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Publication numberUS3472037 A
Publication typeGrant
Publication dateOct 14, 1969
Filing dateDec 28, 1967
Priority dateJan 25, 1967
Also published asDE1601467A1, DE1601467B2
Publication numberUS 3472037 A, US 3472037A, US-A-3472037, US3472037 A, US3472037A
InventorsKohler Jacob Willem Laurens, Prast Gijsbert
Original AssigneePhilips Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Hot-gas reciprocating engine
US 3472037 A
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Description  (OCR text may contain errors)

Oct. 14, 1969 1 W KOHLER ET AL 3,472,037

HOT-GAS RECIPROCATING ENGINE 4 Sheets-Sheet l Filed Deo. 28. 1967 C- 14 1969 l .1. w. L. KOHLER ET AL 3,472,037

HOT-GAS RECIPROCATING ENGINE Filed Deo. 28. 1967 4 Sheets-Sheet i i 21 n w1.1-0.3 u

FIGB

INVENTOR. JACOB W.L,KHLER GIJSBER T PRAST ct. 14, 1969 J, w, KOHLER ET AL HOTQGAS REGIPROCATING ENGINE 4 Sheets-Sheet 4 Filed Dec. 28. 1967 )1v/1am MENT United States Patent O 3,472,037 HOT-GAS RECIPROCATING ENGINE .Iacob Willem Laurens Kohler and Gijsbert, Prast, Emmasingel, Eindhoven, Netherlands, assignors, by mesne assignments, to U.S. Philips Corporation, New York, N.Y., a corporation of Delaware Filed Dec. 28, 1967, Ser. No. 698,371 Claims priority, applieatgllltherlands, Jan. 25, 1967,

Int. Cl. F25b 9/ 00 U.S. Cl 62-6 13 Claims ABSTRACT F THE DISCLOSURE A hot-gas reciprocating machine having first and second compression yand expansion spaces and pistons therein, a third piston within a third space which communicates with one of the first and second spaces, the two spaces in communication having pressure variations during operation, 90 out of phase with the pressure variations in the remaining space, and the stroke-volume of the first and second pistons being related by 1- (1 being the quotient of the absolute temperatures prevailing in the second and iirst spaces respectively), for balancing the dynamic forces in operation of the apparatus and reducing the mechanical losses therein.

The invention relates to a hot-gas reciprocating machine comprising a first space the volume of which can be varied by a lirst piston-like body and to which heat can be supplied during operation, which space is connected to a second space the volume of which can also be varied by la piston-like body and from which heat can be derived during operation, which spaces in operation have relatively different mean temperatures, the link between these spaces accommodating a recuperator through which a working medium can ow to and fro.

In the present application, :a hot gas reciprocating engine is to be understood to mean a cold-gas refrigerator, a hot-gas engine, a heat pump and a cold-gas engine. In these engines, a working medium is compressed when it is contained primarily in a space (compression space) from which heat can be derived, and this medium is eX- panded when it is contained primarily in a space (expansion space) to which heat can be Supplied. The compression-and expansion spaces are separated Iby a regenerator. In known engines of the kind set forth, the volumes of the compression-and expansion spaces are varied by pistons which are displaced by a driving gear with a relative phase difference. The total volume variation of the compression space, the expansion space and the interposed link will be equal to the sum of the volume variations produced lby the compression piston and the expansion piston together. These volume variations involve pressure variations, the phase difference between the compression piston and the expansion piston being chosen so that the pressure variations lead in phase to the movements of the compression piston and lag behind the movements of the expansion piston. The compression energy supplied by a compression piston is determined solely by that part of the pressure variations which leads in phase by 90 to the movements of this piston, while the expansion energy absorbed by an expansion piston is determined solely by that part of the pressure variations which lags by 90 in phase behind the movements of this piston. The other part of the relevant pressure Variations is in co-phase or 180 phase difference with the movement of the piston and does not participate in the supply :and absorption, respectively, of energy. Consequently, these pressure variations do not exert a favorable iniluence on the cycle passed by the medium. However, these pressure variations have the disadvantage that they of course do eXert forces, socalled Cil y 3,472,037 Patented Oct. 14, 1969 blind forces, on the pistons and on the bearings so that they involve considerable mechanical losses.

The invention has for an object to provide a hot-gas reciprocating engine of simple construction, in which the pressure variations in the spaces from which heat can be derived and to which heat can be supplied, respectively, l-ag and lead, respectively, by at least substantially in phase with respect to the movements of the relevant piston-like bodies.

The hot-gas reciprocating engine in accordance with the invention is therefore characterized in that the said piston-like bodies are connected to a driving gear which moves these bodies so that the Volume variations of the space to which heat can be Supplied are in phase opposition to those of the space from which heat can be derived, the stroke volume of the piston-like body for varying the volume of the space from which heat can be derived being substantially equal to r times the stroke volume of the piston-like body for varying the space to which heat can be supplied, where r is equal to the quotient of the 'absolute temperature prevailing during operation in the space from which heat can be derived and the absolute temperature prevailing in the space to which heat can be supplied. The engine also includes one or more further piston-like bodies which each limit by one side a space forming an open communication with the space from which heat can be derived and/or with the space to which heat can be supplied and/or with the link between these spaces, each of these piston-like bodies cooperating with a stroke limiter and/or a further energydissipating device which may be adjustable.

In this hot-gas reciprocating engine, each of the further piston-like bodies co-operates with a spring constituted by the medium in the spaces from which heat can be derived and to which heat can be supplied, respectively, and with a stroke limiter or another energy-dissipating device. Due to the difference in stroke volume of the piston-like bodies limiting the spaces from which heat can be derived and to which heat can be supplied, respectively, no pressure variation will occur during operation of this engine when the medium is transported from one space to the other. When each of the further piston-like bodies performs a movement which lags by 90 in phase behind the movement of the piston-like body varying the space from which heat can be derived, and hence leads by 90 to the movement of the piston-like body varying the space to which heat can be supplied, this is achieved because the pressure variations are in co-phase with the movements of the further piston-like body, the pressure variations are also by 90 out of phase with respect to each of the two said piston-like bodies. This implies that these piston-like bodies are no longer subjected to blind forces so that the mechanical loss is considerably reduced and the overall eiliciency of the hot-gas reciprocating engine is higher. A phase difference of substantially 90 between the movements of each of the further piston-like bodies and the piston-like bodies varying the volumes of the spaces from which heat can be derived and to which heat can be supplied, respectively, is obtained automatically if the latter piston-like bodies move at least substantially at a frequency corresponding to the natural frequency of each of the further piston-like bodies and the co-operating spring and stroke limiter or other energydissipating devices. Since the stroke limiter or energy-dissipating device always requires some energy, if the further piston-like body does not co-operate with a driving member, the pressure variations cannot be fully in co-phase with the piston movements but will slightly lead in phase so that the further piston-like body receives some energy from the medium.

In the present application, a piston-like body is to include not only a piston or a plunger, but also a diaphragm. In a further advantageous embodiment of the hot-gas reciprocating engine according to the invention, the piston-like bodies for varying the volume of the spaces to which heat can be supplied and from which heat can be derived, respectively, are rigidly connected to each other, the centre lines of these piston-like bodies coincide and the space from which heat can be derived, the recuperator and the space to which heat can be supplied lie between the piston surfaces of the said piston-like bodies facing each other. Due to the rigid connection between the two piston-like bodies, the energy supplied to the expansion piston upon expansion is directly transmitted to the compression piston.

In another embodiment, the piston-like bodies for varying the volume of the spaces to which heat can be supplied and from which heat can be derived, respectively, are also rigidly connected to each other while the piston surfaces varying the volumes of said spaces are directed away from each other.

A further advantageous embodiment of the hot-gas reciprocating engine according to the invention is characterized in that each of the further piston-like bodies also co-operates with a further energy-accumulating device which may be adjustable. Thus, this engine includes besides the medium acting as energy accumulator an additional accumulator which also determines its speed. When this further accumulator device is made adjustable, the speed of the operating engine can be varied by varying the adjustment. According to the invention, the energy-accumulating device may comprise a spring or a ilywheel which is connected, if desired, through a transmission, to the relevant piston-like body.

In a further embodiment, the energy-dissipating device comprises a double-acting piston which is connected to the further piston and is adapted to move in a closed cylinder containing a medium, the two spaces on either side of this piston communicating with each other through a narrow opening the passage of which may be adjustable. Also the energy-dissipating device may comprise a brake which may be adjustable, or the energy-dissipating device comprises a cooled tube which closed at one end and limited at its other end by a piston surface coupled with the piston-like body.

In a further favourable embodiment, in which the pressure variations are accurately in co-phase with the movements of each of the further piston-like bodies, these further piston-like bodies are connected, if desired through a transmission, to a driving member, the movements of each of the piston-like bodies lead at least substantially by 90 in phase to the movements of the piston-like body varying the volume of the space to which heat can be supplied. In this embodiment, each of the further piston-like bodies may be coupled with the crankshaft which also cooperates with the piston-like bodies varying the volumes of the spaces from which heat can be derived and to which heat can be suppled, respectively. Alternatively, the driving member may be constituted by a separate electric motor or another driving device rotating in the correct phase.

In order to compensate in this embodiment for the pressure forces acting upon each of the piston-like bodies, according to the invention, each further piston-like body has a stroke, a speed and a mass such that the inertia forces occurring in operation are at least substantially equal to the sum of the pressure variations and spring forces produced in co-phase with the piston movement.

The invention will be described more fully with reference to the drawings.

FIGURES 1 to 6 show diagrammatically and not to scale a number of embodiments of cold-gas refrigerators, in which the volumes of the compressionand expansion spaces vary in relative phase opposition and the ratio between the strokes of the piston-like bodies varying the volumes of these spaces is equal to that between the absolute temperatures prevailing during operation in these spaces. Provision is made of one or more further pistonlike bodies which are each capable of varying the volume of a further space communicating with the compressionand/or expansion space, which these further piston-like bodies perform movements which are by out of phase with respect to the piston-like bodies varying the volumes of the compressionor expansion space. The further piston-like bodies then co-operate with an energy-accumulating and an energy-dissipating device.

FIGURES 7 and 8 show two embodiments of cold-gas refrigerators which roughly correspond to the cold-gas refrigerators of FIGURES 1 to 6, but in which the further piston-like bodies are coupled with a driving member.

FIGURE 9 shows diagrammatically and not to scale an embodiment of a hot-gas engine in which the volumes of the compressionand expansion spaces again vary in relative phase opposition, while the ratio between the stroke volumes of the piston-like bodies varying the volumes of the compressionand expansion space is equal to the quotient of the absolute temperatures prevailing in these spaces during operation, provision being made of one or more further piston-like bodies which each vary the volume of a space communicating with the compressionor expansion space and which co-operate with an energy-dissipating and an energy-accumulating device.

Referring now to FIGURE 1, reference numeral 1 denotes a cylinder in which a compression piston 2 and an expansion piston 3 are adapted to move. The compression piston 2 and the expansion piston 3 are rigidly connected to each other by means of a link 4. Between the piston surfaces facing each other of the pistons 2 and 3, there are disposed a compression space 5, a cooler 6, a recuperator 7, a freezer 8 and an expansion space 10. The expansion piston 3 is connected through a driving rod 11 to a crankshaft 12 which is coupled with a driving member (not shown). The compression piston 2 has a larger diameter than the expansion piston 3 so that the stroke volume of the compression piston 2 is r times that of the expansion piston 3. -r represents the quotient of the absolute temperature prevailing in the compression space and that prevailing in the expansion space 10 during operation.

The cold-gas refrigerator further includes a cylinder 15 in which a further piston 16 is adapted to move. This piston 16 limits by one side a space 17 communicating with the compression space 5 and at by other side a space 18 in which prevails the same mean pressure as in the compression space 5. The piston 16 is connected through a piston rod 19 to a piston 20 which is adapted to move in a closed cylinder 21 containing a liquid. The two spaces on either side of the piston 20 communicate with each other through a duct 22 including an adjustable shutter 23. The piston 16 further co-operates with a spring 25. The piston 16 and the co-operating spring system constituted by the medium in the spaces 17, 5, 6, 7, 8, 10 and the medium in the space S and the spring 25 has a given natural frequency depending upon the spring constant of the said spring system and upon the mass of the moving parts When, after putting the cold-gas refrigerator in operation, the crankshaft is driven at the said natural frequency due to the fact that the same temperature prevails in the spaces 5 and 10, pressure fluctuations resulting from the difference in diameter of the pistons 2 and 3 will be produced at a frequency equal to the natural frequency of the piston 16. As a result, the piston 16 starts moving at its natural frequency, which movements lag, however, by 90 in phase behind these pressure fluctuations. This implies that the movements of the piston 16 will also lag by 90 in phase behind the movements of the compression piston 2, but will lead by 90 in phase to the movements of the expansion piston 3. The pressure fluctuations produced by the movements of the piston 16 will then lead by 90 in phase to the movements of the piston 3. This implies that the piston 2 is a compression piston and piston 3 is an expansion piston.

The medium will be compressed when it is mainly contained in the space 5, the compression heat being derived from the medium in the cooler 6. The medium is expanded when it is mainly contained in space 10, heat, for example, of an article or a medium to be cooled, being supplied to the medium in the freezer 8. The temperature in the space will be low, while the space 5 will be approximately at the cooling-water temperature. The stroke volumes of pistons 2 and 3 are chosen so that they are in the same ratio as the absolute temperatures prevailing in operation in the compression space 5 and in the expansion space 10. This means that during operati-on, i.e. when the expansion space 5 is at the cooling-water temperature and the expansion space 10 is at a low oper-ating temperature, movements of the pistons 2 and 3 no longer produce pressure fluctuations. Pressure fluctuations are then produced only by the vibrating piston 16 which are in co-phase with the movements of this piston. This means that the pressure fluctuations then produced are at right angles to the movements of the compression piston 2 and the expansion piston 3 so that blind forces resulting from pressure fluctuations which are in co-phase with these pistons are avoided in this refrigerator, which will therefore operate with low mechanical losses. In order to limit its stroke, the piston 16 co-oper-ates with a damping device 20, 21, 22, 23 in which an amount of energy is dissipated. In order to maintain the vibration of the piston 16, a quantity of energy will have to be supplied to said piston. Consequently, the pressure fluctuations in the spaces 17, 5, 6, 7, 8 and 10 will slightly lead With respect to the movements of this iston. p FIGURE 1 shows in dotted lines that an alternate cylinder and a piston 16 adapted to move therein, may be connected to the space 10. This piston 16 shown in dotted lines will move in co-phase with the piston 16 described above.

FIGURE 2 shows diagrammatically the same cold-gas refrigerator as FIGURE 1, but in this case, the compression piston 2 and the expansion piston 3 are interconnected inside by means of a rod 25. This provides a slightly more aesthetic construction. In this embodiment, the piston 16 co-operates with a slightly modied springand damping system. The side of the piston 16 remote from the space 17 limits a space 30 which communicates with a space 33 through a duct 31 including a shutter 32. The spaces 30 and 33 contain a gas at the mean pressure prevailing in the space 17. The operation of this cold-gas refrigerator is quite analogous to that of the cold-gas refrigerator of FIGURE l.

FIGURE 3 shows a cold-gas refrigerator having a slightly modified construction. This cold-gas refrigerator has two interconnected pistons 32 and 33 which vary the volumes of a compression space 35 and of an expansion space 40 by their piston surfaces remote from each other. The compression space 35 communicates through a cooler 36, a recuperator 37 and a freezer 38 with the expansion space 40. The compression space 35 again communicates with a space 17 which is limited by a piston 16 which is adapted to move in a cylinder 15; the arrangement is quite analogous to that of FIGURE 1. This refrigerator also operates in quite the same manner as the refrigerators of the preceding figures.

FIGURE 4 shows a cold-gas refrigerator which corresponds to that of FIGURE 3, but in which the piston 16 also limits the expansion space 40. When the crankshaft 12 is moved again at the natural frequency of the piston 16, the piston 16 will again start vibrating and its movements will lead by 90 in phase to the piston surface of the piston 32 varying the volume of the compression space 35 and will lag by 90 in phase behind the piston surface of the piston 33 which also varies the volume of the space 40, so that this cold-gas refrigerator again operates in the same manner as that of FIGURE 1.

FIGURE 5 shows the same cold-gas refrigerator as FIGURE 4, but in this case, the energy-dissipating device is constituted by a tube 50 which is closed at one end and is limited at its other end by a piston 51 which is connected by means of a rod 52 to the piston 16. When the tube 50 is cooled externally, for example, by means of a cooling helix 53, a reciprocating movement of the piston 16 and the piston 51 coupled therewith will result in a phase shift of the pressure variations in the tube 50 with respect to the movements of the piston 51 so that energy is absorbed. By varying the extent of cooling, the dissipated power can be adjusted.

FIGURE 6 shows a cold-gas refrigerator of the same construction as that shown in FIGURE 1, but in this case, the piston 16 does not co-operate with a liquid damper but with a flywheel 60 which is connected by means of a long driving rod 61 to the piston 16. This flywheel thus acts as a stroke limiter and as an energy-accumulating device.

FIGURE 7 shows a cold-gas refrigerator having a compression piston 72 and an expansion piston 73 which are rigidly interconnected by means of a rod 74, While a compression space 75, a cooler 76, a recuperator 77, a freezer 78 and the expansion space 79 are disposed between the piston surfaces of the pistons 72 and 73 facing each other. The compression piston 72 is connected by means of a driving rod 81 to a crank 82 of a crankshift 83. The crankshaft 83 is connected to a driving member (not shown). The crank 82 is further connected by means of a driving rod 84 to a further piston 85, the centre lines of the piston 85 and of the pistons 73 and 72 being at an angle to each other of 90. A space 86 communicating through a duct 87 with the compression space is located above the piston 85. When the crankshaft 83 is driven in the direction of the arrow, the movements of the surface of the piston facing the space 86 will lag by in phase behind the surface of the compression piston 72 facing the space 75 and will lead by 90 in phase to the surface of the expansion piston 73 facing the expansion space 79. The mass of piston 85, the spring constant of the spring system co-operating with these pistons and the speed are adjusted so that the inertia forces produced just cancel the pressure variations.

Thus, a cold-gas refrigerator is obtained in which the pressure variations in the medium lag by accurately 90 in phase behind the movements of the compression piston 72 and lead by accurately 90 in phase to the movements of the expansion piston 73. Thus, no blind forces will be exerted on these pistons.

FIGURE 8 shows diagrammatically a slightly moditied embodiment of the cold-gas refrigerator shown 4in FIGURE 7, in which piston 85 cooperates through a liquid column 88 with a piston 89 for varying the volume of a space 90 which is in open communication with the compression space 75. This refrigerator operates in quite the same manner as that of FIGURE 7. The masses of the pistons 85 and 89 and the liquid column 88, the spring constant of the spring system and the speed are relatively tuned.

The statements made with respect to the gold-gas refrigerators shown in the preceding iigures roughly also apply to a hot-gas engine, however, the difference in temperature between the compression space and the expansion space in the hot-gas engine deviates from that in the cold-gas refrigerator. In the hot-gas engine, the expansion takes place at higher temperature and the comare rigidly interconnected by means of a connecting rod 94. A compression space 95, a cooler 96, a recuperator 97, a heater 98 and the expansion space 100 are located between the surfaces of the said pistons facing each other. The expansion piston 93 is connected by means of a piston rod 101 to a crankshaft 102 which is coupled with a device to be driven (not shown in the drawing). The hot-gas engine further includes a cylinder 105 in which a piston 106 is adapted to move which limits by one side a space 107 which is in open communication with the compression space 95 and by the other side a space 108 in which the mean pressure prevails. The piston 106 is Connected through the rod 109 to a piston 110 which is adapted to move in a close cylinder 111 completely filled with a liquid, the two spaces on either side of the piston 110 communicating with each other through a duct 112 including an adjustable shutter 113. Like in the cold-gas refrigerator of FIGURE l, the piston 106 will start vibrating and the pressure variations produced by the movements of the piston 106 lead by 90 to the movements of the piston 92 and lag by 90 behind the movements of the piston 93. The speed of this hot-gas engine is adjustable by varying the spring constant of a spring system with which the piston 106 co-operates. The power supplied by this hot-gas engine may also be adjusted by a variation of the stroke of the piston 106, resulting from a variation of the adjustment of the shutter 113.

What is claimed is:

1. An apparatus such as a hot and cold gas machine comprising a first space the volume of which can be varied by a piston and to which heat can be supplied during operation, which space is connected to a second space the volume of which can also be varied by a piston and from which heat can be derived during operation, these spaces having in operation relatively different mean temperatures, while the link between these spaces includes a recuperator through which a working medium can flow to and fro, characterized in that the said piston s are connected to a driving gear which moves these pistons so that the volume variations of the first space are in co-phase with the volume variations of the second space, while the stroke volume of the second piston for varying the volume of the second space is substantially equal to 1- times the stroke volume of the piston for varying the volume of the first space, T being equal to the quotient of the absolute temperatures prevailing during operation in the second and first spaces, while the apparatus further includes (i) a cylinder and a third piston therein defining a third space on one side of the third piston, the third space being in open communication with one of the first and second spaces or with the link between these spaces, and ((i) an adjustable means for limiting the stroke of the third piston.

2. In apparatus such as hot gas and cold gas reciproeating machines, each having at least first and second separate spaces for compression and expansion and corresponding first and second pistons therein for varying the volumes of said spaces which are interconnected by a regenerator link through which medium ows alternately in both directions during operation, the spaces having relatively different mean temperatures with heat being supplyable to one space and removable from the other, the improvement in combination therewith comprising:

means fixedly joining the two pistons which are movable to vary the volumes of the first and second spaces in co-phase relationship, and

means including (i) an enclosure with a third space therein in communication with one of the first and second spaces or their interconnecting link, and (ii) a third piston operable in the third space, whereby the pressure variations of the third space and the space with which it communicates are out of phase with the pressure variations of the remaining space.

3. Apparatus as defined in claim 2, wherein the stroke volumes of the first and second pistons respectively are substantially related by r (-r being equal to the quotient of the absolute temperatures prevailing during operation in the second and first spaces respectively).

4. Apparatus as defined in claim 3 wherein said pressure variations are out of phase by approximately 5. Apparatus as defined in claim 4, further comprising means for limiting the stroke of the third piston to provide said pressure variations.

`6. Apparatus as defined in claim 5, further comprising energy-dissipating means operable with the third piston for urging said third piston to oscillate at its natural frequency.

7. Apparatus as defined in claim 6 wherein said strokelimiting means and said energy storage means are formed by a ywheel connected to said third piston.

8. Apparatus as defined in claim 6 wherein said energydissipating means is a spring.

9. Apparatus as defined in claim 5 wherein said strokelimiting means is a dash-pot.

10. Apparatus as defined in claim 4 wherein said first and second pistons are coaxial.

11. Apparatus as defined in claim 2 wherein said third piston and enclosure defines said third space on one side of the piston and a fourth space on the opposite side of the piston, the fourth space having substantially the same mean pressure prevailing therein as in the rst and second spaces.

12. Apparatus as defined in claim 6 wherein said energy-dissipating means is a coolable tube closed at one end and limited at the other end by a piston surface coupled to said third piston, and means for cooling said tube.

13. Apparatus as defined in claim 6 wherein the third piston has stroke, velocity, and mass selected such that the inertia forces produced during operation of the apparatus are substantially equal to pressure variations produced by the first and second pistons.

References Cited UNITED STATES PATENTS WILLIAM I. WYE, Primary Examiner U.S. Cl. X.R. 60-24

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3372539 *Jun 27, 1966Mar 12, 1968Philips CorpHot-gas reciprocating engine
US3397533 *Oct 7, 1966Aug 20, 1968Gen Motors CorpHot gas engine control system
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3678686 *Feb 20, 1970Jul 25, 1972Atomic Energy CommissionModified stirling cycle engine-compressor having a freely reciprocable displacer piston
US3807904 *Feb 18, 1972Apr 30, 1974Schuman MOscillating piston apparatus
US3902328 *Jun 28, 1974Sep 2, 1975Commissariat Energie AtomiqueMethod of refrigeration combining two thermodynamic cycles and a corresponding cryogenic machine
US3906739 *Aug 26, 1974Sep 23, 1975Us ArmyVariable pneumatic volume for cryogenic coolers
US4090858 *Feb 28, 1977May 23, 1978The United States Of America As Represented By The Secretary Of The ArmyTwo-stage split-cycle cooler with pneumatic piston
US4092833 *Feb 28, 1977Jun 6, 1978The United States Of America As Represented By The Secretary Of The ArmySplit-phase cooler with expansion piston motion enhancer
US4101747 *Jan 30, 1976Jul 18, 1978Ranco IncorporatedDifferential pressure operated switch
EP0576202A1 *Jun 16, 1993Dec 29, 1993Gec-Marconi LimitedRefrigerator
Classifications
U.S. Classification62/6, 60/526
International ClassificationF02G1/00, F02G1/043, F25B9/14
Cooperative ClassificationF02G2244/50, F02G1/043, F25B9/14
European ClassificationF25B9/14, F02G1/043