WO2014147412A1

WO2014147412A1 - An improved thermodynamic device

Info

Publication number: WO2014147412A1
Application number: PCT/GB2014/050887
Authority: WO
Inventors: Michael BOWELL
Original assignee: Hybridise Limited
Priority date: 2013-03-22
Filing date: 2014-03-21
Publication date: 2014-09-25
Also published as: WO2014147412A8; GB201305330D0

Abstract

A device that is comprised of a vessel containing a volume of compressible working fluid, the fluid volume being formed into a toroid by the internal structure of the vessel, the toroidal structure having three or more moveable partitions arranged within the toroid so as to segment the enclosed fluid volume into separate sectors, each sectored compartment containing a means for the addition and removal of thermal energy from the working fluid, the moveable partitions being coupled to a rotating shaft such that rotation of the shaft causes each sectored fluid volume to undergo a cycle of compression, heating, expansion and cooling according to the Stirling cycle, each sector and associated pair of partitions comprising a Stirling engine.

Description

An Improved Thermodynamic Device

Field of the Invention

The present invention relates to an improved thermodynamic device. In particular it relates to a device operating

according to the sterling cycle.

Background of the Invention

In the drive for energy efficiency one energy source that is currently under-utilised is waste or low grade heat. A

Stirling engine is a device suitable for converting low grade heat into useful forms of power. However, implementations of a Stirling engine are expensive and necessarily large for a given power output. These drawbacks affect the commercial viability of Stirling engine implementations.

Three types of Stirling engine are known to those skilled in the art: an alpha type; a beta type; and a gamma type. The alpha type employs two pistons mutually compressing a working fluid in a relatively cold space; transitioning the fluid to a relatively hot space where it is expanded; and then

transitioning the fluid back to the relatively cold space, the hot and cold spaces constituting a heat exchanger. The beta and gamma types use a piston to compress and expand a fluid and a displacer to move the fluid through a heat exchanger including a heater and a cooler. In the beta type, the piston and displacer elements are in a common cylinder, while in the gamma type the piston and displacer elements are in separate, fluidly coupled cylinders.

Stirling engines can use linearly reciprocating pistons and high power Stirling engines can employ what is variously called the Siemens, Rinia or double acting alpha arrangement having four fluidly coupled cylinders and four pistons whose motions are phased at 90 degree intervals. Such an arrangement can offer a promising level of power density such that

appreciable power per unit volume may be achieved. However, a disadvantage of such arrangements is an inherently high compression ratio which restricts use to high temperature sources of heat.

Stirling cycle engines can be employed to operate as heat pumps when a mechanical input is provided to a crankshaft. In such operation heat may be conveyed to or from one or more heat exchangers by circulating a heat carrying fluid through them or by the use of heat pipes. A direct contact thermal exchange method as described in US patent 7,694,514 may also be employed in the implementations.

When compared to an internal combustion engine, a Stirling engine is relatively large and expensive, offering a

relatively low power density. As the temperature differential required for the operation of a Stirling engine is reduced, as may be the case when using waste or low grade sources of heat, the relatively low power density has an acute effect on the overall propensity of the engine to deliver power. The power density limitation typically associated with Stirling engines is partly due to the small size of the working fluid volume in relation to the overall engine size and is also associated with the need to add and remove heat to and from the working fluid volume.

Implementations of a Stirling engine having a displacer can employ a displacer piston in the form of a long cylinder to provide good thermal separation between hot and cold regions of an engine. For Stirling engine designs adapted to work at lower temperature differentials a displacer piston is

advantageously shorter in length and greater in diameter. The displacer piston may ultimately take the form of a disc with a short piston stroke. Such a configuration offers greater power density though this must be traded off against a desire for a compact engine. Thus is it difficult to achieve both a compact engine and increased power density.

It would be advantageous to provide for easier passage of a working fluid through a fluid heating section of a Sterling engine relative to a fluid cooling section in order to

accommodate a greater flow volume of heated and expanded regions of working fluid. Passages between cylinders

constitute dead volume of a working fluid, such that dead volumes of fluid are not physically transferred, and restrict flow of the working fluid adversely affecting the power output of an engine.

It would therefore be advantageous to provide a device

operating according to the Stirling cycle without the

aforementioned disadvantages.

Summary of the Invention

In a first aspect, the present invention accordingly provides an engine comprising a toroidal vessel having a shaft located coaxial to a longitudinal axis thereof, the vessel having at least three sectors, each sector suitable for containing a compressible fluid for being substantially sealed therein and being separated by moveable partitions coupled to the shaft, each sector further including: a heating means for heating the fluid; a cooling means for cooling the fluid wherein the heating and cooling means are operable, in use, to cause fluid to undergo a Stirling cycle to displace a moveable partition so as to drive the shaft.

Preferably the engine further comprises a regenerator fluidly coupled between, and operable in conjunction with, the heating and cooling means.

Preferably each moveable partition comprises a pivotable vane or a flexible diaphragm.

Preferably each of the pivotable vanes is hinged and arranged in a radial formation within the toroidal vessel.

Preferably a pivot point for each of the pivotable vanes is equally spaced in the radial formation.

Preferably a pivot point for each of the pivotable vanes is equidistant from the shaft.

Preferably a phase in the cycle of a pair of adjacent sectors is displaced by 360 degrees divided by the number of vanes.

Preferably a crank is disposed between each of the moveable partitions and the shaft to rotate the shaft.

Preferably a crank throw actuates the moveable partitions via an actuator arm coupled to a vane pivot shaft and a master and articulated rod mechanism.

Preferably displacement of the moveable partitions is

translated into rotation of the crank through a mechanical coupling .

Preferably a machine is driven by the rotation of the shaft. Preferably a electromechanical or fluid pumping unit is coupled to the shaft.

Preferably a rotational input drives the crank.

Preferably rotation of the crank is translated into a

displacement of the moveable partitions through a mechanical coupling .

Preferably a rotational input results in the engine pumping heat .

In a second aspect, the present invention accordingly

provides: a device comprising a toroidal vessel for containing a volume of working fluid, the vessel having three or more moveable partitions arranged within so as to divide the volume into sectors of fluid volume, each sector containing a heater and a cooler, the moveable partitions being coupled to a cranked shaft such that rotation of the shaft causes each sector of fluid volume to undergo a cycle of compression, heating, expansion and cooling according to the Stirling cycle .

Preferably the moveable partitions comprise pivoted vanes or flexible diaphragms.

Preferably adjacent pivots of the pivotable vanes are

equidistant, and wherein the pivots are equidistant from the cranked shaft.

Preferably each sector further comprises a regenerator. Preferably the device further comprises an electric or

hydraulic machine coupled to the crankshaft.

Preferably the electric or hydraulic machine is located at a centre of the toroid, and wherein the cranked shaft

constitutes a drive shaft of the machine.

Preferably any or all of the sectors within the device operate as thermally driven engines or mechanically driven heat pumps.

In a third aspect, the present invention accordingly provides a Stirling engine comprising a vessel configured to hold a fluid and having a piston pivotably mounted therein, the piston being coupled to a shaft, and the piston being operable in conjunction with a heating means and a cooling means to cause the fluid to undergo a Stirling cycle, wherein the piston undergoes angular displacement in order to drive the shaft .

In a fourth aspect the present invention accordingly provides a method of operating an engine as described above.

In a fifth aspect the present invention accordingly provides a method of operating an engine as described above wherein a sector may operate as a mechanically driven heat pump.

In a sixth aspect the present invention accordingly provides, a method of increasing the working fluid volume in relation to the overall engine volume by substituting a conventional piston and cylinder with a pivoted vane piston and arcuate cylinder chamber. Further, a number of vanes and chambers are formed into a Stirling engine of double acting alpha

configuration, the arrangement of vanes and chambers taking the form of a circular stack, each chamber being fluidly coupled to the next by a unit containing a heater, a

regenerator and a cooler, the motion of one vane, relative to the motion of an adjacent vane being offset by 360 degrees divided by the number of vanes.

Preferably, the vane pivots are equidistant one from the other and are also equidistant from a central crankshaft. The position of the vane pivots, relative to each other and to the crankshaft determines the correct phasing of each vane's motion relative to the vanes either side of it. A single crank throw actuates the vanes through an actuator arm clamped to the vane pivot shaft and a master and articulated rod

mechanism commonly found on radial piston engines.

Thus, in this way, the benefits offered by the double acting Stirling configuration can be realised at lower temperature differentials by using a greater number of vanes and chambers and a smaller phase displacement between the motions of adjacent vanes. By hinging and arranging the vane pistons in a radial formation a compact method of packaging the pistons is achieved. The circular stacking of the cylinders removes the need for interconnecting fluid passageways between the

cylinders, heaters and coolers and so removes dead volumes of working fluid and resulting flow restrictions.

In a seventh aspect, the present invention accordingly

provides a device that is comprised of a vessel containing a volume of compressible working fluid, the vessel containing three or more moveable partitions arranged so as to segment the enclosed fluid volume into separate sectors, each sector having a means for the addition and removal of heat to the working fluid, the moveable partitions being coupled to a rotating shaft such that rotation of the shaft causes each sectored fluid volume to undergo a cycle of compression, heating, expansion and cooling according to the Stirling cycle, each sector and associated pair of partitions

comprising a Stirling engine.

Preferably, where the volume occupied by each sectored

compartment containing the working fluid is broadly formed into a toroid by the internal structure of the vessel and where each sectored compartment also contains a regenerator. Preferably, where there is an electromechanical or fluid pumping unit located in the space at the centre of the toroid, the rotating shaft of the unit also being the rotating shaft of the device.

Preferably the moveable partitions are pivoted vanes and the device is of radial, double acting alpha configuration with five or more pivoted vanes, the fluid volumes trapped between each pair of vanes being arranged into a ring or toroid. The angular spacing of the vane pivots around the crankshaft and the phase of one vane's motion relative to the next is equal to 360° divided by the number of vanes, for example three vanes at 120° intervals, four vanes at 90°, 5 vanes at 72°, 6 vanes at 60°, 12 vanes at 30°, 18 vanes at 20° and so on. The number of vanes is the main factor in determining the

compression ratio and the optimum temperature differential the device will operate at. There is an inverse relationship between the number of vanes and the optimum operating

temperature differential of the device.

Brief Description of the Drawings

A preferred embodiment of the present invention is described below in more detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a cross-section of a piston Stirling engine known in the art;

Figure 2 is a plan view of a radial vane Stirling engine in accordance in an embodiment of the present invention;

Figure 3a is a plan view of a single sector within a radial vane Stirling engine with an indication of fluid flow during a cooling cycle in accordance with an embodiment of the present invention;

Figure 3b is a plan view of a single sector within a radial vane Stirling engine with an indication of fluid flow during a heating cycle in accordance with an embodiment of the present invention;

Figure 4 is a plan view of a radial vane Stirling engine in accordance with an embodiment of the present invention; and

Figure 5 is a cross-section view of the radial vane Stirling engine as shown in figure 3.

Detailed Description of the Preferred Embodiments

Figure 1 shows a cross-section of a piston Stirling engine 100 known in the art. The engine 100 of Figure 1 is arranged in a double acting alpha configuration having a series of pistons. The engine 100 is arranged with an electrical or hydraulic machine 140 which may be driven through a rotational output. A shaft of the machine 140 is illustrated coupled to a

crankshaft 136 of the engine 100. Accordingly, rotational input into the machine 140 can be brought about by translation of piston displacement 131 into rotational movement through the use of the crank shaft 136. The shaded areas 131 correspond to specific portions of a volume of compressible working fluid within the engine 100, and in particular, highlight a portion of a compressible working fluid within each piston, or sector. Also shown is a flywheel 101 connected to the crank shaft 136 and which can be optionally included to partially or substantially balance the rotating shaft 136.

Figure 2 is a plan view of a radial vane Stirling engine 30 in accordance in an embodiment of the present invention. The Stirling engine 30 of Figure 2 is of double acting alpha configuration having a generally toroidal shape. It will be appreciated by those in the art that the engine 30 could alternatively be configured having a generally hollow

cylindrical, annular or pipe shape. The shaded areas 132 identify specific portions of a compressible working fluid within the engine 30. The portions of working fluid are separated by vanes 16 such that the volume of compressible working fluid within the engine 30 is segmented into separate sectors separated by the vanes 16. Each of the vanes 16 is moveable by displacement. Most preferably the vanes are constituted so as to have a low reciprocating mass.

A machine 40, such as an electrical or hydraulic machine, may be driven through a rotational output of the engine 30. A shaft 36, such as a crank shaft, is provided to drive the machine 40. The rotational output results from a translation of vane displacement into rotational movement by way of a mechanical coupling between the vanes 16 and the shaft 36. It will be apparent to those skilled in the art that a flywheel can be optionally included in the engine 30. The arrangement of the engine 30 of Figure 2 is such as to provide a more compact engine 30 with a smaller footprint compared to that required by a piston engine of the prior art, such as is illustrated in Figure 1, having a comparable volume of working fluid.

Figure 3a is a plan view of a single sector 10 within a radial vane Stirling engine 30 with an indication of fluid flow during a cooling cycle in accordance with an embodiment of the present invention. The sector 10 has an angle of approximately 40 degrees providing 9 sectors in the engine 30. It will be appreciated by those skilled in the art that different numbers of sectors could be employed and that a number of sectors is to be traded off against a corresponding effect on an

available fluid volume in the engine 30. Sector 10 is

comprised of an outer wall of the toroid 11 and an inner wall of the toroid 12. The sector contains a heater 13 in fluid communication with a warm working fluid space and expansion volume 31, a cooler 14 similarly coupled to a cool working fluid space and compression volume 32. Optionally the sector 10 may further comprise a regenerator 15 and two or more thermal baffles 21 which serve to substantially direct an oscillating flow of compressible working fluid 132 through the cooler 14, regenerator 15 and heater 13, and vice versa. A regenerator 15 preferably comprises a fluid volume and a thermal store for the working fluids to move over and between the cool working space 32 and the warm working space 31. Thus the regenerator is operable as a heat exchanger. The baffles 21 may provide the further function of prolonging the contact of the compressible working fluid 132 with the heater 13 and cooler 14, providing thermal barriers and at least partly reducing heat loss especially, although not exclusively, expected through conduction. The compressible working fluid 132 contained within the toroidal sector 10 and between the outer wall 11 and inner wall 12 is substantially sealed. Most preferably, the seal is hermetic. The fluid 132 can flow with a reciprocating flow through the cooler 14, regenerator 15 and heater 13 (and/or vice-versa) , and by at least a pair of vanes 16. Preferably, the vanes 16 are pivotable being hinged on a vane pivot shaft 17. A flexible diaphragm seal 22 and pivot seal 38 may be employed to allow the vane to pivot whilst substantially preventing the escape of compressible working fluid 132 past the vane edges to an adjacent sector. The flexible diaphragm 22 and pivot seal 38 may be comprised of resilient materials including, although not exclusively limited to polymeric and/or elastomeric materials, and may be fixed or attached to a pivoted oscillating vane 16 and toroid sector wall 11 by a method including although not exclusively limited to mechanical or chemical fixing and/or bonding.

Alternatively, the diaphragm seal 22 may comprise a rolling or sprung sliding seal which may additionally allow a greater angle of sweep during motion of the vanes 16.

The flexible diaphragm seal 22 is preferably shaped to

accommodate movement of the vane while reducing the overall surface area of the seal. The pivot seal 38 may be shaped to provide an adequate seal between the inner wall 12 of the toroid and the vane 16. The pivot seal 38 may comprise an 0- ring, gasket, or a length of a polymeric and/or elastomeric material, formed so as to locate within the pivot assembly between the inner wall 12 of the toroid and the vane 16, thus maintaining an adequate seal during movement of the vane 16.

Heat may be supplied to the heater 13 by heat-conducting pipe 43 inclusive of additional heating fins or apparatus arranged around the pipe 43 so as to increase the surface area, and hence ensure increased thermal contact with the compressible working fluid 132. Each heating pipe 43 may comprise a thermal transport fluid, including although not exclusively limited to that of water, glycol, oil or a further fluid suitable for thermal transfer. In a similar arrangement to that presently described within the heating assembly, heat is similarly removed from the cooler 14 by a heat-conducting pipe 44, inclusive of additional heating fins or apparatus arranged around the pipe 43 so as to increase the surface area, and hence ensure increased thermal contact with the compressible working fluid 132. Each cooling pipe 44 may comprise a thermal transport fluid in a similar arrangement to that of the heating pipe 43. The heater 13, cooler 14 and pipes 43 and 44 respectively, may be comprised of a thermally conductive material, preferably comprising a metallic material such as, although not limited to, aluminium and/or copper. The

regenerator 15 may be comprised of a semi or fully fluid permeable membrane, typically comprised of, although not exclusively limited to, wire wool or a material of a similar and/or particulate structure. During use, the regenerator 15 may comprise a fluid volume and a thermal store for the reciprocating working fluids moving over and between sections comprising a cool volume 32 and a warm volume 31, depending on the specific volumes moving between the respective cool and warm volumes 32 and 31 respectively.

Referring to Figure 3b, and in description of the fluid flow expected during use, there is shown a cool volume 32 and a warm volume 31. The cool volume 32 may be fluidly coupled to the warm volume 31 via fluid flow through the cooler 14, regenerator 15 and heater 13.

During a heating stage, as illustrated in Figure 3b,

displacement of a neighbouring vane 16' compresses the cool volume 32 thus pressurising the compressible working fluid 132 contained within the cool volume 32 causing a flow through the cooler 14, regenerator 15 and heater 13. Upon exit from the heater 13, the working fluid is heated and thus expanded, pressurising the warm volume 31. The volume of the pressurised warm volume 31 may be further increased due to thermal expansion following contact with the heater 13 and heating pipe 43. The pressurised warm volume 31 thus provides a pressure on an interior face of the vane 16 causing a

rotational moment of the vane 16 about the vane pivot shaft 17.

During a cooling stage, as referenced in Figure 3a,

displacement of vane 16 compresses the warm volume 31, thus pressurising working fluid and causing a flow through the heater 13, regenerator 15 and cooler 14. Upon exit from the cooler 13, the working fluid may be cooled and thus

compressed, thus pressurising the cool volume 32. The volume of the pressurised cool volume 31 may be further decreased due to thermal contraction following contact with the cooler 14 and cooling pipe 44.

Each vane 16 is coupled to the shaft 36 such that displacement of a vane 16 serves to drive the shaft. Referring to Figure 3a, a vane pivot shaft 17 preferably couples each vane 16 to a vane actuator arm 18. The vane actuator arm 18 is preferably clamped to the vane pivot shaft 17 by a means of mechanical fixing such as, although not limited to, a bolt 20. Vane 16 may be attached to a vane pivot shaft 17 via methods

including, but not limited to mechanical or chemical fixing and/or bonding, or may further be incorporated during

manufacture. The vane pivot shaft 17 is preferably

mechanically or chemically coupled or bonded to a vane

actuator arm 18, which may subsequently be coupled to an articulated rod 37 via a vane arm pin 19. The articulated rod 37 may be further coupled to a master rod 33 via a master rod pin 34, which may in turn be coupled to a crank 35 via a crank bush assembly 39. Via rotation of the crank 35 coupled to the shaft 36, the shaft 36 may be rotated. Accordingly, mechanical output of the engine 30 is suitable for driving the machine 40.

With reference to Figure 4, there is shown an engine 30 comprised of nine toroidal sectors 10, each sector 10 being arranged as described with respect to Figures 3a and 3b. The sectors 10 are arranged around a shaft 36 so as to form a toroidal vessel 50 having the shaft 36 located coaxial to a longitudinal axis thereof, with the shaft 36 rotatable

substantially about the central longitudinal axis of the toroidal vessel 50.

With reference to Figure 4 each vane 16 substantially forms a thermal and physical barrier between the warm working fluid space 31 comprising a warm fluid volume and the cool working fluid space 32 comprising a fluid volume of lower temperature than that than that of the warm fluid volume. Upon a complete Stirling cycle of the working fluid within a sector 10, specifically the heating and cooling of the warm fluid volume 31 and a cool fluid volume 32, each vane 16 may be displaced by an angle, such as an angle of approximately 40 degrees. Accordingly, each pair of vanes 16, their 40 degree offset, the thermal components between them, 13, 14, 15, 31 and 32 and the vane to crankshaft linkage components 17, 18, 19, 33, 34, 35 and 37 substantially combine to form a Stirling cycle machine 30. The machine 30 is substantially contained within a toroidal vessel 50, allowing substantial containment of the compressible working fluid 132 at a pressure at least equal to, and typically above that of, latm. More specifically, the compressible working fluid 132 within the pressure vessel 50 typically operates at pressures at or above 10atm, although most preferably at or between latm and 10atm.

With reference to Figure 5, there is shown a side elevation representing a cross-section of the engine 30 through

centreline A - A' , as referenced in Figure 4. Figure 5

illustrates the engine 30 including a toroid top wall 51, a toroid bottom wall 52, the pivot shaft 17, crank bushes 39 and the machine 40 coupled to the shaft 36 and secured by mounting bolts 41. The walls of the pressure vessel 50, may be

comprised of, although not limited to, a metallic material formed into a cylindrical vessel. Further, toroid walls 11, 12, 51 and 52 may, in addition to the vessel 50, be similarly comprised of a metallic material, thus comprising temperature, pressure and creep resistance between those of ambient

conditions and the elevated temperatures of up and around 600°C, although most preferably between the temperatures of ambient and up to and around 250 °C.

The engine 30 may be hermetically sealed wherein at least one of an electrical connection such as wiring and an arrangement comprising at least one of heating pipes 43 and cooling pipes 44 are the sole articles to intersect the walls of the

pressure vessel and engine 50. In the instance where a single pair of pipes 44 is used to intersect the pressure vessel and engine 50, thermal transport may be achieved through an arrangement comprising heat pipes 43 with a set of manifolds within the pressure vessel to distribute the heat flow to each heating pipe 43 and cooling pipe 44 comprised within each sector 10.

In an arrangement where the machine 40 is a hydraulic machine, the machine 40 may be coupled to an external device by

hydraulic lines passing through the pressure vessel walls 50. During operation, the assembly described in Figures 3a, 3b, 4 and 5 is operable to displace vanes 16 so as to drive the crank 35 and rotate the shaft 36. It will also be appreciated that during rotation of the crank 35, the linkage assembly provides a moment to the crank 35 during heating and

expansion, as shown in Figure 3b. The crank 35 may thus be arranged such that one complete revolution of the crank 35 may also represent one full Stirling cycle of the heating and vane assembly. In this way, the crank 35 and linkage assembly may provide a restoring force on the vane 16 during the cooling and compression stage, thus causing fluid volume to pass through the cooling assembly 14 and into the cool fluid volume 32. The angular offset between a pair of vanes 16 relative to the crankshaft 36 causes the compressible working fluid 132 trapped between each pair of vanes 16 to undergo the four stages of the Stirling cycle, namely: compression; heating; expansion; and cooling.

One full Stirling Cycle occurs during one full crank rotation and each stage can be considered to occur at 90 degree

intervals such that a full cycle constitutes a 360 degree revolution. A phase in the cycle of a pair of adjacent sectors is displaced by 360 degrees divided by the number of vanes. Accordingly, a complete revolution of the cycle in a vane brings about the cooling and compression stage and completes the Sterling cycle.

The multiplicity of vanes is operable to sweep portions of the fluid volume as a 'swept volume' by displacing those portions of the fluid volume. The division of the total swept volume between larger numbers of vanes is advantageous since smaller vanes can be employed and vanes can be arranged so as to oscillate faster for a given total swept volume so providing an improvement in power density. Further, as each vane is accurately located by the vane pivot, the friction from side loads that would normally be encountered in a piston in cylinder arrangement is reduced. Yet further, arrangements in accordance with the present invention also eliminate any requirement for sliding shaft seals.

Due to the shape and configuration of the toroidal volume, a greater proportion of the engine's internal volume is occupied by the working fluid. Arranging vanes in a radial formation allows a greater extent of the internal volume to interface with each vane, thus providing an increased power density.

The radial formation of vanes and heat exchangers allows efficient coupling of the working volumes without the use of additional fluid passages and the dead volumes and fluid flow restrictions that accompany them.

The design provides heat exchangers of large cross section, which gives minimal resistance to the flow of working fluid. This, combined with the low reciprocating mass of the vanes can allow high speed operation, further improving the power density. It is especially beneficial in an engine designed to operate at lower temperature differentials.

The vane is accurately located by the vane pivots, so

eliminating side loads on the vane to chamber wall contact. This minimises both friction and wear.

The cylindrical shape of the containment vessel is the ideal shape to contain a charge of working fluid at elevated

pressure. The toroidal form of the device provides a

convenient location for a driving or driven machine at the centre of the toroid. The device has good dynamic balance and smooth torque delivery so there is very little vibration generated and little

requirement for a flywheel, giving further savings in weight, size and cost.

It is advantageous to provide for easier passage of a working fluid through a fluid heating section relative to a fluid cooling section to accommodate a greater flow volume of heated and expanded regions of working fluid. By positioning coolers closer to a centre axis of an engine than heaters, additional space is provided for larger heaters of increased cross section giving less resistance to the working fluid flow. This can be achieved in the radial arrangement of heaters and coolers by locating the coolers closer to the central axis of the engine than the heaters .

The device can operate as a heat pump when a mechanical input is provided to the shaft. Heat may be conveyed to or from the heat exchangers by circulating a heat carrying fluid through them or by the use of heat pipes. A direct contact thermal exchange method as described in US patent 7,694,514 may also be used in the devices described above.

The device comprises a number of Stirling cycle apparatuses within one unit, each apparatus utilising a thermal gradient to provide a mechanical output, or conversely use a mechanical input to create a thermal gradient. Each apparatus operates independently to other apparatuses within the engine. Thus in one embodiment the engine may be operated as a thermally driven heat pump by providing heat via one or more of the heaters, the remaining heaters can be thermally coupled to an environment so as to draw heat from that environment for space heating or cooling. Thus, for example, engines in accordance with embodiments of the invention can be applied to generate electricity from any suitable heating means, including burned fossil fuels. If the electrical output is not required and the priority is to minimise fossil fuel use, the same device may be easily reconfigured as a thermally driven heat pump to provide the same amount of low grade heat for space heating with less fuel.

The Radial Vane Stirling concept described in this patent allows for a high degree of flexibility in the choice of materials, the configuration, the operating temperature and the mode of operation of the invention. It will be appreciated by someone knowledgeable in the art that the present invention may take many forms without deviating from the scope of this patent .

Claims

1. An engine comprising a toroidal vessel having a shaft located coaxial to a longitudinal axis thereof, the vessel having at least three sectors, each sector suitable for containing a compressible fluid for being substantially sealed therein and being separated by moveable partitions coupled to the shaft, each sector further including:

a heating means for heating the fluid;

a cooling means for cooling the fluid

wherein the heating and cooling means are operable, in use, to cause fluid to undergo a Stirling cycle to displace a moveable partition so as to drive the shaft.

2. The engine of claim 1 further comprising a regenerator fluidly coupled between, and operable in conjunction with, the heating and cooling means.

3. An engine as claimed in any preceding claim wherein each moveable partition comprises a pivotable vane or a flexible diaphragm.

4. An engine as claimed in claim 3 wherein each of the pivotable vanes is hinged and arranged in a radial formation within the toroidal vessel.

5. An engine as claimed in claim 4 wherein a pivot point for each of the pivotable vanes is equally spaced in the radial formation .

6. An enigine as claimed in any of claims 3 to 5 wherein a pivot point for each of the pivotable vanes is equidistant from the shaft.

7. An engine as claimed in any preceding claim wherein a phase in the cycle of a pair of adjacent sectors is displaced by 360 degrees divided by the number of vanes.

8. An engine as claimed in any preceding claim wherein a crank is disposed between each of the moveable partitions and the shaft to rotate the shaft.

9. An engine as claimed in 8 wherein a crank throw actuates the moveable partitions via an actuator arm coupled to a vane pivot shaft and a master and articulated rod mechanism.

10. An engine as claimed in any of claims 8 or 9 wherein displacement of the moveable partitions is translated into rotation of the crank through a mechanical coupling.

11. An engine as claimed in any of claims 8 to 10 wherein a machine is driven by the rotation of the shaft.

12. An engine as claimed in any preceding claim wherein a electromechanical or fluid pumping unit is coupled to the shaft .

13. An engine as claimed in any of claims 8 to 11 wherein a rotational input drives the crank.

14. An engine as claimed in claim 13 wherein rotation of the crank is translated into a displacement of the moveable partitions through a mechanical coupling.

15. An engine as claimed in any of claims 13 to 14 wherein a rotational input results in the engine pumping heat.

16. A device comprising a toroidal vessel for containing a volume of working fluid, the vessel having three or more moveable partitions arranged within so as to divide the volume into sectors of fluid volume, each sector containing a heater and a cooler, the moveable partitions being coupled to a cranked shaft such that rotation of the shaft causes each sector of fluid volume to undergo a cycle of compression, heating, expansion and cooling according to the Stirling cycle .

17. A device as claimed in claim 16 wherein the moveable partitions comprise pivoted vanes or flexible diaphragms.

18. A device as claimed in any of claims 16 or 17 wherein adjacent pivots of the pivotable vanes are equidistant, and wherein the pivots are equidistant from the cranked shaft.

19. A device as claimed in any of claims 16 to 18 wherein each sector further comprises a regenerator.

20. A device as claimed in any of claims 16 to 19

further comprising an electric or hydraulic machine coupled to the crankshaft.

21. A device as claimed in claim 20 wherein the electric or hydraulic machine is located at a centre of the toroid, and wherein the cranked shaft constitutes a drive shaft of the machine .

22. A method of operation of a device as described in any of claims 16 to 21 wherein any or all of the sectors within the device operate as thermally driven engines or mechanically driven heat pumps .

23. A Stirling engine comprising a vessel configured to hold a fluid and having a piston pivotably mounted therein, the piston being coupled to a shaft, and the piston being operable in conjunction with a heating means and a cooling means to cause the fluid to undergo a Stirling cycle, wherein the piston undergoes angular displacement in order to drive the shaft .

24. A method of operating an engine as claimed in any of claims 1 to 15 wherein a sector may operate as a thermally driven engine.

25. A method of operating an engine as claimed in any of claims 1 to 15 wherein a sector may operate as a mechanically driven heat pump.

26. An engine substantially as hereinbefore described with reference to the accompanying drawings.