Patent Publication Number: US-7905090-B2

Title: Steam engine

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a divisional application of U.S. Ser. No. 11/132,653 filed May 19, 2005 and is based on Japanese Patent Application Nos. 2004-149599, 2004-149600 and 2004-149601, each of which was filed on May 19, 2004, the disclosures of which are incorporated herein by reference. 
    
    
     FIELD OF INVESTIGATION 
     The present invention relates to a steam engine having a fluid container, in which working fluid is filled and the working fluid is vibrated in the fluid container in a self-excited vibrating manner as a result of a repeated operation of vaporization and liquefaction of the working fluid by heating and cooling the working fluid. A mechanical energy is generated at an output device of the steam engine, which is operated by the fluid vibration in the fluid container. 
     BACKGROUND OF THE INVENTION 
     An apparatus for a steam engine is known in the art, for example as disclosed in Japanese Patent Publication No. S58-057014, in which working fluid is filled in a fluid container, the working fluid is heated and vaporized by a heating device, and the working fluid is cooled down and liquefied by a cooling device, and in which energy is obtained by repeating vaporization and liquefaction of the working fluid. 
     Namely, a mechanical energy is obtained in the above steam engine at an output device, which is operated by pressure change of the working fluid in the fluid container, wherein the pressure change is generated by change of state (vaporization and liquefaction) of the working fluid. 
     The inventors of the present invention have applied for another patent relating to a steam engine in Japanese Patent Office, which is published as a publication number of 2004-84523. 
     A structure of the steam engine  500  of the prior patent application is shown in  FIG. 24 . 
     The steam engine  500  comprises a U-shaped fluid container  502  in which working fluid is filled, a heating device  504  for heating the working fluid in the fluid container  502 , a cooling device  506  for cooling down and liquefying steam generated by the heat at the heating device  504 , and an output device  508 . 
     The output device  508  comprises a cylinder  510 , a piston  512  reciprocating in the cylinder  510 , a moving shaft  514  connected at its one end with the piston  512 , and a spring  516  connected to the other end of the moving shaft  514 , wherein the piston  512  is reciprocated in the cylinder  510  by receiving fluid pressure of the working fluid in the fluid container  502 . 
     In the above steam engine  500 , a volumetric expansion of the working fluid (steam) is generated, when the working fluid in the fluid container  502  is heated and vaporized by the heating device  504 . The generated steam moves downwardly in the container  502  and is cooled down and liquefied by the cooling device  506 . Then, the volume of the working fluid in the fluid container  502  is contracted. The piston  512  and the moving shaft  514  of the output device  508  receive the pressure change generated in the fluid container  502  due to the volumetric expansion and contraction of the working fluid, and thereby the piston  512  is reciprocated. 
     When a permanent magnet is provided to the moving shaft  514  and an electromagnetic coil is arranged to face to the magnet, an electromotive force is generated in the coil in accordance with the reciprocal movement of the piston  512  and the moving shaft  514 , and an electric power is generated. 
     The above steam engine has, however, some disadvantages or problems as described below: 
     (1) At first, output energy of the steam engine would become smaller, when a cross sectional area of a cooling portion of the fluid container, at which the steam of the working fluid is liquefied, is not properly designed. 
     For example, in the case that a cross sectional area of the cooling portion of the fluid container (at which the cooling device is provided) is made extremely small, a heat transfer time for transferring the heat in a cross sectional direction, from an inner surface of the cooling portion to a center of the working fluid in the fluid container, becomes shorter. As a result, a cooling efficiency for the working fluid at the cooling portion becomes higher, so that gas-phase working fluid (the steam) is liquefied within a very short time. 
     In such a steam engine, the steam generated at the heating device moves toward the cooling device, and the steam is liquefied at once at the cooling portion. A volumetric expansion of the working fluid is suppressed to a small amount, to reduce the output energy at the steam engine. A p-v diagram of the above case is shown in  FIG. 23B , wherein a relation between the pressure and volume of the working fluid is indicated by a solid line. 
       FIG. 23A  shows a p-v diagram in the case that the vaporization and liquefaction of the working fluid is properly performed, and the desired value of  FIG. 23A  is indicated by a dotted line in  FIGS. 23B and 23C . As shown in  FIG. 23B , an area of the p-v diagram becomes smaller than that of the desired value, and the output energy is correspondingly decreased. 
     On the other hand, in the case that a cross sectional area of the cooling portion of the fluid container is made extremely large, the heat transfer time for transferring the heat from the inner surface of the cooling portion to the center of the working fluid, becomes longer. As a result, the cooling efficiency for the working fluid at the cooling portion is decreased, so that a longer timer is necessary for liquefying the gas-phase working fluid (the steam). 
     In such a case, even when the steam generated by the heating device moves to the cooling device, the gas-phase working fluid is maintained for a longer period and the fluid pressure in the fluid container remains at a high value, due to the longer period for the liquefaction. As a result, an area of the p-v diagram becomes smaller, as shown in  FIG. 23C , to likewise decrease the output energy. Furthermore, when the gas-phase working fluid remains at the heating device, the liquid-phase working fluid can be hardly vaporized. As a result, the fluid pressure by the vaporization can not be increased, and thereby the operation of the steam engine may be irregularly stopped. 
     Furthermore, in the case that a cross sectional area of a connecting passage portion of the fluid container (which is a passage portion between the heating device and the cooling device) is made small, the heat transfer time for transferring the heat in a cross sectional direction, from the inner surface of the connecting passage portion to the center of the working fluid in the fluid container, becomes shorter. As a result, the cooling efficiency for the working fluid at the connecting passage portion becomes higher. 
     In such a case, the steam generated at the heating device is liquefied at the connecting passage portion, when the steam is moved toward the cooling device. A volumetric expansion of the working fluid by the vaporization is suppressed to a small amount, to reduce the output energy at the steam engine, as shown by the p-v diagram of  FIG. 23B . 
     (2) It is necessary not only to increase input energy to the steam engine but also to increase amount of heat exchange to be transferred from the heating and cooling devices to the working fluid, in order to increase the output mechanical energy to be generated at the steam engine. It can be possible to increase the amount of the heat exchange, for example, by setting a temperature of the heating device at a higher value and by setting a temperature of the cooling device at a lower value. 
     It is, however, inevitably necessary, in the above method of increasing the temperature at the heating device and decreasing the temperature of the cooling device, to increase the input energy to the heating and cooling devices. The output mechanical energy obtained by the steam engine is thereby increased on one hand, but energy loss would be adversely become larger on the other hand, if energy transfer effectiveness from the heat energy to the mechanical energy is low. 
     The mechanical energy to be generated at the steam engine can be increased by increasing surface areas of a heating and a cooling portion of the fluid container at the respective heating and cooing devices, without changing (increasing or decreasing) preset temperatures of the heating and cooling devices. 
     In the case that cross sectional areas of the heating and cooling portions of the devices are simply enlarged to increase the surface areas, the heat transfer time in the cross sectional direction of the fluid container, from the inner surface to the center of the working fluid, becomes longer. The heating efficiency and cooling efficiency at the respective heating and cooling portions are thereby decreased, so that the energy transfer effectiveness can not be sufficiently improved. As a result, the mechanical energy can not be sufficiently generated at the steam engine. 
     (3) In the steam engine  500  shown in  FIG. 24 , the heating device  504  is so formed to surround the heating portion of the fluid container  502 , so that it heats the working fluid in the fluid container  502  from its outer periphery. It is, however, a problem in such steam engine that the heating efficiency is not sufficiently high. 
     In the heating device  504  as above, namely in which the working fluid is heated from the outer periphery of the fluid container  502 , there is a temperature gradient, as shown in  FIG. 25 . The temperature of the working fluid becomes lower, as a distance from the heating device  504  is longer. 
     Accordingly, the working fluid in the fluid container  502 . consists of “gas-phase (steam) working fluid being vaporized” and “liquid-phase working fluid heated but not vaporized”, as a result of heating operation by the heating device  504 . The liquid-phase working fluid, which moves toward the cooling device  506  together with the steam, is cooled down by the cooling device  506 , without contributing in the fluid vibration (expansion and contraction of the working fluid). Therefore, the steam engine of this kind has a larger heat loss. 
     SUMMARY OF THE INVENTION 
     The present invention is made in view of the above problems. It is an object of the present invention to provide a steam engine, in which working fluid in a fluid container is vibrated in an appropriate vibrating manner as a result of a repeated operation of vaporization and liquefaction of the working fluid, to prevent a decrease of output mechanical energy. 
     It is a further object of the present invention to provide a steam engine, in which energy transfer effectiveness is improved to increase the output mechanical energy. 
     It is a still further object of the present invention to provide a steam engine, in which heating and cooling efficiency are increased. 
     According to a feature of the present invention, a steam engine has a pipe shaped fluid container in which a working fluid is filled, a heating device and a cooling device respectively provided at a heating portion and a cooling portion of the fluid container, and an output device connected to the fluid container so that the output device is operated by the fluid pressure change in the fluid container to generate an energy (electric power), wherein the working fluid is vaporized and liquefied by the heating and cooling device to generate a fluid vibration by the volumetric change of the working fluid. In such a steam engine, an inner radius “r 1 ” of the cooling portion is made to be almost equal to a depth “δ 1 ” of thermal penetration (at a low pressure), which is calculated by the following formula (1); 
     
       
         
           
             
               
                 
                   
                     δ 
                     1 
                   
                   = 
                   
                     
                       
                         2 
                         ⁢ 
                         
                           a 
                           1 
                         
                       
                       ω 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     wherein, “a 1 ” is a heat diffusivity of the working fluid at its low pressure, and 
     “ω” is an angular frequency of the movement of the working fluid in the fluid container, and 
     wherein the heat diffusivity “a 1 ” is selected from those values corresponding to a pressure variable range of the working fluid, which is a range of the fluid pressure from the lower limit to a fluid pressure higher than the lower limit by 25%. 
     According to another feature of the present invention, the fluid container further comprises a connecting portion for connecting the heating portion with the cooling portion, wherein an inner radius “r 2 ” of the connecting portion is made to satisfy the following formulas (2) and (3); 
     
       
         
           
             
               
                 
                   
                     
                       
                         ( 
                         
                           r 
                           2 
                         
                         ) 
                       
                       2 
                     
                     
                       2 
                       · 
                       
                         a 
                         2 
                       
                     
                   
                   = 
                   τ 
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
             
               
                 
                   
                     ω 
                     · 
                     τ 
                   
                   ≥ 
                   10 
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     wherein, “a 2 ” is a heat diffusivity of the working fluid at its high pressure, and 
     “ω” is an angular frequency of the movement of the working fluid in the fluid container. 
     According to a further feature of the present invention, in a steam engine having the pipe shaped fluid container, the heating and cooling devices respectively provided at the heating and cooling portions of the fluid container, and the output device connected to the fluid container, each of the heating portion and the cooling portion comprises multiple small pipe portions. 
     According to a still further feature of the present invention, in a steam engine having the pipe shaped fluid container, the heating and cooling devices respectively provided at the heating and cooling portions of the fluid container, and the output device connected to the fluid container, the heating device is arranged to be vertically higher than the cooling device, a gas is filled in the fluid container at the heating portion so that the inner space of the heating portion is not filled with the liquid-phase working fluid, and a working fluid supply means is provided at the heating portion to supply the liquid-phase working fluid to the heating portion. 
     The working fluid supply means comprises multiple narrow grooves and/or multiple micro grooves formed at an inner surface of the heating portion. The working fluid supply means can be alternatively formed by a water-attracting surface formed at the inner surface of the heating surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
         FIG. 1  is a schematic view showing a steam engine according to a first embodiment of the present invention; 
         FIG. 2  is a schematic view showing a principle of operation of the steam engine; 
         FIG. 3  is a schematic cross sectional view showing a cooling device of the first embodiment; 
         FIG. 4  is a schematic cross sectional view showing a heating device of the first embodiment; 
         FIG. 5  is a graph showing a relation between energy loss and a parameter “ωτ”; 
         FIG. 6  is a schematic view showing a steam engine according to a second embodiment of the present invention; 
         FIG. 7  is a schematic cross sectional view showing a heating and a cooling devices of the second embodiment; 
         FIG. 8  is a perspective view showing a heating device of the second embodiment; 
         FIG. 9  is a graph showing a temperature change and a cross sectional view of the heating device; 
         FIG. 10  is a schematic cross sectional view showing a heating and a cooling devices of a third embodiment; 
         FIGS. 11 to 14  are schematic cross sectional views, respectively showing a heating and a cooling devices of modifications of the third embodiment; 
         FIG. 15  is a schematic view showing a steam engine according to a fourth embodiment of the present invention; 
         FIGS. 16A and 16B  are perspective views showing a heating device of the fourth embodiment shown in  FIG. 15 ; 
         FIGS. 17 and 18  are perspective views showing a heating device according to a modification of the fourth embodiment; 
         FIG. 19A  is a schematic view showing a steam engine according to a fifth embodiment of the present invention; 
         FIG. 19B  is a perspective view showing a heating device according to the fifth embodiment shown in  FIG. 19A ; 
         FIGS. 20A and 20B  are plan views showing a part of the heating device of the fifth embodiment 
         FIG. 21  is a perspective view showing a heating device according to a modification of the fifth embodiment; 
         FIG. 22  is a perspective view showing a part of steam engine according to a sixth embodiment of the present invention; 
         FIGS. 23A ,  23 B and  23 C are p-v diagrams showing a relation between a fluid pressure and a volume of working fluid; 
         FIG. 24  is a schematic view showing a steam engine according to a related art; and 
         FIG. 25  is an enlarged view showing a heating device of FIG.  24 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     A first embodiment of the present invention will now be explained with reference to the drawings. 
     In the first embodiment shown in  FIG. 1 , a steam engine  110  is applied to a linear motor, in which a moving member  102  of an output device (an electric power generator)  101  is vibrated. An electric power device comprises the steam engine  110  and the electric power generator  101 . 
     The electric power generator  101  is a linear vibration generator, in which a permanent magnet (not shown) is fixed to the moving member  102  and electromotive force is generated by vibrating (oscillating) the moving member  102 . 
     As shown in  FIG. 1 , the steam engine  110  comprises a fluid container  111  in which working fluid  120  is filled with a predetermined pressure, a heating device  112  for heating the working fluid  120  in the fluid container  111 , and a cooling device  113  for cooling down steam generated at the heating device  112 . 
     The heating device  112  and the cooling device  113  are arranged to be separated from each other, so that the heating and cooling devices are not directly contacted with each other. 
     In the case that the steam engine  110  is used for a water-cooling type internal combustion engine, the heating device  112  can be designed as a heating device, which heats the working fluid  120  by use of exhaust gas emitted from the internal combustion engine. And the cooling device  113  can be designed as a cooling device, which cools down the working fluid  120  by use of engine cooling water. 
     The fluid container  111  is formed into a U-shaped pipe having a bottom pipe portion  111   a  and a pair of (first and second) vertically extending straight pipe portions  111   b  and  111   c  extending from both ends of the bottom pipe portion  111   a.    
     The first straight pipe portion  111   b  comprises a heating portion  131  at which the heating device  112  is provided, a cooling portion  133  at which the cooling device  113  is provided, and a connecting portion  135  for connecting the above heating and cooling portions  131  and  133  with each other. 
     The heating and cooling portions  131  and  133  of the fluid container  111  are made of such metal having a high heat conductivity, whereas the other portion of the fluid container  111  is preferably made of such material having a high heat insulating characteristic. The fluid container  111  is further made of such material, which has a high anti-corrosion characteristic with respect to the working fluid filled in the fluid container  111 . 
     In the embodiment, water is used as the working fluid  120 , and the heating and cooling portions  131  and  133  of the fluid container  111  are made of copper or aluminum, whereas the other portion is made of stainless steel. 
     As described above, the fluid container  111  is made of the stainless steel and the copper (or the aluminum) and formed into the U-shaped pipe, wherein the bottom pipe portion  111   a  is arranged at a lower most position and two straight pipe portions  111   b  and  111   c  are vertically and upwardly extending from the bottom pipe portion  111   a.    
     The heating portion  131  of the fluid container  111  is formed at a position vertically higher than that of the cooling portion  133 , and a top end of the first straight pipe portion is closed. 
     The heating device  112  is provided to the first pipe portion to surround the heating portion  131 , whereas the cooling device  113  is provided to the first pipe portion to surround the cooling portion  133 . 
     A piston  114  is provided at a top end of the second pipe portion  111   c , at which the piston  114  is movably held in a cylinder  115  to move up and down in accordance with the fluid pressure. 
     The piston  114  is connected to the moving shaft  102   a  of the moving member  102  in the output device  101 . A spring  103  is provided in the output device  101  between the moving member  102  and an end opposite to the moving member  102 , so that it downwardly urges the piston  114  by its spring force. 
     When the heating and cooling devices  112  and  113  of the steam engine  110  start its operation, as shown in  FIG. 2 , the liquid-phase working fluid in the fluid container  111  is at first heated at the heating device  112  and vaporized (isothermal expansion). The vaporized working fluid (steam) is further expanded (adiabatic expansion), to push down the liquid-phase working fluid in the first pipe portion  111   b . The liquid-phase working fluid  120  is moved in the fluid container  111  from the first pipe portion  111   b  toward the second pipe portion  111   c , to move up the piston  114 . 
     A liquid surface (between the liquid-phase and gas-phase working fluid) of the working fluid in the first pipe portion  111   b  is pushed down to the cooling portion  133  of the cooling device  113 . When the steam enters into the cooling portion  133 , the steam is cooled down and liquefied by the cooling device  113 . The pressure for downwardly pushing the liquid-phase working fluid in the first pipe portion  111   b  disappears and thereby the liquid surface is moved up in the first pipe portion  111   b  (in a process from the isothermal compression to the adiabatic compression). The piston  114  of the power generator  101  is correspondingly moved down. 
     The above operation of the expansion and contraction of the working fluid continues until the stop of the heating and cooling devices  112  and  113 , during which the working fluid  120  in the fluid container  111  is periodically vibrated (in a self-excited vibrating manner). As above, the pressure change of the working fluid  120  is generated in the steam engine  110 , and the pressure change is converted into the mechanical energy to move up and down the piston  114 . 
     In the above steam engine  110 , the high temperature and high pressure working fluid (the steam) is not directly brought into contact with the piston  114 . The steam engine  110  has therefore a high durability. 
     The cooling portion  133  of the fluid container  111  is so designed that an inner radius “r 1 ” of the cooling portion  133  is made equal to a depth “δ 1 ” of thermal penetration (at a low pressure), which is calculated by the following formula (1): 
     
       
         
           
             
               
                 
                   
                     δ 
                     1 
                   
                   = 
                   
                     
                       
                         2 
                         ⁢ 
                         
                           a 
                           1 
                         
                       
                       ω 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
       FIG. 3  shows an enlarged cross sectional view of the cooling portion  133  of the fluid container  111 , wherein “φd” is an inner diameter of the cooling portion  133 , and “r 1 ” is the inner radius thereof. 
     In the above formula (1), “a 1 ” is a heat diffusivity [m2/sec.] of the working fluid  120  at the low pressure, and “ω” is an angular frequency [rad/sec.] representing a characteristic of the working fluid  120  in the fluid container  111  (i.e. representing a characteristic of a reciprocating movement of the piston  114 ). 
     A heat diffusivity of the working fluid, in which the fluid pressure of the working fluid  120  in the fluid container  111  is at its lower limit, is used as the heat diffusivity “a 1 ”. The inside fluid pressure of the fluid container  111  varies depending on the change of state (vaporization and liquefaction) of the working fluid. Namely, the heat diffusivity “a 1 ” is a value, when the inside fluid pressure is at the smallest value in a pressure variable range (a pressure range from the maximum to the minimum value of the fluid pressure of the working fluid  120 ). And the depth “δ 1 ” of thermal penetration (at a low pressure) is defined as a value, which is calculated from the formula (1), wherein the above heat diffusivity “a 1 ” is used. 
     The depth “δ 1 ” of thermal penetration is one of parameters for representing a heat transferring condition in the working fluid, which is vibrated in the fluid container at the angular frequency of “ω”. An amount of heat exchange at the cooling portion  133  between the working fluid  120  and the cooling device  113  can be controlled at a predetermined range, when the inner radius “r 1 ” of the fluid container  111  is designed to be equal to the depth “δ 1 ” of thermal penetration (at the low pressure). 
     According to the steam engine  110  of the present invention, the cooling efficiency at the cooling portion  133  is prevented from becoming extremely high or low, and thereby the gas-phase working fluid (the steam) can be liquefied at a proper timing. 
     In particular, since the heat diffusivity of the working fluid  120 , in which the fluid pressure of the working fluid  120  in the fluid container  111  is at its lower limit, is used as the heat diffusivity “a 1 ” in the steam engine  110  of the present embodiment, the cooling efficiency becomes maximum at such a timing at which the inside fluid pressure of the fluid container  111  (the pressure of the working fluid  120 ) becomes at its lower limit. Namely, the gas-phase working fluid  120  can be liquefied most efficiently when the volume of the working fluid  120  becomes at its maximum value, so that the expansion energy of the working fluid can be utilized without energy loss. 
     As described above, the gas-phase working fluid (the steam) can be liquefied at a proper timing, according to the steam engine  110  of the present embodiment. The working fluid  120  can be properly vibrated, to prevent the decrease of the output energy at the output device  101  generated by the reciprocal movement of the piston  114 . And furthermore, since the liquefaction of the gas-phase working fluid  120  is not extremely delayed, the steam engine  110  is prevented from its irregular shut-down due to the stop of the fluid vibration in the fluid container  111 . 
     According to the above embodiment, an inner radius “r 2 ” of the connecting portion  135  of the fluid container  111  is further so designed that the following formulas (2) and (3) are satisfied: 
     
       
         
           
             
               
                 
                   
                     
                       
                         ( 
                         
                           r 
                           2 
                         
                         ) 
                       
                       2 
                     
                     
                       2 
                       · 
                       
                         a 
                         2 
                       
                     
                   
                   = 
                   τ 
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
             
               
                 
                   
                     ω 
                     · 
                     τ 
                   
                   ≥ 
                   10 
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
       FIG. 4  shows an enlarged cross sectional view of the heating portion  131  and the connecting portion  135  of the fluid container  111 , wherein “r 2 ” is an inner radius of the connecting portion  135 . 
     In the above formula (2), “a 2 ” is a heat diffusivity of the working fluid at high pressure, wherein the high pressure means an upper limit of the fluid pressure in the pressure variable range. Namely, the heat diffusivity “a 2 ” (at the high pressure) is a value of the heat diffusivity of the working fluid, when the fluid pressure in the fluid container is at its maximum value. 
       FIG. 5  shows a relation between a left part “ωτ” of the formula (3) and a ratio of thermal loss, which would occur by a heat transfer from the working fluid  120  to the connecting portion  135 . As seen from  FIG. 5 , the ratio of the thermal loss is decreased as the value of “ωτ” is increased. 
     In  FIG. 5 , the ratio of the thermal loss is about 16%, when the value of “ωτ” is “10”. The thermal loss at the connecting portion  135  of the steam engine  110  can be surely suppressed to a value smaller than 20%, because the inner radius “r 2 ” of the connecting portion  135  is designed to meet the formulas (2) and (3), wherein “ωτ” is larger than “10”. 
     As a result that the ratio of the thermal loss at the connecting portion  135  is made to be smaller than 20%, the gas-phase working fluid (the steam)  120  is prevented from being liquefied at the connecting portion  135 . The steam of the working fluid  120  can be liquefied at the cooling portion  133 , so that a sufficient amount of the volumetric expansion of the working fluid can be obtained in the fluid container  111 . 
     The inside fluid pressure of the working fluid  120  in the fluid container  111  can be sufficiently increased to a high value, to effectively operate the piston and thereby to prevent the decrease of the output energy generated at the output device  101 . 
     As shown in  FIG. 4 , an inner radius of the heating portion  131  is designed to be equal to the inner radius “r 2 ” of the connecting portion  135 . Namely, the inner surface of the heating portion  131  is smoothly connected, without any step portion, to the inner surface of the connecting portion  135 , so that the movement of the working fluid  120  between the heating portion  131  and the connecting portion  135  can be smoothly done. 
     Any energy loss of the working fluid, which could be generated when the working fluid is moved from the heating portion  131  to the connecting portion  135  in case that the step portion is formed therebetween, can be prevented. The possible decrease of output energy at the output device  101  can be accordingly prevented. 
     As shown in  FIG. 3  or  FIG. 1 , the inner radius of the heating portion  131 , as well as the inner radius “r 1 ” of the cooling portion  133  is designed to be equal to the inner radius “r 2 ” of the connecting portion  135 . Namely, the inner surfaces of the heating and cooling portions  131  and  133  and the inner surface of the connecting portion  135  are smoothly connected to each other, so that the working fluid  120  can be smoothly moved in the fluid container  111 . 
     The inner radius of the heating and/or cooling portions  131  and  133 , however, is not necessarily designed to be exactly equal to that of the connecting portion  135 . The smooth movement of the working fluid  120  in the fluid container  111  can be obtained, when the inner radius of heating and/or cooling portions  131  and  133  is designed to be close to (almost equal to) the inner radius of the connecting portion  135 . 
     The present invention shall not be limited to the above described embodiment, but any modifications can be possible within the meaning of the present invention. 
     In the above embodiment, for example, the heat diffusivity “a 1 ” is defined as the value, when the inside fluid pressure is at the smallest value (the lower limit) in the pressure variable range. When a pressure range from the lower limit of the pressure variable range to a value, which is higher than the lower limit by 25% of the whole pressure variable range, is defined as a low pressure range, the heat diffusivity “a 1 ” can be selected from any one of the heat diffusivities in the low pressure range, so that the gas-phase working fluid can be vaporized at proper timings. 
     Accordingly, in the fluid container  111  in which the inner radius “r 1 ” of the cooling portion  133  is designed to be equal or almost equal to the depth “δ 1 ” of thermal penetration (at the low pressure range) and the depth “δ 1 ” is calculated from the formula (1) with the heat diffusivity “a 1 ” (at the low pressure range), the amount of heat exchange at the cooling portion  133  between the working fluid  120  and the cooling device  113  can be controlled at a predetermined range. 
     According to the steam engine  110  having the above fluid container  111 , the gas-phase working fluid (the steam)  120  can be liquefied at a proper timing, and thereby the decrease of the output energy at the output device  101  can be prevented. 
     In the above embodiment, the inner radius of the connecting portion  135  is so designed that the value of “ωτ” is set to be more than “10”. In the case that the thermal loss is required to be further decreased, the requirement can be achieved by making the value of “ωτ” at a further higher value. 
     For example, as shown in  FIG. 5 , if the ratio of the thermal loss is required to be lower than 10%, the inner radius “r 2 ” of the connecting portion  135  is to be so designed that the value of “ωτ” is set to be more than “20”. If the ratio of the thermal loss is required to be lower than 5%, the inner radius “r 2 ” of the connecting portion  135  is to be so designed that the value of “ωτ” is set to be more than “30”. And furthermore, if the ratio of the thermal loss is required to be lower than 2%, the inner radius “r 2 ” of the connecting portion  135  is to be so designed that the value of “ωτ” is set to be more than “100”. 
     The heating device  112  should not be limited to such a device in which the exhaust gas from the engine is used as the heating source. An electric heating device or a heating device for using gas combustion can be used as the heating device  112 . 
     Second Embodiment 
     A second embodiment of the present invention is explained with reference to  FIGS. 6 to 9 , wherein the same reference numerals are used to designate the same or similar portions of the first embodiment. 
     In  FIG. 6 , a heating portion  131 , a connecting portion  135  and a cooling portion  133  of a first straight pipe portion  111   b  are formed from multiple small pipe portions  215 , and a lower part of the first straight pipe portion  111   b  is formed from a collecting pipe portion  216 . Each of the lower ends of the small pipe portions  215  is communicated with the collecting pipe portion  216 , whereas each of the upper ends of the small pipe portions  215  is closed. 
     A heating device  112  and a cooling device  113  are respectively formed to surround the heating portion  131  and the cooling portion  133  of the multiple small pipe portions  215 . 
       FIG. 7  schematically shows an enlarged cross sectional view of the heating and cooling devices  112  and  113 , wherein liquid surfaces of working fluid  120  in the respective small pipe portions  215  are pushed down. Arrows in the respective small pipe portions  215  (in  FIG. 7 ) show directions of pressure of gas-phase working fluid for pushing down the liquid-phase working fluid  120 . 
     When the liquid surface of the liquid-phase working fluid  120  is pushed down, as shown in  FIG. 7 , the liquid-phase working fluid is moved from the first straight pipe portion  111   b  toward the second straight pipe portion  111   c , to move a piston  114  upwardly. 
     When the liquid surface is moved down to the cooling portion  133 , and the steam enters into a pipe portion surrounded by the cooling portion  133 , the steam is cooled down and liquefied by the cooling device  113 . The pressure for downwardly pushing the liquid-phase working fluid in the first pipe portion  111   b  disappears and thereby the liquid surface is moved up in the first pipe portion  111   b  (in a process from the isothermal compression to the adiabatic compression). The piston  114  of a power generator (the output device)  101  is correspondingly moved down. 
     Since the cooling and heating portions  112  and  113  are formed from the multiple small pipe potions  215 , surface areas of those portions to be contacted with the working fluid  120  are increased; surface areas for the heat exchange between the heating/cooling devices  112 / 113  and the working fluid  120  are increased. The amount of heat exchange is increased and thereby energy transfer effectiveness is increased. 
     Accordingly, the amount of the heat exchange can be increased, without changing the preset temperatures for the heating and cooling device  112  and  113  (namely without increasing the temperature for the heating device  112  and decreasing the temperature for the cooling device  113 ). 
     The output energy from the output device  101  is thus increased as a result of improving the energy transfer effectiveness. 
     When compared the present embodiment with such a case of a single pipe portion, in which a surface area for the heat exchange is enlarged so that the surface area becomes equal to that of the present embodiment, the solid content of the fluid container  111  of the present invention (having multiple small pipe portions) can be made smaller than that of the single pipe portion. 
     According to the second embodiment, therefore, the output energy can be increased by increasing the heat exchange efficiency, and at the same time the steam engine  110  can be made in a small size. 
     In the second embodiment, the exhaust gas of high temperature emitted from the engine is used as heating source (heating fluid) for the heating device  112 , wherein the exhaust gas is brought into contact with the heating portion  131  of the fluid container  111  to heat the working fluid  120  in the fluid container  111 . 
       FIG. 8  shows a perspective view of an inside structure of the heating device  112  and a flow direction of the heating source (exhaust gas). 
     The heating device  112  comprises a box-shaped casing (not shown) having an inlet and an outlet ports (not shown). The heating device  112  further comprises multiple fins  218  within the casing, wherein multiple through-holes are formed in the fins  218  so that the small pipe portions  215  are inserted through the through-holes. The heating gas (the exhaust gas) flows into the casing through the inlet port and flows through the inside of the casing in a direction indicated by an arrow in  FIG. 8 . 
     When the exhaust gas flows in the casing from an upstream side (the inlet port side) toward a downstream side (the outlet port side), the temperature of the exhaust gas is decreased from the upstream to the downstream side, because the heat of the exhaust gas is absorbed by the working fluid in the small pipe portions  215 . 
       FIG. 9  shows, in its upper portion, a graph showing a temperature change of the exhaust gas with respect to a flow direction (from the upstream to the downstream), and in its lower portion, an enlarged cross sectional view of the heating device  112 . In  FIG. 9 , the multiple small pipe portions  215  are shown as such having the same surface areas to each other. 
     In case of the heating device  112  shown in  FIG. 9 , the amount of heat to be absorbed at the small pipe portions  215  of the upstream side differs from that to be absorbed at the small pipe portions  215  at the downstream side. The pressures to be generated in the respective small pipe portions are different and thereby timings of the vaporization in the respective pipe portions are likewise different from each other. In other words, the timings of the fluid pressure increase in the respective pipe portions  215  are different from each other. 
     When the vaporization timings are different from each other, as in the above heating device of  FIG. 9 , energy for fluid movement of the working fluid  120  in the small pipe portions  215  having a higher fluid pressure is consumed for decreasing a volume of the gas-phase working fluid in the other small pipe portions  215  having a lower fluid pressure. The energy generated by the vaporization of the working fluid is thereby consumed among the small pipe portions  215  having different inside fluid pressures. The fluid movement may not occur in the bottom pipe portion  111   a  and the second straight pipe portion  111   c , and the fluid pressure change in the heating device  112  can not be properly transferred to the piston  114 . 
     According to the embodiment of the present invention, as shown in  FIG. 8 , a diameter “L 2 ” of the small pipe portions  215  at the downstream side of the flow of the exhaust gas is made larger than a diameter “L 1 ” of the small pipe portions  215  at the upstream side (L 1 &lt;L 2 ), so that surface areas of the downstream pipe portions become larger than that of the upstream pipe portions. The surface areas of the small pipe portions are gradually increased, as the pipe portions are separated from the upstream pipe portions in the direction of the exhaust gas flow, so that the heat collecting performance from the exhaust gas is increased, as the small pipe portions are separated from the upstream pipe portions. 
       FIG. 9  shows the graph and the cross sectional view of the heating device  112 , wherein heat amounts Q 1  to Q 5  which can be collected at the respective (five different) small pipe portions  215  are indicated by formulas. 
     In the formulas shown in  FIG. 9 , “h” is a heat transfer coefficient [W/m2×K] and “TW” is a temperature “K” of the small pipe portions  215  before being heated. “T 1 ” to “T 5 ” are temperatures of the exhaust gas having passed by the respective small pipe portions  215  from the upstream side to the downstream side. “A 1 ” to “A 5 ” are surface areas of the heating portions of the respective small pipe portions  215 . 
     It is necessary to make “Q 1 ” to “Q 5 ” equal to each other, in order to make the heat amounts to be collected from the exhaust gas at the respective small pipe portions almost equal to each other. It is clear that the heat transfer coefficients “h” and the temperatures “TW” of the small pipe portions  215  before being heated are almost equal to each other among those five small pipe portions. And it is also clear that there is a relation among the temperatures “T 1 ” to “T 5 ” of the exhausted gas; T 1 &gt;T 2 &gt;T 3 &gt;T 4 &gt;T 5 . 
     It is, therefore, possible to make “Q 1 ” to “Q 5 ” almost equal to each other, by making the surface areas of the respective small pipe portions to meet such a relation as A 1 &lt;A 2 &lt;A 3 &lt;A 4 &lt;A 5 . 
     According to the embodiment of the present invention, the small pipe portions  215  of the fluid container  111  are so formed that the surface areas of those small pipe portions are gradually increased in the direction from the upstream to the downstream side of the exhaust gas flow. 
     In the above fluid container  111 , the heat collecting performances at the respective small pipe portions  215  are increased from the upstream to the downstream side. As a result, even in the case that the temperature of the exhaust gas is decreased from the upstream to the downstream side, a difference among the heat amounts to be collected at the respective pipe portions  215  can be reduced to a small amount, and a disbalance of the fluid inside pressures among the respective small pipe portions  215  can be minimized. 
     As above, the fluid container  111  of the steam engine  110  having multiple small pipe portions  215  prevents that the energy is wastefully consumed among the other small pipe portions  215 , by reducing the difference of the fluid pressure among the small pipe portions to the small amount. The fluid pressure of the working fluid  120  can be properly applied to the piston  114 , and the mechanical energy can be properly obtained at the output device  101 . 
     Third Embodiment 
     The steam engine  110  according to a third embodiment, in which a communication portion  243  is provided to communicate the small pipe portions  215  with one another, is explained with reference to  FIG. 10 . 
     The steam engine  110  differs from the second embodiment ( FIGS. 6 to 8 ) in a structure of a top end portion of the first straight pipe portion  111   b.    
     A cross sectional view of the top end portion of the first straight pipe portion  111   b , the heating device  112 , and the cooling device  113  is shown in  FIG. 10 , wherein the liquid-phase working fluid  120  is pushed down by the fluid pressure of the steam in the fluid container  111 . 
     As shown in  FIG. 10 , the communication portion  243  is formed at the top end of the fluid container  111  to communicat the small pipe portions  215  (at upper ends of the heating portions  131 ) with one another, so that an inside space of the communication portion  243  is communicated with all of the inside spaces of the small pipe portions  215 . 
     Since the working fluid (gas-phase)  120  can be moved among the small pipe portions  215 , the inside fluid pressure of the respective small pipe portions can be made to equal or substantially equal to each other. 
     The gas-phase working fluid can move faster than the liquid-phase working fluid, and most of the high pressure gas-phase working fluid is generated at the upper portions of the small pipe portions  215  (at the heating portions  131  of the fluid container  111 ). The high pressure gas-phase working fluid can be, therefore, moved among the small pipe portions  215  through the communication portion  243 . 
     In the above structure, the pressure difference among the small pipe portions  215  can be immediately eliminated through the communication portion  243 , even when evaporation timing (the timing of the pressure increase) in each of the small pipe portions  215  is different from others. 
     Modifications of the Second &amp; Third Embodiments 
     Various kinds of modifications of the above embodiments can be possible. 
     In a steam engine shown in  FIG. 11 , a length of the heating portion  131  of the small pipe portions  215  is made longer, as a distance of the small pipe portion  215  from the upstream side of the heating device  112  becomes longer. The surface area of the heating portion  131  is increased from the upstream to the downstream side of the heating device  112 . 
     The communication portion  243  is not necessarily provided at the top ends of the small pipe portions  215 , but can be provided at any other portions of the heating portions  131 , as shown in  FIG. 12 . 
     Furthermore, the communication portion  243  is not necessarily provided at the same height of the heating portions  131 , but can be provided at different heights in the small pipe portions  215 , as shown in  FIG. 13 . 
     Furthermore, the communication portion  243  is not necessarily provided to communicate all of the small pipe portions  215  with one another, but can be provided to communicate one group of the small pipe portions with one another and to communicate the other group of the small pipe portions with one another, independently from the first group of the small pipe portions, as shown in  FIG. 14 . 
     In  FIG. 14 , a first communication portion  245  communicates the second and fourth small pipe portions with each other, whereas a second communication portion  246  communicates the first, the third and fifth small pipe portions with one another. 
     According to the experiments by the present inventors, it is confirmed that an average fluid pressure in the above first group ( 245 ) of the small pipe portions is almost equal to an average fluid pressure in the second group ( 246 ) of the small pipe portions. 
     The heating device  112  is not limited to the above described heating device, to which the heating gas from the outside heating source (such as the internal combustion engine) is supplied, but can be comprised of an electric heater or a gas burner. In such a modified steam engine, the respective small pipe portions of the heating device can be independently heated to reduce variation of heat amount to be supplied to the respective small pipe portions. 
     The heating device  112  and the cooling device  113  can be arranged to be close to each other, without the connecting portions. The number of the small pipe portions is not limited to five. 
     Fourth Embodiment 
     A fourth embodiment of the present invention is explained with reference to  FIGS. 15 ,  16 A and  16 B. 
     The first straight pipe portion  111   b  at the heating device  112  will be explained with reference to  FIGS. 15 ,  16 A and  16 B, wherein  FIGS. 16A and 16B  show an inside structure of the heating portion ( 112 ), which is arranged at the top end  318  of the first straight pipe portion  111   b.    
     Multiple narrow grooves  340  are formed at an inner surface of the heating portion ( 112 ) of the pipe portion  111   b . The narrow grooves  340  longitudinally extend toward the cooling portion ( 113 ) of the pipe portion  111   b . The narrow grooves  340  are so formed to cause capillary phenomenon by the liquid-phase working fluid in the pipe portion  111   b . A water-repellant surface  342  is formed at the inner surface of the pipe portion  111   b  at such a position between the heating portion ( 112 ) and the cooling portion ( 113 ) of the pipe portion  111   b  (at a lower end of the narrow grooves  340 ). 
     In the steam engine  110  of the fourth embodiment, a gas is filled in the first straight pipe portion  111   b , so that the inside space of the heating portion ( 112 ) is not filled with the liquid-phase working fluid. 
     As in the same manner to the first embodiment, the piston  114  is movably held in the cylinder  115 . The piston  114  is upwardly moved to its top dead center when the fluid pressure in the fluid container  111  is increased, whereas the piston  114  is downwardly moved to its bottom dead center when the fluid pressure is decreased. 
     The liquid surface of the liquid-phase working fluid in the first straight pipe portion  111   b  is upwardly moved, when the piston  114  is downwardly moved. And when the piston  114  reaches at its bottom dead center, the liquid surface in the first pipe portion  111   b  comes to its highest position. 
     According to the present embodiment, when the liquid surface comes to the highest position in the first pipe portion  111   b , the liquid surface reaches at the lower ends of the narrow grooves  340 , as shown in  FIG. 16A . 
     The liquid-phase working fluid is then supplied to the inner surface of the heating portion ( 112 ) through the narrow groves  340  due to the capillary phenomenon. The working fluid is then heated and vaporized by the heating device  112 , and the volumetric expansion of the working fluid by the vaporization is generated in the fluid container  111 . 
     The liquid surface of the working fluid is pushed down to a position, which is lower than the water-repellant surface  342 , as shown in  FIG. 16B . The liquid surface at an upper end  320  of the second straight pipe portion  111   c  is thereby pushed up. The piston  114  and the moving member  102  of the output device  101  are upwardly moved. 
     A lower part of the gas-phase working fluid is further downwardly moved by the volumetric expansion of the vaporization, and comes into the space of the cooling portion of the cooling device  113 . 
     The gas-phase working fluid is cooled down and liquefied at the cooling portion ( 113 ), and the working fluid in the fluid container  111  is volumetrically contracted. 
     The liquid surface in the first straight pipe portion  111   b  moves up due to the volumetric contraction of the working fluid, and the liquid surface in the second straight pipe portion  111   c  is thereby downwardly moved. The piston  114  as well as the moving member  102  is pushed downwardly by the spring force of the spring  103 . When the piton  114  is moved to its bottom dead center, the liquid surface in the first straight pipe portion  111   b  moves up to the narrow grooves  340  ( FIG. 16A ). 
     The above volumetric expansion and contraction are repeated to reciprocate the piston  114  and the moving member  102 , so that electric power is generated. 
     In the above steam engine  110 , the highest position of the liquid surface in the first straight pipe portion  111   b  is at the lower position of the narrow grooves  340 , and the liquid-phase working fluid to be heated by the heating device  112  is only the working fluid which is supplied to the inner surface of the heating portion ( 112 ) through the narrow grooves  340 . The liquid-phase working fluid at the heating portion ( 112 ) is thereby fully vaporized. 
     As above, the amount of the liquid-phase working fluid, which is heated but not vaporized by the heating device  112 , is minimized. Namely, the thermal loss is minimized. 
     Since the water-repellant surface  342  is formed at the lower portion of the narrow grooves  340 , the movement of the working fluid (the self-excited vibration of the working fluid) in the fluid container  111  can be more properly performed. 
     When the liquid surface is pushed down in the first straight pipe portion  111   b  by the vaporization of the working fluid, the liquid surface is further moved by the water-repellant surface  342  to the position lower than the water-repellant surface  342  ( FIG. 16B ). 
     When the liquid surface is pushed down as above, there is the water-repellant surface  342  between the narrow grooves  340  and the liquid surface. Therefore, the liquid-phase working fluid is prevented from going up to the heating portion ( 112 ) through the narrow grooves  340  by the capillary phenomenon. 
     In the case that the liquid-phase working fluid remaining in the narrow grooves  340  at the heating portion ( 112 ) is continuously heated and vaporized even after the liquid surface has been pushed down, the stable operation of the self-excited vibration of the working fluid can not be possible. However, according to the present embodiment, the continuous vaporization of the liquid-phase working fluid is prevented by the water-repellant surface  342 . 
     The structure of the inner surface of the heating portion ( 112 ) is not limited to the multiple narrow grooves  340  of  FIG. 16A . 
       FIG. 17  shows a modification of the structure of the inner surface of the heating portion. In  FIG. 17 , multiple narrow grooves  340   a  are formed in the inner surface of the first straight pipe portion  111   b , vertically extending at the heating portion as in the same manner to those in  FIG. 16A . In addition, a large number of micro grooves  340   b , which are branched off from the narrow grooves  340   a , is formed in the inner surface. The surface areas of the narrow grooves  340   a  and the micro grooves  340   b  are thus increased, so that a relatively large amount of the liquid-phase working fluid can be supplied to the heating portion ( 112 ). 
     Since the amount of the liquid-phase working fluid, namely the amount of the gas-phase working fluid by the vaporization, can be increased, the output of the steam engine  110  can be correspondingly increased. 
     The narrow groves  340  ( 340   a ), which are regularly formed at the inner surface, can be formed by a machining process or a chemical treatment, such as an etching process. The micro grooves  340   b , which are irregularly formed at the inner surface, can be likewise formed by the chemical treatment, such as an etching process, so that the inner surface is roughened. The micro grooves  340   b  can be alternatively formed by forming irregular micro convex surfaces, in which metal separation is formed by dipping the pipe portion  111   b  into electrolytic solution. 
     A water-attracting surface  343  can be formed at the inner surface of the heating portion ( 112 ), instead of the narrow grooves  340  ( 340   a ) and the micro grooves  340   b , as shown in  FIG. 18 . 
     The water-attracting surface  343  can be, for example, formed by the following methods: 
     (1) A coating layer is formed by a water-attracting ceramic materials, such as CaF 2 , CaO, MgO, Al 2 O 3 , BeO, ZnO, TiO 2 , SiO 2 , SnO 2 , Cu 2 O, Na 2 S, B 2 O 2 , CaS, CuO, etc. 
     In case that a coating layer is formed by the water-attracting ceramic material of SiO 2  (glass) and the heating portion of the first pipe portion  111   b  is made of aluminum, the coating layer can be formed in such a way that the heating portion (on which the liquid glass is adhered) is heated. 
     (2) A hydrophilic group, such as hydroxyl group (—OH group), carboxyl group (—COOH group) is combined. 
     (3) Sintered metal material or diffusion bonding material of foamed metal is adhered to the inner surface of the heating portion ( 112 ) of the pipe portion  111   b , in case the pipe portion  111   b  is made of metal, such as cupper. The adhered material is preferably the same raw material to that of the pipe portion  111   b.    
     (4) In the case that the pipe portion  111   b  is made of the sintered material of carbon, (—Si—O—H group) is combined to the inner surface of the pipe portion  111   b.    
     The above water-attracting surface  343  can be also formed on the surfaces of the narrow grooves  340  ( 340   a ) and the micro grooves  340   b , so that the supply of the liquid-phase working fluid to the heating portion ( 112 ) can be done more quickly. The response of the steam engine  110  is increased, namely a frequency of the self-excited vibration of the working fluid in the fluid container  111  can be sifted to a higher frequency range. 
     A fluid having a lower surface tension than the water, such as ethanol, can be used as the working fluid, so that the supply of the liquid-phase working fluid to the heating portion ( 112 ) can be quickly done. A detergent can be mixed to the water to decrease the surface tension, in case of using the water as the working fluid. 
     Fifth Embodiment 
     A fifth embodiment of the present invention is explained with reference to  FIGS. 19A ,  19 B to  21 . 
       FIG. 19A  shows a schematic view of the steam engine  110  of the fifth embodiment,  FIG. 19B  shows an enlarged perspective view of a heating device  112 A circled by a dotted line in  FIG. 19A , and 
       FIGS. 20A and 20B  are top plan views showing the heating portion of the heating device  112 A. 
     The fifth embodiment differs from the above fourth embodiment, in that the heating portion of the heating device  112 A is formed by a disc shaped hating portion  322 , which is provided at the top end of the first straight pipe portion  111   b  and has a disc shaped inner surface  324  horizontally extending. The heating device  112 A is provided at an outer periphery of the heating portion  322 . 
     In the fifth embodiment, a vertical thickness “T 1 ” of the heating device  112 A is made smaller to increase the thermal efficiency of the steam engine  110 , by minimizing the amount of the working fluid to be heated and vaporized at the heating device  112 A. For example, the thickness “T 1 ” is made smaller than a diameter “T 2 ” of the first straight pipe portion  111   b , as shown in  FIG. 19A . 
     As shown in  FIG. 20A , multiple narrow grooves  327   a , which extend (regularly) outwardly in radial directions from a center opening  326  communicated with the top end of the first straight pipe portion  111   b , are formed at the inner surface  324 . Multiple micro grooves  327   b  are further formed (irregularly) at the inner surface  324 . The narrow grooves  327   a  and the micro grooves  327   b  are so formed to cause capillary phenomenon by the liquid-phase working fluid in the pipe portion  111   b . The narrow grooves  327   a  and the micro grooves  327   b  can be formed by the machining process and chemical etching process, as in the same manner to the above fourth embodiment. 
     The structure of the grooves ( 327   a  and  327   b ) to be formed at the inner surface  324  is not limited to that shown in  FIG. 20A . For example, the structure of the grooves can be made as shown in  FIG. 20B , in which narrow grooves  328  are regularly formed. The narrow grooves  328   a  extend outwardly in the radial directions from the center opening  326 , whereas the narrow groves  328   b  are formed as concentric circles having different diameters to the center opening  326 . 
     In the steam engine  110  of the fifth embodiment, a gas is filled in the heating portion  322 , so that the inside space of the heating portion is not filled with the liquid-phase working fluid. 
     When the piston  114  is moved to its bottom dead center, the liquid surface in the first straight pipe portion  111   b  is moved to its highest position, at which the center opening  326  is filled with the working fluid. 
     The liquid-phase working fluid is spread over the inner surface  324  through the narrow grooves  327  ( 328 ) due to the capillary phenomenon. The working fluid is heated and vaporized by the heating device  112 A, to cause the volumetric expansion of the working fluid in the fluid container  111 . 
     Since the narrow grooves  327  ( 328 ) formed in the heating portion  322  extends horizontally, the supply speed of the liquid-phase working fluid through the grooves  327  ( 328 ) becomes higher than the steam engine of the fourth embodiment ( FIGS. 15 to 18 ), because the horizontal movement of the liquid-phase working fluid is little influenced by the gravity. The response of the steam engine  110  is accordingly increased. 
     A water-attracting surface  329  can be formed at the inner surface  324  of the heating portion, instead of the narrow grooves  327  ( 328 ), to facilitate the supply of the working fluid to the heating portion, as shown in  FIG. 21 . The water-attracting surface can be formed as in the same manner to the fourth embodiment. 
     The water-attracting surface  329  can be further formed at surfaces of the narrow grooves  327  and  328 , to further increase the supply speed of the working fluid. 
     Sixth Embodiment 
     A sixth embodiment of the present invention is explained with reference to  FIG. 22 . 
       FIG. 22  is a modification of the fourth embodiment ( FIGS. 15 to 18 ) and shows an upper portion of the first straight pipe portion  111   b . The sixth embodiment is different from the fourth embodiment in that a branch pipe  350  is provided at the upper portion of the first straight pipe portion  111   b , wherein an upper end of the branch pipe  350  is connected to a part “A” of the heating portion ( 112 ) and connected at its lower end to a part “B” of the straight pipe portion, which is lower than the heating device  112 . An inner diameter of the branch pipe  350  is so designed that the liquid-phase working fluid is supplied to the heating portion (the part A) by the capillary phenomenon. 
     In the steam engine  110  of the sixth embodiment, a gas is filled in the heating portion ( 112 ), so that the inside space of the heating portion is not filled with the liquid-phase working fluid. 
     When the piston provided at the second straight pipe portion is moved to its bottom dead center, the liquid surface in the first straight pipe portion  111   b  is at such a position slightly higher than the part “B” of the branch pipe  350 , so that the liquid-phase working fluid is supplied upwardly to the heating portion ( 112 ) through the branch pipe  350  due to the capillary phenomenon. 
     According to the sixth embodiment, the amount of the liquid-phase working fluid, which is heated and vaporized at the heating device  112 , is limited to such an amount of the working fluid supplied to the heating portion through the branch pipe  350 . The liquid-phase working fluid is thereby fully vaporized. 
     As above, the amount of the working fluid, which is heated but not vaporized and moved toward the cooling device, can be minimized, so that the thermal loss can be minimized. 
     Narrow grooves ( 340 ) and/or water-attracting surface ( 343 ) can be formed at the inner surface of the branch pipe  350 .