Abstract:
A heat pump system that uses variable magnetization to control the amount of MCM subjected to a magnetic field is provided. More particularly, the amount of MCM subjected to a magnetic field can be selected based on the amount of refrigeration needed. As such, the heat pump system can be adjusted based on e.g., changes in ambient conditions, and the energy used in operating such a heat pump system can be conserved so as to increase energy efficiency of the system.

Description:
FIELD OF THE INVENTION 
       [0001]    The subject matter of the present disclosure relates generally to a heat pump system that uses variable magnetization of magneto caloric materials to control the amount of heat exchange. 
       BACKGROUND OF THE INVENTION 
       [0002]    Conventional refrigeration technology typically utilizes a heat pump that relies on compression and expansion of a fluid refrigerant to receive and reject heat in a cyclic manner so as to effect a desired temperature change or i.e. transfer heat energy from one location to another. This cycle can be used to provide e.g., for the receiving of heat from a refrigeration compartment and the rejecting of such heat to the environment or a location that is external to the compartment. Other applications include air conditioning of residential or commercial structures. A variety of different fluid refrigerants have been developed that can be used with the heat pump in such systems. 
         [0003]    While improvements have been made to such heat pump systems that rely on the compression of fluid refrigerant, at best such can still only operate at about 45 percent or less of the maximum theoretical Carnot cycle efficiency. Also, some fluid refrigerants have been discontinued due to environmental concerns. The range of ambient temperatures over which certain refrigerant-based systems can operate may be impractical for certain locations. Other challenges with heat pumps that use a fluid refrigerant exist as well. 
         [0004]    Magneto caloric materials (MCMs)—i.e. materials that exhibit the magneto caloric effect—provide a potential alternative to fluid refrigerants for heat pump applications. In general, the magneto caloric effect refers to a process of entropic change whereby the magnetic moments of an 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 MCMs exhibit the opposite behavior—i.e. generating heat when the magnetic field is removed (which are sometimes referred to as para-magneto caloric material but both types are referred to collectively herein as magneto caloric material or MCM). The theoretical Carnot cycle efficiency of a refrigeration cycle based on an MCM can be significantly higher than for a comparable refrigeration cycle based on a fluid refrigerant. As such, a heat pump system that can effectively use an MCM would be useful. 
         [0005]    Challenges exist to the practical and cost competitive use of an MCM, however. In addition to the development of suitable MCMs, equipment that can attractively utilize an MCM is still needed. It is desirable to provide for the transfer or heat to and from the MCM preferably in a continuous manner so that the equipment does not operate in a start and stop fashion that can be inefficient. Also, currently proposed equipment may require relatively large and expensive magnets, may be impractical for use in e.g., appliance refrigeration, and may not otherwise operate with enough efficiency to justify capital cost. 
         [0006]    Additionally, as stated above, the ambient conditions under which a heat pump may be needed 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 MCMs are capable of accepting and generating heat only within a much narrower temperature range than presented by such ambient conditions. 
         [0007]    Also, the amount of MCM that needs to be magnetized can change as ambient conditions change. For example, for a refrigeration appliance, as the ambient temperature decreases, the amount of MCM that must be magnetized to properly maintain the temperature of food items stored inside the appliance can also decrease. As energy is required to magnetize the MCM, efficiency is reduced when more MCM than necessary is magnetized. However, no practical solutions for controlling the amount of MCM material to be magnetized has been proposed—particularly for a continuously operating machine. 
         [0008]    Accordingly, a heat pump system that can address certain challenges such as those identified above would be useful. Such a heat pump system that can also be used in e.g., a refrigerator appliance would also be useful. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0009]    The present invention provides a heat pump system that uses variable magnetization to control the amount of MCM subjected to a magnetic field. More particularly, the amount of MCM subjected to a magnetic field can be selected or adjusted based on the amount of refrigeration needed. As such, the heat pump system can be adjusted based on e.g., changes in ambient conditions, and the energy used in operating such a heat pump system can be conserved so as to increase energy efficiency of the system. The heat pump can be used for applications where heating, cooling, or both are needed. 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. 
         [0010]    In one exemplary aspect, the present invention provide a method of operating a magneto caloric device. This exemplary method comprises the steps of providing a magnetic field and magneto caloric material; positioning the magneto caloric material into the magnetic field; removing the magneto caloric material from the magnetic field; and controlling the extent of cooling or heating of the magneto caloric material by adjusting the amount of the magneto caloric material subjected to the magneto caloric effect during said steps of positioning and removing. 
         [0011]    In another exemplary embodiment, the present invention provides a heat pump system that includes a regenerator housing defining a circumferential direction and rotatable about an axial direction, the axial direction extending between a first end and a second end of the regenerator housing. The regenerator housing includes a plurality of chambers with each chamber extending longitudinally along the axial direction between a pair of openings. The plurality of chambers are arranged proximate to each other along the circumferential direction. A plurality of stages are provide with each stage comprising magneto caloric material positioned within one of the plurality of chambers and extending along the axial direction. 
         [0012]    This exemplary embodiment further includes a pair of valves with a first valve attached to the first end of the regenerator housing and a second valve attached to the second end of the regenerator housing. The first valve and second valve each include a plurality of apertures spaced apart from each other along the circumferential direction with each aperture positioned adjacent to one of the pair of openings of one of the plurality of chambers. A magnetic element is positioned proximate to the regenerator housing and extends along the axial direction. The magnetic element creates a magnetic field and is positioned so that a subset of the plurality of stages are moved in and out of the magnetic field as the regenerator housing is rotated about the axial direction. 
         [0013]    This exemplary system also includes a pair of seals with a first seal positioned adjacent to the first valve and a second seal adjacent to the second valve such that the regenerator housing and the pair of valves are rotatable relative to the pair of seals. The first seal and the second seal each include a pair of ports positioned in an opposing manner relative to each other and also positioned so that each port can selectively align with at least one of the pair of openings of the plurality of chambers as the regenerator housing is rotated about the axial direction. 
         [0014]    An actuator is configured for moving the magnetic element, the regenerator housing, or both along the axial direction so as to control the amount of magneto caloric material experiencing the magneto caloric effect as said regenerator housing is rotated about the axial direction. 
         [0015]    These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
           [0017]      FIG. 1  provides an exemplary embodiment of a refrigerator appliance of the present invention. 
           [0018]      FIG. 2  is a schematic illustration of an exemplary heat pump system of the present invention positioned in an exemplary refrigerator with a machinery compartment and a refrigerated compartment. 
           [0019]      FIG. 3  provides a perspective view of an exemplary heat pump of the present invention. 
           [0020]      FIG. 4  is an exploded view of the exemplary heat pump of  FIG. 3 . 
           [0021]      FIG. 5  is a cross-sectional view of the exemplary heat pump of  FIG. 3 . 
           [0022]      FIG. 6  is perspective view of the exemplary heat pump of  FIG. 3 . Seals located at the ends of a regenerator housing have been removed for purposes of further explanation of this exemplary embodiment of the invention as set forth below. 
           [0023]      FIG. 7  is a schematic representation of exemplary steps in the use of a stage of the heat pump of  FIG. 3 . 
           [0024]      FIG. 8  is another schematic representation of exemplary steps in the use of a stage of the heat pump of  FIG. 3  and in which only a portion of the stage is subjected to a magnetic field so as to delimit the amount of magneto caloric material subjected to the magneto caloric effect. 
           [0025]      FIG. 9  is a schematic view of a magnet as may be used with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
         [0027]    Referring now to  FIG. 1 , an exemplary embodiment of an appliance refrigerator  10  is depicted as an upright refrigerator having a cabinet or casing  12  that defines a number of internal storage compartments or chilled chambers. In particular, refrigerator appliance  10  includes upper fresh-food compartments  14  having doors  16  and lower freezer compartment  18  having upper drawer  20  and lower drawer  22 . The drawers  20 ,  22  are “pull-out” type drawers in that they can be manually moved into and out of the freezer compartment  18  on suitable slide mechanisms. Refrigerator  10  is 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 in  FIG. 1 . In addition, the heat pump and heat pump system of the present invention is not limited to appliances and may be used in other applications as well 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 to provide for heating applications as well. 
         [0028]      FIG. 2  is a schematic view of another exemplary embodiment of a refrigerator appliance  10  including a refrigeration compartment  30  and a machinery compartment  40 . In particular, machinery compartment  30  includes a heat pump system  52  having a first heat exchanger  32  positioned in the refrigeration compartment  30  for the removal of heat therefrom. A heat transfer fluid such as e.g., an aqueous solution, flowing within first heat exchanger  32  receives heat from the refrigeration compartment  30  thereby cooling its contents. A fan  38  may be used to provide for a flow of air across first heat exchanger  32  to improve the rate of heat transfer from the refrigeration compartment  30 . 
         [0029]    The heat transfer fluid flows out of first heat exchanger  32  by line  44  to heat pump  100 . As will be further described herein, the heat transfer fluid receives additional heat from magneto caloric material (MCM) in heat pump  100  and carries this heat by line  48  to pump  42  and then to second heat exchanger  34 . Heat is released to the environment, machinery compartment  40 , and/or other location external to refrigeration compartment  30  using second heat exchanger  34 . A fan  36  may be used to create a flow of air across second heat exchanger  34  and thereby improve the rate of heat transfer to the environment. Pump  42  connected into line  48  causes the heat transfer fluid to recirculate in heat pump system  52 . Motor  28  is in mechanical communication with heat pump  100  as will further described. 
         [0030]    From second heat exchanger  34  the heat transfer fluid returns by line  50  to heat pump  100  where, as will be further described below, the heat transfer fluid loses heat to the MCM in heat pump  100 . The now colder heat transfer fluid flows by line  46  to first heat exchanger  32  to receive heat from refrigeration compartment  30  and repeat the cycle as just described. 
         [0031]    Heat pump system  52  is provided by way of example only. Other configurations of heat pump system  52  may be used as well. For example, lines  44 ,  46 ,  48 , and  50  provide fluid communication between the various components of the heat pump system  52  but other heat transfer fluid recirculation loops with different lines and connections may also be employed. For example, pump  42  can also be positioned at other locations or on other lines in system  52 . Still other configurations of heat pump system  52  may be used as well. 
         [0032]      FIGS. 3 ,  4 ,  5 , and  6  depict various views of an exemplary heat pump  100  of the present invention. Heat pump  100  includes a regenerator housing  102  that extends longitudinally along an axial direction between a first end  118  and a second end  120 . The axial direction is defined by axis A-A about which regenerator housing  102  rotates. A radial direction R is defined by a radius extending orthogonally from the axis of rotation A-A ( FIG. 5 ). A circumferential direction is indicated by arrows C. 
         [0033]    Regenerator housing  102  defines a plurality of chambers  104  that extend longitudinally along the axial direction defined by axis A-A. Chambers  104  are positioned proximate or adjacent to each other along circumferential direction C. Each chamber  104  includes a pair of openings  106  and  108  positioned at opposing ends  118  and  120  of regenerator housing  102 . 
         [0034]    Heat pump  100  also includes a plurality of stages  112  that include MCM. Each stage  112  is located in one of the chambers  104  and extends along the axial direction. For the exemplary embodiment shown in the figures, heat pump  100  includes eight stages  112  positioned adjacent to each other along the circumferential direction as shown and extending longitudinally along the axial direction. As will be understood by one of skill in the art using the teachings disclosed herein, a different number of stages  112  other than eight may be used as well. 
         [0035]    A pair of valves  114  and  116  are attached to regenerator housing  102  and rotate therewith along circumferential direction C. More particularly, a first valve  114  is attached to first end  118  and a second valve  116  is attached to second end  120 . Each valve  114  and  116  includes a plurality of apertures  122  and  124 , respectively. For this exemplary embodiment, apertures  122  and  124  are configured as circumferentially-extending slots that are spaced apart along circumferential direction C. Each aperture  122  is positioned adjacent to a respective opening  106  of a chamber  104 . Each aperture  124  is positioned adjacent to a respective opening  108  of a chamber  104 . Accordingly, a heat transfer fluid may flow into a chamber  104  through a respective aperture  122  and opening  106  so as to flow through the MCM in a respective stage  112  and then exit through opening  108  and aperture  124 . A reverse path can be used for flow of the heat transfer fluid in the opposite direction through the stage  112  of a given chamber  104 . 
         [0036]    Regenerator housing  102  defines a cavity  128  that is positioned radially inward of the plurality of chambers  104  and extends along the axial direction between first end  118  and second end  120 . A magnetic element  126  is positioned within cavity  128  and, for this exemplary embodiment, extends along the axial direction between first end  118  and second end  120 . Magnetic element  126  provides a magnetic field that is directed radially outward as indicated by arrows M in  FIG. 5 . 
         [0037]    The positioning and configuration of magnetic element  126  is such that only a subset of the plurality of stages  112  is within magnetic field M at any one time. For example, as shown in  FIG. 5 , stages  112   a  and  112   e  are partially within the magnetic field while stages  112   b,    112   c,  and  112   d  are fully within the magnetic field M created by magnetic element  126 . Conversely, the magnetic element  126  is configured and positioned so that stages  112   f,    112   g,  and  112   h  are completely or substantially out of the magnetic field created by magnetic element  126 . However, as regenerator housing  102  is continuously rotated along the circumferential direction as shown by arrow W, the subset of stages  112  within the magnetic field will continuously change as some stages  112  will enter magnetic field M and others will exit. 
         [0038]    A pair of seals  136  and  138  is provided with the seals positioned in an opposing manner at the first end  118  and second end  120  of regenerator housing  102 . First seal  136  has a first inlet port  140  and a first outlet port  142  and is positioned adjacent to first valve  114 . As shown, ports  140  and  142  are positioned 180 degrees apart about the circumferential direction C of first seal  114 . However, other configurations may be used. For example, ports  140  and  142  may be positioned within a range of about 170 degrees to about 190 degrees about the circumferential direction C as well. First valve  114  and regenerator housing  102  are rotatable relative to first seal  136 . Ports  140  and  142  are connected with lines  44  and  46  ( FIG. 1 ), respectively. As such, the rotation of regenerator housing  102  about axis A-A sequentially places lines  44  and  46  in fluid communication with at least two stages  112  of MCM at any one time as will be further described. 
         [0039]    Second seal  138  has a second inlet port  144  and a second outlet port  146  and is positioned adjacent to second valve  116 . As shown, ports  144  and  146  are positioned 180 degrees apart about the circumferential direction C of second seal  116 . However, other configurations may be used. For example, ports  144  and  146  may be positioned within a range of about 170 degrees to about 190 degrees about the circumferential direction C as well. Second valve  116  and regenerator housing  102  are rotatable relative to second seal  138 . Ports  144  and  146  are connected with lines  50  and  48  ( FIG. 1 ), respectively. As such, the rotation of regenerator housing  102  about axis A-A sequentially places lines  48  and  50  in fluid communication with at least two stages  112  of MCM at any one time as will be further described. Notably, at any one time during rotation of regenerator housing  102 , lines  46  and  50  will each be in fluid communication with at least one stage  112  while lines  44  and  48  will also be in fluid communication with at least one other stage  112  located about 180 degrees away along the circumferential direction. 
         [0040]      FIG. 7  illustrates an exemplary method of the present invention using a schematic representation that follows the same stage  112  of MCM in regenerator housing  102  as it rotates in the direction of arrow W between positions  1  through  8  as shown in  FIG. 6 . During step  200 , stage  112  is fully within magnetic field M, which causes the magnetic moments of the material to orient and the MCM to heat as part of the magneto caloric effect. Ordering of the magnetic field is created and maintained as stage  112  is rotated sequentially through positions  2 ,  3 , and then  4  ( FIG. 6 ) as regenerator housing  102  is rotated in the direction of arrow W. During the time at positions  2 ,  3 , and  4 , the heat transfer fluid dwells in the MCM of stage  112  and, therefore, is heated. More specifically, the heat transfer fluid does not flow through stage  112  because the openings  106 , 108 ,  122 , and  124  corresponding to stage  112  in positions  2 ,  3 , and  4  are not aligned with any of the ports  140 ,  142 ,  144 , or  146 . 
         [0041]    In step  202 , as regenerator housing  102  continues to rotate in the direction of arrow W, stage  112  will eventually reach position  5 . As shown in  FIGS. 3 and 6 , at position  5  the heat transfer fluid can flow through the material as first inlet port  140  is now aligned with an opening  122  in first valve  114  and an opening  106  at the first end  118  of stage  112  while second outlet port  146  is aligned with an opening  124  in second valve  116  at the second end  120  of stage  112 . As indicated by arrow Q H-OUT , heat transfer fluid in stage  112 , now heated by the MCM, can travel out of regenerator housing  102  and along line  48  to the second heat exchanger  34 . At the same time, and as indicated by arrow Q H-IN , heat transfer fluid from first heat exchanger  32  flows into stage  112  from line  44  when stage  112  is at position  5 . Because heat transfer fluid from the first heat exchanger  32  is relatively cooler than the MCM in stage  112 , the MCM will lose heat to the heat transfer fluid. 
         [0042]    Referring again to  FIG. 7  and step  204 , as regenerator housing  102  continues to rotate in the direction of arrow W, stage  112  is moved sequentially through positions  6 ,  7 , and  8  where stage  112  is completely or substantially out of magnetic field M. The absence or lessening of the magnetic field is such that the magnetic moments of the material become disordered and the MCM absorbs heat as part of the magneto caloric effect. During the time in positions  6 ,  7 , and  8 , the heat transfer fluid dwells in the MCM of stage  112  and, therefore, is cooled by losing heat to the MCM as the magnetic moments disorder. More specifically, the heat transfer fluid does not flow through stage  112  because the openings  106 ,  108 ,  122 , and  124  corresponding to stage  112  when in positions  6 ,  7 , and  8  are not aligned with any of the ports  140 ,  142 ,  144 , or  146 . 
         [0043]    Referring to step  206  of  FIG. 7 , as regenerator housing  102  continues to rotate in the direction of arrow W, stage  112  will eventually reach position  1 . As shown in  FIGS. 3 and 6 , at position  1  the heat transfer fluid in stage  112  can flow through the material as second inlet port  144  is now aligned with an opening  124  in second valve  116  and an opening  108  at the second end  120  while first outlet port  142  is aligned with an opening  122  in first valve  114  and opening  106  at first end  118 . As indicated by arrow Q C-OUT , heat transfer fluid in stage  112 , now cooled by the MCM, can travel out of regenerator housing  102  and along line  46  to the first heat exchanger  32 . At the same time, and as indicated by arrow Q C-IN , heat transfer fluid from second heat exchanger  34  flows into stage  112  from line  50  when stage  112  is at position  5 . Because heat transfer fluid from the second heat exchanger  34  is relatively warmer than the MCM in stage  112  at position  5 , the MCM will lose some of its heat to the heat transfer fluid. The heat transfer fluid now travels along line  46  to the first heat exchanger  32  to receive heat and cool the refrigeration compartment  30 . 
         [0044]    As regenerator housing  102  is rotated continuously, the above described process of placing stage  112  in and out of magnetic field M is repeated. Additionally, the size of magnetic field M and regenerator housing  102  are such that a subset of the plurality of stages  112  is within the magnetic field at any given time during rotation. Similarly, a subset of the plurality of stages  112  are outside (or substantially outside) of the magnetic field at any given time during rotation. Additionally, at any given time, there are at least two stages  112  through which the heat transfer fluid is flowing while the other stages remain in a dwell mode. More specifically, while one stage  112  is losing heat through the flow of heat transfer fluid at position  5 , another stage  112  is receiving heat from the flowing heat transfer fluid at position  1  while all remaining stages  112  are in dwell mode. As such, the system can be operated continuously to provide a continuous recirculation of heat transfer fluid in heat pump system  52  as stages  112  are each sequentially rotated through positions  1  through  8 . 
         [0045]    As will be understood by one of skill in the art using the teachings disclosed herein, the number of stages for housing  102 , the number of ports in valve  114  and  116 , and/or other parameters can be varied to provide different configurations of heat pump  100  while 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 stages  112  at any particular point in time. Alternatively, regenerator housing  102 , valves  122  and  124 , and/or seals  136  and  138  could be constructed so that e.g., at least two stages are in fluid communication with an inlet port and outlet port at any one time. Other configurations may be used as well. 
         [0046]    As stated, stage  112  includes MCM extending along the axial direction of flow. The MCM may be constructed from a single magneto caloric material or may include multiple different magneto caloric materials. By way of example, appliance  10  may be used in an application where the ambient temperature changes over a substantial range. However, a specific magneto caloric material may exhibit the magneto caloric effect over only a much narrower temperature range. As such, it may be desirable to use a variety of magneto caloric materials within a given stage to accommodate the wide range of ambient temperatures over which appliance  10  and/or heat pump  100  may be used. 
         [0047]    Accordingly, as shown in  FIG. 7 , each stage  112  can be provided with zones  152 ,  154 ,  156 ,  158 ,  160 , and  162  of different magneto caloric materials. Each such zone includes an MCM that exhibits the magneto caloric effect at a different temperature or a different temperature range than an adjacent zone along the axial direction of stage  112 . For example, zone  152  may exhibit the magnet caloric effect at a temperature less than the temperature at which zone  154  exhibits the magnet caloric effect, which may be less than such temperature for zone  156 , and so on. Other configurations may be used as well. By configuring the appropriate number sequence of zones of MCM, heat pump  100  can be operated over a substantial range of ambient temperatures. 
         [0048]      FIG. 8  illustrates another exemplary method of the present invention using another schematic illustration that follows the same stage  112  of MCM in regenerator housing  102  as it rotates in the direction of arrow W between positions  1  through  8  as shown in  FIG. 6 . Steps  300 ,  302 ,  304 , and  306  are similar to steps  200 ,  202 ,  204 , and  206  of  FIG. 7 . Magneto caloric material of stage  112  is positioned into magnetic field M (steps  300  and  302 ) and then removed (steps  304  and  306 ) from magnetic field M to provide heating and cooling of stage  112  as previously described. However, unlike the exemplary aspect of the present invention set forth in  FIG. 7 , in  FIG. 8  the extent of cooling or heating of the magneto caloric material can be controlled by changing or adjusting the amount of magneto caloric material subjected to the magneto caloric effect during these steps. 
         [0049]    More particularly, for this exemplary aspect of the invention, heat pump  100  is equipped with an actuator  154  that is configured for moving magnetic element  126 , stage  112 , or both along the axial direction so as to control the amount of magneto caloric material experiencing the magneto caloric effect as the regenerator housing is rotated in the direction or arrow W. For the exemplary embodiment shown, magnetic element  126  is provided with a rack  148  and pinion  150  connected with a motor  152 . Motor  152  can be used to rotate pinion  150  so as to cause magnetic element  126  to move in the direction or arrow F or R. By moving magnetic element  126  in the direction of arrow F, only a portion  113  of the magneto caloric material of stage  112  is subjected to magnetic field F so as to undergo the magneto caloric effect while another portion  115  remains out of the magnetic field. Accordingly, the amount of magneto caloric material placed into a magnetic field as regenerator housing  102  is rotated about the axial direction can be controlled (e.g., reduced or increased) depending upon e.g., ambient conditions, how much refrigeration is needed, and/or other variables so as to conserve energy. 
         [0050]    Actuator  152  is not limited to the exemplary embodiment shown in  FIG. 8  and other configurations may be used as well. For example, instead of rack  148  and pinion  150 , a solenoid, linear actuator, hydraulic piston, and other mechanisms may be used as will be understood by one of skill in the art. In addition, instead of moving magnetic element  126  relative to stage  112 , actuator  152  could be configured to move regenerator housing  102  and, therefore, stage  112  relative to magnetic element  126 . Alternatively, both magnetic element  126  and housing  102  could be moved relative to each other. 
         [0051]    Other methods may be used as well to control the amount of magneto caloric material subjected to a magnetic field and the magneto caloric effect. For example, magnetic element  126  could be constructed from a plurality of magnets  130  placed side by side along longitudinal axis L in a Halbach array as shown in  FIG. 8 . Although the magnets  130  are shown in a first configuration that is linear in  FIG. 8 , magnets  130  could be changed to a second configuration in which magnets  130  are stacked as shown in  FIG. 9  so as to decrease the size of the magnetic field. Other techniques to change the configuration of magnets  130  may be used as well. 
         [0052]    Although shown as a single stage  112  of magneto caloric material in  FIG. 8 , it will be understood that stage  112  could comprise multiple zones of magneto caloric material arranged along the longitudinal direction of stage  112  as previously described with regard to  FIG. 7 . Accordingly, the number of zones of magneto caloric material in a given stage  112  that are subjected to the magneto caloric effect can be carefully controlled as previously described with regard to  FIG. 8  so as to provide the desired amount of heating and cooling. 
         [0053]    Various methods may be employed to determine the amount of magneto caloric material (or the number of zones of magneto caloric material) for a stage  112  that should be subjected to the magneto caloric effect so as to control the amount of heating and cooling as previously described. For example, a temperature sensor  164  could be provided to measure the ambient temperature. The temperature measurement can then be used to determine e.g., how much MCM should be subjected to the magneto caloric effect. For example, as the ambient temperature decreases, less MCM may be used and vice versa. Alternatively, or in addition thereto, a temperature sensor could be used to determine the temperature in the refrigerator compartment  30  and, therefore, how much heat energy must be removed to provide proper cooling. This information could then be used to control the amount of MCM material used. Still other techniques could be employed as well. 
         [0054]    Referring now to  FIGS. 4 ,  5 , and  6 , magnetic element  126  is constructed in the shape of an arc from a plurality of magnets  130  arranged in a Halbach array for this exemplary embodiment. More specifically, magnets  130  are arranged so that magnetic element  126  provides a magnetic field M located radially outward of magnetic element  126  and towards regenerator housing  102  while 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. A variety of other configurations may be used as well for magnetic element  126  and/or its resulting magnetic field. For example, magnetic element  126  could be constructed from a first plurality of magnets positioned in cavity  128  in a Halbach array that directs the field outwardly while a second plurality of magnetics is positioned radially outward of regenerator housing  102  and arranged to provide a magnetic field that is located radially inward to the regenerator housing  102 . In still another embodiment, magnetic element  128  could be constructed from a plurality of magnets positioned radially outward of regenerator housing  102  and arranged to provide a magnetic field that is located radially inward towards the regenerator housing  102 . Other configurations of magnetic element  128  may be provided as well. For example, coils instead of magnets may be used to create the magnetic field desired. 
         [0055]    For this exemplary embodiment, the arc created by magnetic element  128  provides a magnetic field extending circumferentially about 180 degrees. In still another embodiment, the arc created by magnetic element  128  provides a magnetic field extending circumferentially in a range of about 170 degrees to about 190 degrees. 
         [0056]    A motor  28  is in mechanical communication with regenerator housing  102  and provides for rotation of housing  102  about axis A-A. By way of example, motor  28  may be connected directly with housing  102  by a shaft or indirectly through a gear box. Other configurations may be used as well. 
         [0057]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.