Abstract:
The invention enables the operation of a reciprocating steam engine without the need for timing gears on the inlet and exhaust valves. The valves in this invention are actuated and reversed when the piston reaches the end of the stroke, and are based solely on linear motion. The pistons are dual acting, which means the power stroke operates in both directions. Additionally, the system is self-starting, needing only heat to begin operating. The invention enables the use of a steam engine at low temperature differences (down to 0.5 C) between evaporator and condenser which is useful for closed loop heat transfer applications, when a pure or azeotropic working fluid is used. Additional configurations are possible with the invention, in which part of the heat input may be transformed to a higher temperature and rejected from the system. When the invention is used for either isothermal heat transfer applications or heat transformation, no energy, other than the heat input, is needed for the invention to operate.

Description:
PRIORITY STATEMENT UNDER 35 U.S.C. §119 
       [0001]    This application claims priority under 35 U.S.C. §119 based upon prior U.S. Provisional Patent Application Ser. No. 61/931,759, filed Jan. 27, 2014, in the name of Jeremy Rice, entitled “IMPROVED RECIPROCATING STEAM ENGINE,” the disclosure of which is incorporated herein in its entirety by this reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    There are several existing closed loop heat transfer technologies, including both passive and active methods. The passive methods are generally limited by heat load, transport distance or orientation, while the active methods require an external power source. In applications where an increase in temperature is desired along with the transfer of heat, the external power requirements increase significantly. 
         [0003]    Heat pipes are a passive device relying on two-phase heat transfer (evaporation/condensation). The liquid is pumped by capillarity through a continuous wick, from the condenser, to the evaporator. A capillary wicked heat pipe is reversible (condenser and evaporator can be switched). The heat load and distance are most frequently limited by the capillarity of the wick, but can also be limited by the sonic limit, nucleation limit, and entrainment limit. The heat transport in this device is nearly isothermal. 
         [0004]    Looped heat pipes are similar to heat pipes (passive, two-phase heat transfer), where the condensate is returned to the evaporator through capillarity. The wick structure is only located in the evaporator, and the condensate is returned through tubes, which allows for further transport length. Special considerations for start-up are needed to ensure liquid is continuous from the condenser to the evaporator. The heat transport in this device is also nearly isothermal. 
         [0005]    Thermosyphons are another passive two-phase heat transfer device. The condensate is returned to the evaporator via gravity. The operation of a thermosyphon is not-reversible, since the condenser must be higher, with respect to gravity, than the evaporator. The transport distance can be very high in these devices. Once again, the heat transfer in this device is nearly isothermal. 
         [0006]    Pumping a liquid through a closed heat transfer loop is one of the most common, and oldest, closed loop heat transfer methods. It involves a pump, a heat input heat exchanger (air/liquid, liquid/liquid, refrigerant/liquid, or generically heat source/liquid), and a heat rejection heat exchanger. The pump needs power delivered from an external engine or motor. The heat transfer in this method relies on sensible heating, therefore, the liquid temperature increases and decreases in the heat absorption and rejection processes, respectively. 
         [0007]    Similar to a pumped liquid loop, a pumped two-phase cooling loop, uses a pump, evaporator and a condenser. Condensate is pumped from the condenser to the evaporator. The pump is powered by a motor, converting electricity into mechanical energy. The heat transfer in this loop is nearly isothermal, when its operation is under low pressure differentials. 
         [0008]    A heat pump can take a heat input and elevate the temperature of the heat output by means of a compressor which is driven by a motor. The power needed to drive the motor can increase the energy into this system by twenty percent or more. 
       SUMMARY OF THE INVENTION 
       [0009]    Embodiments of the present invention are directed to a mechanism that enables linear valve actuation on a reciprocating steam engine for use in thermally activated closed loop heat transfer systems. No external power, other than heat load, is needed for the system to operate. Additionally, the system is self-starting, which is created by a directional preference of the inlet and exhaust valve switches on the reciprocating engine. The engine may be applied in at least two distinct forms: a reciprocating heat transfer engine and a reciprocating heat transformer. In each form, power is transferred by the engine to one or more additional pistons via a shaft through linear motion. 
         [0010]    In various embodiments of the reciprocating heat transfer engine, the engine drives a reciprocating pump, and the engine&#39;s power is derived from the available energy between the heat input to the evaporator and the heat rejected through the condenser. All of the power created by the engine is used to overcome the hydrodynamic losses of the fluid flow as well as frictional losses of the pistons. This system may achieve nearly isothermal closed loop heat transfer. 
         [0011]    In various embodiments of the reciprocating heat transformer, the engine drives both a reciprocating pump and compressor. Part of the heat load can be rejected at a higher temperature than the heat input, which is considered to be transformed. All of the engine&#39;s power is utilized to overcome the hydrodynamic losses, friction of the pistons, and the work required to drive the compressor. In this system, there are two condensers, a low temperature condenser and a high temperature condenser. While, a nearly isothermal heat transfer loop can be employed by the heat transfer engine, the heat transformer requires a larger temperature difference between the evaporator and low temperature condenser to allow for power to be available to drive the compressor. The linear valve actuation in the engine is best suited for temperature differences of less than 30° C. In this temperature range, a reasonable percentage of the available energy may be converted to work by the engine. 
         [0012]    The foregoing has outlined rather broadly certain aspects of the present invention in order that the detailed description of the invention that follows may better be understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0013]    For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which like reference numerals indicate like features and wherein: 
           [0014]      FIG. 1  is a schematic of a pumped two-phase closed loop heat transfer system utilizing a reciprocating pump in accordance with prior art; 
           [0015]      FIG. 2  is a schematic of a thermally activated closed loop heat transfer system utilizing a reciprocating engine and pump in accordance with one embodiment of the present invention; 
           [0016]      FIG. 3  is a schematic of a heat pump system utilizing a reciprocating compressor in accordance with prior art; 
           [0017]      FIG. 4  is a schematic of a thermally activated heat transformer utilizing a reciprocating engine, pump and compressor; 
           [0018]      FIGS. 5  A and B are schematics of coolant integration into the two condensers of a heat transformer; 
           [0019]      FIG. 6  is a representation of the inlet valve switch mechanical assembly; and 
           [0020]      FIG. 7  is a representation of the outlet valve switch mechanical assembly. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    A typical reciprocating pumped two-phase closed loop heat transfer system is presented in  FIG. 1 . This system consists of a motor  100 , a pump  104 , an evaporator  101 , and a condenser  102 . The pump  104  which is driven by the motor  100 , receives it&#39;s liquid from the condenser  102 , and delivers the liquid to the evaporator  101 . The direction of flow is dictated by check valves  105 , on the inlet and outlet sides of a piston in the pump  104 . There are three energy exchanges into or out of this system. Electrical energy is input into the motor  100 , which is converted into mechanical energy. Thermal energy is input into the evaporator  101 , which vaporizes the liquid. Thermal energy is removed from the condenser  102 , which condenses the vapor back to liquid. 
         [0022]    A schematic of one embodiment of the present invention is presented in  FIG. 2 . This system consists of a reciprocating pump  104 , an evaporator  101 , a reciprocating engine  106 , a condenser  102 , and several valves  105 ,  107  and  108 . A fluid consisting of liquid and vapor flows through the system. The direction of flow into and out of the pump  104  is controlled by four check valves  105 , located on both sides of the piston, on the intake and exhaust side of the pump  104 . The directionality of flow through the engine  106  is controlled through an inlet valve switch  107  and outlet valve switch  108 . The inlet valve switch  107  directs fluid flow to the side of the piston which is expanding, while stopping fluid flow into the contracting side of the piston. The outlet valve switch  108  allows fluid to exit the contracting side of the piston, while stopping flow from exiting the expanding side. At the end of the stroke, a mechanism allows for the valves  107  and  108  to switch the flow directionality, and enables the piston to be driven in the opposite direction. The pressure differential from the evaporator  101  to the condenser  102 , along with the cross-sectional area of the engine&#39;s piston being greater than that of the pump  104 , allows power to be transferred from the engine  106  to the pump in one embodiment of the present invention through a shaft connected therebetween. The requirement of the engine  106  piston cross-sectional area needing to be greater than the pump  104 , is due to both a force balance, as well as the fact the specific volume of a two-phase mixture exiting an evaporator  101  will be greater than the specific volume of this fluid leaving the condenser  102 . Since all of the work provided by the engine  106  is consumed by the pump  104 , only hydrodynamic losses must be overcome. This system is deemed a reciprocating heat transfer engine. 
         [0023]    Considerations must be taken in selecting a working fluid for the reciprocating heat transfer engine, in order to minimize the temperature difference from the evaporator  101  to the condenser  102 . Specifically, the operating pressure of the working fluid in the desired temperature range of the device must be considered versus the hydrodynamic pressure losses and frictional losses associated with the movement of the piston. Both the hydrodynamic losses and friction losses will increase the pressure needed across the engine  106  to induce movement of the piston and pump  104 . If the pressure differential needed to move the piston is large relative to the operating pressure, large temperature differentials can be observed from the evaporator  101  to the condenser  102 , which can adversely impact the performance of the heat transfer engine or even prevent it from working all together. 
         [0024]    Additional consideration may be taken in selecting the working fluid for the reciprocating heat transfer engine, depending on the desired effect of the heat transfer engine. For instance, if a nearly isothermal performance is desired, a pure or an azeotropic working fluid should be chosen, since evaporation and condensation will happen at a constant temperature with a fixed pressure. If said device is intended to be used as an intermediate heat transfer system between a hot and cool fluid stream, than a zeotropic or non-azeotropic working fluid may be selected. During evaporation, the temperature of a zeotropic or non-azeotropic working fluid will increase as the vapor quality increases, which is referred to as “temperature glide.” The reverse is true during the condensation process. In this scenario, the working fluid selection should also account for the desired temperature drop of the hot fluid as well as the temperature rise of the cool fluid. 
         [0025]    A schematic of a typical heat pump utilizing reciprocating compressor is presented in  FIG. 3 . This system consists of an evaporator  101 , a compressor  109 , a motor  100  which drives the compressor, a condenser  110  and an expansion device  111 . Heat is input to the system, through the evaporator  101 , while heat is rejected through the condenser  102  at a higher temperature than the evaporator  101 . The temperature lift is a result of the compression process, in which the pressure is elevated. The directionality of flow through the compressor  109  is achieved through check valves  105 , on both the inlet and outlet of the compressor  109 . The expansion device  111 , which is located after the condenser  102 , decreases the fluid&#39;s pressure as it passes through it, and results in a lower temperature of the liquid/vapor mixture passes through it. 
         [0026]    Another embodiment of the present invention is presented in  FIG. 4 . This embodiment is henceforth referred to as a heat transformer. It is similar to the heat pump, in that it has an evaporator  101 , a reciprocating compressor  109 , a higher temperature condenser  110  and an expansion device  111 . The heat transformer differs from the heat pump in that is has no motor. The power which is needed to drive the compressor  109  is replaced by a reciprocating engine  106 , a low temperature condenser  102  and a reciprocating pump  104 . The engine  106  and pump  104  operate in the same manner as described in the first embodiment associated with  FIG. 2 . The evaporator  101  is at a temperature that is greater than the low temperature condenser  102  but less than the high temperature condenser  110 . Since part of the heat load may be rejected at a higher temperature than the evaporator  101 , the heat may be considered to be transformed, hence the name of this embodiment. 
         [0027]    In order for the heat transformer to operate, the net force supplied by the engine  106 , must be greater than the force necessary to drive both the pump  104  and the compressor  109 . Therefore, the overall displacement ratio of the heat transformer must be greater than unity. 
         [0000]    
       
         
           
             
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         [0028]    The variables P and A denote the pressure and cross-section area of the respective piston, respectively. The subscripts Evap, Cond,L, and Cond,H represent the evaporator, low temperature condenser and high temperature condenser, respectively. In the heat transformer, a relatively high vapor quality fluid leaves the evaporator, and flows in parallel to both the engine  106  and the compressor  109 . During start-up, the evaporator  101  temperature may temporarily be higher than the high temperature condenser&#39;s  110  temperature. Because of this condition, along with the fact that the engine  106  and compressor  109  are implemented in parallel to each other, the check valves  105   f  and  105   e  must have a cracking pressure that is high enough to compensate for the maximum pressure differential of the evaporator  101  with respect to the high temperature condenser  110  during start-up. If a setting is not accounted for, vapor may bypass the engine  106  entirely, and the system will not operate. Alternately, an on/off valve may be placed upstream of the check valves  105   f  and  105   e , that can be off, until the pressure in the high temperature condenser  110  section of the system is higher than that of the evaporator  110 . 
         [0029]    The degree in which the temperature of the high temperature condenser  110  is elevated, relative to the evaporator  101 , depends on the proportion of fluid that is driven through the compressor  109  versus how much fluid flow drives the engine  106  less the flow driven by the pump  104 . This concept may be observed mathematically in the definition of the heat transformer displacement ratio in EQ 1. Generally, the less fluid that is driven by the compressor  109 , and the more fluid that drives the engine  106 , the higher the degree of heat transformation in the high temperature condenser  110 . Also, the higher the temperature and pressure difference between the evaporator  101  and the low temperature condenser  102 , the greater the degree of heat transformation in the high temperature condenser  110 . 
         [0030]    Since there are two condensers in the heat transformer, rejecting heat at different temperatures, there are two options for coolant passing by these condensers, as presented in  FIG. 5 . In  FIG. 5   a , the low temperature condenser  102  rejects heat into a low temperature coolant  113 . The high temperature condenser  110  rejects heat into a separate higher temperature coolant loop  114 . An alternate scheme is presented in  FIG. 5   b  in which a single coolant  115  is utilized, which passes first through the low temperature condenser  102  and subsequently through the high temperature condenser  110 . 
         [0031]    In both embodiments discussed, an inlet valve switch and outlet valve switch was represented in a schematic. The mechanical implementation of the inlet valve switch is presented in  FIG. 6 . The engine piston  201  and engine housing  202  are the main components which transfer energy to the shaft. Vapor or high quality fluid enters the piston  201  in the middle where it flows past an opening between a valve head  205   a  and the valve housing  207 . The pressure on the right side of the piston  201 , as represented in  FIG. 6  is higher than the pressure on the left side of the piston  201 . This pressure difference, results in a force which drives the piston  201  to the left. The pressure also results in a force, which keeps the valve head  205   b  sealed on the alternate valve housing, thus preventing vapor to flow into the opposite side of the piston  201 . As the piston  201  travels to the left, the valve head  205   b  will engage with a valve actuator  204 . The valve actuator spring will compress, until it bottoms out. When it bottoms out, the piston  201  will provide the force necessary to break the seal on the closed valve head  205   b . Once this seal is broken, the pressure difference from one side of the piston  201  to the other will minimize, and the actuator recoils, forcing, through the valve shaft  203 , the opposing valve head  205   a  to close, resulting in a reversal of flow and piston  201  direction. In order to handle a start-up condition, where the pressure can be equal on either side of the piston  201 , two compression springs  206  are utilized around the valve shaft  203 . These springs are compressed by a different amount by design, thus forcing a directionality, for the valve head to be sealed. In the schematic, this offsetting spring tends to keep the valve head on the left side  205   b  closed. 
         [0032]    The outlet valve switch is presented in  FIG. 7 . The representation of pressure is consistent with  FIG. 6  in that the right side of the piston  201  is at a relatively high pressure and the left side of the piston  201  is at a relatively low pressure. The pressure differential tends to keep the valve head  206   a  on the right side closed, and on the left side  206   b  open, since they are coupled by a valve shaft  203 . The vapor is allowed to exit the chamber on the left and flow to the condenser  102 . As the piston  201  moves to the left, the valve head  206   b  will engage with the valve actuator  204 , at the same time as the inlet valve head  205   b . As the piston  201  travels further to the left, the valve actuator will compress, and the valve head will remain open, as a result of the pressure difference across the opposing valve head  206   a . Once the valve actuator bottoms out, the closed valve head  206   a  will crack, at the same time  205   b  cracks, thus allowing the pressure difference on either side of the piston  201  to rapidly decrease. When the pressure differential decreases, the actuator will recoil and reverse the positions of the valve heads, and the valve on the left side  206   b  will close, and the valve on the right side  206   a  will open. Once this happens the direction of the piston  201  will reverse. This process will repeat itself on the end of the subsequent stroke in the opposite manner and the reciprocating motion will ensue. 
         [0033]    The inlet and outlet valve switches in the present invention allow for the relative high pressure from the evaporator  101  to be exposed to one side of the piston  201 , and the relative low pressure of the condenser  102  to be exposed to the opposing side of the piston  201  for the entire stroke of the piston  201 . This mechanism is best used for relative low temperature differentials, for example less than 30 C, between the evaporator and the low temperature condenser. When this temperature differential is low, it is possible to convert a reasonable percentage of the available energy to work. At higher temperature differentials, the percentage of available energy that can be converted to work decreases because the valve switches do not allow for expansion of the vapor during each stroke. 
         [0034]    Additional considerations also must be taken when designing the system&#39;s displacement ratio (engine to pump or heat transformer displacement ratio), since the reversal process of the inlet and outlet valve switch in the engine  106  takes a finite amount of time, which allows for vapor to directly flow from the evaporator  101  to the condenser  102 . Additionally, the minimum clearance volume must also be accounted for when sizing the pistons of these systems. 
         [0035]    While the present system and method has been disclosed according to the preferred embodiment of the invention, those of ordinary skill in the art will understand that other embodiments have also been enabled. Even though the foregoing discussion has focused on particular embodiments, it is understood that other configurations are contemplated. In particular, even though the expressions “in one embodiment” or “in another embodiment” are used herein, these phrases are meant to generally reference embodiment possibilities and are not intended to limit the invention to those particular embodiment configurations. These terms may reference the same or different embodiments, and unless indicated otherwise, are combinable into aggregate embodiments. The terms “a”, “an” and “the” mean “one or more” unless expressly specified otherwise. The term “connected” means “communicatively connected” unless otherwise defined. 
         [0036]    When a single embodiment is described herein, it will be readily apparent that more than one embodiment may be used in place of a single embodiment. Similarly, where more than one embodiment is described herein, it will be readily apparent that a single embodiment may be substituted for that one device. 
         [0037]    In light of the wide variety of methods for transferring heat known in the art, the detailed embodiments are intended to be illustrative only and should not be taken as limiting the scope of the invention. Rather, what is claimed as the invention is all such modifications as may come within the spirit and scope of the following claims and equivalents thereto. 
         [0038]    None of the description in this specification should be read as implying that any particular element, step or function is an essential element which must be included in the claim scope. The scope of the patented subject matter is defined only by the allowed claims and their equivalents. Unless explicitly recited, other aspects of the present invention as described in this specification do not limit the scope of the claims.