Simultaneous compressor-expander

Abstract

Conventional vapour-compression refrigeration systems have an efficiency significantly below the maximum theoretical limit, commonly due to the inefficiency in conventional compressors and expansion valves. The present invention provides a simultaneous compressor-expander (90) comprising a series of linked liquid ring compressors (100, 200) for compressing a first working fluid in a gaseous phase and decompressing the liquid making up the liquid ring. In this way, the compression of the gas and the expansion of the liquid may both take place in a single device, enabling heat exchange between the gas and the liquid across a full range of temperatures and pressures. This combined compression / expansion process with heat exchange is more efficient than two separate, thermally isolated processes.

Description

RELATED APPLICATIONS

[0001] This application claims priority to GB Application 2501956.3, filed Feb. 10, 2025 under 35 U.S.C. § 119. This GB applications is incorporated by reference herein in its entirety.Field

[0002] The present invention relates generally to a simultaneous compressor-expander and a method of simultaneously compressing a first working fluid in a gaseous phase and decompressing a second working fluid in a liquid phase, and finds particular, although not exclusive, utility in refrigeration systems.BACKGROUND

[0003] Vapour compression refrigeration systems are well known. Such systems comprise four key components, namely a compressor, a condenser, an expansion valve and an evaporator, and a refrigerant, which is moved in a closed loop around the system, through each of the components. The refrigerant enters the compressor as a vapour and is compressed, resulting in an increase in pressure and temperature. The compressed vapour then passes through the condenser where heat is transferred away from the refrigerant (e.g. to the surrounding environment), allowing it to condense into a liquid. This liquid passes through the expansion valve where a rapid decrease in pressure results in a flash evaporation to form a mixture of liquid and vapour. The flash evaporation and the associated auto-refrigeration effect lowers the temperature of the liquid / vapour mixture. Finally, the liquid / vapour mixture passes through the evaporator where heat is transferred to it from the region to be cooled. The transfer of heat away from the region to be cooled provides the desired cooling effect, while the transfer of heat to the refrigerant results in evaporation of the liquid component, so that the refrigerant leaving the evaporator is in a fully gaseous phase.

[0004] In effect, the compressor and expansion valve raise and lower the temperature of the refrigerant respectively, so that heat transfer may occur between the refrigerant and a cold reservoir (i.e. the region to be cooled), and between the refrigerant and a hot reservoir (i.e. the surrounding environment), resulting in a net transfer of heat from the cold reservoir to the hot reservoir.

[0005] The efficiency of a refrigeration system is quantified by its coefficient of performance (COP), defined as the ratio of the amount of heat removed from the region to be cooled to the amount of work required. Conventional vapour-compression refrigeration systems, as described above, typically have a COP significantly below the maximum theoretical limit (known as the Carnot limit). Common points of inefficiency in conventional systems include the compressor and the expansion valve.SUMMARY

[0006] In a first aspect, the present invention provides a simultaneous compressor-expander for simultaneously compressing a first working fluid in a gaseous phase and decompressing a second working fluid in a liquid phase, the simultaneous compressor-expander comprising a first liquid ring compressor and a second liquid ring compressor, each of the first and second liquid ring compressors comprising a respective first end wall at a respective first end thereof; a respective second end wall at a respective second end thereof, the respective second end opposite the respective first end; a respective outer wall extending from the respective first end to the respective second end, the respective outer wall configured to be rotationally symmetric about a respective chamber axis; a respective chamber defined by the respective first end wall, the respective second end wall and the respective outer wall, the respective chamber having a respective gas inlet; a respective gas outlet; a respective liquid inlet; and a respective liquid outlet; and a respective set of vanes disposed within the respective chamber, the respective set of vanes configured to rotate about a respective vane axis parallel to, and spaced from, the respective chamber axis, wherein each respective liquid ring compressor is configured to form a respective liquid ring from a second working fluid moving between the respective liquid inlet and the respective liquid outlet, and to compress a first working fluid in a gaseous phase from the respective gas inlet to the respective gas outlet. The simultaneous compressor-expander further comprises a gas connection between the respective gas outlet of the first liquid ring compressor and the respective gas inlet of the second liquid ring compressor, such that the first working fluid is moved, in use, through the first liquid ring compressor and the second liquid ring compressor in series; and a liquid connection between the respective liquid outlet of the second liquid ring compressor and the respective liquid inlet of the first liquid ring compressor, the liquid connection comprising a flow regulator configured to permit a substantially unidirectional flow of the second working fluid, in use, from the second liquid ring compressor to the first liquid ring compressor.

[0007] In this way, the compression of the gas and the expansion of the liquid may both take place in a single device, enabling heat exchange between the gas and the liquid across a full range of temperatures and pressures. This combined compression / expansion process with heat exchange is more efficient than two separate, thermally isolated processes. Consequently, the simultaneous compressor-expander may form the basis of a refrigeration cycle having a COP greater than that of a conventional vapour-compression refrigeration system.

[0008] As used herein, the term working fluid may refer to any fluid that undergoes a thermodynamic change, in use. For example, a working fluid may be a fluid that undergoes a change of pressure, temperature, volume and / or phase.

[0009] The first working fluid and the second working fluid may have the same chemical composition. That is, the first working fluid may be a substance in a gaseous phase and the second working fluid may be the same substance in a liquid phase. For example, the first working fluid may be a refrigerant in a gaseous phase and the second working fluid may be the same refrigerant in a liquid phase. A refrigerant may be any substance suitable for use in a refrigeration cycle, for example, any substance with an ASHRAE-designated R number.

[0010] A fluid in a gaseous phase may be referred to herein as a gas, and may include a fluid in a vapour phase and / or a fluid in a non-vapour gaseous phase. A fluid in a liquid phase may be referred to herein as a liquid.

[0011] In the following paragraphs, for the sake of brevity, reference will be made to a single liquid ring compressor. However, it is to be understood that references to “the liquid ring compressor” should be construed as references to “either or both of the respective liquid ring compressors”, and other corresponding references (e.g. “the first end wall”, “the outer wall”, “the chamber”, “the chamber axis” etc.) should be construed accordingly.

[0012] Furthermore, the terms “first outer wall”, “first chamber”, “first set of vanes”, “first chamber axis”, “first vane axis”, “first gas inlet”, “first gas outlet”, “first liquid inlet” and “first liquid outlet” may be used to denote, respectively, “the respective outer wall of the first liquid ring compressor”, “the respective chamber of the first liquid ring compressor”, “the respective set of vanes of the first liquid ring compressor”, “the respective chamber axis of the first liquid ring compressor”, “the respective vane axis of the first liquid ring compressor”, “the respective gas inlet of the first liquid ring compressor”, “the respective gas outlet of the first liquid ring compressor”, “the respective liquid inlet of the first liquid ring compressor” and “the respective liquid outlet of the first liquid ring compressor”. Similar terms may be used for the corresponding features of the second liquid ring compressor (e.g. “second outer wall” may be used to denote “the respective outer wall of the second liquid ring compressor etc.), and of any further liquid ring compressors referred to herein.

[0013] The first end wall may be a planar wall and may be oriented in a plane that is perpendicular to the chamber axis and / or the vane axis. The first end wall may be of a shape that is rotationally symmetric about the chamber axis. For example, the first end wall may be circular, or may have the shape of a regular polygon, with the chamber axis passing through its centre point. Alternatively, the first end wall may be rotationally symmetric about the vane axis, for example being circular, or having the shape of a regular polygon, with the vane axis passing through its centre point.

[0014] Similarly, the second end wall may be a planar wall and may also be oriented in a plane that is perpendicular to the chamber axis and / or the vane axis. The second end wall may be of a shape that is rotationally symmetric about the chamber axis. For example, the second end wall may be circular, or may have the shape of a regular polygon, with the chamber axis passing through its centre point. Alternatively, the second end wall may be rotationally symmetric about the vane axis, for example being circular, or having the shape of a regular polygon, with the vane axis passing through its centre point. The second end wall may be of the same shape and size as the first end wall.

[0015] The term “rotationally symmetric” used in the description and the claims may be interpreted as meaning approximately rotationally symmetric. For example, a polygon having side lengths or interior angles that are approximately, but not exactly, equal may be considered to be rotationally symmetric.

[0016] Where a part of the liquid ring compressor (e.g. the first end wall) is described as being at the first end thereof, it is to be understood that the part so described may be spaced from the first end within a tolerance. For example, a part described as being at the first end may be spaced from the first end by up to 10%, up to 20% or up to 30% of the axial length of the liquid ring compressor. Similarly, where a part of the liquid ring compressor (e.g. the second end wall) is described as being at the second end thereof, it is to be understood that the part so described may be spaced from the second end within a tolerance. For example, a part described as being at the second end may be spaced from the second end by up to 10%, up to 20% or up to 30% of the axial length of the liquid ring compressor. The first end may be a first axial end, and the second end may be a second axial end. It may be understood that the axial length of the liquid ring compressor, or of any part thereof, is the length of the liquid ring compressor, or of that part, as measured in a direction parallel to the chamber axis and / or the vane axis.

[0017] The outer wall may form a complete closed loop about the chamber axis. The outer wall may be a continuously curved wall, or may comprise a plurality of flat wall portions and / or a plurality of curved wall portions.

[0018] The outer wall extending from the first end to the second end may mean that the outer wall extends at least from the first end to the second end. That is, the outer wall may extend beyond the first end and / or beyond the second end.

[0019] The outer wall may be flush with the edges of the first end wall and / or the second end wall. Alternatively, there may be a gap between the outer wall and the edges of the first end wall and / or the second end wall. The outer wall may be fixedly joined to the first end wall and / or the second end wall along at least one portion of the edge(s) thereof. Alternatively, the outer wall may be entirely separate from the first end wall and / or the second end wall and may not be attached thereto.

[0020] The chamber may be a cavity that is substantially enclosed by the first end wall, the second end wall and the outer wall. A cavity that is substantially enclosed may include a cavity that is fully enclosed (i.e. bounded by walls on all sides), but is not limited thereto. In particular, a cavity that is substantially enclosed may occupy a volume that is bounded by walls over a majority of its total surface area. For example, the percentage of the cavity's total surface area bounded by walls may be at least 70%, at least 80% or at least 90%.

[0021] The gas inlet may be formed in the first end wall. The gas inlet may comprise an opening in the first end wall through which gas may enter the chamber. Additionally, the gas inlet may comprise means for regulating the flow of gas therethrough. For example, the gas inlet may comprise a valve. Regulating the flow of gas through the gas inlet may include selectively opening and closing the gas inlet; restricting the flow rate of gas through the gas inlet; and / or prohibiting the movement of gas through the gas inlet in a direction from the inside of the chamber to the outside of the chamber.

[0022] The gas inlet may comprise a gas inlet pipe, arranged to pass through an opening in the first end wall and deliver gas to a location within the chamber not immediately adjacent the opening, and / or from a location outside the chamber not immediately adjacent the opening.

[0023] The gas outlet may be formed in the second end wall. The gas outlet may comprise an opening in the second end wall through which gas may leave the chamber. Additionally, the gas outlet may comprise means for regulating the flow of gas therethrough. For example, the gas outlet may comprise a valve. Regulating the flow of gas through the gas outlet may include selectively opening and closing the gas outlet; restricting the flow rate of gas through the gas outlet; and / or prohibiting the movement of gas through the gas outlet in a direction from the outside of the chamber to the inside of the chamber.

[0024] The gas outlet may comprise a gas outlet pipe, arranged to pass through an opening in the second end wall and take in gas from a location within the chamber not immediately adjacent the opening, and / or deliver the gas to a location outside the chamber not immediately adjacent the opening. Alternatively, the gas outlet pipe may be formed integrally with the second end wall, or the first end wall, rather than passing through an opening therein.

[0025] While the gas inlet and gas outlet have been described above as being formed in the first end wall and second end wall respectively, it is contemplated that alternative arrangements may be used. For example, the gas inlet and / or the gas outlet may be formed in a rotor passing through the centre of the chamber on which the set of vanes is mounted.

[0026] The liquid inlet may be an opening in a wall, or a gap between walls, through which a liquid may enter the chamber. For example, the liquid inlet may comprise an opening in the second end wall, the outer wall, or even the first end wall. Alternatively, the liquid inlet may comprise a gap between an outer edge of the second end wall and the outer wall. The liquid inlet may be located at a greater radial distance, as measured from the chamber axis, than either the gas inlet or the gas outlet. As another alternative, the liquid inlet may comprise a hose, tap, pipe, spout or other similar liquid delivery device inserted into the chamber through one of its walls, or formed integrally therewith.

[0027] The liquid outlet may be an opening in a wall, or a gap between walls, through which the liquid may leave the chamber. For example, the liquid outlet may comprise an opening in the first end wall, the outer wall, or even the second end wall. Alternatively, the liquid outlet may comprise a gap between an outer edge of the first end wall and the outer wall. The liquid outlet may be located at a greater radial distance, as measured from the chamber axis, than either the gas inlet or the gas outlet.

[0028] The liquid inlet and the liquid outlet may be spaced apart from each other to prevent the flow of liquid straight from the liquid inlet into the liquid outlet. For example, the liquid inlet may be at the second end and the liquid outlet may be at the first end.

[0029] The liquid ring compressor may comprise at least one further gas inlet, at least one further gas outlet, at least one further liquid inlet and / or at least one further liquid outlet.

[0030] The set of vanes may comprise a single vane, two vanes or three or more vanes; for example, five vanes, eight vanes or ten vanes. The or each vane of the set of vanes may extend axially from the first end wall to the second end wall, and may extend radially outward from the vane axis to a respective vane edge. The vane(s) may be non-porous and may not comprise any openings therein, so as to prohibit the passage of any fluid therethrough.

[0031] The set of vanes may be configured to rotate about the vane axis, for example, at a vane rotational speed.

[0032] The vane(s) may be joined to the first end wall and the second end wall at their respective axial ends, and the set of vanes may rotate about the vane axis together with the first and second end walls. Alternatively, the vane(s) may not be joined to the first and second end walls and may instead be fitted with high precision seals at their respective ends to prevent the flow of fluid between the vanes and the first end wall, or between the vanes and the second end wall.

[0033] Additionally, the outer wall may be configured to rotate, or be rotatable about, the chamber axis, for example at an outer wall rotational speed, which may be the same as, or different to, the vane rotational speed. Where the outer wall is configured to rotate, or be rotatable about, the chamber axis, and the first and / or second end wall is not joined to the vane(s), the first and / or second end wall may rotate about the chamber axis with the outer wall. Alternatively, the first and / or second end wall may remain stationary while the outer wall rotates about the chamber axis.

[0034] The set of vanes being configured to rotate about the vane axis may mean that the set of vanes is driven to rotate about the vane axis, in use, by a vane drive mechanism. The vane drive mechanism may form a part of the set of vanes or, more generally, of the simultaneous compressor-expander, or may be separate therefrom. The vane drive mechanism may include a motor.

[0035] Similarly, the outer wall being configured to rotate about the chamber axis may mean that the outer wall is driven to rotate, in use, by an outer wall drive mechanism. The outer wall drive mechanism may form a part of the outer wall or, more generally, of the simultaneous compressor-expander, or may be separate therefrom. The outer wall drive mechanism may include a motor. The outer wall drive mechanism and the vane drive mechanism may be the same mechanism. The outer wall being configured to be rotatable about the chamber axis may mean that the outer wall is free to rotate about the chamber axis but lacks any driving means for driving the rotation. An outer wall so configured may be caused to rotate, for example, by fluid rotating within the liquid ring compressor and exerting a force on the inner surface of the outer wall.

[0036] The vane axis being parallel to the chamber axis may mean that the vane axis is approximately parallel to the chamber axis. For example, the vane axis may be oriented at an angle of less than 10 degrees, less than 5 degrees or less than 2 degrees relative to the chamber axis.

[0037] The respective vane axis of the first liquid ring compressor may be coincident with the respective vane axis of the second liquid ring compressor, and the respective set of vanes of the first liquid ring compressor and the respective set of vanes of the second liquid ring compressor may be connected by a common rotor extending along the respective vane axis of the first liquid ring compressor from the respective first end of the first liquid ring compressor to the respective second end of the second liquid ring compressor.

[0038] In this way, a torque may be applied simultaneously to the first set of vanes and the second set of vanes through the common rotor. Consequently, a single vane drive mechanism may be used to rotate both sets of vanes. Additionally, the rotational position of the first set of vanes may be kept constant relative to the rotational position of the second set of vanes.

[0039] For the avoidance of doubt, the term “rotor axis” will be used hereinbelow to denote the first and / or second vane axes where said first and second vane axes are coincident.

[0040] The common rotor, which may be referred to herein simply as the rotor, may comprise a hollow or solid shaft to which the first and second sets of vanes are fixedly attached. The shaft may be cylindrical, but may alternatively have a cross-section (in a plane perpendicular to the rotor axis) of any geometric shape, such as a square, a hexagon, an octagon etc.

[0041] The rotor may extend beyond the first end of the first liquid ring compressor and / or beyond the second end of the second liquid ring compressor. The rotor may pass through the first and / or second end walls of the first and / or second liquid ring compressor, for example through respective apertures formed therein. Any such aperture may be fitted with a seal configured to prevent the passage of fluid therethrough between the rotor and the edge of the aperture. Alternatively, the first and / or second end walls of the first and / or second liquid ring compressors may be formed integrally with the rotor. That is, they may be fixedly attached to the rotor and configured to rotate therewith about the rotor axis.

[0042] The rotor may comprise a rotor engagement part configured to engage with a vane drive mechanism. The vane drive mechanism may apply a torque to the rotor, via the rotor engagement part, and the rotor may then transfer this torque to the first and second sets of vanes. For example, where the vane drive mechanism comprises a motor, the rotor engagement part may be configured to engage directly with the motor, or may be configured to engage with the motor via one or more gears. The rotor engagement part, and the vane drive mechanism, may be located at either end of the rotor, or may alternatively be located between the first and second liquid ring compressors.

[0043] The common rotor may comprise a gas passageway in fluid communication with the respective chamber of the second liquid ring compressor via a gas passageway opening; and a liquid passageway, separate from the gas passageway and in fluid communication with the respective chamber of the second liquid ring compressor via a liquid passageway opening.

[0044] In this way, the first working fluid exiting the second liquid ring compressor may pass through the gas passageway to be collected at a location axially spaced from the second end of the second liquid ring compressor. Similarly, the second working fluid may be supplied to the second liquid ring compressor from a location axially spaced from the second end of the second liquid ring compressor. For example, the location at which the first working fluid is collected and / or from which the second working fluid is supplied may be at or near the location from which the first working fluid is supplied to the first liquid ring compressor and / or at which the second working fluid exiting the first liquid ring compressor is collected, thereby enabling a more compact design.

[0045] The gas passageway may be in fluid communication with the respective chamber of the second liquid ring compressor (i.e. the second chamber) via the gas passageway opening and the second gas outlet. Similarly, the liquid passageway may be in fluid communication with the second chamber via the liquid passageway opening and the second liquid inlet. For example, the simultaneous compressor-expander may comprise a high pressure chamber into which the gas and liquid passageway openings open, the high pressure chamber being in fluid communication with the second chamber via the second gas outlet and the second liquid inlet. In use, the (compressed) first working fluid may exit the second chamber, through the second gas outlet, into the high pressure chamber before passing through the gas passageway opening and out along the gas passageway, while the second working fluid may be delivered from the liquid passageway, through the liquid passageway opening, into the high pressure chamber before entering the second chamber through the second liquid inlet.

[0046] The gas passageway and / or the liquid passageway may be formed within the rotor. For example, the rotor may comprise a hollow shaft with the gas passageway and / or liquid passageway passing along the inside of the hollow shaft (e.g. parallel to the rotor axis). However, it is conceivable that the gas passageway and the liquid passageway may be formed on the outside of the rotor, or that one of the gas passageway and the liquid passageway may be formed on the outside of the rotor and the other one of the gas passageway and the liquid passageway may be formed within the rotor.

[0047] The gas passageway and the liquid passageway may be concentric passageways. For example, the liquid passageway may have a smaller diameter than, and be formed within, the gas passageway. Alternatively, the gas passageway may have a smaller diameter than, and be formed within, the liquid passageway. In either case, the liquid and gas passageways may each be rotationally symmetric about the rotor axis, so that the mass distribution of fluid flowing in each of the passageways may also rotationally symmetric about the rotor axis.

[0048] Alternative arrangements of the gas and liquid passageways within the rotor are also contemplated. For example, the gas passageway and the liquid passageway may run side by side within the rotor, parallel to each other and to the rotor axis.

[0049] The gas passageway may extend from the gas passageway opening to a gas collection point at which compressed gas leaving the second liquid ring compressor through the gas passageway may be collected (e.g. for onward use in a condenser). The gas collection point may simply be a second gas passageway opening at an opposite end of the gas passageway to the gas passageway opening. Alternatively, the gas collection point may comprise a fitting configured to connect with a receptacle for collecting the compressed gas and / or directly with a system requiring a supply of compressed gas. It is to be understood that such a fitting may include means for connecting a rotating gas passageway with a static receptacle.

[0050] Similarly, the liquid passageway may extend from the liquid passageway opening to a liquid supply point at which liquid may be introduced into the simultaneous compressor-expander. The liquid supply point may comprise a fitting configured to connect with a liquid supply. It is to be understood that such a fitting may include means for connecting a static liquid supply with a rotating liquid passageway.

[0051] The liquid passageway being separate from the gas passageway may mean that no mixing occurs between a fluid passing though the inner passageway and a fluid passing through the outer passageway.

[0052] The respective chamber axis of the first liquid ring compressor may be coincident with the respective chamber axis of the second liquid ring compressor, and the respective outer walls of the first liquid ring compressor and the second liquid ring compressor may form part of a common outer wall, the common outer wall extending from the respective first end of the first liquid ring compressor to the respective second end to the second liquid ring compressor.

[0053] In this way, where the first and second outer walls are configured to rotate about their respective chamber axes, a single outer wall drive mechanism may be used to simultaneously rotate the first and second outer walls, thereby simplifying the design of the simultaneous compressor-expander.

[0054] For the avoidance of doubt, the term “common chamber axis” will be used hereinbelow to denote the first and / or second chamber axes where said first and second chamber axes are coincident.

[0055] The first and second outer walls forming a part of the common outer wall may mean that the common outer wall comprises the first and second outer walls. The common outer wall may comprise only the first and second outer walls, or may additionally comprise additional outer wall portions. For example, the common outer wall may comprise an intermediate outer wall portion between the first outer wall and the second outer wall. The intermediate outer wall portion may enclose an intermediate chamber, between the first and second liquid ring compressors, in which, or through which, the gas connection and the liquid connection may be arranged.

[0056] The common outer wall may extend beyond the first end of the first liquid ring compressor and / or beyond the second end of the second liquid ring compressor. For example, the common outer wall may extend beyond the second end of the second liquid ring compressor to form an outer wall of a high pressure chamber, as described above.

[0057] It may be understood that a liquid ring is a ring or tube (i.e. an annular prism) of rapidly rotating liquid surrounding a central void, the liquid being prevented from entering the central void by the centrifugal force acting thereon. The liquid ring compressor may be configured to form a liquid ring from the second working fluid through the rotation of the set of vanes about the vane axis and / or through rotation of the outer wall about the chamber axis. The liquid ring compressor may be configured to form a liquid ring inside the chamber, the liquid ring being contained by the outer wall and surrounding a central void in a region around the chamber axis.

[0058] The liquid ring compressor may be configured to form a liquid ring having a liquid ring depth equal to a first depth. As used herein, the term liquid ring depth may be defined as the difference between the inner and outer radii of the liquid ring, as measured from the chamber axis. The first depth may be great enough that the vane edge of each vane of the set of vanes is submerged in the liquid ring, in use, at all rotational angles about the vane axis. In particular, the first depth may be greater than twice the perpendicular distance between the chamber axis and the vane axis. Consequently, the central void within the liquid ring may be sub-divided into compression chambers, each compression chamber being bounded by the first end wall, the second end wall, a first face of a first vane, a second face of a second vane and the liquid ring, and each compression chamber having a volume that varies cyclically between a maximum volume and a minimum volume as the set of vanes rotates about the vane axis. Where the set of vanes comprises only a single vane, the first and second vane may be the same vane.

[0059] The liquid ring compressor may compress the first working fluid by receiving the first working fluid, via the gas inlet, into a compression chamber when its volume is close to the maximum volume; compressing the first working fluid as the volume of the compression chamber decreases; and ejecting the first working fluid, via the gas outlet, when the volume of the compression chamber is close to the minimum volume. Accordingly, the gas inlet may be arranged so that it is in fluid communication with a compression chamber when its volume is close to the maximum volume, and the gas outlet may be arranged so that it is in fluid communication with a compression chamber when its volume is close to the minimum volume.

[0060] The maximum volume of the compression chambers in the second liquid ring compressor may be smaller than the maximum volume of the compression chambers in the first liquid ring compressor. In particular, the maximum volume of the compression chambers in the second liquid ring compressor may be approximately equal to the minimum volume of the compression chambers in the first liquid ring compressor. In this way, the first working fluid may be compressed in the first liquid ring compressor and may be further compressed in the second liquid ring compressor.

[0061] The second liquid ring compressor may have an axial length less than the axial length of the first liquid ring compressor. However, it is contemplated that other differences between the first and second liquid ring compressors may exist and may contribute towards the difference in the volumes of the compression chambers. For example, the second liquid ring compressor may additionally, or alternatively, have a smaller radial extent (i.e. average distance between the outer wall and the chamber axis) than the first liquid ring compressor.

[0062] It is to be understood that the temperature of the first and second working fluids may be higher in the second liquid ring compressor than in the first liquid ring compressor. It is also to be understood that the second working fluid (from which the respective liquid rings are formed, in use) may be at a higher pressure in the second liquid ring compressor than in the first liquid ring compressor.

[0063] The gas connection may be configured to provide a gas flow path therethrough between the gas outlet of the first liquid ring compressor and the gas inlet of the second liquid ring compressor. The gas flow path may be sealed from the external environment to prevent the escape of any gas passing therethrough into the external environment. The gas flow path may have an approximately constant cross-sectional area along its length.

[0064] For example, the gas connection may comprise a gas connection pipe connected between the gas outlet of the first liquid ring compressor and the gas inlet of the second liquid ring compressor. The gas connection pipe may be a flexible pipe, or may be rigid.

[0065] The liquid connection may be configured to provide a liquid flow path therethrough between the liquid outlet of the second liquid ring compressor and the liquid inlet of the first liquid ring compressor. The liquid flow path may be sealed from the external environment to prevent the escape of any liquid passing therethrough into the external environment. For example, the liquid connection may comprise a liquid connection pipe.

[0066] The flow regulator may be located within the liquid flow path. Alternatively, the flow regulator may comprise the liquid flow path, or a part thereof. A flow regulator located within the liquid flow path may be located at one of the ends of the liquid flow path, or at any point along its length. Similarly, a flow regulator comprising a part of the liquid flow path may comprise any part of the fluid flow path, including one of its ends.

[0067] The flow regulator may permit a substantially unidirectional flow of liquid therethrough, in a direction from the liquid outlet of the second liquid ring compressor to the liquid inlet of the first liquid ring compressor, under the influence of the pressure gradient therebetween. For example, the flow regulator may comprise an opening of relatively small cross-sectional area. Alternatively, or additionally, the flow regulator may comprise a valve configured to prevent the flow of liquid therethrough in the opposite direction (i.e. from the liquid inlet of the first liquid ring compressor to the liquid outlet of the second liquid ring compressor).

[0068] The liquid connection may comprise a reservoir in fluid communication with both the liquid outlet of the second liquid ring compressor and the liquid inlet of the first liquid ring compressor, such that liquid may enter the reservoir from the liquid outlet of the second liquid ring compressor, and may leave the reservoir via the liquid inlet of the first liquid ring compressor.

[0069] The liquid connection may comprise a first intermediate liquid ring and a second intermediate liquid ring, the first and second intermediate liquid rings formed within an intermediate chamber between the first liquid ring compressor and the second liquid ring compressor, the intermediate chamber bounded by the common outer wall, the second end wall of the first liquid ring compressor and the first end wall of the second liquid ring compressor, wherein the first intermediate liquid ring is in fluid communication with the respective liquid ring of the first liquid ring compressor via the respective liquid inlet of the first liquid ring compressor; the second intermediate liquid ring is in fluid communication with the respective liquid ring of the second liquid ring compressor via the respective liquid outlet of the second liquid ring compressor; and the first and second intermediate liquid rings are separated by the flow regulator.

[0070] The first and second intermediate liquid rings may be formed by the rotation of the common outer wall about the common chamber axis. The first liquid ring, the second liquid ring, the first intermediate liquid ring and the second intermediate liquid ring may each have the same liquid ring depth, for example being equal to the first depth. However, it is contemplated that the liquid ring depths of these four liquid rings may not be equal.

[0071] The flow regulator may comprise a baffle, extending radially inwards from an inner surface of the common outer wall between the first liquid ring compressor and the second liquid ring compressor.

[0072] In this way, the flow of the second working fluid from the second liquid ring compressor to the first liquid ring compressor may be regulated or restricted without need for valves. For example, the baffle may form a tortuous flow path between the second intermediate liquid ring and the first intermediate liquid ring.

[0073] The baffle may comprise a liquid impermeable barrier configured to prevent the flow of the second working fluid therethrough.

[0074] The baffle extending radially inwards from an inner surface of the common outer wall may mean that the baffle extends radially inwards with respect to the common chamber axis. For example, the baffle may comprise a substantially annular barrier, extending from the inner surface of the common outer wall to a baffle edge, the baffle edge defining a circular opening of constant radius about the common chamber axis. However, it is contemplated that the baffle edge may define an opening of a different shape, such as a regular polygon centred on the common chamber axis.

[0075] The rotor may pass through the opening defined by the baffle edge. Additionally, the gas flow path formed by the gas connection may be arranged to pass though the opening defined by the baffle edge.

[0076] The baffle may have a baffle height greater than the respective liquid ring depths of the first and second intermediate liquid rings, and the baffle may comprise at least one baffle opening configured to permit the flow of liquid therethrough.

[0077] In this way, the baffle may restrict the flow of the second working fluid from the second liquid ring compressor to the first liquid ring compressor by only permitting the second working fluid to move from the second intermediate liquid ring to the first intermediate liquid ring through the at least one baffle opening. The second working fluid may move through the at least one baffle opening from the second intermediate liquid ring to the first intermediate liquid ring under the influence of the pressure gradient therebetween.

[0078] As used herein, the baffle height may be defined as the distance, measured radially with respect to the common chamber axis, between the inner surface of the common outer wall and the baffle edge. Where said distance is not constant for all points on the baffle edge (for example, if the baffle edge defines a polygonal opening), the baffle height being greater than the respective liquid ring depths of the first and second intermediate liquid rings may mean that the minimum baffle height (i.e. the smallest radial distance between the baffle edge and the common chamber wall) is greater than the respective liquid ring depths of the first and second intermediate liquid rings.

[0079] The at least one baffle opening may comprise only one baffle opening, two baffle openings, three baffle openings, or more than three baffle openings. The, or each of the, at least one baffle opening(s) may have a relatively small cross-sectional area. In particular, the, or each of the, at least one baffle opening(s) may be sized such that the flow rate of the second working fluid therethrough is sufficiently low that pressure equilibration between the first and second liquid ring compressors does not occur, thereby maintaining the pressure gradient between the second liquid ring compressor and the first liquid ring compressor.

[0080] Where the intermediate chamber is fully enclosed by the common outer wall, the second end wall of the first liquid ring compressor and the first end wall of the second liquid ring compressor, except at the first liquid inlet and the second liquid outlet, it may not be possible for gas to move in or out of the intermediate chamber. Consequently, a gas bubble or a vacuum may form within the intermediate chamber as liquid moves into and / or out of the intermediate chamber. Such a gas bubble or vacuum may resist, or interfere with, the desired movement of liquid through the intermediate chamber.

[0081] The intermediate chamber may comprise a pressure relief duct.

[0082] In this way, gas may enter the intermediate chamber to prevent formation of a vacuum, and gas may leave the intermediate chamber to prevent the buildup of a gas bubble.

[0083] It is to be understood that the gas in the intermediate chamber is not the first working fluid being passed from the first gas outlet to the second gas inlet, and may not even have the same chemical composition as the first working fluid (it may, for example, be air).

[0084] The pressure relief duct may be or comprise a passageway between the intermediate chamber and an external environment. For example, the pressure relief duct may comprise a pipe having an open first end located within the intermediate chamber, the pipe passing through the common outer wall and having an open second end outside the simultaneous compressor-expander (i.e. in an external environment). The open first end of the pipe may be positioned relatively close to the common chamber axis to prevent the open first end from being sealed by liquid in the first or second intermediate liquid rings.

[0085] Alternatively, the pressure relief duct may comprise a pressure relief passageway formed within, or on the outside of, the shaft of the rotor, the pressure relief passageway configured to permit the flow of gas therethrough between the intermediate chamber and an external environment at the first or second end of the rotor. The pressure relief passageway may be separate from, and may not be in fluid communication with, any gas passageway or liquid passageway that may also be formed within, or on the outside of, the shaft of the rotor (as described above).

[0086] As a further alternative, the pressure relief duct may comprise a passageway between the intermediate chamber and the stream of compressed gas leaving the second liquid ring compressor, instead of the external environment. For example, where the shaft of the rotor comprises a gas passageway, the pressure relief duct may simply comprise an opening between the intermediate chamber and the gas passageway.

[0087] The simultaneous compressor-expander may additionally comprise a further liquid ring compressor, the further liquid ring compressor comprising a respective first end wall at a respective first end thereof; a respective second end wall at a respective second end thereof, the respective second end opposite the respective first end; a respective outer wall extending from the respective first end to the respective second end, the respective outer wall configured to be rotationally symmetric about a respective chamber axis; a respective chamber defined by the respective first end wall, the respective second end wall and the respective outer wall, the respective chamber having a respective gas inlet; a respective gas outlet; a respective liquid inlet; and a respective liquid outlet; and a respective set of vanes disposed within the respective chamber, the respective set of vanes configured to rotate about a respective vane axis parallel to, and spaced from, the respective chamber axis, wherein the further liquid ring compressor is configured to form a further liquid ring from the second working fluid moving between the respective liquid inlet and the respective liquid outlet, and to compress the first working fluid from the respective gas inlet to the respective gas outlet; a further gas connection between the respective gas outlet of the further liquid ring compressor and the respective gas inlet of the first liquid ring compressor; and a further liquid connection between the respective liquid outlet of the first liquid ring compressor and the respective liquid inlet of the further liquid ring compressor, the further liquid connection comprising a further flow regulator configured to permit a substantially unidirectional flow of the second working fluid, in use, from the first liquid ring compressor to the further liquid ring compressor.

[0088] In this way, a greater compression of the first working fluid may be achieved, as the first working fluid will first be compressed in the further liquid ring compressor and then subsequently compressed in the first liquid ring compressor and yet further compressed in the second liquid ring compressor. Similarly, a greater reduction in the pressure of the second working fluid may be achieved, as the second working fluid moves through the second liquid ring compressor, the first liquid ring compressor and the further liquid ring compressor in series. That is, the further liquid ring may be thought of as a “zeroth” liquid ring compressor in a series of liquid ring compressors.

[0089] It may be understood that the above description of the respective first end walls, second end walls, outer walls, chambers, gas inlets, gas outlets, liquid inlets, liquid outlets, sets of vanes, vane axes, chamber axes and liquid rings of the first and second liquid ring compressors may also apply to the respective first end wall, second end wall, outer wall, chamber, gas inlet, gas outlet, liquid inlet, liquid outlet, set of vanes, vane axis, chamber axis and liquid ring of the further liquid ring compressor.

[0090] The further gas connection may be of the same form as the gas connection. That is, the further gas connection may comprise the same features as the gas connection, arranged in a corresponding way, but between the gas outlet of the further liquid ring compressor and the gas inlet of the first liquid ring compressor, rather than between the gas outlet of the first liquid ring compressor and the gas inlet of the second liquid ring compressor.

[0091] Similarly, the further liquid connection and the further flow regulator may be of the same form as the liquid connection and the flow regulator, respectively. That is, the further liquid connection and the further flow regulator may comprise the same features as the liquid connection and the flow regulator, respectively, arranged in a corresponding way, but between the liquid outlet of the first liquid ring compressor and the liquid inlet of the further liquid ring compressor, rather than between the liquid outlet of the second liquid ring compressor and the liquid inlet of the first liquid ring compressor.

[0092] The further vane axis may be coincident with the first vane axis and / or the second vane axis. In particular, where the first and second vane axes are coincident, and the first and second sets of vanes are connected by a rotor having a rotor axis that is coincident with the first and second vane axes, the further vane axis may be coincident with the rotor axis and the further set of vanes may be connected to the rotor.

[0093] Where the first and second liquid ring compressors share a common chamber axis, and the simultaneous compressor-expander comprises a common outer wall comprising the first and second outer walls, the further chamber axis may also be coincident with the common chamber axis and the further outer wall may also form a part of the common outer wall. That is, the common outer wall may extend from the first end of the further liquid ring compressor to the second end of the second liquid ring compressor.

[0094] It may be understood that, in this way, the simultaneous compressor-expander may comprise any number of further liquid ring compressors, arranged such that the first working fluid is passed, in use, through each of the liquid ring compressors in series, ending at the second liquid ring compressor, and the second working fluid is passed, in use, through each of the liquid ring compressors in series in the opposite direction, starting at the second liquid ring compressor. For example, the simultaneous compressor-expander may comprise a total of five, eight, ten, twenty, thirty or more liquid ring compressors.

[0095] In a second aspect, the invention provides a symmetrical-axis compressor-expander comprising a first simultaneous compressor-expander according to the first aspect; a high pressure chamber in fluid communication with the respective chamber of the second liquid ring compressor via the respective gas outlet and respective liquid inlet of the second liquid ring compressor, the high pressure chamber having a high pressure gas outlet and a high pressure liquid inlet; and a second simultaneous compressor-expander according to the first aspect, the second simultaneous compressor-expander arranged symmetrically to the first simultaneous compressor-expander and such that the respective chamber of the second liquid ring compressor of the second simultaneous compressor-expander is in fluid communication with the high pressure chamber via the respective gas outlet and respective liquid inlet of the second liquid ring compressor of the second simultaneous compressor-expander.

[0096] In this way, the first working fluid may be compressed from either end of the symmetrical-axis compressor-expander to the high pressure chamber in the middle. This may reduce the force acting on the second end wall of the second liquid ring compressor, which may otherwise exist as a result of the difference between the pressure within the second chamber and the ambient atmospheric pressure. Additionally, a greater quantity of first working fluid may be compressed, and a greater quantity of second working fluid decompressed, in a given time as the first and second simultaneous compressor-expanders operate at the same time.

[0097] The high pressure chamber may be fully enclosed and sealed, so that fluid may only enter or leave the high pressure chamber through the second gas outlet of the first simultaneous compressor-expander, the second liquid inlet of the first simultaneous compressor-expander, the second gas outlet of the second simultaneous compressor-expander, the second liquid inlet of the second simultaneous compressor-expander, the high pressure gas outlet and / or the high pressure liquid inlet. The high pressure gas outlet may be or comprise a gas passageway, as described above, and / or the high pressure liquid inlet may be or comprise a liquid passageway, as described above.

[0098] The second simultaneous compressor-expander being arranged symmetrically to the first simultaneous compressor-expander may mean that the arrangement of liquid ring compressors in the second simultaneous compressor-expander is a reflection of the arrangement of liquid ring compressors in the first simultaneous compressor-expander in a plane passing through the high pressure chamber and perpendicular to the chamber axis of the second liquid ring compressor of the first simultaneous compressor-expander. In this context, the arrangement of liquid ring compressors may include the number of liquid ring compressors, the shapes and sizes of the liquid ring compressors and the relative positions of the liquid ring compressors, but may not include the precise configuration of vanes, inlets, outlets etc. in each liquid ring compressor.

[0099] In particular, the first working fluid may move through the first simultaneous compressor-expander, in use, in a first direction, from a first end of the symmetrical-axis compressor-expander towards a second end thereof, opposite the first end, and the first working fluid may movie through the second simultaneous compressor-expander, in use, in a second direction, from the second end of the symmetrical-axis compressor-expander towards the first end. For example, the second simultaneous compressor-expander may be structurally identical to the first simultaneous compressor-expander and simply rotated to face the opposite direction (i.e. so the respective sets of vanes in the second simultaneous compressor-expander rotate in an opposite rotational sense to the respective sets of vanes in the first simultaneous compressor-expander).

[0100] Alternatively, the respective sets of vanes in the second simultaneous compressor-expander may be configured to rotate in the same rotational sense as the respective sets of vanes in the first simultaneous compressor-expander.

[0101] As used herein, a rotational sense may mean either clockwise or anti-clockwise, as viewed in an axial direction from a first end of the symmetrical-axis compressor-expander towards the second end thereof.

[0102] The symmetrical-axis compressor-expander may comprise a symmetrical-axis rotor, extending through both the first and second simultaneous compressor-expanders, to which the respective sets of vanes of both simultaneous compressor-expanders are attached. In this way, the respective sets of vanes in both the first and second simultaneous compressor-expanders may be driven to rotate by a single symmetrical-axis rotor drive system.

[0103] In a third aspect, the invention provides a vapour compression refrigeration system comprising a simultaneous compressor-expander according to the first aspect; a condenser arranged to receive a refrigerant, in a first gaseous phase, from the respective gas outlet of the second liquid ring compressor, and configured to condense the refrigerant such that the refrigerant undergoes a phase change to a first liquid phase, the condenser further arranged to deliver the refrigerant in the first liquid phase to the respective liquid inlet of the second liquid ring compressor; and an evaporator arranged to receive the refrigerant, in a second liquid phase, from the respective liquid outlet of the first liquid ring compressor, and configured to evaporate the refrigerant, using heat from an environment to be cooled, such that the refrigerant undergoes a phase change to a second gaseous phase, the evaporator further configured to deliver the refrigerant in the second gaseous phase to the respective gas inlet of the first liquid ring compressor.

[0104] In this way, the simultaneous compressor-expander may act as both the compressor and the expansion valve in a conventional vapour compression cycle, thereby facilitating the transfer of heat between the gaseous refrigerant being compressed and the liquid refrigerant being decompressed.

[0105] The refrigerant may have different thermodynamic properties when in the first gaseous phase, compared with when it is in the second gaseous phase. For example, the refrigerant, when in the first gaseous phase, may have a higher temperature and a higher pressure than when it is in the second gaseous phase. Similarly, the refrigerant may have different thermodynamic properties when in the first liquid phase, compared with when it is in the second liquid phase. For example, the refrigerant, when in the first liquid phase, may have a higher temperature and a higher pressure than when it is in the second liquid phase.

[0106] The condenser being arranged to receive the refrigerant from the second gas outlet and deliver it to the second liquid inlet may mean that the condenser is arranged to receive the refrigerant from the second gas outlet and / or to deliver it to the second liquid inlet via one or more intermediate component parts of the system. In particular, the condenser may be arranged to receive the refrigerant from the second gas outlet via a high pressure chamber and a high pressure outlet, and / or to deliver the refrigerant to the second liquid inlet via a high pressure inlet and a high pressure chamber. This may be the case, for example, when the simultaneous compressor-expander forms a part of a symmetrical-axis compressor expander, according to the second aspect.

[0107] Similarly, the evaporator being arranged to receive the refrigerant from the first liquid outlet and deliver it to the first gas inlet may mean that the evaporator is arranged to receive the refrigerant from the first liquid outlet and / or to deliver it to the first gas inlet via one or more intermediate component parts of the system. In particular, where the simultaneous compressor-expander comprises one or more further liquid ring compressors, the evaporator may be arranged to receive the refrigerant from the first liquid outlet via the respective liquid inlets, chambers and liquid outlets of each of the further liquid ring compressors, and / or to deliver the refrigerant to the first gas inlet via the respective gas inlets, chambers and gas outlets of each of the further liquid ring compressors.

[0108] The condenser may be configured to condense the refrigerant in any appropriate way, as understood in the art. In particular, the condenser may be configured to condense the refrigerant by transferring heat from the refrigerant to an external environment. An external environment may be any environment external to (i.e. not forming part of) the refrigeration system.

[0109] The evaporator may be configured to evaporate the refrigerant using heat from an environment to be cooled in any appropriate way, as understood in the art. The environment to be cooled may be, for example, a room within a building, the inside of a vehicle or a cavity within a refrigerator.

[0110] In a fourth aspect, the invention provides a method of simultaneously compressing a first working fluid in a gaseous phase and decompressing a second working fluid in a liquid phase, the method comprising the steps of providing the simultaneous compressor-expander according to the first aspect; supplying the first working fluid to the respective gas inlet of the first liquid ring compressor; supplying the second working fluid to the respective liquid inlet of the second liquid ring compressor; and operating the simultaneous compressor-expander.

[0111] Where the simultaneous compressor-expander comprises one or more further liquid ring compressors, supplying the first working fluid to the first gas inlet may involve supplying the first working fluid to the respective gas inlet of the, or one of the, further liquid ring compressors, such that the first working fluid is supplied to the first gas inlet via the, or each of the, further liquid ring compressors.

[0112] Where the simultaneous compressor-expander comprises a high pressure chamber, supplying the second working fluid to the second liquid inlet may involve supplying the second working fluid to the high pressure chamber, for example via a high pressure inlet, such that the second working fluid is supplied to the second liquid inlet via the high pressure chamber.

[0113] Operating the simultaneous compressor-expander may involve causing the respective sets of vanes of the first and second (and any further) liquid ring compressors to rotate about their respective vane axes. Operating the simultaneous compressor-expander may additionally involve causing the respective outer walls of the first and second (and any further) chambers to rotate about their respective chamber axes.

[0114] Operating the simultaneous compressor-expander may involve collecting the compressed first working fluid exiting the simultaneous compressor-expander via the second gas outlet and / or collecting the decompressed second working fluid exiting the simultaneous compressor-expander via the first liquid outlet.BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0115] The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.

[0116] FIG. 1 is a schematic illustration of a conventional vapour-compression cycle.

[0117] FIG. 2 is a schematic illustration of a modified refrigeration cycle utilising the present invention.

[0118] FIG. 3 is a schematic cross-sectional view of a simultaneous compressor-expander comprising two liquid ring compressors.

[0119] FIG. 4 is a cross-sectional view of a simultaneous compressor-expander.

[0120] FIG. 5 is a perspective view of a part of a liquid ring compressor used in a simultaneous compressor-expander.

[0121] FIG. 6 is a schematic cross-sectional view of a simultaneous compressor-expander comprising five liquid ring compressors.

[0122] FIG. 7 is a schematic cross-sectional view of a symmetric-axis compressor-expander.

[0123] FIG. 8 is a schematic diagram of a refrigeration system based around the symmetric-axis compressor-expander of FIG. 7.DETAILED DESCRIPTION

[0124] The present invention will be described with respect to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. Each drawing may not include all of the features of the invention and therefore should not necessarily be considered to be an embodiment of the invention. In the drawings, the size of some of the elements may be exaggerated and not drawn to scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

[0125] Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that operation is capable in other sequences than described or illustrated herein. Likewise, method steps described or claimed in a particular sequence may be understood to operate in a different sequence.

[0126] Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that operation is capable in other orientations than described or illustrated herein.

[0127] It is to be noticed that the term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a device comprising means A and B” should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

[0128] Similarly, it is to be noticed that the term “connected”, used in the description, should not be interpreted as being restricted to direct connections only. Thus, the scope of the expression “a device A connected to a device B” should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means. “Connected” may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet still co-operate or interact with each other. For instance, wireless connectivity is contemplated.

[0129] Reference throughout this specification to “an embodiment” or “an aspect” means that a particular feature, structure or characteristic described in connection with the embodiment or aspect is included in at least one embodiment or aspect of the present invention. Thus, appearances of the phrases “in one embodiment”, “in an embodiment”, or “in an aspect” in various places throughout this specification are not necessarily all referring to the same embodiment or aspect, but may refer to different embodiments or aspects. Furthermore, the particular features, structures or characteristics of any one embodiment or aspect of the invention may be combined in any suitable manner with any other particular feature, structure or characteristic of another embodiment or aspect of the invention, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments or aspects.

[0130] Similarly, it should be appreciated that in the description various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Moreover, the description of any individual drawing or aspect should not necessarily be considered to be an embodiment of the invention. Rather, as the following claims reflect, inventive aspects lie in fewer than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

[0131] Furthermore, while some embodiments described herein include some features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form yet further embodiments, as will be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0132] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practised without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

[0133] In the discussion of the invention, unless stated to the contrary, the disclosure of alternative values for the upper or lower limit of the permitted range of a parameter, coupled with an indication that one of said values is more highly preferred than the other, is to be construed as an implied statement that each intermediate value of said parameter, lying between the more preferred and the less preferred of said alternatives, is itself preferred to said less preferred value and also to each value lying between said less preferred value and said intermediate value.

[0134] The use of the term “at least one” may mean only one in certain circumstances. The use of the term “any” may mean “all” and / or “each” in certain circumstances.

[0135] The principles of the invention will now be described by a detailed description of at least one drawing relating to exemplary features. It is clear that other arrangements can be configured according to the knowledge of persons skilled in the art without departing from the underlying concept or technical teaching, the invention being limited only by the terms of the appended claims.

[0136] FIG. 1 is a schematic illustration of a conventional vapour-compression cycle, as used in prior art systems. The system comprises a compressor 20, a condenser 40, a throttle valve 60 and an evaporator 80 through which a working fluid circulates, as indicated by the arrows 10, 30, 50, 70.

[0137] The working fluid 10 entering the compressor 20 is in a gaseous phase at a relatively low pressure and temperature. At the compressor 20, work is input into the system (indicated by the arrow 2) to compress the working fluid, thereby raising both its pressure and temperature. The high pressure, high temperature gaseous working fluid 30 is then passed to the condenser 40 where heat is transferred from the working fluid to the surrounding environment (indicated by arrow 4). As heat 4 is transferred away from the working fluid, it cools at roughly constant pressure until it reaches its boiling point, and then undergoes a phase change to a liquid phase. The resulting high temperature, high pressure liquid working fluid 50 is then passed to the throttle valve 60, where it is subjected to a rapid drop in pressure, resulting in a partial flash evaporation and a drop in temperature. The low pressure, low temperature working fluid 70 leaving the throttle valve 60 comprises a mixture of liquid and gas. In the evaporator 80, heat (indicated by arrow 8) from a region to be cooled is used to vaporise the liquid so that the working fluid leaves the evaporator 80 entirely in a gaseous phase at a low pressure and temperature, ready to start the cycle again.

[0138] It is the transfer of heat 8 from the region to be cooled to the working fluid in the evaporator that results in the desired refrigeration effect.

[0139] FIG. 2 is a schematic illustration of a modified refrigeration cycle utilising the present invention. The system still comprises a conventional condenser 40 and evaporator 80. However, the compressor 20 and throttle valve 60 have been replaced with a simultaneous compressor-expander 90. The simultaneous compressor-expander 90 functions simultaneously as a compressor 25 for compressing the low pressure, low temperature gaseous working fluid 10 into the high pressure, high temperature vaporous working fluid 30, and an expander 65 for decompressing the high pressure, high temperature liquid working fluid 50 into a low pressure, low temperature liquid working fluid 75. Unlike the working fluid 70 leaving the throttle valve 60 in the conventional vapour-compression cycle depicted in FIG. 1, the working fluid 75 leaving the expander 65 is in a fully liquid phase.

[0140] Within the simultaneous compressor-expander 90, heat 6 is exchanged between the liquid working fluid passing through the expander 65 in one direction and the gaseous working fluid passing through the compressor 25 in the opposite direction.

[0141] FIG. 3 shows a schematic cross-sectional view of a simultaneous compressor-expander comprising two liquid ring compressors, including a first liquid ring compressor 100 and a second liquid ring compressor 200. The first liquid ring compressor 100 comprises a first chamber 150 and the second liquid ring compressor 200 comprises a second chamber 250, the second chamber 250 having a smaller volume than the first chamber 150. In the example shown, both the first and second chambers 150, 250 are cylindrical in shape and share a common axis of rotational symmetry 390, and the second chamber 250 has a smaller axial extent (i.e. extent in a direction parallel to axis 390) than the first chamber 150, such that the volume of the second chamber 250 is smaller than that of the first chamber 150. However, other shapes are contemplated for the first and second chambers 150, 250; as are first and second chambers 150, 250 that do not share a common axis of rotational symmetry; and as are alternative ways of making the volume of the second chamber 250 smaller than that of the first chamber 150.

[0142] The first liquid ring compressor 100 has a first gas inlet 110, a first gas outlet 120, a first liquid inlet 130 and a first liquid outlet 140, the first liquid inlet 130 and first liquid outlet 140 being located at a greater distance from the axis 390 than the first gas inlet 110 and the first gas outlet 120. Similarly, the second liquid ring compressor 200 has a second gas inlet 210, a second gas outlet 220, a second liquid inlet 230 and a second liquid outlet 240, the second liquid inlet 230 and second liquid outlet 240 being located at a greater distance from the axis 390 than the second gas inlet 210 and second gas outlet 220. While the first and second liquid ring compressors are shown as each having a single gas inlet, a single gas outlet, a single liquid inlet and a single liquid outlet, it is to be appreciated that each of the liquid ring compressors may have multiple gas inlets, multiple gas outlets, multiple liquid inlets and / or multiple liquid outlets.

[0143] A gas connection 300 is arranged between the first gas outlet 120 and the second gas inlet 210 to provide a closed flow path for gas between the first chamber 150 and the second chamber 250. Additionally, a liquid connection 350 is arranged between the second liquid outlet 240 and the first liquid inlet 130 to provide a closed flow path for liquid between the second chamber 250 and the first chamber 150. The gas connection 300 and the liquid connection 350 are depicted schematically as simple pipes; however, in reality, they may take other forms, as depicted for example in FIG. 4.

[0144] In use, a first liquid ring 160 is formed from liquid within the first chamber 150 and a second liquid ring 260 is formed from liquid within the second chamber 250. Each of the first and second liquid rings 160, 260 has the shape of an annular prism and is rotationally symmetric about axis 390. It is to be understood that the first and second liquid rings 160, 260 are formed by causing liquid to rotate rapidly within the first and second chambers 150, 250 respectively. However, for the sake of clarity, no means for causing the liquid to rotate are shown in FIG. 3. It is also to be understood that a set of vanes (which may be the means, or a means, for causing the liquid to rotate) is present within each of the first and second chambers 150, 250, but these have also been omitted for the sake of clarity.

[0145] In use, relatively cool, low pressure gas 310 enters the first liquid ring compressor 100 via the first gas inlet 110. The gas is compressed in the first liquid ring compressor 100, and exits via the first gas outlet 120. The gas 320 exiting the first gas outlet 120 is at a higher pressure and temperature than the gas 310 entering the first gas inlet. The gas 320 next passes through the gas connection 300 and enters the second liquid ring compressor 200, via the second gas inlet 210, where it is further compressed. The gas 330 exiting the second liquid ring compressor 200, via the second gas outlet 220, is thus at an even higher pressure and temperature than the gas 320 entering the second gas inlet 210.

[0146] At the same time, relatively hot, high pressure liquid 360 enters the second liquid ring compressor 200, via the second liquid inlet 230, where it forms part of the second liquid ring 260. The gas and liquid in the second liquid ring compressor 200 are in direct contact with one another and will therefore approach thermal equilibrium by exchanging heat.

[0147] As liquid enters the second liquid ring compressor 200, some of the liquid in the second liquid ring 260 flows out of the second liquid ring compressor 200 via the second liquid outlet 240. This liquid 370 passes through the liquid connection 350 and enters the first liquid ring compressor 100, via the first liquid inlet 130, where it forms part of the first liquid ring 160. As this happens, some of the liquid in the first liquid ring 160 flows out of the first liquid ring compressor 100 via the first liquid outlet 140.

[0148] The first liquid ring compressor 100 is at a lower pressure than the second liquid ring compressor 200 and so the liquid experiences a reduction in pressure as it moves from the second liquid ring compressor 200 to the first liquid ring compressor 100. Furthermore, the temperature of the gas in the first liquid ring compressor 100 is lower than the temperature of the gas in the second liquid ring compressor and so the liquid entering the first liquid ring compressor 100 also decreases in temperature as it transfers heat to the gas. Consequently, the liquid 380 exiting the first liquid outlet 140 is at a lower pressure and temperature than the liquid entering the second liquid inlet 230.

[0149] FIG. 4 is a cross-sectional view of an example simultaneous compressor-expander comprising a first liquid ring compressor 500 and a second liquid ring compressor 600. The first liquid ring compressor 500 comprises a first chamber 550 in which a first liquid ring 560 is formed, in use, and the second liquid ring compressor 600 comprises a second chamber 650 in which a second liquid ring 660 is formed, in use. The first and second chambers 550, 650 are both cylindrical in shape and share a common axis of rotational symmetry 490.

[0150] The first and second chambers 550, 650 are bounded around their respective circumferential edges by a common outer wall 410, which forms a cylindrical tube, extending from a first end (left hand side of the figure) of the first liquid ring compressor 500 to a second end (right hand side of the figure) of the second liquid ring compressor 600, and being rotationally symmetric about axis 490. The common outer wall 410 may be fixed so that it cannot move, or may be rotatable about axis 490.

[0151] The first chamber 550 is bounded at its axial ends by a first chamber first end wall 570 and a first chamber second end wall 580. Similarly, the second chamber 650 is bounded at its axial ends by a second chamber first end wall 670 and a second chamber second end wall 680. Each of the first chamber first end wall 570, the first chamber second end wall 580, the second chamber first end wall 670 and the second chamber second end wall 680 are formed from circular plates mounted on a common rotor 400 such that the rotational axis 480 of the common rotor 400 passes through their respective centres. The rotational axis 480 of the common rotor 400 is offset from the axis 490 of rotational symmetry of the first and second chamber 550, 650.

[0152] It is to be understood that a first set of vanes (not shown) is present in the first chamber 550, mounted on the common rotor 400 and configured to rotate therewith. Similarly, it is to be appreciated that a corresponding second set of vanes is present within the second chamber 650. An example set of vanes are depicted in FIG. 5.

[0153] The first chamber 550 and the second chamber 650 are axially spaced apart such that an intermediate chamber 450 is formed between them, bounded by the first chamber second end wall 580, the second chamber first end wall 670 and the common outer wall 410.

[0154] A first gas inlet 510 is formed in the first chamber first end wall 570 and a first gas outlet 520 is formed in the first chamber second end wall 580. The first gas inlet 510 and the first gas outlet 520 are formed at different rotational positions about the rotor axis 480 so that, in the position shown in FIG. 4, the first gas inlet 510 is “open” to allow gas to enter the first chamber 550 while the first gas outlet 520 is submerged in the first liquid ring 560 (i.e. it is entirely below the surface 565 of the first liquid ring 560). Consequently, the first gas outlet 520 is effectively “closed” and gas cannot leave the first chamber 550 therethrough. As the first chamber first end wall 570 and the first chamber second end wall 580 rotate with the common rotor 400, the first gas inlet and outlet 510, 520 will periodically be submerged and emerged from the liquid ring, thereby opening and closing. As they are located at different rotational positions about the rotor axis 480, they will open and close at different times. In this way, gas may enter the first chamber 550 when the first gas inlet 510 is open and the first gas outlet is closed; be sealed and compressed within the first chamber 550, or a sub-chamber thereof (e.g. formed between vanes of the first vane set), while both the first gas inlet 510 and the first gas outlet 520 are closed; and then exit the first chamber 550 when the first gas outlet 520 is open and the first gas inlet 510 is closed.

[0155] It is to be appreciated that, while the first gas inlet 510 and the first gas outlet 520 are shown as being rotationally spaced from one another by 180 degrees about the rotor axis 480, different rotational spacings may be used. In particular, the first gas inlet 510 shown in FIG. 4 may be one of several first gas inlets arranged at different rotational positions about the rotor axis 480, and the first gas outlet 520 shown in FIG. 4 may be one of several first gas outlets arranged at different rotational positions about the rotor axis 480.

[0156] A first liquid inlet 530 is formed around the outside of the first chamber second end wall 580, between an outer edge thereof and the common outer wall 410. Similarly, a first liquid outlet 540 is formed around the outside of the first chamber first end wall 570, between an outer edge thereof and the common outer wall 410. As the first chamber first end wall 570 and the first chamber second end wall 580 are centred on the rotor axis 480, which is offset from the axis 490 of rotational symmetry of the first chamber 550, the distance between the outer edge of said end walls 570, 580 and the common outer wall 410 is different at different angles as measured around the rotor axis 480. However, in use, the maximum distance between the outer edges of the first chamber first and second end walls 570, 580 and the common outer wall is less than the liquid ring depth 562 of the first liquid ring 560, such that no gas may enter or leave the first chamber 550 via the first liquid inlet 530 or the first liquid outlet 540.

[0157] At the second liquid ring compressor 600, a second gas inlet 610 is formed in the second chamber first end wall 670 and a second gas outlet 620 is formed in the second chamber second end wall 680. In the position show, the second gas inlet is “closed” while the second gas outlet 620 is “open”. The operation of the second liquid ring compressor 600 and the opening / closing of the second gas inlet and outlet 610, 620 take place in the same way as in the first liquid ring compressor500. A second liquid inlet 630 and a second liquid outlet 640 are formed around the outside of the second chamber second end wall 680 and the second chamber first end wall 670, respectively.

[0158] As described above, an intermediate chamber 450 is formed between the first and second liquid ring compressors 500, 600. An annular baffle 420 projects inwardly from the outer wall 410 into this intermediate chamber 450. A first intermediate liquid ring 460 is formed within the intermediate chamber 450, between the first chamber second end wall 580 and the baffle 420, and is in fluid communication with the first liquid ring 560 via the first liquid inlet 530. A second intermediate liquid ring 470 is also formed within the intermediate chamber 450, between the second chamber first end wall 670 and the baffle 420, and is in fluid communication with the second liquid ring 660 via the second liquid outlet 640.

[0159] The baffle 420 extends inwardly from the common outer wall 410 to a baffle edge such that the (radial) distance between the baffle edge and the common outer wall 410 is greater than the liquid ring depths of the first and second intermediate liquid rings 460, 470 (which are shown in FIG. 4 as being equal to the liquid ring depth 562 of the first liquid ring 560). In this way, liquid may be prevented from moving between the first and second intermediate liquid rings 460, 470 by moving around the baffle edge.

[0160] Rather, liquid may move between the first and second intermediate liquid rings 460, 470 through one or more baffle openings 430. In use, there is a pressure gradient from the second intermediate liquid ring 470 to the first intermediate liquid ring 460 so that liquid moves from the second intermediate liquid ring 470 to the first intermediate liquid ring 460 through the baffle opening(s) 430 and no liquid moves through the baffle opening(s) 430 from the first intermediate liquid ring 460 to the second liquid ring 470. Consequently, there is a unidirectional flow of liquid from the second liquid ring compressor 600 to the first liquid ring compressor 500.

[0161] A gas connection comprising a flexible tube 440 is connected between the first gas outlet 520 and the second gas inlet 610. In use, the flexible tube 440 permits the flow of gas from the first liquid ring compressor 500 to the second liquid ring compressor 600, around the baffle edge of the baffle 420, when the first gas outlet 520 and the second gas inlet 610 are “open”.

[0162] As no route exists for gas to move, in use, between the intermediate chamber 450 and either of the first chamber 550 or the second chamber 650, a pressure relief duct or valve (not shown) may be present in the intermediate chamber 450 to prevent the formation of a vacuum or a gas bubble therein.

[0163] It is to be appreciated that one or more further liquid ring compressors may be connected in a similar manner before (i.e. to the left of) the first liquid ring compressor 500 and / or after (i.e. to the right of) the second liquid ring compressor 600. For example, the first and second liquid ring compressors 500, 600 may form part of a series of 3, 5, 8, 10, 20, 30 or more liquid ring compressors, each liquid ring compressor connected separated from the adjacent liquid ring compressor(s) by a respective intermediate chamber, respective intermediate liquid rings and a respective baffle, in the manner described above with reference to the first and second liquid ring compressors 500, 600. The number of liquid ring compressors in the series may be selected so as to provide a desired overall compression ratio.

[0164] Alternatively, one or more further pairs of liquid ring compressors may be connected before the first liquid ring compressor 500 and / or after the second liquid ring compressor 600, each further pair of liquid ring compressors being separated by a respective intermediate chamber, respective intermediate liquid rings and a respective baffle, in the manner described with reference to the first and second liquid ring compressors 500, 600, but connected directly to the adjacent pair(s) of liquid ring compressors without an intermediate chamber, intermediate liquid rings or baffle. For example, a further pair of liquid ring compressors may be connected directly before the first liquid ring compressor 500 such that the first chamber first end wall 570 simultaneously functions as a second end wall of a second chamber of the further pair of liquid ring compressors; the first gas inlet 510 functions as a second gas outlet of the further pair of liquid ring compressors; and the first liquid outlet 540 functions as a second liquid inlet of the further pair of liquid ring compressors. In this way, the first and second liquid ring compressors 500, 600 may form part of a series of liquid ring compressors wherein an intermediate chamber, intermediate liquid rings and a baffle are present between every other liquid ring compressor in the series.

[0165] FIG. 5 is a perspective view of a part of a liquid ring compressor used in a simultaneous compressor-expander, such as the first liquid ring compressor 500 or the second liquid ring compressor 600 shown in FIG. 4. The part of the liquid ring compressor shown includes a first end wall 770 and a second end wall 780, which define a chamber therebetween. The first and second end walls 770, 780 are both mounted on a rotor 800. It is to be understood that the liquid ring compressor additionally comprises at least an outer wall within which a liquid ring is formed, in use. The surface of the liquid ring is shown by dashed lines 760.

[0166] Mounted on the rotor 800 between the first and second end walls 770, 780 is a set of vanes including a first vane 790A, a second vane 790B and a third vane 790C. A fourth vane is also present but is obscured from view. While a set of four vanes is described herein, it is to be appreciated that any number of vanes may be used.

[0167] Each vane 790A, 790B, 790C extends axially (i.e. in a direction parallel to the rotational axis of the rotor 800) from the first end wall 770 to the second end wall, and extends radially outwards from the rotor 800 to a respective vane tip. The radial extent of each vane is great enough that its respective vane tip remains submerged in the liquid ring 760 at all times as the set of vanes rotates about the rotational axis of the rotor 800. Consequently, the chamber defined between the first and second end walls 770, 780 is sub-divided into four compression chambers. A first compression chamber is visible, bounded by the first and second end walls 770, 780, the first and second vanes 790A, 790B and the liquid ring 760, and a second compression chamber is also visible, bounded by the first and second end walls 770, 780, the second and third vanes 790B, 790C and the liquid ring 760.

[0168] A first gas inlet 710A in the first end wall 770 is in fluid communication with the first compression chamber and a second gas inlet 710B in the first end wall770 is in fluid communication with the second compression chamber. It is to be understood that third and fourth gas inlets are also present in the first end wall 770, being in fluid communication with third and fourth compression chambers respectively, but that they are not visible in the view shown.

[0169] A first gas outlet 720A in the second end wall 780 is in fluid communication with the first compression chamber and a second gas outlet 720B in the second end wall 780 is in fluid communication with the second compression chamber. As can be seen, a third gas outlet 720C and a fourth gas outlet 720D, being in fluid communication with the third and fourth compression chambers respectively, are also present.

[0170] The first gas inlet 710A is positioned closer to the first vane 790A than the second vane 790B, while the first gas outlet 720A is positioned closer to the second vane 790B than the first vane 790A. Consequently, when rotated in the direction indicated by the arrow 805, the first gas outlet 720A is submerged in the liquid ring 760 before the first gas inlet 710A. Similarly, the second gas inlet 710B is positioned closer to the second vane 790B than the third vane 790C, while the second gas outlet 720B is positioned closer to the third vane 790C than the second vane 790B. The opening and closing of the gas inlets and outlets associated with a compression chamber at different times enables the liquid ring compressor to operate as described above with reference to FIG. 4.

[0171] FIG. 6 is a schematic cross-sectional view of a simultaneous compressor-expander 1000 comprising five liquid ring compressors 1100, 1200, 1300, 1400, 1500 arranged in series. As shown, each liquid ring compressor in the series has a smaller volume than the previous one, with the first liquid ring compressor 1100 having the greatest volume and the fifth liquid ring compressor 1500 having the smallest volume.

[0172] The simultaneous compressor-expander 1000 additionally includes a high pressure chamber 1600 connected in the series after the fifth liquid ring compressor 1500. The high pressure chamber 1600 is not shown to scale in FIG. 6 and may have a volume similar to, or smaller than, than of the fifth liquid ring compressor 1500. In use, the high pressure chamber 1600 may be used to collect compressed gas from, and supply high pressure liquid to, the fifth liquid ring compressor 1500.

[0173] The liquid ring compressors 1100, 1200, 1300, 1400, 1500 and the high pressure chamber 1600 all share a common outer wall formed by a canister 1010. Bearings 1020 enable the canister 1010 to rotate, or be rotated, about its axis of rotational symmetry.

[0174] The liquid ring compressors 1100, 1200, 1300, 1400, 1500 also share a common rotor 1050, which is driven to rotate by driving means 1060, which may include a motor. Two concentric passageways, an inner passageway 1070 and an outer passageway 1080, are formed within the shaft of the rotor 1050. The inner passageway 1070 has an inner passageway opening 1075 into the high pressure chamber 1600 and the outer passageway 1080 has an outer passageway opening 1085 into the high pressure chamber 1600.

[0175] In use, cool, low pressure gas is supplied to the first liquid ring compressor 1100 (arrow 1710). The gas is compressed in each of the liquid ring compressors 1100, 1200, 1300, 1400, 1500 in turn, increasing in temperature and pressure, until it reaches the high pressure chamber 1600. The hot, compressed gas then exits the high pressure chamber 1600 via the outer passageway opening 1085 (arrow 1720) and passes along the outer passageway to be collected at, or towards the first end of the rotor 1050 (arrow 1730). At the same time, hot, high pressure liquid is directed into the inner passageway (arrow 1750) at, or towards, a first end of the rotor 1050, opposite the end at which it engages with the driving means 1060. The hot, high pressure liquid passes along the inner passageway 1070 and into the high pressure chamber 1600 via the inner passageway opening 1075 (arrow 1760). From the high pressure chamber 1600, it passes into the fifth liquid ring compressor 1500, and subsequently passes through the other four liquid ring compressors 1400, 1300, 1200, 1100 in turn, in the opposite direction to the gas, undergoing a reduction in pressure and temperature as it does so. The cool liquid then leaves the first liquid ring compressor 1100 (arrow 1770) where it may be collected for onward use.

[0176] It is to be appreciated that the simultaneous compressor-expander 1000 may alternatively be used by providing the hot, high pressure liquid to the high pressure chamber 1600 via the outer passageway 1080, and collecting the hot compressed gas from the high pressure chamber 1600 via the inner passageway 1070.

[0177] FIG. 7 is a schematic cross-sectional view of a symmetric-axis compressor-expander 2000. The symmetric-axis compressor-expander 2000 comprises a first simultaneous compressor expander, similar to the simultaneous compressor-expander 1000 shown in FIG. 6, comprising a first set of five liquid ring compressors 2100A, 2200A, 2300A, 2400A, 2500A arranged in series, and a high pressure chamber 2600. However, the symmetric-axis compressor-expander 2000 additionally includes a second simultaneous compressor-expander, comprising a second set of liquid ring compressors 2100B, 2200B, 2300B, 2400B, 2500B, arranged symmetrically to the first set of liquid ring compressors 2100A, 2200A, 2300A, 2400A, 2500A. With this arrangement of liquid ring compressors, the symmetric-axis compressor-expander 2000 is configured to compress gas from both axial ends thereof to the high pressure chamber 2600 in the middle, while simultaneously decompressing liquid from the high pressure chamber 2600 to either axial end.

[0178] All of the liquid ring compressors and the high pressure chamber 2600 share a common outer wall, formed by a canister 2010, and a common rotor 2050, which is driven to rotate by driving means 2060. Two concentric passageways 2070, 2080 are formed within a portion of the shaft of the rotor 2050, and form separate flow paths between the high pressure chamber 2600 and a first end of the rotor 2050, opposite the end at which it engages with the driving means 2060. In use, one of the passageways 2070, 2080 may be used to deliver hot, high pressure liquid to the high pressure chamber 2600 and the other may be used to convey hot compressed gas away from the high pressure chamber 2600, to be collected or received at or near the first end of the rotor 2050.

[0179] FIG. 8 is a schematic diagram showing a refrigeration system based around the symmetric-axis compressor-expander 2000 shown in detail inFIG. 7. In addition to the symmetric-axis compressor-expander 2000, the system includes a condenser 3000 and an evaporator 4000. While the system is shown using the symmetric-axis compressor-expander 2000, it is to be understood that it could alternatively use a single simultaneous compressor-expander, such as the simultaneous compressor-expander 1000 shown in FIG. 6.

[0180] The movement of refrigerant around the system is shown by arrows 900-990, with solid arrows used to indicate the flow of refrigerant in a liquid phase and broken arrows used to indicate the flow of refrigerant in a gaseous phase.

[0181] Refrigerant initially enters the symmetric-axis compressor-expander 2000 at either end (arrows 900) as a cool, low pressure gas. The gaseous refrigerant is compressed towards the high pressure chamber at the middle of the symmetric-axis compressor-expander 2000. The hot, high pressure gaseous refrigerant exits the high pressure chamber via an outer passageway within the rotor of the symmetric-axis compressor-expander 2000 (arrows 910, 920) before passing along a condenser feed pipe 3100 (arrow 930) to the condenser 3000. A partition 2700 and seal 2750 separates the hot, high pressure gas from the cool, low pressure gas entering the symmetric-axis compressor-expander 2000 and prevents the hot, high pressure gas from being drawn back into the symmetric-axis compressor-expander 2000.

[0182] The refrigerant leaves the condenser 3000 as a hot, high pressure liquid and passes through a condenser return pipe 3200 (arrow 940) to be fed back into the symmetric-axis compressor-expander 2000 via an inner passageway within the rotor thereof (arrow 950). The hot, high pressure liquid refrigerant is delivered to the high pressure chamber in the middle of the symmetric-axis compressor-expander 2000 (arrows 960) and is decompressed as it moves through the symmetric-axis compressor-expander 2000 towards either end thereof. The refrigerant leaves the symmetric-axis compressor-expander 2000 as a cool, low pressure liquid (arrows 970) and is collected and fed to the evaporator 4000 via an evaporator feed pipe 4100 (arrow 980). Finally, the cool, low pressure gaseous refrigerant leaving the evaporator 4000 is returned to the start of the cycle via an evaporator return pipe 4200 (arrow 990).

Claims

1. A simultaneous compressor-expander for simultaneously compressing a first working fluid in a gaseous phase and decompressing a second working fluid in a liquid phase, the simultaneous compressor-expander comprising:a first liquid ring compressor and a second liquid ring compressor, each of the first and second liquid ring compressors comprising:a respective first end wall at a respective first end thereof;a respective second end wall at a respective second end thereof, the respective second end opposite the respective first end;a respective outer wall extending from the respective first end to the respective second end, the respective outer wall configured to be rotationally symmetric about a respective chamber axis;a respective chamber defined by the respective first end wall, the respective second end wall and the respective outer wall, the respective chamber having:a respective gas inlet;a respective gas outlet;a respective liquid inlet; anda respective liquid outlet; anda respective set of vanes disposed within the respective chamber, the respective set of vanes configured to rotate about a respective vane axis parallel to, and spaced from, the respective chamber axis,wherein each respective liquid ring compressor is configured to form a respective liquid ring from a second working fluid moving between the respective liquid inlet and the respective liquid outlet, and to compress a first working fluid in a gaseous phase from the respective gas inlet to the respective gas outlet;a gas connection between the respective gas outlet of the first liquid ring compressor and the respective gas inlet of the second liquid ring compressor, such that the first working fluid is moved, in use, through the first liquid ring compressor and the second liquid ring compressor in series; anda liquid connection between the respective liquid outlet of the second liquid ring compressor and the respective liquid inlet of the first liquid ring compressor, the liquid connection comprising a flow regulator configured to permit a substantially unidirectional flow of the second working fluid, in use, from the second liquid ring compressor to the first liquid ring compressor.

2. The simultaneous compressor-expander according to claim 1, wherein the respective vane axis of the first liquid ring compressor is coincident with the respective vane axis of the second liquid ring compressor, and wherein the respective set of vanes of the first liquid ring compressor and the respective set of vanes of the second liquid ring compressor are connected by a common rotor extending along the respective vane axis of the first liquid ring compressor from the respective first end of the first liquid ring compressor to the respective second end of the second liquid ring compressor.

3. The simultaneous compressor-expander according to claim 2, wherein the common rotor comprises:a gas passageway in fluid communication with the respective chamber of the second liquid ring compressor via a gas passageway opening; anda liquid passageway, separate from the gas passageway and in fluid communication with the respective chamber of the second liquid ring compressor via a liquid passageway opening.

4. The simultaneous compressor-expander according to claim 1, wherein the respective chamber axis of the first liquid ring compressor is coincident with the respective chamber axis of the second liquid ring compressor, and wherein the respective outer walls of the first liquid ring compressor and the second liquid ring compressor form part of a common outer wall, the common outer wall extending from the respective first end of the first liquid ring compressor to the respective second end to the second liquid ring compressor.

5. The simultaneous compressor-expander according to claim 4, wherein the liquid connection comprises a first intermediate liquid ring and a second intermediate liquid ring, the first and second intermediate liquid rings formed within an intermediate chamber between the first liquid ring compressor and the second liquid ring compressor, the intermediate chamber bounded by the common outer wall, the second end wall of the first liquid ring compressor and the first end wall of the second liquid ring compressor, wherein:the first intermediate liquid ring is in fluid communication with the respective liquid ring of the first liquid ring compressor via the respective liquid inlet of the first liquid ring compressor;the second intermediate liquid ring is in fluid communication with the respective liquid ring of the second liquid ring compressor via the respective liquid outlet of the second liquid ring compressor; andthe first and second intermediate liquid rings are separated by the flow regulator.

6. The simultaneous compressor-expander according to claim 4, wherein the flow regulator comprises a baffle, extending radially inwards from an inner surface of the common outer wall between the first liquid ring compressor and the second liquid ring compressor.

7. The simultaneous compressor-expander according to claim 6, wherein the baffle has a baffle height greater than the respective liquid ring depths of the first and second intermediate liquid rings, and wherein the baffle comprises at least one baffle opening configured to permit the flow of liquid therethrough.

8. The simultaneous compressor-expander according to claims 5, wherein the intermediate chamber comprises a pressure relief duct.

9. The simultaneous compressor-expander according to claim 1, additionally comprising:a further liquid ring compressor, the further liquid ring compressor comprising:a respective first end wall at a respective first end thereof;a respective second end wall at a respective second end thereof, the respective second end opposite the respective first end;a respective outer wall extending from the respective first end to the respective second end, the respective outer wall configured to be rotationally symmetric about a respective chamber axis;a respective chamber defined by the respective first end wall, the respective second end wall and the respective outer wall, the respective chamber having:a respective gas inlet;a respective gas outlet;a respective liquid inlet; anda respective liquid outlet; anda respective set of vanes disposed within the respective chamber, the respective set of vanes configured to rotate about a respective vane axis parallel to, and spaced from, the respective chamber axis,wherein the further liquid ring compressor is configured to form a further liquid ring from the second working fluid moving between the respective liquid inlet and the respective liquid outlet, and to compress the first working fluid from the respective gas inlet to the respective gas outlet;a further gas connection between the respective gas outlet of the further liquid ring compressor and the respective gas inlet of the first liquid ring compressor; anda further liquid connection between the respective liquid outlet of the first liquid ring compressor and the respective liquid inlet of the further liquid ring compressor, the further liquid connection comprising a further flow regulator configured to permit a substantially unidirectional flow of the second working fluid, in use, from the first liquid ring compressor to the further liquid ring compressor.

10. A symmetrical-axis compressor-expander comprising:a first simultaneous compressor-expander according to claim 1;a high pressure chamber in fluid communication with the respective chamber of the second liquid ring compressor via the respective gas outlet and respective liquid inlet of the second liquid ring compressor, the high pressure chamber having a high pressure gas outlet and a high pressure liquid inlet; anda second simultaneous compressor-expander according to any one of the preceding claims, the second simultaneous compressor-expander arranged symmetrically to the first simultaneous compressor-expander and such that the respective chamber of the second liquid ring compressor of the second simultaneous compressor-expander is in fluid communication with the high pressure chamber via the respective gas outlet and respective liquid inlet of the second liquid ring compressor of the second simultaneous compressor-expander.

11. A vapour compression refrigeration system comprising:a simultaneous compressor-expander according to claim 1;a condenser arranged to receive a refrigerant, in a first gaseous phase, from the respective gas outlet of the second liquid ring compressor, and configured to condense the refrigerant such that the refrigerant undergoes a phase change to a first liquid phase, the condenser further arranged to deliver the refrigerant in the first liquid phase to the respective liquid inlet of the second liquid ring compressor; andan evaporator arranged to receive the refrigerant, in a second liquid phase, from the respective liquid outlet of the first liquid ring compressor, and configured to evaporate the refrigerant, using heat from an environment to be cooled, such that the refrigerant undergoes a phase change to a second gaseous phase, the evaporator further configured to deliver the refrigerant in the second gaseous phase to the respective gas inlet of the first liquid ring compressor.

12. A method of simultaneously compressing a first working fluid in a gaseous phase and decompressing a second working fluid in a liquid phase, the method comprising the steps of:providing the simultaneous compressor-expander according to claim 1;supplying the first working fluid to the respective gas inlet of the first liquid ring compressor;supplying the second working fluid to the respective liquid inlet of the second liquid ring compressor; andoperating the simultaneous compressor-expander.

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