GB2104155A - Stirling cycle machines - Google Patents

Abstract

The working fluid of a Stirling- cycle machine may need to be kept chemically-pure and thus the displacer assembly 1, Fig. 1, of the machine and the input/output assembly thereof (e.g. a pulsating pressure supply unit if the machine is a heat-pump) are separated by an isolating pressure transmission assembly 13 incorporating a movable pressure transmitting element 17 such as a diaphragm. In the heat pump shown the diaphragm isolates the working fluid from a drive fluid, such as air or oil, supplied at pulsating pressure by a supply unit comprising a rotary valve 25 and a pump 43. Alternatively the supply unit may comprise a flexible tube containing fluid and cyclically compressed between a pair of plates, Fig. 5 (not shown) or by a rotary compressor wheel, Fig. 6 (not shown). <IMAGE>

Description

SPECIFICATION Stirling cycle machines This invention relates to Stirling cycle machines i.e. engines and heat pumps and similar variants thereof such as "Ericsson" cycle machines.

In a Stirling cycle heat pump, a working fluid is displaced between two positions and its pressure is varied in synchronism with the displacement so that heat is pumped from one to the other position. Such a heat pump is theoretically simple but practical problems are associated therewith.

For example, the working fluid may have to be a chemically pure gas such as helium and the pressure variations have to be transmitted thereto without the gas becoming contaminated.

According to one aspect of the present invention, there is provided a Stirling cycle machine or the like including a displacer assembly wherein a displacer displaces a working fluid between respective positions within the assembly in synchronism with cyclic changes of pressure of the fluid, and a pressure-transmitting assembly including a diaphragm, with one side of which said working fluid communicates, and means for bringing a further fluid into communication with the other side of the diaphragm, the diaphragm being operable for moving to transmit cyclic pressure changes between the working fluid and the further fluid while maintaining the working fluid isolated from the further fluid.

The machine may be a heat pump and comprise drive means for supplying said further fluid at pulsating pressure to said other side of said diaphragm, for example, the drive means could comprise apparatus for supplying air or oil at pulsating pressure.

The pressure transmitting assembly may be distant from the displacer assembly and coupled thereto by way of a tube or the two assemblies may be local to each other or constructed as integral parts of a unit.

The invention has the object of providing improved arrangements for cyclically pressurising the working fluid.

According to another aspect of the present invention pressurising means for producing cyclic pressure changes of the working fluid in a Stirling-cycle or like machine includes a region of flexible tube containing fluid and means for cyclically compressing said flexible tube region, such that cyclic pressurising of the fluid is effected.

Preferably, the compressing means includes a backing member, and a presser member, between which the flexible tube region lies.

The presser member can conveniently comprise a plate matching the backing member and a cam member effecting compression of the flexible tube region between the two.

Alternatively, the presser member can comprise a presser wheel having a region or regions effecting compression of successive portions of the flexible tube region as the wheei rotates.

For a better, understanding of the invention, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a view of part of a Stirling-cycle heat pump, Figures 2, 3 and 4 are diagrams illustrating three possible modifications of the Figure 1 pump, Figures 5 and 6 are respective diagrammatic views of parts of two machines incorporating peristaltic-type drive units.

Referring to Figure 1 , the pump includes a displacer assembly 1 comprising a cylinder 2 which is divided by wall 3 into two chambers 4 and 5, the chamber 4 being largest and containing a fluid displacer 6. The fluid displacer 6 consists of a cylindrical member 7 made of lowweight material such as plastics material, and surrounded by a sleeve 8 made of metal gauze for example and constituting a heat regenerator as known in the art. A central bore 9 extends between the chambers 4 and 5 through wall 3 and into this bore there fits a narrow piston defining portion 10 projecting from one end of member 7, the portion having a cross-sectional area much less than that of the displacer 6. A bleed hole 11 extends between the chambers alongside bore 9.

A tube 12 leads from chamber 5 to a pressurepulsation communication assembly 13. The assembly 13 includes a member 14 having a hollow interior bounded by opposed conical internal surfaces 1 5 and 1 6 forming seatings which define the limits of movement of a diaphragm 1 7 made of metal such as phosphorbronze and fixed within member 14 so as to divide its interior into two nonintercommunicating spaces 18 and 19. Assembly 1 3 further includes a cup-shaped member 20 into which the member 14 is removably fitted. An 0ring 21 carried in an annular groove 22 around the internal surface of member 20 engages the outer surface of member 1 3 to provide hermetic sealing between the two members.The two members may be kept coupled one with another by any suitable disengageable catch means or the like (not shown).

The tube 1 2 communicates with the space 18 at one side of the diaphragm 1 7 while the space 19 at the other side of the diaphragm communicates with the interior of member 20 via apertures 23 formed in member 14.

A duct 24 leads from the member 20 to a diverter valve 25, to which valve compressed air is supplied via inlet pipe 26 and union 60 from a compressed air supply 43 and which also has a vent duct 27 and a rotatable valve member 28. As member 28 rotates, for example driven by a motor (not shown), duct 24 is connected to the inlet duct'26 and then the vent duct 27 in repetitive sequence so that air within member 20 and space 19 within member 14 undergoes cyclic pressure variations or pulsations.

The space 18 within member 14, the tube 12 and the chambers 4 and 5 within cylinder 2 are filled with chemically pure helium to which, due to the diaphragm 17, the pressure pulsations of the air in the space 19 are communicated while the helium remains sealed off from that air.

Say that during the operation, the displacer 6 is at a position near the end 28 of chamber 4, next to wall 3. When the pressure of the helium in chamber 5 increases, the communication of that increase to chamber 4 is delayed somewhat due to the small size of bleed hole 11 so, meanwhile, a differential pressure acts on piston-defining portion 10 moving it and displacer 6 so that displacer 6 moves away from wall 3 towards the other end 30 of chamber 4. Due to this movement, the helium previously at this other end 30 of chamber 4 is displaced to the end 29 of the chamber, its pressure increasing meanwhile due to the action of the bleed hole 11. The pressure now decreases in chamber 5 so, before it correspondingly decreases in chamber 4, the displacer 6 is moved back to the end 29 of the chamber while the helium in chamber 4 is displaced back to the end 30.

The effect of the continuing displacements and pressure changes is to pump heat from the end 30 to the end 29 of chamber 4. This heat may be removed via a finned heat-sink 31 connected to the cylinder rear chamber end 29 so the other end 30 gets cold. Alternatively, heat can be supplied to chamber end 30 so that the end 29 gets hotter.

It will be appreciated that, if the arrangement is to work well, its detailed design has to be done properly. For example, as will be known to those skilled in the art, there can be assigned to the displacer assembly a pneumatic frequency value dependent upon the size of the bleed hole 11 and the free volume of chamber 4. This frequency is made greater than the repetition frequency of the pressure pulsations of the helium. The displacer 6 is made sufficiently light that its inertia does not adversely affect the operation.

By way of example, the frequency of the pressure pulsations might be say 50Hz. although a greater frequency may sometimes be advantageous. The pressure pulsations within the helium might be between say 30 and 300 p.s.i.

while those of the air within member 14 would be through a somewhat larger range.

It will be appreciated that various modifications may be made to the illustrated pump. For example, in the displacer assembly 1, the bleed hole 11 may not be necessary if there is a sufficient leakage path past the piston portion 10. The particular construction of displacer 6 may be changed and, in fact, the illustrated displacer assembly may be replaced by any other kind of Stirling cycle heat-pump displacer assembly which is operable to be driven by pressure pulsations from a separate drive engine.

The valve 20 could be discarded if the supply unit 43 is operable per se to provide the pulsating pressure air supply. Instead of air the unit 43 could supply any other suitable fluid able to transmit pressure pulsation to diaphragm 17, for example another gas or even oil or water. The working fluid of the displacer assembly is chosen according to factors such as the temperatures between which it is desired to pump heat and hence could be other than helium, for example hydrogen or nitrogen might be appropriate in some cases.

The pump of Figure 1 could also be modified as shown in Figures 2, 3 or 4. In Figure 2, the vent duct 27 is connected to tube 50 which leads to the displacer assembly 1 where it provides a supply of cooling air for assisting dissipation from heat-sink 31.

In Figure 3, the diverter valve 25, the pressurepulsation communication assembly 1 3 and the displacer assembly are constructed as integral parts of a heat pump unit which, for operation, only need to be connected at union 60 to say a workshop compressed air supply. As in Figure 2, the air vented from duct 27 is led to the heat-sink 31 to assist operation thereof.

In Figure 4, the valve 25 is separated from the heat pump unit which now only comprises assemblies 1 and 13 as integral parts thereof. Air for assisting operation of heat sink 31 is bled-off from the interior of the member 20 via duct 70, which duct is such, e.g. by the provision of a neck obstruction 71, as to not bleed off so much air as to affect the operation of the displacer assembly.

Particularly for the modifications of Figures 2 to 4 but possibly also for the embodiment of Figure 1 it will generally be preferable for the unit 43 to provide a supply of cooled compressed air.

The supply unit 43 may not be necessary if a suitable compressed air supply is already present in the vicinity of the pump.

In Figure 5, a sealed fluid containing assembly has a pressure-transmitting device 101 connected by a coupling tube 102 to pressurising means shown diagrammatically in box 103. The pressurising means includes a flexible tube region 104 located between a backing member 105 and a presser plate 106. The presser plate 106 is cyclically pressed against the backing member by a presser cam 107 which rotates about axis 108, thereby effecting compression of the flexible tube region 104.

Additionally to transmitting the cyclic pressure pulses, the sealed fluid provides a heat transfer medium for transferring heat from the pressuretransmitting device 101, for example to the region of the pressurising means. In this case the backing and presser members are conveniently formed of heat conductive material and cooling means are provided at or near the pressurising means 103. For example, the cam 107 may include cooling fan means.

In Figure 6, a sealed fluid containing assembly has a pressure-transmitting device 110 connected by a coupling tube 111 to pressurising means shown diagrammatically in box 112. The pressurising means 11 2 is of the peristaltic type.

It includes a flexible tube region 11 3, a partcircular rigid back plate 114, and a rotating drum 11 5 rotating about axis 11 6. Naturally the back plate 11 6 has its part-circular portion formed about this axis. The drum 11 5 has a plurality of rollers 11 7 arranged for rotation about axes parallel to the axis 11 6 and equi-distant from it.

The plurality of rollers are such to progressively and successively compress the flexible tube region against the back plate 114; they extend only partially around the periphery of the drum but sufficiently to compress at any one time that flexible region of the tube backed by the back plate 114. Rotation of the drum thus fully compresses the flexible region of the tube once every rotation.

Since the sealed fluid conducts heat from the pressure-transmitting device 110 as well as transmitting cyclic pressure pulses to it, the pressurising means 112 includes cooling means in the form of air circulating impeller blades 11 7 formed upon the rotating drum 11 5. The drum thus conveniently provides two functions, that of the peristaltic pressure and also cooling air blower.

In a further arrangement, to ensure flow of the sealed fluid in arrangements where the means for effecting cyclic pressurising 112 are remote from the pressure-transmitting device 110, the single coupling tube 111 is replaced by twin tubes running in parallel linked in fluid flow connection by the pressure-transmitting device at one end by twin flexible tube regions (replacing the single flexible tube region 11 3) lying between the back plate 114 and the drum 115, and joined in fluid flow connection at their ends remote from the coupling tubes. This arrangement forms a closed loop; in this closed loop a non-return valve is provided to ensure flow in one direction only.

Some of the rollers 117 are configured such that they compress only one of the two flexible tube regions, so that pressurising pulses are interspersed with flow pulses. For example, a roller 11 7 can be positioned and/or formed to provide a flow effecting pulse in one tube thereby causing momentary flow in one direction of the sealed fluid subsequent to that much larger pressure pulse previously described.

Claims (7)

Claims

1. A Stirling-cycle machine including a displacer assembly wherein a displacer displaces a working fluid between respective positions within the assembly in synchronism with cyclic changes of pressure of the fluid, and a pressuretransmitting assembly including a movable member with one side of which said working fluid communicates, and means for bringing a further fluid into communication with the other side of the movable member, said movable member being operable for moving to transmit cyclic pressure changes between the working fluid and the further fluid while maintaining the working fluid isolated from the further fluid.

2. A machine according to Claim 1, wherein said movable member comprises a resiliently movable diaphragm.

3. A machine according to Claim 1, operable as a heat-pump and comprising drive means for supplying said further fluid at pulsating pressure to said other side of said movable member.

4. A machine according to Claim 3, wherein said drive means comprises compressed-air supply means.

5. A machine according to Claim 3, wherein said drive means comprises an oil pump.

6. A machine according to Claim 1, wherein said displacer and pressure transmitting assemblies are separate items not forming parts of an integral structure, and are interconnected by duct means for containing said working fluid.

7. A Stirling-cycle machine substantially as hereinbefore described with reference to the accompanying drawing.