Patent Publication Number: US-2021164707-A1

Title: Mechanical device and operating method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority of Taiwanese Patent Application No. 108143930, filed on Dec. 2, 2019. 
     FIELD 
     The disclosure relates to a mechanical device, and more particularly to a mechanical device, which is approximate to a Carnot heat engine or heat pump, and an operating method thereof. 
     BACKGROUND 
     The Carnot cycle is a theoretical thermodynamic cycle working between two constant-temperature heat reservoirs (i.e., hot and cold reservoirs), and consists of two reversible isothermal processes and two reversible adiabatic (or isentropic) processes. A Carnot heat engine (or heat pump) that operates on the Carnot cycle (or reversed Carnot cycle) provides an upper limit on the efficiency of real thermodynamic engines. However, in reality, there are few thermodynamic engines efficient enough to approximate to the Carnot heat engine. 
     SUMMARY 
     Therefore, the object of the disclosure is to provide a mechanical device and an operating method thereof that can approximate to a Carnot heat engine. 
     According to a first aspect of the disclosure, a mechanical device includes a working medium, a hot end, a cold end, a first volume regulating unit and a second volume regulating unit. 
     The working medium is configured to circulate along a circulation path. The hot end is in thermal contact with the working medium during the circulation thereof. The cold end is in thermal contact with the working medium during the circulation thereof. A temperature of the cold end is lower than a temperature of the hot end. 
     The first volume regulating unit is disposed between the hot and cold ends, and is configured to allow passage of the working medium therethrough to perform one of compression and expansion of the working medium during the circulation thereof. 
     The second volume regulating unit is disposed between the hot and cold ends, and is configured to allow passage of the working medium therethrough to perform the other one of compression and expansion of the working medium during the circulation thereof. 
     During a cycle of circulation of the working medium, a volume of the working medium exiting the first volume regulating unit differs from a volume of the working medium entering the second volume regulating unit, and a volume of the working medium entering the first volume regulating unit differs from a volume of the working medium exiting the second volume regulating unit. 
     According to a second aspect of the disclosure, an operating method for a mechanical device includes the following steps: 
     (a) operating a first volume regulating unit for moving a first volume of a working medium from the first volume regulating unit into thermal contact with a hot end, and simultaneously operating a second volume regulating unit for moving a second volume of the working medium from the hot end into the second volume regulating unit, such that a second volume is greater than the first volume, so as to expand the working medium during thermal contact with the hot end for heat exchange; 
     (b) operating the second volume regulating unit for expanding the working medium in the second volume regulating unit; 
     (c) operating the second volume regulating unit for moving a third volume of the working medium from the second volume regulating unit into thermal contact with a cold end, and simultaneously operating the first volume regulating for moving a fourth volume of the working medium from the cold end into the first volume regulating unit, such that the fourth volume is smaller than the third volume, so as to compress the working medium during thermal contact with the cold end for heat exchange; and 
     (d) operating a first volume regulating unit for compressing the working medium in the first volume regulating unit. 
     According to a third aspect of the disclosure, an operating method for a mechanical device includes the following steps: 
     (a) operating a second volume regulating unit for compressing a working medium in the second volume regulating unit; 
     (b) operating the second volume regulating unit for moving a first volume of the working medium from the second volume regulating unit into thermal contact with a hot end, and simultaneously operating a first volume regulating unit for moving a second volume of the working medium from the hot end into the first volume regulating unit, such that the second volume is smaller than the first volume, so as to compress the working medium during thermal contact with the hot end for heat exchange; 
     (c) operating the first volume regulating unit for expanding the working medium in the first volume regulating unit; and 
     (d) operating the first volume regulating unit for moving a third volume of the working medium from the first volume regulating unit into thermal contact with a cold end, and simultaneously operating the second volume regulating unit for moving a fourth volume of the working medium from the cold end into the second volume regulating unit, such that the fourth volume is greater than the third volume, so as to expand the working medium during thermal contact with the cold end for heat exchange. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the disclosure will become apparent in the following detailed description of the embodiments with reference to the accompanying drawings, of which: 
         FIG. 1  is a schematic diagram of a first embodiment of a mechanical device according to the disclosure, illustrating relationships between a hot end, a cold end, a first volume regulating unit, a second volume regulating unit and a transmission unit; 
         FIG. 2  is a schematic diagram illustrating a step of near-isothermal expansion of an operating method for the first embodiment; 
         FIG. 3  is a schematic diagram of the first embodiment illustrating a first controller that controls a first outer tube valve, a second outer tube valve, a first inner tube valve, and a second inner tube valve, and a second controller that controls a third outer tube valve, a fourth outer tube valve, a third inner tube valve and a fourth inner tube valve; 
         FIG. 4  is a schematic diagram illustrating the first embodiment being operated on a cycle approximating to the Carnot cycle; 
         FIG. 5  is a schematic diagram illustrating a step of near-adiabatic expansion of the operating method for the first embodiment; 
         FIG. 6  is a schematic diagram illustrating a step of near-isothermal compression of the operating method for the first embodiment; 
         FIG. 7  is a schematic diagram illustrating a step of near-adiabatic compression of the operating method for the first embodiment; 
         FIG. 8  is a schematic diagram illustrating the first embodiment being operated on a cycle approximating to the reversed Carnot cycle; 
         FIG. 9  is another schematic diagram illustrating the first embodiment being operated on the cycle approximating to the reversed Carnot cycle; 
         FIG. 10  is a schematic diagram illustrating a step of near-adiabatic compression of the operating method for the first embodiment; 
         FIG. 11  is a schematic diagram illustrating a step of near-isothermal compression of the operating method for the first embodiment; 
         FIG. 12  is a schematic diagram illustrating a step of near-adiabatic expansion of the operating method for the first embodiment; 
         FIG. 13  is a a schematic diagram illustrating a step of near-isothermal expansion of the operating method for the first embodiment; 
         FIG. 14  is a perspective view of a second embodiment of the mechanical device according to the disclosure; 
         FIG. 15  is an exploded perspective view of the second embodiment; 
         FIG. 16  is another exploded perspective view of the second embodiment; 
         FIG. 17  is a sectional view taken along line XVII-XVII in  FIG. 14 ; 
         FIG. 18  is a sectional view taken along line XVIII-XVIII in  FIG. 14 ; 
         FIG. 19  is a sectional view taken along line XIX-XIX in  FIG. 14 ; 
         FIG. 20  is a fragmentary sectional view taken along line XX-XX in  FIG. 14 ; and 
         FIG. 21  is a schematic diagram of a third embodiment of the mechanical device according to the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Before the present disclosure is described in greater detail, it should be noted that where considered appropriate, reference numerals or terminal portions of reference numerals have been repeated among the figures to indicate corresponding or analogous elements, which may optionally have similar characteristics. 
     Referring to  FIGS. 1 and 2 , a first embodiment of a mechanical device  100  according to the disclosure is an external combustion engine that operates on a closed cycle. The mechanical device  100  includes a working medium (not shown), a hot end  1 , a cold end  2 , a first volume regulating unit  3 , a second volume regulating unit  5  and a transmission unit  7 . 
     The working medium is configured to circulate along a circulation path. Under operational condition, the working medium is a compressible fluid. In the present embodiment, the circulation path is a closed path, and the working medium is a gas including, but not limited to, air, helium, argon, nitrogen, or carbon dioxide. 
     The hot end  1  and the cold end  2  are in thermal contact with the working medium during the circulation thereof along the circulation path. In the present embodiment, the hot end  1  is a high-temperature heat reservoir, and is heated by an external heat source (not shown) to maintain its temperature (e.g., 400° C.). The cold end is a low-temperature heat reservoir, and the temperature of the cold end  2  (e.g., room temperature) is lower than the temperature of the hot end  1 . 
     Referring to  FIGS. 2 and 3 , the first volume regulating unit  3  is disposed between the hot end  1  and cold end  2 , and is configured to allow passage of the working medium therethrough to perform one of compression and expansion of the working medium during the circulation thereof. 
     The first volume regulation unit  3  includes a first cylinder  31 , a first piston unit  32 , a first outer tube  33 , a second outer tube  34 , a first inner tube  35 , a second inner tube  36  and a first controller  37 . 
     The first piston unit  32  is movably disposed in the first cylinder  31 , and divides an inner space of the first cylinder  31  into a first outer chamber  311  and a first inner chamber  312 . The first piston unit  32  extends through the first inner chamber  312  out of the first cylinder  31 . Two of the first outer, second outer, first inner and second inner tubes  33 ,  34 ,  35 ,  36  communicate fluidly one of the first outer and first inner chambers  311 ,  312  with the hot and cold ends  1 ,  2 , and the other two thereof communicate fluidly the other one of the first outer and first inner chambers  311 ,  312  with the hot and cold ends  1 ,  2 . In this embodiment, the first and second outer tubes  33 ,  34  communicate fluidly the first inner chamber  311  with the hot and cold ends  1 ,  2 , respectively, and the first and second inner tubes  35 ,  36  communicate fluidly the second inner chamber  312  with the hot and cold ends  1 ,  2 , respectively. 
     Specifically, the first outer tube  33  includes a first outer tube body  331  and a first outer tube valve  332 . The first outer tube body  331  intercommunicates fluidly the first outer chamber  311  with the hot end  1  to allow the working medium to flow therebetween. The first outer tube valve  332  is mounted to the first outer tube body  331  and is operable to open or close the first outer tube body  331 . 
     The second outer tube  34  includes a second outer tube body  341  and a second outer tube valve  342 . The second outer tube body  341  intercommunicates fluidly the first outer chamber  311  with the cold end  2  to allow the working medium to flow therebetween. The second outer tube valve  342  is mounted to the second outer tube body  341  and is operable to open or close the second outer tube body  341 . 
     The first inner tube  35  includes a first inner tube body  351  and a first inner tube valve  352 . The first inner tube body  351  intercommunicates fluidly the first inner chamber  312  with the hot end  1  to allow the working medium to flow therebetween. The first inner tube valve  352  is mounted to the first inner tube body  351  and is operable to open or close the first inner tube body  351 . 
     The second inner tube  36  includes a second inner tube body  361  and a second inner tube valve  362 . The second inner tube body  361  intercommunicates fluidly the first inner chamber  312  with the cold end  2  to allow the working medium to flow therebetween. The second inner tube valve  362  is mounted to the second inner tube body  361  and is operable to open or close the second inner tube body  361 . 
     The first controller  37  is a programmable logic controller (PLC) in the present embodiment, and is operable to control the first outer, second outer, first inner and second inner tube valves  332 ,  342 ,  352 ,  362  so as to open or close the first outer, second outer, first inner and second inner tube bodies  331 ,  341 ,  351 ,  361 . 
     The second volume regulating unit  5  is disposed between the hot end  1  and cold end  2 , and is configured to allow passage of the working medium therethrough to perform the other one of compression and expansion of the working medium during the circulation thereof. 
     The second volume regulating unit  5  includes a second cylinder  51 , a second piston unit  52 , a third outer tube  53 , a fourth outer tube  54 , a third inner tube  55 , a fourth inner tube  56  and a second controller  57 . 
     The volume of the second cylinder  51  is greater than that of the first cylinder  31 , and the cross sectional area of the second cylinder  51  is also greater than that of the first cylinder  31 . 
     The second piston unit  52  is movably disposed in the second cylinder  51 , and divides an inner space of the second cylinder  51  into a second outer chamber  511  and a second inner chamber  512 . The second piston unit  52  extends through the second inner chamber  512  out of the second cylinder  51 . Two of the third outer, fourth outer, third inner and fourth inner tubes  53 ,  54 ,  55 ,  56  communicate fluidly one of the second outer and second inner chambers  511 ,  512  with the hot and cold ends  1 ,  2 , and the other two thereof communicate fluidly the other one of the second outer and second inner chambers  511 ,  512  with the hot and cold ends  1 ,  2 . In this embodiment, the third and fourth outer tubes  53 ,  54  communicate fluidly the second outer chamber  511  with the hot and cold ends  1 ,  2 , respectively, and the third and fourth inner tubes  55 ,  56  communicate fluidly the second inner chamber  512  with the hot and cold ends  1 ,  2 , respectively. 
     Specifically, the third outer tube  53  includes a third outer tube body  531  and a third outer tube valve  532 . The third outer tube body  531  intercommunicates fluidly the second outer chamber  511  with the hot end  1  to allow the working medium to flow therebetween. The third outer tube valve  532  is mounted to the third outer tube body  531  and is operable to open or close the third outer tube body  531 . 
     The fourth outer tube  54  includes a fourth outer tube body  541  and a fourth outer tube valve  542 . The fourth outer tube body  541  intercommunicates fluidly the second outer chamber  511  with the cold end  2  to allow the working medium to flow therebetween. The fourth outer tube valve  542  is mounted to the fourth outer tube body  541  and is operable to open or close the fourth outer tube body  541 . 
     The third inner tube  55  includes a third inner tube body  551  and a third inner tube valve  552 . The third inner tube body  551  intercommunicates fluidly the second inner chamber  512  with the hot end  1  to allow the working medium to flow therebetween. The third inner tube valve  552  is mounted to the third inner tube body  551  and is operable to open or close the third inner tube body  551 . 
     The fourth inner tube  56  includes a fourth inner tube body  561  and a fourth inner tube valve  562 . The fourth inner tube body  561  intercommunicates fluidly the second inner chamber  512  with the cold end  2  to allow the working medium to flow therebetween. The fourth inner tube valve  562  is mounted to the fourth inner tube body  561  and is operable to open or close the fourth inner tube body  561 . 
     The second controller  57  is a programmable logic controller (PLC) in the present embodiment, and is operable to control the third outer, fourth outer, third inner and fourth inner tube valves  532 ,  542 ,  552 ,  562  so as to open or close the third outer, fourth outer, third inner and fourth inner tube bodies  531 ,  541 ,  551 ,  561 . 
     It should be noted that, in other embodiments of the disclosure, the first outer, first inner, second outer, second inner, third outer, third inner, fourth outer and fourth inner tube valves  332 ,  352 ,  342 ,  362 ,  532 ,  552 ,  542 ,  562  may be configured as a valve train, and a connecting structure that interconnects the transmission unit  7  and the aforementioned tube valves  332 ,  352 ,  342 ,  362 ,  532 ,  552 ,  542 ,  562  may be configured as a substitute for the first and second controllers  37 ,  57  for opening and closing these tube valves  332 ,  352 ,  342 ,  362 ,  532 ,  552 ,  542 ,  562 . 
     The transmission unit  7  is connected to the first and second volume regulating units  3 ,  5  for transferring kinetic energy to or from the first and second volume regulating units  3 ,  5 . The transmission unit  7  includes a rotary shaft  71 , a first link  72  and a second link  73 . The first link  72  is movably connected between the rotary shaft  71  and the first piston unit  32 , and the second link  73  is movably connected between the rotary shaft  71  and the second piston unit  52  such that rotation of the rotary shaft  71  drives the first and second links  72 ,  73  to move the first and second piston units  32 ,  52  relative to the first and second cylinders  31 ,  51 . 
     Referring to  FIG. 4 , an operating method for the mechanical device  100  approximating to the Carnot cycle includes the following steps: a near-isothermal expansion (S 1 ), a near-adiabatic expansion (S 2 ), a near-isothermal compression (S 3 ) and a near-adiabatic compression (S 4 ). 
     By conducting the aforementioned four steps, the working medium is driven to circulate along the circulation path. During a cycle of circulation, a volume of the working medium exiting the first volume regulating unit  3  differs from a volume of the working medium entering the second volume regulating unit  5 , and a volume of the working medium entering the first volume regulating unit  3  differs from a volume of the working medium exiting the second volume regulating unit  5 . 
     Specifically, referring to  FIGS. 2, 3 and 4 , during the step of near-isothermal expansion (S 1 ), the first controller  37  of first volume regulating unit  3  is operated to open the first outer tube valve  332  and the second inner tube valve  362 , and to close the second outer tube valve  342  and the first inner tube valve  352 . At the same time, the second controller  57  of the second volume regulating unit  5  is operated to open the fourth outer tube valve  542  and the third inner tube valve  552 , and to close the third outer tube valve  532  and the fourth inner tube valve  562 . 
     By virtue of expansion of the working medium resulting from heat being transferred from the hot end  1 , or movement of the first piston unit  32  in a first sliding direction (D 1 ) resulting from the rotation of the rotary shaft  71  in a first rotational direction (R 1 ), the working medium is driven to flow from the first outer chamber  311  of first volume regulating unit  3  into thermal contact with the hot end  1  via the first outer tube body  331 , and from the cold end  2  into the first inner chamber  312  via the second inner tube body  361 . 
     At the same time, the second piston unit  52  is driven to move in a second sliding direction (D 2 ) opposite to the first sliding direction (D 1 ), and the working medium is drawn from the hot end  1  into the second inner chamber  512  of the second volume regulating unit  5  via the third inner tube body  551 , and from the second outer chamber  511  into thermal contact with the cold end  2  via the fourth outer tube body  541 . 
     Since the cross sectional area of the first cylinder  31  is smaller than that of the second cylinder  51 , and since the distances travelled by the first piston unit  32  and the second piston unit  52  during the rotation of the rotary shaft  71  are approximately the same, a first volume of the working medium moved from the first outer chamber  311  of the first volume regulating unit  3  into thermal contact with the hot end  1  is smaller than a second volume of the working medium moved from, the hot end  1  into the second inner chamber  512  of the second volume regulating unit  5 . The overall volume of the working medium circulating in the first outer chamber  311 , the first outer tube body  331 , the second inner chamber  512  and the third inner tube body  551  expands to perform heat exchange between the working medium the hot end  1 . 
     Referring to  FIGS. 3, 4 and 5 , during the step of near-adiabatic expansion (S 2 ), the first controller  37  opens the second outer tube valve  342 , and closes the first outer tube valve  332  and the second inner tube valve  362 . The second controller  57  closes the third inner tube valve  552 . 
     As the working medium expands in the second inner chamber  512  of the second volume regulating unit  5 , the second piston unit  52  moves in the second sliding direction (D 2 ), thereby driving and the rotary shaft  71  to keep rotating in the first rotational direction (R 1 ) via the second link  73 , and also driving the working medium to flow from the second outer chamber  511  to the cold end  2  via the fourth outer tube body  541 . 
     At the same time, the first piston unit  32  is driven to move in the second sliding direction (D 2 ), drawing the working medium from the cold end  2  into the first outer chamber  311  via the second outer tube body  341 , and simultaneously compressing the working medium in the first inner chamber  312 . 
     Since the working medium in the second inner chamber  512  is not in thermal contact with either of the hot and cold ends  1 ,  2 , it expands in a nearly adiabatic environment and the temperature thereof drops to be approximately the same as that of the cold end  2 . 
     Referring to  FIGS. 3, 4 and 6 , during the step of near-isothermal compression (S 3 ), the first controller  37  opens the first inner tube valve  352 . The second controller  57  opens the third outer tube valve  532  and the fourth inner tube valve  562 , and closes the fourth outer tube valve  542 . 
     By virtue of rotational inertia of the rotary shaft  71 , the rotary shaft  71  continues to rotate in the first rotational direction (R 1 ), and the first piston unit  32  continues to move in the second sliding direction (D 2 ), drawing the working medium from the cold end  2  into the first outer chamber  311  via the second outer tube body  341 . At the same time, the second piston unit  52  is driven by the second link  73  to move in the first sliding direction (D 1 ), and the working medium is driven to flow from the second inner chamber  512  into thermal contact with the cold end  1  via the fourth inner tube body  561 , and from the hot end  1  into the second outer chamber  511  via the third outer tube body  531 . 
     Since, as mentioned above, the transverse cross sectional area of the first cylinder  31  is smaller than that of the second cylinder  51 , and since the distances travelled by the first piston unit  32  and the second piston unit  52  during the rotation of the rotary shaft  71  are approximately the same, a third volume of the working medium moved from the second inner chamber  512  of the second volume regulating unit  5  into the cold end  2  is greater than a fourth volume of the working medium moved from the cold end  2  into the first outer chamber  311  of the first volume regulating unit  3 . The overall volume of the working medium circulating in the second inner chamber  512 , the fourth inner tube body  561 , the cold end  2 , the second outer tube body  341  and the first outer chamber  311  is compressed to perform heat exchange between the working medium and the cold end  2 . 
     Referring to  FIGS. 3, 4 and 7 , during the step of near-adiabatic compression (S 4 ), the first controller  37  opens the second inner tube valve  362 , and closes the second outer tube valve  342  and the first inner tube valve  352 . The second controller  57  closes the third outer tube valve  532 . 
     The working medium continues to move the second piston unit  52  in the first sliding direction (D 1 ), thereby driving and the rotary shaft  71  to keep rotating in the first rotational direction (R 1 ) via the second link  73 , and also driving the working medium to flow from the second inner chamber  512  into thermal contact with the cold end  2  via the fourth inner tube body  561 . At the same time, the first piston unit  32  is driven to move in the first sliding direction (D 1 ), drawing the working medium from the cold end  2  into the first inner chamber  312  via the second inner tube body  361 , and simultaneously compressing the working medium in the first outer chamber  311 . 
     Since the working medium in the first outer chamber  311  is not in thermal contact with either of the hot and cold ends  1 ,  2 , it is compressed in a nearly adiabatic environment and the temperature thereof rises to be approximately the same as that of the hot end  1 . 
     When the step of near-adiabatic compression (S 4 ) ends, a cycle of the operation is completed. After that, the operating method for the mechanical device  100  may be repeated in the order described above. 
     By virtue of configurations of the first and second volume regulating units  3 ,  5  and the transmission unit  7 , the volume of the working medium exiting or entering the first volume regulating unit  3  is smaller than the volume entering or exiting the second volume regulating unit  5  (i.e., the first volume is smaller than the second volume, and the fourth volume is smaller than the third volume), and the the working medium is allowed to expand and be compressed in a nearly adiabatic environment. In addition, it should be noted that the temperature of the working medium exiting the first volume regulating unit  3  is higher than the temperature of the working medium exiting the second volume regulating unit  5 . 
     When the mechanical device  100  is operated in the abovementioned manner, the operation approximates to a Carnot cycle and the mechanical device  100  performs as a heat engine, which can be used as a power source for outputting kinetic energy to external component. For example, when the mechanical device  100  is used with a generator, the rotary shaft  71  is connected to an external component such as a rotor, which can be driven to rotate relative to a stator, thereby generating electricity; and when the mechanical device  100  is used with a vehicle, the rotary shaft  71  is connected to an external component such as a wheel for driving the wheel to rotate. 
     Referring to  FIGS. 8 and 9 , the mechanical device  100  may also be operated in a reversed manner such that the operation approximates to a reverse Carnot cycle. In this case, the mechanical device  100  performs as a heat pump, in which the hot end  1  releases heat to the external environment and the cold end  2  absorbs heat from the external environment, and in which the rotary shaft  71  (see  FIG. 10 ) is connected to an external power source such as a motor to be driven thereby. The schematic diagram shown in  FIG. 9  illustrates the mechanical device  100  being operated in such reversed manner, and an operating method thereof that approximates to the reverse Carnot cycle includes the following steps: a near-adiabatic compression (S 4 ), a near-isothermal compression (S 3 ), a near-adiabatic expansion (S 2 ), and a near-isothermal expansion (S 1 ). 
     Referring to  FIGS. 3, 9 and 10 , during the step of near-adiabatic compression (S 4 ), the first controller  37  of first volume regulating unit  3  is operated to open the second outer tube valve  342 , and to close the first outer tube valve  332 , the first inner tube valve  352 , and the second inner tube valve  362 . At the same time, the second controller  57  of the second volume regulating unit  5  is operated to open the fourth outer tube valve  542 , and to close the third outer tube valve  532 , the third inner tube valve  552 , and the fourth inner tube valve  562 , and the rotary shaft  71  is driven by an external power source to rotate in the second rotational direction (R 2 ). 
     During the rotation of the rotary shaft  71 , the second link  73  drives the second piston unit  52  to move in the first sliding direction (D 1 ) such that the second piston unit  52  compresses the working medium in the second inner chamber  512  of the second volume regulating unit  5 , and the temperature of the working medium in the second inner chamber  512  rises to be approximately the same as that of the hot end  1 . At the same time, the rotary shaft  71  drives the first piston unit  32  to move in the first sliding direction (D 1 ) via the first link  72 . 
     Referring to  FIGS. 3, 9 and 11 , during the step of near-isothermal compression (S 3 ), the first controller  37  opens the first outer tube valve  332  and the second inner tube valve  362 , and closes the second outer tube valve  342 , and the second controller  57  opens the third inner tube valve  552 . 
     At this time, the second piston unit  52  moves in the first sliding direction (D 1 ). A first volume of the working medium is driven by the second piston unit  52  to flow from the second inner chamber  512  of the second volume regulating unit  5  into thermal contact with the hot end  1  via the third inner tube body  551 , and a second volume of the working medium is drawn from the hot end  1  into the first outer chamber  311  via the first outer tube body  331 . The first volume of the working medium is greater than the second volume so that the working medium is compressed during thermal contact with the hot end  1  and performs heat exchange therewith. During this process, the temperature of the working medium remains approximately the same as the hot end  1 . 
     Referring to  FIGS. 3, 9 and 12 , during the step of near-adiabatic expansion (S 2 ), the first controller  37  closes the first outer tube valve  332 , and the second controller  57  opens the fourth inner tube valve  562 , and closes the fourth outer tube valve  542  and the third inner tube valve  552 . 
     At this time, the first volume regulating unit  3  is operated such that the working medium in the first outer chamber  311  expands and the temperature thereof drops to be approximately the same as that of the cold end  2 . 
     Referring to  FIGS. 3, 9 and 13 , during the step of near-isothermal expansion (S 1 ), the first controller  37  opens the second outer tube valve  342  and the first inner tube valve  352 , and closes the second inner tube valve  362 , and the second controller  57  opens the third outer tube valve  532 . 
     At this time, the first piston unit  32  moves in the first moving direction (D 1 ). A third volume of the working medium is driven by the first piston unit  32  to flow from the first outer chamber  311  into thermal contact with the cold end  2  via the second outer tube body  341 , and a fourth volume of the working medium is drawn from the cold end  2  into the second inner chamber  512  via the fourth inner tube body  561 . The third volume of the working medium is smaller than the fourth volume so that the working medium expands during thermal contact with the cold end  2  and performs heat exchange therewith. During this process, the temperature of the working medium remains approximately the same as the cold end  2 . 
     When the step of near-isothermal expansion (S 1 ) ends, a cycle approximating to the reverse Carnot cycle is completed, and such operating method may be repeated in the order described above. 
     Similar to the previous operating method that approximates to the normal Carnot cycle, during the operation in this case, the volume of the working medium entering or exiting the first volume regulating unit  3  is smaller than the volume exiting or entering the second volume regulating unit  5  (i.e., the second volume is smaller than the first volume, and the third volume is smaller than the fourth volume), and the working medium is allowed to be compressed and expand in a nearly adiabatic environment. In addition, it should be noted that the temperature of the working medium exiting the first volume regulating unit  3  is lower than the temperature of the working medium exiting the second volume regulating unit  5 . 
     Referring to  FIGS. 14 and 15 , a second embodiment of the mechanical device  200  according to the disclosure performs similar functions as does the first embodiment. However, in the second embodiment, the mechanical device  200  includes a first complex unit  30  and a second complex unit  50 . 
     Referring to  FIGS. 16, 17 and 18 , the first complex unit  30  includes a first end cap  38  and a first movable disc  39 . The first end cap  38  is adapted to be fixed to an external component (not shown) so as to remain stationary during operation, and includes a first end wall  381 , a first stationary scroll  382  and a first surrounding wall  383 . 
     The first end wall  381  constitutes the cold end. The first stationary scroll  382  is fixed on the first end wall  381  and cooperates with the first end wall  381  to define the first volume regulating unit  384  for the working medium to flow therethrough. The first surrounding wall  383  extends from an outer periphery of the first end wall  381 , and surrounds and is spaced apart from the first stationary scroll  382 . The first end wall  381 , the first stationary scroll  382  and the first surrounding wall  383  cooperatively define a first heat exchange chamber  385  that surrounds the first volume regulating unit  384 . The first volume regulating unit  384  has a first connecting section  386  (see  FIG. 18 ). The first volume regulating unit  384  and the first heat exchange chamber  385  are in spatial communication via the first connecting section  386 . 
     The first end cap  38  further includes a plurality of first heat dissipating components  387  that are configured as cylindrical pins disposed in the first heat exchange chamber  385  and connected to the first end wall  381 . Disposition of the first heat dissipating components  387  increases a total area of contact between the working medium and the first end cap  38 , so as to promote efficiency of heat transfer therebetween. In variations of the embodiment, the first heat dissipating components  387  may also be, but not limited to, fin-shaped. 
     Referring to  FIGS. 15, 16 and 17 , the first movable disc  39  is movably engaged with the first end cap  38 , and includes a first disc body  391  and a first movable scroll  392 . The first movable scroll  392  is received in the first volume regulating unit  384 , and is movable relative to the first stationary scroll  382 . The first disc body  391  is connected to the first movable scroll  392  such that the first movable scroll  392  is disposed between the first disc body  391  and the first end wall  381 , and is surround by the first surrounding wall  383 . 
     The first disc body  391  is formed with a first through hole  393 , a second through hole  394  and a plurality of first connecting holes  395 . The first through hole  393  is located proximate to a periphery of the first disc body  391  and is in spatial communication with the first heat exchange chamber  385 . The second through hole  394  is located proximate to the center of the first disc body  391 , is surrounded by the first movable scroll  392 , and is in spatial communication with the first volume regulating unit  384 . 
     The first connecting holes  395  are spaced-apart blind holes located on a side of the first disc body  391  opposite to the first movable scroll  392 , and are also proximate to the periphery of the first disc body  391 . By virtue of movement of the first movable scroll  392  relative to the first stationary scroll  382 , the working medium flowing therebetween can expand or be compressed. 
     Referring to  FIGS. 15, 16, 17 and 19 , the second complex unit  50  includes a second end cap  58  and a second movable disc  59 . The second end cap  58  is adapted to be fixed to an external component (not shown) so as to remain stationary during operation, and includes a second end wall  581 , a second stationary scroll  582  and a second surrounding wall  583 . 
     The second end wall  581  constitutes the hot end. The second stationary scroll  582  is fixed on the second end wall  581  and cooperates with the second end wall  581  to define the second heat exchange chamber  585  for the working medium to flow therethrough. It should be noted that the capacity of the first volume regulating unit  384  is smaller than that of the second volume regulating unit  584 . The second surrounding wall  583  extends from an outer periphery of the second end wall  581 , surrounds the second stationary scroll  582 , and is connected to an outer periphery of the second stationary scroll  582 . The second end wall  581 , the second stationary scroll  582  and the second surrounding wall  583  cooperatively define a second volume regulating unit  584  that surrounds the second heat exchange chamber  585 . The second volume regulating unit  584  has a second connecting section  586  (see  FIG. 19 ). The second volume regulating unit  584  and the second heat exchange chamber  585  are in spatial communication via the second connecting section  586 . 
     The second end cap  58  further includes a plurality of second heat dissipating components  587  that are configured as cylindrical pins disposed in the second heat exchange chamber  585 , surrounded by the second stationary scroll  582 , and connected to the second end wall  581 . Similar to the first heat dissipating components  387 , the second heat dissipating components  587  increase a total area of contact between the working medium and the second end cap  58 , so as to promote efficiency of heat transfer therebetween. In variations of the embodiment, the second heat dissipating components  587  may also be, but not limited to, fin-shaped. 
     Referring to  FIGS. 15, 16 and 17 , the second movable disc  59  is movably engaged with the second end cap  58 , and includes a second disc body  591  and a second movable scroll  592 . The second movable scroll  592  is received in the second volume regulating unit  584 , and is movable relative to the second stationary scroll  582 . The second disc body  591  is connected to the second movable scroll  592  such that the second movable scroll  592  is disposed between the second disc body  591  and the second end wall  581 , and is surround by the second surrounding wall  583 . 
     The second disc body  591  is formed with a first through hole  593 , a second through hole  594  and a plurality of second connecting holes  595 . The first through hole  593  is located proximate to a periphery of the second disc body  591  and is in spatial communication with the second volume regulating unit  584 . The second through hole  594  is located proximate to the center of the second disc body  591 , is surrounded by the second movable scroll  592 , and is in spatial communication with the second heat exchange chamber  585 . The second connecting holes  595  are spaced-apart blind holes located on a side of the second disc body  591  opposite to the second movable scroll  592 , and are also proximate to the periphery of the second disc body  591 . 
     By virtue of movement of the second movable scroll  592  relative to the second stationary scroll  582 , the working medium flowing therebetween can expand or be compressed. 
     The present embodiment further includes a first connecting tube  40  and a second connecting tube  41 , each of which connects the first movable disc  39  with the second movable disc  59  such that movements of the first and second movable discs  39 ,  59  are synchronized. 
     Specifically, the first connecting tube  40  has opposite ends registered respectively with the first through holes  393 ,  593  of the first and second disc bodies  391 ,  591 , and is welded between the first and second disc bodies  391 ,  591 , such that the first connecting tube  40  and the first and second disc bodies  391 ,  591  cooperatively define a first passage  401 . Similarly, the second connecting tube  41  has opposite ends registered respectively with the second through holes  394 ,  594  of the first and second disc bodies  391 ,  591 , and is welded between the first and second disc bodies  391 ,  591 , such that the second connecting tube and the first and second disc bodies  391 ,  591  cooperatively define a second passage  411 . 
     Referring to  FIGS. 15, 16, 17 and 20 , the transmission unit  7  of the present embodiment is connected to the first and second movable discs  39 ,  59  for transferring kinetic energy to or from the first and second movable discs  39 ,  59  (i.e., either one of the first and second movable discs  39 ,  59  may drive or be driven by the transmission unit  7  to move since movements of the first and second movable discs  39  are synchronized). 
     Specifically, the transmission unit  7  includes two carrier discs  74  and a plurality of transmitting components  75 . The carrier discs  74  are disposed between the first and second movable discs  39 ,  59 . One of the carrier discs  74  is surrounded by and press fitted within the first surrounding wall  383  of the first end cap  38 , and the other one of the carrier discs  74  is surrounded by and press fitted within the second surrounding wall  583  of the second end cap  58  such that both carrier discs  74  remain stationary during operation. 
     Each of the carrier discs  74  is formed with a first opening  741 , a second opening  742  and a plurality of shaft holes  743 . The first and second connecting tubes  40 ,  41  extend respectively through the first and second openings  741 ,  742  of each of the carrier discs  74 . For each of the carrier discs  74 , the first opening  741  is located proximate to a periphery thereof, and has a diameter greater than the outer diameter of the first connecting tube  40  such that the first connecting tube  40  is allowed to move therein; the second opening  742  is located proximate to the center thereof, and has a diameter greater than the outer diameter of the second connecting tube  41  such that the second connecting tube  41  is allowed to move therein; and the shaft holes  743  are spaced apart from each other and are arranged around the second opening  742 . 
     Each of the transmitting components  75  has a wheel body  751  and two shaft bodies  752 . The wheel body  751  of each of the transmitting components  75  is disposed between the carrier discs  74 , and is adapted to be connected to an external structure (not shown) for transferring kinetic energy. For example, in variations of the embodiment, the wheel body  751  may be provided with an external thread to engage an internal thread of the external structure, or configured as a pulley (or sprocket) to be engaged with a belt (or chain). 
     The shaft bodies  752  of each of the transmitting components  75  are connected respectively to opposite sides of the wheel body  751 , extend respectively and rotatably through the carriers discs  74 , are engaged respectively with the first and second movable discs  39 ,  59 , and each have a main portion  753  (see  FIG. 20 ) and an eccentric portion  754 . 
     Referring specifically to  FIG. 20 , for each of the transmitting components  75 , the main portion  753  of each of the shaft bodies  752  has a small segment  755  and a large segment  756 ; the small segment  755  is welded between the wheel body  751  and the large segment  756 , and is received rotatably in a corresponding one the shaft holes  743  of the respective one of the carrier discs  74 ; the large segment  756  has a diameter greater than a diameter of the small segment  755  and a diameter of the corresponding shaft hole  743 ; and the eccentric portion  754  is connected to a side of the large segment  756  of the main portion  753  opposite to the small segment  756 , and is axially misaligned with the main portion  753 . 
     The eccentric portion  754  of one of the shaft bodies  752  of each of the transmitting components  75  is received rotatably in a corresponding one of the first connecting holes  395  of the first movable disc  39 , and the eccentric portion  754  of the other one of the shaft bodies  752  is received rotatably in a corresponding one of the second connecting holes  595  of the second movable disc  59 . 
     It should be noted that by virtue of the diameter of the large segment  756  of each shaft body  752  being greater than the diameter of the corresponding shaft hole  743 , the carrier discs  74  are confined between the large segments  756  of the shaft bodies  752  and the wheel body  751  of each of transmitting components  75 . 
     Referring to  FIGS. 17, 18 and 19 , when the mechanical device  200  is operated on a cycle approximating to the Carnot cycle, during the step of near-isothermal expansion (S 1 ), by virtue of expansion of the working medium in the second heat exchange chamber  585 , or rotational inertia of the transmitting components  75  or an external power source (not shown), the first and second movable discs  39 ,  59  are driven to move simultaneously relative to the first and second end caps  38 ,  58 . At the same time, movement of the first movable scroll  392  relative to the first stationary scroll  382  drives the working medium in the first volume regulating unit  384  to flow into the second heat exchange chamber  585  via the second passage  411  of the second connecting tube  41 , and as the working medium in the second heat exchange chamber  585  absorbs heat from the second end wall  581  of the second end cap  58  (i.e., the hot end), it expands and flows into the second volume regulating unit  584  via the second connecting section  586 . During this process, the working medium in the second heat exchange chamber  585  expands and the temperature thereof remains approximately the same as the hot end  1 , and the volume of the working medium moved from the first volume regulating unit  384  to the second heat exchange chamber  585  is smaller than the volume moved from the second heat exchange chamber  585  to the second volume regulating unit  584 . 
     During the step of near-adiabatic expansion (S 2 ), the working medium expands in the second volume regulating unit  584  and outputs kinetic energy such that the second movable scroll  592  is driven to move relative to the second stationary scroll  582 . During this process, the volume of a space defined between the second stationary and second movable scrolls  591 ,  592  in the second volume regulating unit  584  varies, allowing the working medium to continue to expand and flow through the first passage  401  of the first connecting tube  40 . The temperature of the working medium in the second volume regulating unit  584  drops to be approximately the same as that of the first end wall  381  of first end cap  38  (i.e., the cold end). In addition, movement of the second movable scroll  592  relative to the second stationary scroll  591  also drives the synchronized movements of the first and second movable discs  39 ,  59 , as mentioned above, via the transmission unit  7 . 
     Referring to  FIGS. 17, 18 and 19 , during the step of near-isothermal compression (S 3 ), the working medium flows into the first heat exchange chamber  385  via the first passage  401 , performs heat exchange with the first end wall  381  (i.e., the cold end), and flows into the first volume regulating unit  384  via the first connection section  386 . During this process, the working medium in the first heat exchange chamber  385  is compressed and the temperature thereof remains approximately the same as the cold end, and the volume of the working medium moved from the second volume regulating unit  584  to the first heat exchange chamber  385  is greater than the volume moved from the first heat exchange chamber  385  to the first volume regulating unit  384 . 
     In the step of near-adiabatic compression (S 4 ), during the moving process of the first movable scroll  392  relative to the first stationary scroll  391 , the volume of a space defined between the first stationary and first movable scrolls  391 ,  392  in the first volume regulating unit  384  varies such that the working medium continues to be compressed and flows through the second passage  411  into the second heat exchange chamber  585 . At the same time, the temperature of the working medium in the first volume regulating unit  384  rises to be approximately the same as that of the second end wall  581  (i.e., the hot end). At this point, a cycle of the operation is completed and may be repeated in the order described above. 
     Referring to  FIGS. 15 and 16 , similar to the previous embodiment, the mechanical device  200  of the second embodiment may also be operated in a reversed manner such that the operation approximates to the reverse Carnot cycle. In this case, the second end cap  58  releases heat to the external environment and the first end cap  38  absorbs heat from the external environment. 
     The transmission unit  7  is connected to an external power source such that the wheel body  751  of each of the transmitting components  75  is driven thereby to rotate. 
     Referring to  FIGS. 15 and 16 , during the step of near-adiabatic compression (S 4 ), each of the transmitting components  75  is driven by the external power source to rotate, thereby driving the synchronized movements of the first and second movable discs  39 ,  59 . In virtue of the movement of the second movable scroll  592  relative to the second stationary scroll  591 , the working medium in the second volume regulating unit  584  is compressed and the temperature thereof rises to be approximately the same as that of the second end wall  581  (i.e., the hot end). 
     During the step of near-isothermal compression (S 3 ), the working medium flows from the second volume regulating unit  584  into the second heat exchange chamber  585  via the second connecting section  586 , performs heat exchange with the second end wall  581  (i.e., the hot end), and flows into the first volume regulating unit  384  via the second passage  411 . 
     Referring to  FIGS. 15 and 16 , during the step of near-adiabatic expansion (S 2 ), by virtue of the movement of the first movable scroll  392  relative to the first stationary scroll  391 , the working medium in the first volume regulating unit  384  expands and the temperature thereof drops to be approximately the same as that of the first end wall  381  (i.e., the cold end). 
     During the step of near-isothermal expansion (S 1 ), the working medium flows from the first volume regulating unit  384  into the first heat exchange chamber  385  via the first connecting section  386 , performs heat exchange with the first end wall  381  (i.e., the cold end), and flows into the second volume regulating unit  584  via the first passage  401 . A cycle of the operation is now completed and may be repeated in the same order as described. 
     Similar to the previous embodiment, during a cycle of the operation, the volume of the working medium moved from the second volume regulating unit  584  into the first heat exchange chamber  385  differs from the volume moved from the first heat exchange chamber  385  into the first volume regulating unit  384 , and the volume moved from the first volume regulating unit  384  into the second heat exchange chamber  585  differs from the volume moved from the second heat exchange chamber  585  into the second volume regulating unit  584 . In such a manner, the working medium is allowed to expand and be compressed while the temperature thereof remains approximately constant. 
     Referring to  FIG. 21 , a third embodiment of the mechanical device  300  according to the disclosure is similar to the first embodiment. The difference between the two resides in that, in the third embodiment, each of the first and second volume regulating units  3 ,  5  includes two intermeshed screws. However, in other embodiments, either one of the first and second volume regulating units  3 ,  5  may include a single screw or other structure that provides the equivalent functions. 
     Specifically, in the present embodiment, the first volume regulating unit  3  includes a first casing  42 , a first driving rotor  43  and a first driven rotor  44 . The first casing  42  is in spatial communication with the hot end  1  and the cold end  2  for allowing the working medium to flow therebetween. The first active and first driven rotors  43 ,  44  are disposed in and rotatably connected to the first casing  42 , and are configured as two meshing screws, such that rotations thereof allow the working medium flowing therebetween to expand or be compress thereby. 
     Similarly, the second volume regulating unit  5  includes a second casing  60 , a second driving rotor  61  and a second driven rotor  62 . The second casing  60  is in spatial communication with the hot end  1  and the cold end  2  for allowing the working medium to flow therebetween. The second active and second driven rotors  61 ,  62  are disposed in and rotatably connected to the second casing  60 , and are also configured as two intermeshed screws, such that rotations thereof allow the working medium flowing therebetween to expand or be compressed thereby. 
     The transmission unit  7  is connected between the first driving rotor  43  and the second driving rotor  61  for transferring kinetic energy thereto or therefrom. 
     When the mechanical device  300  is operated on a cycle approximating to the Carnot cycle, the volume of the working medium exiting the first volume regulating unit  3  is smaller than the volume entering the second volume regulating unit  5 , and the volume of the working medium entering the first volume regulating unit  3  is also smaller than the volume exiting the second volume regulating unit  5 . 
     Conversely, when the mechanical device  300  is operated on a cycle approximating to the reversed Carnot cycle, the volume of the working medium exiting the first volume regulating unit  3  is greater than the volume entering the second volume regulating unit  5 , and the volume of the working medium entering the first volume regulating unit  3  is also greater than the volume exiting the second volume regulating unit  5 . 
     It should be noted that, in other embodiments of the disclosure, the transmission unit  7  may be configured in a manner that the first and second volume regulating units  3 ,  5  operate at difference rotational speeds so as to result in different volumes of the working medium entering or exiting the first and second volume regulating units  3 ,  5 . 
     In sum, for each of the embodiments of the mechanical device  100 ,  200 ,  300  according to the disclosure, during a single operation cycle, by virtue of the volume of the working medium exiting or entering the first volume regulating unit  3  being different from the volume entering or exiting the second volume regulating unit  5 , the working medium is allowed to expand or be compressed in a manner that the operation approximates to the Carnot cycle or the reversed Carnot cycle. In the description above, for the purposes of explanation, numerous specific details have been set forth in order to provide a thorough understanding of the embodiments. It will be apparent, however, to one skilled in the art, that one or more other embodiments may be practiced without some of these specific details. It should also be appreciated that reference throughout this specification to “one embodiment,” “an embodiment,” an embodiment with an indication of an ordinal number and so forth means that a particular feature, structure, or characteristic may be included in the practice of the disclosure. It should be further appreciated that in the description, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of various inventive aspects, and that one or more features or specific details from one embodiment may be practiced together with one or more features or specific details from another embodiment, where appropriate, in the practice of the disclosure. 
     While the disclosure has been described in connection with what are considered the exemplary embodiments, it is understood that this disclosure is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.