Regenerator including magneto caloric material with channels for the flow of heat transfer fluid

The present invention provides a regenerator having magneto caloric material (MCM) configured with flow channels for the passage of a heat transfer fluid through the MCM. The flow channels are created by positioning elongate elements of the MCM adjacent to each other. The elongate elements provide surface area necessary for heat transfer while the flow channels reduce the pressure drop incurred by the heat transfer fluid as it flows through the regenerator. The elongate elements can also be configured with MCM having different Curie temperatures (e.g., different Curie temperature ranges) in order to accommodate a variety of ambient conditions in which the regenerator may be used.

FIELD OF THE INVENTION

The subject matter of the present disclosure relates generally to a regenerator having magneto caloric material with one or more channels for the flow of heat transfer fluid.

BACKGROUND OF THE INVENTION

Magneto caloric material (MCM)—i.e. a material that exhibits the magneto caloric effect—provides a potential alternative to fluid refrigerants used in e.g., heat pump applications. In general, the magnetic moments of a normal MCM will become more ordered under an increasing, externally applied magnetic field and cause the MCM to generate heat. Conversely, decreasing the externally applied magnetic field will allow the magnetic moments of the MCM to become more disordered and allow the MCM to absorb heat. Some MCM types exhibit the opposite behavior—i.e. generating heat when a magnetic field is removed and becoming cooler when placed into the magnetic field. This latter type can be referred to as inverse or para-magneto caloric material. Both normal and inverse MCM are referred to collectively herein as magneto caloric material or MCM. The theoretical cycle efficiency of a refrigeration cycle based on an MCM and the magnetic caloric effect can be significantly higher than for a comparable refrigeration cycle based on a fluid refrigerant.

Challenges exist to the practical and cost competitive use of an MCM, however. In addition to the development of suitable types of MCM, equipment that can attractively utilize an MCM is still needed. Some MCM-based devices use a regenerator having a construction where a heat transfer fluid flows between parallel plates constructed of MCM. Other regenerators may use beds of MCM particles through which the heat transfer fluid flows to exchange heat. The plate arrangement can provide for a low pressure drop in the flow of the heat transfer fluid through the regenerator but suffers from an overall low surface area for heat transfer. Regenerators using particle beds provide substantial surface area for heat transfer but also incur a substantial pressure drop in the flow of the heat transfer fluid.

Additionally, the ambient conditions under which the MCM-based regenerator may be applied can vary substantially. For example, for a refrigerator appliance placed in a garage or located in a non-air conditioned space, ambient temperatures can range from below freezing to over 90° F. Some types of MCM are capable of accepting and generating heat only within a much narrower temperature range (sometimes referred to as the Curie temperature range) than presented by such ambient conditions. Also, different MCM types may exhibit the magneto caloric effect more prominently at different temperatures.

Accordingly, a regenerating device that can address certain challenges including those identified above would be useful. Particularly, a regenerator that can provide improved pressure drop and surface area for the heat transfer fluid would be useful. A regenerator that can be equipped for use in a wide range of ambient temperature conditions would be also be beneficial. A heat pump or appliance using such a regenerator would also be useful.

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides a regenerator having magneto caloric material (MCM) configured with flow channels for the passage of a heat transfer fluid through the MCM. The flow channels are created by positioning elongate elements of the MCM adjacent to each other. The elongate elements provide surface area necessary for heat transfer while the flow channels reduce the pressure drop incurred by the heat transfer fluid as it flows through the regenerator. The elongate elements can also be configured with MCM having different Curie temperatures (e.g., different Curie temperature ranges) in order to accommodate a variety of ambient conditions in which the regenerator may be used. The present invention also includes a heat pump or appliance incorporating such a regenerator. Additional aspects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention.

In one exemplary embodiment, the present invention provides a regenerator that includes a working unit extending along a longitudinal direction between a first end of the regenerator and a second end of the regenerator. The working unit includes a plurality of discrete, elongate elements defining a plurality of flow channels extending along the longitudinal direction and configured for the flow of a heat transfer fluid through the flow channels. Each elongate element is constructed from magneto caloric material.

In another exemplary embodiment, the present invention includes a heat pump having a regenerator. The regenerator defines a circumferential direction along which the regenerator is rotatable and extends along an axial direction between a first end and a second end. The regenerator includes a plurality of working units arranged adjacent to each along the circumferential direction and extending along the longitudinal direction between the first end of the regenerator and the second end of the regenerator. Each working unit includes a plurality of discrete, elongate elements defining a plurality of flow channels extending along the longitudinal direction and configured for the flow of a heat transfer fluid therethrough. Each elongate element includes magneto caloric material.

For this embodiment, a magnetic device is positioned proximate to the working units and extends along the longitudinal direction. The magnetic device creates a field of magnetic flux and is positioned so that one or more of the plurality of working units are moved in and out of the magnetic field as the working units are rotated along the circumferential axial direction.

The present invention also includes an appliance, such as e.g., a washing machine, incorporating the exemplary regenerator or heat pump.

DETAILED DESCRIPTION OF THE INVENTION

Referring now toFIG. 1, an exemplary embodiment of a refrigerator appliance10is depicted as an upright refrigerator having a cabinet or casing12that defines a number of internal storage compartments or chilled chambers. In particular, refrigerator appliance10includes upper fresh-food compartments14having doors16and lower freezer compartment18having upper drawer20and lower drawer22. The drawers20,22are “pull-out” type drawers in that they can be manually moved into and out of the freezer compartment18on suitable slide mechanisms.

Refrigerator10is provided by way of example only. Other configurations for a refrigerator appliance may be used as well including appliances with only freezer compartments, only chilled compartments, or other combinations thereof different from that shown inFIG. 1. In addition, the regenerator or heat pump system of the present invention is not limited to appliances and may be used in other applications such as e.g., air-conditioning, electronics cooling devices, and others. Thus, it should be understood that while the use of a heat pump to provide cooling within a refrigerator is provided by way of example herein, the present invention may also be used in other applications to provide for heating and/or cooling as well.

FIG. 2is a schematic view of another exemplary embodiment of a refrigerator appliance10including a refrigeration compartment30and a machinery compartment40. In particular, machinery compartment30includes an exemplary heat pump system52of the present invention having a first heat exchanger32positioned in the refrigeration compartment30for the removal of heat therefrom. A heat transfer fluid such as e.g., an aqueous solution, flowing within first heat exchanger32receives heat from the refrigeration compartment30thereby cooling its contents. A fan38may be used to provide for a flow of air across first heat exchanger32to improve the rate of heat transfer from the refrigeration compartment30.

The heat transfer fluid flows out of first heat exchanger32by line44to heat pump100. As will be further described herein, the heat transfer fluid receives additional heat associated with the magneto caloric effect provided by MCM in heat pump100and carries this heat by line48to pump42and then to second heat exchanger34. Heat is released to the environment, machinery compartment40, and/or another location external to refrigeration compartment30using second heat exchanger34. A fan36may be used to create a flow of air across second heat exchanger34and thereby improve the rate of heat transfer to the environment. Pump42connected into line48causes the heat transfer fluid to recirculate in heat pump system52. Motor28is in mechanical communication with heat pump100as will be further described.

From second heat exchanger34the heat transfer fluid returns by line50to heat pump100where, as will be further described below, due to the magneto caloric effect, the heat transfer fluid loses heat to the MCM in heat pump100. The now colder heat transfer fluid flows by line46to first heat exchanger32to receive heat from refrigeration compartment30and repeat the cycle as just described.

Heat pump system52is provided by way of example only. Other configurations of heat pump system52may be used as well. For example, lines44,46,48, and50provide fluid communication between the various components of the heat pump system52but other heat transfer fluid recirculation loops with different lines and connections may also be employed. Valves can be placed in one or more of lines44,46,48, and50to e.g., control flow and may communicate with a controller (now shown) configured for operating heat pump system52according to certain exemplary aspects of the present invention. Additionally, pump42can also be positioned at other locations or on other lines in system52. Pump42may be e.g., a variable speed pump operated by a controller according to certain exemplary aspects of the present invention. Still other configurations of heat pump system52may be used as well. Heat pump system52could also be configured with e.g., air-conditioning systems and other applications in addition to a refrigeration appliance.

FIGS. 3, 4, 5, and 6depict various views of an exemplary heat pump100of the present invention. Heat pump100includes a regenerator101having a regenerator housing102and extending along a longitudinal direction between a first end118and a second end120. The longitudinal direction is also parallel to axial direction, denoted by axis A-A, about which regenerator housing102rotates during operation. A radial direction R is defined by a radius extending orthogonally from the axis of rotation A-A (FIG. 6). A circumferential direction is indicated by arrows C (FIG. 5), which also denote the direction (clockwise or counter-clockwise) in which regenerator101can be rotated during operation.

Regenerator housing102defines a plurality of chambers104that extend longitudinally along the axial direction defined by axis A-A. Chambers104are positioned proximate or adjacent to each other along circumferential direction C. Each chamber104includes a pair of openings106and108positioned at opposing ends118and120of regenerator housing102(FIG. 4).

For this exemplary embodiment, heat pump100also includes a plurality of working units112—which are depicted schematically inFIGS. 4 and 5and are further described herein. Each working unit112contains MCM, is located in one of the chambers104, and extends along axial direction A-A. For the exemplary embodiment shown in the figures, heat pump100includes eight discrete working units112positioned adjacent to each other along circumferential direction C as shown and extending longitudinally along the axial direction A-A. As will be understood by one of skill in the art using the teachings disclosed herein, a different number of working units112other than eight may be used as well. For example, 2, 4, 6, 12, and other numbers of working units (and associated chambers) may also be used.

As will also be understood using the teachings disclosed herein, the present invention is not limited to a regenerator101with a housing102having the structure shown inFIG. 4. Instead, other configurations may be used for creating multiple working units112. For example, regenerator101can be provided without a housing102having chambers104for each working unit112. In such an embodiment, the working units112can be defined by the MCM. For example, the working units112could be partitioned along circumferential direction C by multiple spaces dividing the MCM into working units112instead of being partitioned by the walls defining chambers104. In still another embodiment, MCM could be provided having channels, grooves, or other features dividing the MCM along the circumferential direction C into multiple working units112. Other configurations where regenerator101or housing102does not include structure such as chambers104for partitioning the MCM into the various working units112could be used as well.

For this exemplary embodiment of heat pump100, a pair of valves113and115are positioned at axial ends of regenerator housing102(FIG. 4). Together valves113and115include a pair of rotatable plates114and116, a pair of fixed plates121and123, and pair of gaskets117and119. As will be further described, gaskets117and119are configured to provide fluids seals between the pair of rotatable plates114,116and the pair of fixed plates121,123, respectively.

First rotatable plate114is attached to first end118and second rotatable plate116is attached to second end120. As shown inFIG. 4andFIG. 7(only rotatable plate114is shown inFIG. 7—plate116would be substantially identical in construction), each rotatable plate114and116includes a plurality of apertures122and124, respectively. For this exemplary embodiment, apertures122and124are configured as circumferentially-extending slots that are spaced apart along circumferential direction C.

Using rotatable plate114by way of example, gasket117is received into a recess131defined by plate114. A plurality of projections129extend from plate114along axial direction A towards fixed plate121and define apertures122. Gasket117defines a plurality of channels125in which projections129are received. As such, channels125and projections129help secure the position of gasket117relative to rotatable plate114by preventing gasket117from rotating relative to plate114during operation of the heat pump. For this exemplary embodiment, the opposing faces133and135of gasket117contact fixed plate121and rotatable plate114, respectively, to form a fluid tight seal therebetween. During operation, as regenerator housing102rotates about axis A-A, gasket117rotates with rotatable plate114and also slides over the inside face137(FIG. 4) of fixed plate121while maintaining the fluid seal. A similar construction and operation is used for fixed plate123with inside face139, gasket119with opposing faces141and143, and rotatable plate116. The plurality of apertures122and124of the first and second rotatable plates114and116are aligned with the plurality of apertures125and127of the pair of gaskets117and119so as to provide fluid communication therebetween.

A variety of constructions may be used for gaskets117and119. For example, gaskets117,119could be constructed from a homogenous material or could be constructed from layers and/or segments of different materials. Gaskets117,119could be a unitary part as shown or could be formed from multiple parts. Also, gaskets117and119could be formed from one or more materials deposited, adhered, or layered onto e.g., plates114,116. For example, gaskets117and119could be formed as coatings on plates114,116. Gaskets117and119could be formed from elastomeric or other pliable materials. Other constructions may be used as well.

Each aperture122is positioned adjacent to a respective opening106of a chamber104. Each aperture124is positioned adjacent to a respective opening108of a chamber104. Accordingly, a heat transfer fluid may flow into a chamber104through a respective aperture122and opening106so as to flow through the MCM in a respective working unit112and then exit through opening108and aperture124. A reverse path can be used for flow of the heat transfer fluid in the opposite direction through the working unit112of a given chamber104.

Referring toFIG. 4, first fixed plate121has a first inlet port140and a first outlet port142and is positioned adjacent to rotatable plate114. As shown, ports140and142are positioned 180 degrees apart about the circumferential direction C of first seal114. However, other configurations may be used. For example, ports140and142may be positioned within a range of about 170 degrees to about 190 degrees about the circumferential direction C as well. Rotatable plate114and regenerator housing102are rotatable relative to first fixed plate121. Ports140and142are connected with lines44and46(FIG. 1), respectively. As such, the rotation of regenerator housing102about axis A-A sequentially places lines44and46in fluid communication with at least two working units112of MCM at any one time as will be further described.

Second fixed plate123has a second inlet port144and a second outlet port146and is positioned adjacent to second rotatable plate116. As shown, ports144and146are positioned 180 degrees apart about the circumferential direction C of second seal116. However, other configurations may be used. For example, ports144and146may be positioned within a range of about 170 degrees to about 190 degrees about the circumferential direction C as well. Second rotatable plate116and regenerator housing102are rotatable relative to second fixed plate123. Ports144and146are connected with lines50and48(FIG. 1), respectively. As such, the rotation of regenerator housing102about axis A-A sequentially places lines48and50in fluid communication with at least two working units112of MCM at any one time as will be further described. Notably, at any one time during rotation of regenerator housing102, lines46and50will each be in fluid communication with at least one working unit112while lines44and48will also be in fluid communication with at least one other working unit112located about 180 degrees away along the circumferential direction.

As shown inFIGS. 4, 5, and 6, regenerator101includes a cavity128that is positioned radially inward of the plurality of chambers104and extends along the longitudinal or axial direction A between first end118and second end120. A magnetic device126is positioned within cavity128and, for this exemplary embodiment, extends along the axial direction between first end118and second end120. Magnetic device126provides a magnetic field M that is directed radially outward as indicated by arrows M inFIG. 5.

The positioning and configuration of magnetic device126is such that only a subset (e.g., one, two, or more) of the plurality of working units112is/are within or subjected to magnetic field M at any one time. For example, as shown inFIG. 5, working units112aand112eare partially within the magnetic field while units112b,112c, and112dare fully within the magnetic field M created by magnetic device126. Conversely, the magnetic device126is configured and positioned so that working units112f,112g, and112hare completely or substantially out of the magnetic field created by magnetic device126. However, as regenerator housing102is continuously rotated along circumferential direction C as shown by arrow W, the subset of working units112within the magnetic field will continuously change as some working units112will enter magnetic field M and others will exit.

FIG. 8illustrates an exemplary method of the present invention using a schematic representation of a working unit112of MCM in regenerator housing102as it rotates in the direction of arrow W between positions1through8as shown inFIG. 6. During step200, working unit112is fully within magnetic field M, which causes the magnetic moments of the material to orient and the MCM to heat (when a normal MCM is used) as part of the magneto caloric effect. Ordering of the magnetic field is created and maintained as working unit112is rotated sequentially through positions2,3, and then4(FIG. 6) as regenerator housing102is rotated in the direction of arrow W. During the time at positions2,3, and4, the heat transfer fluid dwells in the MCM of working unit112and, therefore, is heated. More specifically, the heat transfer fluid does not flow through working unit112because the openings106,108,122, and124corresponding to working unit112in positions2,3, and4are not aligned with any of the ports140,142,144, or146.

In step202, as regenerator housing102continues to rotate in the direction of arrow W, working unit112will eventually reach position5. As shown inFIGS. 3 and 6, at position5the heat transfer fluid can flow through the MCM as first inlet port140is now aligned with an opening122in first valve114and an opening106at the first end118of working unit112while second outlet port146is aligned with an opening124in second valve116at the second end120of working unit112.

As indicated by arrow QH-OUTinFIGS. 3 and 8, heat transfer fluid in working unit112, now heated by the MCM, can travel out of regenerator housing102and along line48to the second heat exchanger34. At the same time, and as indicated by arrow QH-IN, heat transfer fluid from first heat exchanger32flows into working unit112from line44when working unit112is at position5. Because heat transfer fluid from the first heat exchanger32is relatively cooler than the MCM in working unit112, the MCM will lose heat to the heat transfer fluid.

Referring again toFIG. 8and step204, as regenerator housing102continues to rotate in the direction of arrow W, working unit112is moved sequentially through positions6,7, and8where working unit112is completely or substantially out of magnetic field M. The absence or lessening of the magnetic field is such that the magnetic moments of the MCM become disordered and the MCM absorbs heat as part of the magneto caloric effect for a normal MCM. During the time in positions6,7, and8, the heat transfer fluid dwells in the MCM of working unit112and, therefore, is cooled by losing heat to the MCM as the magnetic moments disorder. More specifically, the heat transfer fluid does not flow through working unit112because the openings106,108,122, and124corresponding to working unit112when in positions6,7, and8are not aligned with any of the ports140,142,144, or146.

Referring to step206ofFIG. 8, as regenerator housing102continues to rotate in the direction of arrow W, working unit112will eventually reach position1. As shown inFIGS. 3 and 6, at position1the heat transfer fluid in working unit112can flow through the MCM as second inlet port144is now aligned with an opening124in second valve116and an opening108at the second end120while first outlet port142is aligned with an opening122in first valve114and opening106at first end118. As indicated by arrow QC-OUTinFIGS. 3 and 7, heat transfer fluid in working unit112, now cooled by the MCM, can travel out of regenerator housing102and along line46to the first heat exchanger32. At the same time, and as indicated by arrow QC-IN, heat transfer fluid from second heat exchanger34flows into working unit112from line50when working unit112is at position5. Because heat transfer fluid from the second heat exchanger34is relatively warmer than the MCM in working unit112at position5, the MCM will lose some of its heat to the heat transfer fluid. The heat transfer fluid now travels along line46to the first heat exchanger32to receive heat and cool the refrigeration compartment30.

As regenerator housing102is rotated continuously, the above described process of placing each working unit112in and out of magnetic field M is repeated. Additionally, the size of magnetic field M and regenerator housing102are such that a subset of the plurality of working units112is within the magnetic field at any given time during rotation. Similarly, a subset of the plurality of working units112are outside (or substantially outside) of the magnetic field at any given time during rotation. At any given time, there are at least two working units112through which the heat transfer fluid is flowing while the other working units112remain in a dwell mode. More specifically, while one working unit112is losing heat through the flow of heat transfer fluid at position5, another working unit112is receiving heat from the flowing heat transfer fluid at position1, while all remaining working units112are in dwell mode. As such, the system can be operated continuously to provide a continuous recirculation of heat transfer fluid in heat pump system52as working units112are each sequentially rotated through positions1through8.

As will be understood by one of skill in the art using the teachings disclosed herein, the number of working units for housing102, the number of ports in valve114and116, and/or other parameters can be varied to provide different configurations of heat pump100while still providing for continuous operation. For example, each valve could be provided within two inlet ports and two outlet ports so that heat transfer fluid flows through at least four working units112at any particular point in time. Alternatively, regenerator101—including housing102, valves122and124, and/or seals136and138—could be constructed so that e.g., at least two working units are in fluid communication with an inlet port and outlet port at any one time. Other configurations may be used as well.

FIG. 9provides a perspective view of an exemplary working unit112of the present invention. Each working unit112is constructed from MCM and includes a plurality of discrete, elongate elements145that extend along longitudinal direction L, which is oriented parallel to the axis of rotation A-A of regenerator100. As shown inFIGS. 9 and 10, the cross-sectional shape of elongate elements145creates a plurality of small flow channels147when elongate elements145are stacked or positioned adjacent, and in contact with, each other.

Flow channels147also extend along longitudinal direction L and allow for the flow therethrough of the heat transfer fluid used with heat pump100in e.g., heat pump system52. Flow channels147experience less pressure drop that e.g., packed beds of MCM. At the same time, the outer surfaces149of elongate elements145provide sufficient surface area for heat transfer with the MCM of each elongate element145.

WhileFIGS. 9 and 10depict a circular shape, a variety of different cross-sectional shapes may be used for elongate elements145. For example,FIG. 11illustrates elongate elements145having a cross-sectional C shape that creates flow channels147having a rectangular cross-sectional shape. The elongate elements145ofFIG. 12have a cross-sectional star shape that creates polygonal flow channels147. The exemplary elongate elements145ofFIG. 13are tubular. Accordingly, interstitial flow channels147aare positioned between the elongate elements while channels147bare defined within each elongate element145. Other configurations and shapes may be used as well to provide surface area for heat exchange with the MCM of the elongate elements145while simultaneously reducing the amount of pressure drop as the heat transfer fluid flows through channels147along longitudinal direction L.

As shown inFIG. 14, elongate elements145may be positioned end-to-end along longitudinal direction L in order to create a working unit112. In order to ensure that flow channels147are not blocked, the ends145aand145bcan be beveled or provided with a surface at a non-orthogonal angle to longitudinal direction L as shown inFIGS. 14 and 15. As such, the flow of heat transfer fluid through flow channels147is not obstructed by the end of an elongate element145. The positioning of elongate elements145end-to-end using MCM with different Curie temperatures can be used to provide stages along a working unit112as further described below.

FIG. 16provides an exemplary plot of a single stage of MCM showing the magneto caloric effect (i.e. a change in temperature, rT, in response to an applied magnetic field of sufficient strength) versus the initial temperature of the MCM (i.e. the temperature of the MCM upon initial application of the magnetic field). As used herein, the Curie temperature of an MCM refers to a temperature at which the MCM undergoes the magneto caloric effect due to changes in a magnetic field (e.g., applying or removing the magnetic field). For most MCMs, however, the magneto caloric effect is not exhibited at single, precise temperature and, instead, occurs over a range. Thus, as also used herein, the original peak Curie temperature, or TOC, represents the original initial temperature (before degradation) at which the MCM shows its peak or highest temperature change in response to a magnetic field. As used herein, the original Curie temperature range, or ΔTOC, represents the original range of temperatures (before degradation) over which this MCM exhibits a temperature change in response to the magnetic field. By definition, the original Curie temperature range ΔTOCincludes the original peak Curie temperature TOC.

Appliance10and/or heat pump system52may be used in an application where the ambient temperature changes over a substantial temperature range. However, as indicated inFIG. 16, a specific stage of MCM may exhibit the magneto caloric effect over only a much narrower temperature range ΔTOC. As such, it may be desirable to use multiple stages constructed from a variety of MCMs, each having a different original Curie temperature range ΔTOC, in order to accommodate such ambient temperature changes and to provide the desired temperature to which e.g., cooling or heating is desired. As such, a given working unit112might have multiple stages of MCM along the axial direction A to accommodate the wide range of ambient temperatures over which appliance10and/or heat pump100may be used.

For example, referring now toFIGS. 8 and 17, each working unit112can be provided with stages152,154,156,158,160, and162of different MCMs. These stages are positioned adjacent to each other and are arranged sequentially along a predetermined direction—e.g., along axial direction A-A in this exemplary embodiment. Each such stage includes an MCM that exhibits the magneto caloric effect (before any degradation) at a different original peak Curie temperature TOCor different original Curie temperature range ΔTOCthan an adjacent stage along the axial direction A-A. Various numbers of stages may be used—the use of six in the figures is by way of example only.

As shown inFIG. 17, the stages can be arranged so that e.g., the original Curie temperature ranges ΔTOCof the plurality of stages increases or decreases along a predetermined direction such as longitudinal or axial direction A-A. For example, stage152may exhibit the magnet caloric effect at original Curie temperature range ΔTOCthat is less than the original Curie temperature range ΔTOCat which stage154exhibits the magnet caloric effect, which may be less than the original Curie temperature range ΔTOCfor stage156, and so on. Other configurations may be used as well. By configuring the appropriate number and sequence of stages of MCM, heat pump100can be operated over a substantial range of ambient temperatures to reach the temperature desired for heating cooling.

In one exemplary embodiment, the original Curie temperature ranges ΔTOCof stages152,154,156,158,160, and162are also selected to overlap in order to facilitate heat transfer. For example, in the embodiment shown inFIGS. 8 and 15, stage162could have a Curie temperature range ΔTOCof 20° C. to 10° C.; stage160could have a Curie temperature range ΔTOCof 17.5° C. to 7.5° C.; stage158could have a Curie temperature range ΔTOCof 15° C. to 5° C.; stage156could have a Curie temperature range ΔTOCof 12.5° C. to 2.5° C.; stage154could have a Curie temperature range ΔTOCof 10° C. to 0° C.; and stage152could have a Curie temperature range ΔTOCof 5° C. to −2. These ranges are provided as examples. In still another embodiment of the invention, elongate elements145can be constructed from MCM having a Curie temperature that increases or decreases continually over its length along longitudinal direction L. For example, each elongate element can be constructed such that the Curie temperature decreases or increases in a linear manner from end to end along longitudinal direction L. Other configurations may be used as well.

During operation of a heat pump100having stages152,154,156,158,160, and162as shown inFIG. 8, the stages having a higher Curie temperature range become less important as e.g., cooling takes place and the compartments of the refrigerator approach 0° C. As the temperature is lowered, the stages having lower Curie temperature ranges (e.g., stages152and154) provide the cooling required to maintain the desired temperature. However, because the stages having a higher Curie temperature range (e.g.,160and162) are still being subjected to the field of changing magnetic flux provided by magnetic device126as previously described, heat pump100is still consuming the power needed to cycle these stages.

Accordingly, as shown inFIG. 8, magnetic device126is positioned adjacent to the plurality of stages152,154,156,158,160, and162and is configured to subject those stages to a magnetic field M of decreasing flux along a predetermined direction, which for this example is along axial direction A-A. As shown by arrows M inFIG. 8, the magnetic flux decreases as the Curie temperature range associated with each stage152through162increases. For this exemplary embodiment, magnetic device126can be constructed from one or more magnets. Magnet(s)126have a thickness T along a direction O that is orthogonal to the predetermined direction—i.e. axial direction A-A. Moving along axial direction A-A, the thickness T of magnet(s)126decreases so that the corresponding magnetic flux is also decreased along axial direction A.

Other constructions can also be used to provide for a decrease in magnetic flux. For example, magnetic device126may be configured as an electromagnet or a combination of an electromagnet and one or more magnets—each of which can be configured to decrease the magnetic flux along a predetermined direction.

A variety of configurations can be used to determine the amount or, more particularly, the rate of decrease in the magnetic flux provided by magnetic device126along the predetermined direction. For example, in one exemplary embodiment as shown inFIG. 8, the decrease is substantially linear along axial direction A. The rate or slope of this decrease can be matched to the rate of decrease in the Curie temperature over length of the working units112. Equation 1 below provides an example:
Rate of decrease=(ΔT/stage 152)−(ΔT/stage 162)/(ΔT/stage 152)  Eqn 1:

Other methods may be used for calculating the rate of decrease as well. In addition, the rate of decrease can also include e.g., a non-linear rate of decrease.

By decreasing the magnetic flux provided by magnetic element126as described above, the amount of work associated with cycling working units112through the magnetic field can be decreased—resulting in more efficiency in the operation of heat pump100. In addition, where magnetic element126is constructed from one or more magnets, the cost of manufacturing heat pump100and, therefore, appliance10can be substantially reduced.

Returning toFIGS. 4, 5, and 6, for this exemplary embodiment, magnetic element126is constructed in the shape of an arc from a plurality of magnets130arranged in a Halbach array. More specifically, magnets130are arranged so that magnetic device126provides a magnetic field M located radially outward of magnetic device126and towards regenerator housing102while minimal or no magnetic field is located radially-inward towards the axis of rotation A-A. Magnetic field M may be aligned in a curve or arc shape. In addition, the thickness T of magnetic element decreases along a predetermined direction—axial direction A-A in this example—as also shown inFIG. 4.

A variety of other configurations may be used as well for magnetic device126and/or its resulting magnetic field. For example, magnetic device126could be constructed from a first plurality of magnets positioned in cavity128in a Halbach array that directs the field outwardly while a second plurality of magnets is positioned radially outward of regenerator housing102and arranged to provide a magnetic field that is located radially inward to the regenerator housing102. In still another embodiment, magnetic device128could be constructed from a plurality of magnets positioned radially outward of regenerator housing102and arranged to provide a magnetic field that is located radially inward towards the regenerator housing102. Other configurations of magnetic device128may be provided as well. For example, coils instead of magnets may be used to create the magnetic field desired.

For this exemplary embodiment, the arc created by magnetic device128provides a magnetic field extending circumferentially about 180 degrees. In still another embodiment, the arc created by magnetic device128provides a magnetic field extending circumferentially in a range of about 170 degrees to about 190 degrees.

A motor28(FIG. 2) is in mechanical communication with regenerator101and provides for rotation of regenerator housing102about axis A-A. By way of example, motor28may be connected directly with housing102by a shaft or indirectly through a gear box. Other configurations may be used as well.

In the description above, normal MCM was used to describe the operation of heat pump100. As will be understood by one of skill in the art using the teachings disclosed herein, inverse MCMs could also be used as well. The direction of flow of fluid through heat pump100would be reversed, accordingly.