US2947154A - Method and apparatus for cooling various fluids and more particularly the air in aircraft flying at high speed - Google Patents

Description

Aug. 2, 1960 A. CHAUSSON METHOD AND APPARATUS FOR COOLING VARIOUS AND MORE PARTICULARLY THE AIR IN AIRCRAFT FLYING AT HIGH SPEED Filed July 19, 1956 FLUIDS 2 Sheets-Sheet l INVENTOR. AND?! @mus's'a V Aug. 2, 1960 A. CHAUSSON 2,947,154

METHOD AND APPARATUS FOR COOLING VARIOUS FLUIDS AND MORE PARTICULARLY THE AIR IN AIRCRAFT FLYING AT HIGH SPEED Filed July 19, 1956 2 Sh'eet -Sheet 2 INVENTOR. Ayn/e5 61/110560 BY W Ma W A rive/V 7 United States aten 9 i METHODAND ATPARATUS'FOR COOLING VAR- IOUS FLUIDS AND MORE PARTICULARLY THE AIR IN AIRCRAFT FLYING AT HIGH SPEED Andr Chausson, Asnieres, France, assignor to Societe Anonyme des Usines Chausson, Asnieres, France, a French company Filed July 19,1956,S er.No.598,847. Claims priority, application France July 28, 1955 5 Claims. c1. 62-169 temperatureexceeding that of the ambient air by about 180 0., when the. machine is travelling at a speed of 1,560 miles an hour. With a thoroughly efficient heat exchanger, the .air to be cooled is, under such conditions, at the output of the heat exchanger at a temperature which exceeds that of the cooling air at the input by at least twenty degrees. r

This means that, in conditions of high-speed displace.- ment, the temperature drop to be produced by an expansion turbine becomes too great for apparatus of permissible. weight and size.

Cooling by evaporation enables, in principle, the temperature of the air to be lowered 'to any extent required, independently of thetemperature of the outside air, by means of.a proper selection of the vaporizable coolant liquid.

Nevertheless, it must be considered that fora liquid at rest, only disturbed by natural convection currents, evaporation rapidly becomes slower and slower as the evaporation temperature decreases. Thus, for the same difference of temperature between the wallofthe heat exchanger and the vaporizable coolant liquid, water as the coolant liquid can only evaporate one-twenty fifth as fast, at an altitude of twenty thousand metres from the ground as at sea level, and methyl alcohol as the coolant liquid would evaporate about one twentieth asfast.

This fact considerably limits the employment .of con: ventional evaporators, for it becomes necessary to utilize heat exchange surfaces of very large area, whose dimensions and weight quickly become prohibitive.

This inventionemploys a new method of cooling, and an apparatus for performing it, according to which it becomes possible to utilize the properties of evaporators in a reasonable manner, even at high altitudes.

According tothis invention, the fluid which is to be cooled. (cabin air, for instance) is passed through a heat exchanger through which circulates a coolantliquid. The heat exchanger is divided into two parts, a high pressure, heat absorption compartment and a low .pressure, heat dissipation compartment, through both of which the coolant liquid circulates, although the cabin .air circulates through only the high pressure, heat absorption compartment. T he heat exchanger is so arranged that, although the two compartments communicate, the.com-. partmentthroughWhich the cabin air passes, in heat ex change relation tothe coolant liquid, is always maintained at a higher pressure than the other compartment, which is in communication with the surrounding low pressure V 2 atmosphere. The coolant liquid in the low pressure compartment of the heat exchanger will boil under such conditions, whereas the coolant liquid in the higher pressure compartment will not. The boiling efficiently cools the liquid part of the coolant by the latent heat required to vaporize part of the coolant, which is removed from the low pressure compartment and thus dissipates the heat absorbed from the cabin air in-the higher pressure compartment of the heat exchanger. The liquid form of thecoolant in such higher pressure compartment promotes heat exchange between the cabin air and the liquid coolant much more efficiently-than if the coolant were wholly or partially in'vapor form. Preferably the liquid coolant and the cabin air circulate countercurrently.

While the invention is herein described as applied to the cooling of air for supply to an aeroplane cabin, the principles of the invention are applicable generally to the cooling of a fluid, whether liquid or gaseous, by a liquid coolant under conditions-such as discussed above.

In this invention, according to one embodiment (Figure 1) applicable to a pressurized but not airtight aeroplane cabin, i.e. one to which air is supplied and from which it is discharged constantly, the air intended for supply tothe cabin is bled, under pressure, from a point towards. the output of the compressor section of a jet engine, and passes through a pre-cooler or heat exchanger. Coolant air is supplied to a separate passage through such pre-cooler, at'considerably lower pressure and temperature, from a location at or near theinput of such compressor section, and cools the air to be supplied to the cabin Circulation of the coolant air may be induced or assisted by a blower driven by an expansionturbine which functions in a later stage of the cooling. The

- airto be supplied to the cabin, uponleaving the precooler, passes into a second heat exchanger which utilizes as the coolant a circulating vaporizable coolant liquid.

which absorbs heat in its liquid form under high pres sure from such air and is cooled in a separate compart: ment ofthe heat exchanger under low pressure by evaporation of part of such coolant which is liberated to the atmosphere in the manner already explained. The cabin air may be still further cooled by causing it to drive the expansion turbine mentioned above.

According to a second embodiment (Figure 2) applicable to an airtight aeroplane cabin, the pre-coolcr may be omitted, since the cabin air is recirculated, and is inherently at a pressure and temperature lower than air bled from the output of a compressor section, hencev needs less cooling. The evaporation type heat exchanger described above is then used for required cooling of the circulating cabin air. 7 a

Figure l is a diagram of a cooling apparatus for performing the method of the invention, applicable more particularly to the cooling of a pressurized but not airtight aeroplane cabin.

Figure 2 is a diagram of an alternative embodiment of Figure l, more particularly applicableto the cooling of an air-tight aeroplane cabin. M

Figure 3 is a top plan view, diagrammatically showing a form of embodiment of a heat exchanger of the apparatus of the preceding figures.

Figure 4 is a section taken along the line IV-IV of Figure 3.

Figure 5 is a section taken along the line VV of Figure 4. U

According to the method of the invention, for obtaining suitable cooling, more particularly of the air inside the cabins of aircraft flying at very high speed and at high altitude, the air to .be cooled is passed through at least one heat exchanger which brings it into heat exchange relation with a cooling liquid.

. Cg Patented Aug. 2, 1960 that it is drawn olf from an upper compartment of the heat exchanger, which is in communication with the ambient air and hence is subject to low pressure, and is delivered to a lower compartment, through which the fluid to be cooled is passed, and this lower compartment of the heat exchanger is isolated from the upper compartment sufficiently so that the pressure in said lower compartment can be maintained at a value higher than that prevailing in the upper compartment.

Because of the absorption of the additional heat by the cooling liquid, from the air which is cooled, the temperature of the liquid coolant is above that at which it will boil under the low pressure prevailing'in the upper compartment of the heat exchanger in communication with the atmosphere. As the latent heat of vaporization required to vaporize the liquid during such boiling is extracted from the upper layer of the cooling liquid, such upper layer is cooled and is then conveyed back to the lower compartment of the heat exchanger to cool the cabin air. The pressure maintained in the lowercompartment of the heat exchanger is enough higher than the pressure prevailing in the upper compartment of this exchanger so that the temperature of the coolant liquid in said lower compartment is alwaysbelow boiling. Consequently the heat exchanger walls in the lower compartment are always in contact with liquid and not with vapor.

In the attached drawing, there is shown, by way of example, two alternatives of an apparatus for performing the method described above, for cooling the air intended to be utilized in an aeroplane cabin and more particularly according to Whether such cabin is, or is not, completely airtight.

The apparatus of Figure l is more particularly intended for cooling air to be supplied to a non-airtight pressurized cabin. The air to be introduced into the cabin is bled, by pipe 1, from the outlet 2 of the compressor section of a jet engine, for example, so that this air preferably is under a pressure considerably higher than cabin air pressure. The pressure of the air conveyed by pipe 1 being appreciably greater than the pressure of the ambient air surrounding the aeroplane, its temperature is raised by its compression, and is consequently higher than the temperature of the air at the input of the compressor section.

For carrying out a pre-cooling of the air conveyed by pipe 1, the latter passes into a pre-cooler or heat exchanger 3, in which cooler air circulates. Such air may be that within a duct 4 with its intake at 5, for example, at the input of the compressor section. After the precooling carried out in the pro-cooler 3, the air supplied by the pipe 1 is led by a pipe 6 into a second heat exchanger 7, operating according to the method described above.

The air cooled in the heat exchanger 7, which is always at a pressure exceeding cabin air pressure and which is not yet necessarily lowered to the required temperature, is conveyed by pipe 8 into an expansion turbine 9 intended to supply air to the cabin directly through the duct 10. The work done here lowers the temperature of the cabin air to that desired. The power develo'ped by driving, the turbine 9 is advantageously used for driving a fan 11, intended to induce or assist the circulation of the cooling air supplied by the duct 4 into the pre-cooler. As is also shown in Figure 1, when it is not necessary to utilize the heat exchanger 7, a by-pass duct enables this heat exchanger to be by-passed when a valve 13, mounted on the duct 6, is closed and a valve 14, in the by-pass duct 12, is open.

According to the alternative embodiment of the apparatus of Figure 2, wherein cabin air is to be recirculated, the heat exchanger 7 ismounted so that air is drawn from the cabin by a fan which discharges it into'the heat exchanger nest 19 from which it emerges cooled, and, possibly, filtered by a cartridge 16, before being again 4 delivered to selected parts of the cabin by one of several pipes 17. In this latter case, the air is circulated in a closed circuit, because the air is drawn from the cabin and returned to the cabin after cooling, which is only suitable for an airtight cabin, or one that is practically airtight; in this latter case, the slight addition of air, necessary for re-establishing pressurization and intended to compensate fo'r leakage of air from the cabin, would advantageously be taken directly from the output 2 of the compressor section and conveyed to the fan input 15.

The evaporation heat exchanger 7 according to Figure 1 or according to Figure 2, is advantageously made as shown in Figures 3, 4, and 5. Such heat exchanger comprises a casing 18, at the lower part of which is a cluster or exchanger nest 19 formed, for example, of tubes of rounded or flattened section, connected at their ends by apertured plates 20 and 21 (Figure 3 and 5), or shaped so as themselves to form these tubular plates so that the cabin air to be cooled passes into these tubes of the cluster, for example, in the direction of the arrows f This air is propelled either in the manner described with reference to Figure l, or in the manner described with references to Figure 2.

The apertured plates 20 and 21 are fixed by air-tight joints to the casing 18 which contains coolant liquid '22. Suflicient coolant liquid is provided so that its surface is substantially above the cluster 19. As shown more particularly in Figures 3 and 4, it is advantageous that the cabin air should circulate in the direction opposite to the movement of the liquid 22 which is circulated by means such as a pump 29, as is explained below. The tubes of the cluster 19 preferably are engaged in or extend through baflie-plates 23, clearly shown in Figure 3, which are arranged so that the liquidcontacting the cluser 19 is forced to follow the course indicated by the arrows F The baffle-plates 23 are fixed, at their lower edges to the bottom 18a of the casing 18, and at their top edges to a plate 24, which may be perforated; plate 24 is itself fixed to the lateral sides of the casing 18. In this manner the liquid 22 that contacts the cluster 19 is segregated from that which lies above the plate 24.

The liquid which is inside the casing 18 below the plate 24 is conveyed to the lower compartment of the heat exchanger through an opening 25. This has the eifect of forcing the liquid to follow the zig-zag path defined by the bottom of the casing, the plate 24 land the battle-plates 23, as shown by arrows F Since the perforations of the plate 24 are of small area, if such plate is perforated, and the free passage at the end of the battle-plate is also of small area, the flow of the coolant liquid around these battle-plates encounters considerable resistance which causes an increase of pressure of the liquid circulated below the plate 24, the absolute pressure of which may be thus maintained substantially greater than the atmospheric pressure which prevails above the plate 24. In case the pump 29 used for returning the liquid to the casing 18 is a low delivery pump the plate 34 is not provided with perforations, and/or the passage 27, formed between the casing and the last battle-plate 23, is provided with a valve 40 which is spring loaded to close that passage until a suitable pressure is produced in the portion of the casing 18 surrounding the cluster 19. The liquid pressure which is produced in that casing is selected such that the temperature required to boil the liquid is high enough to prevent the risk of boiling, and consequently the risk of formation of vapor bubbles which might reduce the efiiciency of the heat exchange in case vapor bubbles should contact the walls of the cluster 19.

The perforations which are made in the plate 24 are intended to allow easy escape to the lower pressure upper compartment of vapor bubbles which might, nevertheless, possibly be produced.

The liquid above the plate 24 is brought to ambient atmospheric pressure because the mouth or vent 26 of the casing -18 is open to atmosphere. Since the liquid above the plate 24 has been previously circulated in thermal contact with the cluster 19 as explained above, this liquidhas been heated and in view of the fact that the pressure of this liquid is lowered at the discharge side of perforated plate 24"and/or at the outlet end'of the restricted passage formed by the last bafi'le-plate 23, or at the outlet from the loaded valve 40 mentioned above, it follows that this liquid has been heated to a temperature above the boiling point of the liquid at such lower pressure, and consequently some of the liquid evaporates. As well known, the changing of phase from liquid to gas necessitates the absorption of a large quantity of heat, the exact quantity of which depends on the nature of the coolant liquid. The latent heat or vaporization of water, for example, is known to be 540 calories/cm. Consequently the mass of liquid occupying the space above the plate 24 is cooled rapidly to the boiling temperature at the pressure in the upper compartment, disclosed as being ambient atmospheric pressure.

As clearly shown by Figure 5, the mass of liquid above the plate 24 communicates withthe upright pipe 27 extending downwardly and this pipe is provided at its lower end with an outlet 28 for connection, as diagrammatically shown in Figure l, with the inlet of the liquid-circulating pump 29. Connecting the pump to the lower end of such upright duct prevents the risk of sucking vapor bubbles as might occur if the vent opening 28 were placed near the upper level of the boiling liquid. The liquid drawn off through the vent opening 28 is the coldest portion of the liquid in the upper compartment, since this portion is located at the lowest level of the casing 18, and this liquid sucked by the pump 29 through pipe 30 is then returned under pressure towards the inlet opening 25 to the lower compartment in which the cluster '19 is located, to be recycled as explained above.

' In order to prevent droplets of liquid from being lost to the atmosphere through the vent opening 26 of the casing 18, a porous partition or filter 31 is placed above the level of the liquid 22 in the upper compartment, to retain the droplets entrained in the air.

To obtain adequate cooling by the heat exchanger described above, it is necessary that the level of the liquid in it should be always kept substantially constant, in spite of losses resulting from evaporation. Consequently, a liquid supply 32 (Figure 2) is held in a tank 33, preferably heat-insulated, which is connected to casing 18 by a duct 34 controlled by a valve 35. The interior of the ta-nik 33 can be vented to the atmosphere through a small duct 36, which'is itself controlled by a valve 37. The valves 35 and 37 have their operating members connected by a common link connect-ion 38, controlled by a float 39 (Figures 2 and As can be clearly seen, when the level of the liquid 22 is lowered, the valves 35 and 37 open, which enables enough liquid to flow from tank 33 into the heat exchanger to replace the liquid that has evaporated, whereupon the valves 35 and 37 close automatically.

The liquid utilized in the heat exchanger can, for example, be water, alcohol, ammonia, or any other suitable liquid.

1 claim:

1. An evaporator type heat exchanger comprising a first compartment, a second compartment, vaporizable coolant liquid completely fiilling said first compartment and partly filling said second compartment, means extending through said first compartmentonly, defining a flow path for a fluid to be cooled therein by said coolant liquid, and means for pressurizing said first compartment sulficiently above the pressure in said second compartment to prevent appreciable boiling of said coolant liquid in said first compartment at the temperature to which it is heated bycooling such fluid, but the pressure in said second compartment being suificiently low to promote boiling of the coolant liquid thus heated for cool-ing'such coolant liquid by theevaporation of such boiling, and means providing escape of coolant vapor from said second compartment, said pressurizing means including restricted passagemeans from said first compartment to said second compartment for flow of said coolant liquid therethrough effected by the differential of pressure in said first compartment over that in said second compartment and pressure-producing means operable to produce such pressure difierential and force coolant liquid from said second compartment into said first compartment, then through said first compartment and finally from said first compartment back into said second compartment through said restricted passage means.

2. An evaporator type heat exchanger comprising a first compartment filled with vaporizable coolant liquid, a second compartment containing vaporizable coolant liquid, under atmospheric pressure and in communication with the atmosphere for release of coolant vapor liberated by boiling of the coolant liquidin said second compartment, restricted passage means connecting said first compartment and said'second compartment and requiring a differential pressure in said first compartment higher than the atmospheric pressure in said second compartment to move coolant liquid therethrough from said first compartment to said second compartment, means extending through said first compartment defining a flow path for fluid to be cooled, in heat exchange relation to the coolant liquid, to heat such coolant liquid to a temperature below the boiling point of the coolant liquid at the pressure in the first compartment but above the boiling point of the coolant liquid at the atmospheric pressure of the second compartment, pumping means pumping from said second compartment to said first compartment coolant liquid cooled by the evaporation accompanying boiling of the coolant liquid in said second compartment,

said pumping means then forcing the coolant liquid through said first compartment and finally from said first compartment through said restricted passage means back into said second compartment, a coolant liquid supply source, and valve means controlling flow of coolant liquid from said coolant liquid supply source into said second compartment to replace coolant liquid lost therefrom by evaporation.

3. An evaporator type heat. exchanger comprising a casing, a generally horizontally disposed partition in said casing defining a lower compartment and an upper compartment, said partition being perforated to afiord re- 7 stricted communication between said compartments,

means extending through said lower compartment defining a flow path for a fluid to be cooled, a generally upright duct communicating at its upper end with said upper compartment, coolant liquid completely filling said lower compartment and said upright duct, and partly filling said upper compartment, said upper compartment, above the coolant liquid level therein, communicating with the ambient atmosphere, and pump means connected to the lower end of said upright duct and to said lower compartment, capable of producing a pressure suificient to force liquid coolant to flow from said upright duct through said lower compartment and through the restricted communication afiorded by said perforated parclaim 3, including an air-pervious partition in the upper compartment above the normal level of the liquid in that compartment, to block escape of liquid.

9 References Cited the file of this patent 8 Harris July 30, 1935 Baruch Aug. 23, 19 38 Strang Nov. 12, 1940 Dube Apr. 15, 1941 Kelley Aug. 23, 1949 Whitney Oct. 12, 1954 Worthen et a1. Aug. 21, 1956

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