467 3. 07 3. 54 l. 500 3. 05 3. 55 l. 375 3. J05 3. 48 l. 173 l. 915 2. 08 . 692 3. 38 3. 08 . 782 3. 35 3. 13 . 850 3. 32 3.17 l. 215 2. 38 2. 394 11. 86 15. 4 30. 28 0. 952 14. 93 14. 2:3 ll. 89 15.44 30. 28 . 952 14. 94 14. 24 11. 66 15.14 30. 28 . 952 14. 76 14. 07 6. 96 9.04 30. 39 . 958 8. 875 8. 42 10. 32 13.4 30.72 . 939 13. 70 12. 87 10. 49 13. 62 I 30. 68 . 940 13. 84 13. 02 10. 62 13. 79 30. 65 . 941 13. 94 13.12 8. 68 11. 27 30. 40 . 949 11. 06 10. 50 Similarly, we know that the relation of the carbon The total exhaust gas weight, exclusive of water, per d . "d t b . 44 b . . pound of fuel is t he sum of the carbon dioxide and 10x1 e o car on 1s 12, . nngmg the carbon dioxide nitrogen present, or 44 produced to 12 X 0.833 or 3.050 pounds . The oxygen 3.050 + 11.890 = 14.940 pounds r equired for combustion is then the difference between the weight of t he fuel and t hat of t he products of combustion, l.500 +3.050-1.00 =3.550 pounds Since the air is 77 per cent nitrogen by weight, the nitrogen content of the exhaust gas will be ;~ X3.550 =U.890 pounds. and the total weight of a ir per pound of fuel \\·ill be the sum of the oxygen and nitrogen, or 3.500 +11.890=15.440 pounds. Expressed as a ratio of weight, t his is the correct com-_ bining air-fuel ratio. The weight of water vapor which will be taken up by a pound of dry gas at any temperat ure is proport ional to the specific volume of the gas or inversely proportional to its densit y . · For convenience, t he molecular weight is substituted for density. For air, the molecular weight is 100 77 + 23 = 28.84 28 32 where 28 and 32 are the molecular weights of nitrogen and oxygen, respectively. Similarly, the molecular weight of the exhaust gas products, exclusive of water, is 3.050+11.890 3.050 + 11.890 =30.28. 44 28 From this we obtain t he ratio of molecular weights, and hence of the densities of air and exhaust gas 28.84 = 0 952 30.28 · which is also the in verse ratio of specific volumes, and hence the direct ratio of specific volumes of exhaust gas to air. and th·e product of this with t he ratio above gives the a ir factor shown in the last column of Ta ble 2 14.940 X0.952 = 14.240. Since the air factor is the product of t he rat io of specific volumes of exhaust gas and air and t he weight of the exhaust gas (other than water vapor) per pound of fuel burned, t he vapor content of the exhaust products leaving the condenser may be readily obtained by multiplying this factor by the weight of water necessary to saturate a p ound of dry a ir at the same temperature aud pressure. A physical r epresentation of the air factor is the number of pounds of dry air which would be saturated by the quantity of water leaving the apparatus with the other exhaust products from 1 p ound of fu el, · at t he same temperature and pressure. For a constant fuel composition and mixture ratio the air factor does not change. Referring now to Table 3, the first line is the temperature of the exhaust gases issuing from the condenser. T he second line is the moisture content of 1 pound of dry air saturated, at this temperature and atmospheric pressure (Goodenough's tables). These values mult iplied by t he air factor from Table 2 give the water content of the outgoing gases per pound of fuel in each case. The a ir temperatures in Table 4 are shown as 15° C. lower than those of the final exhaust in Table 3, complying with .the assumption made. To ascertain the moisture entering with the air for each pound of fuel it is only necessary to multiply the water per pound of a ir saturated by 0.60 (assumed relative humidity) and again multiply by the mixture ratio. To find the water condensed (Table 5) at any temperature considered, t he water co ntent of tll°e enteriug air (Table 4) is added to the water of combustion (Table 2) and the water content of the exhaust -gas at the corresponding temperature is subtracted from this sum. The curves in Figure 17 are plotted from values recorded in Table 5. 17 TABLE 3.- Pounds of waler vapor leaving with exhaust gases per pound of Juel. Relative humidity, 100 per cent Exhaust temperature, °C 10 15 w I 25 w u ~ ~ - w ~ c. 00764 0. 01068 o. 01476 1 0. ~2017 0. 02729 0. 03662 0. 04899 0. 0654 0. 0873 0. 1156 Pounds moisture per pound saturated air_ _______ __ _____ _ 0. 00542 -----------1------------------------- ------ ---- - - ------ Hexane ___ __ __ _____ __________ _ Pentane ____ __________________ _ Dodecane ___ _______ ______ ----- Alcohol __ - - - - - ------------ ___ _ Benzol __ -- ---- - - - - - --- _______ _ ToluoJ ___ ___ ___ ______________ _ Xylol _______ _________________ _ Ether -- - - --- -------------··-·- . 0772 . 0772 . 0762 . 0456 . 0697 . 0706 . 0711 . 0569 .1087 .1088 .1074 .0644 .0984 .0995 .1002 .0803 . 1522 . 1523 .lW5 . 0901 . 1370 .1392 . 1403 . 11 22 .W85 .W87 . 2062 .1242 .1 886 . Hl09 . 1923 . 15W . 2872 . 2874 . 2838 . 1699 . 2596 . 2627 . 2647 . 2117 . 3913 . 3918 . 3868 . 2297 . 3540 . 3580 . 3608 . 2918 . 5210 . 5215 . 51W . 3080 . 4712 .4764 . 4800 . 3847 . 6974 . 6977 . 6890 . 4125 . 6305 . 6378 . 6432 . 5147 . 9315 . 9321 . 9210 . 5510 . 8324 . 8524 . 8585 . 6872 1. 240 1. 2415 1. 2265 . 7345 L 122 L 1350 L 1435 . 9168 l. 645 1. 647 1.627 . 974 1. 487 L 506 L 517 L 214 TABLE 4.- Po1mds waler vapor entering with air per pound of fuel. Relative humidity , 60 per cent Air temperature, 0 0 - 10 -5 0 10 15 20 25 30 35 40 -----------,---------------- ----- ------- ----- P ounds moistme per pound saturated air _______________ O. 001643 O. 002553 O. 003782 0. 00542 · 0. 00764 0. 01068 0. 01476 O. OW17 O. 02729 0. 03662 0. 04899 ---- ·~1- - ---- Hexane ____ ______ _____________ . 0152 . 0236 .0350 . OWl .0706 .0987 .1364 .186.1 . 25W . 3383 . 4527 Pentane___ ___ __ _______________ . 0152 . 0237 . 0350 . OW2 . 0708 0990 . 1367 . 1868 . 2528 . 3392 . 4539 Dodecane_ ______ ______________ . 0149 . 0232 . 0344 . 0493 . 0694 ·I . 0971 .1341 .1833 . 2480 . 3327 . 4453 Alcohol __ _____ __ ______________ . 0089 . 0139 . 0205 . 0294 . 0414 I . 0579 . 080l . 1094 .1480 . 1986 . 26,57 ,Benzo]__ ___ ___________________ . 0132 . OW5 . 0304 . 0436 . 0614 . 0859 . 1186 . 1621 . 2193 . 2944 . 393~ roluoL ___ ____________________ . 0134 . 0209 . 0309 . 0443 . 0624. . 087a - . 1206 .1648 . 2230 . 2992 . 4003 XyloL ______________________ __ . 0136 . 02ll . 0313 . 0449 . 0632 . 0884 .1222 .1669 . 2258 . 3031 . 4054 E ther_ ___ ___ ________ __________ . 0111 . 0173 . 0256 . 0366 . 0516 . 0722 . 0998 .1363 . 1845 . 2476 . 33 11 I TABLE 5.-Pouncls waler condensed per pound of f uel, assuming complete.combustion. Relative humidity, 60 per cent Exhaust tempera- Water II ___tu _,·e, oc_ __, _ _g _~_~z_otn- --5--·- -10-- _ _ 15 _ __2_0 _ __:__ __3_0 ___3_ 5 __4_ 0 ___45 _ 1__:__ __55 _ _ Hexane ___________ _ Pentane ______ ___ __ Dodecane ____ _____ Alcohol__ ______ ___ _ _ BenzoL ____ __ _____ _ 'l'oluoL ____ _______ _ Xylol. _ ---------- -Ether __ - - - - - - ---- -- 1. 467 1. 500 1. 375 l. 173 . 692 . 782 . SW l. 215 1 I. 405 I. 438 l. 314 l. 136 .636 . 725 . 792 1.169 I. 382 L 415 1. 291 1.122 . 614 . 703 . 769 1. 152 1. 350 1. 383 1. 259 l. 103 . 585 . 674 . 741 L 128 1. 309 1. 342 1. 218 I. 078 . 547 . 635 . 703 I. 097 At the lowest assumed temperature the water of combustion from · pentane is 1.50 pounds (Ta ble 2). Adding to this the water entering with the air (Ta ble 4) we have 1.500+ 0.015= 1.515 pounds Subtracting the water lost as vapor with the exha ust gas leaving the appa ratus we have 1.515 - 0.077= 1.438 pounds which is the water conden.sed . Since it is improbable that any fu el having exactly the composition of one of those shown in Figure 19 will ever be actually put into service use, thfa figme is supplemented by Figure 20, showing the final t emperature to which the exhaust gas must be cooled in order to condense 1 p ound of water per pound of any hydrocarbon fuel within the range of fuel composition apt to be encountered. This curve was derived by plotting the points at which the curves of Figure 19 cross the 100 per cent condensation line. In order to secure the points for the lower end of the curve, fuels having lower h ydrogen content than t he gasoline group were assumed. To find the required final t emperat ure for 100 per cent condensation from any blend of hydrocarbon fuels it is only necessary to k now the h ydrogen content of the mixt ure. The lower limit of the curve I. 250 I. 283 1. 161 1. 044 . 494 . 582 . 649 1. 055 1.174 1.W7 l.085 l. 001 . 424 . 511 . 578 . 995 I. 082 l. 115 . 994 . 945 . 339 .426 . 492 . 930 0. 956 . 989 . 869 . 870 . 224 . 309 . 374 . 837 0. 788 1 0. 565 . 821 . 598 . 307 . 702 1 . 481 . 193 770 . 637 . 465 . 079 - - -- - --- -- 0. 275 .153 - --- - - -- -- - - -------- . 217 1 .010 . 712 . 546 . 332 of Figure 20 represents a fuel blend of about 41 per cent benzol with a gasoline of 15 per cent hydrogen content. All the curves shown thus far are based on the theoretical combining mixture ratios of air to fuel, which correspond to extremely lean carburetor settings and give the economy so vitally important in the operation of airships. Some multi-cylinder engines are unable to operate on mixtures quite as lean as those shown, but since the leaner mixtures are less advantageous as regards water recovery, the curves are based on the worst expected condition and are on the safe side. The effect of mixture ratio upon water condensed at various temperatLires is shown in Figure 21. These curves were computed in the same way as those of Figure 19, as represented by the computation sheets, Tables 6, 7, 8, and 9. The fuel in this case was assumed to be gasoline having a 15 per cent hydrogen content, which closely approximates the fuel now in service use. The final temperatures required for 100 per cent condensation (1 pound of water per pound of fuel) using this fuel and the indicated mixture ratios, are shown in Figure 22, which is obtained. by plotting the points where the curves of Figure 21 cross the 100 per cent line. • <· ... .18 I ~ n ff / M ~ ~ 2 ~ ~ - Z ~ 3 38 'f'O /7/VAL CXHAU.5T ffMPC:RATURe- °C FIG. 20 so / O zo ~o -fO so 60 7o ~o 9o 100 110 120 /30 #O ,so % Cb.lYL7CIY..l4T/ON FJG. 21 19 Since the humidity is uncontrolled, it may be that for special cases some figure other t han the average one of 60 per cent may be applied. The curves of Figure 23 indicate the limits of t he humidity range between zero a 1Jd 100 per cent when using gasoline having a 15 per cent hydrogen content with a 13 : 1 ai rfu el ratio. The data for t hese curves (Table 10) are largely obtained from the mixture ratio computations . ~ Jix ture ratio ~ fu el Oxygen in air TABLE 6 Exhaust gas content \ Moleru- Weightof Oxygen l\1Iole9u- lar we_ight exhaust in air ,----~--~----,tar weight ra~10 gas per less 1.2 of ex- air pound CO2 N 2 Oz lrn.ust gas exhaust of fuel Air factor -------·--- - --------·I---- - - - - - --- ---------------- -------- 12_ 13 ___ _____ __ ____ _____ _______ _____ _____ ____ _____ ____ _ 14 ____ ___ ___ ___ . ----- -- - · _ --- - - - ------- --- -- - - - - -- IA __ ---- - --- - ---- - - - -- - -- - - --- - ----- - - - - - - -- -- - ---- - 16 ___ ____ ____ ______ _____ __ - - --- --- - - - - - - - - - -- - - --- -- Gasoline assumed l5 per cent hydrogen. Water produced= .15X9= l. 35 #/# fuel. Necessc1ry oxygen= I. 35-. 15= 1. 2 pound~. ::VIolecular weigh t of ai r =28. R4 . . \ ir assumed 2.1 per eent oxygen, 77 per ct>nt nit.ru~en. 2. 76 2. ll9 :1. 22 3. 45 3. 68 l. 56 l. 79 2. 02 2. 25 2. 48 2.14 2. 46 ' 2. 78 3. 09 3. 11 9. 24 29. 7 0.972 10. 01 30. 18 . 956 10. 78 30. 27 . 953 JI. 55 30. 32 . 952 12. 32 0. 22 30. 25 1 . 954 TABLE 7.-Poirnds Wlller vapor losl wilh saluralecl exhcwsl gases per pownd of gasoline 11. 38 11. 05 12. 47 11. 91 13. 56 12. 91 14. 64 13. 93 15. 65 14. 92 Exhaust temperature, °C. 5 ; IO 1;; . 20 I 25 30 :!5 40 · 45 50 55 :lloist ure per ~y~nct saturated O 00542 1 o 00764 O 0 1068 o 01476 I O 02017 O 02729 0. o:l662 0 04899 0 065.J O 0873 0. 1156 1'.lixture ratio: I--- - --------1-------------------------------- . 12 __________ ___ ____ ___ . 060 084 118 163 .223 302 405 542 .723 .965 1 278 13 ___ _________________ .065 .091 . 127 . 176 .240 . 326 .436 .584 .779 1.039 J. 377 . !4 . . ------- - -------- - - - - - -- . 070 . 099 . 13~ . 190 . 260 . 352 . 47;3 . 633 . 845 1.1 27 I. 492 15 ______ _______ ______ .07f5 .106 . 149 .206 .281 .380 .5 10 .683 .912 1.215 J. 612. ]6 _ _ _ _ _ _ _ ___ __ _ ____ ______ __ .081 .114 . 159 . . 220 .301 .407 .546 .730 . 977 1.301 1.727 TABLE 8. - Pounds waler vavor entering with air per pound of gasoline. Relative lwmidily, 60 per cent Air lemperatore, °C. - 10 -5 o 5 :o 15 20 25 30 35 I 40 --- - - - - - --·--- - - !- :lloisture per pound satu rated 1 _ 001643 air . 002553 . 003782 I • 00542 . 00764 . 01068 . 01476 . 02017 . 02729 . 03662 . 04899 Mixfte ratio: ______________ _ \ 13. ____ _____ ______ -·--- - -- 14 . ___ _____ __ ___ _____ __ -- - - :t :::::::::::::::::::::::\ . 012 . 014 . 015 . 016 . om 1 . 018 . 020 . 021 . 023 . 024 I . C27 . o:io . 032 . 0:34 . 036 . 039 . 042 . 046 . 049 . 052 . 055 . 060 . 064 . 069 . 073 . 077 . 083 . 090 . 096 . 103 . 106 .. 1l 2145 1 . 133 . 142 . 145 . 157 . 169 . 181 . 194 .196 . 213 . 230 . 246 262 1 . 263 . 286 . 307 . 329 . 351 . 353 . 382 . 411 . 441 . 470 TABLE 9.-Poimds waler condensed per poimd of gasoline. Relative humidity, 60 per cent 1vl ixture rat io: . 12 ____________________ ___ _ 1143 ______________ _-_--__-_-_- _-_- _- -_-_-_-__-_- -__- -_ 15 _ ______ ______ ___ ___ ____ _ ]6 ____ ___ __ __ _______ _____ __ . 10 15 I 20 25 30 1 35 I 40 45 50 I 55 J. 302 J. 284 I. 259 1 I. 226 1.182 I. 125 , l. 05 L . 953 . 823 ---.:-----: 1. 298 1. 219 1. 2s:i I 1. 216 1. 170 1. 101 1. 029 . 923 . 784 . 597 . 35., I. 294 I. 272 I. 244 I. 206 I. 154 J. 088 I. 001 . 886 . 735 . 530 . 269 1. 290 1. 251 1. 235 1 1. 193 1. 138 1. oori o. 013 . 848 I . 684 . 464 . 1,0 J. 285 J. 260 J. 227 L 182 I. 122 J. 046 0. 946 . 814 . 635 . 400 . 093 I l 'iual exhaust temperature, °C. TABLI,; 10.- Pounds water condensed per po·und of gasoline wilh dry and 8alti-rnled air, mixliire ralio, 13:1; ga:;oline, 15 per cenl hydrogen Final exhaust temperature, °C. 10 15 20 25 30 35 40 45 50 55 Air temperature, °C. -10 -5 10 15 20 25 30 35 40 Water entering with sat urated air __ -- -- - - ---- - - - --- --- -- -- - Water lost with exhaust gas __ . 024 . 033 . 049 . 070 . 099 . 139 . 192 . 262 . 355 . 476 . 637 .065 .091 .127 . 176 . 240 . 326 . 436 . 584 . 779 I. 039 1. 377 Water condensed: Air saturated __ ____ _ l. 309 l. 292 J. 272 l. 244 I. 209 I. 163 I. 106 1.028 . 926 . 787 . 610 Air dry ______ ______ __ ____ I. 285 1.259 I. 223 I. 174 I. J 10 I. 024 . 9JA . 766 . 571 . 311 96997-24-....J4 • 20 /6 /. JO 31 :JZ 33 J,f- 3S ~6 :57 38 J9 -?O "11 42 43 -? riNAL .C%/7AUST «MPeli'ATURe - °C FIG. 22 So l $0 ~1.; "' ~10 K ~ ~.15 ~~ 3o .... ':> :i ~ZS ~ l(J 20 "I' . ~ ;:,- /0 "o / 0 2o Jo 0 .,.0 60 70 6'0 0 /00 / / 0 /ZO /30 /. 0 /~O % C'ONDEIV.SATION F IG. 23 21 The effect of humidity upon the final temperature I The equations are developed from the simple as- '.rnce~sary for 100 ~er cent water condensed is shown j s.u~ption th~t . in a given len~th of pipe for equi- 111 Figure 24. This figure was obtamed by plottmg a hbnum cond1twns, the heat given up by t he passing series of curves similar to those of Figure 21 for several exhaust gas is equal to that taken up by the pipe wall, conditions of humidity, and picking off the points of which is equal to that dissipated by the pipe wall and intersection with the 100 per cent condensing line as equal in turn to that taken up by the external air before. stream. These conditions give three equations in The points plotted on Figure 23 represent a verage four variables, of which one is readily eliminated, values of the water collected in the endurance t est of giving a pair of simultaneous differential equations to Model I condenser. It will be noted that most of express 0, the t emperature ,of the exhaust gas, and cf,, these points lie within the range indicated. Any the t emperature of the air st.ream, as fun ctions of x, /. 90 /0 0 ZS JO 3~ ,f-O .P.~ 17/VAL fYltAUST TCMPfRATURc- °C FIG. 24 leakage of exhaust gas or condensed water would-tend I t he coordinate along the pipe to lower the apparent condensation, so that the as- ' direction of exhaust gas flow. sumption of 100 per cent separation is felt to be cor - simultaneous equations is length, posit ive in the The solut ion of these r ect within reasonable limits. It is _obvious from the foregoing p aragraphs and curves tha t it is a relatively simple matt er to determine a desirable fin al exhaust temperature, ha ving ass_umed the kind of fuel, mixture ratio, a ir temperature, and relative humidit y . From t h is point on the task is so to select a nd arrange the cooling system as to a rrive at the desired final t emperature. The equations for heat transfer which are the basis of the design of the exhaust cooling syst em ha ve been derived under the following assumptions : (a) The t emperature of the pipe surfaces is the same inside and out at any given point in the length of t he pipe and is of course uniform around the circumference; (b) the a ir flowing over the external pipe surface is of temperat ure, density, pressure, and humidity characterizing normal atmospheric conditions, and the velocity of this air is uniform and perfectly turbulent. O =AeN +B (1) (2) Where N =-p -qh+qc ( H1 + H1 ) X . qh qC h C e = base of natural logarithms. p = perimet er of pipe - cm. q" = coeffici ent of surface heat transfer between exhaust gas and pipe wall -cal/secX°C. Xcm2• q0 = t he same coefficient, air st ream and pipe wall, cal/secX°C. X cm2• Hb = heat capacity of the mass of exhaust gas which passes any point in a unit time-cal/°C.Xsec. H0 =heat capacity of the mass of air stream - cal/°C.Xsec. 22 A and B a re constants of integration . To eliminate these constants the following end ditions are applied: For co unterflow of e),haust gas aed air-fJ =T.} > =lb when x = 0. fJ=1\} > =l. when x_· L. And for parallel flow-fJ= T • } w:rnn .c = 0. > =l. o--T b }w hen x = L. > =lb . Where T,.=initial exhaust temperature, °C. Tb =final exhaust temperature, °C. l,. = initial air temperature, °C. lb =final air temperature, °C. L =length of pipe, cm. con- The res ulting equations arranged in the form most convenient for design work are : For counter flow- (3) And for parallel flow- (4) The terms Hh and H 0 are obtained from the relation in which Mh mass flow of ·exhaust in one tube, g/sec Ci, = specific heat, at constant pressure of exhaust i\1 0 = mass flow of air around or.e tube, g/sec C0 = specific heat of air. The terms qh and q0 are obtained from the Lanchester- Stanton relation 1, 2. q = c"M [ o.0765 Cvf D) 0 ·" 5 + 0.0009 J (5) in ,,·hich C" specific heat at co nstant pressure μ viscosity, c. g. s. units ~I mass flow, g/sec X cm2 D = diameter of t11 be, cm In " ·orking to,Yard a satisfactory heat dissipating apparat us t he first determination 11ecessary is the total rate of mass flow of exhaust gas coming from the engin e. This \\·ill , of course, be the product of the brake horsepower, the fuel economy, expr~ssed in p ounds per brake horsep ower-hour, and the weight of mixture taken by the ellgine per pound of fuel , ·giving the mass flo"· in pounds per hour. From consideration of equations 3 and 4, for maximum efficiency of heat transfer, it is desirable that the velocities in side and outside of the tube be somewhere near the same. Hence having a known flying speed 1 Great Britain Committee for Aeronautics, Tech. Rep. 1912-13, p. 45. ' B. S. Tech. P aper No. 211, page 320. it is an easy matter to set this equal to the mean velocity of flow inside the pipe, and from the mean density over the temperature range within the pipes compute the mass flow. There is no point in folJowing through this process in this paper. Suffice it to say that for an air speed of 45 miles per hour the desirable mass flow inside the pipes works out to be 0.017 pound per second per square inch of cross sectional area (1.195 g/sec. X cm2), provided the temperature of the exhaust gas lies in the neighborhood of 650° C. at the hot end and 32° at the cold end. This figure (0.017) may be increased or decreased in proportion to the air speed, but since little gain is to be expected from any but broad approximations in this respect, it is probably as well to use this mass flow as a constant when working ,Yith airships having the cruising speeds of any now in serv ice or likely to be fo r some time to come. The selection· of the most advantageous size of tubes, must of necessity be a compromise between heat transfer efficiency and mechanical consid eratioH s. The effectiveness of the apparatus will be found (equation 5) to be increased as the d iameter of the t ubes is . decreased, whereas the smaller the t ubes, t he greater will be the exhaust back press ure and liability· to clogging, and the less the mechanical strength of the tubes both as self-supporting beams and as long columns. An indication of the relative resistance to flow wit h increase or decrease of pipe sizes may easily be ol::tained, but for the purposes of this work it is safe to let the limiting factor in redu cing tube diameter l;e the mechanical strength necessary in a structure of the type contemplated. Soon after the beginnillg of design " ·ork on the full ai r-cooled type of " ·ater recovery apparatus a tube of 1 inch diameter ,,·as assumed and the strength of thin tube of this size was computed. This choice of dimensions has, since been vindicated by the ground and fl ying tests, ~ince tubes of this diameter and the thinnest walls commercially obtainable have proven amply strong, while the back pressure is nearJ~, at the allowable limit. In the theory and design sections of this paper, therefore , only tubing of circular section, 1 inch in diameter, is considered . Having the assumed tube size, t he known total mass flow, and adYantageous mass flow per unit area, the total number of tubes and mass flow per tube is easily computed. In solving equation 5 for q, the mass flow of ai r i\l is determined by the air dcnsit.v, flying speed, nnd spacing and munber of the tubes, " ·bile D has a Yalue a lso determi11ed by t he tube spacing. The diameter of a circle equivalent in area to the space include:l by four tubes was used as an approximat ion. D=-J4:B-d2 in which D=equivalent diameter used in equation 5. d=diameter of tube. ~} =vertical and transverse spacing of tubes, respectiyely. 23 The specific heat of the exhaust gas is approximately constant for the range from 600° C. down to 53°, the temperature at which condensation starts. Assuming t he gas 90 per cent air, with Cp=0.24 and 10 per cent. steam, with Cμ=0.45, the equivalent C11 is 0.26. For the range below 53°, the effective specific heat is very high due to the latent heat of condensation. This was approx imately determined by computing the total heat of 1 gram of the gas mixture at frequent temperatu re intervals below 53° and finding the rate of change of total heat "·ith temperature. This rate of change was taken as the effective specific heat with a mean value of 2.83 in the range 53° to 45° and 1.92 in the range 45° to 35° or 2.20 for the ent ire range 53° to 35° . The figure 45° C. for the exhaust temperature at the end of the second condenser bank \Yas secured b~· successive approximations, and is used only to determine the effective specific heats over the ranges indicated. These values were. checked by a more rigorous mathematical determination which can well be omitted here. The viscosity of the gas changes considerably with ten:iperature but an average value of μ over the range 600° to 50° was taken as 2.4 X 10-, c. g. s. units, t he viscosity of air at 150° C. For the range below 53° it was assumed the effect of the condensing vapor was negligible and the value 2.0 X 10-, c. g. s. units, for the viscosity of air ,Yas used . For the air flowing outside t he tubesμ = l.8.5 X 10-•. Thus we have constant values for the variables in equation (5) so that qb and q0 an'cl consequently qh+q" . qh qc may be taken as constant for each range above and below the condensation point. For a t hree-bank condenser of the general form of Model II it is impossible to directly compute the necessary L on account of the changing functions of t he variables during parallel and counterflow as ·well as t he change of CP with temperature of the e·xhaust gas. The most convenient method is to assume an over-all length for the condenser and work through using the equations given. It is of course necessary to measure or assume the temperature of the exhaust gas received by the condenser, as well as the air temperature. It will be found that there will be left two variables in each case, but that one of them can be eliminated by solving simultaneo11 sl_1· the eq uation expressing t he fact that the heat lost by the exhaust is equal to the heat taken up by the air Design computations will be taken up and examples given in another section of this paper. Inasmuch as the heat to be abstracted from t he exhaust gas varies 1Yith change in composition of the fu el this total heat has been computed for th ree fuels, gasoline and two half-and-half mixtures of gasoline with benzol and alcohol, r espectively. These latter represent two classes of nondetonating fuel P!L rt icula rly suited to the requirements of h igh compression engines. The change in total heat thus computed is equivalent to the heat abstracted in a constant pressure process between 650° C. and 32° C. The ex haust gas is assumed to have been cooled to 650° C. by the piping from the engines. Under these conditions, assuming each fu el burned with a chemically correct mixture rad io, t he heat abstracted is as follows : B. t. u. Gasoline __ _______ ______ ___________________ 5,226 Gasoline-benzoL ___________________________ 4, 564 Gasolin e-alcohol_ ___ ______ . __ __________ _____ 4, 2211 By using Figures 19 and 21 it will be found tliat at the fi nal temperature of 32° C. the water condensed from these three fu els will be 103.0 per cent, 71.3 per cent, and 98.0 per cent, respectively. Owing to the differnnee in mixture ratio, the same engine would burn about 25 per cent more of the alcohol mixture, so that the heat to be abstracted would be brought to about the same figure as that for gasoline alone. For 100 per cent condensation the exhaust from this mixture must be cooled to 30° C. The benzol blend, while having a low exhaust heat value, must be brought below 0° C. before 100 per cent condensation can be obtained. It is indicated, t herefore, that blending of antiknock fuels for airship engines, especially for mixtures containing large proportions of the antiknocking component, should be accomplished b~· the use of alcohol rather than benzol. It is to be noted that exhaust water produced b? the combustion of commercial benzol is very apt to contain sulph ur compounds having a corrosive action on some of t he metal parts of the condensing apparatus. PART III- DESIGN AND CONSTRUCTION For_purposes of illustration the design of a condenser for a class " D " airship is taken up, assuming Maximum B. H. P. equals 300. Fuel equa ls aviation gasoline. Cruising speed equa ls 45 miles per ho ur. Mixt ure ratio equals 15 :1. Referring now to Figure 21, the 15 :1 mixture ratio curve crosses t he 100 per cent condensation line at a temperature of 33.5° C. This is the final temperature to which t he exhaust gas must be cooled. The total mass flow, based on the assumption of 0.50 pound fuel per brake horsepower hour, is 0.50X (15.0 + 1.0) X 300 =2,400 lb ./hr. For a sp eed of 45 miles per hour, a mass flow of exhaust gas of 0.017 pound per second per square inch cross-sectiona l area is about right (see p. 22). Assuming round t ubes of 1 inch diameter (p. 22) t he cross-sectional area of each is -i square inch. The mass flow per tube is 0.017X-i =0.0133 lb. /sec. =6.0 g/sec. The total mass flow is 2,400 3,6oo=0.667 lb./sec. Hence, the n umber of tubes necessary is The r ise in temperatu re of the cooling air must be kept small if the final temperature of the cooled exha ust is to be low. The mass flow of a ir, t herefore, must be much greater than that of the exhaust gas. For this reason the spacing of the Model II condenser was chosen as 2~-inch center to center of t11bes in both directions. The cross-sectional a rea of the a ir Rpare under this co ndit ion is 2~ X2X-i'=4.277 sq . in. per t.1 1be. The mass fl ow of a ir is pVA=Mc in whi ch-p= density = 0.754 lb ./cu. ft. (750 mm. Hg. 15° C.). V =velocity =45 m . p. h. =66 ft. /sec. A= cross-sectional area= 4.277 sq. in . = 0.0297 sq. ft. M0 =0.0754 X66 X0.0297=0.148 lb. /sec. =67 g/scc. From page 23- C0 =0.24. Ch =0.26 above 53° C. Ch =2.83 between 53° C. and 45° C. C1, = 1.92 between 45° C. and 35° C. H ence H c=Mc Cc=67X0.24 = 16.08 and Hh=6X0.26=1.56 above 53° C. = 6 X 2.83 = 17 .0 between 53° C. and 45° C. =6Xl.92=11.5 between 45° C. and 35° C. The t hree values of Hh apply , r espectively, to the first, and first part of the second section , t he last part of the second, and all of the third sect ion, in a t hreebank condenser, since these general temperature ranges prevail as noted. Small departures from the indicated temperature ranges will not affect the values of Hh to an appreciable extent, so that they may with reasonable accuracy be considered as constants. Let us consider the condenser as d ivided into four sectons of which 1 is the first bank, 2 is the first part of t he second , 3 the last part of t he second , and 4 the whole of the third bank. Then, since t he first bank is in counterflow, t he function of H 0 and H h is HI - H1 , h C while the sign changes to plus for the second bank and back again to minus for the third. Calling this fun ct ion of H 0 and Rh, H0 we may compute the following values: Section 1 2 3 4 Ho 0. 580 . 703 . 121 . 0247 The coefficients of heat transfer qh and q0 for t his size pipe and spacing and the corresponding mass flow of gas and air per unit area are computed from equation (5). From pages 22, 23, and 24 the values Cv, M, μ , and D are as follows: c. ______ ____ _________ _______ ____ _ M sec.; cm2 ---- - --- - - -- ----- - -~- D \,t~:-~~'.~s_:: :::::::::::::::::: Exhaust gas above 53° C. 0. 26 L 19 2. 4X l0-' 2. 54 Exhaust gas below 53° C. 2. 2 1.19 2.0X JQ-! 2.54 S11bstituting t hese values in equation (5) qh = 0.0012 above 53° C. q1, =0.0090 below 53° C. g. = 0.0014. Outside air. 0. 24 2. 43 J. 85X l H 5. 93 Hence the values of qh+q. for t he sections numbered 1 to qh qc 4 above are as follows, Q0 representing the fun ction of q1, and q0 : Section Q. 1 and 2 0. 000647 3 and 4 0. 001211 .(24) 25 We may now combine all the fun ctions of q1, , q0 , H1,, H0 , and pin a single list of constants by multiplying together H0 , Q0 , and p. Call t his constant K . The res ults follow: Section K 1 0. 00299 2 0. 00362 3 0. 001169 4 0. OOOZJ9 With t he, above values equat ions 3 and 4 take t i1e fo rm T - t log. - • - "= KL for counterflow Tb- t, and T -t log0 T: - l:= KL for parallel fl ow. For Ta, t he initial exha ust temperat ure at ent rance to t he condenser, 650° C. may well be taken . This approximates t he melting p oint of aluminum. For t,., t he ini t ia l a ir temperature, 15° C. is probably a fairly high fi gure. With t hese assumpt ions only two temperatures and t he length remain to be determined . T he only way to arrive at the desired temperature of 33.5° C. for Tb is to assume a length and apply t he equations for each section, finding t he final T., for t he last section. The length of t he condeuser may t hen be increased or decreased according as t he final t emperature of exhaust is too high or too low. For t his purpose an effective over-a ll leugth of 20 feet has been assumed , making a total length of 60 feet in t hree banks, of which t he second is parallel flow. Keeping to t he same designa ti on of t he four sections involved in t he calculation , we ha ve for section 1 L =20 ft. =610 cm. T . =650° C . . t. = 15° C. K =0.00299 log. i:·= ~:=KL =0.00299 X610 = 1.824 = log. 6.20 650-tb=6 20 T1, -15 · tb = 650- 6.20 T b+93.0 =734.0-6.20 1\ . Simultan eously (T 0 -T1,) H1, = (t1,-t,) H e or Therefore (650 -1\) 1.56 = (tb - 15) 16.08 lb =15 + 63.1-0.09711\ = 78.1-0.0971 1\ . 743.0 -6.201\ = 78.1 - 0.09711\, 6.103 1\ = 664 .9 Tb= 108.9° C. T he condit ions at section 2 are thus determined: T . =108.9°C. t. =l5°C. Tb = 53° C. K =0.00362. Since parallel flow now prevails, the main equation becomes T -t log. T • t"=KL = 0.00362L 1,- b log. 10 ;/_~b 15 =0.00362L 93.9 . L log. 53 -l" =0.00362 a nd al ·o (T . - 1\) l:-Ii, = (l0 -t") He (108.9 -53) 1.56 = (t1, -15) 16.08 ti,= 15+1 1 /0 6 8 (108.9-53) =15+5.42 =20.42 sustituting above for tb 93.9 L 93.9 log. 53 _ 20_42 = O. 00362 = log.32.58 loge 2.88 = 1.058 1.058 L=_00362=292 cm. The le11gth for section 3 will be the d iffe rence bebrnen 610 and 292 centimeters. The condit ions at this section are then Ta=5:{° C. t. =20.42 L=610-292=31S cm. K =0.0011 69. T he fl u,,· is still parallel as in sectiuu 2 so t hat l T.-t, YL ug. 1\-tb = "- 53-20.42 loge T t 0.001169X318 =.3717 =loge 1.-!50 b - b 32.58 = l -! -o T.,-tb . ::, t" = rI\ -22.46. Simultaueously (Ta - T.,) H11 (t., -l,) H0 (53 - 1\) 17 = (lb -20.42) 16.08 l1, =20.42 +56 - 1.056rl\ Droppiug t., rl\-22.46 = 76.-!2 - 1.056T., 1.056 T., =98.88 Tb =48.1° C. The condit ions for section 4 arc now determined ati T.=48.1 t. = 15° C. L,;610 cm. E =0.000239 Tlic flu,,· i~ 110 ,,· changed again tu counterflow so t hat T ,. -tb 1-1, loge rr -t = \. b a loge 4-T8. 1 -lt' b= 0.000239X 6 10 = 0 .1 4 5,s b- ;J = loge 1.157 tb =48.1 -1.1571\ + 17 .35 =65.-!5 - 1.157Tb 26 Simultaneously Heuce (1'. -T,,J H11 = (t1,-t.)Hc (48. 1 -'1\) ll.5 =(t,,- 15) 16.08 tb = 15 +34.4-0.716T,, =49.4 - 0.7161\ 65.45-l.157T" =±9.J -0.716T,, 0.4411\ = 16.05 Tb =36.4° C. This temperature is some1d1at higher t lian that required for 100 per cent condensation under the 14 zz 10 ra /6 14 ~ "~' fl ~ ~ ~ /0 i:: ~ ~ 8 " " 4- ,l 0 -z --+ 17 flO It may be found advisable on account of drainage to cha nge t he position so t hat the long dimension of cross-section is vert ical, as if, for example, it were p laced agaiust the side wall of the car of a D or C class ship. It is by no means certain t hat the use of the same number of t ubes in each bank is desirable for t he best condit ion of heat exchange. It is suggested that valuable data m ight be made available by a mathematical comparison of t he present type exemplified by Model II, and one in which the number of tubes in the CoNoJ<"NSE"R L,rNr;rH-/'iu:r F1G. 25 assumed condit ions, but tl1e d ifference is no greater than the probable error in lhe as8111ned values used in comput ing the heat trausfer. The fact that the cool ing surface of the cast aluminum headers has not been taken iuto consideration a lso makes probable a somewhat better performance than that indicated by t he computations. It is not assumed that a three-bank condenser of t he same type as Models I and II is the ultimate solution of the p roblem of exhaust heat transfer. ,vhen t he construction and arrangement of the a irship permit, it may be possible to secure better res ul ts by using fewer banks and a greater overall length or vice versa. first bank is increased by one-third or one-half and the number in the last bank co rrespondingly deereased. This would give a more uniform velocity of exhaust gas and might on this account increase t he overall efficiency of the unit. For the p urpose of designing apparatus similar to the two condensers already b uilt, t he computations have been worked out between wide limits of a ir speed, condenser length, and initial exhaust temperature. The final temperature of the exhaust necessary for 100 per cent condensation was taken as 32° C., which allows a ma rgin of safety of 1.5° C. The curves a re shown on Figure 25, which requires little explanation. 27 Assuming the same conditions used in the design computations just preceding, that is, an entrance exhaust gas temperature of 650° C., air temperature 15° and air speed 45 miles per hour, the required length is readily determined. It is only necessary to project the horizontal line of 15° air temperature to its intersection with the second curve of the lowest group and then to read the required length 011 the scale at the bottom of the sheet. The value thus obtained is approximately 25 feet, which is somewhat longer than the value computed. It is to be remembered that the final exhaust temperature in this case (32°) is some 5° lower than that computed for the 20-foot condenser, and that the cooling over the ra11ge of temperature covered by this difference is extremely ineffective, owing to the small temperature head between the exhaust gas a11d the cooling air stream. CONSTRUCTION-MODEL I The parts of the Model I condenser are few in kind if not in number, and the machine work necessary is not excessive after the necessary tools and fix tures are at hand. The materials used are a commercially pure aluminum for the tubes, and F lynite, 3 a light alumi11um alloy, for the castings. The aluminum tubes used are seamless, 1 inch in outside diamet er, and have a wall 0.016 inch thick. The manufacture of these tubes is a process susceptible of being held within close limits and 'no trouble whatever was experienced with variation i11 diameter. The weight of the tubing as it comes from the mill is 0.0591 pound per foot. There are 51 parallel tubes in each of the three banks of this unit, of which two require a tubing length of 20 feet and the other 20 feet 10 inches. This gives an aggregate of 3,102.5 feet and a total weight of 183.4 pounds for the tubing alone. The principal castings are those used as return bends and entrance and exit headers. The pattern was made with removable lugs and flanges, thereby serving for four different castings as indicated in Figure 26. The use of the lugs for anchorage of horizontal and vertical tie rods is best illustrated by Figures 5 and 7. The castings made with the flange in place were sawed t hrough with a narrow milling cutter, thus provjding wi th one operation two entrance or exit headers provided \Yith flanges having a finished surface for reception of ~ gasket when attached to the header manifold, as indicated in Figure 6. The only other castings are the three-hole tube connectors, Figure 27, and the header manifold 8hown in Figures 28 and 29. The former serves the purpose of joining the fore and aft tubes of the lowest bank of the condenser, while the latter distributes the exhaust gas from the line to the individual headers at the entering encl, and collects it again at the exit for conveyance into the separator. The problem of joining the tubes with the headers was the subject of much consideration before the 3 F lynite is a copper-a.Juminum alloy containing about 10 per cent copper, balance aluminum . It closely corresponds to alloy No. 2 as . described under Specification for A)uminum Alloy Castings, International Aircraft Standards, 3 N 11; October, 1917. method used was tried and found to be satisfactory . This joint is made by forcing the thin tube into a hole whose sides a re first parallel and then tapered until a shoulder is reached. Details of the holes into which the tubes are pushed are shown in Figure 30. A leakage test of a joint thus made was conducted ~s follows: A 10-foot tube was driven into one of the nipples of a return bend header casting (Figure 6), using a mixture of litharge and glycerine as a cement. The other holes of the casting were plugged with corks, and the whole assembly filled with water and left with the tube extending upward for a period of 24 hours. No leakage was discoverable. On attempting to remove the tube from the nipple, it was found necessary to drive the header off the tube by means of a heavy hammer. The process of machining the header nipples and three-hole connectors for r eception of the tubes is relatively simple, but req uires care and can not be hurried greatly with the tools thus far developed. The header casting or tube connector is first clamped to a fixture on the bed of a vertical spindle mill with the nipples pointing straight up. A rough boring tool is then carried right through the nipple, leaving it approximately the diameter of the inside of the tube. This tool is removed and a finishing cut is made with a piloted reamer which leaves a 1-inch hole having parallel sides for a distance of one-half inch and tapering 0.006 inch in the next three-eighths inch, ending in a shoulder at a depth of seven-eighths inch. The headers used to connect the tubes with the header ma nifold a re machined for reception of the tubes before being cut through the flange. The assembly is accomplished by driving the headers on the tubes after first smearing a t hin mixture of litharge and glycerin _in the holes. The condenser is first built up in sections as shown in Figure 31, and 17 of these are bolted together with -A--in ch chrome vanadium st_eel rods. Short pieces of aluminum tube strung on the rods keep the headers properly spaced. The entrance and exit headers are then secured to the machined face of the header manifold with filli ster head machine screws. An asbestos gasket in terposed between headers and manifold sec ures gas tightness at t his point. The vertical tie rods a lready mentiouecl are made up of !--inch stock in order to provide s ufficien t flexibility to allow for differential expansion clue to temperature differences between the upper and lower sect. ions. The front and rear upper banks are mechanically connected by stiff steel straps strung on the transverse tie rods between the headers as shown at A in Figure 32. The collect ion of condensed water is taken care of by drains from the low poi nts as shown in Figure 5. The drain at t he extreme left is made up of i -inch copper t ubes running from fittings screwed into the header castings to a i -inch iron pipe which conducts the collected water to the ballast tank. The other drain from the condenser proper is shown in Figure .5 emerging from the center of the apparatus. On account of limited space, short tee fittings are screwed into these headers, and these are connected straight UN/Yclf'.f"AL #EA.t?Elf' ...9LUN'/NU/V C..4S77NG :28 @-MT/r fi8NG'E ~ . ONLY - EST. W6"T I. 7 LL?. ~ Jf'/T# fl..4/VoE JI '/ Lu'6J#" - E.f'T. Jf/67. 1. ll L#. @-JWT# LU6S"C" IJ&Y-/Vt1 /Z/W6"E- EfT. H'6'T. !.S LO: ~WITH L.t/GfLl"(-C"-/V,?/ZA/Vtf'E-EfT.M,T. /.GL§. WALL TH/0<,'NEff Tt? BE ,;/TIYRL/t?UT#EA',tJER, PATTERNJ' Ft?R fiAIVuc :4" ,LUo ,r~ z-·= ,fY J'E-TE,/ fl' PETACIYABLE F.-.V #E,9,tJE,(! P,9T?cR,V. FIG. 2C t--t--+;,-,--.., :-··_ ------- . 3.--' >---------+-1 / --+------< c;: I I I t-.!<0 I - j__j_J..:::fj~f - -I I---+--_,__.,___;_.,, I • . I I I 1. -r1 > ,1cu I.- +--'-f--'-t-,--i-~ 'ri--t-Jro -+---+-+--41<-H--J-¥-,~ I I I 1 1 I 1 1 I I I ..l,..4-~- /0 - S/9 CIJ/1//JE/YSER Tv'L?E CIJ/Y/VEC!TOR 17- fiLt//JI//Vt//11 C/ISTI/VG (LY/V/TE) SVP£RS£0E~ /0-4~ I( /4I' 0 . I " I " --~~~12~~--+-+I~ 7 " 8 /" i--+--1--11----+---+-++---+-s 4- -+- - _L__---+-'-- F IG. 27 ~ ~. +-+-+-t-i - ~ r ";' :~ j~H~111T~~+hrl~-~~-~-~-=~-=-~-~-=~-~~-~-~-~-~~~~~-~-~-~~-~-~-~-=-~---------------- f ~ ---,---.i:=:r---3[- --t----t--,-.t--,f ------.A ----- ,9 - -I~.. . r--- , , , ~TT ·-- -ti -"- -..,-- ,·---~ T - ..J- -.&.--•L-.J-l t 1, - ----- ----+--------------1 ------ --- ----------- FlG. 28 -- ---------- --~-- I ...! B "'1 .. ,'9 l' CIQ1~ .r _____ ,,, ----,/1 ----;· _,. .r _,. ! ·(-~ ! _._ --: rT ,--1-n--1- l -'-- u_.J __ ._ _ _..__..__ ;> 111, --+.. ------ --:~rl - - -- - ---- - /r'E/?OER M/JIY/FULP r'f'L'U/>r//VU/'? C"'9S'T//VG 8,1 ------- -?~ - __ ___.:_::.i'llll!alllli1111--tt---tt--__JL-- 7:;J- ._. ------+----+------- 7" G# #-~------f---t---~ • -1~~~~ :::j::j::=-:::-=J:t==t==,,~ F IG. 29 32 ~~ Tapered /rom / 'to.99,I.~ B in this len_gth. :Shoulder eQ'uc1! to tube w«/1 th/ckne.ss . De TAILS or= UN1VE.1?0"'1L /J'e;4DE-/? TY.P.c-1-A ScEO!r'AWIN6JX-!O-I FIG. 3:) F IG . 31 t hrough by short alumin um tu bes, t hus bringing all t he collected wa t er out to one point from which it d rains to t he t an k . The other d rain is from t he false bott om of t he baffl e-type sepa rator Rh own a t upper ri gh t in Figure 5. In orrler to counteract a nY t endency of the tubes to creep out of t he headers, a nd to t ake care of t he poss ible end t hrust d ue to explosions of unburned gas in t he condenser , ~o. 22 steel p iano wires wi t l1 t urnbuckles were strnng between and paral lel to the tubes, ty ing t h.e headers together and t ru ssing t he stru cture d iago na lly in the vert ical pl a ne in o rder to gua rd aga inst st resses imposed b.,· un equal tension of support ing cables . These wires may be seen in Figure 7, and are indica t ed by t he lines BC, CD, E F , a nd GR in F igure 32. MODEL II The castings of the Model II conde nser a rc of t he same mater ial (F lyn ite) as t hose of Model I. Figures 33 and 34 show the deta il of t he ma in header casting, nsed for both en t rance a nd exit a nd return bends. The header cover , Figures ·35 and 36, is 1he return bend used to co nnect a dj acen t banks. The e ntrance und ex it elbows a rc idcnt icul, a nrl a re i11u strated b)' F igure 37. The condenser tube suppor t s, Figure 38, serve to connect I he 10-foot lengt hs of t ubing in ea ch bunk. T he joints between t u bes and headers a re made as in t he Model I conde nser b.v pressing the t ubes into t he tapered h oles in t he header nipples and t he bushings of t he tube supports. _GAS /=4-ow /="HOM .E'N6I NS- ·17 ,v,,w.s 17 lf'OWJ' 17 N'OW'J" 10.ts'' - ----10..!. 5'· -------- ~ ----- 10~0" ==- F IG. 32 ~ ; - e { I I m--f ----- ' I --4-- e 4-· i f.--- 1 - - -- e.f - + COVE!f r/lCE 5eCTIOIV T/1/W t 11-/i FIG. 33 --,- I B +-------------- 7/" __ .J.._ _______ -'-----'---------/1.f:" --------------< L__l~~~=---\j/,,- =--~~:tj-~~-- ,:~.1T.p.-.-- ~' -_--}-:::: ~.,~i/,,' ::::::_-_-_-_ \-:]."~ ----- -'.~. j-?:.,;I ~',c::_~ :;. ,' -------~ ... -j-_, l, I( ·,' ,'- . ·------·, , ! . i ! l :7 '1 - - r---------, I I r, ---1-- 1 I I 1 : l I I I I I I I I I I 1 1 I I ·I ----'LL! ___ ul ___ ...LL _ __J1.J_ _ _J_.__ __ -11.L_ __ __Llc___:._ I __J 1tJF -I EJ ,, I 5/DE VIEW if SeCTION" T/1rW . i.. 3-5 Fra . 34 36 ~ lttl. I I I I I I~ --" .\J" I I - I J~ ~ 1,1 \J I I ,~ I I " \ I ·J+ --~ \ I I I .,~ I \ I I I ") I \ I ' I I \ I I I I I I \ I I I ~ I \ .1 .... ,1, I \ I I ~ I \ I I I I I \ I I I -i- \ ~ I I I '- ~ ,__ \ ,J, I I t0-~ CS) I _ll@- \ € -k- I I I I \~ ,,,,\t I I I I ,-1.- 4~ I I, 111 I I I A_!_ I ,~ I \~ I 1:~ ~/I I ' -+-1 I - -- I I .,,..:::,::~ I ---~ ~I I I- - I /,::, / I I I I ' ~ ~ / / I I I ~ I I I / / ' ~ v/m I I I I 111 -++ \ I I I ., ., I - 11'1 I I I I\ : I I s ~ ,, I -1--9-- li I -~B- ] \\ I I I "" : ,j ,, I I I ,, _.,,_;::;,, I I - r--- j I ,v I I '*--,~,. I JI; lr~' I I ( ~\ I I ~ I 1 ' r I I -~+ ~ I I i I I I {~ D "" I I · I I I ~ 1 I I I I I I I I I I I I I I I I I I I I I I I-I ' ' 'Z" ' l ' I _a __ '_., I I i I I_,, J I ~ I ,- -- I I I I ~·- _2 _ _ H I ~ I I I I --1!::f._ H-I I I I I I '3i: I I I I I I I I Ei -- 1- ~ -- __ J ___ I I I I 19* : ,_ ,_ I I - I -- I - \~ ) ,, 164- ,, ~) V. I #E..-1'£'.?ER COVER ( ,,e~TP ~/V $£NP} ~/ l ~ / -/1".LV ,.A,1"'/NP,¥ c ,,..,...,..r/NG ~ -~/ ..... / £.s-7". ff'E/ G /rT- L .i' -~~ I '---\_-~~ 1 17HJW Tl/JC£, !:U[Q J( l)I J;,r ,.,~,i BlJRfJ ll or SONOAR!)S . - • W46'HfiY010N. 0 . O SO l <( /"QU.r/.~ =-'"'"'"" H.,,.,j ulY. lit ! CO..-V.OE/VS~,E' ,~""-'*" 111•,u "1·1-ZI 14 -?-ll ?·l·Z,/ l S(CT. 1 IHE-9Db~~ff~-""- ,/,1'-,!-,Z FIG. J5 I I I I I I I I I I I I I I I I I I I I I I I I I / / / · / I I / / / / 37 --- ----- £NP VIEW SECT!O!Y / / / I / / / ,,, .... / SECTICN 8-8 IJIA# TH(IEO llfOIE ,.... -Z-Z/ -,--,.z1 .,£er. 1 F IG. 36 B,,C,,A,U ..F R.I. ,.r.t.. , .u-~-?# Jr1 -=:-:=:=:-.-=::-==:=-:-=-=-=-=:-=-=:-=-::-=----j~+ rh+-~ -------------- -~L-- '- --+----- ----- --------- - - --1' -- ---r---....,.'--------- ~ ~ i\_ \ 1, -- --- - - - -------:-..'}'.'.....l~,,:.....- . ~ i-----,. - --:r ~ - " r --- ---------------------i:f---~----i;~· -=-::..:::..:=-::::-=:-==-=-==:============j~~ , . \ t' : I : I I ' I I r , , . -., . I 38 ~ r ,Ly;;,-;;;,-::=:=-=-===·' ' ' 1 .lf"'" I ._.-;;;•, .... ._ I I I --------'_'_, :,::,, ;::.~I -#--f/•- -'1\ ~--.Ji:. ..J..,.~ - - -----'---- --- \1 \._ j [l-..:1 ,. ... ;, :!'.~ i \. 'J!_E'!_:-:-==t='="-='"9 l' IG. 37 -- -- .h'E/9P~~ ELL -A'L.V.H/NM"f' e,,,.s-r/NG F.S-T. ff/E/6"Hr 8 L8. ) £ ,,7 --- BUREAU OF STANDARDS · •• WM.HINOTON I ,I' I I I I I I I I I I j f1' I ~ 1-.: l------~~- I I I L-- ~--.J r-- L-..J, : I I I I ' • I I I I ,...______.., f----+-L'-- - 1 - _J (~1--·: -· I I ''I '' I I I I I L - -- -.J r'-- - -', I l.- - - _ , f- --', I' ~Emf? _sec~ VB"E ..S-L/r",C,O~T -/?Lb'/1:V/VV/>? C"h'.S-T/A/G" EST. ,.-VC/Gh'r- .w!f?. F IG. as 2. '' ' '' I I I ' I I I I '-- _.,, ',-- -4 ;'- - _,. ;'-- '' I I ' ...S-/ D. R~WlfiO IUHII ,/X-L'·,f ' 40 The assembly of this condenser is as follows : Fifty tubes are pushed by hand into the nipples of one header, while a grid or frame near the center of their length keeps the tubes properly spaced. A tube support is then placed against the projecting tube ends, and each tube is withdrawn a slight amount from its position in the header so that it just enters t he corresponding hole in the central tube support. The header and support are then backed up by 6- inch st eel H beams connected by six long !-inch steel rods having nuts for forcing the header and support together. These nuts are taken up until no further movement of the tubes into the nipples can be detected. The beam back of the tube snpport is then removed, more tubes inserted on this side, and the process repeated with another header on the end. It was found that simply extending the rods through from end to end of the two sections would not serve to force on the second header because of the tendency of the whole bank to buckle. For this reason steel bars were inserted between the tubes back of the centra\ tube support and the rods were threaded into them thus leaving the first end unstressed during the as~ sembly of the second. To keep the headers from moving off the tube ends, five 11-gauge spring steel wires were run straight through each section from end to end and secured to eye-bolts passing through bosses between the tubes on the face of the headers. These bolts were drawn up with nuts inside the headers before installing the header covers. The assembly proved to be so stiff t hat the addition of diagonal braces was unnecessary. Differential expansion is taken care of by slipjoints between the banks as indicated by Figure 39. An attempt was made in this condenser to drain all the water condensed in the tubes through the two bosses which may be seen at the bottom of the header bends at the rear end,· Figure 8. It was found that the greater part of the water condensed in the first two sections swept past these drain holes and collected in the lower tubes and elbows or was swept on and out into the separator, overloading the separator drain and causing a considerable loss of water. Sheet metal gutters inside the header casting and leading to the drain hoies remedied the condition only to a slight extent and these drains were finally replaced by a series of tubes attached by fittings to the lowest elbows on the rear lower header. The fi t tings may be seen at the bottom of Figure 8. Operation with the new drains proved fairly satisfactory, although from inspection of the drainage systems of Models I and II it will be seen that the form er has the better chance since the last drains are only 10 feet from the outlet end and hence are in a position to t ake care of the water C'omlensed in the first fi ve-sixths of the condenser. SUGGESTIONS It has been thought advisable to assemble some of t he general points bearing on furt her work. These apply, of course, only to apparatus of the same general type as that exemplified by Models I and II. Probably the most obvious fault of either condenser has been clogging of separator drains. It is of the utmost importance that these be made Jarge and smooth with no shoulders or contractions of any kind whicl; might catch and retain any clogging ma terial. It would doubtless be advisable to make these drains of a diameter of not less t.han ! inch. A noncorrosive ma terial, such as Benedict nickel or Mone! metal could readily be drawn thin and light for this purp~se and should serve admirably for making joints. In laying out a separator it is well to keep toward the lower limit of gas velocity. The limiting values a re about 900 and 500 feet per minute, but 600 should prove an acceptable figure. Below 500 feet per minute the velocity is too low to throw out the water, while above 900 the drops deposited on the baffles are again torn off and return to the gas stream. In assembling a condenser care must be taken to avoid stressing any tube so highly tha t it is distorted at the entrance to the header nipple. Such a distortion is a_ weak point which is apt to crack in service, just as a kmked wire is weakened. The wires used to connect adjacent headers must be designed with regard not only to strength but to elasticity, since the linear expansion of the t ubes is enough to stress them severely as long columns if this is not taken care of by stretching of the wires. It is quite possible that rearrangement of the tubes in order to decrease the velocity in the first section and increase it in the last section would result not only in decreased back pressure but also in increased effici~ncy of heat transfer with a corresponding decrease in weight. If a condenser of the type of Model II could be so mounted that the long dimension of cross section were vertical it might simplify the draining problem to some extent since only four drain connections would be necessary on the lowest nipples of the second and last section. The greatest care must be employed in coupling the condenser to the engine of an airship in order to avoid transmission of the engine vibration s, as · well as to eliminate excessive stresses on the flexible connections. It is al so essential that a condenser be mounted so that only the end where the exhaust enters is rigidly anchored to the car in a fore-and-aft direct ion. The other end must be free to allow over-all expa nsion of t he unit. The most promising fi eld for decreasing the weight of condensers of this t ype appears to be r educt.ion of t he w~ight of the h eaders . Castings can· doubtless be designed which will weigh fa r less t han t hose used and the possibility of building up headers of Rheet ~1.ock should be worth investigating. 'T 111:THOC OF CONNECtlN& CONOl':NSl:R BI/IYJf~ FIG. 39 0 T DETIIILS OF CONDENSER 1tAwrw• NO. .SUP-JOINTS .JK·/O-f |
|
|
|
A |
|
C |
|
D |
|
E |
|
F |
|
H |
|
I |
|
L |
|
M |
|
O |
|
P |
|
T |
|
U |
|
V |
|
W |
|
|
|