Abstract:
A magnetic refrigerator includes independent hot heat exchange unit and cold heat exchange unit wherein separate heat transfer fluids are circulated.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of International Application No. PCT/KR2006/004653, filed on Nov. 9, 2006, entitled “Magnetic Refrigerator,” which claims priority under 35 U.S.C. §119 to Application Nos. KR 10-2005-0107305 filed on Nov. 10, 2005; KR 10-2005-0107306 filed on Nov. 10, 2005; KR 10-2005-0107308 filed on Nov. 10, 2005; and KR 10-2005-0126983 filed on Dec. 21, 2005, the entire contents of which are hereby incorporated by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to a magnetic refrigerator having independent hot heat exchange unit and cold heat exchange unit wherein separate heat transfer fluids are circulated. 
   BACKGROUND 
   A conventional magnetic refrigerator is disclosed in U.S. Pat. No. 6,668,560. As shown in  FIGS. 1 and 2 , in accordance with the conventional magnetic refrigerator, while a heat transfer fluid  17  entering into a cold side inlet port  22  through a cold side inlet pipe  21  flows to a hot side outlet port  34 , the heat transfer fluid  17  absorbs a heat generated by a magnetocaloric effect of a magnetocaloric material  12  having a magnetic field applied thereto and exits to a hot side outlet pipe  33  through a hot side outlet ports  34  to cool the magnetocaloric material  12 . A hot side sequentially passes the hot side outlet pipe  33 , a valve  71 , a pump  60 , and a hot heat exchanger  62  and flows into a magnetic heat exchange compartment  13 . In a hot side inlet pipe  31 , the hot side is divided into the hot side inlet pipe  31  and a cold side outlet port  23 , and meets a cold side at a cold side outlet pipe  24  and proceed to a valve  74 . When the hot side moves from a hot side inlet port  32  to the cold side outlet pipe  24 , the hot side is cooled by passing the magnetocaloric material  12  already cooled by the hot side. The cold side that has passed through the valve  74  passes a cold heat exchanger  63  and flows to pipes  83  and  21  to repeat a cycle (a detailed description is omitted. See U.S. Pat. No. 6,668,560 for omitted reference numerals). 
   As described above, since the conventional magnetic refrigerator comprises twelve magnetic heat exchange compartments, four valves  71 ,  72 ,  73  and  74  and more than  24  pipes, it is difficult to manufacture the conventional magnetic refrigerator. 
   Moreover, since a single heat transfer fluid is circulated to serve as the hot side and the cold side simultaneously, that is, since the hot side enters at the hot side inlet port  32  to pass the cold magnetocaloric material (See  FIG. 2 ) and cooled into the cold side to exit through the cold side outlet pipe  24 , a efficiency of a heat exchange is degraded. It is known from this fact that when the heat transfer fluid having a temperature lower than that of the hot side entering the hot side inlet port  32  enters the hot side inlet port  32  and passes the cooled caloric material, the heat transfer fluid having a temperature lower at the cold side outlet pipe  24  may be flown out to improve the efficiency of the heat exchange. 
   In addition, since amount of the heat transfer fluid passing through the hot side cannot be controlled, a heat of the magnetocaloric material cannot be cooled promptly, thereby degrading the efficiency of the heat exchange. 
   On the other hand, when the magnetocaloric material passes through the magnetic heat exchange compartment, the magnetocaloric material is in direct contact with the heat transfer fluid, thereby causing an oxidation. 
   Moreover, the magnetocaloric material of a power type is lost through an exit (a mesh) when passing through the magnetic heat exchange compartment and the magnetocaloric material may be accumulated at the exit according to a strength of the heat transfer fluid to block a flow thereof. 
   SUMMARY 
   It is an object of the present invention to provide a magnetic refrigerator wherein a hot side and a cold side are divided to simplify a structure, to achieve a high heat efficiency, and to be capable of controlling an amount of a heat transfer fluid. 
   In order to achieve the above-described object, there is provided a magnetic refrigerator, comprising: a plurality of magnetic heat exchange units including a magnetocaloric material for passing through a flow of a heat transfer fluid; a rotating plate having the plurality of magnetic heat exchange units disposed along a circumference thereof, the plurality of magnetic heat exchange units having a predetermined distance therebetween; a magnet disposed between an upper surface and a bottom surface of the rotating plate, the magnet applying a magnetic field to increase a temperature when the plurality of magnetic heat exchange units pass; a hot heat exchange member disposed at a hot side of the plurality of magnetic heat exchange units; and a cold heat exchange member disposed at a cold side of the plurality of magnetic heat exchange units, wherein the heat transfer fluid is divided into a first heat transfer fluid circulating in the hot heat exchange member and a second heat transfer fluid circulating in the cold heat exchange member. 
   In accordance with the refrigerator, a hot side and a cold side are divided to simplify a structure, to achieve a high heat efficiency, and to be capable of controlling an amount of a heat transfer fluid. 
   It is preferable that the hot heat exchange member comprises a hot heat exchanger, a first pipe for moving the first heat transfer fluid at a cold side outlet of the hot heat exchanger to the hot side of the plurality of magnetocaloric exchange units, and a second pipe for moving the first heat transfer fluid to a hot side inlet of the hot heat exchanger, wherein the first heat transfer fluid absorbs a heat of the magnetocaloric material to be heated, and the cold heat exchange member comprises a cold heat exchanger, a third pipe for moving the second heat transfer fluid at a hot side outlet of the cold heat exchanger to the cold side of the plurality of magnetocaloric exchange units, and a fourth pipe for moving the second heat transfer fluid to a cold side inlet of the cold heat exchanger, wherein the second heat transfer fluid emits a heat to the magnetocaloric material to be cooled. 
   The refrigerator in accordance with claim  1 , wherein the plurality of magnetocaloric exchange units comprises a mounting case mounted in a mounting hole disposed through the rotating plate, a mesh disposed at both ends of the mounting case, and the magnetocaloric material contained between the mesh and the mounting case. 
   In addition, it is preferable that the plurality of magnetocaloric exchange units comprises a mounting case mounted in a mounting hole disposed through the rotating plate, a mesh disposed at both ends of the mounting case, and the magnetocaloric material contained between the mesh and the mounting case. 
   Moreover, it is preferable that each of the plurality of magnetocaloric exchange units comprises a case including an upper case and lower case, and the magnetocaloric material sealed in the case, the magnetocaloric material changing a temperature thereof when the magnetic field is applied. 
   In addition, the case comprises a groove at a sidewall thereof to increase a contact length with the heat transfer fluid. 
   Moreover, the groove is slanted from an upper portion of the uppercase toward a lower portion of the lower case to increase a contact length with the heat transfer fluid. In addition, the case comprises an aluminum for superior heat transfer characteristic and processing characteristic. 
   Moreover, it is preferable that the upper case and the lower case are sealed by a copper brazing. 
   In addition, the case further comprises a through-hole for passing the heat transfer fluid therethrough to increase an amount of the heat transfer fluid passing therethrough. 
   When each of the plurality of magnetocaloric material pieces has a shape of plate arranged to have a gap therebetween or a shape of a rod having a constant circular cross-section in a lengthwise direction, a sufficient contact as well as smooth flow of the heat transfer fluid is provided. 
   It is preferable that the case is mounted in a manner that a portion of the case extends from a lower surface the rotating plate, and the magnet is disposed at both sides of the extending portion of the case. 
   It is preferable that an upper portion of the case has a shape of a funnel, and a supporting piece for supporting each of the plurality of magnetocaloric material pieces is disposed at a lower portion of the case. 
   It is preferable that the case comprises a groove at a sidewall thereof in a lengthwise direction to increase a contact area with the heat transfer fluid, thereby improving a heat exchange efficiency. 
   It is preferable that the magnetocaloric material comprises a gadolinium. 
   There is also provided a magnetic refrigerator comprising: a first rotating plate having a plurality of first magnetic heat exchange units disposed along a circumference thereof, the each of the plurality of first magnetic heat exchange units including a first magnetocaloric material for passing through a first heat transfer fluid; a first magnet disposed between an upper surface and a bottom surface of the first rotating plate, the first magnet applying a magnetic field to increase a temperature of the first magnetocaloric material when the plurality of first magnetic heat exchange units pass; a hot heat exchange member disposed at a hot side of the plurality of first magnetic heat exchange units; a second rotating plate having a plurality of second magnetic heat exchange units disposed along a circumference thereof, the each of the plurality of second magnetic heat exchange units including a second magnetocaloric material for passing through a second heat transfer fluid; a second magnet disposed between an upper surface and a bottom surface of the second rotating plate, the second magnet applying the magnetic field to increase a temperature of a second magnetocaloric material when the plurality of second magnetic heat exchange units pass; a cold heat exchange member disposed at a cold side of the plurality of first magnetic heat exchange units; and an intermediate circulation member for guiding an intermediate heat transfer fluid circulating between the cold side of the plurality of first magnetic heat exchange units and a hot side of the plurality of second magnetic heat exchange units. 
   In accordance with the refrigerator, a hot side and a cold side are divided for simplification of the structure, the high heat efficiency, and controlling an amount of a heat transfer fluid as well as increasing a temperature range of the heat transfer fluid. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a plan view illustrating a heat transfer fluid in a conventional rotational magnet magnetic refrigerator. 
       FIG. 2  is a plan view exemplifying a magnetic heat exchange unit including a magnetocaloric material of  FIG. 1 . 
       FIG. 3  is a perspective view illustrating elements of a magnetic refrigerator in accordance with a first preferred embodiment of the present invention. 
       FIG. 4  is a front view of  FIG. 3 . 
       FIG. 5  is a cross-sectional view illustrating a magnetic heat exchange unit in accordance with a first alternate example of the first preferred embodiment of the present invention. 
       FIG. 6  is a perspective view illustrating a magnetic heat exchange unit in accordance with a second alternate example of the first preferred embodiment of the present invention. 
       FIG. 7  is a lateral cross-sectional view of  FIG. 6 . 
       FIG. 8  is a perspective view illustrating a case of  FIG. 6  disassembled. 
       FIG. 9  is a lateral view of  FIG. 6  taken from A direction for describing a groove schematically. 
       FIG. 10  is a lateral view of  FIG. 6  taken from A direction for describing other groove schematically. 
       FIG. 11  is a perspective view illustrating elements of a magnetic refrigerator in accordance with a second preferred embodiment of the present invention. 
       FIG. 12  is a front view of  FIG. 11 . 
       FIG. 13  is a perspective view illustrating a magnetic heat exchange unit in accordance with a first alternate example of the second preferred embodiment of the present invention. 
       FIG. 14  is a cross-sectional view taken along a line B-B of  FIG. 13 . 
       FIGS. 15 through 17  are cross-sectional views taken along a line B-B of  FIG. 13  of a second alternate example 
       FIG. 18  is a perspective view illustrating a magnetocaloric piece having a shape of a rod. 
       FIG. 19  is a front view illustrating a magnetic refrigerator in accordance with a third preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   The above-described objects and other objects and characteristics and advantages of the present invention will now be described in detail with reference to the accompanied drawings. 
   First Embodiment 
     FIG. 3  is a perspective view illustrating elements of a magnetic refrigerator in accordance with a first preferred embodiment of the present invention, and  FIG. 4  is a front view of  FIG. 3 . 
   As shown in  FIGS. 3 and 4 , the magnetic refrigerator in accordance with the first preferred embodiment of the present invention comprises a plurality of magnetic heat exchange units  113 , a rotating plate  118  having the plurality of magnetic heat exchange units  113  disposed along a circumference thereof such that the plurality of magnetic heat exchange units  113  have a predetermined distance therebetween, a magnet  140  disposed on opposite sides of an upper surface and a lower surface of the rotating plate  118  wherein the magnet  140  applies a magnetic field to increase a temperature when the plurality of magnetic heat exchange units  113  pass, a hot heat exchange member disposed at a hot side  113   a  of the plurality of magnetic heat exchange units  113 , and a cold heat exchange member disposed at a cold side  113   b  of the plurality of magnetic heat exchange units  113 . 
   The heat transfer fluid is divided into a first heat transfer fluid  17   a  circulating in the hot heat exchange member and a second heat transfer fluid  17   b  circulating in the cold heat exchange member to form a cycle. 
   That is, the hot heat exchange member comprises a hot heat exchanger  162 , a first pipe  130  for moving a first heat transfer fluid  17   aa  at a cold side outlet of the hot heat exchanger  162  to the hot side  113   a  of the plurality of magnetic heat exchange units  113 , and a second pipe  131  for moving a first heat transfer fluid  17   ab  to a hot side inlet of the hot heat exchanger  162 , wherein the first heat transfer fluid  17   a  absorbs a heat of a magnetocaloric material  112  to be heated. 
   Similarly, the cold heat exchange member comprises a cold heat exchanger  163 , a third pipe  132  for moving a second heat transfer fluid  17   bb  at a hot side outlet of the cold heat exchanger  163  to the cold side  113   b  of the plurality of magnetic heat exchange units  113 , and a fourth pipe  133  for moving a second heat transfer fluid  17   bc  to a cold side inlet of the cold heat exchanger  163 , wherein the second heat transfer fluid  17   bc  emits a heat to the magnetocaloric material  112  to be cooled. 
   The plurality of magnetic heat exchange units  113  comprises the magnetocaloric material  112  which passes a flow of the heat transfer fluid. The magnetocaloric material  112  has a characteristic wherein the temperature thereof is changed when the magnetic field is applied. The magnetocaloric material  112  comprises a gadolinium (Gd) of a fine powder type. The gadolinium has pores having a high osmosis to the flow of the heat transfer fluid, and a superior absorption and emission of a heat. 
   The rotating plate  118  is rotated by a motor  144  rotating a shaft  148  fixed to a center of the rotating plate  118 . The magnetocaloric materials  112  spaced apart by a predetermined distance are disposed in a circumferential direction. 
   That is, the rotating plate  118  includes mounting holes punched along the circumference thereof, and the plurality of magnetic heat exchange units  113  shown in  FIG. 5  are mounted in the mounting holes. 
   The plurality of magnetic heat exchange units  113  comprises a mounting case  115  mounted in the mounting holes, meshes  116  and  117  mounted at both ends of the mounting case  115 , the magnetocaloric material  112  contained in the mounting case  115  between the meshes  116  and  117 . Accordingly, this constitution facilitates mounting of the plurality of magnetic heat exchange units  113  on the rotating plate  118 . 
   The magnet  140  is fixed over and under the rotating plate  118  immediately prior to the first pipe  130  and the second pipe  131  such that the meshes  116  and  117  magnetic field is applied to raise the meshes  116  and  117  temperature when the plurality of magnetic heat exchange units  113  passes. 
   On the other hand, as shown in  FIGS. 6 through 8 , it is preferable that a magnetic heat exchange unit  213  includes a case  215  mounted in the mounting hole of the rotating plate  118 , and a magnetocaloric material  212  sealed in the case  215 . The case  215  comprises a lower case  215   a  and an upper case  215   b  assembled together to carry out a heat exchange without a direct contact between the magnetocaloric material  212  and the heat transfer fluid. Therefore, the oxidation and the loss of the magnetocaloric material  212  are prevented. 
   It is preferable that the case  215  comprises an aluminum having superior heat transfer characteristic and processing characteristic. 
   In addition, it is preferable that the upper case  215   b  and the lower case  215   a  are sealed by a copper brazing in order to improve a sealing efficiency. 
   Moreover, the case  215  includes grooves  217  having a predetermined distance therebetween at a sidewall thereof to increase a contact area with the heat transfer fluid, thereby increasing the heat transfer efficiency. 
   It is preferable that each of the grooves  217  is slanted in order to increase a contact length with the heat transfer fluid. 
   As shown in  FIG. 9 , each of the grooves  217  is slanted such that a width of each of the grooves  217  is increased from an upper portion to a lower portion, or as shown in  FIG. 10 , the grooves  219  itself is slanted to improve the heat exchange efficiency. 
   In addition, as shown in  FIG. 6 , the case  215  comprises a through-hole  221  for passing the heat transfer fluid therethrough to improve the heat exchange efficiency. 
   A cycle of the magnetic refrigerator in accordance with the present invention will now be described considering a characteristic of the magnetocaloric material wherein a temperature thereof rises by 3° C. when the magnetocaloric material is magnetized and drops by 3° C. when cooled by the heat transfer fluid to experiment the characteristic of the magnetocaloric material by setting an atmospheric temperature which carries out an heat exchange with the hot heat exchanger  162 , and an atmospheric temperature which carries out an heat exchange with the cold heat exchanger  163  are set at 26° C. respectively. 
   As shown in  FIGS. 3 and 4 , the rotating plate  118  rotates by the motor  144  and the plurality of magnetic heat exchange units  113  sequentially pass the magnet  140 , the hot heat exchanger  162  and the cold heat exchanger  163 . 
   A magnetic heat exchange units  113  that passes the magnet  140  is heated to 29° C. by the magnetocaloric effect of the magnetocaloric material  112 , and the plurality of magnetic heat exchange units  113  are cooled to 26° C. by the first heat transfer fluid  17   aa  of the first pipe  130  through which the magnetocaloric material  112  passes while the first heat transfer fluid  17   ab  are heated to 29° C. simultaneously. The heated first heat transfer fluid  17   ab  dissipates the heat by passing through the hot heat exchanger  162  via the second pipe  131 , and the first heat transfer fluid  17   aa  cooled to 26° C. passes through the plurality of magnetic heat exchange units  113  via the first pipe  130 . The above-described cycle is repeated. 
   The temperature of the magnetocaloric material which lost the heat to the heat transfer fluid drops to 23° C. while moving to the cold heat exchanger. The cold side  113   b  of 23° C. restores the temperature thereof to 26° C. by passing the second heat transfer fluid  17   bb  (26° C.) of the third pipe  132  while the temperature of the second heat transfer fluid drops to 23° C. The cooled second heat transfer fluid  17   bc  passes through the cold heat exchanger  163  via the fourth pipe  133  to emit a cold air (23° C.), the second heat transfer fluid  17   bb  heated to 26° C. passes through the plurality of magnetic heat exchange units  113  via the third pipe  132 . The above-described cycle is repeated. 
   Pumps  160  and  161  is mounted at the second pipe  131  and the fourth pipe  133  respectively to propel the first heat transfer fluids  17   aa  and  17   ab  the second heat transfer fluids  17   bb  and  17   bc.    
   As described above, the circulation of the heat transfer fluid is divided into the hot heat exchanger and the cold heat exchanger to have two cycles, and the magnetocaloric material  112  is mounted in the rotating plate  118  to be rotated between the hot heat exchanger and the cold heat exchanger for the heat exchange, thereby simplifying a structure of a magnetic refrigeration cycle. 
   In addition, in accordance with the system, since the heat transfer fluid at the atmospheric temperature is injected to the magnetocaloric material, the heat transfer fluid is heated and cooled more according to a state of the material to improve an efficiency of the heat exchanger. 
   Moreover, since the magnetic refrigerator is divided into the hot heat exchanger  162  and the cold heat exchanger  163 , amounts of the first heat transfer fluid  17   aa  and the second heat transfer fluid  17   bb  are controlled to be different. Therefore, a larger amount of the first heat transfer fluid may be flown to the hot side of the magnetic heat exchange unit to maximize the cooling of the magnetocaloric material. 
   Second Embodiment 
   While a magnetic refrigerator in accordance with the second embodiment shown in  FIGS. 11 and 12  is similar to that of the first embodiment, a magnet  1140  is disposed below the rotating plate  118  and on opposite sides of lower surfaces of a magnetic heat exchange units  1113  due to a difference in a mounting structure of the magnetic heat exchange unit. 
   First Alternate Example 
   The Magnetic Heat Exchange Unit  1113   
   As shown in  FIGS. 13 and 14 , the magnetic heat exchange unit  1113  in accordance with the first alternate example of the second embodiment comprises a case  1115  extending vertically, and a plurality of magnetocaloric material pieces  1112  disposed in the case  1115  to form a gap  1114 . 
   An upper portion of the case  1115  has a shape of a funnel, a supporting piece  1115   b  supporting the plurality of magnetocaloric material pieces  1112  is disposed at a lower portion of the case  1115 . 
   An upper case  1115   a  having the shape of the funnel carries out a function of guiding the heat transfer fluid into the case as well as a function of supporting itself by suspending from the mounting hole of the rotating plate  118 . 
   In addition, as shown in  FIGS. 11 and 12 , it is preferable that the case  1115  is mounted in a manner that a portion of the case extends from the lower surface of the rotating plate  118 . 
   The magnet  1140  may be disposed at both sides of the extending portion of the case  1115  to improve the heat exchange efficiency since the heat transfer fluid flows while the magnetic field is applied. 
   The plurality of magnetocaloric material pieces  1112 , which have a shape of a plate manufactured from a gadolinium powder, are disposed in parallel in a manner that the gap  1114  prevents a contact with the case. The plurality of magnetocaloric material pieces  1112  having the shape of the plate may be a thin foil or a thick sheet according to a flow velocity and a heat exchange rate of the heat transfer fluid. 
   As described above, the plurality of plate type magnetocaloric material pieces  1112  having the gap  1114  prevents the loss of the material even when the mesh is not used, a contact with the entire plurality of magnetocaloric material pieces  1112  as well as a smooth flow is obtained since the heat transfer fluid flows through the gap  1114 , and a higher heat exchange rate compared to that of the conventional art is obtained since a contact area is larger in case of the plate type. 
   Second Alternate Example 
   Magnetic Heat Exchange Unit  1213   
   As shown in  FIG. 15 , the magnetic heat exchange unit  1113  in accordance with the second alternate example of the second embodiment comprises a plurality of magnetocaloric material pieces  1212  having a shape of a rod instead of the plurality of magnetocaloric material pieces  1112  having the shape of the plate. That is, each of the plurality of magnetocaloric material pieces  1212  has the shape of the rod having a constant circular cross-section in a lengthwise direction. 
   A gap  1214  between the plurality of magnetocaloric material pieces  1212  having the shape of the rod is formed when in contact or not in contact due to the circular cross-section even when the plurality of magnetocaloric material pieces  1212  are randomly arranged such that an effect of the first embodiment is obtained when the heat transfer fluid flows through the gap  1214 . 
   It is preferable that the plurality of magnetocaloric material pieces  1212  having the shape of the rod are inserted in a batch arranged vertically. 
   On the other hand, as shown in  FIG. 18 , it is preferable that the plurality of magnetocaloric material pieces  1212  having the shape of the rod comprises a groove  1212   a  in a lengthwise direction to increase the contact area with the heat transfer fluid, thereby improving the heat exchange efficiency. 
   Third Alternate Example 
   Magnetic Heat Exchange Unit  1313   
   As shown in  FIG. 16 , the magnetic heat exchange unit  1213  in accordance with the third alternate example of the second embodiment comprises a plurality of magnetocaloric material pieces  1312  having the shape of the rod arranged in a manner similar to the plurality of magnetocaloric material pieces  1112  having the shape of the plate of the first alternate example instead of a random arrangement of the plurality of magnetocaloric material pieces  1212  having the shape of the rod of the second alternate example. 
   It is preferable that the plurality of magnetocaloric material pieces  1312  having the shape of the rod are inserted in a batch arranged vertically. 
   As shown in  FIG. 18 , it is preferable that the plurality of magnetocaloric material pieces  1312  having the shape of the rod comprises the groove  1212   a  in the lengthwise direction. 
   Fourth Alternate Example 
   Magnetic Heat Exchange Unit  1413   
   As shown in  FIG. 17 , the magnetic heat exchange unit  1413  comprises a plurality of magnetocaloric material pieces  1412   a  and a plurality of magnetocaloric material pieces  1412  having the shape of the plate are arranged to have a gap  1414  therebetween. 
   The rotating plate  118  is rotated by a motor  144  rotating a shaft  148  fixed to a center of the rotating plate  118 . The magnetic heat exchange unit  1113 ,  1213 ,  1313  or  1413  spaced apart by the predetermined distance are disposed in the circumferential direction. 
   That is, the rotating plate  118  includes mounting holes punched along the circumference thereof, and the magnetic heat exchange unit  1113 ,  1213 ,  1313  or  1413  shown in  FIGS. 14 through 17  are mounted in the mounting holes. 
   Third Embodiment 
   As shown in  FIG. 19 , a two-step cycle is embodied to increase a temperature range of the heat transfer fluid. 
   That is, a magnetic refrigerator of  FIG. 19  comprises a first rotating plate and a second rotating plate having a motor, a magnet, a hot heat exchanger, a cold heat exchanger and a magnetic heat exchange unit containing a heat transfer fluid mounted thereon. The first rotating plate and the second rotating plate are rotated simultaneously by the motor, and, accordingly, a first magnetic heat exchange unit and a second magnetic heat exchange unit pass the magnet, a hot side and a cold side sequentially. 
   In accordance with the first rotating plate, the first magnetic heat exchange unit that passed a first magnet is heated by the magnetocaloric effect by the heat transfer fluid and the heat is cooled by a first heat transfer fluid passing the magnetocaloric material while the first heat transfer fluid is heated simultaneously. 
   The heated first heat transfer fluid emits the heat by passing through the hot heat exchanger and then is passed through the first magnetic heat exchange unit. The above-described cycle is repeated. 
   While the magnetocaloric material that has lost the heat to the first heat transfer fluid of the hot side (a first cooling) regains the lost heat by passing an intermediate cold side heat transfer fluid, a temperature of an intermediate heat transfer fluid drops to 23° C. 
   The intermediate heat transfer fluid cooled by a second cooling is magnetized by a second magnet of the second rotating plate and passes the magnetocaloric material heated to a temperature of 29° C. (a third cooling) to return to an original temperature thereof, and returns to the second cooling. The above-described cycle is repeated. 
   The magnetocaloric material is cooled to the intermediate heat transfer fluid having the temperature lower than those of the first cooling and the second cooling in the third cooling such that the temperature of the magnetocaloric material drops even more, and enters the cold heat exchanger at a temperature of 20° C. which is an optimized cooling temperature through a fourth cooling to lower the atmospheric temperature. 
   That is, when the atmospheric temperature is 26° C., the temperature of the magnetocaloric material heated to 29° C. by the first magnet of the first rotating plate (upper plate), the magnetocaloric material is cooled to 23° C. while the first heat transfer fluid  17   ab  is elevated to 29° C. when the magnetocaloric material is cooled by the first heat transfer fluid  17   aa  having the temperature of 26° C. in the first cooling to be passed through the hot heat exchanger to dissipate the heat and through the first magnetic heat exchange unit at the atmospheric temperature. The above-described cycle is repeated. 
   When the intermediate heat transfer fluid having the atmospheric temperature of 26° C. meets the magnetocaloric material of 23° C. to be cooled in the second cooling, the magnetocaloric material returns to the original temperature of the atmospheric temperature while the temperature of the intermediate heat transfer fluid drops to 23° C. 
   When the intermediate heat transfer fluid of 23° C. is magnetized by the second rotating plate (lower plate) to cool the heated magnetocaloric material (29° C.) in the third cooling, the intermediate heat transfer fluid returns to the original temperature of 26° C. to return to the second cooling. The above-described cycle is repeated. 
   The magnetocaloric material is cooled by the intermediate heat transfer fluid of 23° C. in the third cooling such that the temperature thereof drops to 23° C. The magnetocaloric material enters the cold heat exchanger at a cooling temperature of 20° C. through the fourth cooling to maintain the atmospheric temperature at 20° C. 
   A temperature variation of the intermediate heat transfer fluid is expanded due to a more cooling opportunity from two coolings to four coolings by an intermediate circulation member for guiding the intermediate heat transfer fluid circulating between a cold side of the plurality of first magnetocaloric exchange units and a hot side of the plurality of second magnetocaloric exchange units. 
   While the magnetic refrigerator of the present invention is not limited to the embodiments described above, it will be understood by those skilled in the art that various changes in form and details may be effected therein without departing from the spirit and scope of the invention. For instance, while the magnet  140  or  1140  is described to be a permanent magnet facing one another, it will be understood by those skilled in the art that the magnet  140  or  1140  may be embodied by en electromagnet. 
   As described above, the magnetic refrigerator in accordance with the present invention provides following advantages. 
   The circulation of the heat transfer fluid is divided to the hot heat exchanger and the cold heat exchanger to have two cycles and the magnetocaloric material is mounted on the circular rotating plate to be rotated between the hot heat exchanger and the cold heat exchanger for the heat exchange, thereby simplifying the structure of the magnetic refrigerating cycle. 
   In addition, in accordance with the system, since the heat transfer fluid at the atmospheric temperature is injected to the magnetocaloric material, the heat transfer fluid is heated and cooled more according to a state of the material to improve an efficiency of the heat exchanger. 
   Moreover, since the magnetic refrigerator is divided into the hot heat exchanger and the cold heat exchanger  163 , amounts of the first heat transfer fluid and the second heat transfer fluid  17   bb  are controlled to be different. Therefore, a larger amount of the first heat transfer fluid may be flown to the hot side of the magnetic heat exchange unit to maximize the cooling of the magnetocaloric material. 
   In addition, the magnetocaloric material is sealed in the case to be in indirect contact with the heat transfer fluid so that the loss by the flowing the heat transfer fluid is prevented as well as preventing the oxidation for a semi-permanent use. 
   Moreover, the groove is formed at the sidewall of the case to increase the contact area with the flowing the heat transfer fluid, thereby improving the heat exchange efficiency. 
   In addition, the groove is slanted to increase the contact length, thereby improving the heat exchange efficiency even more. 
   Since the case comprises the aluminum, the superior heat transfer characteristic and the processing characteristic are provided. 
   The magnetic heat exchange unit is constructed to comprise the case extending vertically and the plurality of magnetocaloric material pieces disposed in the case to form the gap so that the heat transfer fluid may be flown through the gap, thereby improving the heat exchange efficiency through a uniform contact between the plurality of magnetocaloric material pieces and the heat transfer fluid and eliminating a need for the mesh for the smooth flow of the heat transfer fluid. 
   In addition, the heat exchange efficiency is improved by increasing the contact area with the heat transfer fluid when the groove is formed on the plurality of magnetocaloric material pieces having the shape of the rod in the lengthwise direction. 
   Moreover, the plurality of magnetocaloric material pieces have the shape of the plate or the rod such that the plurality of magnetocaloric material pieces are not lost. 
   In addition, the two-step cycle is embodied to increase a temperature range of the heat transfer fluid due to the more cooling opportunity from two coolings to four coolings, thereby increasing an application range of a filed of a magnetic refrigerating or the magnetic heat exchange refrigerator. 
   LIST OF REFERENCE SYMBOLS 
   
       
       
         
             60 ,  160 ,  161 : pump 
             62 ,  162 : hot heat exchanger 
             63 ,  163 : cold heat exchanger 
             13 : magnetic heat exchange unit 
             17   aa ,  17   ab : first heat transfer fluid 
             17   bb ,  17   bc : second heat transfer fluid 
             112 ,  212 ,  1312 ,  412   a ,  412   b : magnetocaloric material piece (Gd) 
             113 ,  213 ,  1113 ,  1213 ,  1313 ,  1413 : magnetic heat exchange unit 
             113   a : a hot side of magnetic heat exchange unit 
             113   b : a cold side of magnetic heat exchange unit 
             115 : mounting case 
             116 ,  117 : mesh 
             130 ,  131 ,  132 ,  133 : pipe 
             140 ,  1140 : magnet 
             144 : motor 
             148 : shaft 
             215 : case 
             217 ,  219 : groove 
             221 : through-hole 
             1114 ,  1214 ,  1314 ,  1414 : gap 
             1115 : case 
             1115   a : funnel portion 
             1115   b : supporting piece