US20110162388A1

US20110162388A1 - Magnetocaloric device

Info

Publication number: US20110162388A1
Application number: US12/652,197
Authority: US
Inventors: Jayeshkumar Jayanarayan Barve; Shishir Chandrasekhar Menon; Ramasamy Anbarasu; Pradip Radhakrishnan Subramaniam; Vijay Kumar; Sudhakar Eddula Reddy; Ravikumar Hanumantha
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 2010-01-05
Filing date: 2010-01-05
Publication date: 2011-07-07

Abstract

A magneto-caloric (MC) device is disclosed. The MC device comprise a rotor, a housing disposed about and concentric with the rotor and mechanically coupled to the rotor, wherein the housing comprises at least one axial slot, at least one set of MC elements, wherein each set of MC elements comprises at least one MC element, and at least one MC element of each set of MC elements is disposed within each of the at least one axial slots, and at least one working-segment corresponding to each set of MC elements, wherein each working-segment is disposed axially around the rotor and external to the housing, and wherein each working-segment comprises, a yoke substantially defining an inner volume comprising a first inner volume and a second inner volume, and a magnetic field production (MFP) unit magnetically coupled to the yoke and configured to provide a magnetic field within the first inner volume.

Description

BACKGROUND

The subject matter disclosed herein generally relates to magneto-caloric (MC) devices, and refrigeration or a cooling systems based on MC devices.
Conventional refrigeration technologies suffer from several drawbacks. For instance, one of the more common conventional refrigeration technologies, namely, vapor compression (VC) refrigeration, is based on exploitation of the Joule-Thomson (JT) effect, as per which effect, an adiabatic expansion or compression of a gas results in a temperature change of the gas. Such VC refrigeration technologies typically employ chlorofluorocarbon (CFC) based gases as working fluids, or refrigerants, which CFC based working fluids pose well documented environmental challenges, for instance, recycling of the working fluids is known to present significant environment challenges. Furthermore, refrigeration technologies based on the JT effect are mature technologies and extracting additional energy savings out of such technologies has proved difficult.
An alternative refrigeration technique involves a method that takes advantage of entropy change that accompanies a magnetic or magneto-structural phase transition of a MC material. Such refrigeration techniques, quite generally may be referred to as magnetic refrigeration techniques. In the magnetic refrigeration technique, cooling is effected by using a change in temperature resulting from the entropy change of the MC material. More specifically, the MC material used in this method alternates between a low magnetic entropy state with a high degree of magnetic orientation created by applying a magnetic field to the MC material near its Curie transition temperature, and a high magnetic entropy state with a low degree of magnetic orientation that is created by removing the magnetic field from the MC material. Under adiabatic conditions, such transition between high and low magnetic entropy state manifests as transition between low and high lattice entropy state, in turn resulting in warming up or cooling down of the MC material when exposed to magnetization and demagnetization. This is known as the “magneto-caloric effect” (MC effect).
Magnetic refrigeration systems that employ the MC effect provide several advantages over conventional vapor compression refrigeration systems. For instance, magnetic refrigeration systems do not employ CFC based gases. Additionally, magnetic refrigeration systems do not need a gas compressor and therefore are free of compressor-reliability related issues. Furthermore, magnetic refrigeration systems are known to have enhanced energy efficiency as compared to conventional VC based refrigeration systems. Also, magnetic refrigeration systems have reduced vibration and noise levels as compared to conventional VC based refrigeration systems. Accordingly, significant research has been directed at leveraging the MC effect to develop magnetic systems or refrigerators.
Conventional MC effect based magnetic systems require a magnet assembly to effect periodic magnetization and demagnetization cycling of the MC material. Magnetic assemblies according to presently available designs however, suffer from several drawbacks. For instance, presently available designs often utilize complex fluid transfer mechanisms via which circulates a heat exchange fluid. Such designs often suffer from reliability issues or prohibitively high manufacturing costs. Furthermore, many of the present generation designs are not readily scaleable.
A magnetic system that is reliable, energy efficient, and scaleable, would therefore be highly desirable.

BRIEF DESCRIPTION

Embodiments of the invention are directed to a MC device incorporating MC materials and to magnetic refrigeration systems including such MC devices.
A magneto-caloric (MC) device, comprising, a rotor, a housing disposed about and concentric with the rotor and mechanically coupled to the rotor, wherein the housing comprises at least one axial slot, at least one set of MC elements, wherein each set of MC elements comprises at least one MC element, and at least one MC element of each set of MC elements is disposed within each of the at least one axial slots, and at least one working-segment corresponding to each set of MC elements, wherein each working-segment is disposed axially around the rotor and external to the housing, and wherein each working-segment comprises, a yoke substantially defining an inner volume comprising a first inner volume and a second inner volume, and a magnetic field production (MFP) unit magnetically coupled to the yoke and configured to provide a magnetic field within the first inner volume, wherein the rotor is configured to oscillate the at least one axial slot so that the MC elements disposed therein are oscillated between their respective first and second inner volumes, which MC elements are thereby subjected to magnetization-demagnetization cycling.
A refrigeration system, comprising, a first heat exchanger, a second heat exchanger, a MC device, comprising, a rotor, a housing disposed about and concentric with the rotor and mechanically coupled to the rotor, wherein the housing comprises at least one axial slots, at least one set of MC elements, wherein each set of MC elements comprises at least one MC element, and at least one MC element of each set of MC elements is disposed within each of the at least one axial slots, and at least one working-segment corresponding to each set of MC elements wherein each working-segment is disposed axially around the rotor and external to the housing, and wherein each working-segment comprises, a yoke substantially defining an inner volume comprising a first inner volume and a second inner volume, and a magnetic field production (MFP) unit magnetically coupled to the yoke and configured to provide a magnetic field within a first portion of the inner volume, wherein the rotor is configured to oscillate the at least one axial slot so that the MC elements disposed therein are oscillated between their respective first and second inner volumes, which MC elements are thereby subjected to heating-cooling cycling, and a fluid-circuit mechanically coupled to the housing and configured to selectively thermally couple the at least one axial slot to the first heat exchanger or to the second heat exchanger, or to the first heat exchanger and to the second heat exchanger.
A magnetocaloric (MC) device comprising, a rotor comprising a magnetically permeable material, a hermetic housing disposed about and concentric with the rotor and mechanically coupled to the rotor, wherein the hermetic housing comprises at least one axial slot, at least one set of MC elements, wherein each set of MC elements comprises at least one MC element comprising a finned structure, and at least one MC element of each set of MC elements is disposed within each of the at least one axial slot, and at least one working-segment corresponding to each set of MC elements, wherein each working-segment is disposed axially around the rotor and external to the hermetic housing, and wherein each working-segment comprises, a yoke formed as a mechanically closed loop defining an inner volume comprising a first inner volume and a second inner volume, wherein the yoke comprises a magnetically permeable material, and a magnetic field generation and concentration (MFGC) unit magnetically coupled to the yoke and configured to provide a magnetic field within the first inner volume, wherein the rotor is configured to oscillate the at least one axial slot so that the MC elements disposed therein are oscillated between their respective first and second inner volumes, which MC elements are thereby subjected to magnetization-demagnetization cycling.
These and other advantages and features will be more readily understood from the following detailed description of preferred embodiments of the invention that is provided in connection with the accompanying drawings.

DRAWINGS

FIG. 1 is an axial cross-sectional illustration of a MC device according to one embodiment of the invention.

FIG. 2 is a radial cross-sectional view of an MC device according with one embodiment of the invention.

FIG. 3 is a diagrammatic illustration of an exemplary housing for use within MC device embodiments according to aspects of the present invention.

FIG. 4 schematically representation of a refrigeration system, according to one embodiment of the invention.

FIG. 5 schematically representation of a refrigeration system, according to one embodiment of the invention.

FIG. 6 illustrates an exemplary MC element design for use within MC device embodiments according to the present invention.

DETAILED DESCRIPTION

In the following description, whenever a particular aspect or feature of an embodiment of the invention is said to comprise or consist of at least one element of a group and combinations thereof, it is understood that the aspect or feature may comprise or consist of any of the elements of the group, either individually or in combination with any of the other elements of that group.
Those of skill in the art would be aware that MC materials may be classified as positive MC materials or as negative MC materials. Positive MC materials are those which warm up when magnetized and cool down when demagnetized, while negative MC materials cool down when magnetized and warm up when demagnetized. It is stated that the discussions herein are applicable to both positive and negative MC materials. However, for the sake of brevity, the discussions herein are developed with reference to “positive” MC materials. Furthermore, it is noted that, in the discussions herein, the terms “demagnetized” and “unmagnetized” are used interchangeably.
As discussed in detail below, embodiments of the invention are directed to improved magneto-caloric (MC) device designs. The designs proposed herein provide for a magnetic assembly including MC elements. The proposed designs are improved over present generation MC device designs in several ways. Firstly, the inter-related considerations of placement of magnets, and of the design of a return path, within the MC device, for a magnetic field generated by the magnets, have been addressed, resulting in MC devices having efficiency improved over present generation MC devices. Secondly, the MC devices disclosed herein are readily scaleable, in that, changing operational requirements (for example, an increase in heat load), and conditions (for example, constraints as to the space “volume” available for placement of the MC device) can be readily accommodated. Thirdly, disturbance due to movement of MC elements, within a fluid-circuit, is mitigated since the designs proposed herein require only a minimal movement of the MC elements. This results in an enhancement of operational reliability, of the proposed MC devices, over presently available MC devices. These and other aspects of the invention are elaborated in more detail below.
FIG. 1 is an axial cross-sectional illustration of a MC device 100 according to one embodiment of the invention. The MC device 100 includes a rotor 118, and a housing 134 disposed about and concentric with the rotor 118 and mechanically coupled to the rotor 118, wherein the housing 134 includes at least one axial slot 139. The housing 134 may be formed as a hermetic housing or as a semi-hermetic housing, as will be discussed in more detail at least in context of FIGS. 3, 4 and 5. Particular embodiments of the invention comprise housings comprising non-magnetic materials such as steel or plastic. It is clarified that, even though in the MC device embodiment 100 shown in FIG. 1, the housing 134 includes four axial slots 140, 142, 144, and 146, MC device embodiments including other number of axial slots fall within the purview of the present invention. The MC device 100 further includes at least one set of MC elements 120, wherein each set of MC elements comprises at least one MC element and at least one MC element of each set of MC elements is disposed within each of the at least one axial slot 139. For instance, in the MC device embodiment shown in FIG. 1, a particular set of MC elements comprising four MC elements 126, 128, 130, and 132, which four MC elements are disposed individually and respectively within the axial slots 140, 142, 144, and 146. Also, each MC element is appropriately formed so that it does not preclude completely the ability of a fluid to flow across itself when it (that is, the MC element) is placed within an axial slot. For instance, in the embodiment shown in FIG. 1, the MC element 126 is formed so as to include one or more ridges 170 across which a fluid can flow through the axial slot 140.
Furthermore, the at least one set of MC elements 120 are disposed within the housing along an axial direction (of the rotor 118) 122, wherein each member of any particular set of MC elements (120) are disposed at substantially the same axial location within the axial slots 139. For instance, the set of MC elements 120 comprising four individual MC elements 126, 128, 130, and 132, is depicted disposed substantially radially symmetrically individually within the axial slots 140, 142, 144, and 146 at a given axial location of the rotor 118.
The MC device 100 further includes at least one working-segment 138 corresponding to each set of MC elements of the at least one set of MC elements 120. The at least one working-segment 138 is disposed axially around the rotor 118 and external to the housing 134. Each working-segment includes a yoke 104 that substantially defines an inner volume 136, which inner volume may be considered as including a first inner volume 148 and a second inner volume 150. The first inner volume 148, and the second inner volume 150, respectively are defined respectively as those portions of the inner volume 136 wherein is substantially present, or is substantially absent, a magnetic field. The magnetic field in question is a substantially static, that is, substantially time invariant, magnetic field 112 that is produced by a magnetic field production (MFP) unit 152. The MFP unit 152 is magnetically coupled to the yoke 104, which coupling allows the closure of the magnetic field 112 loop within the MC device 100. Quite generally, those of skill in the art would appreciate that the MFP unit 152 is configured to provide the magnetic field 112 within a volume, which volume is referred to herein as the first inner volume 148.
Those of skill in the art would appreciate that the present design of the yoke 104, wherein the yoke forms a closed ring provides for stability against mechanical stresses produced within the yoke 104 due to the passage, within itself (that is, within the yoke 104), of the magnetic field 112 that is produced by the MFP unit 152. The rotor 118 also serves a “magnetic” purpose, in that the rotor 118 helps complete the return path 108 for the magnetic field 112. Particular embodiments of the invention therefore, include a rotor that includes a magnetically permeable material.
In particular embodiments of the invention, the MFP unit 152 comprises at least one of an electromagnet, a permanent magnet, or a superconducting magnet, or a group of permanent magnets in a Hallbach arrangement. The MC device 100 may further include a magnetic field concentrator (MFC) unit 114 configured to concentrate the magnetic field produced by the MFP unit 152. In one embodiment of the invention, the MFP unit is configured to produce a magnetic field of up to about 10 Tesla. In a particular embodiment of the invention, the MFP unit is configured to produce a magnetic field of up to about 7 Tesla. In more particular embodiment of the invention, the MFP unit is configured to produce a magnetic field of up to about 5 Tesla. In more particular embodiment of the invention, the MFP unit is configured to produce a magnetic field of up to about 3 Tesla. In more particular embodiment of the invention, the MFP unit is configured to produce a magnetic field of up to about 2 Tesla. In more particular embodiment of the invention, the MFP unit is configured to produce a magnetic field of up to about 1 Tesla.
For embodiments of the invention that comprise more than one working-segment, the MFP units corresponding to each working-segment are disposed substantially radially symmetrically about the rotor 118. The MC device 100 further includes an air-gap 154 mediate the MFP unit 152 and the housing 134. The provision of the air-gap 154 allows a configuration of the rotor 118 for rotatory motion. In particular embodiments of the invention, the rotor is configured to oscillate the at least one axial slot 139 so that the MC elements disposed therein are oscillated between their respective first and second inner volumes, which MC elements are thereby subjected to magnetization-demagnetization cycling. Evidently, the magnetization-demagnetization cycling of MC elements disposed within any given axial slot occurs substantially simultaneously. However, it is pointed out that MC devices, configured so that one or more MC elements disposed inside any particular axial slot remain unmagnetized, fall within the purview of the present invention. In one embodiment of the invention, the rotor 118 is configured for semi-rotatory motion. Quite generally, it is pointed out that the oscillatory motion of the rotor 118 may comprise rotary motion over any angle.
As discussed, the rotor is configured to oscillate the at least one axial slot so that the MC elements disposed therein are oscillated between their respective first and second inner volumes, which MC elements are thereby subjected to magnetization-demagnetization cycling. It is evident that those MC elements that are moved (during the oscillatory motion of the rotor 118) to within their first inner volumes undergo magnetization, while those MC elements that are moved (during the oscillatory motion) to their second inner volumes undergo demagnetization. For instance, according to the particular “snapshot” view shown in FIG. 1, MC elements 128 and 132, would be magnetized, while MC elements 126 and 130 would be substantially unmagnetized. Those of skill in the art would appreciate that magnetization of an MC element will result in a rise of temperature of the MC element, which rise in temperature may result in the MC element potentially becoming capable of expelling heat to its surroundings or ambient. Similarly, those of skill in the art would appreciate that demagnetization of an MC element will result in a fall in temperature of the MC element, which fall in temperature may result in the MC element potentially becoming capable of absorbing heat from its surroundings or ambient. It will be evident that the expulsion or absorption of heat by an MC element would result respectively in a cooling or heating of the particular MC element. Embodiments of the invention utilize the cooling and heating of the MC elements for realization of a refrigeration or cooling system as is discussed in context of FIGS. 4 and 5.
Based on the descriptions of FIG. 1 herein, those of skill in the art will recognize that each of the MC elements are disposed within any one of the axial slots 139 correspond to a different set of MC elements, wherein each set of MC elements corresponds to a particular working-segment, wherein each working-segment includes a yoke defining a respective inner volume comprising a respective first inner volume and a respective second inner volume. Based on the descriptions herein, it will also be evident that all of the MC elements disposed within any particular axial slot move together (due the oscillation of the rotor 118) into their respective first inner volumes (magnetic field present), as also into their respective second inner volumes (magnetic field substantially absent or much smaller in magnitude as compared to the corresponding first inner volume). Evidently therefore, the MC elements disposed within any particular axial slot get magnetized or demagnetized together. As will be discussed in detail in context of FIGS. 4 and 5, embodiments of the MC device disclosed herein are configurable for use within refrigeration systems. For the purposes of discussion of such refrigeration systems, it will be convenient to regard all of the MC elements disposed within any particular axial slot as a single entity, all portions of which entity (that is, the component MC elements) get magnetized or demagnetized substantially together. Therefore, in the discussions herein, the term “MC element assembly” will refer to such an entity. It is noted that each MC element of an MC element assembly belongs to a different set of MC elements. It is further pointed out that the different MC elements corresponding to any particular MC element assembly may comprise MC materials having substantially different compositions and therefore substantially different Curie temperatures. Furthermore, any particular MC element may comprise more than one MC materials having substantially different compositions and therefore substantially different Curie temperatures.
MC device embodiments comprising a plurality of sets of MC elements and a plurality of working-segments fall within the purview of the present invention. In particular embodiments of such MC devices, each set of MC elements comprises an MC material of a different composition.
In particular embodiments of the MC device 100, the at least one set of MC elements 120 comprises a plurality of sets of MC elements, wherein each set of the plurality of sets of MC elements includes the same number of MC elements. In more particular embodiments of the MC device 100, each set of the at least one set of MC elements 120 consists of an even number of MC elements. Non-limiting examples of MC materials from which the MC elements may be fabricated include alloys including gadolinium (Gd), alloys including manganese and iron, alloys including lanthanum and silicon, alloys of manganese and tin, alloys including nickel, manganese and gadolinium, alloys including lanthanum and manganese and oxygen, and combinations thereof.
FIG. 2 is a radial cross-sectional view of an MC device 200 according with one embodiment of the invention. The MC device 200 includes at least one working-segment 204 (of type 138) and a rotor 206, wherein the working segments (204) are arranged along an axial direction 208 of rotor 206. It is clarified that, the MC device embodiment shown in FIG. 2 is shown as including four working-segments, namely, 212, 214, 216, and 218 for illustrative purposes only. In other words, MC devices including any number of working-segments fall within the purview of the present invention. The number of working-segments required would be dictated by operational requirements such as load, and/or desired cooling temperature span to be covered by the device, and/or MC materials used, and/or space constraints. The MC device 200 further includes a housing 210 (of type 134) disposed axially along axial direction 208 and including at least one axial slot 236. Each of the working-segments has a corresponding set of MC elements, wherein the number of MC elements within a set is the same as the number of axial slots, and one MC element of a set of MC elements is disposed within one of the axial slots. For the sake of clarity, no MC elements are shown disposed within the axial slots 236. However, a manner of disposition of the MC elements within the axial slots is evident from FIG. 1, wherein the MC elements 126, 128, 130, and 132 are disposed respectively within axial slots 140, 142, 144, and 146.
Ports are provided at the axial extremities of, for example, the two axial slots 238 and 240 of the housing 210, via which ports the MC device may 200 be coupled (“connected”) to a fluid-circuit, as is discussed in more detail in context of FIGS. 4 and 5. For instance, ports 224 and 226 are provided at the axial extremities of axial slot 238 and allow for a fluid flow path 234, while ports 228 and 230 are provided at the axial extremities of axial slot 240, and allow for a fluid flow path 235.
FIG. 3 is a diagrammatic illustration of an exemplary housing 300 for use within MC device, some embodiments of which MC device (for instance, MC device embodiments 100, 200) are disclosed herein. The housing 300 includes an inner surface 318, and an outer surface 320. The volume enclosed within the inner surface 318, and the outer surface 320 is substantially solid except that it includes four axial slots (not visible/shown) that run along the axial direction 322 of the housing 300. Ports are provided at the extremities of each of the four axial slots, which ports may be used to couple the housing to a fluid-circuit, as discussed in detail in context of FIGS. 4 and 5. In the housing illustrated in FIG. 3, ports 302 and 304, 306 and 308, 310 (not visible/shown) and 312 (not visible/shown), and 314 and 316 are provided respectively at the extremities of the four axial slots. It is remarked that, even though the housing embodiment shown in FIG. 3 includes four axial slots, housings with other numbers of axial slots (and therefore, including correspondingly other numbers of ports) fall within the purview of the present invention.
MC devices, representative embodiments of which are disclosed herein (for instance, MC device 100, or MC device 200) are configurable for use within refrigeration systems. Refrigeration systems that incorporate embodiments of the MC device disclosed herein, therefore, fall within the purview of the present invention. FIG. 4 schematically depicts principles of design and operation of one embodiment of a refrigeration system 400 according to the present invention. The refrigeration system 400 depicted in FIG. 4 includes an MC device 402 including four MC element assemblies 404, 406, 408, and 410. The MC device 402 is similar in design and construction to MC device embodiments 100 or 200 disclosed herein. Accordingly, only those components that are more pertinent for the present discussions are illustrated in FIG. 4. Accordingly, blocks 404, 406, 408, and 410 are schematic representations of four MC element assemblies that are provided as part of the MC device 402. As discussed earlier, each of the four MC device assemblies are disposed within a corresponding axial slot, wherein each of the axial slots are coupled, via for example, ports (as discussed earlier), to a fluid-circuit. These and other aspects of the invention are now discussed in detail.
The refrigeration system 400 includes a first heat exchanger 412 and a second heat exchanger 414. The refrigeration system 400 further includes the MC device 402 including a rotor (not shown; similar, for example, to rotor 118), a housing (not shown; similar, for example, to housing 300) disposed about and concentric with the rotor and coupled to the rotor, wherein the housing includes at least one axial slot (not shown; similar, for example to axial slots 139). The axial slots are positioned radially symmetrically within the housing. In other words, the MC element assemblies 404, 406, 408, and 410 are disposed radially symmetrically about the rotor. As discussed earlier, the refrigeration system 400 includes at least one set of MC elements (not indicated in FIG. 4; each set of the at least one set of MC elements being similar, for example, to the set of MC elements 124), wherein each set of MC elements includes at least one MC element, and at least one MC element of each set of MC element is disposed within each of the at least one axial slot. The refrigeration system further includes a plurality of working-segments (not depicted; each of the plurality of the working-segments being similar, for example, to working-segment 212) disposed axially around the rotor (that is, along the length of the rotor 206) and external to the housing. Each working-segment includes a yoke (not depicted; similar to yoke 104) substantially defining an inner volume (for instance, of type 148) including a first inner volume (for instance, of type 148) and a second inner volume (for instance, of type 150), and a magnetic field production (MFP) unit (not depicted; similar for example, to MFP unit 152) magnetically coupled to the yoke and configured to provide a magnetic field within the first inner volume. The rotor is configured to oscillate the at least one axial slot so that the MC elements disposed therein are oscillated between their respective first and second inner volumes, which MC elements are thereby subjected to heating-cooling cycling. In other words, the rotor is configured to oscillate each of the MC element assemblies so that the constituent MC elements of the MC element assemblies are oscillated between their respective first inner volumes and their respective second inner volumes, subjecting the constituent MC elements to magnetization-demagnetization cycling, or equivalently, in light of the magneto-caloric effect, to heating-cooling cycling.
In order to illustrate a mode of operation of the refrigeration system 400, consider the situation wherein, for instance, the MC element assemblies 404 and 406 are magnetized due to, for instance, a first half-cycle of an oscillatory motion of the rotor, via which motion the constituent MC elements of which MC element assemblies are moved (together) into their respective first inner volumes. Evidently, the same motion of the rotor would result in a demagnetization of the constituent MC elements of the remaining MC element assemblies, namely, 408 and 410, by moving the constituent MC elements into their respective second inner volumes. According the magneto-caloric effect, the temperature of the magnetized MC element assemblies will rise (that is, they will heat up), while the temperature of the demagnetized MC element assemblies will fall (that is, they will cooled down). The refrigeration system 400 utilizes the heating and cooling of the MC element assemblies as just described, to perform its refrigeration action as is now discussed.
The refrigeration system 400 further includes a fluid-circuit 416 coupled to the housing and configured to selectively thermally couple, via a thermal or heat transfer fluid, the at least one axial slots to the first heat exchanger 412 or to the second heat exchanger 414, or to the first heat exchanger 412 and the second heat exchanger 414. The fluid-circuit 416 as described will, evidently, also selectively thermally couple the MC element assemblies corresponding to the at least one axial slot, to the first heat exchanger 412 or to the second heat exchanger 414, or to the first heat exchanger 412 and the second heat exchanger 414. The fluid-circuit 416 together with the axial slots 404, 406, 408, and 410 form a fluid flow path, the flow of thermal fluid within portions of which flow path is independently controllable via appropriate operation of provided valving. In particular embodiments of the refrigeration system 400, the fluid-circuit 416 includes at least one control valve as part of the valving. A mode of operation of any of the control valves may a latching mechanism wherein the latching mechanism comprises magnetic latching, mechanical latching, hydraulic latching, pneumatic latching, magneto-rheological latching, electro-rheological latching, or combinations thereof. In particular embodiments of the invention, the control valve comprises a solenoid valve.
In one mode of operation of the refrigeration system 400, via appropriately provided and operated valving 418, a thermal fluid provided within the fluid-circuit 416, and having an initial temperature substantially lower than the lowest temperature within the MC element assemblies 404 and 406, is allowed to extract heat from the MC element assemblies 404 and 406. As a result of the extraction of heat, the thermal fluid heats up. The thermal fluid is subsequently channeled, again via appropriately provided and operated valving 420, to the first heat exchanger 412, which first heat exchanger 412 is configured to extract heat from the thermal fluid, and at least a portion of the extracted heat is disposed to the ambient. In other words, the refrigeration system 400 is configured to enable the first heat exchanger to extract heat from the thermal fluid. The thus cooled thermal fluid is now channeled to the MC element assemblies 408 and 410, via appropriately provided and operated valving 422. The thermal fluid, upon contact with the MC element assemblies 408 and 410, dispels heat to the MC element assemblies 408 and 410 and thereby is cooled down further to a sufficiently low temperature below ambient. Subsequently, the thermal fluid, now at a temperature below ambient, is channeled, via appropriately provided and operated valving 424, to a second heat exchanger 414, wherein, being at a temperature lower than the temperature of the second heat exchanger 414, the thermal fluid extracts heat from the second heat exchanger 414, which extraction of heat results in a cooling at the second heat exchanger. In other words, the refrigeration system 400 is configured to enable the second heat exchanger to inject heat to the thermal fluid. Evidently, MC elements having substantially different Curie temperatures, may be arranged “sequenced” within any particular MC element assembly in a canonical manner (for instance, in either increasing, or for instance, in decreasing order of their respective Curie temperatures) in order to achieve, during operation of the MC device, a required temperature change of the thermal fluid.
Similar to the above description of operation of refrigeration system 400 during the first half-cycle of the oscillatory motion of the rotor, during a second half-cycle of the oscillatory motion of the rotor, the MC element assemblies 408 and 410 are magnetized, while MC element assemblies 404 and 406 are demagnetized. The flow direction of the thermal fluid across the MC element assemblies during the second half-cycle is reversed in comparison to the flow direction during the first-half cycle. Consider now FIG. 5 for a description of the operation of the refrigeration system 400 during the second half-cycle of the oscillatory motion of the rotor. Via appropriately provided and operated valving 424, a thermal fluid provided within the fluid-circuit 416, and having an initial temperature substantially lower than the lowest temperature within the MC element assemblies 408 and 410, is allowed to extract heat from the MC element assemblies 408 and 410. As a result of the extraction of heat, the temperature of the thermal fluid rises above the temperature of the ambient. The thermal fluid is subsequently channeled, again via appropriately provided and operated valving 422, to the first heat exchanger 412, wherein, at least a portion of the extracted heat is dispelled to the ambient. The thus cooled thermal fluid is now allowed to dispose heat to the MC element assemblies 404 and 406, and therefore cool down further to a temperature below ambient, and, via appropriately provided and operated valving 420 is now channelled to the MC element assemblies 404 and 406. Subsequently, the thermal fluid, now at a temperature below ambient, is channeled, via appropriately provided and operated valving 418, to a second heat exchanger 414, wherein, being at a temperature lower than the temperature of the second heat exchanger 414, the thermal fluid extracts heat from the second heat exchanger 414, which extraction of heat results in a cooling down at the second heat exchanger.
In particular embodiments of the refrigeration system 400, the thermal fluid includes at least one liquid, or at least one gas, or combinations thereof. Non-limiting examples of a suitable liquid include water, propylene glycol, ethylene glycol, Silicone oil, mineral oil, and other commercially available heat transfer fluids such as dynalene, paratherm, syltherm, and combinations thereof. Non-limiting examples of a suitable gas include air, helium, argon, nitrogen, and combinations thereof. Non-limiting examples of the second heat exchanger include a cold storage chamber or freezer used for storing food materials.
As discussed herein, the design of an MC element needs to enable efficient heat transfer between the MC element (or an MC element assembly), and the thermal fluid. Accordingly, MC elements designed for use within embodiments of the present invention, may advantageously possess a high heat-transfer surface-area to volume ratio, typically of up to about 50 per millimeter (mm) FIG. 6 illustrates an exemplary MC element design 600 as may be used within MC device embodiments according to the present invention. The MC element design includes a double-layered structure 602, including a “top” layer 604 and a “bottom” layer 606, wherein the top layer 604 and the bottom layer 606 include multiple channels or “grooves” 602 of width between about 0.01 to about 10 mm and height between about 0.01 to about 100 mm. It may be appreciated that the multiple channels serve to enhance the surface area of the double-layered structure, as well as provide a convenient mechanism to admit flow of the thermal fluid across the MC element, when it is disposed within a housing. More particular embodiments of the MC element may include protective coatings 608 to protect the MC element from any corrosive action of the thermal fluid. In particular embodiments of the invention, the protective are thermally conductive. Non-limiting examples of coatings including a nitride compound, nickel, aluminum, copper, carbon, silver, or gold. Quite generally, any protective coating that does not chemically react with, and/or is otherwise compatible with the MC elements and/or the thermal fluid, and/or has appropriate thermal conductivity, and/or remains sufficiently robust during the operational life of the MC element to which it corresponds, are appropriate for use within embodiments of the present invention. In more particular embodiments of the invention, the MC element, comprises a single layered structure. In more particular embodiments of the invention, the MC element comprises a structure with fluid flow paths that span the axial length of the MC element. In more particular embodiments of the invention, the MC element comprises a fluid-permeable structure. The surfaces of the MC elements may be fashioned to include features such as dimples, groves, threads, micro-fins, or multiple spiral coils to increase the flow rate and/or turbulence, and hence increase thermal transfer efficiency between the thermal fluid and the MC elements. In one embodiment of the invention, surface roughness of the protective coatings lies within a range from about 1 micrometer to about 1000 micrometers.
Based on the discussions herein, according to one embodiment of the invention, a MC device (for instance, of type 100) is provided. The MC device includes a rotor (for instance, of type 118) including a high magnetic permeability material, a hermetic housing (for instance, of type 300) disposed about and concentric with the rotor and mechanically coupled to the rotor, wherein the hermetic housing includes at least two axial slots (for instance, of type 139). The MC device further includes at least one set of MC elements (for instance, of type 120), wherein each set of MC elements includes at least two double-layer-finned MC elements (for instance, of type 600), and at least one MC element of each set of MC elements is disposed within each of the at least two axial slots (for instance, of type 139), and at least one working-segment (for instance, of type 204) disposed axially around the rotor and external to the hermetic housing. Each working-segment includes a yoke (for instance, of type 104) formed at least as a mechanically closed loop defining an inner volume (for instance, of type 136) including a first inner volume (for instance, of type 148) and a second inner volume (for instance, of type 150), wherein the yoke includes a high magnetic permeability material, and a magnetic field generation and concentration (MFGC) unit magnetically coupled to the yoke and configured to provide a magnetic field within the first inner volume. Furthermore, rotor is configured to oscillate each of the at least one axial slots between the first inner volume and the second inner volume, subjecting the MC elements disposed therebetween to magnetization-demagnetization cycling.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

Claims

1. A magneto-caloric (MC) device, comprising:

a rotor;

a housing disposed about and concentric with the rotor and mechanically coupled to the rotor, wherein the housing comprises at least one axial slot;

at least one set of MC elements, wherein each set of MC elements comprises at least one MC element, and at least one MC element of each set of MC elements is disposed within each of the at least one axial slots; and

at least one working-segment corresponding to each set of MC elements, wherein each working-segment is disposed axially around the rotor and external to the housing, and wherein each working-segment comprises:

a yoke substantially defining an inner volume comprising a first inner volume and a second inner volume; and

a magnetic field production (MFP) unit magnetically coupled to the yoke and configured to provide a magnetic field within the first inner volume;

wherein the rotor is configured to oscillate the at least one axial slot so that the MC elements disposed therein are oscillated between their respective first and second inner volumes, which MC elements are thereby subjected to magnetization-demagnetization cycling.

2. The MC device of claim 1, wherein the rotor is configured for semi-rotatory motion.

3. The MC device of claim 1, wherein the housing comprises, a hermetic housing, or a semi-hermetic housing.

4. The MC device of claim 1, further comprising an air-gap mediate the MFP unit and the housing.

5. The MC device of claim 1, wherein the MFP unit comprises at least one of an electromagnet, a permanent magnet, a superconducting magnet, or a group of permanent magnets in a Hallbach arrangement.

6. The MC device of claim 1, wherein the MFP unit can produce a magnetic field of up to about 10 Tesla.

7. The MC device of claim 1, further comprising a magnetic field concentrator (MFC) unit configured to concentrate the magnetic field produced by the MFP unit.

8. The MC device of claim 1, wherein each of the at least one set of MC elements comprises alloys including gadolinium (Gd), alloys including manganese and iron, alloys including lanthanum and silicon, alloys of manganese and tin, alloys including nickel, manganese and gadolinium, alloys including lanthanum and manganese and oxygen, and combinations thereof.

9. The MC device of claim 1, wherein the at least one set of MC elements comprises a plurality of sets of MC elements, wherein each set of the plurality of sets of MC elements comprises the same number of MC elements.

10. The MC device of claim 1, wherein the housing comprises a non-magnetic material.

11. The MC device of claim 1, wherein the rotor comprises a magnetically permeable material.

12. The MC device of claim 1, comprising a plurality of sets of MC elements and a plurality of working-segments.

13. The MC device of claim 12, wherein the sets of MC elements comprise MC materials comprising more than one composition.

14. A refrigeration system, comprising:

a first heat exchanger;

a second heat exchanger;

a MC device, comprising:

a rotor,

at least one set of MC elements, wherein each set of MC elements comprises at least one MC element, and at least one MC element of each set of MC elements is disposed within each of the at least one axial slots;

and at least one working-segment corresponding to each set of MC elements wherein each working-segment is disposed axially around the rotor and external to the housing, and wherein each working-segment comprises:

a magnetic field production (MFP) unit magnetically coupled to the yoke and configured to provide a magnetic field within a first portion of the inner volume;

wherein the rotor is configured to oscillate the at least one axial slot so that the MC elements disposed therein are oscillated between their respective first and second inner volumes, which MC elements are thereby subjected to heating-cooling cycling; and

a fluid-circuit mechanically coupled to the housing and configured to selectively thermally couple the at least two axial slots to the first heat exchanger or to the second heat exchanger, or to the first heat exchanger and to the second heat exchanger.

15. The refrigeration system of claim 14, wherein the housing comprises a hermetic housing, or a semi-hermetic housing.

16. The refrigeration system of claim 14, wherein the fluid-circuit comprises at least one solenoid valve.

17. The refrigeration system of claim 16, wherein a mode of operation of the solenoid valve comprises a latching mechanism.

18. The refrigeration system of claim 17, wherein the latching mechanism comprises magnetic latching, mechanical latching, hydraulic latching, pneumatic latching, or combinations thereof.

19. The refrigeration system of claim 13, further comprising a thermal fluid wherein the thermal fluid comprises at least one liquid, or at least one gas, or combinations thereof.

20. The refrigeration system of claim 19, configured to enable the first heat exchanger to extract heat from the thermal fluid.

21. The refrigeration system of claim 19, configured to enable the second heat exchanger to inject heat to the thermal fluid.

22. A magnetocaloric (MC) device comprising:

a rotor comprising a magnetically permeable material;

a hermetic housing disposed about and concentric with the rotor and mechanically coupled to the rotor, wherein the hermetic housing comprises at least one axial slots;

at least one set of MC elements, wherein each set of MC elements comprises at least one MC element comprising a finned structure, and at least one MC element of each set of MC elements is disposed within each of the at least one axial slot; and

at least one working-segment corresponding to each set of MC elements, wherein each working-segment is disposed axially around the rotor and external to the hermetic housing, and wherein each working-segment comprises:

a yoke formed as a mechanically closed loop defining an inner volume comprising a first inner volume and a second inner volume, wherein the yoke comprises a magnetically permeable material; and

a magnetic field generation and concentration (MFGC) unit magnetically coupled to the yoke and configured to provide a magnetic field within the first inner volume;

23. The MC device of claim 22, wherein the MC elements comprise a protective coating.

24. The MC device of claim 23, wherein the coating comprises a nitride compound, nickel, aluminum, copper, carbon, silver, gold, or combinations thereof.

25. The MC device of claim 22, wherein at least one MC element comprises a double finned structure.