Patent Publication Number: US-6338248-B1

Title: Heating and refrigerating machine, especially a vuilleumier heat pump or a stirling engine

Description:
FIELD OF THE INVENTION 
     The present invention relates to a heating and refrigerating machine, especially a Vuilleumier heat pump or a Stirling engine, in which a gas-air mixture is combusted in a combustion chamber and the exhaust gas radiates thermal energy to a heater head, which functions as a housing for the hot piston of the machine, part of the outer surface of the heater head forming a portion of the combustion chamber. 
     BACKGROUND INFORMATION 
     A previously proposed heating and refrigerating machine is described in German Published Patent Application No. 195 16 499 and U.S. Pat No. 5,214,923. In this machine, the gas-air mixture is fed directly into the combustion chamber, ignited and combusted. In the process, the heat transmission is brought about by convection of the exhaust gas on the wall of the combustion chamber and, thus, directly to the heater head. Therefore, only a corresponding efficiency in the energy transmission is achievable. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to improve the heat transmission efficiency of a heating and refrigerating machine and, in the process, to achieve a compact design. 
     This object is achieved, in one case, in that the heater head itself has a concave receptacle functioning as the combustion chamber for a porous-medium burner, the receptacle encompassing the predominant portion of the outer side of the porous-medium burner, with the exception of the intake surface for the gas-air mixture, and in that the heat transmission is brought about by convection and radiation to the heater head, and, in another case, this object is achieved in an equivalent manner in that the heater head is configured as a cylinder and is encompassed by a porous-medium burner in the form of a hollow cylinder, the gas-air mixture being admissible at the end face of the porous-medium burner or at its outer-jacket side, and in that the heat transmission is brought about by convection and radiation to the heater head. 
     In each case, by using a porous-medium burner, a substantial portion of the heat transmission is brought about by radiation, and by directly coupling the porous-medium burner to the heater head functioning as a part of the combustion chamber, the machine can have a compact structure and can be optimally adapted to space requirements. Moreover, in addition to the improved efficiency of the heat transmission accompanied by low emissions, a large output modulation range is achieved. 
     One beneficial embodiment of the present invention provides that the porous-medium burner can be arranged at a distance from the heater head or so as to have a large surface area set against the heater head in order to achieve an optimal adjustment with regard to efficiency, removal of emissions, and modulation range. 
     In this configuration, the porous-medium burner can completely fill the concave receptacle in the heater head. 
     The combustion of the gas-air mixture in the porous-medium burner can be stabilized in that the gas-air mixture can be fed to the porous-medium burner through a porous anti-blowback body, which covers the intake surface thereof. In this way, a uniform combustion process is achieved inside the porous-medium burner. 
     The same purpose is also served by an embodiment that is characterized in that a distribution chamber, whose output cross-section corresponds to the input cross-section of the anti-blowback body, is arranged upstream of the anti-blowback body. 
     The removal of the exhaust gas is ensured, in one case, in that the combustion chamber in the area of the intake surface of the porous-medium body and in the area of the anti-blowback body is covered by a housing having an exhaust outlet, or, in another case, in that the porous-medium burner is covered by a part of a housing having an exhaust gas outlet, the housing part being formed as an anti-blowback body in the area of the intake surface of the porous-medium burner. 
     A further benefit of the new machine is achieved in that at least one portion of the housing part is formed as a heat exchanger for a circulating liquid, which can be used as water for industrial purposes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a heater head having a concave receptacle and a porous-medium burner that is arranged at a distance from the receptacle. 
     FIG. 2 shows a heater head having a concave receptacle and a porous-medium burner that completely fills the receptacle. 
     FIG. 3 shows a cylindrical heater head along with a porous-medium burner in the form of a hollow cylinder, which encompasses the heater head and to which the gas-air mixture is fed at its end face. 
     FIG. 4 shows a cylindrical heater head along with a porous-medium burner in the form of a hollow cylinder, which encompasses the heater head and to which the gas-air mixture is fed at its outer-jacket side. 
    
    
     DETAILED DESCRIPTION 
     For all exemplary embodiments, only the point of interconnection between the burner and the heater head of the machine, which is the subject of the present invention, is shown. The remaining structure of the machine can be implemented in a known way as a Vuilleumier heat pump or Stirling engine, since this is not significant for the present invention. It is, after all, of primary importance that the efficiency of the heat transmission from the burner to the heater head be improved and that this be done with a structural configuration that permits a compact design of the machine. 
     In the exemplary embodiment according to FIG. 1, heater head  20  has a concave receptacle  21  in its end face in which a porous-medium burner  10  is inserted. Porous-medium burner  10  is cylindrical and can be formed as wire mesh, a porous ceramic element, and the like. It has the benefit that a more stable combustion process can thus be achieved having low emissions over a broad output modulation range. 
     Receptacle  21  encompasses at a distance the majority of the outer surface of porous-medium burner  10 , with the exception of the intake surface for the gas-air mixture, the intake surface being covered by a plate-shaped, porous anti-blowback body  11 . A distribution chamber, whose output cross-section corresponds to the input cross-section of anti-blowback body  11 , can be arranged upstream from anti-blowback body  11 . A fan  12  transports air L and mixes it with gas G. As a gas-air mixture, this fuel arrives in porous-medium burner  10  and combusts there after ignition (not shown). 
     In the area of the intake surface of porous-medium burner  10 , a housing part  15 , which is provided with exhaust outlet AG, completes the covering of the combustion chamber. 
     The heat transmission from porous-medium burner  10  to heater head  20  is brought about by convection and radiation, the proportion of the latter being especially high when a porous-medium burner  10  is used. 
     In the exemplary embodiment according to FIG. 2, porous-medium burner  10  completely fills concave receptacle  21  in heater head  20  and is set against it. A pot-type, porous anti-blowback body  11 , through which the gas-air mixture is fed, is inserted in the center of porous-medium burner  10 . In all other respects, the exemplary embodiment according to FIG. 2 is indistinguishable from the exemplary embodiment according to FIG.  1 . In this context, the configuration can also vary between the two exemplary embodiments and can be adapted for porous-medium burner  10 , either the variant at a distance or the one having the filled-in volume. 
     In the exemplary embodiments according to FIGS. 3 and 4, heater head  20  is cylindrical and is encompassed by porous-medium burner  10  in the form of a hollow cylinder. 
     In the exemplary embodiment according to FIG. 3, housing part  15  is placed over the open face of heater head  20 , covering the outer-jacket surface of porous-medium burner  10  down to the bottom face, which is utilized as the intake surface for the gas-air mixture and is covered by porous, annular anti-blowback body  11 . Housing part  15  is provided with exhaust outlet AG. A portion of housing part  15 , especially in the area of the outer-jacket surface of porous-medium burner  10 , can be configured as heat exchanger  30 . The circulating liquid can be used, for example, as water for industrial purposes. In this configuration, anti-blowback body  11  can also be combined with a distribution chamber arranged upstream for the gas-air mixture. 
     In the exemplary embodiment according to FIG. 4, the outer-jacket surface of porous-medium burner  10  is used as the intake surface for the gas-air mixture, housing part  15  in this area being configured as porous anti-blowback body  11  and being combinable with a distribution chamber. 
     Also in these exemplary embodiments according to FIGS. 3 and 4, porous-medium burner  10  can either be set against heater head  20  or arranged at a distance from it without detrimentally affecting the compact design of this area of the machine.