US20250164161A1

US20250164161A1 - Near-isothermal compression, and systems and methods with near-isothermal compression

Info

Publication number: US20250164161A1
Application number: US18/950,725
Authority: US
Inventors: K. Reinhard Radermacher; Yunho Hwang; Jan Muehlbauer; Lei Gao; Cheng-Yi Lee; Haopeng Liu
Original assignee: University of Maryland College Park
Current assignee: University of Maryland College Park
Priority date: 2023-11-17
Filing date: 2024-11-18
Publication date: 2025-05-22

Abstract

A system can comprise one or more near-isothermal compression (NIC) systems. Each NIC system can have one or more chambers and cooling means. Each NIC system can increase a pressure of a working fluid in the one or more chambers via an incompressible fluid acting as a liquid piston. The cooling means can remove from the working fluid at least some heat generated by the increased pressure. In some embodiments, NIC systems can alternately operate with incompressible fluid flow reversing direction through the one or more chambers based on mode of operation. Alternatively, in some embodiments, a direction of the incompressible fluid flow can be the same regardless of the mode of operation. Alternatively, in some embodiments, a mechanical piston is used to move the incompressible fluid within the chamber to effect compression of the working fluid.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of and priority under 35 U.S.C. § 119(e) to and is a non-provisional of U.S. Provisional Application No. 63/600,240, filed Nov. 17, 2023, entitled “Systems, Devices, and Methods for Highly Efficient Isothermal Compression,” which is hereby incorporated by reference herein in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with government support under DE-EE009685 awarded by the U.S. Department of Energy. The government has certain rights in the invention.

STATEMENT REGARDING PRIOR DISCLOSURES

Pursuant to 35 U.S.C. § 102(b)(1)(A), the following were published by the instant inventors, each of which is incorporated by reference herein in its entirety:
LEE et al., “Development of a Near-isothermal Compressor for Transcritical Carbon Dioxide Cycle,” 14 ^th IEA Heat Pump Conference, May 15-18, 2023, Chicago, Illinois.
LIU et al., “Dynamic Modeling of Near Isothermal Compressor for Transcritical Carbon Dioxide Cycle,” International Compressor Engineering Conference, 2024, Paper 2851.

FIELD

The present disclosure relates generally to gas compression systems, and more particularly, to near-isothermal compression, for example, for use in thermodynamic cycles, such as vapor compression systems.

BACKGROUND

Compressors are employed in vapor compression systems for various thermodynamic applications, such as gas processing, air conditioning, heat pumping, and refrigeration. Since the compressor is the largest consumer of power in vapor compression systems, the efficiency of the compressor impacts overall energy consumption and operating costs for the system. Improving compressor efficiency is therefore a key factor in enhancing the performance of vapor compression systems. However, such conventional compressors typically employ an isentropic (or near isentropic) process. In contrast, an isothermal compression process can help to minimize, or at least reduce, the amount of compression work, thereby improving system performance and saving energy. Embodiments of the disclosed subject matter may address one or more of the above-noted problems and disadvantages, among other things.

SUMMARY

Embodiments of the disclosed subject matter provide systems and methods for near-isothermal compression, as well as systems and methods employing near-isothermal compression, for example, as part of a vapor compression system. An incompressible fluid can be used to increase a pressure of a working fluid within a chamber, while heat can be removed from the chamber via a cooling means (e.g., a cooling fluid flow around the chamber, a cooling fluid flow through conduit(s) around, within, or part of the chamber, etc.). In some embodiments, the incompressible fluid acts as a liquid piston. A storage vessel proximal to and in fluid communication with the chamber can store incompressible fluid for delivery to and from the chamber. In some embodiments, the movement of the liquid piston through the chamber is bidirectional, with the incompressible fluid moving in a first direction to provide compression to the working fluid and subsequently moving in an opposite second direction to provide suction to refill the chamber with working fluid. Alternatively, in some embodiments, the movement of the liquid piston is in a single direction (unidirectional) regardless of operation in compression or suction modes. In some embodiments, the incompressible fluid transfers pressure from a mechanical piston to the working fluid.
The near-isothermal compression and/or the system utilizing the near-isothermal compression can be designed to enhance heat transfer from the working fluid (e.g., during the compression), to improve efficiency, and/or to ensure optimal functionality. For example, in some embodiments, various open loop and/or direct cooling features can be applied to the near-isothermal compression (e.g., to the chamber). Alternatively or additionally, various closed loop and/or second fluid cooling features can be applied to the near-isothermal compression (e.g., to the chamber). In some embodiments, the working fluid, the incompressible fluid, or both can be injected into the chamber for near-isothermal compression, for example, to enhance cooling.
Alternatively or additionally, the thermodynamic system can employ an economizer (e.g., integrated with the compressor), can recover work (e.g., utilizing multiple compressors, recovering work from the expansion process, using an ejector, etc.), can control the discharge flow for the compressed working fluid (e.g., using multiple compression chambers, using a pressure vessel for storing compressed working fluid, using a variable speed fluid pump, etc.), can control the flow within the thermodynamic system (e.g., monitoring outlet pressure of the evaporator, adjusting superheat via the expansion process, using valves to respond to outlet conditions of the evaporator, etc.), and/or altering pump design.
In one or more embodiments, a system can comprise at least two near-isothermal compression (NIC) systems, one or more pumps, and a switching system. Each NIC system can comprise one or more chambers and cooling means. Each NIC system can increase a pressure of a working fluid in the one or more chambers via an incompressible fluid acting as a liquid piston. The cooling means can remove from the working fluid at least some heat generated by the increased pressure. In some embodiments, each NIC system further comprises a staging vessel for the incompressible fluid. The staging vessel can be disposed between the switching system and the corresponding one or more chambers. The staging vessel can have a fluid volume greater than a combined fluid volume of the corresponding one or more chambers. The one or more pumps can be coupled to the at least two NIC systems. The one or more pumps can pump the incompressible fluid to or from the one or more chambers. The switching system can be between the one or more pumps and the at least two NIC systems. The switching system can control a flow direction of the incompressible fluid within the respective NIC system.
In one or more embodiments, a system can comprise at least two NIC systems, one or more pumps, a switching system, and a controller. Each NIC system can comprise one or more chambers and a cooling means. Each NIC can increase a pressure of a working fluid in one or more chambers via an incompressible fluid acting as a liquid piston. The cooling means can remove from the working fluid at least some heat generated by the increased pressure. The one or more pumps can be coupled to the at least two NIC systems. The one or more pumps can pump the incompressible fluid through the one or more chambers. The switching system can be coupled to the at least two NIC systems. The switching system can control connections of each NIC system to a fluid circuit.
The controller can be operatively coupled to the switching system and can comprise one or more processors and one or more non-transitory computer-readable storage media. The computer-readable storage media can store computer-readable instructions that, when executed by the one or more processors, cause the one or more processors to control the switching system to have a first state where a first of the at least two NIC systems operates in compression mode, and a second of the at least two NIC systems operates in suction mode; and, in response to a predetermined input, control the switching system to have a second state where the first of the at least two NIC systems operates in the suction mode, and the second of the at least two NIC systems operates in the compression mode. For each NIC system, each of the one or more chambers can have opposing first and second ends. In both the compression mode and the suction mode, a direction of the incompressible fluid flow through the one or more chambers can be from the first end to the second end.
In one or more embodiments, a system can comprise one or more NIC systems and one or more motors. Each NIC system can comprise a chamber, a mechanical piston disposed within the chamber, an incompressible fluid disposed within the chamber, and cooling means. Each NIC system can increase a pressure of a working fluid within the chamber via axial movement of the mechanical piston. During the pressure increase, the incompressible fluid can be disposed between the working fluid and a leading end of the mechanical piston. The cooling means can remove from the working fluid at least some heat generated during the pressure increase. The one or more motors can move the mechanical piston axially within the chamber of the one or more NIC systems.
In some embodiments, the system can further comprise a thermodynamic fluid circuit can comprise a first heat exchanger, an expansion device, and a second heat exchanger. The first heat exchanger can be coupled to the one or more NIC systems so as to receive pressurized working fluid from the one or more NIC systems. The first heat exchanger can transfer heat from the pressurized working fluid flowing through the first heat exchanger. The expansion device can be coupled to the first heat exchanger so as to receive the working fluid from the first heat exchanger. The expansion device can reduce a pressure of the working fluid flowing through the expansion device. The second heat exchanger can be coupled to the expansion device so as to receive the working fluid from the expansion device. The second heat exchanger can transfer heat to the working fluid flowing through the second heat exchanger. The second heat exchanger can be further coupled to the one or more NIC systems so as to deliver heated working fluid from the second heat exchanger to the one or more NIC systems.
Any of the various innovations of this disclosure can be used in combination or separately. This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. The foregoing and other objects, features, and advantages of the disclosed technology will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will hereinafter be described with reference to the accompanying drawings, which have not necessarily been drawn to scale. Where applicable, some elements may be simplified or otherwise not illustrated in order to assist in the illustration and description of underlying features. For example, in some figures, heat and/or fluid flow has not been shown or has been illustrated using block arrows or solid/dashed lines. Throughout the figures, like reference numerals denote like elements.

FIG. 1A is a simplified schematic diagram of a generalized vapor compression system employing near-isothermal compression, according to one or more embodiments of the disclosed subject matter.

FIG. 1B is a simplified schematic diagram illustrating further details of near-isothermal compression in a vapor compression system, according to one or more embodiments of the disclosed subject matter.

FIG. 2A is a simplified schematic diagram of a dual-stage liquid-piston system for near-isothermal compression, according to one or more embodiments of the disclosed subject matter.

FIG. 2B is a simplified schematic diagram illustrating further details of a hydraulic switch employed in the dual-stage liquid-piston system of FIG. 2A, according to one or more embodiments of the disclosed subject matter.

FIG. 2C is a simplified schematic diagram illustrating a vapor compression system employing a dual-stage liquid-piston system for near-isothermal compression, according to one or more embodiments of the disclosed subject matter.

FIG. 3 is a simplified schematic diagram illustrating aspects of another liquid-piston system for near-isothermal compression, according to one or more embodiments of the disclosed subject matter.

FIG. 4A is a simplified schematic diagram illustrating aspects of a unidirectional liquid-piston system for near-isothermal compression, according to one or more embodiments of the disclose subject matter.

FIG. 4B is a simplified schematic diagram illustrating a vapor compression system employing a dual-stage unidirectional liquid-piston system for near-isothermal compression, according to one or more embodiments of the disclosed subject matter.

FIG. 5 is a simplified schematic diagram illustrating aspects of another vapor compression system employing a dual-stage liquid-piston system for near-isothermal compressing, according to one or more embodiments of the disclosed subject matter.

FIG. 6 depicts a generalized example of a computing environment in which the disclosed technologies may be implemented.

FIG. 7 is a graph illustrating CO₂refrigeration capacity, subcooler outlet temperature, and suction superheat at 1250 RPM pump speed in a first experimental setup of a system employing near-isothermal compression.

FIG. 8 is a graph illustrating pressures at the 1250 RPM pump speed in the first experimental setup of the system employing near-isothermal compression.

FIG. 9 is a pressure-enthalpy (P-h) diagram illustrating the CO₂compression process in the first experimental setup of the system employing near-isothermal compression.

FIG. 10 is a graph illustrating pressure, temperature, and level sensor effectiveness in a second experimental setup of a system employing near-isothermal compression.

FIG. 11 is a graph illustrating pump, heater power, and suction mass flow rate in the second experimental setup of the system employing near-isothermal compression.

FIG. 12 is a P-h diagram illustrating the CO₂compression process in the second experimental setup of the system employing near-isothermal compression.

FIGS. 13-14 are graphs illustrating test chamber temperature, evaporating temperature, and evaporating pressure under 25° C. and 32° C. ambient conditions, respectively, for a third experimental setup of a system employing near-isothermal compression.

DETAILED DESCRIPTION

General Considerations

For purposes of this description, certain aspects, advantages, and novel features of the disclosed subject matter are described herein. The disclosed methods and systems should not be construed as being limiting in any way. Instead, the present disclosure is directed toward all novel and nonobvious features and aspects disclosed herein, alone and in various combinations and sub-combinations with one another. The methods and systems are not limited to any specific aspect or feature or combination thereof, nor do the disclosed aspects require that any one or more specific advantages be present, or problems be solved. The technologies from any aspect or example can be combined with the technologies described in any one or more of the other aspects or examples. In view of the many possible aspects to which the principles of the disclosed technology may be applied, it should be recognized that the illustrated aspects of the disclosure are exemplary only and should not be taken as limiting the scope of the disclosed technology.
Although the operations of some of the disclosed methods are described in a particular, sequential order for convenient presentation, it should be understood that this manner of description encompasses rearrangement, unless a particular ordering is required by specific language set forth below. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed methods can be used in conjunction with other methods. Additionally, the description sometimes uses terms like “provide” or “achieve” to describe the disclosed methods. These terms are high-level abstractions of the actual operations that are performed. The actual operations that correspond to these terms may vary depending on the particular implementation and are readily discernible by one skilled in the art.
The disclosure of numerical ranges should be understood as referring to each discrete point within the range, inclusive of endpoints, unless otherwise noted. Unless otherwise indicated, all numbers expressing quantities of components, molecular weights, percentages, temperatures, times, and so forth, as used in the specification or claims are to be understood as being modified by the term “about.” Accordingly, unless otherwise implicitly or explicitly indicated, or unless the context is properly understood by a person skilled in the art to have a more definitive construction, the numerical parameters set forth are approximations that may depend on the desired properties sought and/or limits of detection under standard test conditions/methods, as known to those skilled in the art. When directly and explicitly distinguishing aspects from discussed prior art, the numbers are not approximates unless the word “about,” “substantially,” or “approximately” is recited. Whenever “substantially,” “approximately,” “about,” or similar language is explicitly used in combination with a specific value, variations up to and including 10% of that value are intended, unless explicitly stated otherwise.
Directions and other relative references may be used to facilitate discussion of the drawings and principles herein but are not intended to be limiting. For example, certain terms may be used such as “inner,” “outer,” “upper,” “lower,” “top,” “bottom,” “interior,” “exterior,” “left,” right,” “front,” “back,” “rear,” and the like. Such terms are used, where applicable, to provide some clarity of description when dealing with relative relationships, particularly with respect to the illustrated aspects. Such terms are not, however, intended to imply absolute relationships, positions, and/or orientations. For example, with respect to an object, an “upper” part can become a “lower” part simply by turning the object over. Nevertheless, it is still the same part, and the object remains the same.
As used herein, “comprising” means “including,” and the singular forms “a” or “an” or “the” include plural references unless the context clearly dictates otherwise. The term “or” refers to a single element of stated alternative elements or a combination of two or more elements unless the context clearly indicates otherwise.
Although there are alternatives for various components, parameters, operating conditions, etc. set forth herein, that does not mean that those alternatives are necessarily equivalent and/or perform equally well. Nor does it mean that the alternatives are listed in a preferred order, unless stated otherwise. Unless stated otherwise, any of the groups defined below can be substituted or unsubstituted.
Unless explained otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one skilled in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure, suitable methods and materials are described below. The materials, methods, and examples are illustrative only and not intended to be limiting. Features of the presently disclosed subject matter will be apparent from the following detailed description and the appended claims.

Overview of Terms

The following are provided to facilitate the description of various aspects of the disclosed subject matter and to guide those skilled in the art in the practice of the disclosed subject matter.
Near-Isothermal Compression (NIC): Compression of a working fluid (e.g., a gas, such as but not limited to, carbon dioxide, hydrogen, air, and compressed natural gas) while transferring heat therefrom such that a temperature rise of the working fluid during the compression is avoided (e.g., a change in temperature of less than 5 K), or least minimized (e.g., a change in temperature of no more than 15 K). In some embodiments, a temperature of the working fluid after NIC (e.g., prior to discharge to the thermodynamic circuit for subsequent use) may be 0-10 K, inclusive, greater than a temperature of the working fluid prior to NIC (e.g., from the thermodynamic circuit are use and/or after introduction to a chamber of the NIC for compression).
Liquid Piston: An incompressible fluid used to apply pressure to a working fluid (e.g., refrigerant) to increase a pressure of the working fluid (e.g., effect compression thereof). In some embodiments, the working fluid may be substantially immiscible (or have at least limited miscibility) in the incompressible fluid for the temperatures at which NIC occurs. In some embodiments, the incompressible fluid can be, but is not limited to, oil (e.g., mineral oil), an ionic liquid (e.g., when hydrogen is the working fluid), water (e.g., when air is the working fluid), or brine.

Introduction

Disclosed herein are systems and methods for enhancing efficiency of gas compression, for example, by using heat-exchange enhanced compression techniques to achieve isothermal, or at least near-isothermal, compression. In some embodiments, an incompressible fluid (e.g., oil, water, brine, ionic fluid, etc.) can function as a liquid piston to compress a working fluid (e.g., carbon dioxide, hydrogen, air, compressed natural gas, etc.) within a chamber, which can also function as a heat exchanger to remove heat from the working fluid so as to achieve NIC. For example, aspects of the disclosed NIC and systems including NIC may be similar to that described in U.S. Publication No. 2022/0010934, published Jan. 13, 2022, and entitled “System and Method for Efficient Isothermal Compression,” which is incorporated by reference herein in its entirety.
When the working fluid is near its critical point (e.g., as part of a transcritical CO₂cycle), there may be additional challenges associated with performing NIC, for example, with respect to the dynamic heat transfer amount during the compression process. Thus, in some embodiments, the heat transfer performance of the compression chamber can be enhanced and/or tailored (e.g., internal or external to the chamber) in order to enhance heat dissipation and thereby achieve NIC. In addition, the NIC process in a single chamber takes more time as compared to conventional reciprocating compressors, to accommodate the heat transfer process. As such, NIC utilizing a single chamber exhibits an intermittent flow pattern for the compressed working fluid. In some embodiments, the NIC is designed to provide continuous, or at least near continuous, discharge of compressed working fluid, for example, by employing multiple chambers, by employing a storage vessel, and/or by discharge fluid flow control (e.g., using valves and/or switches). Alternatively or additionally, efficiency of the NIC or a system utilizing NIC can be improved, for example, using an economizer, compressor work recovery, discharge flow control mechanisms, and/or alternative compression designs.

Vapor Compression Systems Employing Near-Isothermal Compression

In some embodiments, a vapor compression system can comprise and/or employ an NIC system. For example, FIG. 1A illustrates an exemplary vapor compression system 100 having an NIC system 102, a first heat exchanger 108, an expansion device 112, and a second heat exchanger 114. In some embodiments, the NIC system can include at least two compression units. For example, in the illustrated example, the NIC system 102 includes multiple compression units 104-1, 104-2, . . . 104-n (where n≥3). The NIC system 102 receives working fluid input 118 from the second heat exchanger 114, and distributes the working fluid to at least one of the compression units 104 for compression. The NIC system 102 provides a compressed working fluid output 120, for example, from at least one of the compression units 104 after the compression. Within the compression unit 104, a pressure of the working fluid is increased (e.g., using a liquid piston) to effect the compression, and at least some of the heat 106 generated during the compression is removed. In some embodiments, the heat removal 106 is such that a temperature of the compressed working fluid output 120 is substantially the same as, or at least no more than 15 K higher than, a temperature of the working fluid input 118, such that the compression is considered near-isothermal.
The compressed working fluid output 120 from the NIC system 102 can be provided (directly or indirectly) as input 122 to the first heat exchanger 108, where at least some heat 110 is removed from the working fluid. In some embodiments, the first heat exchanger 108 operates as a condenser, such that the heat removal 110 causes the working fluid to condense. Alternatively, in some embodiments, the first heat exchanger 108 operates as a gas cooler, such that the heat removal 110 cools the working fluid but otherwise remains in a gas phase (e.g., cooling of supercritical CO₂). The working fluid output 124 from the first heat exchanger 108 can be provided (directly or indirectly) as input 126 to expansion device 112, where a pressure of the working fluid is reduced, for example, by expanding a volume thereof.
In some embodiments, the expansion device 112 can comprise a mechanical expansion valve (e.g., throttle valve. Alternatively, in some embodiments, the expansion device 112 can comprise an electronic expansion valve (EEV), for example, to provide enhanced and/or dynamic control of the pressure of the working fluid output 128. The working fluid output 128 from the expansion device 112 can be provided (directly or indirectly) as input 130 to the second heat exchanger 114, where at least some heat 116 is added to the working fluid.
In some embodiments, the second heat exchanger 114 operates as an evaporator, such that the heat addition 116 causes the working fluid to evaporate. In some embodiments, the heat addition 116 can be heat removed from an area or environment, for example, to provide refrigeration or air conditioning of the area or environment. The working fluid output 132 from the second heat exchanger can then be provided (directly or indirectly) as input to the NIC system 102 to restart the cycle.
FIG. 1B illustrates further details of an exemplary NIC system 152 in the context of a vapor compression system 150. As with the system 100 of FIG. 1A, the system 152 of FIG. 1B includes a first heat exchanger 108, an expansion device 112, and a second heat exchanger 114, each of which operates in a similar manner to that described above. In the illustrated example of FIG. 1B, however, the NIC system 152 includes a fluid pump 154 (e.g., a gear pump or plunger pump), a fluid supply network 156, multiple fluid staging vessels 158-1 through 158-n, multiple compression chambers 160-1 through 160-n, and a fluid collection network 162. For example, the fluid supply network 156 can include conduits, valves, and/or switches for providing an incompressible fluid to and/or removing an incompressible fluid from the compression chambers 160, and the fluid collection network 162 can include conduits, valves, and/or switches for providing the working fluid to and/or removing working fluid from the compression chambers 160. In some embodiments, at least some of the components of the fluid supply network 156 and the fluid collection network 162 may overlap (e.g., a conduit, valve, and/or switch used for both incompressible fluid and working fluid conveyance and/or routing).
In some embodiments, each staging vessel 158-1 through 158-n can be associated with a corresponding one of the compression chambers 160-1 through 160-n. The fluid pump 154 can pump an incompressible fluid, for example, stored in the respective staging vessel 158, into and/or through the compression chambers 160 to function as a liquid piston for compressing the working fluid within the compression chambers 160, while at least some of the heat 106 generated during the compression is removed from the working fluid within the compression chambers 160. In some embodiments, the provision of the staging vessels 158 can allow a size of the compression chambers 160 (and the volume from which heat 106 is removed) to be reduced, thereby helping to reduce a size and/or expense of the heat exchanging features for NIC.
In some embodiments, each compression chamber 160 is constructed such that the working fluid therein is only discharged (e.g., for use in the vapor compression cycle and/or storage) after the working fluid attains the desired pressure (e.g., via the liquid piston) and temperature (e.g., via heat removal 106). The time needed for sufficient heat removal and compression may thus produce compressed working fluid on a periodic basis. To provide a continuous, or at least near continuous, supply of compressed working fluid for the vapor compression cycle, the NIC system 152 can employ multiple compression chambers 160. For example, a first one of the compression chambers 160 can operate to compress the working fluid and remove heat therefrom (e.g., without yet dispensing any working fluid) while a second one of the compression chambers 160, having already completed its compression and heat removal, can dispense the compressed working fluid for use. Once the first compression chamber has completed its compression and heat removal, it can then dispense its compressed working fluid for use, while the second compression chamber proceeds to compress a next batch of the working fluid, thereby providing a more continuous flow of compressed working fluid.
Alternatively or additionally, in some embodiments, the NIC system 152 can optionally include a pressure vessel 164, which can store pressurized working fluid from the individual compression chambers. In some embodiments, compressed working fluid from the compression chambers 160 (e.g., in parallel batch operation or in alternating sequential batch operation) can be stored in the pressure vessel 164 as it is produced, and the compressed working fluid can be discharged from the pressure vessel 164 for use in the vapor compression cycle on a continuous basis. In some embodiments, the fluid volume of the pressure vessel 164 can be greater than that of each of the compression chambers 160, for example, at least equal to a total fluid volume of all of the compression chambers 160.

Heat Transfer Enhancements

The ability for the compression to follow a near isothermal process can be improved using one or more heat transfer enhancement techniques, for example, by optimizing geometry of the compression chamber (or at least the heat exchanging portion of the compression chamber) and selection of suitable cooling options, in order to improve heat transfer efficiency over the compression process and ensure effective cooling of the working fluid. Categories for such heat transfer enhancements can include, but are not limited to, direct cooling techniques, secondary closed loop cooling techniques, and/or fluid injection techniques. Selection of one, some, or all of these heat transfer techniques can be based on operational factors, such as, but not limited to, heat load, temperature range, and desired thermal management goals, and in view of the specific advantages and disadvantages associated with each technique and the requirements of a particular application.

Direct Cooling

Direct cooling summarizes a category of techniques that use open-loop coolant (e.g., ambient air) to cool down the surface of the chamber, and thereby the working fluid within the chamber. In some embodiments, the specific surface area can be enhanced based on the dynamic heat transfer coefficient requirement over the compression process due to the property of the working fluid. Exemplary direct cooling techniques can include, but are not limited to, use of a tube heat exchanger, a finned tube heat exchanger, a microchannel heat exchanger, a complex heat exchanger, and/or multi-stage integration for the compression chamber.
The tube heat exchanger technique can involve the use of one or more tubes, each with or without internal or external enhancements (e.g., fins). Each tube can have a small diameter (e.g., ≤1 cm in diameter), which can allow for high heat transfer rates. The finned tube heat exchanger technique can involve the use of one or more tubes with fins attached to the external surface of the chamber to increase surface area and improve heat transfer, for example, in a manner similar to conventional heating, ventilation, and air-conditioning (HVAC) system and refrigeration appliances. The microchannel heat exchanger technique can involve the use of a heat exchanger with multiple narrow channels (e.g., ≤1 mm in diameter, such as 0.1-1 mm, inclusive) integrated into a “flat” tube structure to increase surface area and improve heat transfer, for example, in a manner similar to conventional aerospace and automotive applications.
The complex heat exchanger technique can involve the use of a branching network of conduits. In some embodiments, the branching network can mimic structures in nature, such as a honeycomb, dendritic network, or bronchial tree (e.g., lung). In some embodiments, the complex heat exchanger can be 3D-printed. Such a technique may help improve heat transfer while reducing weight and/or materials. The multi-stage integration technique can involve integrating multiple heat transfer techniques, for example, to accommodate dynamic heat transfer requirements and/or optimize performance. For example, a microchannel heat exchanger can be combined with a 3-D printed complex design to achieve high heat transfer rates while reducing weight and/or materials.

Closed Loop Cooling

Closed loop cooling summarizes a category of techniques that use a secondary fluid introduced into a closed volume surrounding the compression chamber (e.g., a heat exchanger structure outside the compression chamber) in order to absorb heating from the working fluid in the compression chamber, thereby cooling the working fluid. Such secondary fluid cooling can offer several advantages, such as, but not limited to, improving heat transfer efficiency, improving control of temperature, and improving the ability to handle high heat loads. In some embodiments, the secondary fluid cooling can allow for effective heat removal from the working fluid to improve performance and follow an isothermal process.
There are different approaches to implementing secondary fluid cooling in heat exchangers. For example, a secondary loop with a separate heat exchanger in thermal communication with the compression chamber can be used, and the secondary fluid can flow through the secondary loop. The secondary fluid can absorb heat from the working fluid via the heat exchanger and can then be cooled at another location (e.g., via another heat exchanger). The cooled secondary fluid can then be recirculated back to the heat exchanger to continue cooling of the working fluid. The secondary fluid can remain single-phase or incur a phase change process (heat pipe operation). Exemplary heat exchangers for the closed loop cooling can include, but are not limited to, a plate heat exchanger, a shell-and-tube heat exchanger, a tube-in-tube heat exchanger, a triply periodic minimal surface (TPMS) heat exchanger, and/or any other suitable heat transfer mechanism.
In some embodiments, the plate heat exchanger can have multiple thin plates arranged in parallel, creating alternating channels for the working fluid and the secondary fluid. The working fluid can flow through a first set of channels, while the secondary fluid can flow through the adjacent second set of channels. This design can allow for efficient heat transfer between the two fluids due to the large surface area provided by the plates. In some embodiments, compression of the working fluid by the incompressible fluid can occur within the first set of channels.
In some embodiments, the shell-and-tube heat exchanger can have a bundle of tubes enclosed within a shell. The working fluid can flow through the tubes, while the secondary fluid circulates around the tubes in the shell. Heat can be exchanged through the tube walls, enabling effective cooling of the working fluid. In some embodiments, compression of the working fluid by the incompressible fluid can occur with the bundle of tubes. In some embodiments, the secondary fluid at the shell side can be either flooded or sprayed. In the flooded type, the secondary fluid can be introduced as a continuous flow that completely fills the shell side of the heat exchanger. This flooding effect can increase the contact area between the working fluid and the secondary fluid, thereby promoting efficient heat transfer. In the sprayed type, the secondary fluid can be introduced in the form of sprays or jets. For example, the secondary fluid can be sprayed onto the tube bundle, creating a dispersed flow pattern. This spraying action can enhance the heat transfer by promoting turbulent flow and increasing the interaction between the working fluid and the secondary fluid.
In some embodiments, the tube-in-tube heat exchanger can have an inner tube nested within an outer tube, creating an annular space between them. The working fluid can flow through the inner tube, while the secondary fluid can circulate within the annular space. This configuration allows for efficient heat transfer due to the large surface area available between the two fluids.
In some embodiments, the TPMS heat exchanger can have a complex, continuous shape that repeats in three dimensions, providing a large surface area for heat exchange. These surfaces are often derived from mathematical minimal surfaces, meaning they have zero mean curvature, making them highly efficient in distributing stress and optimizing material usage. Thus, the TPMS heat exchanger can have a high surface area to volume ratio, can enhance the fluid mixing, and/or can reduce pressure drop for the fluids flowing therethrough.

Fluid Injection

In some embodiments, compression is achieved by pumping or suctioning incompressible fluid (acting as a liquid piston) into the compression chamber. A distinct interface can be formed between the incompressible fluid (e.g., oil) and the working fluid (e.g., CO₂), which may remain relatively stable over the compression process. In some embodiments, instead of or in addition to pumping of the incompressible fluid, the incompressible fluid can be injected into the compression chamber, which injection can further enhance heat dissipation from the working fluid. For example, the injected incompressible fluid can facilitate forced convective heat transfer between the incompressible fluid and the working fluid, and the interaction between the injected incompressible fluid and the working fluid can promote efficient heat transfer within the compression chamber. Thus, the injected incompressible fluid can function as a coolant for the working fluid, effectively transferring the additional cooling process from the surface of the compression chamber to the liquid piston itself. By leveraging the properties of the injected incompressible fluid (e.g., higher thermal conductivity and greater heat capacity as compared to the working fluid), heat dissipation within the compression chamber can be improved. In addition, the injected incompressible fluid can serve as an additional heat transfer medium, effectively cooling the working fluid and maintaining operating conditions (e.g., within an optimal, or at least workable range) within the compression chamber.
Alternatively or additionally, in some embodiments, liquid working fluid (e.g., CO₂) can be injected into the compression chamber, for example, the high-pressure side (e.g., discharge end) of the compression chamber. The injected working fluid can further enhance internal heat transfer performance. For example, the injected liquid working fluid can promote efficient heat transfer within the compression chamber. As the liquid comes into contact with the high-temperature working fluid, it absorbs heat rapidly, effectively cooling the working fluid and facilitating better heat dissipation. This enhanced heat transfer improves the overall thermal management of the compression process. In addition, the injected working fluid can undergo a phase change process within the compression chamber, where the liquid working fluid absorbs heat as it transitions from a liquid state to a vapor state. This phase change process can allow the working fluid to absorb superheat, further reducing the temperature and maintaining the isothermal status within the compression chamber.

System Enhancements

As noted above, the compression process in a single compression chamber differs from conventional reciprocating compressors in that it requires additional time to dissipate sufficient heat to achieve near-isothermal conditions. This is due, for example, to the nature of the NIC process and the desire for efficient heat transfer. As a result, the flow of compressed working fluid from the compression chamber is intermittent, characterized by periods of compression, discharge, and suction. In some embodiments, the NIC system and/or a system utilizing the NIC system can be configured to increase the functionality of the NIC system, for example, to enable continuous operation, improve energy efficiency, and/or increase performance. Such system configurations can include, but are not limited to, use of an economizer, recovering compressor work, and/or flow control.

Economizer

In some embodiments, an economizer can be used to recover heat and utilize the remaining cooling capacity from the evaporator (e.g., second heat exchanger 114 in FIGS. 1A-1B). After the NIC process, the working fluid can be further cooled in the economizer, utilizing the available cooling capability, which heat recovery process can further reduce energy consumption and enhance the overall performance of the compressor. In some embodiments, the economizer can be integrated with the compression chamber of the NIC system, which may allow for a more compact system design and efficient utilization of space. Alternatively, the economizer can be designed as a standalone unit, for example, to provide better control and flexibility in the cooling process. Such a standalone economizer can be optimized separately to meet the specific requirements of the compression system. By using an economizer, the cooling capacity that would otherwise go unused is effectively utilized, resulting in improved energy efficiency and performance.

Compressor Work Recovery

In some embodiments, high-pressure energy derived from the liquid piston and/or the working fluid can be recovered, for example, to enhance overall compression efficiency by capturing and utilizing energy that would otherwise be wasted. For example, the NIC system can have multiple compression chambers incorporated together. The compression chambers can be operated in an alternating manner, such that when working fluid is being compressed by a liquid piston in a first compression chamber, a suction stroke is conducted by the liquid piston in a second compression chamber. In some embodiments, appropriate valve design can allow the liquid piston of the second compression chamber (operating in suction) to be utilized to compress the working fluid in the first compression chamber (operating in compression), thereby recovering high-pressure energy from the liquid piston.
Alternatively or additionally, in some embodiments, high-pressure recovery from the working fluid can be had during the expansion process. For example, an expander can be connected to the same axis as the fluid pump that drives liquid piston, such that work from the expansion at least partially drives the liquid piston pumping. In another example, recovery from the expansion process can be realized through simultaneous compression and expansion in a three-dimensional space, for example, where rotation and articulation occur simultaneously, thereby allowing for recovery of high-pressure energy during the expansion process.
Alternatively or additionally, in some embodiments, an ejector can be used to provide work recovery. The ejector can operate on the venturi principle, where the working fluid passes through a jet nozzle that initially narrows, accelerates the fluid, and then expands in cross-sectional area. This acceleration generates a low-pressure zone, which entrains working fluid from the evaporator. The two fluid streams mix within the ejector, resulting in an increase in the pressure of the mixed fluid. This higher intermediate pressure reduces the suction pressure required by the compressor, thereby lowering the compression ratio. By reducing the workload of the compressor, the ejector improves the coefficient of performance (COP).
In some embodiments, the compression employing a liquid piston can experience degassing of the working fluid, for example, degassing when the compression phase transitions to the suction phase. This degassing can cause a difference in pressure and solubility of gases within the fluid and can reduce the volumetric efficiency of the pump. By incorporating an ejector into the system, the pressure difference can be minimized, or at least reduced, thereby reducing the solubility fluctuations and mitigating degassing. This also leads to more stable fluid properties and improves the volumetric efficiency of the compressor.

Discharge Flow Control

In some embodiments, the discharge port (e.g., high-pressure line conveying compressed working fluid from the NIC system) may be unable to provide a continuous flow when only two compression chambers are used. Thus, to provide a more continuous flow at the discharge port, additional strategies for the NIC system and/or the system using the NIC system can be employed, such as, but not limited to increasing the numbers of compression chambers, providing a high-pressure storage tank, and/or using a variable speed pump. For example, by providing additional compression chambers (e.g., more than 2) in the NIC system and by interconnecting the discharge from the compression chambers, a more continuous and/or uninterrupted flow of compressed working fluid can be provided at the discharge port. In some embodiments, the high pressure storage tank can store pressurized working fluid from the compression chambers and can release it to the thermodynamic cycle via the discharge port on an as needed basis, thereby providing a more steady flow at the discharge port and mitigating any interruptions or pulsations due to compression chamber cycling. Thus, the storage tank can function as a flow capacitance element in the system. Alternatively or additionally, in some embodiments, a fluid pump for the incompressible fluid can be a variable speed pump, where the speed of the pump is responsively adjusted to regulate the incompressible fluid flow to the compression chambers and thereby maintain a consistent flow rate for the working fluid from the discharge port.

Other Flow Control

In some embodiments, the flow conditions at the outlet of the evaporator (e.g., second heat exchanger 114 in FIGS. 1A-1B) can be monitored, and system operation controlled responsively thereto, for example, to maintain predetermined and/or desired conditions. For example, the outlet pressure of the evaporator can be regulated via pressure control valves or other pressure regulation mechanisms. Alternatively or additionally, the superheat of the working fluid (e.g., CO₂) can be adjusted via an electronic expansion valve or other valve design, for example, to achieve a particular temperature and thereby prevent, or at least reduce, overheating or undercooling of the working fluid prior to the evaporator. Alternatively or additionally, a valve can be provided at or downstream of the outlet of the evaporator and can be configured to respond to specific outlet conditions of the evaporator, such as pressure, temperature, and/or flow rate. By adapting based on the outlet conditions, the valve can effectively maintain desired conditions and enhance overall performance.

Bi-Directional NIC Systems

In some embodiments, an NIC system can employ a pair of compression chambers sequentially operated in opposing configurations, for example, to provide compression via one of the compression chambers (e.g., to deliver compressed working fluid from a vapor compression cycle) and to provide suction via the other of the compression chambers (e.g., to receive spent working fluid from the vapor compression cycle). In some embodiments, a direction of fluid flow through the compression chamber can depend on the mode of operation, for example, with incompressible fluid and/or working fluid flowing in a first direction during a compression stage and in an opposite second direction during the suction stage. The NIC system may thus be considered bi-directional.
For example, FIG. 2A illustrates an exemplary bi-directional NIC system 200. In the illustrated example, the NIC system 200 includes a liquid piston provision module 226 and a pair of compression units 206-1, 206-2 that alternate operation based on state of a hydraulic switch 214 (also referred to herein as a hydraulic directional control valve). First compression unit 206-1 includes a first heat transfer chamber 208-1 comprising and/or defined by one or more conduits 210-1 (e.g., acting as compression chamber(s)), a fluid staging vessel 212-1, an input/output control network 220-1, and an input/output junction 222-1. Similarly, second compression unit 206-2 includes a second heat transfer chamber 208-2 comprising and/or defined by one or more conduits 210-2 (e.g., acting as compression chamber(s)), a fluid staging vessel 212-2, an input/output control network 220-2, and an input/output junction 222-2. In some embodiments, a volume of each fluid staging vessel 212-1, 212-2 can be greater (e.g., at least 2×) than a total volume of the conduits 210-1, 210-2 in the corresponding heat transfer chamber 208-1, 208-2. For example, each fluid staging vessel 212 can have a volume of about 3785 ml (1 gallon), and each chamber 208 can have a volume of 1480 ml).
The liquid piston provision module 226 can be connected to the hydraulic switch 214 and can include a fluid pump 216, incompressible fluid supply line 236, incompressible fluid return line 238, incompressible fluid input line 232, and incompressible fluid supply 218. Compression unit fluid lines 234-1, 234-2 respectively connect the fluid staging vessels 212-1, 212-2 to corresponding ports of the hydraulic switch 214, and incompressible fluid input line 232 connects fluid pump 216 to an input port (P) of the hydraulic switch 214. Incompressible fluid can be provided to the pump 216 from supply 218 via input line 232 and/or from the compression units 206-1, 206-2 via the return line 238 connected to an output port (T) of the hydraulic switch 214.
In a first mode of operation (A), the first compression unit 206-1 can provide compression by incompressible fluid flowing from the pump 216, via hydraulic switch 214 and fluid line 234-1, along direction 202A, and the second compression unit 206-2 can provide suction by incompressible fluid flowing toward the pump 216, via hydraulic switch 214 and fluid line 234-2, along direction 204A. Conversely, in a second mode of operation (B), the first compression unit 206-1 can provide suction with the flow of incompressible fluid reversed to direction 202B, and the second compression unit 206-2 can provide compression with the flow of incompressible fluid reversed to direction 204B.
Prior to compression being performed in the compression unit, working fluid can be introduced into the conduit(s) of the respective heat transfer chamber via a working fluid return line, for example, return line 242-1 coupled to port 228-1 via junction 222-1 and input/output control network 220-1 in compression unit 206-1 and return line 242-2 coupled to port 228-2 via junction 222-2 and input/output control network 220-2 for compression unit 206-2. The working fluid can be compressed by the incompressible fluid flowing into the respective heat transfer chamber 208-1, 208-2 via port 230-1, 230-2, and heat 224-1, 224-2 can be removed from the respective heat transfer chamber to cool the compressed working fluid therein (e.g., with the heat transfer occurring concurrent with or subsequent to the compression). After compression, the working fluid can be discharged from port 228-1, 228-2 and directed to the rest of the vapor compression cycle via working fluid supply line 240-1, 240-2 coupled to port 228-1, 228-2 via junction 222-1, 222-2 and input/output control network 220-1, 220-2, respectively.
In some embodiments, port 230-1, 230-2 (e.g., suction-side) can be include a header and/or other flow control components for diverting incompressible fluid flow from the respective staging vessel 212-1, 212-2 into some or all of the respective conduits 210-1, 210-2 in the respective heat transfer chamber 208-1, 208-2, for example, as a parallel flow. Alternatively or additionally, in some embodiments, port 228-1, 228-2 (e.g., pressure-side) can include a separate header and/or other flow control components for combining working fluid flow (and/or incompressible fluid flow) from some or all of the respective conduits 210-1, 210-2 in the respective heat transfer chamber 208-1, 208-2.
In some embodiments, each input/output control network 220-1, 220-2 can include conduits, valves, and/or switches to provide working fluid from and/or deliver working fluid to the respective heat transfer chamber 208-1, 208-2. For example, input/output control networks 220-1, 220-2 can include a first check valve for the working fluid supply line 240-1, 240-2, which first check valve allows fluid to flow therethrough only in a single direction (e.g., away from the heat transfer chamber) and only when a predetermined pressure threshold has been exceeded. Alternatively or additionally, input/output control networks 220-1, 220-2 can include a second check valve for the working fluid return line 242-1, 242-2, which second check valve allows fluid to flow therethrough only in a single direction (e.g., toward the heat transfer chamber 208).
In the illustrated example, the hydraulic switch 214 is installed after an outlet of the fluid pump 216. The hydraulic switch 214 can facilitate the switching of flow direction when the compression chamber completes the compression stroke (e.g., when the incompressible fluid level is detected (e.g., via a sensor) at an upper level limit, for example, within or after second port 228. In operation, the pump 216 draws in low-pressure incompressible fluid from the suction port T of the hydraulic switch 214, from the supply 218, and/or from the vapor compression cycle (e.g., from separator 269 and/or vessel 284 in FIG. 2C). FIG. 2B shows the hydraulic switch 214 and its connection diagram. Port P is connected to the outlet of pump 216 via input line 232, and port T is connected to the suction via return line 238. Port A is connected to the first compression unit 206-1 via fluid line 234-1, and Port B is connected to the second compression unit 206-2 via fluid line 234-2. At the center position, ports A, B, P, and T are open. When the switch 214 is energized to the left (e.g., such that configuration 250B aligns with the ports A-T), incompressible fluid flows from port P to port B, and suction flows from port A to port T. When the switch 214 is energized to the right (e.g., such that configuration 250A aligns with the ports A-T), incompressible fluid flows from port P to port A, and suction flows from port B to port T. In some embodiments, the use of hydraulic switch 214 can reduce a size of the incompressible fluid supply loop and can be easier to control as compared to the use of multiple solenoid valves to effect di-directional sequential operation of the compression units 206.
FIG. 2C illustrates NIC system 200 incorporated into a vapor compression system 260. In the illustrated example, additional details are shown. For example, an adjustable pressure relief valve 290 can be installed at the outlet of the pump 216 to ensure safety. This valve 290 can be opened to create a short circuit in the incompressible fluid flow when an overpressure is detected. Additionally, pressure and temperature sensors 261 are positioned at the outlet of the pump 216, for example, to monitor variations in incompressible fluid (acting as a liquid piston). Each fluid line 234-1, 234-2 can include a respective diaphragm accumulator 262-1, 262-2, and respective sensor 263-1, 263-2 (e.g., light level sensor). At the pressure side of each compression unit, a further sensor 264-1, 264-2 (e.g., light level sensor) can be provided, check valves 265-1, 265-2 can be provided for the respective working fluid supply lines 240-1, 240-2, and check valves 266-1, 266-2 can be provided for the respective working fluid return lines 242-1,242-2.
For example, when the first compression unit 206-1 operates in compression, incompressible fluid from the pump 216 is directed to the fluid line 234-1 via the hydraulic switch 214. The incompressible fluid passes the sensor 263-1, enters the staging vessel 212-1 (e.g., high-pressure tank), and continues on to the heat transfer chamber 208-1. The incompressible fluid acts as a liquid piston to compress the working fluid within the heat transfer chamber 208-1 as the incompressible fluid moves upward (e.g., from port 230-1 to port 228-1) through the heat transfer chamber 208-1. Once the incompressible fluid level reaches sensor 264-1, the hydraulic switch 214 can be actuated to the opposite side (e.g., configuration 250B), thereby providing incompressible fluid from the pump 216 to the second compression unit 206-2 via the other fluid line 232-2.
To minimize dead volume in each compression cycle, each upper sensor 264-1, 264-2 can be placed close to the respective discharge check valve 265-1, 265-2. However, this may cause some of the incompressible fluid to exit with the working fluid from the compression unit 206-1, 206-2 into the working fluid supply line 240-1, 240-2 (e.g., compressed refrigerant line). Thus, in some embodiments, any incompressible fluid can be separated from the compressed working fluid in the input line 268 using a separator 269 (e.g., liquid separator. The separated incompressible fluid can be directed from the separator 269 via output line 283 to a storage vessel 284 and/or connected back to the suction of the pump 216 via recovery line 289. The collection of the incompressible fluid by the separator can ensure that enough incompressible fluid is maintained in the line for full compression to the top of each chamber. Alternatively or additionally, a separate fluid balance loop 285 can be provided between the vessel 284 and the fluid lines 234-1, 234-2 into the compression units (e.g., on a side of the hydraulic switch 214 opposite to the pump 216).
As noted above, sensors 264-1, 264-2 are installed proximal to ports 228-1, 228-2 of the compression chambers 208-1, 208-2, and two check valves 265-1, 265-2, 266-1, 266-2 are placed proximal to the sensors 264-1, 264-2 to avoid, or at least reduce, dead volume. One check valves 265-1, 265-2 allow the compressed working fluid (e.g., CO₂) to flow into first heat exchanger 272 (e.g., together with chiller 273, operating as a subcooler) via input line 268. The other check valves 266-1, 266-2 facilitates the flow of low-pressure working fluid (e.g., superheated CO₂) back into the compression chambers 208-1, 208-2 via return line 282.
A mass flow rate meter 270 can positioned after the compression chambers 208-1, 208-2, for example, to monitor the fluctuation phenomenon resulting from the longer compression cycle. Another mass flow rate meter 281 can be installed after second heat exchanger 278 (e.g., operating as an evaporator; or replaced with an electric heater in experimental setups) to ensure a constant mass flow rate for a stable cooling capacity supply. The output of the first heat exchanger 272 can be directed via line 275 to an expansion valve 276, which decreases a pressure of the working fluid. Alternatively, in some embodiments, the expansion valve 276 can be replaced with an electronic expansion valve, for example, to allow control of either low-side pressure or constant mass flow rate. The working fluid is conveyed from the expansion valve 276 to the second heat exchanger 278 for heating before being returned to the compression chambers 208-1, 208-2 via return line 282.
Various sensors and flow control components can be provided at various points throughout system 260 to monitor operation thereof. For example, pressure and temperature sensors 267-1, 267-2 can be provided proximal to port 228-1, 228-2 of each compression chamber 208-1, 208-2. Pressure and temperature sensors 271 can also be provided prior to the first heat exchanger 272, and pressure and temperature sensors 280 can be provided after the second heat exchanger 278. A temperature sensor 274 can be provided after the first heat exchanger 272 and prior to the expansion valve 276, and a pressure sensor 291 can be provided along the incompressible fluid return line 238. Recovery line 289 can include a pressure regulator 287 and a solenoid valve 288. A charge/discharge port 277 can be provided between the expansion valve 276 and the second heat exchanger 278.

Piston Driven NIC Systems

In a conventional vapor compression cycle, the gas compressor drives the refrigeration cycle by compressing the refrigerant gas to achieve the necessary pressure and temperature for heat exchange. In contrast, the above-described examples of NIC systems employ a high-pressure incompressible fluid to compresses the working fluid (e.g., gas). The design and efficiency of this hydraulic fluid pump can influence the overall performance of the vapor compression system. A well-optimized pump design can provide efficient pressure delivery, reduced energy losses, and improved efficiency of the NIC process.
In the above described examples, the liquid piston compressor operates through a mechanism that uses a fast-acting, small-displacement pump to transfer pressurized fluid from the suction chamber to the compression chamber. This process is referred to as an indirect actuation method because the motor's power input drives the hydraulic pump, which then moves the incompressible fluid between the chambers to compress the working fluid, rather than the motor directly compressing the working as in conventional systems. In this approach, the hydraulic pump indirectly provides the force required for working fluid compression. Depending on the configuration of the motor relative to the pump, these systems can be classified as open pumps, semi-hermetic pumps, or hermetic pumps. While the examples described herein utilize open pumps, semi-hermetic pumps or hermetic pumps are also possible according to one or more contemplated embodiments.
In contrast to indirect actuation, using a piston charged with incompressible fluid (e.g., hydraulic fluid) in the compression chamber could eliminate volumetric efficiency losses caused by degassing. For example, FIG. 3 illustrates an NIC system 300 employing a mechanical piston 306 charged with incompressible fluid 308 and configured to move axially within a compression chamber 304. A first region 312 of the compression chamber 304 can be a heat transfer region, for example, with a heat transfer means 322. For example, the heat transfer means 322 can include a plurality of heat transfer flow channels 324, which can extend through the first region 312 (e.g., internal to the compression chamber) or around the first region 312 (e.g., external to the compression chamber). Cooling fluid input 328 can be provided to an input port 326, and heated cooling fluid output 332 can be provided from output port 330. Although a particular heat transfer means for cooling the working fluid has been illustrated in FIG. 3 , embodiments of the disclosed subject matter are not limited thereto. Rather, other heat transfer means, such as but not limited to direct cooling or closed loop cooling, are also possible according to one or more contemplated embodiments. Working fluid can be input to the first region 312 via suction-side control valve 314 (e.g., check valve) and input line 316, and compressed working fluid can be output from the first region 312 via pressure-side control valve 318 (e.g., check valve) and output line 320. A second region 310 of the compression chamber 304 can be a non-heat transfer region, for example, where the incompressible fluid 308 is initially disposed during the first stage 302 a of operation.
In the initial stage 302 a of operation, the volume of the incompressible fluid (e.g., filling the second region 310) above the mechanical piston 306 can be greater than or at least substantially equal to the volume of the first region 312 (e.g., partially or fully filled with working fluid). In an intermediate stage 302 b, the piston 306 is drive upward (e.g., by a motor, not shown), and the incompressible fluid compresses any working fluid within the first region 312, thereby facilitating heat exchange with the secondary loop and enabling NIC. When the mechanical piston 306 reaches the peak of its axial motion in the final stage 302 c, the incompressible fluid 308 compresses the working fluid to the top dead center (TDC) of the chamber 304, and the compressed working fluid can be discharged from the chamber via output line 320 and valve 318. Recharging with working fluid can be achieved by reversing operation (e.g., from stage 302 c to stage 302 a), with a next batch of working fluid being provided via input line 316 and valve 314. In some embodiments, the NIC system 300 of FIG. 3 can offer one or more of the following benefits, among other benefits: (1) reduced volumetric efficiency loss due to degassing; (2) avoiding use of a liquid-level sensor; (3) increased compression frequency to reduce compressor size; and (4) reducing the liquid friction loss caused by moving liquid through the pipe(s) connecting chambers.

Uni-Directional NIC Systems

In the examples of FIGS. 2A-3 described above, the NIC systems are reciprocating type systems, where either a liquid or mechanical piston returns to its initial position before the next compression cycle. However, other types are also possible according to one or more contemplated embodiments. In some embodiments, a system employing uni-directional fluid flow can be employed, for example, to reduce friction and/or momentum losses. FIG. 4A illustrates an exemplary configuration of such a uni-directional NIC system 400. In the illustrated example, the NIC system 400 includes a compression chamber 404, a pump 426, a pair of switching devices 412, 428, and a fluid reservoir 420. Similar to the above described examples, in compression stage 402 a, incompressible fluid 406 is pumped from fluid reservoir 420 (e.g., via supply line 422, as shown by arrow 424) into the chamber 404 (e.g., via switch 428 and chamber input line 430) by pump 426 to act as a liquid piston for compressing working fluid 408, and heat 410 can be removed from the compressed working fluid 408. The compressed working fluid 408 can then be discharged (e.g., as shown by arrow 416) to the thermodynamic cycle, for example, via supply port 414.
Once compression in the chamber 404 is complete, the system 400 transitions to the reset stage 402 b, for example, by changing a state of switches 412, 428. In some embodiments, one or both of the switches can be three-way valves. Alternatively, other mechanisms for regulating fluid flow are also possible according to one or more contemplated embodiments. In some embodiments, the incompressible fluid can be redirected from the pump 426 to another chamber (not shown) for compression. Meanwhile, the chamber 404 filled with incompressible fluid 406 can be pushed through the compression chamber 404 by working fluid from the thermodynamic cycle (e.g., as shown by arrow 434), for example, via return port 432 and chamber input line 430. The incompressible fluid 406 can thus flow from the compression chamber 404 back to the reservoir 420 (e.g., as shown by arrow 436) via switch 412 and fluid collection line 418. Thus, regardless of whether the NIC system 400 operates in compression or suction, fluid only enters the chamber 404 via the bottom valve 428, fluid exits the chamber 404 via the top switching device 412, and the direction of fluid flow through the chamber 404 can be kept the same.
FIG. 4B illustrates NIC system 400 incorporated into a vapor compression system 440. In the illustrated example, additional details are also shown. For example, system 440 includes a pair of NIC units 450-1, 450-2, a first heat exchanger 464 (e.g., operating as a condenser or gas cooler via heat removal 465), an expansion device 466 (e.g., EEV), a second heat exchanger 468 (e.g., operating as an evaporator via heating 467), a pump 426, a reservoir 420, a fluid accumulator 476, and switches 460-1, 460-2, 470-1, and 470-2 (e.g., three-way valves). Each NIC unit 450-1, 450-2 has a plurality of flow channels 454-1, 454-2 extending between respective input headers or manifolds 452-1, 452-2 and respective output headers or manifolds 456-1, 456-2.
As discussed above, the direction of fluid flow through the channels 454-4, 454-2 can be the same regardless of mode of operation, for example, from the bottom to the top in FIG. 4B. When operating in compression, switches 460-1, 460-2 and switches 470-1, 470-2 can be selected such that incompressible fluid is directed from the pump 426 (e.g., via respective supply lines 480-1, 480-2 and manifold 452-1, 452-2) to the flow channels 454-1, 454-2 to compress the working fluid therein, and such that the compressed working fluid is directed from the channels 454-1, 454-2 (e.g., via respective manifold 456-1, 456-2, respective output lines 458-1, 458-2, and supply line 462). When operating in suction, switches 460-1, 460-2 and switches 470-1, 470-2 can be selected such that working fluid is directed from the second heat exchanger 468 (e.g., via return line 469, respective input line 472-1, 472-2, and respective manifold 452-1, 452-2) to the flow channels 454-1, 454-2, and such that the incompressible fluid is directed from the channels 454-1, 454-2 (e.g., via respective manifold 456-1, 456-2, respective output lines 458-1, 458-2, and supply line 462) to the reservoir 420.

Vapor Compression System Examples

In some embodiments, the compression chambers in the NIC unit can be in the form of plate heat exchangers, for example to improve efficiency and/or reduce a size of the system. Alternatively or additionally, the expansion device can be replaced by an electronic expansion valve (EEV) and a pressure regulator cascade, for example, to allow automatic control of the suction pressure according to the cooling load. Alternatively or additionally, a suction line heat exchanger can be provided. A vapor compression system 500 incorporating such changes is illustrated in FIG. 5 .
In the illustrated example of FIG. 5 , the vapor compression system 500 employs a pair of NIC units 502-1, 502-2, each comprising a sensor 263-1, 263-2, a staging vessel 212-1, 212-2, a plate heat exchanger 504-1, 504-2, and another sensor 264-1, 264-2. A heat transfer fluid (e.g., water) can be provided from an outlet 510 a of heat exchanger 508 (e.g., radiator) to a fluid inlet 506 a-1, 506 a-2 of each plate heat exchanger 504-1, 504-2, and heated heat transfer fluid can be returned from the fluid outlet 506 b-1, 506 b-2 of each plate heat exchanger 504-1, 504-2 to an inlet 510 b of the heat exchanger 508, for example, via junction 528. In addition, the heat transfer fluid can be provided from an outlet 510 a of heat exchanger 508, for example, via junction 530 and input line 522, to the first heat exchanger 520 (e.g., operating as a gas cooler). Heated heat transfer fluid can be returned from the outlet 524 of the first heat exchanger 520 to the inlet 510 b of heat exchanger 508.
Compression and suction modes of the NIC units 502-1, 502-2, as enabled by operation of the pump 216 and configuration of the hydraulic switch 214, may be similar to that described above with respect to FIG. 2C. For example, the compressed working fluid can be discharged from the NIC units 502-1, 502-2 into the first heat exchanger 520 via respective check valves 265-1, 265-2, respective working fluid supply lines 514-1, 514-2, separator 269, and working fluid input 518. The compressed and cooled working fluid can be provided from the first heat exchanger 520 as output 532, which can be directed as input 538 to a suction line heat exchanger 536. Further cooled working fluid can be provided from the suction line heat exchanger 536 as output 540, which can be subjected to pressure reduction via an expansion module 546. For example, the expansion module 546 can comprise a pressure regulator cascade 548 and a back pressure regulator 550. The reduced pressure working fluid can be provided from the expansion module 546 as input 556 to a second heat exchanger 558 (e.g., evaporator). The working fluid can be provided from the second heat exchanger 558 as output 560, which can be directed as input 542 a to the suction line heat exchanger 536. The working fluid can be provided from the suction line heat exchanger 536 as output 542 b, which can be directed as input to the respective NIC units 502-1, 502-2 via junction 568, returns lines 570-1, 570-2, and valves 266-1, 266-2.
Similar to the example of FIG. 2C, system 500 can be provided with various sensors and flow control components at various points throughout to monitor operation thereof. For example, a mass flow rate meter 566 can be installed after the suction line heat exchanger 536 to ensure a constant mass flow rate for a stable cooling capacity supply. Pressure and temperature sensors 267-1, 267-2 can be provided proximal to ports 228-1, 228-2 of each NIC unit 502-1, 502-2. Pressure and temperature sensors 534 can also be provided after the first heat exchanger 520, and pressure and temperature sensors 554 can be provided after the expansion module 546. A temperature sensor 526 can be provided for the heat transfer fluid after the first heat exchanger 520. Another temperature sensor 544 can be provided for the working fluid after the suction line heat exchanger 536 and before the expansion module 546. Another temperature sensor 562 can be provided for the working fluid after the second heat exchanger 558. Yet another temperature sensor 564 can be provided for the working fluid after the suction line heat exchanger 536. Further temperature sensors 512 a, 512 b can be provided for monitoring temperatures of the heat transfer fluid to/from heat exchanger 508.

Computer Implementation Examples

FIG. 6 depicts a generalized example of a suitable computing environment 631 in which the described innovations may be implemented, such as but not limited to a controller for system 100, system 150, system 200, system 260, system 300, system 400, system 440, system 500, or aspects thereof. The computing environment 631 is not intended to suggest any limitation as to scope of use or functionality, as the innovations may be implemented in diverse general-purpose or special-purpose computing systems. For example, the computing environment 631 can be any of a variety of computing devices (e.g., desktop computer, laptop computer, server computer, tablet computer, etc.).
With reference to FIG. 6 , the computing environment 631 includes one or more processing units 635, 637 and memory 639, 641. In FIG. 6 , this basic configuration 651 is included within a dashed line. The processing units 635, 637 execute computer-executable instructions. A processing unit can be a central processing unit (CPU), processor in an application-specific integrated circuit (ASIC), or any other type of processor (e.g., hardware processors, graphics processing units (GPUs), virtual processors, etc.). In a multi-processing system, multiple processing units execute computer-executable instructions to increase processing power. For example, FIG. 6 shows a central processing unit 635 as well as a graphics processing unit or co-processing unit 637. The tangible memory 639, 641 may be volatile memory (e.g., registers, cache, RAM), non-volatile memory (e.g., ROM, EEPROM, flash memory, etc.), or some combination of the two, accessible by the processing unit(s). The memory 639, 641 stores software 633 implementing one or more innovations described herein, in the form of computer-executable instructions suitable for execution by the processing unit(s).
A computing system may have additional features. For example, the computing environment 631 includes storage 661, one or more input devices 671, one or more output devices 681, and one or more communication connections 691. An interconnection mechanism (not shown) such as a bus, controller, or network interconnects the components of the computing environment 631. Typically, operating system software (not shown) provides an operating environment for other software executing in the computing environment 631, and coordinates activities of the components of the computing environment 631.
The tangible storage 661 may be removable or non-removable, and includes magnetic disks, magnetic tapes or cassettes, CD-ROMs, DVDs, or any other medium which can be used to store information in a non-transitory way, and which can be accessed within the computing environment 631. The storage 661 can store instructions for the software 633 implementing one or more innovations described herein.
The input device(s) 671 may be a touch input device such as a keyboard, mouse, pen, or trackball, a voice input device, a scanning device, or another device that provides input to the computing environment 631. The output device(s) 681 may be a display, printer, speaker, CD-writer, or another device that provides output from computing environment 631.
The communication connection(s) 691 enable communication over a communication medium to another computing entity. The communication medium conveys information such as computer-executable instructions, audio or video input or output, or other data in a modulated data signal. A modulated data signal is a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media can use an electrical, optical, radio-frequency (RF), or another carrier.
Any of the disclosed methods can be implemented as computer-executable instructions stored on one or more computer-readable storage media (e.g., one or more optical media discs, volatile memory components (such as DRAM or SRAM), or non-volatile memory components (such as flash memory or hard drives)) and executed on a computer (e.g., any commercially available computer, including smart phones or other mobile devices that include computing hardware). The term computer-readable storage media does not include communication connections, such as signals and carrier waves. Any of the computer-executable instructions for implementing the disclosed techniques as well as any data created and used during implementation of the disclosed embodiments can be stored on one or more computer-readable storage media. The computer-executable instructions can be part of, for example, a dedicated software application or a software application that is accessed or downloaded via a web browser or other software application (such as a remote computing application). Such software can be executed, for example, on a single local computer (e.g., any suitable commercially available computer) or in a network environment (e.g., via the Internet, a wide-area network, a local-area network, a client-server network (such as a cloud computing network), or any other such network) using one or more network computers.
For clarity, only certain selected aspects of the software-based implementations are described. Other details that are well known in the art are omitted. For example, it should be understood that the disclosed technology is not limited to any specific computer language or program. For instance, aspects of the disclosed technology can be implemented by software written in C++, Java™, Python®, and/or any other suitable computer language. Likewise, the disclosed technology is not limited to any particular computer or type of hardware. Certain details of suitable computers and hardware are well known and need not be set forth in detail in this disclosure.
It should also be well understood that any functionality described herein can be performed, at least in part, by one or more hardware logic components, instead of software. For example, and without limitation, illustrative types of hardware logic components that can be used include Field-programmable Gate Arrays (FPGAs), Program-specific Integrated Circuits (ASICs), Program-specific Standard Products (ASSPs), System-on-a-chip systems (SOCs), Complex Programmable Logic Devices (CPLDs), etc.
Furthermore, any of the software-based embodiments (comprising, for example, computer-executable instructions for causing a computer to perform any of the disclosed methods) can be uploaded, downloaded, or remotely accessed through a suitable communication means. Such suitable communication means include, for example, the Internet, the World Wide Web, an intranet, software applications, cable (including fiber optic cable), magnetic communications, electromagnetic communications (including RF, microwave, and infrared communications), electronic communications, or other such communication means. In any of the above-described examples and embodiments, provision of a request (e.g., data request), indication (e.g., data signal), instruction (e.g., control signal), or any other communication between systems, components, devices, etc. can be by generation and transmission of an appropriate electrical signal by wired or wireless connections.

Fabricated Examples and Experimental Results

Example 1

A one-ton capacity prototype refrigeration system was designed and built according to the configuration of FIG. 2C. The prototype system used carbon dioxide as the working fluid and oil as the liquid piston. The prototype system was tested in an environmental chamber maintained at a temperature of 35° C. (environment temperature). The evaporating temperature was set to −5° C., which was finely adjusted using the pressure regulator. The driving speeds of the pumps were configured at 900, 1080, and 1250 revolutions per minute (RPM). FIGS. 7-8 show that a one-ton capacity was attained when the pump speed was set to 1250 RPM. The capacity test result of this prototype demonstrates the viability of integrating an enhanced compression chamber, a control valve, and an advanced system design.
In FIG. 9 , pressure and enthalpy data were graphed to visualize the enthalpy variation during compression. The inclusion of the isothermal line on the graph demonstrates the degree to which the compression process aligns with the ideal isothermal behavior. The striking similarity in the final stages of both chambers not only underscores the reliability of the process but also highlights its consistency and continuity. The isothermal efficiency was determined by comparing it with the ideal isothermal work. At 1250 RPM, Chamber 1 provided a calculated work input of 33.5 KJ/kg, an isothermal work input of 30.8 KJ/kg, and isothermal efficiency of 92%, while Chamber 2 provided a calculated work input of 27.9 KJ/kg, an isothermal work input of 24.6 KJ/kg, and isothermal efficiency of 88%. This exceptionally efficient compression process contributes to the enhancement of the system's COP. If this prototype was implemented on a larger scale, it could potentially lead to a 36% reduction in energy consumption compared to current refrigeration products on the market, offering significant energy savings.

Example 2

Another prototype refrigeration system was designed and built according to the configuration of FIG. 5 . This second prototype system also used carbon dioxide as the working fluid and oil as the liquid piston. Compared with the NIC system of the first prototype of Example 1, the NIC system in this second prototype reduced the overall dimension by 30%. Two water radiators with 3,000 CFM fans discharge compression heat to the ambient. Two capacitance-level sensors are installed to distinguish the gas and fluid levels. The experiments were initially conducted in a psychrometric room to verify the effectiveness of the improvement techniques. As shown in FIG. 10 , the compression chambers exhibit symmetrical temperature and pressure profiles, resulting in a similar isothermal efficiency. Additionally, the level sensors accurately and instantaneously detect when the fluid reaches the top dead center, automatically sending a signal to the DAQ system to switch the directional valve. FIG. 11 presents the results of using an EEV. Unlike pressure regulators, the EEV is sensitive to pressure variation. Hence, the mass flow rate showed a saddle-like profile whenever the gas cooler pressure fluctuated.
FIG. 12 depicts the pressure and enthalpy variations within the compression chamber. Similar to FIG. 9 of Example 1, FIG. 12 illustrates the contributions of heat discharge in the compression chamber, residual gas cooler, and suction line heat exchanger. The calculated isothermal efficiency for the second prototype is 89%, which is 1% lower than the first prototype. This reduction is attributed to the use of a secondary loop, which introduced additional thermal resistance for discharging compression heat. However, based on the average pump and heater power shown in FIG. 11 , the average COP is calculated to be 1.82, representing a 40% improvement over the prototype of Example 1, thus validating the effectiveness of these techniques.

Example 3

The second prototype refrigeration system of Example 2 was subsequently transported to and installed adjacent to a test chamber, which was constructed using a wooden framework and measured as 2.4 m×2.4 m×2.4 m. The roof and walls of the test chamber were covered with Foamular NGX R5 insulation material, with a thermal resistance of 0.88 K·m²/W. The gaps between the board boundaries were sealed with aluminum tape. The floor was the only side without insulation. Inside the chamber, the evaporator was equipped with a 200 W fan, and an additional electric heater was placed to provide extra loading if needed. The first test (Test 1) aimed to demonstrate that the second prototype system delivers cooling capacity at a mild ambient temperature to achieve medium refrigeration conditions of 5° C. Hence, the ambient and chamber temperatures were both initially set to 25° C., and the second prototype system was operated under the subcritical cycle condition.
FIG. 13 shows the test chamber temperature and evaporating temperature/pressure under 25° C. ambient. In FIG. 13 , the test chamber temperature reached 5° C. within 50 minutes, decreasing from 18° C. It should be noted that the data recording was started with the delay, so it does not show the data plot from 25° C. to 18° C. The highest average mass flow rate of CO₂reached 12.9 g/s. The average gas cooler pressure was 7300 kPa, and the average temperature at the hot outlet of the suction line heat exchanger (SLHX) (e.g., heat exchanger 536 in FIG. 5 ) was 29.3° C., delivering an enthalpy of 290.5 KJ/kg. The average evaporator pressure was 3517 kPa, and the average evaporator outlet temperature was 6.9° C., delivering an enthalpy of 442 KJ/kg. This results in an enthalpy difference of 151.5 KJ/kg. Consequently, the cooling capacity of the near-isothermal compressor is 1954 W under this condition. Additionally, the average pump power was 1192 W, yielding a compressor COP of 1.64.
Test 1 demonstrated that the near-isothermal compressor could be operated effectively under subcritical cycle conditions, achieving a cooling capacity of 1954 W. The subsequent test, Test 2, aimed to evaluate the compressor's performance under transcritical cycle conditions. Before initiating Test 2, several air leaks were identified at the floor and wall junctions. These leaks were subsequently sealed and reinforced with aluminum tape to ensure the integrity of the testing environment. FIG. 14 shows the test chamber temperature and evaporating temperature/pressure under 32° C. ambient (Test 2). In Test 2, the test chamber temperature reached 8° C. from 21° C. after 70 minutes of operation and could not be further reduced. The same analysis as in Test 1 was performed. The average gas cooler pressure was 8500 kPa, and the average temperature at the hot outlet of the SLHX was 32.9° C., delivering an enthalpy of 293.9 KJ/kg. The average evaporator pressure was 3267 kPa, and the average evaporator outlet temperature was 10.4° C., delivering an enthalpy of 452 KJ/kg. This resulted in an enthalpy difference of 158.1 KJ/kg. The highest average mass flow rate of CO₂reached 11.1 g/s. Consequently, the cooling capacity of the near-isothermal compressor was 1754 W under this condition. The average pump power was also 1340 W, yielding a compressor COP of 1.31. The system's COP was calculated by subtracting the fan power from the cooling capacity and then dividing it by the total power consumption of the pump and fan. Given a cooling capacity minus fan power of 1554 W and a combined pump and fan power of 1540 W, the COP was about 1.01.

Conclusion

Although the examples and embodiments discussed above primarily focus on vapor compression systems, embodiments of the disclosed subject matter are not limited thereto. Rather, one of ordinary skill in the art would readily appreciate that the teachings for NIC disclosed herein can be readily adapted to other thermodynamic systems and/or compression processes (e.g., standalone compressor for the compression of, for example, air, methane, hydrogen, or other small molecule gas). Moreover, although the term “working fluid” has been used herein, one of ordinary skill in the art will appreciate that this term is not restricted to particular phase. Indeed, the working fluid exist as a liquid phase, a gas phase, or a supercritical phase, according to one or more embodiments of the disclosed subject matter.
Any of the features illustrated or described herein, for example, with respect to FIGS. 1A-14 , can be combined with any other feature illustrated or described herein, for example, with respect to FIGS. 1A-14 , to provide systems, devices, structures, methods, and embodiments not otherwise illustrated or specifically described herein. All features described herein are independent of one another and, except where structurally impossible, can be used in combination with any other feature described herein. In view of the many possible aspects to which the principles of the disclosed technology may be applied, it should be recognized that the illustrated features are only examples and should not be taken as limiting the scope of the disclosed technology. Rather, the scope is defined by the following claims. Applicant therefore claims all that comes within the scope and spirit of these claims.

Claims

1. A system comprising:

at least two near-isothermal compression (NIC) systems, each NIC system comprising one or more chambers and cooling means, each NIC system being constructed to increase a pressure of a working fluid in the one or more chambers via an incompressible fluid acting as a liquid piston, the cooling means being constructed to remove from the working fluid at least some heat generated by the increased pressure;

one or more pumps coupled to the at least two NIC systems and constructed to pump the incompressible fluid to or from the one or more chambers; and

a switching system between the one or more pumps and the at least two NIC systems and constructed to control a flow direction of the incompressible fluid within the respective NIC system,

wherein each NIC system further comprises a staging vessel for the incompressible fluid disposed between the switching system and the corresponding one or more chambers, the staging vessel having a fluid volume greater than a combined fluid volume of the corresponding one or more chambers.

2. The system of claim 1, wherein, for each NIC system:

the fluid volume of the staging vessel is at least two times the fluid volume of the combined fluid volume of the corresponding one or more chambers.

3. The system of claim 1, wherein, for each NIC system:

the cooling means is not in thermal communication with the staging vessel.

4. The system of claim 1, further comprising:

a thermodynamic fluid circuit comprising a first heat exchanger, an expansion device, and a second heat exchanger,

the first heat exchanger being coupled to the at least two NIC systems so as to receive pressurized working fluid from the at least two NIC systems and being constructed to transfer heat from the working fluid flowing through the first heat exchanger,

the expansion device being coupled to the first heat exchanger so as to receive the working fluid from the first heat exchanger and being constructed to reduce a pressure of the working fluid flowing through the expansion device,

the second heat exchanger being coupled to the expansion device so as to receive the working fluid from the expansion device and being constructed to transfer heat to the working fluid flowing through the second heat exchanger, and

the second heat exchanger being further coupled to the at least two NIC systems so as to deliver heated working fluid from the second heat exchanger to the at least two NIC systems.

5. The system of claim 4, wherein:

the switching system comprises a hydraulic switch;

the expansion device comprises an expansion valve or electronic expansion valve;

the first heat exchanger is constructed to operate as a gas cooler or condenser;

the second heat exchanger is constructed to operate as an evaporator; or

any combination of the above.

6. The system of claim 4, further comprising:

a pressure vessel constructed to alternately receive pressurized working fluid from one of the NIC systems and to store the pressurized working fluid for dispensing to the first heat exchanger,

wherein, for each NIC system, a fluid volume of the pressure vessel is greater than a combined fluid volume of the one or more chambers.

7. The system of claim 1, wherein the working fluid is carbon dioxide, and the incompressible fluid is oil.

8. The system of claim 4, further comprising:

a controller operatively coupled to the switching system and comprising one or more processors and one or more non-transitory computer-readable storage media, the computer-readable storage media store computer-readable instructions that, when executed by the one or more processors, cause the one or more processors to:

control the switching system to have a first state where a first of the at least two NIC systems operates in compression mode, and a second of the at least two NIC systems operates in suction mode; and

in response to a predetermined input, control the switching system to have a second state where the first of the at least two NIC systems operates in the suction mode, and the second of the at least two NIC systems operates in the compression mode,

wherein, in each NIC system, each of the one or more chambers has opposing first and second ends, the first end being closer than the second end to the respective staging vessel,

in the compression mode, the incompressible fluid flows in a direction from the first end toward the second end, such that the working fluid is compressed within the one or more chambers and flows toward the thermodynamic fluid circuit via the second end, and

in the suction mode, the incompressible fluid flows in an opposite direction from the second end toward the first end, such that working fluid from the thermodynamic fluid circuit flows into the one or more chambers via the second end.

9-11. (canceled)

12. The system of claim 1, wherein each NIC system is constructed such that the working fluid, the incompressible fluid, or both are injected into the one or more chambers.

13. The system of claim 4, further comprising an economizer constructed to cool the pressurized working fluid from the at least two NIC systems.

14. The system of claim 4, further comprising a separator device disposed between the at least two NIC systems and the first heat exchanger, the separator device being constructed to separate the pressurized working fluid from the incompressible fluid en route to the first heat exchanger.

15. A system comprising:

at least two near-isothermal compression (NIC) systems, each NIC system comprising one or more chambers and a cooling means, each NIC being constructed to increase a pressure of a working fluid in one or more chambers via an incompressible fluid acting as a liquid piston, the cooling means being constructed to remove from the working fluid at least some heat generated by the increased pressure;

one or more pumps coupled to the at least two NIC systems and constructed to pump the incompressible fluid through the one or more chambers;

a switching system coupled to the at least two NIC systems and constructed to control connections of each NIC system to a fluid circuit; and

in response to a predetermined input, control the switching system to have a second state where the first of the at least two NIC systems operates in the suction mode, and the second of the at least two NIC systems operates in the compression mode, wherein, for each NIC system:

each of the one or more chambers has opposing first and second ends, and

in both the compression mode and the suction mode, a direction of the incompressible fluid flow through the one or more chambers is from the first end to the second end.

16. The system of claim 15, further comprising:

the first heat exchanger being coupled to the at least two NIC systems so as to receive pressurized working fluid from the at least two NIC systems and being constructed to transfer heat from the pressurized working fluid flowing through the first heat exchanger,

17. (canceled)

18. The system of claim 16, wherein the switching system comprises:

a first plurality of three-way switches disposed between the second ends of the at least two NIC systems and the thermodynamic fluid circuit; and

a second plurality of three-way switches disposed between the first ends of the at least two NIC systems and the thermodynamic fluid circuit.

19-21. (canceled)

22. A system comprising:

one or more near-isothermal compression (NIC) systems,

each NIC system comprising a chamber, a mechanical piston disposed within the chamber, an incompressible fluid disposed within the chamber, and cooling means,

each NIC system being constructed to increase a pressure of a working fluid within the chamber via axial movement of the mechanical piston,

the incompressible fluid being disposed between the working fluid and a leading end of the mechanical piston during the pressure increase,

the cooling means being constructed to remove from the working fluid at least some heat generated during the pressure increase; and

one or more motors constructed to move the mechanical piston axially within the chamber of the one or more NIC systems.

23. The system of claim 22, further comprising:

the first heat exchanger being coupled to the one or more NIC systems so as to receive pressurized working fluid from the one or more NIC systems and being constructed to transfer heat from the pressurized working fluid flowing through the first heat exchanger,

the second heat exchanger being further coupled to the one or more NIC systems so as to deliver heated working fluid from the second heat exchanger to the one or more NIC systems.

24. The system of claim 23, wherein:

each NIC system has at least one first port and at least one second port,

heated working fluid is delivered from the second heat exchanger to the chamber via the at least one first port, and

pressurized working fluid is supplied from the chamber to the first heat exchanger via the at least one second port.

25. The system of claim 22, wherein:

the cooling means is in thermal communication with only a first portion of the chamber distal from the leading end of the mechanical piston, and

a fluid volume of the first portion is equal to or less than a volume of the incompressible fluid within the chamber.

26. The system of claim 25, wherein:

prior to increasing the pressure, the working fluid fills the first portion of the chamber, and the incompressible fluid fills a second portion of the chamber between the first portion and the leading end of the mechanical piston, and

after increasing the pressure, the incompressible fluid fills the first portion of the chamber.

27. The system of claim 22, wherein the working fluid is carbon dioxide, and the incompressible fluid is oil.

28-29. (canceled)