Abstract:
In a heat transporting apparatus, a cylinder is filled with a refrigerant and pistons are arranged in the cylinder, which compress and expand the refrigerant in the cylinder. A magnet unit is movably provided around the cylinder to apply a magnetic field to the cylinder, which is alternately increased and decreased in accordance with a movement of the magnet unit. A thermal accumulator is received in the cylinder, which produces heat depending on one of the increasing and decreasing of the magnetic field at the compression of the refrigerant, and absorbs heat depending on the other of the increasing and decreasing of the magnetic field at the expansion of the refrigerant. Heat exchangers are located in the cylinder, which radiates the heat from the refrigerant and thermal accumulator to an exterior of the apparatus, and absorbs external heat and transfers the heat to the refrigerant and thermal accumulator.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2005-352242, filed Dec. 6, 2005, the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a heat transporting apparatus for transporting heat with utilizing a refrigerating cycle having a refrigerant compressing and expanding processes.  
         [0004]     2. Description of the Related Art  
         [0005]     Refrigerators or heat pumps have been known as apparatuses that utilize a refrigerating cycle to transport heat. Among the refrigerators serving as heat transporting apparatuses, Stirling refrigerators are gathering much attention for their high energy efficiency. The Stirling refrigerator is essentially expected to offer a very high refrigerating efficiency. However, the Stirling refrigerator is actually used mainly to provide very low temperatures (which are almost equal to liquid helium temperature). On the other hand, the Stirling refrigerator can use helium as a refrigerant; helium is a natural refrigerant which is harmless to human beings and which is not involved in ozone layer destruction or global warming.  
         [0006]     The Stirling refrigerator operates in accordance with a Stirling refrigerating cycle including four basic processes, isothermal compression, isovolumetric cooling, isothermal expansion, and isovolumetric heating. To implement the Stirling refrigerating cycle, a high- and low-temperature cylinder sections are provided in which a refrigerant is sealed. A higher-temperature heat exchanger, a thermal accumulator or heat storage device, and a lower-temperature heat exchanger are disposed between the cylinder sections. Compression and expansion of the refrigerant are repeated in the cylinder sections to transport heat from the lower-temperature heat exchanger to the higher-temperature heat exchanger. Of the four basic processes of the Stirling refrigerating cycle, the isovolumetric heating and cooling are mainly based on the heat exchange between the heat exchanger and the thermal accumulator. The heat radiation and absorption by the higher- and lower-temperature heat exchangers occur during the isothermal compression and expansion processes.  
         [0007]     However, the efficiency of the Stirling refrigerating cycle used for the Stirling refrigerator is mainly limited by the heat conducting performance of the higher- and lower-temperature heat exchangers and thermal accumulator. Consequently, in spite of the theoretical high efficiency, actual apparatuses are disadvantageously inefficient and fail to achieve the desired performance.  
         [0008]     Thus, to improve the performance of the refrigerator, it is important to increase the heat exchanging efficiency during the Stirling refrigerating cycle. To increase the heat exchanging efficiency, it is necessary to improve the heat exchanging performance of the higher- and lower-temperature heat exchangers and thermal accumulator.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     According to an aspect of the present invention, there is provided a heat transfer apparatus comprising:  
         [0010]     a container filled with a refrigerant;  
         [0011]     an operation unit which compresses the refrigerant to produce heat and expands the refrigerant to absorb heat in the container, alternately;  
         [0012]     a generating unit configured to generate a magnetic field which is increased and decreased, alternately;  
         [0013]     a thermal accumulator received in the container, to which the magnetic field is applied, and which produces heat depending on one of the increasing and decreasing of the magnetic field at the time of compression of the refrigerant and absorbs heat depending on the other of the increasing and decreasing of the magnetic field at the time of expansion of the refrigerant; and  
         [0014]     first and second heat transfer units, the first heat transfer unit transferring the heat produced in the refrigerant and the thermal accumulator to the outside of the apparatus, and the second heat transfer unit transferring external heat to the refrigerant and the thermal accumulator.  
         [0015]     According to another aspect of the present invention, there is provided a heat transporting apparatus comprising:  
         [0016]     a cylindrical container provided with compression and expansion chambers communicating with each other and filled with a refrigerant;  
         [0017]     a compression piston received in the cylindrical container, which compresses the refrigerant in the expansion chamber and an expansion piston which expands the refrigerant in the expansion chamber;  
         [0018]     a generating unit configured to generate a magnetic field which is increased and decreased, alternately;  
         [0019]     a thermal accumulator received in the cylindrical container, to which the magnetic field is applied, and which produces heat depending on one of the increasing and decreasing of the magnetic field at the time of compression of the refrigerant, and absorbs heat depending on the other of the increasing and decreasing of the magnetic field at the time of expansion of the refrigerant; and  
         [0020]     first and second heat transfer units, the first heat transfer unit transferring the heat produced in the refrigerant and the thermal accumulator to the outside of the apparatus, and the second heat transfer unit transferring external heat to the refrigerant and the thermal accumulator.  
         [0021]     According to yet another aspect of the present invention, there is provided a heat transporting apparatus comprising:  
         [0022]     a cylindrical container filled with a refrigerant;  
         [0023]     pistons received in the cylindrical container, which compress and expand the refrigerant;  
         [0024]     a generating unit configured to generate a magnetic field which is increased and decreased, alternately;  
         [0025]     a thermal accumulator received in the cylindrical container, to which the magnetic field is applied, and which produces heat depending on one of the increasing and decreasing of the magnetic field at the time of compression of the refrigerant and absorbs heat depending on the other of the increasing and decreasing of the magnetic field at the time of expansion of the refrigerant; and  
         [0026]     first and second heat transfer units, the first heat transfer unit transferring the heat produced in the refrigerant and the thermal accumulator to the outside of the apparatus, and the second heat transfer unit transferring external heat to the refrigerant and the thermal accumulator. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0027]      FIGS. 1A  to  1 D are schematic diagrams schematically showing a refrigerator that is applied to a first embodiment, to describe the basic operation and structure of the refrigerator;  
         [0028]      FIG. 2  is a schematic diagram specifically and three-dimensionally showing a refrigerator that is applied to a second embodiment;  
         [0029]      FIGS. 3A and 3B  are diagrams showing the general configuration of a magnetic material for a thermal accumulator in the refrigerator shown in  FIG. 2 ;  
         [0030]      FIGS. 4A and 4B  are schematic diagrams showing the general configuration of a mechanism used in the refrigerator shown in  FIG. 2  to increase or reduce the magnitude of a magnetic field;  
         [0031]      FIGS. 5A  to  5 D are schematic diagrams illustrating operations of the refrigerator shown in  FIG. 2 ;  
         [0032]      FIGS. 6A  to  6 D are schematic diagrams showing the general configuration of a refrigerator that is applied to a third embodiment;  
         [0033]      FIG. 7  is a schematic diagram specifically and three-dimensionally showing a refrigerator that is applied to a fourth embodiment;  
         [0034]      FIGS. 8A and 8B  are schematic diagrams illustrating operations of the refrigerator shown in  FIG. 7 ;  
         [0035]      FIGS. 9A and 9B  are schematic diagrams showing the general configuration of a refrigerator that is applied to a fifth embodiment;  
         [0036]      FIG. 10  is a schematic diagram showing the general configuration of a refrigerator that is applied to a sixth embodiment; and  
         [0037]      FIGS. 11A and 11B  are schematic diagrams illustrating operations of the refrigerator shown in  FIG. 10 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0038]     With reference to the drawings, description will be given of heat transporting apparatuses according to embodiments of the present invention.  
       FIRST EMBODIMENT  
       [0039]      FIGS. 1A  to  1 D show a basic configuration of a heat transporting apparatus such as a refrigerator, which utilizes a Stirling refrigerating cycle.  
         [0040]     In  FIG. 1 , reference numeral  1  denotes a cylinder that is a cylindrical container. The cylinder  1  is open at its opposite ends and is filled with a gas refrigerant, for example, helium or nitrogen. The cylinder  1  has a heat storage device  2  in the center of its hollow portion; the heat storage device  2  serves as a thermal accumulator. The heat storage device  2  is composed of a magnetic material  3  having its temperature changed in response to an increase or decrease in the magnitude of a magnetic field. In this embodiment, the magnetic material  3  is a positive one, for example, a GD-based material, which has its temperature raised (heat generation) in response to an increase in the magnitude of the magnetic field, while having its temperature lowered (heat absorption) in response to a decrease in the magnitude of the magnetic field.  
         [0041]     Inside the cylinder  1 , a higher-temperature heat exchanger  4  is placed in proximity to one end of the heat storage device  2 . A lower-temperature heat exchanger  5  is placed in proximity to the other end of the heat storage device  2 . The higher-temperature heat exchanger  4  radiates heat from the refrigerant and heat storage device  2  to the exterior of the apparatus. The lower-temperature heat exchanger  5  absorbs external heat on the basis of heat absorption by the refrigerant and heat storage device  2 .  
         [0042]     A compression piston  6  is provided in an opening of the cylinder  1  which is closer to the higher-temperature heat exchanger  4 . An expansion piston  7  is provided in an opening of the cylinder  1  which is closer to the lower-temperature heat exchanger  5 . The compression piston  6  and expansion piston  7  constitute an operation unit. The compression piston  6  moves in the direction of arrow A shown in  FIG. 1A  to compress a refrigerant inside the cylinder  1 . The expansion piston  7  moves in the direction of arrow C shown in  FIG. 1C  to compress the refrigerant inside the cylinder  
         [0043]     A mechanism  8  for generating a magnetic field and increasing and reducing the magnetic field is placed outside the cylinder  1  around the periphery of the heat storage device  2 . The magnetic field increasing and reducing mechanism  8  increases and reduces the magnitude of a magnetic field that is applied to the magnetic material  3  in the heat storage device  2 . The magnetic field increasing and reducing mechanism  8  is not limited to a particular one shown in  FIGS. 1A  to  1 D. The mechanism may be modified or altered to various units or apparatuses that provide a function for increasing and reducing the magnitude of a magnetic field that is applied to the magnetic material  3 . The magnetic field increasing and reducing mechanism  8  may be an electromagnet that can be turned on and off, or a magnetic field generating unit, for example, a permanent magnet.  
         [0044]     Now, description will be given of the operation of the refrigerator configured as described above.  
         [0045]     First, the compression piston  6  is moved in a direction A, that is, from the left to right of the figure, to compress the refrigerant in the cylinder  1  as shown in  FIG. 1A . During the compression process, actuation of the higher-temperature heat exchanger  4  radiates heat generated from the refrigerant by compression, in the direction of arrow B in  FIG. 1A  to the exterior of the apparatus via the higher-temperature heat exchanger  4 . An isothermal refrigerant compressing process is thus executed. Simultaneously with the compression of the refrigerant, the magnetic field increasing and reducing mechanism  8  applies a magnetic field to the heat storage device  2 . Here, the heat storage device  2  is composed of the magnetic material  3  having its temperature changed in response to an increase or decrease in the magnitude of a magnetic field. However, this embodiment uses a positive magnetic material which has its temperature raised (heat generation) in response to an increase in the magnitude of the magnetic field and which has its temperature lowered (heat absorption) in response to a decrease in the magnitude of the magnetic field. The temperature of the heat storage device  2  thus rises. The higher-temperature heat exchanger  4  is in operation even during the application of the magnetic field. Thus, heat generated from the heat storage device  2  is also radiated in the direction of arrow B to the exterior of the apparatus via the higher-temperature heat exchanger  4 . In other words, during the refrigerant compressing process shown in  FIG. 1A , not only heat from the refrigerant but also heat generated from the magnetic material  3  can be radiated to the exterior of the apparatus via the higher-temperature heat exchanger  4 .  
         [0046]     Then, as shown in  FIG. 1B , with the volume of the cylinder  1  between the compression piston  6  and the expansion piston  7  remaining fixed, the compression piston  6  and expansion piston  7  are simultaneously moved rightward to move the refrigerant rightward in the cylinder  1 .  
         [0047]     Then, as shown in  FIG. 1C , the expansion piston  7  is moved in a C direction, that is, from the right to left of the figure, to expand the refrigerant in the cylinder  1 . At this time, actuation of the lower-temperature heat exchanger  5  allows the refrigerant cooled by expansion to absorb external heat in the direction of arrow D. An isothermal refrigerant expansion process is thus executed. Simultaneously with the expansion of the refrigerant, the magnetic field increasing and reducing mechanism  8  removes the magnetic field applied to the heat storage device  2 . The heat storage device  2  is composed of a positive magnetic material that has its temperature lowered (heat absorption) in response to a decrease in the magnitude of a magnetic field. The temperature of the heat storage device  2  thus lowers. The lower-temperature heat exchanger  5  is in operation even during the decrease in temperature. Consequently, external heat can further be absorbed via the lower-temperature heat exchanger  5 . In other words, during the refrigerant expansion process shown in  FIG. 1C , heat is absorbed not only by the refrigerant but also by the magnetic material  3 . Under these conditions, external heat can be absorbed via the lower-temperature heat exchanger  5 .  
         [0048]     Then, as shown in  FIG. 1D , with the volume of the cylinder  1  between the compression piston  6  and the expansion piston  7  remaining fixed, the compression piston  6  and expansion piston  7  are moved leftward in the figure to move the refrigerant leftward in the cylinder  1 .  
         [0049]     The process shown in  FIGS. 1A  to  1 D is repeated as described above to repeatedly execute the four basic processes, isothermal compression, isovolumetric cooling, isothermal expansion, and isovolumetric heating. The Stirling refrigerating cycle is thus implemented. Specifically, repetition of the compression and expansion processes allows the refrigerant to generate and absorb heat. The heat storage device  2 , composed of the magnetic material  3 , is caused to repeat a heat generating and absorbing reactions by increasing and reducing the magnitude of the magnetic field simultaneously with the repeated compression and expansion processes. This allows the higher-temperature heat exchanger  4  to radiate heat, while allowing the lower-temperature heat exchanger  5  to absorb heat.  
         [0050]     Accordingly, in the refrigerating cycle having the refrigerant compression and expansion processes, the compression process not only allows the refrigerant to generate heat but also applies a magnetic field to the magnetic material  3  constituting the heat storage device  2  to allow the magnetic material  3  to make a heat generating reaction. The heat from the magnetic material  3  is radiated via the higher-temperature heat exchanger  4 . Consequently, this refrigerator can radiate more heat to the exterior of the apparatus. The expansion process not only expands the refrigerant to allow it to absorb heat but also removes the magnetic field to allow the magnetic material  3  to make a heat absorbing reaction. This enables more external heat to be absorbed via the lower-temperature heat exchanger  5 . Thus, simultaneously with the heat generation and absorption by the refrigerant, the heat storage device  2  composed of the magnetic material  3  is caused to make heat generating and absorbing reactions. The present refrigerating cycle having the compression and expansion processes offers a drastically increased heat exchanging efficiency. Therefore, a Stirling refrigerating cycle with a good heat transporting capability can be implemented.  
         [0051]     The above first embodiment repeats the four basic processes, isothermal compression, isovolumetric cooling, isothermal expansion, and isovolumetric heating, to implement a Stirling refrigerating cycle. An Ericsson cycle can be implemented by substituting isobaric processes for the two isovolumetric processes in the Stirling refrigerating cycle. A Brayton cycle can be implemented by substituting adiabatic processes for the compression and expansion processes in the Stirling refrigerating cycle and substituting isobaric processes for the two isovolumetric processes.  
       SECOND EMBODIMENT  
       [0052]      FIG. 2  is a three-dimensional cross sectional view showing a refrigerator of a second embodiment which is realized in accordance with the first embodiment.  
         [0053]     In  FIG. 2 , reference numeral  11  denotes a cylindrical casing. A compression cylinder  12  and an expansion cylinder  13  are arranged in parallel inside the casing  11 . Each of the compression cylinder  12  and expansion cylinder  13  is open at one end and is closed at the other end. The closed ends are connected together via a communication pipe  14  that allows the interior of the compression cylinder  12  to communicate with the interior of the expansion cylinder  13 . The compression cylinder  12  and expansion cylinder  13  are filled with a gas refrigerant, for example, helium or nitrogen.  
         [0054]     A heat storage device  15  is placed in the compression cylinder  12 . The heat storage device  15  is provided with a magnetic material  16  having its temperature changed in response to an increase or decrease in the magnitude of a magnetic field. In this embodiment, the magnetic material  16  is a positive one, for example, a GD-based material, which has its temperature raised (heat generation) in response to an increase in the magnitude of the magnetic field, while having its temperature lowered (heat absorption) in response to a decrease in the magnitude of the magnetic field. As the magnetic material  16 , generally spherical magnetic materials  16   a  of diameter about 1 mm or less may be filled in to the heat storage device  15  to form a porous member containing a large number of voids as shown in  FIG. 3A . Alternatively, a bulk material may be used which contains communication holes  16   b  which consist of small holes and which communicate with the exterior as shown in  FIG. 3B .  
         [0055]     A higher-temperature heat exchanger  17  is placed in proximity to the heat storage device  15 . The higher-temperature heat exchanger  17  is placed opposite the communication pipe  14  across the heat storage device  15 . The higher-temperature heat exchanger  17  radiates heat from the refrigerant and heat storage device  15  to the exterior of the apparatus.  
         [0056]     A compression piston  18  is provided in the compression cylinder  12 . The compression piston  18  is inserted into the compression cylinder  12  through its opening to compress the refrigerant in the compression cylinder  12 . A piston shaft  19  is connected to the compression piston  18 . A connecting bar  20  is connected to the piston shaft  19  and to a flywheel  21  at a position away from its rotating center. The connecting bar  20  thus constitutes a crank mechanism that converts a rotating motion of the flywheel  21  into a reciprocating motion to reciprocate the piston shaft  19  in the direction of arrow E in  FIG. 2 . The flywheel  21  has its rotating center connected to a rotating shaft  221  of a driving motor  22 . The flywheel  21  is rotated at a predetermined speed.  
         [0057]     A lower-temperature heat exchanger  23  is placed inside the expansion cylinder  13 . The lower-temperature heat exchanger  23  absorbs external heat on the basis of heat absorption by the refrigerant and heat storage device  15 . An expansion piston  24  is provided in the expansion cylinder  13 . The expansion piston  24  is inserted into the expansion cylinder  13  through its opening to compress the refrigerant in the expansion cylinder  13 . A piston shaft  25  is connected to the expansion piston  24 . A connecting bar  26  is connected to the piston shaft  25  and to a flywheel  27  at a position away from its rotating center. The connecting bar  26  thus constitutes a crank mechanism that converts a rotating motion of the flywheel  27  into a reciprocating motion to reciprocate the piston shaft  25  in the direction of arrow F in  FIG. 2 . The flywheel  27  has its rotating center connected to the rotating shaft  221  of the driving motor  22 . The flywheel  27  is rotated at a predetermined speed.  
         [0058]     A disk-like support plate  28  is integrally provided on the piston shaft  19 . A mechanism  30  for generating a magnetic field and increasing and reducing the magnetic field is provided on the support plate  28  via a support arm  29 . The magnetic field increasing and reducing mechanism  30  has a cylindrical shape with the compression cylinder located in its hollow portion. The piston shaft  19  reciprocates in the direction of arrow E to allow the magnetic field increasing and reducing mechanism  30  to increase or reduce the magnitude of a magnetic field that is applied to the heat storage device  15 .  
         [0059]     In the refrigerator shown in  FIG. 2 , the connecting bar  20  is attached to the flywheel  21 , located closer to the compression piston  18 , so as to rotate about 90° earlier in rotation phase than a connecting bar  26  attached to the flywheel  27 , located closer to the expansion piston  24 . The connecting bars  20  and  26  are arranged so as to meet the above relationship, and the piston shafts  19  and  25  reciprocate on the basis of this positional relationship. This serves to implement the four basic processes, isothermal compression, isovolumetric cooling, isothermal expansion, and isovolumetric heating, described above and shown in  FIGS. 1A  to  1 D.  
         [0060]     The magnetic field increasing and reducing mechanism  30  may be, for example, a double cylindrical magnet called a Halbach magnet, such as the one shown in  FIGS. 4A and 4B . This double cylindrical magnet is composed of an outer cylindrical magnet  302  and an inner cylindrical magnet  301  placed in a hollow portion of the outer cylindrical magnet  302  at a predetermined spacing from the magnet  302 . In the cylindrical magnets  301  and  302 , the directions of magnetic anisotropy at different areas are denoted by reference numerals  303  and  304 . As shown in  FIG. 4A , when the direction of a magnetic field  305  generated in the hollow portion by the inner cylindrical magnet  301  coincides with the direction of a magnetic field  306  generated in the hollow portion by the outer cylindrical magnet  302 , a strong magnetic field is generated in a space  307  in the hollow portion of the inner cylindrical magnet  301 . In this state, the whole double cylindrical magnet is moved coaxially with the compression piston  18  by the piston shaft  19 . This enables an increase or reduction in the magnitude of a magnetic field that is applied to the heat storage device  15 .  
         [0061]     Further, a weak magnetic field can be generated in the hollow portion of the inner cylindrical magnet  301  by making the direction of the magnetic field  305  generated in the hollow portion by the inner cylindrical magnet  301 , opposite to the direction of the magnetic field  306  generated in the hollow portion by the outer cylindrical magnet  302  so that the magnetic fields  305  and  306  cancel each other, as shown in  FIG. 4B . With this double cylindrical magnet, the magnitude of the magnetic field for the heat storage device  15  can be increased or reduced by rotating one of the inner cylindrical magnet  301  and outer cylindrical magnet  302  in conjunction with the reciprocating motion of the piston shaft  19  to establish the conditions shown in  FIG. 4A  or  4 B.  
         [0062]      FIGS. 5A  to  5 D are diagrams illustrating the operation of the refrigerator configured as described above. In  FIGS. 5A  to  5 D, the same components as those in  FIG. 2  are denoted by the same reference numerals.  
         [0063]     A cylinder main body  31  shown in  FIGS. 5A  to  5 D comprises the above compression cylinder  12  and expansion cylinder  13 . The cylinder main body  31  is filled with a refrigerant. The heat storage device  15 , higher-temperature heat exchanger  17 , and lower-temperature heat exchanger  23  are arranged inside the cylinder main body  31 ; the heat storage device  15  is provided with the magnetic material  16 , which has its temperature changed in response to an increase or decrease in the magnitude of a magnetic field. The compression piston  18  is placed in one of the openings of the cylinder main body  31 . The expansion cylinder  24  is placed in the other opening. The mechanism  30  is placed outside the cylinder main body  31  to increase and reduce the magnitude of a magnetic field that is applied to the periphery of the heat storage device  15 . The magnetic field increasing and reducing mechanism  30  is connected to piston shaft  19  of the compression piston  18  via the support arm  29 . The magnetic field increasing and reducing mechanism  8  can reciprocate in conjunction with the compression piston  18 .  
         [0064]     In this refrigerator, first, as shown in  FIG. 5A , the compression piston  18  is moved in the direction A, that is, from the left to right in  FIG. 5A , to compress the refrigerant in the cylinder main body  31  (compression cylinder  12 ). At this time, actuation of the higher-temperature heat exchanger  17  radiates heat generated from the refrigerant by compression, in the direction of arrow B in  FIG. 5A  to the exterior of the apparatus via the higher-temperature heat exchanger  17 . An isothermal refrigerant compressing process is thus executed. Simultaneously with the compression of the refrigerant, the magnetic field increasing and reducing mechanism  30 , connected to the piston shaft  19 , moves, as the compression piston  18  moves, to a position where it applies a magnetic field to the heat storage device  15 . In this case, the heat storage device  15  has its temperature raised. This is because the heat storage device  15  is composed of the magnetic material  16  having its temperature raised (heat generation) in response to an increase in the magnitude of a magnetic field and lowered (heat absorption) in response to a decrease in the magnitude of the magnetic field. At this time, the higher-temperature heat exchanger  17  is in operation. Thus, heat generated from the heat storage device  15  can also be radiated in the direction of arrow B in  FIG. 5A  to the exterior of the apparatus via the higher-temperature heat exchanger  17 . In other words, during the refrigerant compressing process shown in  FIG. 5A , not only heat from the refrigerant but also heat generated from the magnetic material  16  can be radiated to the exterior of the apparatus via the higher-temperature heat exchanger  17 .  
         [0065]     Then, as shown in  FIG. 5B , with the volume of the cylinder main body  31  between the compression piston  18  and the expansion piston  24  remaining fixed, the compression piston  18  and expansion piston  24  are simultaneously moved rightward in  FIG. 5B  to move the refrigerant rightward in the cylinder main body  31 .  
         [0066]     Then, as shown in  FIG. 5C , the expansion piston  7  is moved in a direction C, i.e., from the right to left in  FIG. 5C , to expand the refrigerant in the cylinder main body  31  (expansion cylinder  13 ). At this time, actuation of the lower-temperature heat exchanger  23  allows the refrigerant cooled by expansion to absorb external heat in the direction of arrow D in  FIG. 5C  via the lower-temperature heat exchanger  23 . An isothermal refrigerant expansion process is thus executed.  
         [0067]     Then, as shown in  FIG. 5D , with the volume of the cylinder main body  31  between the compression piston  18  and the expansion piston  24  remaining fixed, the compression piston  18  and expansion piston  24  are moved leftward to move the refrigerant leftward in the cylinder main body  31 . At this time, the magnetic field increasing and reducing mechanism  30 , connected to the piston shaft  19 , moves away from the heat storage device  15  as the compression piston  18  moves. This removes the magnetic field for the heat storage device  15 . The heat storage device  15  is composed of a positive magnetic material that has its temperature (heat absorption) lowered in response to a decrease in the magnitude of a magnetic field. The temperature of the heat storage device  15  thus lowers. At this time, the lower-temperature heat exchanger  23  is in operation. Consequently, external heat can be absorbed via the lower-temperature heat exchanger  23 . In other words, during the refrigerant expansion process shown in  FIG. 5D , heat is absorbed not only by the refrigerant but also by the magnetic material  16 . Under these conditions, external heat can be absorbed via the lower-temperature heat exchanger  23 .  
         [0068]     The process shown in  FIGS. 5A  to  5 D is repeated as described above to repeatedly execute the four basic processes, isothermal compression, isovolumetric cooling, isothermal expansion, and isovolumetric heating. The Stirling refrigerating cycle is thus implemented.  
         [0069]     Therefore, the above embodiment can produce effects similar to those of the first embodiment. Moreover, the compression piston  18 , expansion piston  24 , and magnetic field increasing and reducing mechanism  30  perform the series of operations using the driving motor  22  as a driving source. This enables the Stirling refrigerating cycle to be executed both automatically and stably. Furthermore, the rotation speed of the driving motor can be increased to achieve high-speed refrigeration.  
         [0070]     The magnetic material  16  constituting the heat storage device  15  is a porous member containing a large number of voids or a bulk material containing communication holes which consist of small holes and which communicate with the exterior. The refrigerant can thus pass through the interior of the magnetic material  16 . This makes it possible to increase the contact area between the magnetic material  16  and the refrigerant as well as the rate of heat transfer between the magnetic material  16  and the refrigerant. The magnetic material  16  and the refrigerant can thus efficiently exchange heat with each other to further improve the heat generating and absorbing effects of the heat storage device  15 .  
         [0071]     Moreover, a strong magnetic field required to operate the magnetic material  16  can be easily obtained by using a cylindrical magnet called a Halbach magnet as the magnetic field increasing and reducing mechanism  30  and composed of the outer cylindrical magnet  302  and the inner cylindrical magnet  301 , located in the hollow portion.  
       THIRD EMBODIMENT  
       [0072]      FIGS. 6A  to  6 D show the general structure of another example of a refrigerator using a Stirling refrigerating cycle according to the present invention. In  FIGS. 6A  to  6 D, the same components as those in  FIG. 5  are denoted by the same reference numerals.  
         [0073]     In the refrigerator shown in  FIGS. 6A  to  6 D, a cool storage section  32 , the higher-temperature heat exchanger  17 , and the lower-temperature heat exchanger  23  are arranged inside the cylinder main body  31 . The compression piston  18  is placed in one of the openings of the cylinder main body  31 . The expansion cylinder  24  is placed in the other opening. The magnetic field increasing and reducing mechanism  30  is placed outside the cylinder main body  31  along the circumference of the heat storage device  32 . The magnetic field increasing and reducing mechanism  30  is connected to piston shaft  19  of the compression piston  18  via the support arm  29 . The magnetic field increasing and reducing mechanism  30  can reciprocate in conjunction with the compression piston  18 .  
         [0074]     The cool storage section  32  includes a heat storage device  321  composed of a positive magnetic material  331  which has its temperature raised in response to an increase in the magnitude of the magnetic field and which has its temperature lowered in response to a decrease in the magnitude of the magnetic field, and a storage device  322  composed of a negative magnetic material  332  which has its temperature lowered in response to an increase in the magnitude of the magnetic field and which has its temperature raised in response to a decrease in the magnitude of the magnetic field. The positive magnetic material  331  is what is called a ferromagnetic substance or a meta-magnetic substance which is in a paramagnetic state (magnetic spins are disordered) with no magnetic field applied to the material and which is brought to a ferromagnetic state (magnetic spins are ordered) when a magnetic field is applied to the material (a substance that exhibits a order-disorder transition from the ferromagnetic state to paramagnetic state in response to application and removal of a magnetic field). The negative magnetic material  332  exhibits different ordered states depending on whether or not a magnetic field is applied and exhibits an order-order transition between the two ordered states in response to application and removal of a magnetic field; the degree of order is higher (the degree of freedom of the system is lower) when no magnetic field is applied to the segments. Specific examples of the positive magnetic material  331  include ferromagnetic substances such as Gd and Gd-based alloys, that is, Gd-Y, Gd-Dy, Gd-Er, and Gd-Ho alloys, and meta-magnetic substances and ferromagnetic substances based on La(Fe, Si)  13  or La(Fe, Al)  13 . Specific examples of the negative magnetic material  332  include substances such as a FeRH alloy which exhibit an order-order transition from the ferromagnetic state to an antiferromagnetic state in response to application and removal of a magnetic field. With the FeRh alloy, the magnitude of magnetic moment of Rh changes significantly between the two states owing to a difference in the polarization of Rh. This changes the entropy of an electron system.  
         [0075]     In this refrigerator, first, as shown in  FIG. 6A , the compression piston  18  is moved in the direction A in this figure, that is, from the left to right of the figure, to compress the refrigerant in the cylinder main body  31  (compression cylinder  12 ). At this time, actuation of the higher-temperature heat exchanger  17  radiates heat generated from the refrigerant by compression, in the direction of arrow B in  FIG. 6A  to the exterior of the apparatus via the higher-temperature heat exchanger  17 . An isothermal refrigerant compressing process is thus executed. Simultaneously with the compression of the refrigerant, the magnetic field increasing and reducing mechanism  30 , connected to the piston shaft  19 , moves, as the compression piston  18  moves, to a position where it applies a magnetic field to the heat storage device  321 . The heat storage device  321  has its temperature raised. This is because the heat storage device  321  is composed of the magnetic material  331  having its temperature raised (heat generation) in response to an increase in the magnitude of a magnetic field and lowered (heat absorption) in response to a decrease in the magnitude of the magnetic field. At this time, the higher-temperature heat exchanger  17  is in operation. Thus, heat generated from the heat storage device  321  can also be radiated in the direction of arrow B in  FIG. 6A  to the exterior of the apparatus via the higher-temperature heat exchanger  17 . On the other hands, the magnetic field from the magnetic field increasing and reducing mechanism  30  is removed from the cools storage device  322 . The cools storage device  322  thus has its temperature raised. This is because the heat storage device  322  is composed of the negative magnetic material  332  having its temperature raised (heat generation) in response to removal of the magnetic field. Since the higher-temperature heat exchanger  17  is in operation, heat from the heat storage device  322  can also be radiated to the exterior of the apparatus via the higher-temperature heat exchanger  17 . Thus, during the refrigerant compressing process shown in  FIG. 6A , not only heat from the refrigerant but also heat generated from the magnetic materials  331  and  332  can be radiated to the exterior of the apparatus via the higher-temperature heat exchanger  17 . More heat can thus be radiated.  
         [0076]     Then, in  FIG. 6B , with the volume of the cylinder main body  31  between the compression piston  18  and the expansion piston  24  remaining fixed, the compression piston  18  and expansion piston  24  are simultaneously moved rightward in  FIG. 6B  to move the refrigerant rightward in the cylinder main body  31 .  
         [0077]     Then, as shown in  FIG. 6C , the expansion piston  7  is moved in the direction C in this figure, from the right to left of the figure, to expand the refrigerant in the cylinder main body  31  (expansion cylinder  13 ). At this time, actuation of the lower-temperature heat exchanger  23  allows the refrigerant cooled by expansion to absorb external heat in the direction of arrow D in  FIG. 6C  via the lower-temperature heat exchanger  23 . An isothermal refrigerant expansion process is thus executed.  
         [0078]     Then, as shown in  FIG. 6D , with the volume of the cylinder main body  31  between the compression piston  18  and the expansion piston  24  remaining fixed, the compression piston  18  and expansion piston  24  are moved leftward to move the refrigerant leftward in the cylinder main body  31 . At this time, the magnetic field increasing and reducing mechanism  30 , connected to the piston shaft  19 , moves  15 , as the compression piston  18  moves, to a position where it applies a magnetic field to the heat storage device  322 . This removes the magnetic field for the heat storage device  321  and now applies it to the heat storage device  322 . The heat storage device  321  is composed of the positive magnetic material  331  that has its temperature lowered (heat absorption) in response to a decrease in the magnitude of the magnetic field. The temperature of the heat storage device  321  thus lowers. However, at this time, the lower-temperature heat exchanger  23  is in operation. Consequently, external heat can be absorbed via the lower-temperature heat exchanger  23 . The heat storage device  322 , to which the magnetic field is applied, is composed of the negative magnetic material  332  that has its temperature lowered (heat absorption) in response to application of a magnetic field. The temperature of the heat storage device  322  thus lowers. However, since the lower-temperature heat exchanger  23  is in operation, external heat can be absorbed via the lower-temperature heat exchanger  23 . In other words, during the process shown in  FIG. 6D , heat is absorbed not only by the refrigerant but also by the magnetic materials  331  and  332 . More heat can thus be absorbed.  
         [0079]     The process shown in  FIGS. 6A  to  6 D is repeated as described above to repeatedly execute the four basic processes, isothermal compression, isovolumetric cooling, isothermal expansion, and isovolumetric heating. The Stirling refrigerating cycle is thus implemented.  
         [0080]     Therefore, the above embodiment can produce effects similar to those of the second embodiment. Moreover, the cool storage section  32  includes the heat storage device  321  composed of the positive magnetic material  331  which has its temperature raised in response to an increase in the magnitude of a magnetic field and which has its temperature lowered in response to a decrease in the magnitude of the magnetic field, and the storage device  322  composed of the negative magnetic material  332  which has its temperature lowered in response to an increase in the magnitude of the magnetic field and which has its temperature raised in response to a decrease in the magnitude of the magnetic field. When heat is radiated from the refrigerant, heat can also be radiated from the magnetic materials  331  and  332 . When the refrigerant absorbs heat, the magnetic materials  331  and  332  can also absorb heat. This enables more heat to be radiated and absorbed to further improve the heat exchanging efficiency of the refrigerating cycle.  
       FOURTH EMBODIMENT  
       [0081]     In the description of the above embodiments, the refrigerator uses the Stirling refrigerating cycle having the four basic processes, isothermal compression, isovolumetric cooling, isothermal expansion, and isovolumetric heating. However, the fourth embodiment shows a refrigerator to which a refrigerating cycle of two basic processes, isothermal compression and isothermal expansion is applied.  
         [0082]      FIG. 7  three-dimensionally shows an embodiment of this refrigerator.  
         [0083]     In the figure, reference numeral  41  denotes a cylindrical casing in which a cylindrical cylinder main body  42  is placed. The cylinder main body  42  is open at one end and is closed at the other end. The cylinder main body  42  is filled with a gas refrigerant, for example, helium or nitrogen.  
         [0084]     A heat storage device  43  is placed inside the cylinder main body  42  closer to the closed end. The heat storage device  43  is composed of a magnetic material  44  having its temperature changed in response to an increase or decrease in the magnitude of a magnetic field. In this embodiment, the magnetic material  44  is a positive one, for example, a GD-based material, which has its temperature raised (heat generation) in response to an increase in the magnitude of the magnetic field, while having its temperature lowered (heat absorption) in response to a decrease in the magnitude of the magnetic field. As the magnetic material  44 , a porous member or a bulk material with a plurality of communication holes for external communication is used as described in  FIGS. 3A and 3B .  
         [0085]     A higher-temperature heat exchanger  45  and a lower-temperature heat exchanger  46  are arranged on the respective sides of the heat storage device  43 . In this case, the higher-temperature heat exchanger  45  is placed closer to the opening of the cylinder main body  42 . The higher-temperature heat exchanger  45  radiates heat from a refrigerant and the heat storage device  43 . The lower-temperature heat exchanger  46  is placed closer to the closed end of the cylinder main body  42 . The lower-temperature heat exchanger  46  absorbs external heat on the basis of heat absorption by the refrigerant and heat storage device  43 .  
         [0086]     A piston  47  is provided in the cylinder main body  42 . The piston  47  is inserted into the cylinder main body  42  through its opening to compress the refrigerant inside the cylinder main body  42 . A piston shaft  48  is connected to the piston  42 . A connecting bar  49  is connected to the piston shaft  48  and to a flywheel  50  at a position away from its rotating center. The connecting bar  49  thus constitutes a crank mechanism that converts a rotating motion of the flywheel  50  into a reciprocating motion to reciprocate the piston shaft  48  in the direction of arrow H in  FIG. 48 . The flywheel  50  has its rotating center connected to a rotating shaft  52  of a driving motor  51 . The flywheel  50  is rotated at a predetermined speed.  
         [0087]     A disk-like support plate  53  is integrally provided on the piston shaft  47 . A magnetic field increasing and reducing mechanism  55  is provided on the support plate  53  via a support arm  54 . The magnetic field increasing and reducing mechanism  55  is cylindrical with the cylinder main body  42  located in its hollow portion. The piston shaft  48  reciprocates in the direction of arrow H to allow the magnetic field increasing and reducing mechanism  30  to increase or reduce the magnitude of a magnetic field that is applied to the heat storage device  43 . Also in this case, the magnetic field increasing and reducing mechanism  30  may be a double cylindrical magnet called a Halbach magnet, described with reference to  FIGS. 4A and 4B .  
         [0088]      FIGS. 8A and 8B  are diagrams illustrating the operation of the refrigerator configured as described above. In  FIGS. 8A and 8B , the same components as those in  FIG. 7  are denoted by the same reference numerals.  
         [0089]     In the refrigerator shown in  FIGS. 8A and 8B , the cylinder main body  42  is filled with a refrigerant. The heat storage device  43 , higher-temperature heat exchanger  45 , and lower-temperature heat exchanger  46  are arranged inside the cylinder main body  42 ; the heat storage device  43  is composed of the magnetic material  44 , which has its temperature changed in response to an increase or decrease in the magnitude of a magnetic field. The piston  47  is placed in the opening of the cylinder main body  42 . The magnetic field increasing and reducing mechanism  55  is placed outside the cylinder main body  42  around the heat storage device  43 . The magnetic field increasing and reducing mechanism  55  is connected to the piston shaft  48  of the piston  47  via the support arm  54 . The magnetic field increasing and reducing mechanism  55  can reciprocate in conjunction with the piston  47 .  
         [0090]     In this refrigerator, first, as shown in  FIG. 8A , the piston  47  is moved in direction A, that is, from the left to right in  FIG. 8A , to compress the refrigerant in the cylinder main body  42 . At this time, actuation of the higher-temperature heat exchanger  45  radiates heat generated from the refrigerant by compression, in the direction of arrow B in  FIG. 8A  to the exterior of the apparatus via the higher-temperature heat exchanger  45 . An isothermal refrigerant compressing process is thus executed. Simultaneously with the compression of the refrigerant, the magnetic field increasing and reducing mechanism  55 , connected to the piston shaft  48 , moves, as the piston  47  moves, to a position where it applies a magnetic field to the heat storage device  43 . In this case, the heat storage device  43  has its temperature raised. This is because the heat storage device  43  is composed of the positive magnetic material  44  having its temperature raised (heat generation) in response to an increase in the magnitude of a magnetic field and lowered (heat absorption) in response to a decrease in the magnitude of the magnetic field. At this time, the higher-temperature heat exchanger  45  is in operation. Thus, heat generated from the heat storage device  43  can also be radiated in the direction of arrow B in  FIG. 8A  to the exterior of the apparatus via the higher-temperature heat exchanger  45 . In other words, during the refrigerant compressing process shown in  FIG. 8A , not only heat from the refrigerant but also heat generated from the magnetic material  44  can be radiated to the exterior of the apparatus via the higher-temperature heat exchanger  45 .  
         [0091]     Then, as shown in  FIG. 8B , the piston  47  is moved in a direction C in this figure, that is, from the right to left of the figure, to expand the refrigerant in the cylinder main body  42 . At this time, actuation of the lower-temperature heat exchanger  46  allows the refrigerant cooled by expansion to absorb external heat in the direction of arrow D in  FIG. 8B  via the lower-temperature heat exchanger  46 . An isothermal refrigerant expansion process is thus executed. At the same time, the magnetic field increasing and reducing mechanism  55 , connected to the piston shaft  48 , moves, as the piston  47  moves, to a position where it removes the magnetic field from the heat storage device  43 . The heat storage device  43  has its temperature raised. This is because the heat storage device  43  is composed of the positive magnetic material  44  having its temperature raised (heat generation) in response to an increase in the magnitude of a magnetic field and lowered (heat absorption) in response to a decrease in the magnitude of the magnetic field. At this time, the lower-temperature heat exchanger  46  is in operation. This enables external heat to be absorbed via the lower-temperature heat exchanger  46 . In other words, the refrigerant expansion process shown in  FIG. 8B  excites not only heat absorption by the refrigerant but also heat absorption by the magnetic material  44 . In this state, external heat can be absorbed via the lower-temperature heat exchanger  46 .  
         [0092]     The process shown in  FIGS. 8A and 8B  is similarly repeated to enable the implementation of a refrigerating cycle of two basic processes, isothermal compression and isothermal expansion; heat is radiated to the exterior via the higher-temperature heat exchanger  45 , and external heat is absorbed via the lower-temperature heat exchanger  46 .  
         [0093]     Therefore, also with the refrigerating cycle of two basic processes, isothermal compression and isothermal expansion, when the refrigerant generates heat, the magnetic material  44  is also allowed to radiate heat. Further, when the refrigerant absorbs heat, the magnetic material  44  is also allowed to absorb heat. This enables a refrigerating cycle with an increased heat exchange efficiency to be implemented. Such a refrigerating cycle can be implemented using the cylinder main body  42  and piston  47 . This makes it possible to simplify the entire configuration of the apparatus to reduce costs.  
       FIFTH EMBODIMENT  
       [0094]      FIGS. 9A and 9B  show the general configuration of another exemplary refrigerator that uses a refrigerating cycle of two basic processes, isothermal compression and isothermal expansion. In  FIGS. 9A and 9B , the same components as those in  FIGS. 8A and 8B  are denoted by the same reference numerals.  
         [0095]     In the refrigerator shown in  FIGS. 9A and 9B , a cools storage section  56  and the higher-temperature heat exchanger  45  and lower-temperature heat exchanger  46  are arranged inside the cylinder main body. The piston  47  is placed in the opening of the cylinder main body  42 . The magnetic field increasing and reducing mechanism  55  is placed outside the cylinder main body  42  along the periphery of the heat storage device  56 . The magnetic field increasing and reducing mechanism  55  is connected to the piston shaft  48  of the piston  47  via the support arm  54 . The magnetic field increasing and reducing mechanism  55  can reciprocate in conjunction with the piston  47 .  
         [0096]     The cool storage section  56  has a heat storage device  431  and a heat storage device  432  arranged in parallel; the heat storage device  431  is composed of a positive magnetic material  441  having its temperature raised in response to an increase in the magnitude of a magnetic field, while having its temperature lowered in response to a decrease in the magnitude of the magnetic field, and the heat storage device  432  is composed of a negative magnetic material  442  having its temperature lowered in response to an increase in the magnitude of a magnetic field, while having its temperature raised in response to a decrease in the magnitude of the magnetic field. The positive magnetic material  441  and negative magnetic material  442  are similar to those described in the third embodiment.  
         [0097]     In this configuration, first, as shown in  FIG. 9A , the piston  47  is moved in a direction A, that is, from the left to right in  FIG. 9A , to compress the refrigerant in the cylinder main body  42 . At this time, actuation of the higher-temperature heat exchanger  45  radiates heat generated from the refrigerant by compression, in the direction of arrow B in  FIG. 9A  to the exterior of the apparatus via the higher-temperature heat exchanger  45 . An isothermal refrigerant compressing process is thus executed. Simultaneously with the compression of the refrigerant, the magnetic field increasing and reducing mechanism  55 , connected to the piston shaft  48 , moves, as the piston  47  moves, to a position where it applies a magnetic field to the heat storage device  431 . In this case, the heat storage device  431  has its temperature raised. This is because the heat storage device  431  is composed of the positive magnetic material  441  having its temperature raised (heat generation) in response to an increase in the magnitude of a magnetic field and lowered (heat absorption) in response to a decrease in the magnitude of the magnetic field. At this time, the higher-temperature heat exchanger  45  is in operation. Thus, heat generated from the heat storage device  431  can also be radiated in the direction of arrow B in  FIG. 8A  to the exterior of the apparatus via the higher-temperature heat exchanger  45 . On the other hand, the magnetic field from the magnetic field increasing and reducing mechanism  55  has been removed from the heat storage device  432 . In this case, the heat storage device  432  has its temperature raised. This is because the heat storage device  432  is composed of the negative magnetic material  442  that has its temperature raised (heat generation) in response to removal of the magnetic field. Since the higher-temperature heat exchanger  45  is in operation, heat from the heat storage device  432  can be radiated to the exterior of the apparatus via the higher-temperature heat exchanger  45 . Thus, during the refrigerant compressing process shown in  FIG. 9A , not only heat from the refrigerant but also heat generated from the magnetic materials  441  and  442  can be radiated to the exterior of the apparatus via the higher-temperature heat exchanger  17 . Therefore, more heat can be radiated.  
         [0098]     Then, as shown in  FIG. 9B , the piston  47  is moved in a direction C, that is, from the right to left in  FIG. 9B , to expand the refrigerant in the cylinder main body  42 . At this time, actuation of the lower-temperature heat exchanger  46  allows the refrigerant cooled by expansion to absorb external heat in the direction of arrow D in  FIG. 8B  via the lower-temperature heat exchanger  46 . An isothermal refrigerant expansion process is thus executed. At the same time, the magnetic field increasing and reducing mechanism  55 , connected to the piston shaft  48 , moves, as the piston  47  moves, to a position where it applies a magnetic field to the heat storage device  432 . This removes the magnetic field from the heat storage device  431 , while a magnetic field is applied to the heat storage device  432 . The heat storage device  431  has its temperature lowered. This is because the heat storage device  431  is composed of the positive magnetic material  441  that has its temperature lowered (heat absorption) in response to a decrease in the magnitude of the magnetic field. However, since the lower-temperature heat exchanger  46  is in operation, external heat can be absorbed via the lower-temperature heat exchanger  46 . At the same time, the heat storage device  432  has its temperature lowered. This is because the heat storage device  432  is composed of the negative magnetic material  442  that has its temperature lowered (heat absorption) in response to application of a magnetic field. However, since the lower-temperature heat exchanger  46  is in operation, external heat can be absorbed via the lower-temperature heat exchanger  46 . During the refrigerant expanding process shown in  FIG. 9B , external heat can be absorbed via the lower-temperature heat exchanger  46  on the basis of not only heat absorption by the refrigerant but also heat absorption resulting from a decrease in the temperature of the magnetic materials  441  and  442 . Therefore, more heat can be absorbed.  
         [0099]     Similar repetition of the process shown in  FIGS. 9A and 9B  enables the implementation of a refrigerating cycle of two basic processes, isothermal compression and isothermal expansion; external heat is absorbed via the lower-temperature heat exchanger  46 , and heat is radiated to the exterior via the higher-temperature heat exchanger  45 .  
         [0100]     This also makes it possible to exert effects similar to those of the fourth embodiment. Further, when the refrigerant radiates heat, the magnetic materials  441  and  442  are also allowed to radiate heat. When the refrigerant absorbs heat, the magnetic materials  441  and  442  are also allowed to absorb heat. This enables more heat to be radiated and absorbed, further increasing the heat exchange efficiency of the refrigerating cycle.  
       SIXTH EMBODIMENT  
       [0101]     In the above embodiments, the magnetic field increasing and reducing mechanism is moved to enable an increase or reduction in the magnitude of a magnetic field for the heat storage device. However, a sixth embodiment keeps the magnetic field increasing and reducing mechanism stationary while enabling an increase or reduction in the magnitude of a magnetic field for the heat storage device.  
         [0102]      FIG. 10  shows the general configuration of the sixth embodiment. The same components as those in  FIG. 1  are denoted by the same reference numerals and their description is omitted.  
         [0103]     In this case, the compression piston  6 , expansion piston  7 , heat storage device  2 , higher-temperature heat exchanger  4 , and lower-temperature heat exchanger  5  are arranged in the cylinder  1  filled with a refrigerant; the heat storage device  2  is composed of the magnetic material that has its temperature changed in response to an increase or decrease in the magnitude of a magnetic field.  
         [0104]     A magnetic field increasing and reducing mechanism  61  is placed outside the cylinder  1  in association with the heat storage device  2 . As shown in  FIG. 11A , the magnetic field increasing and reducing mechanism  61  is composed of a pair of permanent magnets  62   a  and  62   b  and a pair of yokes  63   a  and  63   b . In this case, the permanent magnets  62   a  and  52   b  are arranged so that the cylinder  1  (heat storage device  2 ) is sandwiched between the magnets  62   a  and  62   b . The yokes  63   a  and  63   b  can open and close a magnetic path between the permanent magnets  62   a  and  62   b . As shown in  FIG. 11A , with the magnetic path between the permanent magnets  62   a  and  62   b  closed, the magnitude of a magnetic field for the heat storage device is increased. As shown in  FIG. 11B , with the magnetic path between the permanent magnets  62   a  and  62   b  open, the magnitude of the magnetic field for the heat storage device is reduced.  
         [0105]     This refrigerator can increase or reduce the magnitude of a magnetic field for the heat storage device by moving the yokes  63   a  and  63   b  with the permanent magnets  62   a  and  62   b  remaining stationary to open or close the magnetic path between the permanent magnets  62   a  and  62   b . Consequently, effects similar to those of the first embodiment can be produced by repeatedly increasing or reducing the magnitude of the magnetic field in association with the isothermal compression, isovolumetric cooling, isothermal expansion, and isovolumetric heating processes, described in the first embodiment.  
         [0106]     The magnetic field increasing and reducing mechanism  61  configured as described above is also applicable to the above second to fifth embodiments.  
         [0107]     In the above embodiments, the magnetic material constituting the heat storage devices in the above embodiments consists of a uniform component with a fixed operating temperature. However, for example, the heat storage devices may each be composed of different components such that the operating temperature sequentially decreases from the higher-temperature heat exchanger toward the lower-temperature heat exchanger. Such a magnetic material makes it possible to emphasize the different operations of the higher- and lower-temperature heat exchangers, that is, heat generation and heat absorption. This enables more efficient heat radiation and absorption. Further, the higher-temperature heat exchanger and lower-temperature heat exchangers in the above embodiments may be composed of a magnetic material that has its temperature changed in response to an increase or decrease in the magnitude of a magnetic field. Moreover, the above embodiments all relate to the refrigerator. However, the present invention is of course applicable to a heat pump that transfers heat from a lower temperature side to a higher temperature side.  
         [0108]     As described above, the present invention can provide a heat transporting apparatus which has good heat transporting capability and which enables an increase in heat exchange efficiency.  
         [0109]     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.