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Patent Searching and Data


Title:
COMPRESSOR OR EXPANDER
Document Type and Number:
WIPO Patent Application WO/2019/135083
Kind Code:
A1
Abstract:
A compressor or expander (100) comprises two opposed end faces (106), at least four rotors ( 102) arranged in a group to form an enclosed volume (104) additionally bounded by the end faces (106), and a valve in fluid communication with the enclosed volume for the inlet and/or outlet (116, 118) of a fluid. The four rotors (102) each have a toothed circumferential surface (1 10) configured to engage with a corresponding toothed circumferential surface (110) of the adj acent rotors (102) such that the rotors (102) rotate simultaneously. Each rotor (102) has a substantially constant diameter. Rotation of the rotors (102) causes the enclosed volume (104) to expand and contract.

Inventors:
CASH, Ian James (Henbrook, 40 Mayfield Road, Ashbourne Derbyshire DE6 1AS, DE6 1AS, GB)
Application Number:
GB2019/050018
Publication Date:
July 11, 2019
Filing Date:
January 03, 2019
Export Citation:
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Assignee:
INTERNATIONAL ELECTRIC COMPANY LIMITED (Harwell Innovation Centre, Curie AvenueHarwell, Oxford OX11 0QG, OX11 0QG, GB)
International Classes:
F04C28/14; F01C1/14; F01C1/28; F04C18/12; F04C18/14; F04C18/28
Domestic Patent References:
WO2002038918A12002-05-16
Foreign References:
DE4110545A11992-10-01
US3929402A1975-12-30
CN1068875A1993-02-10
US4324537A1982-04-13
DE4440450A11996-05-09
DE4227786A11994-02-24
Attorney, Agent or Firm:
BARKER BRETTELL (100 Hagley Road, Edgbaston, Birmingham West Midlands B16 8QQ, B16 8QQ, GB)
Download PDF:
Claims:
CLAIMS

1. A compressor or expander comprising:

two opposed end faces;

at least four rotors arranged in a group to form an enclosed volume additionally bounded by the end faces;

a valve in fluid communication with the enclosed volume for the inlet and/or outlet of a fluid;

wherein the four rotors each have a toothed circumferenti al surface configured to engage with a corresponding toothed circumferenti al surface of the adjacent rotors such that the rotors rotate simultaneously, each rotor having a substantially constant diameter, rotation of the rotors causing the enclosed volume to expand and contract.

2. A compressor or expander according to claim 1 , wherein each rotor has a cross-section the shape of a Reuleaux triangle.

3. A compressor or expander according to claim 1 or claim 2, further comprising a filler within the enclosed volume, the filler reducing dead-space within the enclosed volume.

4. A compressor or expander according to claim 3, wherein the filler is thermally- insulating.

5. A compressor or expander according to claim 3, wherein the filler acts as a heat exchanger.

6. A compressor or expander according to claim 5, wherein the filler includes a channel for the passage of a heat-transfer fluid. 7. A compressor or expander according to claim 6, wherein the channel is parallel to rotational axes of the rotors.

8. A compressor or expander according to any of claims 5 to 7, wherein the filler includes vanes extending perpendicular to a longitudinal axis of the filler.

9. A compressor or expander according to any of claims 3 to 8, wherein the filler has a four-sided cross-sectional envelope.

10. A compressor or expander according to claim 9, wherein three of the four sides of the filler have different curve profiles.

1 1. A compressor or expander according to claim 10, wherein all four sides of the filler have different curve profiles.

12. A compressor or expander according to any preceding claim, wherein two of the rotors rotate about an axis free to translate relative to a first of the rotors .

13. A compressor or expander according to claim 12, wherein a further one of the rotors rotates about an axis free to translate in two dimensions relative to the first of the rotors.

14. A compressor or expander according to claim 12 or claim 13, wherein the first of the rotors rotates about a fixed axis .

15. A compressor or expander according to any preceding claim, further comprising two additional rotors, the two additional rotors being arranged in conjunction with two of the four rotors to enclose an additional enclosed volume.

16. A compressor or expander according to any of claims 1 to 14, further comprising five additional rotors , the five additional rotors being arranged in conjunction with the four rotors to form three additional enclosed volumes, the rotors and additional rotors being arranged in a 3 x 3 grid.

17. A compressor or expander according to claim 16, wherein the four enclosed volumes each include a filler.

18. A compressor or expander according to claim 17, wherein two of the enclosed volumes include a thermally-insulating filler and two of the enclosed volumes include a heat-exchanger filler.

19. A compressor or expander according to any of claims 16 to 18, wherein the rotors at apices of the grid rotate around fixed axes.

20. A compressor or expander according to claim 19, wherein the rotors directly between two apices of the grid rotate about axes free to translate along a path extending directly between the apices of the grid.

21. A compressor or expander according to claim 19 or claim 20, wherein the rotor central in the grid is free to translate in two dimensions.

22. A compressor or expander according to any of claims 16 to 21 , wherein each enclosed volume includes at least one valve for the inlet and/or outlet of fluid.

23. A compressor or expander according to claim 22, wherein each enclosed volume includes two valves - a first valve for inlet of fluid and a second valve for outlet of fluid.

24. A compressor or expander according to any preceding claim, further comprising a biasing means arranged to bias one of the faces towards the other of the faces.

25. A compressor or expander according to any preceding claim, wherein each rotor includes a low-friction material and/or a low-friction coating.

26. A compressor or expander wherein the low-friction material and/or low- friction coating includes a lubricant, optionally a dry lubricant.

27. A compressor or expander according to any preceding claim, wherein each valve includes a rotary valve.

28. A compressor or expander according to claim 27, wherein each rotary valve is driven by the rotation of the rotors.

29. A compressor or expander according to claim 28, wherein each rotary valve is driven in a 3 : 1 ratio compared to the rotors , one valve rotation being completed for every 120° rotation of the rotors .

30. A compressor or expander comprising:

two end faces;

four rotors arranged to form an enclosed volume between the end faces , each rotor having a substantially constant diameter ;

a valve in fluid communication with the enclosed volume for the inlet and/or outlet of a fluid; and

a filler within the enclosed volume, the filler reducing dead-space in the enclosed volume.

31. A compressor or expander according to claim 30, wherein the filler is thermally-insulating.

32. A compressor or expander according to claim 30, wherein the filler acts as a heat exchanger.

33. A compressor or expander according to claim 32, wherein the filler includes a channel for the passage of a heat-transfer fluid.

34. A compressor or expander according to claim 33, wherein the channel is parallel to rotational axes of the rotors.

35. A compressor or expander according to any of claims 32 to 34, wherein the filler includes vanes extending perpendicular to a longitudinal axis of the filler.

36. A compressor or expander according to any of claims 30 to 35, wherein the four rotors each have a toothed surface configured to engage with a corresponding toothed surface the rotors adjacent such that the rotors rotate simultaneously.

37. A heat engine comprising a compressor or expander according to any preceding claim.

38. A heat engine according to claim 37, wherein the compressor or expander includes four enclosed volumes.

Description:
COMPRESSOR OR EXPANDER

The present invention relates to a compressor or expander. The present invention also relates to a heat engine comprising at least one of said compressor or expander.

Compressors and expanders are used widely as components in heat engines, or in many other guises. However, it is known that compressors, as they will be referred to for brevity, suffer from some common drawbacks. For example, many known compressors necessarily include a number of dynamic seals - that is, seals between moving surfaces and static surfaces, where the moving surfaces has a rubbing contact with the static surface. In such cases, the seal and/or compressor body around the seal can suffer from wear which diminishes the efficiency of the compressor.

Moreover, some compressors are capable of acting with single phase fluids, i.e. gaseous, but fail quickly if subjected to fluids in two phases, i.e. gaseous and liquid. This can prevent them working or at the very least lower their efficiency. Therefore, it is desired to develop a compressor that is capable of operation without failure in both cases.

The present invention therefore seeks to provide a compressor that prevents or limits some of the inadequacies of known compressors.

According to a first aspect, there is provided a compressor or expander comprising: two opposed end faces; at least four rotors arranged in a group to form an enclosed volume additionally bounded by the end faces; a valve in fluid communication with the volume for the inlet and/or outlet of a fluid; wherein the four rotors each have a toothed circumferenti al surface configured to engage with a corresponding toothed circumferenti al surface of the adjacent rotors such that the rotors rotate simultaneously, each rotor having a substantially constant diameter, rotation of the rotors causing the enclosed volume to expand and contract .

Arranging four rotors with constant diameter to enclose a volume allows the rotation of the rotors to compress fluid within the volume, whilst preventing or limit ing any leakage between the rotors. The inclusion of toothed surfaces provides a rolling contact during rotation of the rotors decreasing friction over a sliding contact. Furthermore, the teeth act to create a labyrinthine seal which helps to decrease leak age of a working fluid, in use. The enclosed volume may be sealed by the teeth and the end faces.

Advantageously, two or more teeth of each rotor may be at least partially engaged with two or more teeth of the adj acent rotors, to provide an enhanced seal. At least partial engagement of three or more or four or more teeth may provide further enhanced sealing of the enclosed volume.

The teeth may be continuous down a total length of each rotor, engagement of the teeth on adjacent rotors providing the sealing of the enclosed volume on the sides of the enclosed volume facing the rotors. The enclosed volume may be sealed at upper and lower bounds by the upper and lower faces of the rotors acting on the end faces of the end plates.

Although each enclosed volume is disclosed as being bound by the two end faces and at least four rotors, more specific examples could include each enclosed volume being bound by six rotors or eight rotors, or any other equal integer number of rotors.

Although described as a compressor or expander, the apparatus could be arranged to operate as just a compressor or just an expander, or the apparatus may be switchable between being a compressor and being an expander. The invention is not intended to be limited to being both a compressor and expander and it will be apparent to the skilled person that compressors and expanders operate using the same principles and that therefore the use of the term compressor in the present text is considered to encompass expanders and vice versa. Equally, apparatus capable of function as a compressor may also be capable of acting as a pump. For brevity, the term “compressor” will be used from now on , although this is not intended to be limiting to the scope of the invention.

Each rotor may have a cross-section the shape of a Reuleaux triangle. The rotors may be aligned in a 2 x 2 array which may be in a roughly square shape, at least during a portion of the rotation of the rotors. The rotors may rotate about substantially parallel rotational axes. The shape of a Reuleaux triangle is considered to include such shapes as are substantially the same shape but differ in minor or insignificant ways. For example, whilst a perfect Reuleaux triangle includes three apices, the rotors may have rounded corners. The toothed surfaces of the rotors also ensure that the cross -section cannot be a perfect Reuleaux triangle, but the virtual perimeter formed from the midpoints where opposing meshed teeth overlap to maximum extent may be substantially the same.

Alternatively, the rotors may have the cross-section of another Reuleaux polygon, such as an equilateral-curve heptagon. Such shapes have a diameter that is constant across any bisection.

The compressor may include a filler within the enclosed volume, the filler reducing dead-space within the enclosed volume. The filler may comprise a single filling element or a plurality of filling elements.

Due to the geometries of the rotors, it is inevitable that some dead -space, i.e. space that is never occupied by the rotors, will exist in the enclosed volume, in use. Dead- space limits the compression ratio of the compressor. By including a filler, the amount of dead-space can be reduced and the compression ratio increased to a desired level.

The filler may be thermally-insulating. By this, it is meant that the filler should be designed, for example by material choice, to remove as little heat as possible from the enclosed volume. By doing so, the compressor can operate with a cycle similar to that of an adiabatic cycle.

Alternatively, the filler may operate as a heat exchanger. Use of the filler as a heat exchanger may, for example, allow the compressor to operate with a cycle similar to an isothermal cycle. For example, when compressing a fluid, the heat can be removed by the filler acting as a heat exchanger in order to limit the temperature increase of the fluid.

The filler may include a channel for the passage of a heat -transfer fluid, such as a coolant. One or more channels may be provided, each of which may assist with the thermal conductivity of the heat-exchanger. The or each channel may be parallel to rotational axes of the rotors. The channels may be substantially parallel such that they run from one end face to the other, but their paths may deviate to enhance thermal conduction from the enclosed volume.

The filler may include vanes extending perpendicular to a longitudinal axis of the filler. The vanes may increase the surface area of the filler without extending out of the dead-space between the rotors. Therefore the heat-exchanger may be optimised for heat-transfer.

Two of the rotors may rotate about an axis free to translate in one dimension relative to a first of the rotors . A further one of the rotors may rotate about an axis free to translate in two dimensions relative to the first of the rotors . The first of the rotors may rotate about a fixed axis.

Providing at least one of the rotors with a fixed rotational axis simplifies the construction of the assembly and may be particularly useful when considering expanding the array of rotors to include a number of rotors greater than four, for example a 3 x 3, 5 x 5, or greater array of rotors. In such a case, more than one rotor may be fixed, and particularly the corner rotors may be fixed.

Providing two of the rotors with rotational axes that can translate in one dimension, a seal can be maintained with the fixed rotor. In the 2 x 2 array of rotors, the two rotors with axes of rotation that are translatable in one dimension may be provided orthogonal to the fixed rotor. The translatable dimension of each of these two rotors will be perpendicular to one another in the plane of rotation.

Providing a further one of the rotors with an axis that is free to move in two dimensions allows sealing of the enclosed volume to be maintained during rotation of the rotors and the volume of the enclosed volume to be optimised. This fourth rotor may follow a complex path dictated by the rotation of the other three rotors.

The filler may have a four-sided cross-section envelope, three of the four sides having different curve profiles or radii. For example, this is the case where different tooth profiles are used, i.e . where two rotors with“female” tooth profiles and two rotors with“male” tooth profiles are used. Alternatively, all four sides may have different curve profiles. For example, this is the case where hermaphroditic tooth profiles are used, i.e. the tooth profiles for each rotor are identical.

The applicant has noted that it is possible to provide a cross -sectional shape for the filler, the shape optimally filling the dead-space. By cross-sectional shape it is meant the shape in a section taken normal to a longitudinal axis of the filler, i.e. the same cross-sectional plane as that including the constant diameter of the rotors.

The curve profiles or radii may be defined by calculation of the motion of each rotor. A first curve radius will be defined for the side of the filler facing the rotor that rotates about a fixed axis, a second curve radius will be defined for the rotors that rotate about an axis movable in one dimension, and a third curve radius will be defined for the rotor that rotates about an axis movable in two dimensions. Thus, the cross-sectional envelope of the filler may be optimised for the particular characteristics of the rotor. Each curve radius may be constant for each of the four sides, or may vary along each side.

The compressor may include two additional rotors, the two additional rotors being arranged in conjunction with two of the four rotors to enclose an additional enclosed volume. Extra chambers or enclosed volumes can therefore be made by adding additional rotors. By connecting the chambers, this may allow the creation of closed- cycle heat engines.

The compressor may include five additional rotors, the five additional rotors being arranged in conjunction with the four rotors to form three additional enclosed volumes, the rotors and additional rotors being arranged in a 3 x 3 grid.

Such an arrangement creates a total of four enclosed volumes , each of which may be configured to act as a compressor or expander.

Each of the four enclosed volumes may include a filler, and two of the enclosed volumes may include a thermally-insulating filler and two of the enclosed volumes may include a heat-exchanger filler. Thus, the arrangement can be configured in a manner suitable for use as a Carnot-like heat engine, i.e. two adiabatic and two isothermal cycles enabled by the two types of filler. Alternatively, the enclosed volumes or chambers could be configured to operate in a manner suitable for use in a Brayton cycle. Each state of the Brayton cycle would therefore have an enclosed volume acting as an adiabatic compressor and one acting as an adiabatic expander. The Brayton cycle can then be completed by the use of isobaric compression and expansion that is external to the rotors and enclosed volumes. For example, these may take the form of heat exchangers.

Rotors at the apices of the grid may be configured to rotate around fixed axes. The rotors directly between two apices of the grid may rotate about axes free to move along a path extending directly between the apices of the grid . The rotor central in the grid may be free to translate in two dimensions.

Such an arrangement as described above ensures that the 3 x 3 array of rotors is dimensionally constant, due to the fixed corners. The freedom of movement of the other rotors ensures good sealing of the enclosed volumes and therefore good operation of the compressor or expander.

Each enclosed volume may include at least one valve for the inlet and/or outlet of fluid. Each enclosed volume may include two valves - a first valve for inlet of fluid and a second valve for outlet of fluid. Providing multiple valves can optimise operation as each valve can be operated independently to alter timings, etc. It can also mean that the compressor can be operated as a pump, by providing the valves as one way valves, for example. The valves may be provided in the end faces or end plates, for example an inlet valve being located on one end plate and an outlet valve being located on the opposing end plate, flow of the working fluid being provided between the inlet valve and the outlet valve through the enclosed volume .

A biasing means may be arranged to bias one of the faces towards the other of the faces. As there is a moving interface between the rotors and faces, wear may occur. By biasing at least one of the faces towards the other, any gap created through wear can be closed up, ensuring that the enclosed volume remains sealed from the outside.

Although it may be preferable to seal the volumes, by placing the compressor in a controlled environment, the compressor could be configured to replenish its working fluid from said controlled environment, for example during an expansion operation that pulls in working fluid from the controlled environment. Where the working fluid is air, the controlled environment could include air that is dried by a desiccant and can be drawn through small gaps into the rotors.

Working fluid may also be replenished by it being drawn into the enclosed volume or into a part of a circuit connected to a compressor or expander. For example, when using air the working fluid may be drawn through a valve and desiccant to replenish the working fluid with dry air.

Each rotor may include a low-friction material and/or a low-friction coating. The low- friction material and/or low-friction coating may include a lubricant, optionally a dry lubricant. Low-friction materials, coatings, and lubricants can operate to reduce wear on the compressor, especially between the rotors themselves and between the rotors and faces. Lubricants can also assist with sealing of the enclosed volumes.

Each valve could include a rotary valve which may be driven by the rotation of the rotors. Each rotary valve may be driven in a 3 : 1 ratio compared to the rotors, one valve rotation being completed for every 120° rotation of the rotors. Where different shaped rotors are used, each rotation of a rotary valve may be configured in accordance with that shape’s degree of rotational symmetry.

According to a second aspect, there is provided a compressor or expander comprising: two end faces; four rotors arranged to form an enclosed volu me between the end faces, each rotor having a substantially constant diameter; a valve in fluid communication with the enclosed volume for the inlet and/or outlet of a fluid; and a filler within the enclosed volume, the filler reducing dead-space in the enclosed volume.

It is inevitable that some dead-space, i.e. space that is never occupied by the rotors, will exist in the enclosed volume, in use. Dead-space limits the compression ratio of the compressor. By including a filler, the amount of dead-space can be reduced and the compression ratio increased to a desired level.

The filler may be thermally-insulating. By this, it is meant that the filler should be designed, for example by material choice, to remove as little heat as possible from the enclosed volume. By doing so, the compressor can operate with a cycle similar to that of an adiabatic cycle.

Alternatively, the filler may operate as a heat exchanger. Use of the filler as a heat exchanger may, for example, allow the compressor to operate with a c ycle similar to an isothermal cycle. For example, when compressing a fluid, the heat can be removed by the filler acting as a heat exchanger in order to limit the temperature increase of the fluid.

The filler may include a channel for the passage of a heat-transfer fluid, such as a coolant. One or more channels may be provided, each of which may assist with the thermal conductivity of the heat-exchanger. The or each channel may be parallel to rotational axes of the rotors. The channels may be substantially parallel such that they run from one end face to the other, but their paths may deviate to enhance thermal conduction from the enclosed volume.

The filler may include vanes extending perpendicular to a longitudinal axis of the filler. The vanes may increase the surface area of the filler without extending out of the dead-space between the rotors. Therefore the heat-exchanger may be optimised for heat-transfer.

The compressor or expander may include any further features as described above in relation to the first aspect.

According to a third aspect, there is provided a heat engine comprising a compressor or expander according to any preceding claim.

Non-limiting examples of the present invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of a compressor or expander in accordance with the first aspect, with features removed for clarity;

Figure 2 is a side view of the compressor of Figure 1 , with removed features included; Figure 3 is a schematic view of a second embodiment of a compressor, showing the rotational axes of the rotors; Figure 4 is an example of a filler configured as a heat-exchanger;

Figures 5a to 5d are schematics of the operation of a compressor in accordance with the first aspect, including a filler, showing the stages of compression;

Figure 6 is a schematic diagram of a part of another embodiment of a compressor;

Figure 7 is a schematic of the compressor of Figure 1 configured for operation using a Carnot-like cycle;

Figure 8 is a schematic of the compressor of Figure 1 configured for operation using a Brayton cycle ; and Figure 9 is a diagram of rotors forming a compressor according to the first aspect, showing construction lines of one of the rotors .

Referring firstly to Figure 1 , a first embodiment of a compressor 100 is shown. The compressor 100 comprises a total of nine rotors 102, each of which contacts at least an adjacent two rotors 102. The rotors 102 are arranged in a 3 x 3 array. The 3 x 3 array can be split into a series of four 2 x 2 arrays, with each 2 x 2 array surrounding a chamber or enclosed volume 104. Although not shown in Figure 1 , the ends of the enclosed volume 104 are formed by two faces 106, in the present embodiment these faces 106 being formed by end plates 108, as shown in Figure 2.

The end plates 108 are formed of low-friction material in order to minimise friction and thus wear between the end plates and the upper and lower faces of the rotors. Low-friction materials include polytetrafluoroethene (PTFE) and phenolic sheet, amongst others. A dry-film lubricant or other lubricant may also be used, to assist with sealing and wear -resistance. Each of the rotors 102 of the embodiment of Figure 1 is formed with a cross-section through their axis of rotation that is substantially the shape of a Reuleaux triangle. Such a shape has a constant diameter, enabling each rotor 102 to rotate together whilst maintaining the enclosed volumes 104. Whilst formed as a Reuleaux triangle in order to maxi mi se the enclosed volume and to provide good compression ratios, other cross - sections with constant diameters may be used in place of Reuleaux triangles.

By“substantially the shape of a Reuleaux triangle” it is meant that the shape closely resembles a Reuleaux triangle but may differ in some respects. For example, the rotors 102 of the present invention include teeth 1 10 and have slightly rounded corners which assist with the formation of the teeth 110. Other slight differences between shapes with perfectly constant diameter that do not affect the operation of the compressor 100 are also considered to be included in the definition.

As briefly mentioned, each rotor 102 of the first embodiment includes a number of teeth 1 10, the teeth 1 10 engaging with teeth 1 10 of adjacent rotors 102. As each rotor 102 rotates, the adjacent rotors 102 will be forced to rotate due to the action of the teeth 1 10. Thus, a single rotor 102 being driven may result in the rotation of every rotor 102 in the array. This is shown in Figure 2 where only a single rotor 102 is driven. However, it is also possible to provide drive to a number of the rotors 102, for example to decrease stress on a single rotor 102 and to split loading.

Considering the contact of the teeth 1 10 of adjacent rotors 102, it is clear that teeth 1 10 will mesh with rolling contact and that therefore wear will be limited. As the number of teeth 1 10 is increased on each rotor 102, the size of the teeth 1 10 can be reduced and the friction between teeth 1 10 is also reduced. Moreover, by reducing the size of the teeth 1 10 the enclosed volume 104 increases, as does the compression ratio of the compressor 100. The use of teeth 1 10 ensures that small inaccuracies in the manufacturing process are prevented or limited from adverse impact on the operation of the compressor 100. For example, small discrepancies in the positioning of teeth 1 10 can be mitigated for by relative rotation of the rotors 102. In addition, the teeth 1 10 of the rotors 102 may act as labyrinthine seals against egress of fluid. Each rotor 102 may be manufactured by an extrusion process to provide the desired cross -section, the extrusion product being cut to length to provide each rotor 102. As can be seen in Figure 1 , the rotors 102 are each enabled to rotate around their own axis of rotation. Depending on their position in the array, the or each axis of rotation may be free to translate in certain directions in the plane of rotation. The axes of rotation and their relative translational paths are shown in Figure 3. Whilst Figure 3 shows an embodiment with smooth rotors 202 not having teeth, the movement of the axes is identical to the embodiment of Figure 1.

Each apex rotor 202a - those in positions [1,1] , [1,3] , [3,1], and [3,3] of the array - rotate around fixed axes of rotation, these being central within the rotor 202a. The rotors 202b located in contacting positions directly between the apex rotors 202a - those in positions [1,2] , [2,1] , [2,3] , and [3,2] of the array - also rotate around their centres, but these axes of rotation are allowed to translate along a path extending directly between the apex rotors 202a. This movement ensures that contact is maintained throughout rotation of the rotors 202. Finally, the central rotor 202c - that in position [2,2] of the array - rotates about its central axis, this axis being allowed to translate in two dimensions, effectively allowing it to freely translate within the plane of the array. Thus, whatever position the remaining eight rotors 202 are in, the central rotor 202c will always seal the four enclosed volumes 204.

It is clear that the array could be expanded to any desired size. In such a case, the pattern of rotational axes would be maintained throughout, this pattern being clear to the skilled person in view of the disclosure herein. Beneficially, where the array has an odd number of rotors in both directions of the array, and the rotor in position [1,1] of the array has a fixed rotational axis, the other apex rotors will also have fixed rotational axes and thus the overall outer dimension of the array will be constant. Thus, the array will be easily enclosed within a housing with fixed dimensions.

As shown in Figure 3, it is possible to provide the array with rotors 202 that do not include teeth. In such a case, these rotors 202 must remain in good contact to provide sealing of the enclosed volumes. However, providing this is maintained, the operation of the compressor 200 will not be negatively affected.

Now referring to Figures 5a to 5d, a compression cycle of a single enclosed volume 304 will be discussed. Although shown in reference to an array of four rotors 302, the compression cycle will be the same for all enclosed volumes. However, adjacent enclosed volumes will be at different stages of the compression cycle.

Figure 5a shows the rotors 302 in a first position whereby the volume of the enclosed volume 304 is greatest. It can be seen that a filler 312 is located within the enclosed volume 304. The filler 312 acts to lower the dead-space within the enclosed volume 304. Dead-space is the space within which no rotor 302 passes at any point during rotation. As the difference between the maximum size of the enclosed volume 304 - shown in Figure 5a - and the minimum size of the enclosed volume 304 - shown in Figure 5d - defines the compression ratio or expansion ratio of the compressor 300 or expander, limiting the amount of dead-space allows the compression ratio to be adjusted and, in the present application, raised significantly. In Figures 5a to 5d, the rotor 302a in the bottom left position has a fixed axis of rotation.

The compression ratio achieved varies depending on the geometry of the rotors, including tooth profiles. Where rotors are substantially in the form of Reuleaux triangles, have apices that are rounded by approximately 5%, and have 48 teeth, the theoretically-achievable compression ratios vary between a low of 16.6: 1 where no filler is present to 27.4: 1 where an ideal filler is present (i.e. there are zero or infi nite teeth). Therefore the filler gives a 65% improvement in compression ratio in these circumstances. Where a nominal filler is used, a compression ratio of 21.3 : 1 can be achieved, a 28% improvement.

Where it is said that the apices are rounded by approximately 5% , the percentage of rounding is calculated as the radius of the apices compared to the length of a side of an equilateral triangle formed between the origins of each radius. For this calculation, the radius can be defined as s and the length of the side of the equilateral triangle as t. Thus, for a rounding of 5%, s = 0.05t. For example: s - l .4mm, t - 27.2mm

1.4 / 27.2 = 0.5 147 = 5.147% « 5%

An example of a rounded Reuleaux triangle rotor is shown in Figure 9, with s and t labelled. The radius of the long sides of the rotor is calculated as (s + t). It will be apparent to the skilled person that, as s decreases and t increases, the rotor will become more similar to a perfect Reuleaux triangle and compression ratio will increase. Conversely, as s increases and t decreases, the rotor will be become less similar to a Reuleaux triangle and compression ratio will decrease. Where t = 0, the rotor will become completely circular and no compression will be possible. Hence, a compressor formed entirely of rotors with a circular geometry is not included within the scope of the present invention. Whatever the values of s, t, and the resultant rounding value, constant width across a diameter of the rotors is maintained.

As the rotors 302 rotate through the positions of Figure 5b, Figure 5c, and 5d, it can be seen that the size of the enclosed volume 304 decreases. With rotors 302 of the depicted shape, having three ‘sides’, a full rotation of the rotors 302 includes three compression and three expansion cycles, a complete compression and expansion being completed every 120°. Therefore, it can be seen - indicated by the green angle mark on the fixed axis rotor 302a - that the completion of the compression cycle between Figure 5a and Figure 5d involves a rotation of the fixed axis rotor 302a of only 60°. Due to the rolling motion of the rotors 302 in contact with one another, the other three rotors 302 also go through a rotation of 60° through the compression cycle.

The shape of the filler 312 is defined in order to minimise clearance between the rotors 302 and the filler 312, during rotation. As can be seen, the filler 312 includes four faces 314a, 314b, 314c, with three different profiles. A profile of the first face 314a has a continuous curve radius that is substantially the maximum radius of the rotor 302a with the fixed axis of rotation. Thus, during rotation, and as can be seen in Figures 5a to 5d, the bottom left rotor 302a starts at a maximum distance from the filler 312 and rotates to lessen this distance.

The second and third faces 314b, which are adjacent to the first face 314a, have the same profile, although mirrored between the faces 314b. The profile of the second and third faces 314b is more complex as it is designed not only so that rotation of the rotors 302b is allowed but the translational movement of the axes of rotation in one dimension must also be allowed. However, the required profile of the second and third faces 314b will be apparent to the skilled person who has constructed a compressor 300 in accordance with the present disclosure. The fourth face 3 l4c, adjacent the second and third faces 3 l4b and opposing the first face 3 l4a, has a third profile. The third profile is also complex as it must be defined to be within the free space allowing for the rotation of the rotor 302c and its movement in two dimensions within the plane of the compressor 300. However, the required profile of the fourth face 314c will be apparent to the skilled person who has constructed a compressor 300 in accordance with the present disclosure.

Referring again to Figure 2, an inlet 1 16 and outlet 1 18 are provided for each enclosed volume 104, each inlet 116 and outlet 1 18 being provided in the form of a valve , two of which are shown. For ease of use, these valves are rotary valves, the benefit of which will be discussed below. Each valve is configured to open and close at specific times in order to implement compression or expansion. Taking, for example, a compression cycle, the enclosed volume 104 will be full of working fluid at the position shown in Figure 5a. At this point, the inlet valve 1 16 will close and compression will occur. At the position shown in Figure 5d, or shortly beforehand, the outlet valve 1 18 will open in order to release the compressed fluid. Once the outlet valve 1 18 is shut the inlet valve 1 16 can open such that further rotation of the rotors 102 will draw more working fluid into the enclosed volume 104 during expansion of the enclosed volume 104. The cycle can then repeat. It will be apparent how the valves 1 16, 1 18 may operate in reverse in order to provide an expansion cycle. In addition, simple one-way valves may be used to facilitate pump -like operation of the compressor.

One benefit of the use of rotary valves is that they may be driven by the same mechanism providing drive to the rotors 102. As shown in Figure 2, a motor 120 provides drive to one of the corner rotors 102, with a fixed rotational axis , which in turn causes the rotation of the other rotors 102. A transmission mechanism, depicted in the form of a drive belt 122, is provided between the motor 120 and one of the inlet and outlet valves 1 16, 1 18. In turn, idler gears 124 are provided between the valves 1 16, 1 18 and those adjacent. As one rotation of each rotor 102 results in three full cycles of compression and expansion of the enclosed volume 104, each valve 1 16, 1 18 is operates three times for each rotation of the rotors 102. Therefore, a 3 : 1 ratio is provided by each transmission mechanism. Although described as a drive belt 122 and an idler gear 124, transmission may be provided in any suitable form. The filler 312 of Figures 5a to 5d is shown as a solid filler. Advantageously, the filler 312 is composed of a thermally-insulating material and therefore transfer of heat away from a working fluid held within the enclosed volume 304 can be limited. By providing the filler 312 as thermally-insulating, a near-adiabatic cycle can be implemented - that is, compression is provided without significant transfer of heat away from the working fluid. As the rotors 302 are large and can also be provided as insulating elements, heat loss from the system can be minimised. The filler 312 may be provided in other ways which maintain thermal -insulation, such as a hollow filler that encloses a vacuum or near-vacuum. Other ways of implementing fillers that provide thermal insulation will be known to the skilled person.

Alternatively, the filler may be implemented to have different heat-transfer characteristics. For example, a filler 412 designed to maximi se heat-transfer away from the working fluid is shown in Figure 4. By maximising heat -transfer away from the working fluid, a near-isothermal cycle can be implemented - that is, compression is provided without significant increase in temperature of the working fluid.

The filler 412 of Figure 4 includes a channel 426 that extends through the length of the filler 412. The channel 426 would therefore extend from one face of the compressor to the other. Coolant can therefore flow through the filler 412 in order to take away any excess heat that is provided from the compression of the working fluid. As long as the heat transfer away from the filler 412 is equal or near-equal to that generated by the compression of the working fluid, an isothermal or near -isothermal cycle can be implemented. Multiple channels through the filler 412 could be provided and coolant could flow in different directions in order to maximi se heat transfer. The coolant channels 426 could also be provided with more complex geometries rather than extending directly from one face to the other. Although not shown, the coolant channel or channels can be connected to an external heat sink or coolant circuit.

Around the outside of the channel 426 are provided a plurality of vanes 428. The vanes 428 extend away from the channel 426, in a direction perpendicular to the channel 426 such that they radiate out from the channel 426. As the vanes 428 have a large surface area, heat-transfer from the working fluid to the channel 426 can be maximi sed. Whilst the provision of vanes 428 necessarily increases the dead-space in comparison to a solid filler, the benefits of the enhanced heat-transfer characteristics may outweigh the relatively lower compression ratio. Though, in the present embodiment the vanes 428 extend radially away from the channel 426, more complex shapes could instead be used.

As will be apparent, although the channel 426 and vanes 428 alter the cross-section of the filler 412, the outer envelope of the filler 412 - i.e. the shape of the filler 412 if enclosed around the ends of the vanes 428 - remains the same as that of the solid filler 312 of Figures 5a to 5d. Therefore, the filler 412 still provides the dead-space reduction and subsequent increase of compression ratio compared to a compressor without filler.

The end faces 106 that provide sealing of the enclosed volume 104, or the rotors 102 upon which they bear, may be worn down due to the rubbing of the rotors 102 on the end faces 106 during rotation. In order to ensure that sealing is maintained, biasing means in the form of springs 130 are provided between the two end faces 106. Thus, the end faces 106 will remain in contact with the rotors 102 even if wear occurs. Other alternative biasing means may also be provided.

Although operation thus far has been described with reference to compressible working fluids, it is possible to operate the apparatus of the present disclosure such that it can cope with bi-phase working fluids. In such a situation, a relief valve may be provided on each enclosed volume, the relief valve allowing the release of pressure, for example if the compressor attempts to compress an incompressible working fluid, such as a liquid. Thus, damage to the compressor can be prevented. A schematic diagram of such a compressor 500 is shown in Figure 6.

The implementation of a bi-phase cycle, such as the Rankine cycle, can be achieved and the typical throttle expander used in most typical refrigeration equipment can be replaced with a reversible expander. This can therefore improve efficiency by recovering energy mechanically. Bi-phase capability can also form the basis for low- temperature, low-pressure boiling - an enabling technology for efficient desalination, for example.

Figure 6 shows two rotors 502 between two end plates 508, with an inlet valve 516 and an outlet valve 518 leading into the enclosed volume which is formed between the depicted rotors 502 and two other rotors (not shown). In order that the compressor 500 is not damaged by attempted compression of incompressible liquids, a relief valve 532 is provided that operates to open if pressure increases past a threshold, this threshold being below a pressure that would cause damage to the compressor 500. The compressor 500 of Figure 6 is configured for the use of dry air as a working fluid and therefore the relief valve 532 can operate to remove water that may find its way into the compression/expansion circuit.

A housing 534 is provided around the compressor, the housing 534 have an inlet valve 536 and being sealed against leakage. Adj acent to the inlet valve 536 is a desiccant 538 that acts to remove moisture from the inlet air. Release of working fluid from the relief valve 532 may result in a partial vacuum within the compressor 500 and therefore the housing 534 provides a reservoir of additional dry air from which the compressor 500 can replenish its supply of working fluid. If a partial vacuum is present within the compressor 500, a limited supply of dry air from the housing 534 may be brought into the enclosed volume through the small gaps between the teeth of the rotors 502, or between the rotors 502 and the end plates 508. The controlled environment therefore mitigates for leakage into the compressor 500.

Figure 7 depicts a Carnot-like cycle enabled by the disclosed compressor/expander. Two of the chambers 604 are operated in an adiabatic configuration, as described above, whilst the other two chambers 604 are operated in an isothermal configuration, also as described above. The compressor can therefore approximate a Carnot cycle - the most efficient theoretical cycle possible. The closeness of the approximation of the Carnot cycle is limited primarily by the thermal resistance of the embedded heat exchangers.

As shown in Figure 8, a two-stage Brayton cycle can be implemented by a compressor containing four chambers or enclosed volumes . Such a cycle can drive a cryogenic cooler 740, for example. Two of the chambers 704 are operated as compressors and two chambers are operated as expanders. Two-stage compression is provided and heat then dissipated through an external heat exchanger 742. The remaining two chambers 704 expand the working fluid, cooling it to cryogenic temperatures, the working fluid then passing through a heat exchanger 744 in the cryogenic cooler 740, in the present embodiment cooling liquid nitrogen. Such a cycle could be used to enable technology for mobile/portable superconductor technologies, including SQUIDs (superconducting quantum interference devices) for hand-portable MRI scanners.

When operating in a Brayton cycle as a cryo-cooler, one heat exchanger will be a low- temperature heat exchanger and the other will be a high -temperature heat exchanger. The low-temperature heat exchanger may operate at a lower pressure, below ambient pressure, than the high-temperature heat exchanger, which may operate above ambient pressure. The compressor and expander situated either side of the high -temperature heat exchanger 742 may therefore leak working fluid to the environment, whilst the compressor and expander situated either side of the low -temperature heat exchanger 744 may draw working fluid from the environment.

As the high-temperature heat exchanger 742 may operate at pressures of around 1 160 kPa compared to the low-temperature heat exchanger 744 which may operate at pressures of around 7 kPa, the leakage out of the high-temperature heat exchanger 742 may be far greater than the leakage into the low -temperature heat exchanger 744. Therefore, working fluid may be controllably added to the cycle, for example at the interstage 746, which may operate at around ambient pressure. By implementing the Brayton and/or Carnot cycles, for example, using the compressor of the present disclosure, refrigeration cycles can be achieved without the use of HFC refrigerants. These cycles could use nitrogen gas or be self-charging from ambient air, as discussed above. This can avoid the use of potent greenhouses gases as refrigerants, these gases also being highly damaging to the ozone layer.