US2567454A - Process of and apparatus for heat pumping - Google Patents

Description

Sept. 11, 1951 K. w. TACONIS PROCESS OF AND APPARATUS FOR HEAT PUMPING 2 Sheeis-Shet 1 Filed March 2, 1950 bLT INVENTOR KRIJN W. TACONIS 'ATN P- 1951 K. w. TAcoNls 2,567,454

PROCESS OF AND APPARATUS FOR HEAT PUMPING Filed March 2, 1950 2 Sheets-Shea; 2

Patented Sept. 11, 1951 OFFICE PROCESS OF AND APPARATUS FOR HEAT PUMPING Krijn Wijbren Taconis, Leiden, Netherlands Application March 2, 1950, Serial No. 147,205 In Sweden October 6, 1947 15 Claims.

This invention relates to a process of and apparatus for heat pumping in which a quantity of gas is periodically cooled and subsequently heated, either partly or entirely, to the original temperature, the expansion or compression of a portion of the gas due to the cooling or heating of the whole providing useful cooling or heating effects.

The invention relates more specifically to a process of and apparatus fo producing refrigeration by thermal expansion of a gas in an oblong vessel provided with one or more displacers that can be moved lengthwise in the vessel independently of each other and which together occupy the greater part of the Vessel, such displacers when moved causing the gas to flow from one end of the vessel to the other Without any appreciable difierence of the pressure at any instant throughout the vessel, and including means for efiecting regenerative heat exchange during the flow of gas from one portion to another of the vessel.

This application is a continuation-in-part of my copending application Serial No. 782,288 filed October 2'7, 1947.

A principal object of the present invention is to provide an improved method of and apparatus for producing low-temperature refrigeration whereby it is possible to obtain low and extremely low temperature with a high degree of emciency. Another principal object is to provide an improved method and apparatus for producing refrigeration by processing a gas through a cycle of compression and expansion events which avoids the difficulties attendant the use of an expansion engine or turbine by effecting at least the expansion thermally.

A particular object is to provide a method and apparatus in which a gas is subjected to thermal compression as well as thermal expansion events so arranged that low temperature refrigeration is efiiciently produced from a supply of heat energy without the intermediate conversion of heat energy to mechanical energy and the reconversion of mechanical energy to heat energy.

Further objects of the invention are to provide an improved method of and apparatus for providing a net cooling effect in a body to be refrigerated by subjecting a confined body of gas to a cycle of alternate heating and cooling in a manner which produces a quantity of refrigeration by the secondary cooling of a portion of such gas in heat exchange with the body to be refrigerated, which quantity is a large 2 r7 portion of the product of the temperature change and the difference of the specific heats of the gas at constant pressure'and at constant volume.

In such cycles the gas may be compressed mechanically, for example, by a cylinder fitted with a piston in which by asingle stroke the gas is given the required pressure and, if desired, .a low pressure reservoir may be employed to reduce pressure fluctuations. It is also possible to use a high-speed multi-stroke compressor, or a number of compressors and pressure reservoirs containing gases with increasing pressures.

The invention particularly relates to a very economical expedient .for compressing the low pressure gas to the required higher pressure in the process and apparatus of the present invention. To this end the gas is compressed by a caloric compressor, which may 'be efiectively combined with the cold generating portion of the apparatus so that a very simple low-temperature refrigerating machine is obtained with a high economic yield.

A caloric compressor is one :in which heat is imparted to a body of gas to be compressed, which heating causes the gas pressure to rise so that a portion of the heated gas may be delivered at higher pressure. Little if any mechanical work is involved in a caloric or thermal compressor. Such compressors have been previously proposed (see, for example, United States Patent No. 2,157,229 of V. Bush).

These and other objects and advantages of the invention will become apparent from the following description and the accompanying drawings, in which:

Fig. 1 is a diagrammatic view of an embodiment of the invention in which the gas is mechanically compressed;

Figs. 2-0. and 2-2) are diagrammatic views 1illus trating the principle of operation of a thermal compressor;

Figs. 3-a, 3-2), and 3-c are three diagrammatic sectional views of a preferred embodiment of the invention for carrying out the process of producing low-temperature refrigeration, the

three views illustrating three different stages of the operating cycle;

Fig. 4 is a fragmentary diagrammatic sectional view of a chamber having two gas displa'cers therein, the lower of which has portions of different diameter to provide the refrigeration at several steps;

Fig. 5 is a similar view of another alternative construction in which the lower Tdisplacer is provided with concentric annular steps;

Fig. 6 is a similar view illustrating a modification employing a multiple number of displacers, the lower of which are arranged to b lifted successively;

Figs. '7 and 8 are respectively cross-sectional and fragmentary longitudinal sectional views of a vessel with displacers therein and means between the displacer and vessel wall for increasing th capacity of the wall for regenerator action; and

Fig. 9 is a diagrammatic view of another embodiment of the apparatus of Figs. 4 to 6 in which the regenerator is external to the wall of the vessel.

With reference to the accompanying drawing, a refrigerating machine employing a mechanical compressor, and a thermal expander with a movable displacer within an elongated vessel, is illustrated, in Fig. 1. For simplicity only one displacer is employed in the vessel and the inner wall of the vessel acts as a regenerator.

An oblong, for example cylindrical, vessel which may be externally insulated, is indicated at II and this contains a displacer body I2 which although closely fitting the'inner wall of the cylinder has substantial clearance so that it is capable of being moved freely longitudinally. The displacer is moved by suitable means, for example, by an operating rod I3 or the like, movable through the end of the vessel II. At the top, vessel I I is connected toa tank or gas reservoir lfi'through a conduit I4 controlled by a valve I5, and to a'high pressure gas reservoir I9 by a conduit I'I controlled by valve I8. Reservoirs I6 and I9 are connected by a conduit I I] having interposed therein a compressor C for pumping gas from tank I6 to reservoir I9 at a rate required for keeping the pressure in tank I6 at a constant low value. The inner walls of vessel II are of a material, and may be so constructed, that such walls in cooperation with the walls of the displacer I2 will act as heat accumulators or regenerators. Alternatively the displacer may be closely fitted to smooth inner walls of the vessel I I and passages filled with regenerative material may connect the upper and lower ends of the vessel II. 1

With the aid of the apparatus illustrated in Fig. 1, one modification of the process according to the invention is realized as follows: a quantity of gas is admitted from reservoir I9, in which the pressure is at a high value P, through conduit I'I into the top of vessel II by opening valve I8. The displacer I2 is in its lowest position as shown. It is assumed that the apparatus is in thermal equilibrium condition, in which the temperature at the top of the vessel I I is relatively high, hereafter designated Tm, while the temperature at the bottom is low and is designated Tb. The wall of the vessel II acting as a regenerator insures that the gas being displaced from the top to the bottom is cooled to temperature Tb and heated again to temperature Tm when passed from the bottom to the top of vessel I. For the purpose of an illustrative example, temperature Tm may be taken to be 300 K. and temperature Tb to be 100 K., the pressure P amounting to approximately 10 atmospheres. When displacer I2 is lifted, the ga in chamber II passes between the displacer and the walls and absorbs so much cold that on reaching the bottom it has assumed the temperature Tb.

Thus inlifting displacer I2 an ever increasing portion of the gas is cooled from temperature Tm to temperature Tb. Since this occur under 4 conditions in which the total volume of the gas remains constant, the gas pressure is gradually reduced from the original value P to a low value p, which final pressure is attained upon the total amount of gas reaching the bottom portion of the vessel II.

The pressures P and p are more or less proportionate to the temperatures Tm and Tb. When the gas is displaced from the top to the bottom of the vessel, the pressure consequently decreases and refrigeration due to expansion is produced preferably exclusively at the top and the bottom of vessel II, when of course the gas volume of the regenerator space is left out of consideration. Such volume is the volume of gas present in the space between the displacer I2 and the wall of vessel II, which space is small in respect to the other volumes concerned.

The refrigeration produced at the top of the vessel II is removed by suitable means such as cooling water that may be flowed in heat exchange with the top of vessel II to keep it at the constant temperature Tm. Such quantity of refrigeration generally cannot be effectively used. The refrigeration produced at the bottom of the vessel II at a temperature Tb, however, may be applied usefully to cool a substance to be refrigerated. For example, a fluid to be refrigerated may be flowed in heat exchange with the bottom of the vessel I I.

Thereupon valve I5 is opened and the displacer I2 is moved downward. The cold gas now flows upward at the low pressure p and during such flow through the regenerator walls the gas is heated to the temperature Tm. The tank I6 provides a space for the gas to flow into at a substantially constant low pressure p since provision is made for the pressure in the vessel I6 to be maintained at th value 7). During this stage of the process the regenerator gives up as much heat to the gas as it absorbed therefrom in the first step. Finally the gas may be compressed by means of compressor C from the low pressure p to the high pressure P and passed to the high pressure reservoir I9. Valve I5 is now closed and valve I8 is opened so that a new quantity of gas at a high pressure can be admitted into vessel I I, after which valve I8 is again closed and the process is repeated.

Assuming an ideal gas, that Cp is the specific heat of such gas at constant pressure per mole, Cv is the specific heat at constant volume per mole, and Tm and Tb are the original and final temperatures, in the first step of the process the regenerator absorbs per 1 mole of the gas an amount of heat equivalent to CpX (Tm-Tb). The condition that the regenerator is cooled at constant pressure is closely approximated if the pressure of the gas remains practically unchanged when a certain part by volume of the gas passes through the regenerator. Actually since the cooling of the gas is effected in such a manner that the total volume of the gas in vessel II remains constant, the total quantity of heat withdrawn from the gas amounts only to The difference between these two quantities, i. e. C72Cv (TmTb) therefore constitutes the amount of heat to be supplied to the gas at both the top and bottom of vessel II, in other words, the total quantity of cold produced per mole of the gas under ideal conditions. In the second step of the process, the quantity of cold absorbed by the regenerator at constant pressure p is equivalent to. Op- (CZ-Zm: Tb).= so that: each. time the amount of cold. absorbed by the. re enerator inthesecond step equals thequantity of; cold. delivered. in the first; step and. during the. second step. of the process no; more. cold. or heat is produced.

The cooling of: the. topof the vessel H by cool.- i-ng water precludes. heating of the gas in the. top of vessel H due. to compression. Furthermore, compressor C. has its. own cooling arrangement so. that. the; temperature of. the; gas in. the; pressure vessel; |9 will be. about; equal to; the temperature of the surrounding atmosphere or of the cooling water:

The operation: of; a. caloric compressor, which according. to the. invention. is: advantageously combined with the above. described: thermal ex.- pansion device, is diagrammatically illustrated in Figs. 2-0. and 27b; The thermal. compressor comprises a. chamber or. cylinder 2.0 in which a displacer '2'! is movable up and down by a; driving rod 22. Inlet and outlet conduits 23- audl l con.- nect to the bottom of the: cylinder Zll andiare. controlled by valves 25. and 26 respectively; 'Ilhebottom of the cylinder 20 may be maintained at. a temperature I'm, for example, by cooling coils not shown through which cooling water is passed or similar to cooling passage I3- in the aforementioned Patent No. 2,157,229.. Heat is supplied to the top of the; cylinder 2t; in such. a. manner, for example, by a gas burner not. shown, that a constant temperature Tit. prevails there. For the sake of uniformity withv the previously assumed. ex:- am-ple, the temperature Tmmay be taken to be 390 K. while the temperature 'It may have a I value of about 909 K.

In- Fig. '2--a. the displacer Zxl in. the. cylinder. 20. has assumed the top position and gas: has been admitted through the valve 25 and conduit 23 into the bottom of the cylinder. This gas has a pressure which would amount.- to 1 atmosphere if the gas is supplied. directly from the: atmosphere. Although displacer 2f closely fits. the: wall of cylinder 20, it iscapable of moving'freelytherein with enough clearance so that. the. gas may easily pass between the displacer 2 I. and the. wall of vessel 2|] from one end to the other. Displacer ZI- is now moved downwardly, which causes part of the gas to flow upward intotheheatedltop. of the cylinder 28-. expander, the wall of cylinder 20. acts as, a generator and insures that the cold gas passing upward is heated to the; temperature It. Since. the total volume of the; gas during this step: remains constant and the temperature of. at: least part of the gas rises, the pressure of. the gas: in.- creases. The gas having attained: the desired higher pressure P may be discharged. via valve 26 and conduit 24 from the: bottom of the: cylinder. It should be noticed that the gas, passing through the line 2-4 has the relatively lower temperature Tm. The further dis-placer H is moved downward, more gas is forced out through line 24' at the constant pressure P. This process is: continued until displacer 2-1. has reached its: lowest position, as illustrated by Fig. 2b.

Valve 26 is then closedand displacer 21 lifted again, which reduces. the gas pressure to the value p. This value having been attained, the valve 2'5 may be opened toadmit gas through line 23 duringthe period through which the displacer H is moved further to its highest position; thereupon the aboveoutlined steps may be repeated.

In accordance with the preferred embodiment of the invention, by combining such a caloric As in the case of the thermal 1 compressor with the thermal expansion. apa paratus, a cooling machine obtained havin a. high economic yield. The work. required to bring. the gas from the lower pressure p to the high pressure P in the case of Fig; 1. is supplied by a mechanical energy consuming; compressor. By transforming mechanical energy into com.- pression work, a fairly high yield; is obtained, viz., approximately 60%. However, this is: not the case when the energy containedin fuel. is converted in the customary manner into the mechanical used by the compressor, for: example, from. heat energy to electric energy to mechanical energy. such conversion. at best usually results in a. yield of. less than 3.0%. By converting heat energy of fuel. directly into compression energy and. omitting.- the intermediate conversions, an improvement in the yield bya factor of approximately 5 may be ob.- tained; under certain. conditions. Even if the yield of the. cold generating portion. of the: apparatus is not particularly high, a combination of such apparatus with. the caloric; compressor may result in very high economic yield ofirefrigeration. as compared with that of the known refrigeration machines.

The caloric compressor: described above may be substituted. directly for the. compressor II in Fig. 1, however according to the invention the caloric compressor and cold generating apparatus are further combined into avery simple eflicient refrigerating machine which will. now be described in detail with reference. to Figs; 3'-a, 3-b, and. 3-0.

An oblong or cylindrical vessel 30 is provided with two. displacers 3;! and 32 disposed therein, each being capable of being independently or simultaneously moved longitudinally in the vessel 31!. They maybe moved, for example; by driving rods 33 and 34, the rod 34 being secured to the upper end of displ'acer- 3.2 and. passing through an axial? passage through the displacer 3 The driving rod 33 for the displacer 3i may bea tube surrounding the driving rod 34-. The driving rodsare secured to suitable lifting elements not shown in the interests of clearness of the drawing, for example, a lifting mechanism for a driving rod of a single displaceris shown in the aforementioned United States Patent No. 2,157,229. the displacers and the wall of the vessel to allow the gas to pass from one end to the other and provide regenerator action along the walls. At the top of vessel 30 heating means indicated as a heating coil 35 is provided to maintain the temperature there at the value Tz'z' (which. may, according to the. example, be about. 900 K). At approximately the middle of the vessel 30 there, is provided. a cooling coil, for. example, a passage 35' for cooling. water which surrounds the vessel to, maintain the temperature. in, the middle zone substantially constant, for example, about300 K. Thebottom-of the, vessel is maintained at the. low. temperature Tb. which may, for example, be andv which, temperature is maintained. by a. heat exchange. coil- 31 carrying a fluid to be. cooled. When theapparatus is inoperation and in astateof thermaLequil-ibrium, the temperatures prevailing atv the top, themiddle, and the: bottom zones are: therefore respectively 'I-t, Tm, and Th. Those parts of the vessel wall lying between the top. and the middle and between the middle; and bottom zones act. as regenerators.v The combined length of the dis.-

Sufiicient space may be left between placer-s is less than the length of the chamber 30 by approximately or less.

In the first position, as shown in Fig. 3a, both displacers are as close to the bottom of the vessel as possible, so that substantially all the gas is at the top, the height of the gas column at the top being denoted by the double-headed arrow a. The displacers 3| and 32 are then lifted together over a distance b as denoted by the space between the arrows in Fig. 3-b. The distance b is a fraction of distance a which is dependent upon the temperature ratios employed and for the example indicated, this distance b will amount to approximately a. Part of the gas is displaced downwardly along the regenerative walls and is cooled, causing the pressure to drop from P to p. In passing downward, the gas transfers heat to the regenerator, refrigeration being simultaneously produced at the bottom and the top of the vessel 30 at the respective temperatures Tb and Ti. In the next step of the process, displacer 3| is lifted while displacer 32 is moved downward again in such a manner as to cause the gas portion at the bottom of the vessel 30 to be forced upward to the middle zone, whereby it is heated to temperature Tm, and the gas portion in the upper zone to be forced down into the middle zone and thus cooled to temperature Tm. This step is conducted so that the mean temperature of the total active gas remains constant and the pressure remains constant at p. The end result of this step is illustrated in Fig. 23-0. In the last stage of the process, displacer 3| is moved downward so that all the active gas passes from the middle zone to the top zone of vessel 30 and is heated from the temperature Tm to the temperature Tt. Since the total volume occupied by the gas remains constant, the pressure rises again to the original value P.

It may be calculated that the production of refrigeration per mole of the gas at the top of vessel 30 at the temperature level of 900 K. amounts to approximately 1100 calories and the production of refrigeration at the bottom at a temperature level of 100 K. amounts approximately to 100 calories. Due to the compression in the last stage of the process, 900 calories of heat are developed at the top of the vessel at the temperature level of 900 K. and 300 calories are produced in the middle zone of the vessel at the temperature level of 300 K. Consequently a total of 200 calories per mole must be added to the gas at a temperature of 900 K., and 100 calories of heat, which corresponds to the refrigeration production at 100 K., must be added at the bottom of the vessel. The amount of heat to be discharged to the cooling water at 300 K. is therefore 300 calories.

The above-described cycle may be termed a modified three-step cycle and it will be seen to be a great improvement over a straight threestep cycle in which the distance b is 100% of distance a. Thus if the displacers were simply shifted back and forth in the chamber, no useful net effect would result because the expansion due to pressure drop when the gas was put into the cold end zone would be balanced by the compression due to the equal pressure increase when the gas was shifted into the hot end zone. If, however, the displacers are moved in a straight three-step cycle, starting with the gas all in the hot zone; on the first step the displacers lift all the way so that b equals a and all the gas moves into the cold zone, the pressure drop through a maximum range and refrigeration due to expansion is developed in the gas. On the second stroke or step only the lower displacer is lowered and all the gas is displaced to the middle zone. The gas is warmed to intermediate temperature, pressure rises to an intermediate value, and the later portions of the gas to leave the cold end zone are partly recompressed before they leave this zone. Such partial recompression destroys part of the refrigeration at the cold end, so that only a part is recoverable for usefully cooling a fluid in heat exchange with the cold end. The third stroke drops the upper displacer and returns all the gas to the hot zone so that the pressure rises to the maximum. That heat of compression developed in the later portions of gas to leave the middle zone is removed by heat exchange to the cooling water.

The modified three-step cycle according to the invention avoids the destruction of useful refrigeration at the cold end by removing the gas in the cold end under a constant pressure. The first stroke raises the displacers 3| and 32 only a selected part b of the distance a such that the volume of gas transferred to the cold zone is a selected fraction of the total volume of gas that was in the hot zone. This fraction may be from 15 to 44% and for the specific examples of temperatures herein suggested, is preferably about 26%. The pressure will drop only to the pressure (p) corresponding to the pressure when all the gas is in the intermediate zone because part of the gas is still at high temperature. For the second stroke the displacers 3| and 32 are moved apart preferably in timed relation such that the average temperature of all the gas remains constant and the pressure does not change. The gas portion in the cold zone is heated at constant pressure as it is transferred to the middle zone and the gas portion in the hot zone is cooled at constant pressure as it is transferred to the middle zone. Thus, although the refrigeration produced in the cold zone is not as great as in the straight three-step cycle, none of the refrigeration is destroyed. In the third stroke the lower displacer 32 remains at the bottom and the upper displacer 3| is dropped to shift all the gas from the middle zone to the hot zone. It will also be seen that the smaller pressure change greatly improves conditions in the hot zone because less expansion occurs in the hot zone gas and its actual temperature remains more nearly constant. Ideally all the heat added at the hot zone should be at the high temperature (900 K.) and with a smaller pressure change more of the heat is added at the high temperature and less is added at lower temperatures.

When suitable allowance is made for thermodynamic losses including the deviation of the gas from the ideal, that the compressions and expansions follow adiabatic laws, allowance for dead gas holding spaces such as clearance spaces and regenerator space, allowance for gas flow friction losses and heat exchange inefficiencies; it is found that the straight three-step cycle is so affected by these losses that the useful refrigeration obtained is too small to be economically useful, while on the other hand the modified three-step cycle according to the preferred embodiment of the invention provides an unexpectedly large amount of useful refrigeration for a given input of heat energy in an economical size of apparatus.

The following sets forth a specific example of the effect of selecting the ratio 12/11 of lift for step 1. It is assumed in the following that the *9 mean temperatures at the hot middle and cold ,zones are maintained at 700 K., 300 K., and 100 K., and that suitable allowances for losses are the same in each instance and the gas is monatomic Below about lift and above 44% lift the results become uneconomical for the production of refrigeration at the low temperature of 100 K. This temperature is particularly useful for liquefaction of air under moderate pressures. Still lower temperatures for liquefaction of other "permanent gases are readily attainable.

Sometimes it may be desired to produce part Of the refrigeration at different temperature levels higher than the lowest temperature produced, for example, for the cooling as well as the liquefaction of air. In such a case, the total quantity of refrigeration may be produced at the various temperatures required. To this end the shape of the vessel and the displacer may be modified, for example, as shown in Fig; 4, where the lower displacer I32 may have successively smaller diametral steps toward its bottom end and the vessel I39 is shaped correspondingly at its lower end. This modified structure provides the result that the refrigeration is produced not only at the bottom but also at each of the shoulders I38 and I39 of the lower end of the chamber. The steps are to be of substantially equal height and regenerative action is provided along the walls at each step.

Another modification for accomplishing similar results is diagrammatically illustrated in Fig. 5, wherein the steps at the bottom are in the form of concentric annular projections from the bottom of the vessel 230, in which are fitted corresponding annular portions 238, 239 of the displacer 232. Upon upward movement of the displacer the gas will fiow substantially radially inward toward the center and the lowest temperature refrigeration will be produced in the central depression.

A similar efiect may also be achieved by a modification illustrated in Fig. 6 in which the vessel .330 is cylindrical and a plurality of equal diameter displacers therein are employed. These displacers are moved so that the lower displacers are moved through shorter distances than the upper displacers. Five displacers are shown for example, there being one upper displacer 33I and a group of four lower displacers 3.32-A, 332-3, 332-C, and 332-D, all of which may be moved by the same operating rod 333 by providing successively larger clearance spaces between projections 333-3, 333-0, and 333-D on the rod and a portion of the displacer engaged by the projection. The displacer 332-A may be directly connected to the operating rod 333, while the clearance space between projection 333-13 and displacer 332-13 is a small amount and those between projections 333-C, 333-D and displacers 332-0, 332-D are respectively larger. Thus when the rod 333 is lifted, the displacer 332-A is moved throughout the full lift distance and the lower displacer portions are successively lifted over increasingly smaller distances, whereby refrigeration at several temperature levels may be developed in the several spaces created between the several members of thelower displacer group. The energy-supplying means in the form of a suitable heating means, for example a gas burner, may be disposed externally at the top of the vessel 330. The coolingcoil for cooling water is disposed externally around the vessel 339 in the region between displacers 33l and 332-A. The fluid to be cooled may be passed in thermal contact; with the vessel 330 in the region from below displacer portion 332-A toward the bottom, and if such fluid is flowed in the downward direction it will be cooled gradually to the lowest temperature. The embodiment illustrated in Fig. 6 has an additional advantage in that the distance traversed by the displacers in respect to the vessel will .be reduced. This fact is of importance because an increase of such distance would involve an increase in the temperature gradient between opposite points of the displacer and the wall of the vessel, which. would result in increased thermo-dynamic losses.

Such losses can also be reduced by fitting between the inner wall of the vessel 30 and the outer wall of a displacer 32, as shown in Figs. '7 and .8, one or more coiled bands, as diagrammatically indicated at 40. Such band is preferably helically coiled and provided with several turns between the wall, thus the displacer retains its freedom of movement, the heat capacity of the wall acting as .a regenerator is increased and the heat exchange between the wall and the vessel is reduced.

The losses caused by the difference in temperature of momentarily opposed parts of the displacer and the wall of the vessel may also ,be reduced by providing between them. a movable partition or wall capable of being shifted along or half the distance covered by the displacer, or the perspective part of the displacer. If desired, there may be an arrangement of more than one such partition. The valves, displacers, and the like employed in the various embodiments described herein are preferably operated by suitable mechanism so as to be moved automatically in timedsequence.

In the embodiments of the invention described above, the vessel walls were described as arranged to act as regenerators as the gas flowed between the wall of the vessel and the wall of the displacer. It is also -possible, and in some practical cases preferable, to cause the gas to pass through passages in or outside the inner wall of the vessel or regenerative passages through the displacers.

An embodiment employing regenerators in a passage associated with the wall of the vessel is illustrated diagrammaticallyin Fig. 9. In Fig. 9 a regenerator passage 50 filled with suitable ,regenerator mass 5!, such for example as crosscoiled wire, punched metal pieces, et cetera, is

connected at both ends to the ends of the vessel 430 by passages 52 and 53, and an intermediate connection 54 is provided between the regenerator 50 and the intermediate region of the vessel 430. In Fig. 9 the heating means for the hot end is indicated by a gas burner 55 the coolingcoil carrying cooling water is indicated at 56, anda coil for the substance to be refrigerated is indicated at 51 wound around the cold end of the vessel 430. To provide free communication to the middle connection between the vessel and regenerator the inner end of the displacer 43I is provided. with a somewhatreduced diameter at 58. If it is de- 1 1 sired that the regenerator passages shall be within the displacers, such regenerator passages may extend from one end to the other of the displacers. In such modifications, with regenerators associated with the wall of the vessel or within the displacers, the displacers need not be fitted gastightly against the inner wall of the vessel, however a closer fit is required so that the flow resistance of the gas along the walls is sufficiently greater in respect to the flow resistance through the regenerators that most of the gas will pass through the regenerators.

The gas which is employed may be any gas which is not liquefied at the lowest temperature produced. When very low temperature refrigeration is being produced, a gas such as hydrogen or helium is preferable. Specific conditions to be met will indicate whether monatomic or diatomic gas is preferable. In general the size of the apparatus is reduced by charging the chamber initially with the gas under a high pressure, for example, atmospheres. When hydrogen or helium is used, substantially higher initial pressures may be used because such gases are not liquefiable at temperatures as low as 100 K. and substantially lower.

The portion of the apparatus that serves as a heat accumulator or regenerator may be regarded as a body or mass, the temperature of which decreases gradually from one end to the other. Such a body should have a high heat capacity in relation to the capacity of the gas, while the other parts of the apparatus should have a low heat capacity to avoid secondary losses. When the cylinder wall is constructed to serve as a heat accumulator it should have a high heat capacity, and the'displacers then should have low heat capacity. When the displacers are employed as heat accumulators, they should have a high heat capacity and the wall of the vessel should have low heat capacity. In both cases the heat conductivity of the wall as well as of the displacers should be relatively low in the longitudinal direction. The length of the portion of the vessel not occupied by the displacers should be preferably small in proportion to the length of the vessel. Otherwise the difference in temperature in the spaces available for the gas when the displac'ers are moved would be so large that undesirable heat exchanges may take place.

That the degree of lift or volume of gas admitted to the cold zone should be less than 50% of the original gas space or of the total volume of active gas, is seen to be due to the greatly increased density of the gas at the lower temperature. Thus if the lift is only 26%, about 0.7 of the total weight of gas will be in the 100 K. zone and about 0.3 of the total weight of gas will remain in the -700 K. zone. A lift of about 12% still results in about one-half the gas by weight flowing into the cold zone. In general, the smaller lifts appear to be more useful with larger temperature differences and vice versa and the useful range of lifts is found to lie between about 12% and under 50%. As hereinbefore indicated; the high temperature, for example 600 K. to 900 K., will be selected preferably according to the materials of construction, the temperature efllciently produced by the specific heat source employed, and considerations of efficient heat exchange; the intermediate temperature is preferably a value providing efficient heat exchange to a convenient cooling medium such as water, for example, of the order of 300 K.; and the low temperature is selected to provide efficient heat exchange with a fluid to be refrigerated, such as a gas to be liquefied. Obviously, heat insulation and apparatus constructions are to be employed with a view to minimizing adverse heat leakages.

The process and apparatus according to the invention is useful broadly as a heat pump in which heat energy is supplied or rejected at one temperature, is absorbed or rejected at another temperature, and is rejected or supplied at a different temperature. For refrigeration, heat at low temperature absorbed from a substance to be refrigerated is rejected to a cooling medium at a higher temperature as a result of the rejection to the cooling medium of heat supplied at high temperature; for heating, expensive high-temperature heat energy may effect abstraction of additional heat from a low-cost low-temperature source so that more heat at intermediate temperature may be gained; and by a reversal of the cycle, heat may be absorbed at intermediate temperature and rejected to a warmer cooling medium and a colder refrigerant. The working fluid employed is preferably a gas deviating as little as possible from the properties of an ideal gas. Air or nitrogen may be used if the cold zone temperatures are not extremely low and for temperatures in the range of the boiling points of oxygen and nitrogen, hydrogen or helium are preferred.

It will be understood that modifications of the process and apparatus accordingto the invention may be made without departing from the essentials of the invention and that subject matter in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A process for producing refrigeration which comprises providing a confined body of gas under pressure and at an initial high temperature; cooling at least a portion of the gas to a relatively low temperature at constant total volume to reduce the pressure, thereby inducing refrigeration in said portion and in the remainder; heating said portion while cooling said remainder, both at constant pressure to an intermediate temperature; heating said gas from the intermediate temperature to said initial high temperature; and abstracting for use a substantial amount of the refrigeration induced in said portion.

2. A process for producing refrigeration according to claim 1, in which the amount'by volume of said portion with respect to the total active volume of the gas is selected to be between 10 to 50% according to the temperature levels.

3. A process for producing refrigeration according to claim 1 in which the initial high temperature is 700 K. to 900 K., the intermediate temperature is about 300 K., the relatively low temperature is about K., and the amount by volume of said portion with respect to the total active volume of the gas is of the order of 26%.

4. A process for producing refrigeration which comprises confining a body of gas in a closed system having hot, intermediate, and cold zones, the gas being initially under a desired pressure and high temperature in said hot zone; passing the gas from the hot zone directly to the cold zone while cooling it to a relatively low temperature at constant total volume, to reduce the pressure and thereby induce refrigeration therein; passing the gas from the cold zone to said intermediate zone while heating it to an intermediate temperature, thereby increasing the pressure and inducing heat of compression therein; removing heat from said intermediate zone to maintain the temperature acetate therein substantially constant; passing the gas from the intermediate to the hot zone while heating it to said high temperature; supplying heat to the hot zone to maintain the temperature therein substantially constant;-and abstracting for use a substantial amount of the refrigeration induced in the cold zone.

5. A process'for heat pumping which comprises confining a bodyof gas in a closed system having hot, intermediate, and cold zones, the gas being initially at a desired pressure and high temperature in said hot zone; passing at least a portion of the gas from the hot zone to the cold zone while cooling it to a relatively low temperature at constant total volume to reduce the pressure and induce refrigeration in said portion at low temperature and in the remainder at high temperature; passing said portion while heating it and said remainder while cooling it both to said intermediate zone and to an intermediate temperature; passing the gas from the intermediate zone to the hot zone while heating it from intermediate to high temperature; and cyclically repeating such steps while removing heat from said intermediate zone at the intermediate temperature and supplying heat to the hot and cold zones at their respective temperatures.

6. A process for heat pumping according to claim in which the heating and cooling of the gas during the passages between zones is effected regeneratively by heat exchange with heat storing material.

7. A process for heat pumping according to claim 5 in which the amount by volume of said portion of the gas with respect to the total active volume of the gas is selected to be between to 50%.

8. An apparatus for heat pumping comprising a closed chamber having a hot Zone at one end, a cold zone at the opposite end, and an intermediate zone of intermediate temperature; gas displacing means occupying a major part of the space of said chamber, said displacing means comprising at least two displacers; a charge of gas in said chamber under pressure; passage means interconnecting said zones for passing gas between the zones without appreciable pressure difference; operating means for cyclically moving said displacers to displace substantially all the gas to the hot zone, to displace gas from the hot zone directly to the cold zone, to displace the gas all to the intermediate zone, and to displace all the gas from the intermediate zone to the hot zone; and means for removing heat from the intermediate zone while supplying heat to the hot and cold zones.

9. An apparatus for heat pumping according to claim 8 which includes regenerator means in said passages between said zones.

10. An apparatus for heat pumping according to claim 8 in which said passages between zones are provided by clearance space between the wall of the displacing means and the wall of the chamber and in which one of said walls is constructed to provide regenerative heat storage.

11. An apparatus for heat pumping according to claim 8 in which said passage means is associated with the wall of said chamber and is constructed to provide regenerative heat storage.

12. An apparatus for heat pumping comprising a closed chamber having a hot zone at one end, cold zones at the opposite end, and an intermediate zone of intermediate temperature; gas displacing means occupying a major part of the ill) 14 space of said chamber, said displacing means comprises first and second displacer .units mov= able respectivelyinto the hotiand colder portions of the chamb'enisa'id colder portion of the :cham-' ber and 'said second displacer unit being coop= eraitively'constructed to divide the colder portion into a plurality oficol'd zones interconnected by passages; a charge of gas in said chamber under pressure; passage means interconnecting said zones :for passing .gas between the zones without appreciable pressure difference; operating means for cyclically moving said displacing means to displace gas from the hot zone directly to the cold zones, to displace the gas all to the intermediate zone, and to displace all the gas from the intermediate zone to the hot zone; and means for removing heat from the intermediate zone while supplying heat to the hot and cold zones.

13. An apparatus for producing refrigeration directly from heat energy which comprises a closed chamber having a charge of gas under pressure therein, hot and cold zones adjacent opposite ends, and an intermediate zone; two gas displacers within said chamber which together occupy a major part of the volume of the chamber, the first displacer being movable into said hot zone and the second displacer being movable into the cold zone, the displacers being also movable toward and away from contact with each other; passage means interconnecting said zones providing for the flow of gas without substantial pressure difference between the zones when displaced by the displacers; means for removing heat from the intermediate zone while supplying heat to the hot and cold zones; and operating means for cyclically moving the displacers constructed and arranged to move both displacers simultaneously from a position nearest the cold end to a position part way toward the hot end, then move the displacers apart, the first into the hot zone and the second into the cold zone, and finally move the first displacer out of the hot zone and into contact with the second displacer.

14. A process for producing refrigeration directly from heat energy which comprises confining a body of gas in a closed system; cyclically cooling a portion of such gas from a high temperature to a low temperature, the total gas volume remaining substantially constant and the pressure in the system dropping; heating said portion of gas at substantially constant pressure to an intermediate temperature, the remainder of the gas being simultaneously cooled from said high temperature to said intermediate temperature to keep the pressure in the system substantially constant; recombining said remainder with said portion; heating the combined gas from the intermediate temperature to said high temperature, the total gas volume being maintained substantially constant and the pressure rising to the original higher value; and removing heat from the gas when at the intermediate temperature while supplying heat to the gas respectively at the high temperature and the low temperature.

15. A process for heat pumping which comprises confining a body of gas in a closed system having warm and cold end zones and an intermediate zone, the gas being initially in the intermediate zone at an intermediate temperature; displacing the gas to one of said end zones while effecting a heat exchange to change its temperature to the temperature of such end zone; displacing at least a portion of said gas directly to the other end zone while effecting heat xchange to change its temperature to that of said other end zone; displacing the gas from both end zones 2597,45 1 K 15 g 18 to said intermediate zone to return all said gas to the intermediate zone under substantially con- REFERENCES CITED stant pressure while effecting heat exchange to change the gas temperatures to the temper- The following references are of record in the file of this patent:

ature of the intermediate zone; and cyclically re- 5 peating such steps while effecting heat exchanges UNITED STATES PATENTS with said zones to maintain their respective tem- N e ame Date peratures. 1,275,507 Vuilleumier Aug. 13, 1918 2,127,286 Bush Aug. 16, 1938 KRIJN WIJBREN TACONIS. 10 2,175,376 Bush et a1. Oct. 10, 1939

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