Abstract:
In a heat engine that utilizes the energy content of a warm medium by a better exploitation of the isochoric changes of state in a cycle process having six changes of state (two isobars, two isochores and two isotherms) it is possible by means of the presently disclosed embodiments to minimize the constructive complexity. The heat engine comprises at least one pair of heat exchangers having one condenser and one evaporator. At least one working medium transfer device is arranged between the condenser and the evaporator of the pair of heat exchangers. At least one working engine driven by the working medium is provided. A conduit is provided between the condenser and the working engine and another conduit is provided between the evaporator and the working engine. Valve means are arranged between the pair of heat exchangers and the working engine and selectively open and close a fluid communication between these.

Description:
[0001]    The present invention relates to a heat engine that implements a cycle process consisting of six changes of state (two isobars, two isochors and two isotherms). In particular it relates to such a heat engine having a simplified mechanical construction. 
         [0002]    Heat engines currently used for power generation are mainly steam and gas turbines, combined heat and power (CHP) units and power generators with diesel or internal combustion engines. These generators, except the steam generation for steam turbines, operate to a minor extent with regenerative fuels. 
         [0003]    All these heat engines have in common that they are only able to transform just a comparatively small part of the used energy, approx. 30-40%, into mechanical work, which is equivalent to electric power. The remaining 60-70% of primary energy is lost as heat energy, unless it is used as thermal heat. 
         [0004]    In order to utilize this excess energy according to the heat requirements, different heat engines were developed, which also work at low temperatures with acceptable efficiency. One of these developments is the Organic Rankine Cycle (ORC), where organic compounds are employed instead of using water and steam as working substance, whose vaporisation temperatures and vapour pressures allow an operation at low temperatures. In recent years some of the ORC-systems have been taken into operation. By using ORC-systems, regenerative energy like geothermal power can be transformed into work. 
         [0005]    With respect to the prior art, reference is made to the publication DE 10 2005 013287 B3 “Wärmekraftmaschine”, where a heat engine having heat exchangers is described, which performs its work using an external heat source. The work is generated by a cycle process that consists, of six changes of state: two isobars, two isochors and two isotherms. In the heat engine several of the cycles described above, take place at the same time, but chronologically displaced. 
         [0006]    The heat exchangers of this known heat engine consist of two parts. One part is a condenser being cooled, the other part is an evaporator being heated. All heat exchangers are arranged in a star shaped manner around the central axis of the working cylinder and rotate around the same. 
         [0007]    The heat engine according to the present invention has a relatively high efficiency even at low-temperature operating conditions. Among other things, the main purpose of this invention is to recover a part of waste heat of industrial process or power stations, which would normally be lost in warm or hot exhaust air. 
         [0008]    Further, it is generally possible to recover energy from liquids as well as gases that were heated by regenerative energy sources to low temperature levels. Especially it is intended to convert a part of the heat, which usually cannot be utilized efficiently, by means of the presently described heat engine into electricity or work. 
         [0009]    The invention is based on the problem to reduce the constructive complexity of a heat engine that makes use of the energy content of a hot medium by a better utilization of the isochoric changes of state. 
         [0010]    The aim of the present invention is achieved by a heat engine that comprises at least one pair of heat exchangers comprising a condenser and an evaporator, at least one working medium transfer device being arranged between the condenser and the evaporator of the pair of heat exchangers, at least one working engine driven by the working medium having a conduit between the condenser and the working engine and a conduit between the evaporator and the working engine as well as valve means being arranged between the pair of heat exchangers and the working engine and that selectively open and close a fluid communication between these. In this way the number of components may be reduced and the sealing of the individual components is simplified. 
         [0011]    Preferably the valve means comprise a valve, which is arranged between the condenser and the working engine within the conduit; and a valve, which is arranged between the evaporator and the working engine within the conduit, to allow for a flexible control of the operating sequence. 
         [0012]    The condenser defines a closed internal chamber, and preferably the working fluid transfer device is connected to the lower part of the internal chamber in order to gather the condensed working medium as completely as possible. 
         [0013]    The evaporator defines a closed internal chamber, and preferably the working fluid transfer device is connected to the upper part of the internal chamber in order to disperse the inserted condensed working fluid over the entire evaporator as uniformly as possible. 
         [0014]    The working fluid transfer device preferably comprises at least one switchable working medium transport chamber, which is selectively connected to the evaporator in a first position, which is connected to the condenser in a second position, and which is closed towards the evaporator as well as the condenser in a third position. By this means an overflow or a pressure compensation between the evaporator and the condenser is prevented to minimize losses. 
         [0015]    The working engine preferably comprises a working piston that defines a variable operation chamber in the working engine to directly generate work by means of the pressure differences between the condenser and the evaporator. 
         [0016]    Further, the working engine advantageously comprises a working piston which defines a first and a second variable operation chamber together with the working cylinder in order to enable the working piston to be driven from two sides, which increases the efficiency of the heat engine. 
         [0017]    Advantageously the conduit between the condenser and the working engine and the conduit between the evaporator and the working engine are both connected to the operation chamber to simplify the piping. 
         [0018]    Advantageously a plurality of pairs of heat exchangers is provided with their condenser and evaporator being connected to an operation chamber. Thus, faster stroke times may be achieved as different cycles of the thermal cycle (evaporation and condensation) may take place at the same time in the heat exchangers. 
         [0019]    Advantageously at least two pairs of heat exchangers are provided with each pair of heat exchangers being connected to the first or the second operation chamber to enable the working piston being driven from both sides. In this way a higher output of the heat engine is achieved. 
         [0020]    Advantageously a plurality of pairs of heat exchangers is provided, the condensers and evaporators thereof being connected to a first operation chamber, and another plurality of pairs of heat exchangers is provided the condensers and evaporators thereof being connected to a second operation chamber. Thus faster stroke times may be achieved as different cycles of the thermal cycle (evaporation and condensation) may take place in the heat exchangers simultaneously. At the same time a higher output of the heat engine is achieved. 
         [0021]    Advantageously means for distributing the working medium are arranged in the evaporators to achieve a better distribution and therefore a faster evaporation of the inserted condensed working medium. 
         [0022]    Preferably the distribution means are capable of distributing the working medium over a large surface to provide for a fast heat transfer to the working medium and to enable faster stroke times in this way. The distribution means comprise an injection device, metallic wool, metal threads, surface structures or heat transfer fins to achieve a fast evaporation of the working medium. 
         [0023]    Alternatively the aim of the invention is achieved by a heat engine further comprising a plurality of pairs of heat exchangers, each comprising a condenser and an evaporator; a plurality of working medium transfer devices, each being arranged between the condenser and the evaporator of each pair of heat exchangers; at least one working engine having first and second operation chambers, wherein a first group of pairs of heat exchangers is connected to the first operation chamber and wherein a second group of pairs of heat exchangers is connected to the second operation chamber. Conduits are arranged between the condensers of the first group of pairs of heat exchangers and the first operation chamber of the at least one working engine, and further conduits are arranged between the condensers of the second group of pairs of heat exchangers and the second operation chamber of the working engine. A plurality of valves is provided, wherein one of these valves is arranged within the conduit between each condenser and the operation chamber connected thereto of the at least one working engine, respectively. Furthermore, conduits are arranged between the evaporator of the first group of pairs of heat exchangers and the first operation chamber of the at least one working engine, and further conduits are arranged between the evaporator of the second group of pairs of heat exchangers and the second operation chamber of the at least one working engine. A plurality of valves is provided, wherein one of these is arranged in the conduit between each evaporator and the attached operation chamber of the at least one working engine, respectively. This results in the advantage that a plurality of cycles of the thermal cycle may be executed simultaneously, and faster stroke times may be achieved. 
         [0024]    Alternatively the aim of the invention is achieved by a heat engine further comprising a plurality of pairs of heat exchangers, each comprising a condenser and an evaporator; a plurality of working medium transfer devices, each being arranged between the condenser and the evaporator of each pair of heat exchangers; at least one working engine having first and second operation chambers, wherein a first group of pairs of heat exchangers is connected to the first operation chamber, and wherein a second group of pairs of heat exchangers is connected to the second operation chamber. A conduit is provided between the condenser of the first group of pairs of heat exchangers and the first operation chamber of the working engine, wherein each condenser is connected to the conduit via a junction line, respectively. Furthermore a conduit is provided between the condensers of the second group of pairs of heat exchangers and the second operation chamber of the working engine, wherein each condenser is connected to the conduit via a junction line, respectively. In each case, a plurality of valves is individually arranged in the junction line between the condenser and the conduit connected thereto. Additionally a conduit is arranged between the evaporators of the first group of pairs of heat exchangers and the first operation chamber of the working engine, wherein each evaporator is connected to the conduit via a junction line. Conduits are arranged between the evaporators of the second group of pairs of heat exchangers and the second operation chamber of the working engine, wherein each evaporator is connected to the conduit via a junction line respectively. A plurality of valves is in each case individually arranged in the junction line between each evaporator and attached conduit connected thereto. This results in the advantage that a plurality of cycles of the thermal cycle may be executed simultaneously and faster stroke times may be achieved. 
         [0025]    Advantageously the first group and the second group of pairs of heat exchangers each consist of three pairs of heat exchangers such that the six strokes of the employed thermal cycle may run offset by one stroke, respectively. 
         [0026]    Advantageously the working engine is a piston engine having a linearly reciprocating piston to enable the use of established sealing and construction principles. 
         [0027]    Alternatively the working engine is a rotary piston engine having rotating pistons to enable simple forwarding of the generated (rotational) output to a standard electric generator. Furthermore, the employment of a rotary piston engine results in a smaller size of the working engine. 
         [0028]    Preferably the working medium transfer device comprises two valves between which a chamber is provided for the intake of condensate. This results in the advantage that simply controllable valves may be used, which are available in a large variety as purchased parts. In this way the constructional effort may be reduced. 
         [0029]    The aim of the invention is achieved by a method for controlling the heat engine described above, the method comprising the following steps: a) closing the valve between the working cylinder and the condenser, b) closing the valve between the working cylinder and the evaporator, c) condensing a gaseous working medium in the condenser, d) collecting the condensed liquid working medium in the working medium transport chamber of the working medium transfer device, e) opening the valve between the working cylinder and the condenser, f) introducing the gaseous working medium into the condenser, g) collecting the condensed, liquid working medium in the working medium transport chamber of the working medium transfer device, h) closing the valves between the working cylinder and the condenser, i) pressure-tight sealing of the condensed liquid working medium in the working medium transport chamber of the condenser, j) directing the condensed liquid working medium into the evaporator, k) evaporating the condensed liquid working medium within the evaporator, l) opening the valve between the working cylinder and the evaporator, m) directing the evaporated working medium into the working cylinder, n) closing the valve between the working cylinder and the evaporator, o) repeating the steps starting from step c). Thus advantageously a high efficiency of the thermal cycle may be achieved without pressure losses. 
         [0030]    The step k) of evaporating the working medium preferably takes place at least partly during the following steps: l) opening the valve and m) directing into the working cylinder to increase the thermal efficiency. 
         [0031]    Preferably the method for controlling the above described heat engine comprises the following steps:
   a) opening valves  40 A,  41 X, closing the valves  40 B,  40 C,  40 X,  40 Y,  40 Z,  41 A,  41 B,  41 C,  41 Y,  41 Z, collecting the condensed working medium in the working medium transfer devices  30 A,  30 B,  30 C,  30 X,  30 Z;   b) opening valves  41 B,  40 Z, closing the valves  40 A,  40 B,  40 C,  40 X,  40 Y,  41 A,  41 C,  41 Y,  41 Z, collecting the condensed working medium in the working medium transfer devices  30 B,  30 C,  30 X,  30 Y,  30 Z;   c) opening valves  40 C,  41 Y, closing the valves  40 A,  40 B,  40 X,  40 Y,  40 Z,  41 B,  41 C,  41 X,  41 Y,  41 Z collecting the condensed working medium in the working medium transfer devices  30 A,  30 B,  30 C,  30 X,  30 Y;   d) opening valves  40 X,  41 A, closing the valves  40 A,  40 B,  40 C,  40 Y,  40 Z,  41 B,  41 C,  41 X,  41 Y,  41 Z collecting the condensed working medium in the working medium transfer devices  30 A,  30 B,  30 X,  30 Y,  30 Z;   e) opening valves  40 B,  41 Z, closing the valves  40 A,  40 C,  40 X,  40 Y,  40 Z,  41 A,  41 B,  41 C,  41 X,  41 Y collecting the condensed working medium in the working medium transfer devices  30 A,  30 B,  30 C,  30 Y,  30 Z;   f) opening valves  40 Y,  41 C, closing the valves  40 A,  40 B,  40 C,  40 X,  40 Z,  41 A,  41 B,  41 X,  41 Y,  41 Z collecting the condensed working medium in the working medium transfer devices  30 A,  30 C,  30 X,  30 Y,  30 Z;   d) repeating steps a) to f).   
 
         [0039]    Thus advantageously a high efficiency of the thermal cycle may be achieved without pressure losses. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0040]    The invention as well as other features and advantages of it are described with respect to preferred embodiments with reference to the following figures. 
           [0041]      FIG. 1  shows a schematic representation of the heat engine according to a first embodiment of the present invention; 
           [0042]      FIG. 2   a - 2   f  show a schematic representation of the heat engine of  FIG. 1  in different strokes of its operation process; 
           [0043]      FIG. 3  shows a schematic representation of the heat engine according to a second embodiment of the present invention; 
           [0044]      FIG. 4  shows a schematic representation of the heat engine according to a third embodiment of the present invention; 
           [0045]      FIG. 5   a - 5   f  show a schematic representation of the heat engine of  FIG. 4  in different cycles of its operation process; 
           [0046]      FIG. 6  shows a schematic representation of the heat engine according to a fourth embodiment of the present invention; 
           [0047]      FIG. 7  shows a schematic representation of the heat engine according to a fifth embodiment of the present invention; 
           [0048]      FIG. 8   a - 8   f  show a schematic representation of the heat engine of  FIG. 7  in different strokes of its operation process; 
           [0049]      FIG. 9  shows a P-h-graph (pressure-enthalpy-diagram) of the working medium C 2 H 2 F 2 , refrigerant  134   a , of the operation process of the heat engine according to the present invention; 
           [0050]      FIG. 10  shows a P-v-graph (pressure-volume-diagram) of the working medium C 2 H 2 F 2 , refrigerant  134   a , of the operation process of the heat engine according to the present invention with respect to the P-h-diagram shown in  FIG. 6 ; 
           [0051]      FIG. 11  shows a T-s-graph (pressure-enthropy-diagram) of the working medium C 2 H 2 F 2 , refrigerant  134   a , of the operation process of the heat engine according to the present invention with respect to the P-h-diagram shown in  FIG. 6 ; 
       
    
    
     DETAILED DESCRIPTION 
     Heat Engine According to the First Embodiment 
       [0052]    The heat engine  1  according to the first embodiment of the invention comprises a pair of heat exchangers  10 , a cylinder  20 , a working medium transfer device  30  and valve means  40 ,  41 . The valve means consist of a first valve or condenser valve  40  and a second valve or evaporator valve  41 . The pair of heat exchangers  10  consists of a first heat exchanger or condenser  11  (hereinafter condenser) and a second heat exchanger or evaporator  12  (hereinafter evaporator). The condenser  11  has a lower end part  13  and the evaporator has an upper end part  14 . 
         [0053]    The upper end part  14  of the evaporator  12  as well as the parts of the heat engine  1  described below may be insulated from the rest of the evaporator  12  by insulation  15 . The insulation is made from a material that is suitable for the pressures and the mechanical stress but is a bad heat conductor. The insulation  15  is employed to minimize the heat conduction from evaporator  12  to the rest of heat engine  1 . Further, it is contemplated to insulate the working engine and the conduits to the evaporator in order to prevent or at least minimize heat losses and the condensation of the gaseous working medium. 
         [0054]    The condenser  11  and the evaporator  12  are each shown as tube  16  having fins  17 . Nevertheless, it should be noted that other types of heat exchangers may also be employed. Further, it should be noted that, even though only one tube  16  is shown in the figures, each heat exchanger may comprise any number of tubes  16 . The condenser  11  and the evaporator  12  may also have an appropriate design for a heat exchange by means of radiation. 
         [0055]    Means for distributing the working medium over a large inner surface are arranged in the evaporator  12  in order to allow for an improved heat transfer to the working medium. The distribution means may comprise e.g. metal wool, metal filament or threads, surface structures or heat transfer fins or other surface structures that are arranged inside the evaporator. With fine surface structures the working medium is also distributed by means of capillary attraction which causes a better heat absorption from the wall of the evaporator  12 . 
         [0056]    The condenser  11  is surrounded by a flowing cooling medium  18 . The cooling medium  18  may be gaseous or liquid. The evaporator  12  is surrounded by a flowing heating medium  19  that may be gaseous or liquid, as well. 
         [0057]    The condenser  11  and the evaporator  12  are connected to the working medium transfer device  30 . The working medium transfer device  30  comprises at least one working medium transport chamber  31  that may be selectively connected to the evaporator  12  and the condenser  11 . 
         [0058]    The working medium transfer device  30  may be positioned in at least three positions. In the first position the working medium transport chamber  31  is connected to the condenser  11  to receive the condensate and is disconnected from the evaporator  12 . In the present embodiment, the working medium transport chamber  31  is connected to the condenser  11  at its lower end part  13 . In the second position the working medium transport chamber  31  is disconnected from both the condenser  11  and the evaporator  12 . In the third position the working medium transport chamber  31  is connected to the evaporator  12  to introduce the condensate, but is disconnected from the condenser  11 . In the present embodiment the working medium transport chamber  31  is connected to the evaporator  12  at its upper end part  14 . The working medium transfer device  30  may comprise an electric, pneumatic, hydraulic or other drive that may be actuated according to the operation process described below in more detail. 
         [0059]    The working medium transfer device  30  may have any design. However, there must be no pressure exchange between the condenser  11  and the evaporator  12  during the transfer of the liquid condensed working medium. The working medium transfer device  30  simply has to transfer the condensate of the working medium formed in the condenser  11  into the evaporator  12  without establishing any direct connection between the condenser  11 , and the evaporator  12 . 
         [0060]    The heat engine  1  further comprises the cylinder  20  in which a piston  21  is arranged. The cylinder  20  and the piston  21  define an operation chamber  22 . The operation chamber  22  is connected to the condenser  11  via a conduit  24 . Further, the operation chamber  22  is connected to the evaporator  12  via a conduit  25 . Within the conduit  24 , a valve  40  is arranged, which is able to open or close the connection between the operation chamber  22  and the condenser  11 . Within the conduit  25 , a valve  41  is arranged, which is able to open or close the connection between the operation chamber  22  and the evaporator  12 . The valves  40 ,  41  may comprise an electric, pneumatic, hydraulic or other drive that may be activated by the operation process described below in more detail. 
       Operation of the Heat Engine According to the First Embodiment 
       [0061]    The operation of the first embodiment of heat engine  1  takes place with the following changes of state of the working medium in a closed cycle process. During operation, a cooling medium flows around condenser  11 , whereas evaporator  12  simultaneously experiences a heat addition by the heating medium. The changes of state of the cycle process proceed in the following sequence ( FIG. 2   a - 2   f ): 
         [0000]    1. Isochoric Heat Extraction (Steps  1 - 2  in  FIG. 9 ,  FIG. 2   a ) 
         [0062]    The working medium is cooled at constant volume to the lower temperature level in condenser  11 . Valve  40  is closed, and the working medium transport chamber  31  of the working medium transfer device  30  is connected to the evaporator  11 . Valve  41  is closed. 
         [0000]    2. Isothermal Compression (Steps  2 - 3  in  FIG. 9 ,  FIG. 2   b ) 
         [0063]    Valve  40  between cylinder  20  and condenser  11  is open, and more vapour of the working medium flows from cylinder  20  into condenser  11 . This takes place partly because of the low or negative pressure in condenser  11  and partly because of the pressure on piston  21  in cylinder  20  from the opposite (right) side (see also second and third embodiment). Due to the continuous cooling by the cooling medium, more vapour of the working medium is liquefied and is collected in the working medium transport chamber  31 . An isothermal compression takes place as the inflowing warm vapour contracts because of cooling in the condenser  11 . As the gaseous working medium flows from cylinder  20  into condenser  11 , further heat is extracted from condenser  11 . Valve  41  is closed. 
         [0000]    3. Isobaric Condensation (Steps  3 - 4  in  FIG. 9 ,  FIG. 2   c ) 
         [0064]    Once the condensation temperature is reached, the working medium liquefies at constant pressure and temperature. Due to the continuous cooling additional vapour of the working medium is condensed. The vapour condenses until the pressure in the condenser  11  reaches the vapour pressure at the condensation temperature. The vapour of the working medium does not fully condense but is compressed with concurrent heat extraction. The condensed liquid working medium is collected in the working medium transport chamber  31 . Valve  41  is closed. 
         [0000]    4. Isochoric Heat Input (Steps  4 - 5  in  FIG. 9 ,  FIG. 2   d ) 
         [0065]    Valve  40  is closed. By actuating the working medium transfer device  30 , the condensate of the working medium flows into the evaporator  12 . Due to the preceding condensation of the working medium in the condenser  11  a substantial quantity of condensate was present in the working medium transport chamber  31 . This condensate gets into the hot evaporator  12 , the evaporator&#39;s temperature (upper temperature level) being higher than the boiling point of the working medium. Part of the working medium is evaporated and creates pressure in the evaporator  12 . Valve  41  arranged in direction to the working cylinder  20  remains closed during the heating. Therefore this change of state takes place at constant volume. The evaporation of the working medium takes place until the vapour pressure at the upper temperature level is reached. 
         [0000]    5. Isobaric Evaporation (Steps  6 - 1  in  FIG. 9 ,  FIG. 2   f ) 
         [0066]    Valve  41  is opened. Due to the pressure in the evaporator  12 , the working medium flows out of the evaporator  12  and into the working cylinder  20 , while additional heat is fed into the evaporator  12  from outside. Due to the increase of volume and the continuous heat input, another part of the condensate evaporates at constant pressure. 
       6. Isothermal Expansion 
       [0067]    After the condensate is fully evaporated, the gaseous working medium further expands, while additional heat is fed into the evaporator  12 . An isothermal expansion takes place. Valve  41  closes. After the expansion, the working medium transfer device  30  is returned to its initial position to gather condensate accumulating in the condenser. 
         [0068]    In this cycle process, condenser  11  and evaporator  12  are always used as a pair. The condenser  11  and evaporator  12  of a pair of heat exchangers  10  are connected to each other via the working medium transfer device  30  in such a way that the liquid condensate of the working medium generated in the condensation in the condenser  11  is transferred to the evaporator  12  by means of the working medium transfer device  30  without pressure equalization. Each condenser  11  is always connected to an evaporator  12  with similar or larger heat capacity. 
         [0069]    In this invention the above described cycle process may take place in different pairs of heat exchangers  10  simultaneously but chronologically offset. The design as well as the mode of operation of a heat engine  100  having multiple heat exchangers will be explained with reference to  FIG. 3 . 
         [0070]    A stroke corresponds to half a piston period. A piston period (back and forth) corresponds to two cycles. 
       Heat Engine According to the Second Embodiment 
       [0071]      FIG. 3  shows a schematic representation of another embodiment of a heat engine  100  according to the present invention. The heat engine  100  according to the second embodiment is constructed of similar parts as heat engine  1 . Therefore, corresponding parts are labelled with the same reference numbers. For parts on the left side ( FIG. 3 ) of cylinder  20  an “A” is attached to the reference number. For parts on the right side ( FIG. 3 ) of cylinder  20  an “X” is attached to the reference number. Furthermore, corresponding parts are not described in detail. 
         [0072]    Heat engine  100  according to the second embodiment of the invention comprises two pairs of heat exchangers  10 A,  10 X, a cylinder  20 , two working medium transfer devices  30 A,  30 X and valves  40 A,  41 A and  40 X,  41 X. Pairs of heat exchangers  10 A,  10 X each comprise a first heat exchanger or condenser  11 A,  11 X (hereinafter condenser) and a second heat exchanger or evaporator  12 A,  12 X (hereinafter evaporator). As in the first embodiment, each condenser  11 A,  11 X has a lower end part  13  and each evaporator  12 A,  12 X has an upper end part  14 . 
         [0073]    The upper end part  14  as well as the parts of the heat engine  100  described below may be insulated from the rest of the evaporator  12 A,  12 X by insulation  15 , respectively. The insulation is made from a material, which is suitable for the pressures and mechanical stresses but is a bad heat conductor at the same time. Insulation  15  is employed to minimize the heat transfer from the evaporators  12 A,  12 X to the rest of the heat engine  100 . 
         [0074]    The condenser  11  and the evaporator  12  are each shown as a tube  16  having fins  17 . But it should be noted, that other types of heat exchangers may also be employed. Further, it should be noted that, even though only one tube  16  is shown in the figures, each heat exchanger may comprise any number of tubes  16 . The pairs of heat exchangers  10 A,  10 X may also have an appropriate design for a heat exchange by means of radiation. 
         [0075]    In the evaporators  12 A,  12 X, means for distributing the working medium over a large inner surface are arranged to allow for an improved heat transfer to the working medium. The distribution means may comprise e.g. metal wool, metal filament or threads, surface structures or heat transfer fins or other surface structures arranged inside the evaporator. With fine surface structures, the working medium is also distributed by means of capillary attraction which causes a better heat absorption from the wall of the evaporator  12 . 
         [0076]    The condensers  11 A,  11 X are surrounded by a flowing cooling medium  18 . The cooling medium  18  may be gaseous or liquid. The evaporators  12 A,  12 X are surrounded by a flowing heating medium  19 , which may be gaseous or liquid as well. 
         [0077]    Each the lower end parts  13  of the condensers  11 A,  11 X and the upper end parts  14  of the evaporators  12 A,  12 X are connected by means of a working medium transfer device  30 A,  30 X. The respective working medium transfer devices  30 A,  30 X comprise at least one working medium transport chamber  31  that may selectively be connected to the respective evaporator  12 A,  12 X and the respective condenser  11 A,  11 X. 
         [0078]    As in the first embodiment, the working medium transfer devices  30 A,  30 X may be positioned in at least three positions. In the first position, the working medium transport chamber  31  is connected to the lower end part  13  of the condenser. In the second position, the working medium transport chamber  31  is disconnected from the condenser as well as from the evaporator. In the third position, the working medium transport chamber  31  is connected to the upper end part  14  of the evaporator. The working medium transfer device  30  may comprise an electric, pneumatic, hydraulic or other drive that may be actuated according to the operation process described below in more detail. 
         [0079]    The heat engine  100  further comprises cylinder  20 , in which piston  21  is arranged. Contrary to the first embodiment, cylinder  20  and piston  21  define two operation chambers  22 ,  23 . The operation chambers are located to the right and the left (in  FIG. 3 ) of piston  21 . 
         [0080]    In the second embodiment, the first operation chamber  22  is connected to the first pair of heat exchangers  10 A via conduits  24 A,  24 X,  25 A,  25 X, and the second operation chamber  23  is connected to the second pair of heat exchangers  10 X. That is, the operation chambers  22 ,  23  are each connected to the condenser of the respective pair of heat exchangers  10 A,  10 X via a conduit  24 A,  24 X. Furthermore, the operation chambers  22 ,  23  are connected to the evaporator of the respective pair of heat exchangers  10 A,  10 C via a conduit  25 A,  25 X. 
         [0081]    A valve  40 A,  40 X is arranged in the conduits  24 A,  24 X, respectively, the valve  40 A,  40 X being able to open or close the connection between the operation chamber  22 ,  23  and the corresponding condenser. In conduits  25 A,  25 X, a valve  41 A,  41 X is arranged, which is able to open or close the connection between the operation chamber  22 ,  23  and the evaporator. Valves  40 A,  40 X,  41 A,  41 X may comprise an electric, pneumatic, hydraulic or other drive that may be activated by the operation process described below in more detail. 
       Operation of Heat Engine According to the Second Embodiment 
       [0082]    The operation of heat engine  100  according to the second embodiment is based on the same principle as the operation of the first embodiment. Therefore, the whole process will not be described again. 
         [0083]    As the cylinder  20  defines two operation chambers  22 ,  23  in the second embodiment, chronologically displaced cycles take place in the first (left) pair of heat exchangers  10 A and in the second (right) pair of heat exchangers  10 X, the cycles reinforcing each other. 
         [0084]    For example, piston  21  is pushed to the left during stroke  5  (isobaric evaporation) and  6  (isothermal expansion) of the right pair of heat exchangers  10 X. Accordingly, strokes  2  and  3  take place in the left pair of heat exchangers  10 A that pull or suck piston  21  to the left. 
         [0085]    By means of cooling the left condenser  11 A, the enclosed gaseous working medium is cooled to the lower temperature level, and the pressure inside the condenser  11 A maximally corresponds to the vapour pressure of the working medium at the temperature of the cooling medium. Likewise, the gaseous working medium enclosed in the right evaporator  12 X is heated by the continuing heating of the evaporator  12 X. 
         [0086]    Piston  21  is located at the right hand side. Valve  40 A located at condenser  11 A and valve  41 X located at the evaporator  12 X are opened at the same time. The lower pressure in the left evaporator  11 A and the higher pressure in the right condenser  12 X act upon the piston  21  via the respective conduits  24 A,  25 X. By means of the pressure difference that now exists on both sides of piston  21 , piston  21  is pushed leftwards. 
         [0087]    Once piston  21  reaches its end position on the left hand side, valves  40 A and  41 X are closed. 
         [0088]    Furthermore, respective cycle processes take place in the left and right pairs of heat exchangers  10 A,  10 X according to the above described sequence (see first embodiment). 
       Heat Engine According to Third Embodiment 
       [0089]      FIG. 4  shows a schematic representation of a third embodiment of a heat engine  200  according to the present invention. Similar to the second embodiment, cylinder  20  defines two operation chambers  22 ,  23 . In the third embodiment, the left operation chamber  22  is connected to three pairs of heat exchangers  10 X,  10 Y,  10 Z. The side of the cylinder  20  on which the pairs of heat exchangers  10 A,  10 B and  10 C are arranged is hereinafter referred to as “left side”, the side on which the pairs of heat exchangers  10 X,  10 Y and  10 Z are arranged is referred to as “right side”. 
         [0090]    Heat engine  200  according to the third embodiment is based on similar parts as heat engine  100 . Therefore, corresponding parts are labelled with the same reference numbers. For parts on the left side ( FIG. 4 ) of cylinder  20  reference numbers “A”, “B” or “C” are attached to the reference numbers (according to the respective pair of heat exchangers). For parts on the right side ( FIG. 4 ) of cylinder  20  reference numbers “X”, “Y” or “Z” are attached to the reference numbers. Furthermore, corresponding parts will not be described in detail. 
         [0091]    Heat engine  200  according to the third embodiment of the invention comprises six pairs of heat exchangers  10 A,  10 B,  10 C,  10 X,  10 Y,  10 Z, a cylinder  20 , six working medium transfer devices  30 A,  10 B,  30 C,  30 X,  30 Y,  30 Z and valves  40 A,  40 B,  40 C,  40 X,  40 Y,  40 Z,  41 A,  41 B,  41 C,  41 X,  41 Y,  41 Z. The pairs of heat exchangers  10 - 10 Z each consist of a first heat exchanger or condenser  11 A- 11 Z (hereinafter condenser) and a second heat exchanger or evaporator  12 A- 12 Z (hereinafter evaporator). As in the first embodiment, each condenser  11 A- 11 Z has a lower end part  13  and each evaporator  12 A- 12 Z has an upper end part  14 . 
         [0092]    It should be noted that it is generally possible to implement a heat engine having more or less pairs of heat exchangers. But the number of pairs of heat exchangers should be an even number. 
         [0093]    The upper end part  14  as well as the parts of the heat engine  200  described below may be insulated from the rest of the evaporator  12 A- 12 Z by insulation  15 , respectively. The insulation is made from a material that is suitable for the pressures and mechanical stresses but is a bad heat conductor at the same time. Insulation  15  is employed to minimize the heat transfer from the evaporators  12 A- 12 Z to the rest of the heat engine  200 . 
         [0094]    Each the condensers  11 A- 11 Z and the evaporators  12 A- 12 Z are shown as a tube  16  having fins  17 . But it should be noted that other types of heat exchangers may also be employed. Further it should be noted that, even though only one tube  16  is shown in the figures, each heat exchanger may comprise any number of tubes  16 . The pairs of heat exchangers  10 A- 10 Z may also have an appropriate design for a heat exchange by means of radiation. 
         [0095]    In evaporators  12 A- 12 Z, means for distributing the working medium over a large inner surface are arranged to allow for an improved heat transfer to the working medium. The distribution means may comprise e.g. metal wool, metal filament or threads, surface structures or heat transfer fins or other surface structures, which are arranged inside the evaporator. With fine surface structures the working medium is also distributed by means of capillary attraction which causes a better heat absorption from the wall of the evaporator  12 . 
         [0096]    The condensers  11 A- 11 Z are surrounded by a flowing cooling medium  18 . The cooling medium  18  may be gaseous or liquid. The evaporators  12 A- 12 Z are surrounded by a flowing heating medium  19  that may be gaseous or liquid as well. 
         [0097]    As in the first embodiment, the working medium transfer devices  30 A- 30 Z may be positioned in at least three positions. In the first position, the working medium transport chamber  31 A- 31 Z is connected to the respective condenser  11 A- 11 Z, but is disconnected from the evaporators  12 A- 12 Z. In the second position, the working medium transport chamber  31 A- 31 Z is disconnected from the condensers  11 A- 11 Z as well as from the evaporators  12 A- 12 Z. In the third position, the working medium transport chamber  31 A- 31 Z is connected to evaporator  12 A- 12 Z, but is disconnected from condenser  11 A- 11 Z. The working medium transfer device  30 A- 30 Z may comprise an electric, pneumatic, hydraulic or other drive that may be actuated according to the operation process described below in more detail. 
         [0098]    The heat engine  200  further comprises cylinder  20 , in which piston  21  is arranged. Similarly to the second embodiment cylinder  20  and piston  21  define two operation chambers  22 ,  23 . The operation chambers  22 ,  23  are located to the right and the left (in  FIG. 4 ) of piston  21 . 
         [0099]    In the third embodiment, the first operation chamber  22  is connected to pairs of heat exchangers  10 A,  10 B,  10 C (left group), and the second operation chamber  23  is connected to pairs of heat exchangers  10 X,  10 Y,  10 Z (right group). 
         [0100]    A conduit  24  runs from the operation chambers  22 ,  23  in direction of the evaporators  11 A- 11 Z of the right and left groups of pairs of heat exchangers respectively. Furthermore a conduit  25  runs from the operation chambers  22 ,  23  in direction of the evaporators  12 A- 12 Z of the right and left groups of pairs of heat exchangers, respectively. The condensers  11 A- 11 Z are connected to the respective left and right conduits  24  via junction conduits  24 A- 24 Z. The evaporators  12 A- 12 Z are connected to the respective left and right conduits  25  via junction conduits  25 A- 25 Z. The conduits  24 ,  25  are therefore designed as manifolds. 
         [0101]    In junction conduits  24 A- 24 Z, a valve  40 A- 40 Z is arranged respectively that is able to open or close the connection between the operation chamber  22 ,  23  and the corresponding condenser. In junction conduits  25 A- 25 Z, a valve  41 A- 41 Z is arranged that is able to open or close the connection between the operation chamber  22 ,  23  and the evaporator. Valves  40 A- 40 Z and  41 A- 41 Z may comprise an electric, pneumatic, hydraulic or other drive that may be activated by the operation process described below in more detail. 
         [0102]    Another alternative for connecting condensers  11 A- 11 Z and evaporators  12 A- 12 Z to the operation chambers  22 ,  23  is also contemplated: condenser  11 A- 11 Z may be connected to the respective operation chamber directly via a separate junction conduit  24 A- 24 Z. Similarly, the evaporators  12 A- 12 Z may be connected to the respective operation chamber directly via a separate junction conduit  25 A- 25 Z. Valves  40 A- 40 Z and  41 A- 41 Z would then be arranged directly in the junction conduits  24 A- 24 Z and  25 A- 25 Z, respectively. 
       Operation of Heat Engine According to Third Embodiment 
       [0103]      FIGS. 5   a  to  5   g  schematically show the cycle process of heat engine  200  of  FIG. 4  having six pairs of heat exchangers. It should be noted that an adapted operation sequence may also be executed by more or less pairs of heat exchangers. The number of pairs of heat exchangers should be an even number. During operation, a cooling medium flows around the condensers  11 A- 11 Z, while the evaporators  12 A- 12 Z experience a heat input by a heating medium at the same time. 
         [0104]    The operation of the third embodiment of the heat engine proceeds with the same changes of state of the working medium in the above described closed cycle process as in the preceding embodiments. Therefore in the following, the sequence of the switching operations of valves  40 A- 40 Z,  41 A- 41 Z and the working medium transfer devices  30 A- 30 Z will mainly be described. In order to avoid an unnecessary long description, the changes of state in each pair of heat exchangers  10 A- 10 Z will only be mentioned if such mentioning simplifies the description. 
         [0105]    The changes of state or strokes of the cycle process proceed in the following sequence: 
         [0000]    Stroke  1  ( FIG. 5   a ) 
         [0106]    Opening valves  40 A,  41 X, closing valves  40 B,  40 C,  40 X,  40 Y,  40 Z,  41 A,  41 B,  41 C,  41 Y,  41 Z, collecting condensed working medium in the working medium transfer devices  30 A,  30 B,  30 C,  30 X,  30 Z. 
         [0107]    The working medium is cooled by cooling the condenser at constant a volume in the condensers  11 B,  11 C,  11 X,  11 Y,  11 Z to the lower temperature level. The working medium is heated by heating the evaporators  12 A,  12 B,  12 C,  12 Y,  12 Z to the upper temperature level ( FIGS. 9-11 ). The working medium transport chambers  31 A,  31 B,  31 C,  31 X,  31 Z of the working medium transfer devices are connected to the respective condensers  11 A,  11 B,  11 C,  11 X,  11 Z. The pressure in the condensers maximally corresponds to the vapor pressure of the working medium at the temperature of the cooling medium. 
         [0108]    The piston  21  is located at the right hand side. The pressure in evaporator  12 X is directed to the right operation chamber  23 . The lower pressure generated by isochoric heat extraction in condenser  12 A is connected to the left operation chamber  22 . Due to the pressure difference that now exists on both sides of the piston, the piston is pushed to the left. 
         [0109]    While the piston  21  is moving, the condensate is transferred from the condenser  11 Y to the evaporator  12 Y via the working medium transfer device  31 Y. Once piston  21  has reached its end position on the left side, valves  40 A and  41 X are closed and stroke  1  is finished. 
         [0000]    Stroke  2  ( FIG. 5   b ) 
         [0110]    Opening valves  41 B,  40 Z, closing valves  40 A,  40 B,  40 C,  40 X,  40 Y,  41 A,  41 C,  41 Y,  41 Y,  41 Z, collecting the condensed working medium in the working medium transfer devices  30 B,  30 C,  30 X,  30 Y,  30 Z. 
         [0111]    The working medium is cooled by cooling of the condenser at constant volume in the condensers  11 A,  11 B,  11 C,  11 X,  11 Y to the lower temperature level. The working medium is heated by heating of the evaporators  12 A,  12 C,  12 X,  12 Y,  12 Z to the upper temperature level ( FIGS. 9-11 ). The working medium transport chambers  31 B,  31 C,  31 X,  31 Y,  31 Z of the working medium transfer devices are connected to the respective condensers  11 B,  11 C,  11 X,  11 Y,  11 Z. The pressure in the condensers maximally corresponds to the vapor pressure of the working medium at the temperature of the cooling medium. 
         [0112]    The piston  21  is located at the left hand side. The pressure in evaporator  12 B is directed to the left operation chamber  22 . The lower pressure generated by isochoric heat extraction in condenser  12 Z is connected to the right operation chamber  23 . Due to the pressure difference, which now exists on both sides of the piston, the piston is pushed to the right. 
         [0113]    While the piston  21  is moving, the condensate is transferred from the condenser  11 A to the evaporator  12 A via the working medium transfer device  31 A. Once piston  21  has reached its end position on the right side, valves  40 Z and  41 B are closed and stroke  2  is finished. 
         [0000]    Stroke  3  ( FIG. 5   c ) 
         [0114]    Opening valves  40 C,  41 Y, closing valves  40 A,  40 B,  40 X,  40 Y,  40 Z,  41 A,  41 B,  41 C,  41 X,  41 Z, collecting the condensed working medium in the working medium transfer devices  30 A,  30 B,  30 C,  30 X,  30 Y. 
         [0115]    The working medium is cooled by the cooling of the condenser at constant volume in the condensers  11 A,  11 B,  11 X,  11 Y,  11 Z to the lower temperature level. The working medium is heated by the heating of the evaporators  12 A,  12 B,  12 C,  12 X,  12 Z to the upper temperature level ( FIGS. 9-11 ). The working medium transport chambers  31 A,  31 B,  31 C,  31 X,  31 Y of the working medium transfer devices are connected to the respective condensers  11 A,  11 B,  11 C,  11 X,  11 Y. The pressure in the condensers maximally corresponds to the vapor pressure of the working medium at the temperature of the cooling medium. 
         [0116]    The piston  21  is located at the left hand side. The pressure in evaporator  12 Y is directed to the right operation chamber  23 . The lower pressure generated by isochoric heat extraction in condenser  12 C is connected to the left operation chamber  22 . Due to the pressure difference, which now exists on both sides of the piston, the piston is pushed to the left. 
         [0117]    While the piston  21  is moving, the condensate is transferred from the condenser  11 Z to the evaporator  12 Z via the working medium transfer device  31 Z. Once piston  21  has reached its end position on the left side, valves  40 C and  41 Y are closed and stroke  3  is finished. 
         [0000]    Stroke  4  ( FIG. 5   d ) 
         [0118]    Opening valves  40 X,  41 A, closing valves  40 A,  40 B,  40 C,  40 Y,  40 Z,  41 B,  41 C,  41 X,  41 Y,  41 Z, collecting the condensed working medium in the working medium transfer devices  30 A,  30 B,  30 X,  30 Y,  30 Z. 
         [0119]    The working medium is cooled by the cooling of the condenser at constant volume in the condensers  11 A,  11 B,  11 C,  11 Y,  11 Z to the lower temperature level. The working medium is heated by the heating of the evaporators  12 B,  12 C,  12 X,  12 Y,  12 Z to the upper temperature level ( FIGS. 9-11 ). The working medium transport chambers  31 A,  31 B,  31 X,  31 Y,  31 Z of the working medium transfer devices are connected to the respective condensers  11 A,  11 B,  11 X,  11 Y,  11 Z. The pressure in the condensers maximally corresponds to the vapor pressure of the working medium at the temperature of the cooling medium. 
         [0120]    The piston  21  is located at the left hand side. The pressure in evaporator  12 A is directed to the left operation chamber  22 . The lower pressure generated by isochoric heat extraction in condenser  12 X is connected to the right operation chamber  23 . Due to the pressure difference, which now exists on both sides of the piston, the piston is pushed to the right. 
         [0121]    While the piston  21  is moving, the condensate is transferred from the condenser  11 C to the evaporator  12 C via the working medium transfer device  31 C. Once piston  21  has reached its end position on the right side, valves  40 X and  41 A are closed and stroke  4  is finished. 
         [0000]    Stroke  5  ( FIG. 5   e ) 
         [0122]    Opening valves  40 B,  41 Z, closing valves  40 A,  40 C,  40 X,  40 Y,  40 Z,  41 A,  41 B,  41 C,  41 X,  41 Y, collecting the condensed working medium in the working medium transfer devices  30 A,  30 B,  30 C,  30 Y,  30 Z. 
         [0123]    The working medium is cooled by the cooling of the condenser at constant volume in the condensers  11 A,  11 C,  11 X,  11 Y,  11 Z to the lower temperature level. The working medium is heated by the heating of the evaporators  12 A,  12 B,  12 C,  12 X,  12 Y to the upper temperature level ( FIGS. 9-11 ). The working medium transport chambers  31 A,  31 B,  31 C,  31 Y,  31 Z of the working medium transfer devices are connected to the respective condensers  11 A,  11 B,  11 C,  11 Y,  11 Z. The pressure in the condensers maximally corresponds to the vapor pressure of the working medium at the temperature of the cooling medium. 
         [0124]    The piston  21  is located at the right hand side. The pressure in evaporator  12 Z is directed to the right operation chamber  23 . The lower pressure generated by isochoric heat extraction in condenser  12 B is connected to the left operation chamber  22 . Due to the pressure difference, which now exists on both sides of the piston, the piston is pushed to the right. 
         [0125]    While the piston  21  is moving, the condensate is transferred from the condenser  11 X to the evaporator  12 X via the working medium transfer device  31 X. Once piston  21  has reached its end position on the left side, valves  40 B and  41 Z are closed and stroke  5  is finished. 
         [0000]    Stroke  6  ( FIG. 5   f ) 
         [0126]    Opening valves  40 Y,  41 C, closing valves  40 A,  40 B,  40 C,  40 X,  40 Z,  41 A,  41 B,  41 X,  41 Y,  41 Z, collecting the condensed working medium in the working medium transfer devices  30 A,  30 C,  30 X,  30 Y,  30 Z. 
         [0127]    The working medium is cooled by the cooling of the condenser at constant volume in the condensers  11 A,  11 B,  11 C,  11 X,  11 Z to the lower temperature level. The working medium is heated by the heating of the evaporators  12 A,  12 B,  12 X,  12 Y,  12 Z to the upper temperature level ( FIGS. 9-11 ). The working medium transport chambers  31 A,  31 C,  31 X,  31 Y,  31 Z of the working medium transfer devices are connected to the respective condensers  11 A,  11 C,  11 X,  11 Y,  11 Z. The pressure in the condensers maximally corresponds to the vapor pressure of the working medium at the temperature of the cooling medium. 
         [0128]    The piston  21  is located at the left hand side. The pressure in evaporator  12 C is directed to the left operation chamber  22 . The lower pressure generated by isochoric heat extraction in condenser  12 Y is connected to the right operation chamber  23 . Due to the pressure difference, which now exists on both sides of the piston, the piston is pushed to the right. 
         [0129]    While the piston  21  is moving, the condensate is transferred from the condenser  11 B to the evaporator  12 B via the working medium transfer device  31 B. Once piston  21  has reached its end position on the right side, valves  40 Y and  41 CA are closed and stroke  6  is finished. 
         [0130]    Thereafter, strokes  1  to  6  are executed again. 
       Heat Engine According to Fourth Embodiment 
       [0131]      FIG. 6  shows a schematic representation of a fourth embodiment of a heat engine  300  according to the present invention. Contrary to the third embodiment, a rotary piston engine is provided instead of cylinder  20 . 
         [0132]    The body  50  of the rotary piston engine and the triangular rotor  51  define three operation chambers. Due to the odd number of operation chambers, the distribution of the chambers with respect to the connections of the respective conduits is changing. Thus, two operation chambers  22 ,  23  are defined, wherein one of the operation chambers is divided in two separate chambers. The divided operation chamber is denoted with suffixes “a” and “b”. The operation chambers are therefore chambers  23 ,  22   a  and  22   b  or the operation chambers are chambers  22 ,  23   a  and  23   b . In  FIG. 6  the “top” operation chamber is denoted  22  and the “bottom” operation chamber is denoted  23 . 
         [0133]    In the fourth embodiment the top operation chamber  22  is connected to the condenser  11 A and the evaporator  12 X. The bottom operation chamber  23   b  is connected to the condenser  11 X, and the operation chamber  23   a  is connected to the evaporator  12 A. 
         [0134]    The rest of heat engine  300  according to the fourth embodiment is formed of similar parts as heat engine  200 . Therefore, the same reference numbers will be used for corresponding parts. For the parts on the left side (of  FIG. 6 ) of the rotary piston engine  50 , “A” is added to the reference number, and for the parts on the right side (of  FIG. 6 ) of cylinder  20  accordingly “X” is added to the reference number. Furthermore, corresponding parts will not be described in detail. 
         [0135]    Heat engine  300  according to the fourth embodiment of the invention comprises two pairs of heat exchangers  10 A and  10 X, a rotary piston engine  50 , two working medium transfer devices  30 A and  30 X and four valves  40 A,  40 X,  41 A and  41 X. The pairs of heat exchangers  10 A and  10 X each consist of a first heat exchanger or condenser  11 A and  11 X (hereinafter condenser) and a second heat exchanger or evaporator  12 A and  12 X (hereinafter evaporator), respectively. As in the first embodiment each condenser  11 A,  11 X comprises a lower end part  13 , and each evaporator  12 A,  12 X comprises an upper end part  14 . 
         [0136]    The upper end part  14  of each evaporator as well as the parts of heat engine  300  described below may be insulated from the rest of the evaporators  12 A- 12 X by insulation  14 A and  14 X, respectively. The insulation is made from a material that is suitable for the pressures and mechanical stresses but is a bad heat conductor at the same time. Insulation  14 A,  14 X is employed to minimize the heat transfer from the evaporators  12 A,  12 X to the rest of heat engine  300 . 
         [0137]    The condensers  11 A and  11 X and the evaporators  12 A and  12 X are each shown as tube  16  having fins  17 . It should be noted that other types of heat exchangers may also be employed. Further, it should be noted that, even though only one tube  16  is shown in the figures, each heat exchanger may comprise any number of tubes  16 . The pairs of heat exchangers  10 A and  10 X may also have an appropriate design for a heat exchange by means of radiation. 
         [0138]    In evaporators  12 A and  12 X, means for distributing the working medium over a large inner surface are arranged to allow for an improved heat transfer to the working medium. The distribution means may comprise e.g. metal wool, metal filament or threads, surface structures or heat transfer fins or other surface structures, that are arranged inside the evaporator and which, by means of capillary attraction, distribute the liquid working medium uniformly over the inner surface. 
         [0139]    The condensers  11 A and  11 X are surrounded by a flowing cooling medium  18 . The cooling medium  18  may be gaseous or liquid. The evaporators  12 A and  12 X are surrounded by a flowing heating medium  19  that may be gaseous or liquid as well. The heating medium  19  may also be gaseous or liquid. Each the lower end parts  13  of the condensers  11 A and  11 X and the upper end parts  14  of the evaporators  12 A and  12 X are connected by means of a working medium transfer device  30 A and  30 X. The respective working medium transfer devices  30 A and  30 X comprise at least one working medium transport chamber  31  that may selectively be connected to the respective evaporator  12 A and  12 X and the respective condenser  11 A and  11 X. 
         [0140]    As in the previously described embodiments the working medium transfer devices  30 A and  30 X can take at least three positions. In the first position, the working medium transport chamber  31  is connected to the lower end part  13  of the condenser. In the second position, the working medium transport chamber  31  is disconnected from the condenser as well as the evaporator. In the third position, the working medium transport chamber  31  is connected to the upper end part  14  of the evaporator. The working medium transfer device  30 A and  30 X may comprise an electric, pneumatic, hydraulic or other drive that may be actuated according to the operation process described below in more detail. 
       Operation of the Heat Engine According to the Fourth Embodiment 
       [0141]    The operation of heat engine  300  according to the fourth embodiment differs from that of the previously described embodiments. Therefore the process is described in more detail. 
         [0142]    As the rotary piston engine defines the three operation chambers  23 ,  22   a  and  22   b  or  22 ,  23   a  and  23   b  in the fourth embodiment, chronologically displaced cycle processes take place in the first (left) pair of heat exchangers  10 A and in the second (right) pair of heat exchangers  10 X which reinforce each other. 
         [0143]      FIG. 6  is taken as a starting point for the following description. The rotary piston is located in such a way that one of the triangle corners  51 A points vertically downwards, whereas the corners  51 B (right) and  51 C (left) are situated at the connection ports of the conduits  25 X (right) and  24 A (left). 
         [0144]    In the present illustration of  FIG. 6 , the rotary piston  51  is pushed counter-clockwise to the right due to the eccentricity of the drive shaft  53  during stroke  5  (isobaric evaporation) and  6  (isothermal expansion) of the left evaporator  12 A which generate a high pressure in the operation chamber  23   a . Correspondingly, strokes  2  (isothermal compression) and  3  (isobaric condensation) take place in the right condenser  11 X, which generate a low pressure in the operation chamber  23   b  and pull the rotary piston  51  counter-clockwise to the right. 
         [0145]    In a further counter-clockwise rotation away from the position shown in  FIG. 6 , the connections of the conduits  24 X and  25 X are connected by the same operation chamber. Valve  41 X is closed at that time until the next corner of the rotary piston  51 A separates these two connections into two different operation chambers. Immediately after the rotary piston tip  51 A has passed over the connection of the conduit  24 X on the right side (of  FIG. 6 ) valve  40 X closes, so that no overflow takes place between the connection ports of the conduits  40 X and  41 X and therefore between the condenser  11 X and the evaporator  12 X during the subsequent opening of a common operation chamber. 
         [0146]    On the left side of the rotary piston engine, the piston tip  51 C moves away from the connection of conduit  24 A towards the connection port of conduit  25 A. Valve  41 A closes before the piston tip runs over the connection port of conduit  25 A in order to prevent the emerging common operation chamber from generating a short-circuit or overflow between condenser  11 A and evaporator  12 A. 
         [0147]    Due to the cooling of the left condenser  11 A, the enclosed gaseous working medium is cooled to the lower temperature level. The pressure within condenser  11 A corresponds maximally to the vapour pressure of the working medium at the temperature of the cooling medium. In the same way the gaseous working medium enclosed in the right evaporator  12 X is heated up by the continued heating of evaporator  12 X. 
         [0148]    Now the piston  51  cooperating with corner  51 B defines two operation chambers  22   a  and  22   b  (besides a third operation chamber  23 ). At the same time the connection of condenser  11 A is located in the left chamber  22   b , and the connection of evaporator  12 X is located in the right chamber  22   a . Valve  40 A at condenser  11 A and valve  41 X at evaporator  12 X are closed. 
         [0149]    The low pressure in the left condenser  11 A and the high pressure in the right evaporator  12 X act upon the rotary piston  51  that is now eccentrically supported to the top via the respective conduits  24 A,  25 X. By means of the pressure difference that is now present in the operation chambers  22   a  and  22   b , the rotary piston  51  is further rotated counter-clockwise. During this sequence the valves  41 A and  40 X remain closed. 
         [0150]    Before the rotary piston corner  51 B crosses over the connection of the conduit  24 A, valves  40 A and  41 X are closed. 
         [0151]    Now the rotary piston defines two operation chambers  23   a  and  23   b  at the bottom of  FIG. 6 . As soon as the corner  51 B has passed the connection port of conduit  24 A, valves  41 A and  40 X are opened and the sequence is repeated, wherein corner  51  is located at the bottom. 
       Heat Engine According to Fifth Embodiment 
       [0152]      FIG. 7  shows a schematic representation of a fifth embodiment of a heat engine  400  according to the present invention. As in the fourth embodiment the drive system is a rotary piston engine  50 . But contrary to the fourth embodiment the top operation chamber  22  is connected to multiple condensers  11 A,  11 B and  11 C as well as multiple evaporators  12 X,  12 Y and  12 Z and the bottom operation chamber  23  is connected to the condensers  11 X,  11 Y and  11 Z as well as the evaporators  12 A,  12 B and  12 C. 
         [0153]    The rest of heat engine  400  according to the fifth embodiment is constructed of similar parts as heat engine  300 . Therefore, corresponding parts are denoted by the same reference numbers. For parts on the left side ( FIG. 6 ) of the rotary piston engine  50 , “A”, “B” or “C” are added to the reference numbers (corresponding to pair of heat exchangers), and for parts on the right side ( FIG. 6 ) of the rotary piston engine, “X”, “Y” and “Z” are added to the reference numbers. Furthermore, corresponding parts are not described in detail. 
         [0154]    Heat engine  400  according to the fourth embodiment of the invention comprises six pairs of heat exchangers  10 A,  10 B,  10 C,  10 X,  10 Y,  10 Z, a rotary piston engine  50 , six working medium transfer devices  30 A,  30 B,  30 C,  30 X,  30 Y,  30 Z and twelve valves  40 A,  40 B,  40 C,  40 X,  40 Y,  40 Z,  41 A,  41 B,  41 C,  41 X,  41 Y,  41 Z. Pairs of heat exchangers  10 A- 10 Z each consist of a first heat exchanger or condenser  11 A- 11 Z (hereinafter condenser) and a second heat exchanger or evaporator  12 A- 12 Z (hereinafter evaporator). As in the first embodiment, each condenser  11 A- 11 Z has a lower end part  13  and each evaporator  12 A- 12 Z has an upper end part  14 . 
         [0155]    The upper end part  14  of each heat exchanger as well as the parts of the heat engine  400  described below may be insulated from the rest of evaporators  12 A- 12 Z by insulation  15 . The insulation is made from a material that is suitable for the pressures and the mechanical stress but is a bad heat conductor. Insulation  15  is employed to minimize the heat conduction from evaporators  12 A- 12 Z to the rest of heat engine  400 . 
         [0156]    Both condensers  11 A- 11 Z and evaporators  12 A- 12 Z are shown as tube  16  having fins  17 . It should be noted that other types of heat exchangers may also be employed. Further, it should be noted that, even though only one tube  16  is shown in the figures, each heat exchanger may comprise any number of tubes  16 . Pairs of heat exchangers  10 A- 10 Z may also have an appropriate design for a heat exchange by means of radiation. 
         [0157]    In evaporators  12 A- 12 Z, means for distributing the working medium over a large surface are arranged to allow for an improved heat transfer to the working medium. 
         [0158]    Condensers  11 A- 11 Z are surrounded by a flowing cooling medium  18 . The cooling medium  18  may be gaseous or liquid. Evaporators  12 A- 12 Z are surrounded by a flowing heating medium  19 . The heating medium  19  may be gaseous or liquid as well. Each the lower end part  13  of condenser  11 A- 11 Z and the upper end part  14  of evaporator  12 A- 12 Z are connected to a working medium transfer device  30 A- 30 Z. The respective working medium transfer device  30 A- 30 Z comprises at least one working medium transport chamber  31  that may selectively be connected to the respective evaporator  12 A- 12 Z and the respective condenser  11 A- 11 Z. 
         [0159]    As in the previously described embodiments, the working medium transfer devices  30 A- 30 Z may be positioned in at least three positions. In the first position, the working medium transport chamber  31  is connected to the lower end part  13  of the condenser. In the second position, the working medium transport chamber  31  is disconnected from condensers  11 A- 11 Z as well as from the evaporator. In the third position, the working medium transport chamber  31  is connected to the upper end part  14  of evaporator  12 A- 12 Z. The working medium transfer device  30 A- 30 Z may comprise an electric, pneumatic, hydraulic or other drive that may be actuated dependent on time according to the operation process described below in more detail. 
       Operation of the Heat Engine According to the Fifth Embodiment 
       [0160]    The operation of the heat engine according to the fifth embodiment is schematically shown in  FIG. 8   a - 8   f.    
         [0000]    Stroke  1  ( FIG. 8   a ) 
         [0161]    Due to the cooling of condenser  11 A, the enclosed working gas is cooled to the lower temperature level, and the pressure within condenser  11 A corresponds maximally to the vapour pressure of the working medium at the temperature of the cooling medium. The working medium enclosed in evaporator  12 X is also sufficiently heated up due to the continuous heating of evaporator  12 X. 
         [0162]    The rotary piston  51  is arranged as illustrated in  FIG. 8   a  with corner  51 A being directed upwards. Valve  40 A at condenser  11 A and valve  41 X at evaporator  12 X are opened. The pressures in condenser  11 A and in evaporator  12 X proceed in the respective conduits  24  and  24 A as well as  25  and  25 X to the operation chambers  22   a  and  22   b . Due to the pressure difference between operation chamber  22   a  and operation chamber  22   b  on both sides of the eccentric part of rotary piston  51 , the rotary piston is rotated counter-clockwise. 
         [0163]    While the rotary piston is rotating, the condensate is transferred from condenser  11 Y to evaporator  12 Y via the working medium transfer device  30 Y. As soon as corner  51 A of rotary piston  51  reaches the connection of conduit  24  on the left side, valves  40 A and  41 X are closed and stroke  1  is finished. 
         [0000]    Stroke  2  ( FIG. 8   b ) 
         [0164]    In the meantime the working medium in evaporator  12 B is sufficiently heated, and the working medium in condenser  11 Z is sufficiently cooled. Valves  41 B at evaporator  12 B and  40 Z at condenser  11 Z are opened at the same time, as soon as corner  51 A has crossed the connection port of conduit  24  on the left side and corner  51 C has passed the connection port of conduit  25  on the right side. The pressures within the condenser and within the evaporator continue in the respective conduits  25 B and  24 Z to the working cylinder  20 . Due to the pressure difference, which now prevails between operation chambers  23   a  and  23   b  on both sides of the rotary piston  51 , the rotary piston is further rotated counter-clockwise. 
         [0165]    As the rotary piston rotates further, the condensate is transferred from condenser  11 A to evaporator  12 A by the working medium transfer device  30 A. As soon as corner  51 B of rotary piston  51  reaches the connection of conduit  24  on the right side, valves  41 B and  40 Z are closed and stroke  2  is finished. 
         [0000]    Stroke  3  ( FIG. 8   c ) 
         [0166]    In the same way as described for stroke  1 , the rotary piston  51  is rotated further counter-clockwise in stroke  3  by means of the action of the pressures from the evaporator  12 Y and the condenser  11 C and the resulting pressure difference therefrom, while the liquid condensed working medium is transferred from condenser  11 Z into evaporator  12 Z. 
         [0000]    Stroke  4  ( FIG. 8   d ) 
         [0167]    As described in stroke  2  the rotary piston  51  is rotated further counter-clockwise in stroke  4  by means of the action of the pressure from evaporator  12 A and condenser  11 X and the resulting pressure difference that now occurs between the operation chambers  23   a  and  23   b  on both sides of rotary piston  51 , while the liquid condensed working medium is transferred from condenser  11 C into evaporator  12 C. 
         [0000]    Stroke  5  ( FIG. 8   e ) 
         [0168]    In the same way as described for stroke  1 , the rotary piston  51  is rotated further counter-clockwise in stroke  5  by means of the action of the pressure from evaporator  12 Z and condenser  11 B and the resulting pressure difference that now occurs between  22   a  and  22   b  on both sides of the rotary piston  51 , while the liquid condensed working medium is transferred from condenser  11 X into evaporator  12 X. 
         [0000]    Stroke  6  ( FIG. 8   f ) 
         [0169]    As described for stroke  2 , the rotary piston  51  is rotated further counter-clockwise in stroke  6  by means of the action of the pressure from evaporator  12 C and condenser  11 Y and the resulting pressure difference that now occurs between  23   a  and  23   b  on both sides of the rotary piston  51 , while the liquid condensed working medium is transferred from condenser  11 B into evaporator  12 B. 
         [0170]    After stroke  6  the process restarts again with stroke  1 . 
         [0171]    Again, it should be noted that, although six pairs of heat exchangers  10  were described in some embodiments, an arbitrary number of heat exchangers may be employed. Nevertheless, the number of pairs of heat exchangers on the left side has to correspond to the number on the right side. 
         [0172]    It generally applies to all embodiments of the heat engine that a fast evaporation of the condensate introduced into an evaporator is advantageous to increase the output and to reduce the stroke or cycle times. The distribution means comprise metallic wool, metal threads, surface structures or heat transfer fins that are arranged inside the evaporator. Furthermore, it is considered to inject the condensate into the evaporator. 
         [0173]    In all shown embodiments, heat engine  1 ,  100 ,  200 ,  300 ,  400  may drive a machine. In cooperation with a linear generator, the movement and work of the piston may be converted directly into electricity. The piston movement is alternatively transmitted by a drive rod on a crank shaft having fly wheel (both not shown) so that the performed work is delivered by the rotating crank shaft. In a design of heat engine  300 ,  400  having a rotary piston engine, the work may be converted into electricity by a conventional (rotating) generator. 
         [0174]    As the utilization of heat by a single heat engine is limited by the obtainable temperature decrease with heat exchangers  10 , it is contemplated that an arbitrary number of heat engines are connected in series. The heating medium flows through each heat engine in a cascade manner. In a similar way the cooling medium flows through the heat engine as well, but flows in an opposite direction and in a reversed order to the heating medium. 
         [0175]    The temperature of the heating medium decreases with every passed heat engine. The temperature of the cooling medium increases with every passed heat engine. Due to the counter flow principle the temperature difference between the heating and the cooling medium remains more or less constant. 
         [0176]    In each heat engine connected in series, different working media are employed that are adjusted to the respective temperature level. 
         [0177]    Alternatively, several heat engines through which a hot medium flows in series may each be passed by a cooling medium with the same temperature. 
         [0178]    In the present invention, the pairs of heat exchangers  10  are stationary and do not rotate around the working engine as described in publication DE 10 2005 013287. Condensers  11  are arranged at the top and evaporators  12  at the bottom. Condenser  11  and evaporator  12  may be steadily circumflowed by the heating or cooling medium. 
         [0179]    Contrary to the heat engine described in publication DE 10 2005 013287, the internal space of the condenser and the evaporator of a pair of heat exchangers  10  are never connected to each other. For this reason a separate valve  40  and  41  respectively is necessary for each condenser  11  and evaporator  12 . The internal space of the condenser  11  and the evaporator  12  are separated by the working medium transfer device  30 , wherein the working medium transfer device  30  transports the condensed working medium from the condenser  11  into the evaporator  12 , without a pressure equalization taking place between condenser  11  and evaporator  12 . 
         [0180]    In this invention, a rotary piston engine or another rotary machine may be employed in lieu of a cylinder with a piston, in which each change of state of the working medium acts directly upon the rotary piston. 
         [0181]    The invention was described with respect to preferred embodiments. Those skilled in the art will gather that numerous modifications and designs are possible without departing from the spirit of the invention.