Patent Application
20110162388
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.
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.
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.
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
Based on the descriptions of
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.
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
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.
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
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
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)
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.
