Patent Publication Number: US-2023152009-A1

Title: Heat generating device

Description:
TECHNICAL FIELD 
     The present invention relates to a heat generating device. 
     BACKGROUND ART 
     In recent years, a heat generation phenomenon in which heat is generated by occluding and discharging hydrogen using a hydrogen storage metal or the like is reported (see, for example, NPL 1). Hydrogen can be generated from water and is thus inexhaustible and inexpensive as a resource, and does not generate a greenhouse gas such as carbon dioxide and is thus clean energy. Unlike a nuclear fission reaction, the heat generation phenomenon using the hydrogen storage metal or the like is safe since there is no chain reaction. Heat generated by occluding and discharging hydrogen can be utilized as it is, and can be further utilized by being converted into electric power. Therefore, the heat is expected as an effective energy source. 
     CITATION LIST 
     Non Patent Literature 
     NPL 1: A. Kitamura, A. Takahashi, K. Takahashi, R. Seto, T. Hatano, Y. Iwamura, T. Itoh, J. Kasagi, M. Nakamura, M. Uchimura, H. Takahashi, S. Sumitomo, T. Hioki, T. Motohiro, Y. Furuyama, M. Kishida, H. Matsune, “Excess heat evolution from nanocomposite samples under exposure to hydrogen isotope gases”, International Journal of Hydrogen Energy 43 (2018) 16187-16200. 
     SUMMARY OF INVENTION 
     Technical Problem 
     Research and development of a heat generating device that obtains thermal energy using occluding and discharging of hydrogen has been advanced, but there has been a problem that energy efficiency is low because heat loss is large and energy required to maintain the operation of the device is also large. 
     Therefore, an object of the present invention is to provide a heat generating device that suppresses heat loss and is excellent in energy efficiency. 
     Solution to Problem 
     A heat generating device according to the invention includes: a hollow container, a heat generating element provided inside the container, a heater for heating the heat generating element, a conductive wire part connecting a wall portion of the container and the heater, a hydrogen supply unit for supplying a hydrogen-containing hydrogen-based gas to the heat generating element, and a vacuum evacuation unit for evacuating the inside of the container. The heat generating element includes a base composed of a hydrogen storage metal, a hydrogen storage alloy, or a proton conductor, and a multilayer film provided on a surface of the base; and the multilayer film has a stacking structure in which a first layer and a second layer are stacked, the first layer being made of a hydrogen storage metal or a hydrogen storage alloy and having a thickness of less than 1000 nm, and the second layer being made of a hydrogen storage metal or a hydrogen storage alloy, which is different from that of the first layer, or ceramics and having a thickness of less than 1000 nm. When the heat generating element is heated by the heater, the hydrogen permeates through or diffuses through a heterogeneous material interface which is an interface between the first layer and the second layer by quantum diffusion, and thus the heat generating element generates heat; and when heater temperature is T H  [K], external environmental temperature is T W  [K], equivalent heat conduction area is A HC  [m 2 ], equivalent thermal conductivity is k eq  [W/mK], equivalent thermal conduction length is L eq  [m], sample radiation surface area is A S  [m 2 ], sample surface temperature is T S  [K], equivalent emissivity is ε eq , Stefan-Boltzmann constant is σ [W/m 2 K 4 ], energy required for maintaining operation is P m  [W], and thermal energy generated by the heat generating element is H ex  [W], the following formula (1) is satisfied: 
         A   HC η eq ( T   H   −T   W )+ A   s ε eq σ( T   S   4   −T   W   4 )+ P   m   &lt;H   ex    (1),
 
     wherein, η eq  is a value (k eq /L eq ) obtained by dividing the equivalent thermal conductivity by the equivalent thermal conduction length. 
     Advantageous Effects of Invention 
     According to the present invention, heat loss can be suppressed and energy efficiency can be improved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is an explanatory diagram for explaining an outline of a heat generating device according to a first embodiment. 
         FIG.  2    is an explanatory diagram for explaining a detailed configuration of a heat generating device according to the first embodiment. 
         FIG.  3    is a cross-sectional view showing a structure of a heat generating element having a first layer and a second layer. 
         FIG.  4    is an explanatory diagram showing generation of excess heat. 
         FIG.  5    is a perspective view showing a configuration of a heater. 
         FIG.  6    is a perspective view showing a configuration of a reflection unit. 
         FIG.  7    is a perspective view showing a state in which an upper support plate is moved upward. 
         FIG.  8    is a cross-sectional view of a support plate. 
         FIG.  9    is an explanatory diagram for explaining a configuration of a heat generating device according to a second embodiment. 
         FIG.  10    is an explanatory diagram for explaining a configuration of a heat generating device according to a third embodiment. 
         FIG.  11    is an explanatory diagram for explaining an action of the heat generating device according to the third embodiment. 
         FIG.  12    is an explanatory diagram for explaining a configuration of a heat generating device according to a fourth embodiment. 
         FIG.  13    is a cross-sectional view of a heat generating element formed in a bottomed cylindrical shape. 
         FIG.  14    is an explanatory diagram for explaining a configuration of a heat generating device according to a fifth embodiment. 
         FIG.  15    is an explanatory diagram for explaining an action of the heat generating device according to the fifth embodiment. 
         FIG.  16    is a cross-sectional view of a heat generating element formed in a columnar shape. 
         FIG.  17    is an explanatory diagram for explaining a configuration of a heat generating device according to a sixth embodiment. 
         FIG.  18    is a cross-sectional view showing a structure of a heat generating element having a first layer, a second layer, and a third layer. 
         FIG.  19    is a cross-sectional view showing a structure of a heat generating element having a first layer, a second layer, a third layer, and a fourth layer. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     In  FIG.  1   , the heat generating device  10  includes a container  11 , a heater  12 , a conductive wire part  13 , a heat generating element  14 , a hydrogen supply unit  15 , a vacuum evacuation unit  16 , and a reflection unit  17 . The container  11  is a hollow vacuum container. The heater  12  generates heat by applying a voltage and heats the heat generating element  14 . The conductive wire part  13  connects the wall portion of the container  11  and the heater  12 . The heat generating element  14  is provided inside the container  11 . By being heated by the heater  12  in a vacuum state, the heat generating element  14  is heated to a temperature equal to or higher than the temperature heated by the heater  12 . Heat generated by the heat generating element  14  which has been heated to a temperature equal to or higher than the temperature heated by the heater  12  is referred to as excess heat. The mechanism by which the heat generating element  14  generates the excess heat will be described later with reference to other drawings. The hydrogen supply unit  15  supplies a hydrogen-containing hydrogen-based gas to the heat generating element  14 . The vacuum evacuation unit  16  evacuates the inside of the container  11 . The reflection unit  17  reflects the radiant heat radiated by the heat generating element  14 . 
     When heater temperature which is the temperature of the heater  12  is T H  [K], external environmental temperature which is the temperature outside the container  11  is T W  [K], equivalent heat conduction area of the conductive wire part  13  is A HC  [m 2 ], equivalent thermal conductivity of the conductive wire part  13  is k eq  [W/mK], equivalent thermal conduction length of the conductive wire part  13  is L eq  [m], sample radiation surface area which is the surface area of the heat generating element  14  is A S  [m 2 ], sample surface temperature which is the temperature of the surface of the heat generating element  14  is T S  [K], equivalent emissivity between the heat generating element  14  and the wall portion of the container  11  is ε eq , Stefan-Boltzmann constant is σ [W/m 2 K 4 ], operation maintaining energy which is the energy required for maintaining operation of the device is P m  [W], and thermal energy generated by the heat generating element  14  is H ex  [W], the heat generating device  10  satisfies the above formula (1). In the above formula (1), η eq  is a value (k eq /L eq ) obtained by dividing the equivalent thermal conductivity by the equivalent thermal conduction length. “Equivalent” means a case where a plurality of elements are replaced with one element. For example, when the conductive wire part  13  is composed of two types of conductive wires and the conductive wires have different heat conduction areas, the heat conduction area when each conductive wire is replaced with one conductive wire is referred to as an equivalent heat conduction area. It should be noted that the term “equivalent” in this disclosure includes the case of only one element. For example, when the conductive wire part  13  is composed of one type of conductive wire, the heat conduction area of the conductive wire is also referred to as the equivalent heat conduction area. 
     The first term on the left side of the above formula (1) represents a heat loss caused by heat conduction from the heater  12  to the container  11  through the conductive wire part  13 , and is referred to as a heat conduction energy loss. The second term on the left side of the above formula (1) represents a heat loss due to radiant heat from the heat generating element  14 , and is referred to as a radiant energy loss. The third term on the left side of the above formula (1), i.e., the operation maintaining energy, is the energy required to maintain the generation of the excess heat in the heat generating element  14  for a long period of time, and includes at least the electric energy for driving the vacuum evacuation unit  16 . In the heat generating device  10 , after the heat generating element  14  generates excess heat, the heater  12  is turned off. Therefore, the operation maintaining energy does not include the electric energy for driving the heater  12 . 
     Heat loss due to heat conduction is suppressed by making the contact area of the heat generating device  10  with the outside as small as possible and using a member made of a material having low thermal conductivity. In addition, in the heat generating device  10 , heat loss due to radiation is suppressed by suppressing radiant heat of the heat generating element  14  by installing a reflection plate or configuring the container  11  with a material that reflects radiant heat. Further, in the heat generating device  10 , the inside of the container  11  is evacuated by a vacuum pump or the like to suppress the convective flow of the hydrogen, thereby suppressing the heat loss due to the convective flow. In the heat generating device  10 , after the heat generating element  14  generates excess heat, the heater  12  is turned off. Since the heat generating device  10  can continue generation of excess heat in the heat generating element  14  for a long period of time by using apart of the outputted energy as inputted energy, self-sustained operation is possible. 
     The configuration of the heat generating device  10  according to the first embodiment will be described in detail with reference to  FIG.  2   . 
     The container  11  is composed of an upper portion  11   a , a bottom portion  11   b  and a side portion  11   c.  The upper portion  11   a  and the bottom portion  11   b  are spaced apart from each other and are arranged facing each other. The upper portion  11   a  is located above the bottom portion  11   b.  The side portion  11   c  is formed in a cylindrical shape and connects the upper portion  11   a  and the bottom portion  11   b.  The container  11  is sealed by the connection of the upper portion  11   a,  the bottom portion  11   b,  and the side portion  11   c.  In the following description, when the upper portion  11   a,  the bottom portion  11   b,  and the side portion  11   c  are not distinguished from each other, they are referred to as wall portion. As a material of the container  11 , a material having heat resistance and pressure resistance is used. Examples of the material of the container  11  include carbon steel, austenitic stainless steel, and heat-resistant non-ferrous alloy. The material of the container  11  may be the same material as that of a reflection plate to be described later. By constituting the container  11  by using the same material as that of the reflection plate, the radiant heat of the heat generating element  14  is reflected on the inner surface of the container  11 , and the radiant energy loss is suppressed. The shape of the container  11  is not particularly limited, and may be a cylindrical shape, an elliptical cylindrical shape, a rectangular cylindrical shape, or the like. A pressure sensor (not shown) is provided inside the container  11 . 
     The wall portion of the container  11  is provided with a gas introduction port  25 , a gas discharge port  26  and a connecting portion  27 . The gas introduction port  25  connects the inside of the container  11  and the hydrogen supply unit  15 . The gas discharge port  26  connects the inside of the container  11  and the vacuum evacuation unit  16 . The connecting portion  27  is connected to the conductive wire part  13 . Although the gas introduction port  25  and the gas discharge port  26  are provided in the side portion  11   c  in the present embodiment, they are not limited thereto and they may be provided in the upper portion  11   a  or the bottom portion  11   b . The connecting portion  27  is provided on the upper portion  11   a  in the present embodiment, but is not limited thereto and may be provided on the side portion  11   c  or the bottom portion  11   b.    
     The heater  12  is provided inside the container  11 . In the present embodiment, the shape of the heater  12  is a plate shape. The heater  12  includes a heating unit  29  and a temperature sensor  30 . The heating unit  29  generates heat when a voltage is applied from a power supply (not shown) provided outside the container  11 . The shape of the heating unit  29  in a plan view is a square having a side length of 25 mm. The temperature sensor  30  detects the temperature of the heater  12 . The heater  12  raises the temperature of the heat generating element  14  to a predetermined temperature when the operation of the heat generating device  10  is started. 
     The conductive wire part  13  includes a heating conductive wire part  32  connected to the heating unit  29  and a temperature detecting conductive wire part  33  connected to the temperature sensor  30 . The heating conductive wire part  32  and the temperature detecting conductive wire part  33  are electrically connected to a control unit  37  to be described later via the connecting portion  27  of the container  11 . 
     The heat generating element  14  is provided on both surfaces of the heater  12 . That is, the heat generating device  10  includes two heat generating elements  14 . In the present embodiment, the shape of the heat generating element  14  is a plate shape. The shape of the heat generating element  14  in a plan view is a square having a side length of 25 mm. Among surfaces constituting the heat generating element  14 , a surface in contact with the heater  12  is referred to as a back surface, a surface opposite to the back surface is referred to as a front surface, and four surfaces perpendicular to the front surface and the back surface are referred to as side surfaces. The number of the heat generating element  14  is not particularly limited. Details of the configuration of the heat generating element  14  will be described later with reference to other drawings. 
     The hydrogen supply unit  15  is provided outside the container  11 . The hydrogen supply unit  15  introduces a hydrogen-based gas into the inside of the container  11  via the gas introduction port  25 . Although not shown, the hydrogen supply unit  15  includes a buffer tank that stores the hydrogen-based gas, a pipe that connects the buffer tank and the gas introduction port  25  of the container  11 , and a pressure-regulating valve that regulates the flow rate of the hydrogen-based gas introduced into the inside of the container  11  and the pressure in the pipe. The hydrogen-based gas is a gas containing an isotope of hydrogen. As the hydrogen-based gas, at least one of a deuterium gas and a light hydrogen gas is used. The light hydrogen gas includes a mixture of naturally occurring light hydrogen and deuterium, i.e., a mixture in which the abundance ratio of light hydrogen is 99.985% and the abundance ratio of deuterium is 0.015%. In the following description, when light hydrogen and deuterium are not distinguished from each other, they are referred to as “hydrogen”. 
     The vacuum evacuation unit  16  is provided outside the container  11 . The vacuum evacuation unit  16  evacuates the inside of the container  11  via the gas discharge port  26 . Although not shown, the vacuum evacuation unit  16  includes a vacuum pump, a pipe connecting the vacuum pump and the gas discharge port  26  of the container  11 , and a pressure-regulating valve that regulates the flow rate of the hydrogen-based gas discharged from the inside of the container  11  and the pressure in the pipe. The vacuum evacuation unit  16  continuously evacuates the inside of the container  11  during the operation of the heat generating device  10 . As a result, the vacuum state inside the container  11  is maintained, convective flow of hydrogen is suppressed, and heat loss due to the convective flow is suppressed. 
     The reflection unit  17  is provided inside the container  11 . The reflection unit  17  has a box shape as a whole and is configured to cover each heat generating element  14 . In the present embodiment, the shape of the reflection unit  17  is a substantially rectangular parallelepiped shape. The reflection unit  17  is formed of a material that reflects radiant heat. The material of the reflection unit  17  is preferably a material that reflects radiant heat and has low thermal conductivity. 
     The reflection unit  17  has at least a reflection plate  35  corresponding to the surface of the heat generating element  14 . The reflection plate  35  reflects radiant heat radiated from the surface of the heat generating element  14  toward the heat generating element  14 . The reflection plate  35  has a front surface on the surface of the heat generating element  14  side and a back surface on the surface of the container  11  side. In the present embodiment, there are three sheets of the reflection plate  35  arranged at intervals in a direction orthogonal to the surface of the heat generating element  14 . Therefore, the heat generating device  10  has a configuration in which three sheets of the reflection plate  35  are provided for each heat generating element  14 . The radiant heat radiated from the surface of the heat generating element  14  may be partially reflected by the reflection plate  35  and partially transmitted through the reflection plate  35 . Since the three sheets of the reflection plate  35  are provided, the radiant heat transmitted through the first reflection plate  35  corresponding to the front surface of the heat generating element  14  is reflected by the second reflection plate  35 , and the radiant heat transmitted through the second reflection plate  35  is reflected by the third reflection plate  35 . As the number of the reflection plate  35  increases, the radiant energy loss can be suppressed more. Here, it is known that heat flux decreases in proportion to 1/(n+1) when n sheets of reflection plate are provided between two surfaces and the emissivity of all the surfaces is equal (see, for example, “Heat Transfer, Revised Fifth Edition, The Japan Society of Mechanical Engineers, 2009, pp. 208-209”). In the present embodiment, since three sheets of the reflection plate  35  are provided between the front surface of the heat generating element  14  and the inner surface of the container  11 , the radiant energy loss can be suppressed to about ¼ as compared with the case where the reflection plate  35  is not provided. 
     In addition, the reflection unit  17  further includes a plurality of reflection plates  35  respectively corresponding to the four side surfaces of the heat generating element  14 . In the present embodiment, three sheets of the reflection plates  35  are provided to be spaced apart from each other in a direction orthogonal to one side surface of the heat generating element  14 . Therefore, the reflection unit  17  is configured to cover the two heat generating elements  14  with a total of eighteen reflection plates  35 . As a material of the reflection plate  35 , Ni, Cu, Mo, or the like is used. The shape of the reflection plate  35  in a plan view is not particularly limited, but is rectangular in the present embodiment. Among the plurality of reflection plates  35 , the three reflection plates  35  arranged above are provided with through holes into which the conductive wire part  13  to be described later is inserted. Further, each reflection plate  35  is provided with a through hole (not shown) into which a support column  53  to be described later is inserted. 
     The heat generating device  10  further includes a control unit  37 . The control unit  37  is provided outside the container  11 . The control unit  37  is electrically connected to each unit of the heat generating device  10  and controls the operation of each unit. The control unit  37  includes, for example, an arithmetic device (Central Processing Unit), a storage unit such as a read-only memory (Read Only Memory) or a random access memory (Random Access Memory). The arithmetic device executes various kinds of arithmetic processing using, for example, a program and data stored in the storage unit. In addition, the control unit  37  is electrically connected to a power supply (not shown) provided outside the container  11 , and controls a voltage applied from the power supply to the heater  12 . 
     The configuration of the heat generating element  14  will be described in detail with reference to  FIG.  3    and  FIG.  4   . As shown in  FIG.  3   , the heat generating element  14  includes a base  39  and a multilayer film  40 . The base  39  is made of a hydrogen storage metal, a hydrogen storage alloy, or a proton conductor. Examples of the hydrogen storage metal include Ni, Pd, V, Nb, Ta, and Ti. Examples of the hydrogen storage alloy include LaNi 5 , CaCu 5 , MgZn 2 , ZrNi 2 , ZrCr 2 , TiFe, TiCo, Mg 2 Ni, and Mg 2 Cu. Examples of the proton conductor include a BaCeO 3 -based conductor (for example, Ba(Ce 0.95 Y 0.05 )O 3-6 ), a SrCeO 3 -based conductor (for example, Sr(Ce 0.95 Y 0.05 )O 3-6 ), a CaZrO 3 -based conductor (for example, CaZr 0.95 Y 0.05 O 3-α ), a SrZrO 3 -based conductor (for example, SrZr 0.9 Y 0.1 O 3-α ), β-Al 2 O 3 , and β-Ga 2 O 3 . The base  39  may be formed of a porous body or a hydrogen permeable membrane. The porous body has pores of a size that allows passage of the hydrogen-based gas. The porous body is formed of, for example, a metal, a nonmetal, ceramics, or the like. The porous body is preferably formed of a material that does not inhibit the reaction between the hydrogen-based gas and the multilayer film  40 . The hydrogen permeable membrane is formed of, for example, a hydrogen storage metal or a hydrogen storage alloy. The hydrogen permeable membrane includes one having a mesh-like sheet. 
     The multilayer film  40  is provided on the base  39 . Although the multilayer film  40  is provided on the front surface of the base  39  in  FIG.  3   , the multilayer film  40  may be provided on the back surface of the base  39  or on both surfaces of the base  39 . When the multilayer film  40  is provided on the front surface or the back surface of the base  39 , the base  39  is provided on the front surface of the heater  12  (not shown). When the multilayer films  40  are provided on both surfaces of the base  39 , one of the multilayer films  40  is provided on the surface of the heater  12 . The multilayer film  40  has a first layer  41  made of a hydrogen storage metal or a hydrogen storage alloy and a second layer  42  made of a hydrogen storage metal or a hydrogen storage alloy, which is different from that of the first layer  41 , or ceramics. An interface between the base  39  and the first layer  41  and an interface between the first layer  41  and the second layer  42  are heterogeneous material interfaces  43 . 
     The first layer  41  is made of, for example, any one of Ni, Pd, Cu, Mn, Cr, Fe, Mg, Co, and an alloy thereof. The alloy for forming the first layer  41  is preferably an alloy made of two or more of Ni, Pd, Cu, Mn, Cr, Fe, Mg, and Co. As the alloy for forming the first layer  41 , an alloy obtained by adding an additive element to Ni, Pd, Cu, Mn, Cr, Fe, Mg, or Co may be used. 
     The second layer  42  is made of, for example, any one of Ni, Pd, Cu, Mn, Cr, Fe, Mg, Co, an alloy thereof, and SiC. The alloy for forming the second layer  42  is preferably an alloy made of two or more of Ni, Pd, Cu, Mn, Cr, Fe, Mg, and Co. As the alloy for forming the second layer  42 , an alloy obtained by adding an additive element to Ni, Pd, Cu, Mn, Cr, Fe, Mg, or Co may be used. 
     When the types of elements are expressed as “first layer  41 -second layer  42 ”, the combination of the first layer  41  and the second layer  42  is preferably Pd—Ni, Ni—Cu, Ni—Cr, Ni—Fe, Ni—Mg, or Ni—Co. When the second layer  42  is made of ceramics, the “first layer  41 -the second layer  42 ” is preferably Ni—SiC. 
     The thickness of the first layer  41  and the thickness of the second layer  42  are each preferably less than 1000 nm. When the thickness of each of the first layer  41  and the second layer  42  is 1000 nm or more, it becomes difficult for hydrogen to permeate through the multilayer film  40 . In addition, by setting the thickness of each of the first layer  41  and the second layer  42  to be less than 1000 nm, it is possible to maintain a nanostructure that does not exhibit bulk characteristics. The thickness of each of the first layer  41  and the second layer  42  is more preferably less than 500 nm. By setting the thickness of each of the first layer  41  and the second layer  42  to be less than 500 nm, it is possible to maintain a nanostructure that does not completely exhibit bulk characteristics. 
     In  FIG.  3   , the multilayer film  40  has a configuration in which the first layer  41  and the second layer  42  are alternately stacked in this order on the surface of the base  39 . Each of the first layer  41  and the second layer  42  includes five layers. The number of layers of the first layer  41  and the second layer  42  may be appropriately changed. The multilayer film  40  may have a configuration in which the second layer  42  and the first layer  41  are alternately stacked in this order on the surface of the base  39 . It is sufficient that the multilayer film  40  has one or more first layers  41  and one or more second layers  42 , and one or more heterogeneous material interfaces  43  are formed. 
     As shown in  FIG.  4   , the heterogeneous material interface  43  is permeable to hydrogen atoms.  FIG.  4    is a schematic diagram showing a state in which hydrogen atoms in a metal lattice of the first layer  41  permeate through the heterogeneous material interface  43  and move into a metal lattice of the second layer  42  when the first layer  41  and the second layer  42  each made of a hydrogen storage metal having a face-centered cubic structure are made to occlude hydrogen and then the first layer  41  and the second layer  42  are heated. A mechanism in which the heat generating element  14  generates excess heat will be described with reference to  FIG.  4   . 
     The heat generating element  14  occludes hydrogen by the base  39  and the multilayer film  40  when the hydrogen-based gas is introduced into the container  11 . Even when the introduction of the hydrogen-based gas into the inside of the container  11  is stopped, the heat generating element  14  maintains a state where hydrogen is occluded in the base  39  and the multilayer film  40 . When the heating of the heat generating element  14  is started by the heater  12 , the hydrogens occluded in the base  39  and the multilayer film  40  are discharged and quantum diffusion occurs while hopping the inside of the multilayer film  40 . It is known that hydrogen is light and undergoes quantum diffusion while hopping at a site (octahedral site or tetrahedral site) occupied by hydrogen of a certain substance A and substance B. When the heat generating element  14  is heated in a vacuum state, hydrogen permeates through the heterogeneous material interface  43  by quantum diffusion or diffuses through the heterogeneous material interface  43  by quantum diffusion to generate excess heat. 
     The heat generating element  14  is supplied with the hydrogen-based gas, is heated by the heater  12 , and is raised to a predetermined temperature to generate excess heat. The heat generating element  14  is heated to, for example, 270 to 300° C. by the heater  12 , thereby generating excess heat. The temperature of the heat generating element  14  in a state of generating excess heat is set to fall within a range of, for example, 300° C. or higher and 1500° C. or lower. When excess heat is generated, the heat generating element  14  continues to generate heat for a predetermined period even if the heater  12  is turned off. 
     An example of a method for producing the heat generating element  14  will be described. The heat generating element  14  can be produced using, for example, a sputtering method. First, the plate-shaped base  39  is formed. Next, the first layer  41  and the second layer  42  are alternately formed on the base  39  to form the multilayer film  40 . Thus, the heat generating element  14  in which the multilayer film  40  is provided on the surface of the base  39  is obtained. The base  39  is preferably formed to be thicker than the first layer  41  and the second layer  42 , and Ni is used as the material of the base  39 , for example. It is preferable that the first layer  41  and the second layer  42  are formed continuously in a vacuum state. This is because a natural oxide film is not formed between the first layer  41  and the second layer  42  and only the heterogeneous material interface  43  is formed. The production method of the heat generating element  14  is not limited to the sputtering method, and a vapor deposition method, a wet method, a thermal spraying method, an electroplating method, or the like can be used. The shape of the heat generating element  14  is a plate shape in the present embodiment, but is not limited thereto, and may be a cylindrical shape or a columnar shape. 
     An example of a heat generation method using the heat generating element  14  will be described. First, a hydrogen-based gas is introduced into the inside of the container  11  to cause the heat generating element  14  to occlude the hydrogen contained in the hydrogen-based gas. Next, the introduction of the hydrogen-based gas is stopped, the inside of the container  11  is evacuated, and the heat generating element  14  is heated to discharge the hydrogen occluded in the heat generating element  14 . In the heat generating element  14 , when hydrogen is occluded, the hydrogen permeates through the heterogeneous material interface  43  by quantum diffusion to generate heat, and when hydrogen is discharged, the hydrogen permeates through the heterogeneous material interface  43  by quantum diffusion to generate heat. Occluding and discharging of hydrogen may be repeatedly performed. A system of generating heat of the heat generating element  14  by alternately occluding and discharging hydrogen is called a batch system. 
     The method and results of an experiment for generating heat of the heat generating element  14  in a batch system will be described below. 
     As the base  39  of the heat generating element  14 , a Ni substrate made of Ni and having a thickness of 0.1 mm was used. The first layer  41  made of Cu and the second layer  42  made of Ni were alternately formed on the surface of the base  39  to obtain the multilayer film  40 . The thickness of the first layer  41  was 14 nm. The thickness of the second layer  42  was 2 nm. Each of the first layer  41  and the second layer  42  included five layers. Two sheets of the heat generating element  14  were prepared and arranged on both surfaces of a plate-shaped ceramic heater. The heat generating element  14  was placed inside a vacuum container together with the ceramic heater. Then, the introduction of the hydrogen-based gas into the inside of the vacuum container and the evacuation of the inside of the vacuum container were repeated. The hydrogen-based gas was introduced into the inside of the vacuum container at a pressure of about 50 Pa. The time for occluding hydrogen in the heat generating element  14  was set at about 64 hours. In addition, before occluding hydrogen, the inside of the vacuum container was previously baked with a heater for about 36 hours at 200° C. or higher to remove moisture or the like adhering to the surfaces of the heat generating element  14 . The input power of the heater was switched to 9 W, 18 W, and 27 W. It was confirmed that excess heat was generated at the temperature within the range of 500° C. to 1000° C. The excess heat was about 5 W at around 900° C. The excess heat per unit area in the vicinity of 900° C. was determined to be about 0.5 W/cm 2 . It was confirmed that even when the heater was turned off after the heat generating element  14  generated excess heat, heat generation continued for a predetermined period. 
     Another example of a heat generation method using the heat generating element  14  will be described. A difference is created in the partial pressure of hydrogen on both sides of the heat generating element  14 . For example, the heat generating element  14  is housed in a container, and the inside of the container is partitioned into a first chamber and a second chamber. A hydrogen-based gas is introduced into the inside of the first chamber, and the inside of the second chamber is evacuated. As a result, a hydrogen partial pressure in the first chamber increases and a hydrogen partial pressure in the second chamber decreases, resulting in a difference in the hydrogen partial pressure between both sides of the heat generating element  14 . When a difference in the hydrogen partial pressure occurs between both sides of the heat generating element  14 , hydrogen molecules contained in the hydrogen-based gas are adsorbed on one surface (referred to as a front surface) of the heat generating element  14  arranged on the high-pressure side, and the hydrogen molecules are dissociated into two hydrogen atoms. The dissociated hydrogen atoms penetrate into the inside of the heat generating element  14 . That is, hydrogen is occluded in the heat generating element  14 . The hydrogen atoms diffuse and pass through the inside of the heat generating element  14 . On the other surface (referred to as a back surface) of the heat generating element  14  arranged on the low-pressure side, the hydrogen atoms that have passed through the heat generating element  14  are recombined and discharged as hydrogen molecules. In other words, hydrogen is discharged from the heat generating element  14 . Thus, the heat generating element  14  allows hydrogen to permeate from the high-pressure side to the low-pressure side. The term “permeation” as used herein means that hydrogen is occluded in the front surface of the heat generating element and discharged from the back surface of the heat generating element. The heat generating element  14  generates heat by occluding and discharging hydrogen. By generating a difference in the hydrogen partial pressure between both sides of the heat generating element  14 , hydrogen occlusion on the front surface of the heat generating element  14  and hydrogen discharge on the back surface of the heat generating element  14  are simultaneously performed, and since the hydrogen continuously permeates the heat generating element  14 , excess heat can be efficiently generated. A system in which the heat generating element  14  is caused to generate heat by permeating hydrogen using a difference in the hydrogen partial pressure is referred to as a permeation system. In the following description, the hydrogen partial pressure may be referred to as “pressure of hydrogen”. 
     The method and results of an experiment for generating heat of the heat generating element  14  in a permeation system will be described below. 
     As the base  39  of the heat generating element  14 , a Ni substrate made of Ni and having a thickness of 0.1 mm was used. The first layer  41  made of Cu and the second layer  42  made of Ni were alternately formed on both surfaces of the base  39  to obtain the multilayer film  40 . Each of the first layer  41  and the second layer  42  included six layers. The heat generating element  14  was baked at 300° C. for 3 days before the experiment was started. The experiment was started after baking as described above. The heat generating element  14  was fixed to the tip of a pipe made of stainless steel using a VCR joint. The tip of the pipe was placed inside a quartz glass tube. A hydrogen-based gas was introduced from the proximal end of the pipe, and the inside of the quartz glass tube was evacuated. The internal space of the pipe is a first chamber, and the internal space of the quartz glass tube is a second chamber. The hydrogen partial pressure in the first chamber was adjusted to 100 kPa. The hydrogen partial pressure in the second chamber was adjusted to 1×10 −4  Pa. The heater was driven to heat the heat generating element  14  at a predetermined preset temperature. An electric furnace was used as the heater. The preset temperature was changed about every half day and increased stepwise within the range of 300° C. to 900° C. It was confirmed that excess heat was generated at the temperature within the range of 300° C. to 900° C. It was confirmed that the excess heat was about 10 W at around 800° C. The excess heat per unit area in the vicinity of 800° C. was determined to be about 5 W/cm 2 . It was confirmed that even when the heater was turned off after the heat generating element  14  generated excess heat, heat generation continued for a predetermined period. 
     As described above, the thermal energy H ex  generated by the heat generating element  14  is about 5 W in the batch system and about 10 W in the permeation system. The heat generating device  10  according to the present embodiment is configured to generate heat in the batch system. 
     The configuration of the heater  12  will be described in detail with reference to  FIG.  5   . In the present embodiment, the heater  12  is a plate-shaped ceramic heater having a built-in thermocouple. The heater  12  is not limited to a ceramic heater but may be an electric furnace or the like. The temperature sensor  30  is a thermocouple built in the heating unit  29 . In the thermocouple, the material of the element wire of the negative electrode is platinum (Pt), and the material of the element wire of the positive electrode is a platinum-rhodium alloy (PtRh) containing 13% rhodium. In the present embodiment, the heater temperature T H  is measured by a thermocouple as the temperature sensor  30 . 
     The heater  12  and the heat generating element  14  are integrated using a holder  45 . The holder  45  is made of, for example, ceramics. The holder  45  has a square shape in a plan view. The holder  45  is composed of a pair of holder half bodies  45   a  and  45   b.  The holder half body  45   a  and the holder half body  45   b  have the same configuration. Therefore, the holder half body  45   a  will be described, and description of the holder half body  45   b  will be omitted. The holder half body  45   a  has a stepped portion  46  provided on a surface in contact with the heat generating element  14 , and an opening  47  opened in the thickness direction. In  FIG.  5   , the stepped portion  46  of the holder half body  45   b  is hidden on the back side of the paper. When the pair of holder half bodies  45   a  and  45   b  are integrated with each other, the heat generating element  14  is disposed in the stepped portion  46 , and the heat generating element  14  is exposed from the opening  47 . In the present embodiment, the opening  47  has a circular shape with a diameter of 23 mm, but is not limited thereto. The heat generating element  14  housed in the holder  45  radiates radiant heat toward the reflection unit  17  from the surface corresponding to each opening  47  of the pair of holder half bodies  45   a  and  45   b.  Therefore, in the present embodiment, the area of the opening  47  is used as the sample radiation surface area A S . 
     The configuration of the conductive wire part  13  will be described in detail. The heating conductive wire part  32  includes a heater conducting wire  32   a  connected to the heating unit  29  and a conducting wire  32   b  connecting the heater conducting wire  32   a  and the connecting portion  27 . The temperature detecting conductive wire part  33  includes a thermocouple conducting wire  33   a  which is a portion of the thermocouple protruding from the heating unit  29 , and a compensation conducting wire  33   b  that connects the thermocouple conducting wire  33   a  and the connecting portion  27 . The conductive wire part  13  has two heater conducting wires  32   a,  two conducting wires  32   b,  two thermocouple conducting wires  33   a,  and two compensation conducting wires  33   b.    
     The conductive wire part  13  is a heat conduction path through which heat is conducted from the heater  12  to the container  11 . The equivalent heat conduction area A HC  of the conductive wire part  13  is obtained based on the respective cross-sectional areas of the heater conducting wire  32   a,  the conducting wire  32   b,  the thermocouple conducting wire  33   a,  and the compensation conducting wire  33   b  constituting the conductive wire part  13 . The equivalent thermal conductivity K eq  of the conductive wire part  13  is obtained based on the respective thermal conductivities of the heater conducting wire  32   a,  the conducting wire  32   b,  the thermocouple conducting wire  33   a,  and the compensation conducting wire  33   b  constituting the conductive wire part  13 . The equivalent thermal conduction length L eq  of the conductive wire part  13  is obtained based on the respective lengths of the heater conducting wire  32   a,  the conducting wire  32   b,  the thermocouple conducting wire  33   a,  and the compensation conducting wire  33   b  constituting the conductive wire part  13 . 
     The configuration of the reflection unit  17  will be described in detail with reference to  FIG.  6    to  FIG.  8   . As shown in  FIG.  6   , the reflection unit  17  includes a plurality of reflection plates  35  and a support portion  48  that supports the plurality of reflection plates  35 . The support portion  48  is formed of a material having low thermal conductivity such as SiO 2  or ceramics, and has a function as a heat insulator that reflects radiant heat from the heat generating element  14 . The support portion  48  includes a plurality of bases  49  fixed to the bottom portion  11   b  of the container  11  at predetermined intervals from each other and a plurality of support plates  50   a  to  50   c  fixed to each base  49 . In the present embodiment, the support portion  48  includes four bases  49 , one support plate  50   a  constituting an upper portion, one support plate  50   b  constituting a bottom portion, and four support plates  50   c  constituting a side portion. Each base  49  is formed in a columnar shape and extends from the bottom portion  11   b  to the upper portion  11   a  of the container  11 . Each of the support plates  50   a  to  50   c  is configured in a box shape as a whole, and is a substantially rectangular parallelepiped in the present embodiment. Each of the support plates  50   a  to  50   c  is fixed to each of the bases  49  using a screw member (not shown). The shape of each of the support plates  50   a  to  50   c  in a plan view is not particularly limited, but is a rectangle in the present embodiment. 
     Between the support plate  50   a  at the upper portion and each of the support plates  50   c  at the side portion, a gas flow portion  51  through which the hydrogen-based gas flows is provided. The gas flow portion  51  may be provided between the support plate  50   b  at the bottom portion and each of the support plates  50   c  at the side portion, or may be provided between the four support plates  50   c  at the side portion. 
       FIG.  7    shows a state in which the support plate  50   a  at the upper portion is moved upward. The heat generating element  14  and the heater  12  (not shown) are housed inside the support portion  48 . A through hole into which the conductive wire part  13  of the heater  12  is inserted is provided in the support plate  50   a  at the upper portion. A plurality of reflection plates  35  are supported on the inner surface of each of the support plates  50   a  to  50   c.    
     As shown in  FIG.  8   , each of the support plates  50   a  to  50   c  is provided with a plurality of support columns  53  and a plurality of spacers  54 . The support column  53  and the spacer  54  will be described using the support plate  50   a.  The support column  53  is inserted into a through hole provided in the reflection plate  35 . The spacer  54  is arranged between the support plate  50   a  and the reflection plate  35  and between the plurality of reflection plates  35 . Thus, the plurality of reflection plates  35  are arranged at predetermined intervals. 
     Each of the support plates  50   a  to  50   c  is fixed to each of the bases  49  such that the surfaces on which the plurality of reflection plates  35  are provided face each other (see  FIG.  6    and  FIG.  7   ). Thus, the heat generating element  14  is surrounded by the plurality of reflection plates  35 , the radiant heat radiated by the heat generating element  14  is reflected by the plurality of reflection plates  35 , and heat loss due to the radiation is suppressed. 
     As described above, when the operation of the heat generating device  10  is started, the heater  12  is turned on to raise the temperature of the heat generating element  14  to a predetermined temperature, thereby generating excess heat from the heat generating element  14 . When the operation of the heat generating device  10  is stopped, the heat generating element  14  is cooled. As a method of cooling the heat generating element  14 , for example, low-temperature water, inert gas, or the like is introduced into the inside of the container  11 . The heat generating element  14  can also be cooled by increasing the heat loss due to the convective flow of hydrogen by setting the hydrogen pressure inside the container  11  to, for example, 1 atm or more. 
     The heat conduction energy loss, the radiant energy loss, and the operation maintaining energy are calculated by using the above formula (1). 
     First, the heat conduction energy loss is estimated. The estimated conditions and results are as follows. 
     The heater conducting wire  32   a  is made of Ni, has a thermal conductivity of 40 W/mK, has a diameter of 0.5 mm, and has a length of 100 mm. The conducting wire  32   b  is made of Cu, has a thermal conductivity of 400 W/mK, has a diameter of 0.5 mm, and has a length of 50 mm. In the thermocouple conducting wire  33   a,  a material for the element wire of the negative electrode is Pt, a material for the element wire of the positive electrode is PtRh, each element wire has a thermal conductivity of 80 W/mK, the thermocouple conducting wire  33   a  has a diameter of 0.3 mm, and has a length of 90 mm. The compensation conducting wire  33   b  is made of Cu, has a thermal conductivity of 400 W/mK, has a diameter of 0.3 mm, and has a length of 60 mm. The heater temperature T H  is set to 900° C. (1173.15 K). The external environmental temperature T W  is set to 27° C. (300.15 K). When the first term on the left side of the above formula (1) is used, the heat conduction energy loss occurring in the heating conductive wire part  32  (the heater conducting wire  32   a  and the conducting wire  32   b ) is 0.88 W, and the heat conduction energy loss occurring in the temperature detecting conductive wire part  33  (the thermocouple conducting wire  33   a  and the compensation conducting wire  33   b ) is 0.39 W. Therefore, the total heat conduction energy loss in the conductive wire part  13  is estimated as 1.27 W. 
     Next, the radiant energy loss is estimated. The estimated conditions and results are as follows. 
     A diameter of the opening  47  of the holder  45  is defined as 23 mm, and an area of a surface of the heat generating element  14  corresponding to the opening  47  is defined as a sample radiation surface area A S . The sample surface temperature T S  is set to 700° C. (973.15 K). The external environmental temperature T W  is set to 27° C. (300.15 K). The emissivity ε is all set to 0.11. Using the second term on the left side of the above formula (1), the radiant energy loss is estimated as 2.43 W. This estimation is based on the case where there is no reflection plate  35 . In the present embodiment, since three sheets of reflection plate  35  are provided for each heat generating element  14 , the radiant energy loss is 0.61 W which is approximately ¼ of the estimated result in the case where the reflection plate  35  is not provided. 
     Next, the operation maintaining energy is calculated. The estimated conditions and results are as follows. 
     While the heat generating device  10  is in operation, the inside of the container  11  is evacuated by the vacuum evacuation unit  16 , and the hydrogen pressure inside the container  11 , p, is adjusted to about 10 −4  Pa. Since the operation maintaining energy is a constant pressure process, it can be calculated using the following formula (2) and the following formula (3). 
       pΔV=Δn 1 RT   (2)
 
       P m =Δn 2 RT   (3)
 
     p is the hydrogen pressure inside the container  11 . ΔV is the volume of the space inside the container  11 . Δn 1  is the number of moles of hydrogen present inside the container  11  before hydrogen occlusion by the heat generating element  14 . R is the gas constant. T is the temperature inside the container  11 . Δn 2  is the number of moles of hydrogen present inside the container  11  after hydrogen occlusion by the heat generating element  14 . First, Δn 1  is calculated using the above formula (2). Next, Δn 2  is calculated by subtracting the number of moles of hydrogen occluded in the heat generating element  14  from the calculated Δn 1 . Here, it is assumed that the number of moles of hydrogen occluded in the heat generating element  14  is about 10 −4  mol at the maximum and the hydrogen occluded in the heat generating element  14  is discharged from the heat generating element  14  in about 6 hours. Using the above formula (3), the operation maintaining energy is estimated as P m  of about 4×10 −5  W. 
     The thermal energy generated by the heat generating element  14  is H ex  of about 5 W in the batch system as described above. When there is no reflection plate  35 , the total value of the heat conduction energy loss (1.27 W), the radiant energy loss (2.43 W), and the operation maintaining energy (4×10 −5  W) is about 3.70 W. Therefore, even when the reflection plate  35  is not provided, the thermal energy generated by the heat generating element  14  becomes larger than the total value of the heat conduction energy loss, the radiant energy loss, and the operation maintaining energy, and the above formula (1) is satisfied. Thus, it is possible to suppress the heat loss and realize the heat generating device having excellent energy efficiency. Therefore, the heat generating device according to the present invention may not include the reflection unit  17  and the reflection plate  35 , but may include the container  11 , the heater  12 , the conductive wire part  13 , the heat generating element  14 , the hydrogen supply unit  15 , and the vacuum evacuation unit  16 . 
     In the heat generating device  10  according to the present embodiment, since three sheets of the reflection plate  35  are provided for each heat generating element  14 , the radiant energy loss is suppressed to approximately ¼ as compared with the case where the reflection plate  35  is not provided. Therefore, in the heat generating device  10 , the total value of the heat conduction energy loss, the radiant energy loss, and the operation maintaining energy is about 1.88 W, and the above formula (1) is sufficiently satisfied, so that the energy efficiency is further improved. 
     Second Embodiment 
     In the above first embodiment, the temperature of the heater  12  is detected by using the thermocouple (temperature sensor  30 ) built in the heater  12 . However, in the second embodiment, a radiation temperature indicator is used. In the following description, the same members as those of the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. 
     As shown in  FIG.  9   , a heat generating device  60  includes a container  61 , a heater  62 , a conductive wire part  63 , the heat generating element  14 , the hydrogen supply unit  15 , the vacuum evacuation unit  16 , and a reflection unit  64 . The heat generating device  60  is configured to generate heat in a batch system. 
     The container  61  includes an upper portion  61   a,  a bottom portion  61   b,  and a side portion  61   c.  Since the upper portion  61   a  and the bottom portion  61   b  have the same configurations as the upper portion  11   a  and the bottom portion  11   b  of the first embodiment, description thereof will be omitted. The side portion  61   c  has a window portion  65  that transmits infrared rays. The window portion  65  has a configuration in which silica glass is fitted into a through hole formed in the side portion  61   c.  The container  61  is different from the container  11  of the first embodiment in that the window portion  65  is provided in the side portion  61   c.    
     The heater  62  is constituted by the heating unit  29 . The heater  62  is different from the heater  12  (see  FIG.  2   ) of the first embodiment in that the temperature sensor  30  is not built in. 
     The conductive wire part  63  is constituted by the heating conductive wire part  32  connected to the heating unit  29 . The conductive wire part  63  is different from the conductive wire part  13  (see  FIG.  2   ) of the first embodiment in that the conductive wire part  63  does not include the temperature detecting conductive wire part  33 . 
     The reflection unit  64  includes a plurality of reflection plates  66  and a support portion  67  that supports the plurality of reflection plates  66 . The support portion  67  includes a plurality of bases  69  and a plurality of support plates  70   a  to  70   c  fixed to the plurality of bases  69 . The support plates  70   a  to  70   c  are configured in a box shape as a whole. A first measurement hole  71  is provided in the support plate  70   c  constituting a side portion of the support portion  67 . The first measurement hole  71  is provided at a position corresponding to the window portion  65  provided in the container  61  in the support plate  70   c  of the side portion. A second measurement hole  72  is provided in each of the plurality of reflection plates  66  supported by the support plate  70   c  provided with the first measurement hole  71 . Each second measurement hole  72  is provided at a position corresponding to the first measurement hole  71  in the plurality of reflection plates  66 . The support portion  67  is different from the support portion  48  of the first embodiment in that the first measurement hole  71  is provided in the support plate  70   c  and the second measurement hole  72  is provided in the reflection plate  66 . 
     The heat generating device  60  further includes a temperature sensor  74 . The temperature sensor  74  is provided outside the container  61 . The temperature sensor  74  is a radiation temperature indicator that detects the temperature of the heater  62  from the window portion  65  provided in the container  61  via the first measurement hole  71  of the support plate  70   c  and the second measurement hole  72  of the reflection plate  66 . In the second embodiment, the heater temperature T H  is measured by a radiation temperature indicator as the temperature sensor  74 . 
     In the heat generating device  60 , since the conductive wire part  63  includes only the heating conductive wire part  32  and is configured to detect the temperature of the heater  62  by using the radiation temperature indicator as the temperature sensor  74 , the heat conduction energy loss is suppressed more than that of the heat generating device  10  of the above first embodiment having the temperature detecting conductive wire part  33 . Therefore, since the heat generating device  60  is configured to satisfy the above formula (1), it is excellent in energy efficiency. 
     Third Embodiment 
     While the first and second embodiments are configured to perform heat generation by a batch system, the third embodiment is configured to perform heat generation by a permeation system. 
     In  FIG.  10   , a heat generating device  80  includes a container  81 , a heater  82 , a conductive wire part  83 , the heat generating element  14 , the hydrogen supply unit  15 , the vacuum evacuation unit  16 , and a reflection unit  84 . 
     The container  81  is composed of a first container  81   a  and a second container  81   b  provided inside the first container  81   a.  Each of the first container  81   a  and the second container  81   b  is a hollow vacuum container, and is constituted by an upper portion, a bottom portion, and a side portion, similarly to the container  11  of the first embodiment. The wall portion of the first container  81   a  is provided with the gas discharge port  26  and the connecting portion  27 . The vacuum evacuation unit  16  evacuates the inside of the first container  81   a.  The wall portion of the second container  81   b  is provided with the gas introduction port  25  and a gas recovery port  87  to be described later. In the present embodiment, three gas introduction ports  25  and four gas recovery ports  87  are provided in the wall portion of the second container  81   b.  The hydrogen supply unit  15  introduces a hydrogen-based gas into the inside of the second container  81   b.    
     In the third embodiment, a plurality of heat generating elements  14  are provided inside the second container  81   b.  In  FIG.  10   , six heat generating elements  14  are provided. The plurality of heat generating elements  14  are arranged at intervals from each other in a direction orthogonal to the front surface or the back surface. The inside of the second container  81   b  is partitioned into a plurality of first chambers  85  and a plurality of second chambers  86  by the plurality of heat generating elements  14 . The first chamber  85  and the second chamber  86  are alternately arranged in the arrangement direction of the plurality of heat generating elements  14 . The first chamber  85  is connected to the gas introduction port  25 . The second chamber  86  is connected to the gas recovery port  87 . The pressure of the first chamber  85  is increased by introducing the hydrogen-based gas from the gas introduction port  25 . The second chamber  86  is depressurized by recovering the hydrogen-based gas from the gas recovery port  87 . As a result, the hydrogen partial pressure in the first chamber  85  becomes higher than the hydrogen partial pressure in the second chamber  86 . As described above, in the third embodiment, a difference in hydrogen pressure (hydrogen partial pressure) is generated between the first chamber  85  and the second chamber  86 . 
     The heater  82  is provided inside the first container  81   a  and heats the plurality of heat generating elements  14  via the second container  81   b.  The heater  82  is, for example, an electric heating wire of an electric resistance heating type, and is wound around the outer periphery of the second container  81   b.  The heater  82  is electrically connected to a power supply (not shown) and generates heat when a voltage is applied from the power supply. The heater  82  may be an electric furnace disposed so as to cover the outer periphery of the second container  81   b.    
     The conductive wire part  83  connects the connecting portion  27  provided on the wall portion of the first container  81   a  and the heater  82 . The conductive wire part  83  is electrically connected to a control unit (not shown) and a power supply (not shown) provided outside the first container  81   a  via the connecting portion  27 . 
     The reflection unit  84  reflects the radiant heat radiated by the heat generating element  14 . The reflection unit  84  also reflects radiant heat radiated by the heater  82 . The reflection unit  84  includes a plurality of reflection plates  88  and a support portion (not shown) that supports the plurality of reflection plates  88 . The reflection unit  84  is covered with a heat insulating material  89 . 
     The heat generating device  80  further includes a temperature sensor (not shown), and detects the temperature of the heater  82  using the temperature sensor. As the temperature sensor, for example, a radiation temperature indicator is used as in the second embodiment. 
     The hydrogen supply unit  15  and the gas introduction port  25  are connected by a hydrogen-introducing pipe  90 . The hydrogen-introducing pipe  90  introduces the hydrogen-based gas from the hydrogen supply unit  15  into the first chamber  85  through the gas introducing port  25 . The hydrogen-introducing pipe  90  is provided with a pressure regulating valve  91 . The pressure regulating valve  91  regulates the flow rate of the hydrogen-based gas introduced into the first chamber  85  and the pressure in the hydrogen-introducing pipe  90 . A portion of the hydrogen-introducing pipe  90  between the first container  81   a  and the heat insulating material  89  is inserted into a heat insulating pipe  92  to be heat-insulated. 
     The hydrogen supply unit  15  and the gas recovery port  87  are connected by a hydrogen recovery pipe  94 . The hydrogen recovery pipe  94  recovers the hydrogen-based gas in the second chamber  86  from the gas recovery port  87 . The hydrogen recovery pipe  94  is provided with a circulation pump  95 . The circulation pump  95  recovers the hydrogen-based gas in the second chamber  86  into the hydrogen recovery pipe  94 , pressurizes the hydrogen-based gas to a predetermined pressure, and sends the hydrogen-based gas to a buffer tank (not shown) of the hydrogen supply unit  15 . The flow rate of the hydrogen-based gas circulated by the circulation pump  95  is 0.1 SCCM. As the circulation pump  95 , for example, a metal bellows pump is used. A portion of the hydrogen recovery pipe  94  between the first container  81   a  and the heat insulating material  89  is inserted into a heat insulating pipe  96  to be heat-insulated. 
     As shown in  FIG.  11   , due to the difference in hydrogen partial pressure generated between the first chamber  85  and the second chamber  86 , the hydrogen-based gas introduced from the hydrogen-introducing pipe  90  into the first chamber  85  permeates through the heat generating element  14 , moves to the second chamber  86 , and is recovered in the hydrogen recovery pipe  94 . Each heat generating element  14  generates excess heat respectively due to the permeation of the hydrogen-based gas. In this way, the heat generating device  80  is configured to generate heat in a permeation system. 
     The heater  82  is turned on when the operation of the heat generating device  80  is started, and is turned off after the heat generating element  14  generates excess heat. The circulation pump  95  continuously circulates the hydrogen-based gas during the operation of the heat generating device  80 . Therefore, the operation maintaining energy does not include the electric energy for driving the heater  82 , but includes the electric energy for driving the vacuum evacuation unit  16  and the electric energy for driving the circulation pump  95 . The electric energy for driving the vacuum evacuation unit  16  is 4×10 −5  W as described above. The electric energy for driving the circulation pump  95  is 1×10 −3  W at a flow rate of 0.1 SCCM. 
     In the heat generating device  80 , since the circulation pump  95  is used, the operation maintaining energy is slightly larger than that of the heat generating device  10  of the first embodiment in which the pump for circulating the hydrogen-based gas is not used. However, since the heat generating device  80  is configured to generate heat by a permeation system, a larger thermal energy H ex  (about 10 W) can be obtained than the heat generating device  10  in a batch system of the first embodiment in which the generated thermal energy H ex  is about 5 W. In the heat generating device  80 , the operation maintaining energy is increased as compared with the heat generating device  10 , but the increment of the generated thermal energy is larger than the increment of the operation maintaining energy. Therefore, since the heat generating device  80  is configured to satisfy the above formula (1), it is excellent in energy efficiency. 
     Fourth Embodiment 
     Although the hydrogen-based gas is circulated by using the circulation pump  95  in the third embodiment, in the fourth embodiment, the hydrogen-based gas is not circulated. 
     In  FIG.  12   , a heat generating device  100  includes the container  81 , the heater  82 , the conductive wire part  83 , the heat generating element  14 , the hydrogen supply unit  15 , the vacuum evacuation unit  16 , and the reflection unit  84 . The heat generating device  100  further includes a gas tank  101  that stores inert gas and a gas pipe  102  that connects the gas tank  101  and the gas recovery port  87 . The heat generating device  100  is different from the heat generating device  80  of the third embodiment in that the gas tank  101  and the gas pipe  102  are provided instead of the hydrogen-recovery pipe  94  and the circulation pump  95 . As the inert gas, for example, argon gas, nitrogen gas or the like is used. The inert gas in the gas tank  101  is introduced into the inside of the second chamber  86  through the gas pipe  102  before the operation of the heat generating device  100  is started. In this way, the gas tank  101  has a function as an inert gas introduction portion for introducing the inert gas into the inside of the second chamber  86 . 
     In the heat generating device  100 , when the inert gas is introduced into the inside of the second chamber  86 , a difference in hydrogen partial pressure is generated between the first chamber  85  and the second chamber  86 . Due to the difference in the hydrogen partial pressure generated between the first chamber  85  and the second chamber  86 , the hydrogen-based gas in the first chamber  85  permeates through the heat generating element  14 , moves to the second chamber  86 , and is sent to the gas tank  101  through the gas recovery port  87  and the gas pipe  102 . Each heat generating element  14  generates excess heat due to the permeation of the hydrogen-based gas. In this way, the heat generating device  100  is configured to generate heat in a permeation system. 
     By periodically replacing the gas tank  101 , it is possible to maintain a state in which a difference in hydrogen partial pressure is generated between the first chamber  85  and the second chamber  86 . The gas tank  101  may be provided with a hydrogen permeable membrane to remove hydrogen accumulated in the inside of the gas tank  101 . 
     Since a pump for circulating the hydrogen-based gas is not used in the heat generating device  100 , the operation maintaining energy is smaller than that of the heat generating device  80  of the third embodiment using the circulation pump  95 . Therefore, since the heat generating device  100  is configured to satisfy the above formula (1), it is excellent in energy efficiency. 
     Fifth Embodiment 
     Although the heat generating element  14  has a plate shape in each of the above-described embodiments, the heat generating element has a cylindrical shape in the fifth embodiment. 
     As shown in  FIG.  13   , a heat generating element  106  is formed in a bottomed cylindrical shape with one end opened and the other end closed. The heat generating element  106  has the same configuration as that of the heat generating element  14  of the first embodiment except that it has a bottomed cylindrical shape. The heat generating element  106  has a configuration in which a multilayer film  108  is provided on the surface of a base  107 . Since the materials of the base  107  and the multilayer film  108  are the same as those in the first embodiment, description thereof will be omitted. The base  107  is provided with an attachment tube  109 . The attachment tube  109  is formed of, for example, stainless steel. Although the heat generating element  106  is formed in a bottomed cylindrical shape in  FIG.  13   , it may be formed in a bottomed rectangular cylindrical shape. 
     An example of a method for producing the heat generating element  106  will be described. For the heat generating element  106 , the base  107  formed in a bottomed cylindrical shape is prepared, and the multilayer film  108  is formed on the outer surface of the base  107  using a wet film forming method. As a result, the bottomed cylindrical heat generating element  106  is formed. As the wet film forming method, a spin coating method, a spray coating method, a dipping method or the like is used. The multilayer film  108  may be formed by an atomic layer deposition (ALD) method, or the multilayer film  108  may be formed on the base  107  while the base  107  is rotated with the use of a sputtering apparatus including a rotation mechanism for rotating the base  107 . Note that the multilayer film  108  is not limited to being provided on the outer surface of the base  107 , and may be provided on the inner surface of the base  107  or on both surfaces of the base  107 . 
     As shown in  FIG.  14   , the heat generating device  110  includes a plurality of heat generating elements  106 . The heat generating device  110  has the same configuration as that of the heat generating element  80  of the third embodiment except that a bottomed cylindrical heat generating element  106  is used. The heat generating device  110  includes the container  81 , the heater  82 , the conductive wire part  83 , a plurality of heat generating elements  106 , the hydrogen supply unit  15 , the vacuum evacuation unit  16 , and the reflection unit  84 . 
     The plurality of heat generating elements  106  are provided inside the second container  81   b.  The attachment pipe  109  of the heat generating element  106  is connected to the gas introduction port  25  provided in the wall portion of the second container  81   b.  The first chamber  85  is formed by the inner surface of the heat generating element  106 . The second chamber  86  is formed by the inner surface of the second container  81   b  and the outer surface of the heat generating element  106 . Therefore, in the heat generating element  106 , the base  107  is disposed on the first chamber  85  side (high pressure side), and the multilayer film  108  is disposed on the second chamber  86  side (low pressure side) (see  FIG.  13   ). Due to the difference in the hydrogen partial pressure generated between the first chamber  85  and the second chamber  86 , the hydrogen-based gas introduced into the first chamber  85  from the gas introduction port  25  and the attachment pipe  109  permeates through the heat generating element  106  and moves to the second chamber  86 . Each heat generating element  106  generates excess heat due to the permeation of the hydrogen-based gas. In this way, the heat generating device  110  is configured to generate heat in a permeation system. 
     As shown in  FIG.  15   , in the heat generating device  110 , nine heat generating elements  106  are provided inside the second container  81   b.  In the present embodiment, nine gas introduction ports  25  (not shown) and one gas recovery port  87  (not shown) are provided in the wall portion of the second container  81   b.  The attachment pipe  109  of each heat generating element  106  and the hydrogen-introducing pipe  90  are connected to each other via the gas introduction port  25 , and the hydrogen-based gas is introduced into the inside (first chamber  85 ) of each heat generating element  106 . The gas recovery port  87  of the second container  81   b  is connected to the hydrogen recovery pipe  94 , and the hydrogen-based gas in the second chamber  86  is recovered. The recovered hydrogen-based gas is pressurized to a predetermined pressure by the circulation pump  95  and sent to a buffer tank (not shown) of the hydrogen supply unit  15 . The hydrogen-based gas in the hydrogen supply unit  15  is introduced again into the inside (first chamber  85 ) of each heat generating element  106  through the gas recovery port  87  and the hydrogen-introducing pipe  90 , and moves to the outside (second chamber  86 ) of each heat generating element  106 . In this way, the heat generating device  110  can circulate the hydrogen-based gas. 
     The heat generating device  110  has the same configuration as that of the heat generating device  80  of the third embodiment except that the heat generating element  106  is used. Therefore, similarly to the heat generating device  80  of the third embodiment, since the heat generating device  110  is configured to satisfy the above formula (1), it is excellent in energy efficiency. 
     As the heat generating device  110 , a heat generating element  112  formed in a columnar shape shown in  FIG.  16    may be used instead of the heat generating element  106 . The heat generating element  112  includes a base  113  formed in a columnar shape and the multilayer film  108  provided on the surface of the base  113 . The heat generating element  112  differs from the heat generating element  106  by having a solid base  113 . The base  113  improves the mechanical strength of the heat generating element  112  while allowing the hydrogen-based gas to pass therethrough. Although the heat generating element  112  is formed in a cylindrical shape in  FIG.  16   , it may be formed in a prismatic shape. 
     Sixth Embodiment 
     Although the hydrogen-based gas is circulated by using the circulation pump  95  in the fifth embodiment, in the sixth embodiment, the hydrogen-based gas is not circulated. 
     As shown in  FIG.  17   , a heat generating device  115  includes the container  81 , the heater  82 , the conductive wire part  83 , the heat generating element  106 , the hydrogen supply unit  15 , the vacuum evacuation unit  16 , the reflection unit  84 , the gas tank  101 , and the gas pipe  102 . The heat generating device  115  is different from the heat generating device  110  of the fifth embodiment in that the gas tank  101  and the gas pipe  102  are provided instead of the hydrogen-recovery pipe  94  and the circulation pump  95 . 
     In the heat generating device  115 , the hydrogen-based gas is introduced into the inside of the first chamber  85  and the inert gas is introduced into the inside of the second chamber  86 , so that a difference in hydrogen partial pressure is generated between the first chamber  85  and the second chamber  86 . Due to the difference in the hydrogen partial pressure generated between the first chamber  85  and the second chamber  86 , the hydrogen-based gas in the first chamber  85  permeates through the heat generating element  106 , moves to the second chamber  86 , and is sent to the gas tank  101  through the gas recovery port  87  and the gas pipe  102 . Each heat generating element  106  generates excess heat respectively due to the permeation of the hydrogen-based gas. In this way, the heat generating device  115  is configured to generate heat in a permeation system. 
     Since a pump for circulating the hydrogen-based gas is not used in the heat generating device  115 , the operation maintaining energy is smaller than that of the heat generating device  110  of the fifth embodiment using the circulation pump  95 . Therefore, since the heat generating device  115  is configured to satisfy the above formula (1), it is excellent in energy efficiency. 
     The present invention is not limited to the above-described embodiments, and can be appropriately modified without departing from the scope of the present invention. 
     Although the multilayer film  40  of the heat generating element  14  and the multilayer film  108  of the heat generating element  106  and the heat generating element  112  are composed of the first layer  41  and the second layer  42 , the configuration of the multilayer film is not limited thereto. 
     A first example of the multilayer film will be described below. 
     As shown in  FIG.  18   , a heat generating element  133  includes the base  39  and a multilayer film  134 . The multilayer film  134  further includes a third layer  135  in addition to the first layer  41  and the second layer  42 . Description of the base  39 , the first layer  41 , and the second layer  42  will be omitted. The third layer  135  is made of a hydrogen storage metal, a hydrogen storage alloy, or ceramics different from those of the first layer  41  and the second layer  42 . The thickness of the third layer  135  is preferably less than 1000 nm. In  FIG.  18   , the first layer  41 , the second layer  42 , and the third layer  135  are stacked on the surface of the base  39  in the order of the first layer  41 , the second layer  42 , the first layer  41 , and the third layer  135 . The first layer  41 , the second layer  42 , and the third layer  135  may be stacked on the surface of the base  39  in the order of the first layer  41 , the third layer  135 , the first layer  41 , and the second layer  42 . That is, the multilayer film  134  has a stacking structure in which the first layer  41  is provided between the second layer  42  and the third layer  135 . The multilayer film  134  may include one or more third layers  135 . An interface between the first layer  41  and the third layer  135  is a heterogeneous material interface  136 . The heterogeneous material interface  136  is permeable to hydrogen atoms in the same manner as the heterogeneous material interface  43 . 
     The third layer  135  is made of, for example, any one of Ni, Pd, Cu, Cr, Fe, Mg, Co, an alloys thereof, SiC, CaO, Y 2 O 3 , TiC, LaB 6 , SrO, and BaO. The alloy for forming the third layer  135  is preferably an alloy made of two or more of Ni, Pd, Cu, Cr, Fe, Mg, and Co. As the alloy for forming the third layer  135 , an alloy obtained by adding an additive element to Ni, Pd, Cu, Cr, Fe, Mg, or Co may be used. 
     In particular, the third layer  135  is preferably made of any one of CaO, Y 2 O 3 , TiC, LaB 6 , SrO, and BaO. In the heat generating element  133  having the third layer  135  made of any one of CaO, Y 2 O 3 , TiC, LaB 6 , SrO, and BaO, the amount of hydrogen occlusion increases, the amount of hydrogen permeating through the heterogeneous material interface  43  and the heterogeneous material interface  136  increases, and a high output of excess heat can be achieved. The thickness of the third layer  135  made of any one of CaO, Y 2 O 3 , TiC, LaB 6 , SrO, and BaO is preferably 10 nm or less. Accordingly, hydrogen atoms easily permeate through the multilayer film  134 . The third layer  135  made of any one of CaO, Y 2 O 3 , TiC, LaB 6 , SrO, and BaO may not be formed into a complete film shape and may be formed into an island shape. The first layer  41  and the third layer  135  are preferably formed continuously in a vacuum state. Accordingly, between the first layer  41  and the third layer  135 , no natural oxide film is formed and only the heterogeneous material interface  136  is formed. 
     As a combination of the first layer  41 , the second layer  42 , and the third layer  135 , it is preferably Pd—CaO—Ni, Pd—Y 2 O 3 —Ni, Pd—TiC—Ni, Pd—LaB 6 —Ni, Ni—CaO—Cu, Ni—Y 2 O 3 —Cu, Ni—TiC—Cu, Ni—LaB 6 —Cu, Ni—Co—Cu, Ni—CaO—Cr, Ni—Y 2 O 3 —Cr, Ni—TiC—Cr, Ni—LaB 6 —Cr, Ni—CaO—Fe, Ni—Y 2 O 3 —Fe, Ni—TiC—Fe, Ni—LaB 6 —Fe, Ni—Cr—Fe, Ni—CaO—Mg, Ni—Y 2 O 3 —Mg, Ni—TiC—Mg, Ni—LaB 6 —Mg, Ni—CaO—Co, Ni—Y 2 O 3 —Co, Ni—TiC—Co, Ni—LaB 6 —Co, Ni—CaO—SiC, Ni—TiC—SiC, or Ni—LaB 6 —SiC when types of elements are expressed as “first layer  41 -third layer  135 -second layer  42 ”. 
     A second example of the multilayer film will be described below. 
     As shown in  FIG.  19   , a heat generating element  143  includes the base  39  and a multilayer film  144 . The multilayer film  144  further includes a fourth layer  145  in addition to the first layer  41 , the second layer  42 , and the third layer  135 . The fourth layer  145  is made of a hydrogen storage metal, a hydrogen storage alloy, or ceramics different from those of the first layer  41 , the second layer  42 , and the third layer  135 . The thickness of the fourth layer  145  is preferably less than 1000 nm. In  FIG.  19   , the first layer  41 , the second layer  42 , the third layer  135 , and the fourth layer  145  are stacked on the surface of the base  39  in the order of the first layer  41 , the second layer  42 , the first layer  41 , the third layer  135 , the first layer  41 , and the fourth layer  145 . The first layer  41 , the second layer  42 , the third layer  135 , and the fourth layer  145  may be stacked on the surface of the base  39  in the order of the first layer  41 , the fourth layer  145 , the first layer  41 , the third layer  135 , the first layer  41 , and the second layer  42 . That is, the multilayer film  144  has a stacking structure in which the second layer  42 , the third layer  135 , and the fourth layer  145  are stacked in an arbitrary order, and the first layer  41  is provided between the second layer  42  and the third layer  135 , and the third layer  135  and the fourth layer  145 . The multilayer film  144  may include one or more fourth layers  145 . An interface between the first layer  41  and the fourth layer  145  is a heterogeneous material interface  146 . The heterogeneous material interface  146  is permeable to hydrogen atoms in the same manner as the heterogeneous material interface  43  and the heterogeneous material interface  136 . 
     The fourth layer  145  is made of, for example, any one of Ni, Pd, Cu, Cr, Fe, Mg, Co, an alloys thereof, SiC, CaO, Y 2 O 3 , TiC, LaB 6 , SrO, and BaO. The alloy for forming the fourth layer  145  is preferably an alloy made of two or more of Ni, Pd, Cu, Cr, Fe, Mg, and Co. As the alloy for forming the fourth layer  145 , an alloy obtained by adding an additive element to Ni, Pd, Cu, Cr, Fe, Mg, or Co may be used. 
     In particular, the fourth layer  145  is preferably made of any one of CaO, Y 2 O 3 , TiC, LaB 6 , SrO, and BaO. In the heat generating element  143  having the fourth layer  145  made of any one of CaO, Y 2 O 3 , TiC, LaB 6 , SrO, and BaO, the amount of hydrogen occlusion increases, the amount of hydrogen permeating through the heterogeneous material interface  43 , the heterogeneous material interface  136 , and the heterogeneous material interface  146  increases, and a high output of excess heat can be achieved. The thickness of the fourth layer  145  made of any one of CaO, Y 2 O 3 , TiC, LaB 6 , SrO, and BaO is preferably 10 nm or less. Accordingly, hydrogen atoms easily permeate through the multilayer film  144 . The fourth layer  145  made of any one of CaO, Y 2 O 3 , TiC, LaB 6 , SrO, and BaO may not be formed into a complete film shape and may be formed into an island shape. The first layer  41  and the fourth layer  145  are preferably formed continuously in a vacuum state. Accordingly, between the first layer  41  and the fourth layer  145 , no natural oxide film is formed and only the heterogeneous material interface  146  is formed. 
     As a combination of the first layer  41 , the second layer  42 , the third layer  135 , and the fourth layer  145 , it is preferably Ni—CaO—Cr—Fe, Ni—Y 2 O 3 —Cr—Fe, Ni—TiC—Cr—Fe, or Ni—LaB 6 —Cr—Fe when types of elements are expressed as “first layer  41 -fourth layer  145 -third layer  135 -second layer  42 ”. 
     In the present invention, thermal energy (referred to as usable energy) corresponding to a value obtained by subtracting each energy on the left side from the thermal energy on the right side of the above formula (1) can be used for various applications. The usable energy can be recovered, for example, by means of a heating medium. The heating medium is heated to a high temperature by being given usable energy. The high-temperature heating medium is used for, for example, home heating, a home water heater, an automobile heater, an agricultural heater, a road heater, a heat source for seawater desalination, and a geothermal power generation auxiliary heat source. As the heating medium, a gas or a liquid can be used, and it is preferable that the heating medium has excellent thermal conductivity and is chemically stable. As the gas, for example, helium gas, argon gas, hydrogen gas, nitrogen gas, water vapor, air, carbon dioxide, or the like is used. As the liquid, for example, water, molten salt (such as KNO 3  (40%)-NaNO 3  (60%)), liquid metal (such as Pb) or the like is used. As the heating medium, a mixed phase heating medium in which solid particles are dispersed in a gas or a liquid may be used. Examples of the solid particles include a metal, a metal compound, an alloy, and ceramics. As the metal, copper, nickel, titanium, cobalt or the like is used. As the metal compound, an oxide, a nitride, a silicide or the like of the above-mentioned metal is used. As the alloy, stainless steel, chromium molybdenum steel or the like is used. As the ceramics, alumina or the like is used. The usable energy is not limited to the case where it is recovered by using a heating medium, but may be recovered as electric energy by using, for example, a thermoelectric element. 
     Applications for the usable energy include heat exchangers and power units. Examples of the heat exchanger include an apparatus that performs heat exchange between a heating medium and a gas, an apparatus that performs heat exchange between a heating medium and a liquid, and an apparatus that performs heat exchange between a heating medium and a solid. The apparatus that performs heat exchange between a heating medium and a gas is used for air conditioning, preheating of air to be supplied to a combustion apparatus, generation of hot air for drying or hot air for heating, and the like. Examples of the combustion apparatus include a boiler, a rotary kiln, a heat treatment furnace for metals, a heating furnace for metal processing, a hot-air furnace, a firing furnace for ceramics, a petroleum refining tower, a dry distillation furnace, and a drying furnace. The apparatus that performs heat exchange between a heating medium and a liquid is used as a heat source of a boiler, oil heating, a chemical reaction tank, and the like. The apparatus that performs heat exchange between a heating medium and a solid is used for a double-pipe rotary heater, heating of particulate matter in a double pipe, and the like. Examples of the power unit include a gas turbine, a steam turbine, a Stirling engine, and an ORCS (Organic Rankine Cycle System). 
     The usable energy may be used to separate carbon dioxide (CO 2 ) from an exhaust gas discharged from a combustion apparatus such as a boiler. The CO 2  contained in the exhaust gas is recovered by a carbon dioxide-separating and recovering apparatus which performs a chemical absorption method or a physical adsorption method. In the chemical absorption method, CO 2  contained in the exhaust gas is absorbed in an absorption liquid such as an amine compound aqueous solution, and the absorption liquid that has absorbed the CO 2  is heated to discharge the CO 2  from the absorption liquid. The usable energy can be used to heat the absorption liquid that has absorbed the CO 2  in the chemical absorption method. In the physical adsorption method, CO 2  contained in the exhaust gas is adsorbed on an adsorbent such as active carbon or zeolite, and the adsorbent on which the CO 2  is adsorbed is heated to desorb the CO 2  from the adsorbent. The usable energy can be used to heat the adsorbent on which the CO 2  has been adsorbed in the physical adsorption method. 
     The usable energy may be used to react CO 2  with hydrogen (H 2 ) to convert it to methane (CH 4 ). CO 2  recovered from the exhaust gas by a carbon dioxide-separating and recovering apparatus or the like may be used. By bringing a raw material gas containing CO 2  and H 2  into contact with a catalyst using the catalyst for promoting the reaction between CO 2  and H 2  (methanation reaction), CH 4  is generated from the raw material gas, but the reaction does not proceed sufficiently if the temperature of the raw material gas is low. The usable energy can be used to heat a raw material gas containing CO 2  and H 2 . 
     The usable energy may be used in an IS cycle to produce hydrogen from water. In the IS cycle, water, iodine (I), and sulfur (S) are reacted to produce hydrogen iodide (HI), and the hydrogen iodide is then pyrolyzed to produce hydrogen. The usable energy can be used to pyrolyze hydrogen iodide. 
     The usable energy may be used in an ISN cycle to produce ammonia (NH 3 ) from water and nitrogen (N 2 ). In the ISN cycle, nitrogen is reacted with hydrogen iodide produced in the IS cycle to produce ammonium iodide (NH 4 I), and the ammonium iodide is then pyrolyzed to produce ammonia. The usable energy can be used to pyrolyze the ammonium iodide. 
     REFERENCE SIGNS LIST 
     
         
           10 ,  60 ,  80 ,  100 ,  110 ,  115  heat generating device 
           11 ,  61 ,  81  container 
           12 ,  62 ,  82  heater 
           13 ,  63 ,  83  conductive wire part 
           14 ,  106 ,  112 ,  133 ,  143  heat generating element 
           15  hydrogen supply unit 
           16  vacuum evacuation unit 
           17 ,  64 ,  84  reflection unit 
           30  temperature sensor 
           35 ,  66 ,  88  reflection plate 
           39 ,  107 ,  113  base 
           40 ,  108 ,  134 ,  144  multilayer film 
           41  first layer 
           42  second layer 
           43 ,  136 ,  146  heterogeneous material interface 
           65  window portion 
           74  temperature sensor 
           81   a  first container 
           81   b  second container 
           85  first chamber 
           86  second chamber 
           101  gas tank 
           135  third layer 
           145  fourth layer