Patent Application
20110271676
This disclosure relates to the conversion of heat energy to another form of energy, e.g. mechanical energy. The disclosure further relates to such conversion where the heat energy source is concentrated solar energy or a low grade or waste heat source.
Several different types of heat engines have been used in practice to convert concentrated solar radiation to mechanical power, notably Stirling cycle engines and Rankine cycle engines, however, all such known engines have had disadvantages relating to complexity, cost or low efficiency, Apparatus which convert heat energy into mechanical energy, namely the heat energy of concentrated beam of solar radiation into the movement of a piston through the explosion or expansion of a droplet of substantially uncompressed liquid targeted by the concentrated solar beam are described in patent application Ser. No. 11/512,568, referred to above. In patent application Ser. No. 11/512,568, (granted U.S. Pat. No. 7,536,861) a method of utilizing a droplet or thin film of water or other liquid, which is heated and explosively expanded in a six-sided expander, is described. The six-sided expander absorbs substantially all of the energy in the droplet and converts a large fraction of that energy to mechanical power through the motion of a linear piston. Mechanical power is in turn converted to electrical power by a linear generator on each of the six sides complete with field excitation and output coil.
In theoretical, conventional Rankine cycles, expansion of working fluid takes place under reversible adiabatic conditions. Also in conventional Rankine cycles as applied to solar energy conversion, the fluid is first vaporized in a boiler then passed into an expander.
Methods whereby liquid is injected into a working space above a piston have also been described. Conventionally, the hot liquid vaporizes at the point of injection, with consequent loss of available energy or exergy. Some of the initial energy loss on vaporization of liquid injected into the cylinder may be regained as heat transferred from the compressed vapor already within the cylinder; however, the energy thus transferred comprises no net heat addition from outside but merely constitutes energy re-circulated within the system. Such recirculation cannot, of itself, produce a useful energy output by the system.
Thus, in the liquid injection prior art, fluid is injected, with exergy loss into a chamber, during which relatively uncontrolled vaporization takes place reducing the amount of available energy, then work is done by adding heat back into the already partially expanded vapor to cause the further expansion of the vapor which moves a piston to perform useful work.
In one practical embodiment, a concentrated beam of solar radiation is directed through a high temperature resistant window, for example, of sapphire or any other suitable material, onto a thin film or droplet of water. The thin film or droplet can be sitting on or near a “target” disk or plate. The target disk or plate can be a material with high absorptivity, low emissivity in the near and far infra red range and very high surface area. The thin film or droplet of liquid is heated and subsequently expanded or exploded, to provide mechanical power.
Some embodiments use a boiler-less, thermodynamic cycle in which the working fluid is heated in contact with the expansion system and the expansion takes place whilst heat input is still going on. Fluid heating takes place at near constant volume, and with substantially no pre-compression resulting in achievement of pressures much higher than conventional Rankine cycles. Also, uniquely, expansion and heating take place on the constant pressure, constant temperature line in the liquid T s and h-s diagrams, unlike in conventional, Rankine cycle devices hitherto described in the prior art.
According to some embodiments, another part of the cycle comprises a constant volume heat recovery which pre-heats the unexpanded working fluid, while the exhausted, expanded working fluid experiences a constant pressure and constant temperature compression back to the liquid state. Due to the aforementioned heat recovery step whilst exhausting, in a particularly efficient embodiment, the cycle will receive input energy during the expansion process only.
According to an embodiment, an engine comprises a chamber defined by at least one fixed wall and at least one movable wall, the volume of the chamber variable with movement of the movable wall; an injector arranged to inject liquid into the chamber while the chamber has a substantially minimum volume; apparatus through which energy is introduced that is absorbed by the fluid which then explosively vaporizes, performing work on the movable wall; and apparatus which returns the movable wall to a position prior to the work being performed thereon so the chamber has the substantially minimum volume, substantially evacuating the chamber of vaporized fluid without substantially compressing the vaporized fluid.
According to another embodiment, a method of converting energy from one form to another in a system comprises confining a quantity of substantially unexpanded liquid within a chamber; adding energy to the system, so as to heat the liquid sufficiently to vaporize the liquid and expand a resulting vapor; and receiving mechanical energy from the expanding vapor in a form of movement of a wall of the chamber responsive to the expansion.
According to yet another embodiment, a method of converting energy from one form to another by passing a working material through a closed liquid-vapor thermodynamic cycle, comprises expanding the working material from a liquid phase into a vapor phase by addition of heat; recovering heat from the working material in the vapor phase so as to condense the working material from the vapor phase into the liquid phase to await expansion; and adding the recovered heat to working material awaiting expansion, without changing the phase thereof.
According to another embodiments, an engine is disclosed including: a chamber defined by at least one fixed wall and at least one movable wall, the volume of the chamber variable with movement of the movable wall; an injector arranged to inject liquid without expansion into the chamber while the chamber has a substantially minimum volume; an apparatus constructed and arranged to introduce energy into the chamber at a rate sufficient to explosively vaporize the liquid, performing work on the movable wall; an apparatus constructed and arranged to return the movable wall to a position prior to the work being performed thereon so the chamber has the substantially minimum volume; and a valve constructed and arranged to substantially evacuate the chamber of vaporized fluid without substantially compressing the vaporized fluid.
In some embodiments, the apparatus configured and arranged to introduce energy into the chamber is further configured and arranged to deliver energy to a target disk in contact with the liquid.
In some embodiments, the apparatus through which energy is introduced includes a window of a material with high transmissivity, low reflectivity and low absorptivity. In some embodiments, the window is sapphire.
In some embodiments, the apparatus configured and arranged to introduce energy into the chamber includes a textured surface in thermal contact with target disk. In some embodiments, the textured surface is in thermal contact with a heat exchanger with flow passages on the outside of the chamber.
In some embodiments, the apparatus configured and arranged to introduce energy into the chamber includes a porous block fitted between the moveable wall and the at least one fixed wall. In some embodiments, the porous block is constructed and arranged such that it may be heated by applying heat external to the cylinder, which is then transferred through a head of the cylinder into the block.
Some embodiments include a series of heat pipes embedded in the head of the cylinder.
In some embodiments, the moveable wall includes a face of a piston, the piston including a groove, the piston configured such that the groove is aligned with an exhaust port in the fixed wall of the chamber after work is performed on the moveable wall. In some embodiments, the apparatus constructed and arranged to return the movable wall to a position prior to the work being performed thereon includes a spring constructed and arranged to exert a force on the piston in a direction toward a portion of the fixed wall.
In some embodiments, the spring is constructed and arranged to rotate the piston upon a movement of the piston through the chamber. In some embodiments, the spring includes a plurality of fixed length members, the spring mechanically coupled to a shaft of the piston and constructed and arranged to convert a lateral motion of the piston into a rotational motion of the piston.
In some embodiments, the engine includes: a valve; and an actuator mechanically coupled to the valve; the valve disposed on a piston, a surface of the piston including the moveable wall.
In some embodiments, actuator includes a solenoid or a mechanical lifter.
In some embodiments, the vaporized fluid is condensed during a time period when work is performed on the moveable wall.
Some embodiments include a heat exchanger mounted within an area defined by the fixed wall, an input to the heat exchanger in fluid communication with the valve, and an output of the heat exchanger in fluid communication with the injector. In some embodiments, the heat exchanger includes a variable bypass.
Some embodiments include a valve formed from the combination of a slot in a piston, a surface of the piston including the moveable wall, and a slot disposed in a sleeve disposed to the outside of the piston, the sleeve and piston constructed and arranged to rotate relative to one another.
Some embodiments include a heat recovery jacket surrounding at least a portion of the engine and in fluid communication with a heat exchanger, an input to the heat exchanger in fluid communication with the valve, and an output of the heat exchanger in fluid communication with the injector.
Some embodiments include a bypass splitter in fluid communication with the injector, the heat recovery jacket, and a bypass line, the bypass splitter constructed and arranged to divide a portion of the liquid to be injected into the chamber into a portion flowing through the heat recovery jacket and a portion flowing through the bypass line.
In some embodiments, the fluid is water.
In some embodiments, the engine has a rotary configuration. Some such embodiments may include an epitrochoid-shaped chamber and/or a roughly triangular rotor,
According to another embodiment, a method is disclosed of converting energy from one form to another in a system, including: confining a quantity of substantially unexpanded liquid within a chamber; adding energy to the system, so as to heat the liquid sufficiently to vaporize the liquid in the absence of a chemical reaction and expand a resulting vapor; and receiving mechanical energy from the expanding vapor in a form of movement of a wall of the chamber responsive to the expansion.
In some embodiments, receiving mechanical energy from the expanding vapor further includes rotating the wall of the chamber relative to a second wall of the chamber.
In some embodiments, expanding the vapor includes expanding the vapor to a volume of over 80 times that of the unexpanded liquid.
Some embodiments include performing a closed liquid-vapor thermodynamic cycle in which one or more or all of the following hold: the liquid is not compressed in the chamber prior to expanding the vaporized liquid; the liquid heating takes place at near constant volume; the liquid is vaporized at a constant temperature and pressure; the expansion takes place while heat is being input; the vapor is exhausted from the chamber at a constant pressure; heat is recovered from the vapor with the vapor maintained at a constant temperature and pressure; the vapor phase is condensed at a constant pressure and temperature; and heat is recovered from the vapor by transferring the recovered heat to liquid awaiting expansion while maintaining a constant volume of the liquid awaiting expansion. In some embodiments, the temperature of the system during the expansion is maintained at a constant level as energy is added to the system, and the input of heat during the expansion results in substantially no change of internal energy to the system.
In some embodiments, the method includes performing a closed liquid-vapor thermodynamic cycle in which one or more or all of the following hold: the liquid is not compressed in the chamber prior to expanding the vaporized liquid; the liquid heating takes place at near constant volume; the liquid is vaporized whilst doing work; the expansion takes place while heat is being input; the vapor is exhausted from the chamber at a constant pressure; heat is recovered from the vapor during the expansion, with a change in internal energy; the vapor phase is condensed at a constant pressure and temperature; and heat is recovered from the vapor by transferring the recovered heat to liquid awaiting expansion while maintaining a constant volume of the liquid awaiting expansion.
In some embodiments, the thermodynamic cycle receives input energy during the expansion process only.
In some embodiments, the liquid is water.
According to another embodiment, a method of converting energy from one form to another by passing a working material through a closed liquid-vapor thermodynamic cycle, is disclosed including: expanding at least a portion of the working material from a liquid phase into a vapor phase by addition of heat; recovering heat from the working material after expanding; condensing the working material, after recovering heat, from the vapor phase into the liquid phase, in a condenser, thus restoring the working material to a state where the working material awaits expansion to start a new cycle; varying the quantity of heat recovered by varying a bypass of the working material during recovering heat from the working material, so as to vary thermodynamic efficiencies and select desired specific work output; and adding the recovered heat to working material awaiting expansion, without changing the phase thereof; whereby efficiency of the method is improved over a method lacking recovering heat.
In some embodiments, the working material is expanded within a chamber and the working material is not compressed in the chamber prior to expanding the working material.
In some embodiments, heating the working material in the liquid phase takes place at near constant volume and the expansion takes place while heat is being input.
In some embodiments, expanding the working material from a liquid phase into a vapor is performed at a constant temperature and pressure. In some embodiments, expanding the working material from a liquid phase into a vapor is performed in a reversible; adiabatic cycle, where internal energy within the cycle is converted to mechanical work.
Some embodiments include exhausting working material in the vapor phase from the chamber, the working material in the vapor phase maintaining at a constant volume.
In some embodiments, recovering heat from the working material in the vapor phase is performed with the working material in the vapor phase maintained at a constant temperature and pressure.
In some embodiments, recovering heat from the working material in the vapor phase is performed with the working material in the vapor phase maintained at a constant volume.
In some embodiments, the working material in the vapor phase is condensed at a constant pressure and temperature.
In some embodiments, recovering heat from the working material in the vapor phase includes adding the recovered heat to working material awaiting expansion while maintaining a constant volume of the working material awaiting expansion.
In some embodiments, the temperature of the system is maintained at a constant level as energy is added to the system.
In some embodiments, varying a bypass of the working material during recovering heat from the working material includes varying a ratio of feed liquid mass flow in a heat recovery jacket to a total feed liquid mass flow, the heat recovery jacket surrounding a portion of an engine in which the method is performed.
Some embodiments include decreasing a specific power output of the engine while increasing the thermodynamic efficiency of the engine by increasing the ratio of feed liquid mass flow in the heat recovery jacket to the total feed liquid mass flow.
In some embodiments, the working material is water.
Some embodiments including putting the water in a supercritical state.
According to another embodiments, an engine is disclosed including: a chamber defined by at least one fixed wall and at least one movable wall, the volume of the chamber variable with movement of the movable wall; an injector arranged to inject liquid into the chamber while the chamber has a substantially minimum volume; an apparatus constructed and arranged to introduce energy into the chamber while the chamber has a substantially minimum volume at a rate sufficient to explosively vaporize the liquid, where the movable wall is adapted to move in response to work performed by the vaporized liquid, thereby increasing the volume of the chamber; an apparatus constructed and arranged to return the movable wall to a position prior to the work being performed thereon so the chamber has the substantially minimum volume; and a valve constructed and arranged to substantially evacuate the chamber of vaporized fluid without substantially compressing the vaporized fluid.
According to another embodiment, a method of converting energy from one form to another in a system is disclosed, including: confining a quantity liquid within a chamber at a constant minimum volume; adding energy to the system while maintaining the chamber at the constant minimum volume, so as to heat the liquid sufficiently to vaporize the liquid; expanding a resulting vapor; and receiving mechanical energy from the expanding vapor in a form of movement of a wall of the chamber responsive to the expansion.
In some embodiments, adding energy to the system while maintaining the chamber at the constant minimum volume, so as to heat the liquid sufficiently to vaporize the liquid includes vaporizing the liquid in the absence of a chemical reaction.
According to another embodiment a method of converting energy from one form to another by passing a working material through a closed liquid-vapor thermodynamic cycle, including: expanding at least a portion of the working material from a liquid phase into a vapor phase by addition of heat; recovering heat from the working material after expanding; condensing the working material, after recovering heat, from the vapor phase into the liquid phase, in a condenser, thus restoring the working material to a state where the working material awaits expansion to start a new cycle; and adding the recovered heat to working material awaiting expansion, without changing the phase thereof.
In one aspect, a method is disclosed of converting thermal energy into another energy form using a thermodynamic cycle, the method including the steps of: pressurizing a working fluid; supplying thermal energy to heat the working fluid from a liquid or substantially liquid state to a supercritical fluid state; in a first expander, substantially isentropically expanding the working fluid to yield energy in the other energy form; separating the expanded working fluid to form a first portion of the fluid diverted to a second expander and a second portion of the working fluid diverted to bypass the second expander; in the second expander, substantially isentropically expanding the first portion of the working fluid to yield energy in the other energy form; condensing the expanded first portion of the working fluid to a liquid or substantially liquid state; and recombining the first and second portions of the working fluid to be recirculated in the cycle.
In some embodiments, in the first expander, the working fluid is progressively dried during at least a portion of the expansion. In some embodiments, in the second expander, the first portion of the working fluid is progressively dried during at least a portion of the expansion.
In some embodiments, the other form of energy includes mechanical energy.
In some embodiments, the first expander or the second expander includes a turbine expander.
In some embodiments, the first expander or the second expander includes a piston expander.
In some embodiments, the working fluid is an organic fluid. In some embodiments, the organic fluid includes at least one fluid from the list consisting of: ammonia, benzene, butane, isobutane, carbon tetrachloride, HCFC-123, propane, R-245fa, R-245ca, and toluene. In some embodiments, the organic fluid has a critical temperature of about 200 degrees C. or less. In some embodiments, the organic fluid has a critical temperature of about 175 degrees C. or less. In some embodiments, the organic fluid has a critical temperature of about 150 degrees C. or less. In some embodiments, the organic fluid has a critical temperature in the range of 150-200 degrees C.
In some embodiments, the step of condensing the expanded first portion of the working fluid to a liquid or substantially liquid state includes rejecting heat from the cycle at a temperature of about 45 degrees C. or more.
In some embodiments, the step of heating the working fluid include accepting heat from a heat sources at a temperature of about 200 degrees or less (e.g. 175 degrees C. or less, 150 degrees C. or less, etc).
In some embodiments, the cycle has a Carnot efficiency of about 30% or more.
In some embodiments, the efficiency of the first expander and the second expander is about 80% or more.
In some embodiments, the net cycle efficiency in about 15% or more.
In some embodiments, the specific net work output of the cycle is about 20 kJ/Kg or more.
In some embodiments, the step of separating the working fluid includes separating the working fluid with a bypass ratio of about 50%.
In some embodiments, in the step of in a first expander, substantially isentropically expanding the working fluid, the expansion is characterized by an expansion ratio of in the range of 4:1 and 8:1.
In some embodiments, in the step of, in a second expander, substantially isentropically expanding the first portion of the working fluid, the expansion is characterized by an expansion ratio in the range of 4:1 and 12:1.
Some embodiments further include the step of: after condensing the expanded first portion of the working fluid and prior to recombining the first and second portions of the working fluid, substantially isentropically pressurizing the first portion of the working fluid.
In some embodiments, the step of recombining the first and second portions of the working fluid, the first portion of the working fluid is at a lower temperature than the second portion of the working fluid.
In some embodiments, the step of recombining the first and second portions of the working fluid includes transferring heat from the second portion to the first portion by direct contact of the first and second portions of the working fluid.
Some embodiments further include the step of after the step of separating the expanded working and prior to the step of recombining the first and second portions of the working fluid, extracting heat from the second portion of the working fluid.
Some embodiments further include using the heat extracted from the second portion of the working fluid to drive a secondary thermodynamic cycle to convert the heat to another form of energy.
In some embodiments, the secondary cycle converts the heat extracted from the second portion of the working fluid to mechanical work.
In some embodiments, the secondary thermodynamic cycle includes a trilateral flash cycle or a Rankine cycle.
In some embodiments, the secondary thermodynamic cycle operates on an organic working fluid.
In some embodiments, the secondary thermodynamic cycle operates on an inorganic working fluid.
In some embodiments, the step of supplying thermal energy to heat the working fluid from a liquid or substantially liquid state to a supercritical fluid state includes: injecting a quantity of the working fluid in the liquid or substantially liquid state into a chamber without substantially expanding the fluid; and holding the chamber at fixed volume while introducing energy to the quantity of the working fluid to vaporize the quantity of the working fluid.
In some embodiments, introducing energy to the quantity of the working fluid includes introducing optical energy to the quantity of the working fluid through at least one light transmissive region of the chamber.
In some embodiments, the quantity of working fluid is explosively vaporized without a chemical reaction.
Some embodiments further include: prior to condensing the expanded first portion of the working fluid, transferring heat from the expanded first portion of the working fluid to the recombined the first and second portions of the working fluid to be recirculated in the cycle.
Some embodiments include using a heat exchanger to transfer the heat from the expanded first portion of the working fluid to the recombined the first and second portions of the working fluid to be recirculated in the cycle.
In some embodiments, the heat exchanger does not mix the expanded first portion of the working fluid with thee combined the first and second portions of the working fluid.
Some embodiments include separating the first portion of expanded working fluid from the second expander to form a third portion of the fluid diverted to a third expander and a forth portion of the working fluid diverted to bypass the third expander.
Some embodiments include, in the second expander, substantially isentropically expanding the first portion of the working fluid to yield energy in the other energy form.
In another aspect, an apparatus for converting thermal energy into another energy form including a closed cycled heat engine including: a first pump configured to pressurize a working fluid; a first heat exchanger configured to supply thermal energy for a heat source to heat the working fluid from a liquid or substantially liquid state to a supercritical fluid state; a first expander configured to receive the heated working fluid in the supercritical state and substantially isentropically expand the working fluid to yield energy in the other energy form; and a bypass mechanism configured to separate the expanded working fluid to form a first portion of the fluid diverted to a second expander and a second portion of the working fluid diverted to bypass the second expander; the second expander configured to substantially isentropically expand the first portion of the working fluid to yield energy in the other energy form; a condenser configured to reject heat from the expanded first portion of the working fluid to condense the expanded first portion of the working fluid to a liquid or substantially liquid state; and a combining mechanism configured to recombine the first and second portions of the working fluid and directed the combined working fluid to the first pump to be recirculated in the cycle.
In some embodiments, in the first expander, the working fluid is progressively dried during at least a portion of the expansion. In some embodiments, in the second expander, the first portion of the working fluid is progressively dried during at least a portion of the expansion.
In some embodiments, the other form of energy includes mechanical energy.
In some embodiments, the first expander or the second expander includes a turbine expander.
In some embodiments, the first expander or the second expander includes a piston expander.
In some embodiments, the working fluid is an organic fluid. In some embodiments, the organic fluid includes at least one fluid from the list consisting of: ammonia, benzene, butane, isobutane, carbon tetrachloride, HCFC-123, propane, R-245fa, R-245ca, and toluene. In some embodiments, the organic fluid has a critical temperature of about 200 degrees C. or less. In some embodiments, the organic fluid has a critical temperature of about 200 degrees C. or less. In some embodiments, the organic fluid has a critical temperature of about 175 degrees C. or less. In some embodiments, the organic fluid has a critical temperature of about 150 degrees C. or less. In some embodiments, the organic fluid has a critical temperature in the range of 150-200 degrees C.
In some embodiments, the condenser is configured to reject heat at a temperature of about 45 degrees C. or more.
In some embodiments, the heat source is at a temperature of about 200 degrees or less. In some embodiments, the cycle has a Carnot efficiency of about 30% or more. In some embodiments, the efficiency of the first expander and the second expander is about 80% or more. In some embodiments, the net cycle efficiency in about 15% or more. In some embodiments, the specific net work output of the cycle is about 20 kJ/Kg or more.
In some embodiments, the bypass mechanism separates the working fluid with a bypass ratio of about 50%.
In some embodiments, the first expander is characterized by an expansion ratio in the range of 4:1 to 8:1 In some embodiments, the second expander is characterized by an expansion ratio in the range of 4:1 to 12:1.
Some embodiments further include: a second pump configured to receive the first portion of the working fluid from the condenser, isentropically pressurize the first portion of the working fluid, and direct the pressurized first portion of the working fluid to the combining mechanism.
In some embodiments, the combining mechanism receives the first portion of the working fluid at a lower temperature than the second portion of the working fluid. In some embodiments, the combining mechanism includes a direct contact heat exchanger configured to transfer heat from the second portion to the first portion of the working fluid by direct contact of the first and second portions of the working fluid.
Some embodiments include: a second heat exchanger configured to extract heat from the second portion of the working fluid.
Some embodiments include: a secondary thermodynamic cycle heat engine which receives the heat extracted from the second portion of the working fluid and converts the heat to another form of energy.
In some embodiments, the secondary thermodynamic cycle heat engine converts the heat extracted from the second portion of the working fluid to mechanical work.
In some embodiments, the secondary thermodynamic cycle heat engine includes a trilateral flash cycle heat engine or a Rankine cycle heat engine.
In some embodiments, the secondary thermodynamic cycle heat engine operates on an organic working fluid.
In some embodiments, the secondary thermodynamic cycle heat engine operates on an inorganic working fluid.
In some embodiments, the first heat exchanger includes: an injector configured to introduce a quantity of the working fluid in the liquid or substantially liquid state into a chamber without substantially expanding the fluid; and a heating mechanism for introducing energy to the quantity of the working fluid to vaporize the quantity of the working fluid while holding the chamber at fixed volume.
In some embodiments, the heating mechanism includes at least one light transmissive region of the chamber configured to transmit optical energy to the quantity of the working fluid.
In some embodiments, in response to the introduced energy, the quantity of working fluid is explosively vaporized without a chemical reaction.
In some embodiments, the at least one light transmissive region includes a material of relatively high transmissivity and relatively low absorptivity to solar radiation.
In some embodiments, the at least one light transmissive region includes a material low emissivity at wavelengths in the near infrared an infrared portions of the spectrum.
In some embodiments, the closed cycle heat engine further includes a recuperating heat exchanger configured to transfer heat from the expanded first portion of the working fluid to the condensed working fluid which has exited the condenser.
In some embodiments, the closed cycle heat engine further includes a second bypass mechanism configured to separate the first portion of expanded working fluid from the second expander to form a third portion of the fluid diverted to a third expander and a forth portion of the working fluid diverted to bypass the third expander; the third expander configured to substantially isentropically expand the first portion of the working fluid to yield energy in a form other than heat.
Some embodiments include a second combining mechanism configured to combine the third and fourth portions of the expanded first portion of the working fluid
In another aspect, a method is disclosed of converting thermal energy into another energy form including the steps of: converting thermal energy to another energy form using a first trilateral flash cycle operating on a first working fluid, where the first trilateral flash cycle receives heat from a source at a first temperature T1 and rejects heat at a second temperature T2 lower that the first temperature; converting thermal energy to another energy form using a second trilateral flash cycle operating on a second working fluid, where the second trilateral flash cycle receives heat rejected from the first trilateral flash cycle at a third temperature T3 equal to or lower than T2 and rejects heat at a fourth temperature T4 lower than T3.
In some embodiments, the working fluid is an organic fluid. In some embodiments, the organic fluid includes at least one fluid from the list consisting of: ammonia, benzene, butane, isobutane, carbon tetrachloride, HCFC-123, propane, R-245fa, R-245ca, and toluene. In some embodiments, the organic fluid has a critical temperature of about 200 degrees C. or less. In some embodiments, the organic fluid has a critical temperature of about 200 degrees C. or less. In some embodiments, the organic fluid has a critical temperature of about 175 degrees C. or less. In some embodiments, the organic fluid has a critical temperature of about 150 degrees C. or less. In some embodiments, the organic fluid has a critical temperature in the range of 150-200 degrees C.
In some embodiments, the converting thermal energy to another form using the first and second trilateral flash cycles includes, respectively: substantially isentropically pressurizing the respective first or second working fluid; supplying thermal energy to heat the respective first or second working fluid; in a respective first or second expander, substantially isentropically expanding the respective heated first or second working fluid to yield energy in the other energy form; condensing the expanded respective first or second working fluid exhausted from the respective first or second expander; and recirculating the condensed respective first or second working fluid for recompression.
In some embodiments, the other form of energy includes mechanical work.
In some embodiments, the first and second expanders include reciprocating piston expanders.
Some embodiment use the first and second piston expanders to drive a common shaft.
In some embodiments, T1 is about 300 degrees C. or less. In some embodiments, T2 is about 100 degrees C. or more. In some embodiments, T3 is about 100 degrees C. or less. In some embodiments, T4 is about 40 degrees C. or more.
In some embodiments, the first cycle and second cycles are characterized by a net efficiency of about 10% or greater.
In some embodiments, at least one of the first and second expanders includes a turbine expander.
In some embodiments, for at least a respective one of the first and second trilateral flash cycles, the converting thermal energy to another form using the respective trilateral flash cycle includes: prior to the isentropic expansion, injecting a quantity of the heated respective first or second working fluid into a chamber without substantially expanding the fluid; and holding the chamber at fixed volume while introducing energy to the quantity of the working fluid to vaporize the quantity of the working fluid.
In some embodiments, introducing energy to the quantity of the working fluid includes introducing optical energy to the quantity of the working fluid through at least one light transmissive region of the chamber.
In another aspect, an apparatus is disclosed for converting thermal energy into another energy form including: a first trilateral flash cycle heat engine operating on a first working fluid configured to convert thermal energy to another energy form using a first trilateral flash cycle, where, during operation, the first trilateral flash cycle heat engine receives heat from a source at a first temperature T1 and rejects heat at a second temperature T2 lower that the first temperature; and a second trilateral flash cycle heat engine operating on a first working fluid configured to convert thermal energy to another energy form using a first trilateral flash cycle, where, during operation, the second trilateral flash cycle heat engine receives heat rejected from the first trilateral flash cycle heat engine at a third temperature T3 equal to or lower than T2 and rejects heat at a fourth temperature T4 lower than T3.
In some embodiments, the first working fluid has a higher boiling point that the second working fluid.
In some embodiments, the first working fluid includes water and the second working fluid includes an organic fluid.
In some embodiments, the organic fluid includes at least one fluid from the list consisting of: ammonia, benzene, butane, isobutane, carbon tetrachloride, HCFC-123, propane, R-245fa, R-245ca, and toluene. In some embodiments, the organic fluid has a critical temperature of about 200 degrees C. or less. In some embodiments, the organic fluid has a critical temperature of about 200 degrees C. or less. In some embodiments, the organic fluid has a critical temperature of about 175 degrees C. or less. In some embodiments, the organic fluid has a critical temperature of about 150 degrees C. or less. In some embodiments, the organic fluid has a critical temperature in the range of 150-200 degrees C.
In some embodiments, the first and second trilateral flash cycles include, respectively: a respective first or second pump configured to substantially isentropically pressurize the respective first or second working fluid; a respective first or second heat exchanger configured to supply thermal energy to heat the respective first or second working fluid: a respective first or second expander configured to substantially isentropically expand the heated respective first or second working fluid to yield energy in the other energy form; a respective first or second condenser configured to condense the expanded respective first or second working fluid exhausted from the respective first or second expander; and a conduit configured to recirculate the condensed respective first or second working fluid for recompression.
In some embodiments, the other form of energy includes mechanical work.
In some embodiments, the first and second expanders include reciprocating piston expanders.
In some embodiments, the first and second piston expanders to drive a common shaft.
In some embodiments, the common shaft drives a generator to convert mechanical work to electrical energy.
In some embodiments, T1 is about 300 degrees C. or less. In some embodiments, T2 is about 100 degrees C. or more. In some embodiments, T3 is about 100 degrees C. or less. In some embodiments, T4 is about 40 degrees C. or more. In some embodiments, the first cycle and second cycles are characterized by a net efficiency of about 10% or greater. In some embodiments, at least one of the first and second expanders includes a turbine expander.
In some embodiments, at least a respective one of the first and second trilateral flash cycle heat engine includes: an injector configured to inject a quantity of the heated respective first or second working fluid into a chamber without substantially expanding the fluid; and a mechanism for holding the chamber at fixed volume while introducing energy to the quantity of the working fluid to vaporize the quantity of the working fluid prior to expansion in the respective first or second expander. In some embodiments, the mechanism includes at least one light transmissive region of the chamber configured to transmit optical energy to the quantity of the working fluid through at least one light transmissive region of the chamber.
In some embodiments, the first expander is characterized by an expansion ratio of in the range of 4:1 to 8:1. In some embodiments, the first expander is characterized by an expansion ratio in the range of 4:1 to 12:1.
Various embodiments may include an of the above features, elements, steps, or techniques, either alone or in any suitable combination.
The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:
This invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having,” “containing,” “involving,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.
A single sided expander and its working cycle is now described. The single sided expander includes an oscillating piston and linear electrical generator. The single sided expander is derived from actual experimental rig results. It will be understood that expanders operating on the principles illustrated by the single sided expander but employing more than one moveable wall element are possible. Moreover, the single sided expander is described in the context of a cylindrical chamber having a piston which moves to vary the size of the chamber; however, it will be understood that other expander configurations are possible, for example based on a rotary configuration similar to the Wankel internal combustion engine, which also has an expansion chamber having a single side which moves to vary the size of the chamber. Any suitable expander chamber configuration in which the expander chamber varies in size responsive to the force of the expanding vapor within and which is returned to a starting position by excess energy temporarily stored in a flywheel or other device for the purpose.
The operating thermodynamic cycle for the expanders, according to various embodiments, is a closed cycle, having relatively high conversion efficiency. It will be contrasted with a conventional Rankine thermodynamic cycle. It is based on the heating and expansion of a droplet or thin film of any suitable liquid, without any substantial precompression of the liquid or any substantial pre-compression of any gas surrounding the liquid.
Reference will now be made to
The Expander 101 includes a piston 107 in a cylinder 108, the piston having a piston top 109, which forms a suitable cavity boundary, together with the cylinder 108 and a cylinder head 110. When it is in top dead centre (TDC) position a water droplet or film 111 is injected into this cavity, with necessary propellant force being provided by the liquid pump 104.
A concentrated solar beam 105 is applied intermittently through a sapphire window 112 or other means provided in the cylinder head 110, such that the trapped water droplet or film 111 is vaporized and expands against the piston top 109, producing mechanical power, during an expansion stroke. See also
In addition to utilizing a beam of concentrated solar radiation, any other suitable method of introducing heat into the chamber may be used. For example, a heat exchanger with flow passages on the outside of the chamber may be configured to heat up a flat surface or surface with enhanced area (e.g., textured to have additional surface area), which is directly in contact with the water film inside the cylinder and trapped between piston and cylinder head. Alternatively, a porous block or plate may be fitted between the piston and cylinder head. The porous block, which, as a result of its porosity, has a very substantial surface to volume ratio, can be heated by applying heat externally, which is then transferred through the cylinder head into the block. In yet another alternative, a series of heat pipes embedded in the cylinder head, may enable heat to be transferred at a very high rate from external sources. This last alternative can be combined with the use of the porous block or heat transfer surface explained above.
Exhaust of spent vapor at point 2 on the T-s diagram is carried out by a rotation of the piston such that exhaust ports 122 on the cylinder wall line up with grooves 120a and 120b in the piston, as shown in
In addition to piston rotation, any other suitable method for exhausting spent vapor may be used. For example, a poppet type valve can be disposed in the cylinder head, operated by a solenoid, mechanical lifters or any other suitable means. Alternatively, a valve can comprise a combination of a slot in the piston together with a slot disposed in a rotating sleeve disposed to the outside of the piston. The rotating sleeve may comprise the whole of the cylinder. A cyclical rotation of the sleeve can alternately bring into alignment and take out of alignment the slot in the piston wall in relation to the corresponding slot in the cylinder wall. In yet another alternative, a poppet valve may be disposed on the top surface of the piston, exhausting spent vapor to the area behind the piston. This last alternative has some advantages, notably that the constant pressure condensation step (step 3-4 in
Spent vapor must be condensed, also referred to herein as Process 3-4, prior to reinjection into the cylinder, for example, in condenser 103. The process pathway is given as line 3-4 in the T-s diagram. The spent vapor condensation, Process 3-4, is represented as a constant pressure process. At point 4, the spent vapor is wholly in liquid form, ready for injection into the expander cylinder to start a new cycle. Thus, a continually refreshed supply of working fluid is not required, as the cycle is closed.
Condensed liquid from the condenser 103 is pumped up to injection pressure by means of pump 104, through heat exchanger 102 and then injected into cylinder 108 as a liquid droplet or thin film. The heat exchanger 102 permits otherwise wasted heat in the vapor to be recovered for the useful purpose of increasing the energy available in the next expansion cycle, rather than simply disposing of waste heat. This part of the cycle is indicated as lines 4-5 (liquid pumping, Process 4 5) and 5-6 (constant volume heat gain, Process 5-6), in the T-s diagram. Notably, because the heat recovered by the heat exchanger 102 provides insufficient energy to the liquid to vaporize the liquid prior to or dining injection into the cylinder 108, the full energy of expansion of the liquid into expanded vapor after adding some quantum of externally supplied heat is available to perform work on the piston 107.
The inventive cycle is distinguished from conventional Rankine cycles in part by eliminating the boiler and also because inward heat transfer occurs while the working fluid is in the cylinder 108. Other differences include the presence of two constant volume heat transfer processes, (1) Process 2-3, and (2) Process 5-6, in the T-s diagram, and a low pressure compression step, 3-4. The portion 6-1 is an external heat addition step, because the total recovered heat in the 5-6 step is insufficient to heat the condensed fluid awaiting expansion to the fluid's saturation temperature at point 1.
In comparison with conventional Rankine cycles, the ability to do external work during the heat addition process has not previously been considered practical by those skilled in this art, possibly because of the difficulty of implementation. The described and heretofore unknown embodiment, and the variations suggested herein, each demonstrate a way to accomplish this useful result.
In contrast with conventional Rankine cycles a very high expansion ratio is achieved by embodiments in a single cylinder. Because the working fluid is expanding directly from a condensed liquid state to vapor within the cylinder of the expander, expansion ratios of over 80:1 may be achieved in a single cylinder with a four inch diameter and 5 inch stroke. See
Embodiments further employ a single piston on a rod; to the opposite end of this rod a linear generator 106 is mounted, capable of absorbing mechanical energy produced and converting that mechanical energy in the form of motion to electrical energy, at high efficiency. The linear generator consists of permanent magnet 116 and/or coil 114 type system for excitation field and a coil 114 based electrical output system, with necessary software based field current control for production of sinusoidal power output. A rotary crank and suitable connecting rod can also permit connection to a conventional, rotary generator.
In general terms, the invention consists of a unique liquid film-based, constant-temperature, wet-region, expansion heat engine device, running on a unique, hitherto unexploited thermodynamic power cycle, with heating during expansion resulting in an expansion with no internal energy change, constant volume heat transfer, isothermal compression, leading to very high conversion efficiency,
The theoretical basis for the operation of the inventive engine is now presented using non-flow, 1st Law analyses. The theoretical underpinning of each of the processes discussed above is given.
Q
1-2
−W
1-2
=δH
1-2 Process 1-2:
In the general case, δH is non zero. Therefore, rearranging, the heat input during Process 1-2 is
Q
1-2
=W
1-2+(h2, h1)
Q
2-3=(h2−h3) Process 2-3:
Q
3-4
−W
3-4
=h
4
−h
3 Process 3-4:
This process constitutes pressurization of the liquid to operating pressure PI and is a work input term. Since the pressurization is being done on a liquid and not vapor, the magnitude of this term is usually low,
W
4-5=(P1−P3)×v1
This process constitutes a constant volume heat gain to the pressurized liquid and receives heat from the heat output process of process 2-3. No external or internal work is done, in this process. This is the transfer of heat from spent vapor which is to be condensed back to liquid (for subsequent injection into the expander), into the liquid that is presently awaiting injection into the expander, thus recovering heat that would otherwise be discarded as waste heat. Since the working fluid at 6 is in liquid form whereas the working fluid at 2 is a mixture of vapor and liquid, the total quantum of heat that may be recovered and introduced to the liquid in the process 5-6 is limited by the fluid temperature at 2.
Therefore, Q5-6=Q2′-3,
where point 2′ represents the liquid condition pertaining to the pressure and temperature at point 6. Therefore the enthalpy at 6 is given by
h
6=(h2′−h4)+h5
Generally U5=U4, hence
h6=h2′
To bring the working fluid up to the working temperature and pressure, additional heat input, for example by transferring into the expansion chamber concentrated solar energy, is required, as follows:
Q
6-1
=h
1
−h
6
Hence
Q
6-1
=h
1
−h
2′
Therefore total heat input to the cycle is
Q
in total
=Q
6-1
+Q
1-2,
Or
Q
in total=(h1−h2′)+W1-2+(h2−U1).
Hence,
Q
in total=h2−h2′)+W1.
I a difference in the recovered energy in the constant volume heat transfer and the net work output is equal to gross work out less the low pressure vapor compression work and the liquid compression work.
Part of the heat available at point 2 of the cycle, after expansion, is recovered and utilized for preheating of the fluid prior to commencement of the cycle, at point 1 of the cycle, with additional heat addition to make up any shortfall,
One example of a novel thermodynamic cycle has been described, above. Further specific, novel modifications of a general class of cycles, based on the above cycle, are now presented.
The novel thermodynamic cycle described above, and the related cycles described now are part of a general class of cycles characterized by the Trilateral Flash Cycle described in U.S. Pat. No. 5,833,446, issued to Smith et al. The Trilateral Flash Cycle is presented in
Process 1-2 Heat Addition at constant pressure
Process 2-3 Adiabatic, reversible expansion from saturated liquid state at 2
Process 3-4 Constant pressure condensation
The work described in the Smith at al. patent indicates the Trilateral Flash Cycle is suitable for low grade and geothermal heat recovery and highly suited to utilization with organic fluids. Smith et al. were unable to identify any wider range of suitable application for the particular cycle they describe.
During any Rankine cycle process in the wet vapor region, heat may be recovered during expansion. The quantity of heat recovered affects the improvement achieved in the power output and the efficiency.
According to an aspect of an embodiment, as illustrated by
This bypass ratio may theoretically vary from 0 to 1 but very low bypass ratios result in low specific power outputs hence a more practical approach would be in the range 0.2 to 1.0. The expansion processes resulting from finite stepwise variation of bypass flow is generally shown as lines 2-3a, 2-3b, 2-3c etc. In each of these cases,
There is a progressive increase in specific power output and a decrease in overall efficiency as the line from 2-3n approaches vertical (not shown).
To describe the cycle more fully, feedwater at point 1 is pressurized by the pump (see
The Trilateral Flash Cycle identified by Smith et al. is a special case of the general class of liquid to vapor expansion bypass cycles, with a bypass ratio equal to 1, thereby resulting in a high specific power output but a low overall efficiency, for this class of cycles.
A conventional Rankine cycle calculation may be applied to the liquid to vapor expansion bypass cycle; the resulting pressure volume diagram is given in
Although it was not apparent to Smith et al., we have discovered that lower bypass ratios lead to a substantial efficiency increase. As a result of these high efficiencies water, which is readily available in many locales, may be used as the working fluid, whereas Smith et al. propose organic fluids due to perceived low efficiencies using water. Low efficiency using water in the trilateral cycle appears unavoidable in the literature, but we have discovered that low bypass ratio cycles lift this ceiling and permit consideration of water as a working fluid,
The new cycle with bypass may be logically and rationally extended to the supercritical region of the fluid, see
The new cycle when extended to the superheated region shows higher efficiency than in the wet vapor region, in keeping with Carrot efficiency temperature dependence correlations. There is, however, substantial improvement in work done per unit mass of fluid, which is clearly apparent from the fact that internal energy and enthalpy are much higher in the supercritical region. A cycle with a reversible, adiabatic expansion directly from point 2 down to condensing temperature and pressure, as in the case of the trilateral flash cycle of
The general class of liquid to vapor expansion cycles in the wet vapor and supercritical region with bypass constitute a new class of thermodynamic cycles and provides enhanced efficiency possibilities in a multitude of applications: fixed bypass ratio systems may be used in constant output applications such as geothermal power generation; and, variable bypass ratio systems may be considered for hybrid vehicle applications, wherein a low bypass ratio is used during cruising only to charge a battery at a high efficiency, with a momentary high bypass ratio used to produce higher power output for overtaking, etc.
In another embodiment, instead of recovering heat from a jacket external to the expansion cylinder, it is possible to recover heat by splitting the working fluid into two parts after a first expansion process, see
The cycle process steps are as follows. In process 1-2 the working fluid is preheated by means of extracted working fluid from an expansion process, in heat exchanger 131. In process 2-3 heat is added to the preheated working fluid from outside source in a heat exchanger. In process 3-4, a primary expansion of all of the working fluid occurs, e.g. in piston/cylinder expander 112. As shown, the primary expansion is isentropic (i.e. reversible and adiabatic). In some embodiments, the primary expansion may take place in any other suitable type of expander, e.g. a turbine expander. In some embodiments, mechanical work extracted during the primary expansion process (e.g. from piston expander 112) may be used for any suitable application, e.g. to drive the shaft of a generator (e.g. a linear generator as shown) to generate electrical energy.
The working fluid is then exhausted at point 4 and divided into two parts in the flow splitter 129. A first portion of the working fluid, having a fluid fraction k where 0<k<1 is diverted into heat exchanger 131, as a heating fluid used to preheat the working fluid as described above. In process 4-2′-1 heat is transferred in exchanger 131 from the first portion (i.e. the diverted portion) of the working fluid to the condensed and pressurized working fluid moving from condenser 103 through pump 104.
A second portion of the working fluid, having fluid fraction 1-k, is sent to a second expander 130. As shown expander 130 is a piston expander, but any other suitable expander (e.g. a turbine expander) may be used. In process 4-5 the second portion of the working fluid undergoes further expansion to the condition at the fluid condenser 103 denoted as point 5, with production of additional work. In process 5-6 the second portion of the working fluid is condensed in the condenser 103.
In process 6-6′ the first (diverted) and second (undiverted) portions of the working fluid are mixed at the suction entrance to the pump. In process 6-1 the combined fluid is pressurization by the pump, and is ready to be recirculated to start new cycle
By utilizing a fraction k of the working fluid to preheat all of the working fluid, a significant efficiency gain is achieved in the thermodynamic cycle. Not wishing to be bound by theory, the inventors have found that the overall cycle efficiency may be calculated by the formula:
Where h3 is enthalpy at point 3, h5 is enthalpy at point 5, h2 is the liquid enthalpy at point 2, h4 is the liquid vapor mix enthalpy at point 4, k is the fraction of working fluid diverted to be used in preheating, and T4 is the temperature at point 4. This simple but elegant formula provides a convenient method of calculating ideal cycle efficiency.
Notably, as shown in
A cycle of this type may have it's highest temperature and pressure point in the supercritical or subcritical region, in
Referring to
Referring to
The heated supercritical working fluid undergoes an isentropic expansion process 2-3 in the first high pressure expander 202. As shown the first expander is a turbine expander, but any suitable expander (e.g. a reciprocating piston expander) may be used. Work Whp (e.g. mechanical work) is extracted during the expansion process. Referring to
The working fluid exhausted from the first expander 202 enters a flow splitter 203 which directs a first portion of the working fluid to second low pressure expander 204, as indicated by process 3-4. The flow splitter 203 directs a second portion of the working fluid to bypass the second expander 204, as indicated by process 3-6.
The first portion of the working fluid undergoes an isentropic expansion process 4-5 in the second low pressure expander 205. As shown the first expander is a turbine expander, but any suitable expander (e.g. a reciprocating piston expander) may be used. Work WIp (e.g. mechanical work) is extracted during the expansion process. As in the first expansion process, the working fluid becomes progressively drier, which, in some embodiments, may advantageously allow for the use of smaller, less costly expanders.
In some embodiments, mechanical work extracted from the first and second expanders 202 and 204 may be used to drive a common shaft, e.g., which may in turn drive a generator to produce electrical energy. In other embodiments, the work generated by each of the expanders may be directed to separate applications.
Each of the first and second expanders may have expansion ratios greater than 1:1, 2:1: 4:1, 8:1; 12:1 or more, e.g. in the range of 4:1 to 8:1 or 4:1 to 12:1 or any other suitable value. In some embodiments the expansion ration of the first expander may be greater than less than or equal to that of the second expander.
The first portion of the working fluid exhausted from the second expander 204 is directed to condenser 205. The condenser condenses the expanded vapor back to a liquid or substantially liquid state in process 5-7. The condenser rejects heat to the surrounding environment (as shown at temperature T7=45 degrees C.).
The condensed first portion of the working fluid is directed to the first low pressure pump 206, which isentropically pressurized the condensed fluid. The pressurized fluid is them mixed with the second portion of working fluid that was diverted to bypass the second low pressure expander 204. The first and second portions of the working fluid are mixed in direct contact heat exchanger 207 (point 6 in
In process 9-10 the combined fluid is pressurization by the second high pressure pump 208. In process 10-1, the mixed, preheated, pressurized working fluid is recirculated to start new cycle.
A cyclic power generation process of this type with heat acceptance at a higher temperature and heat rejection at a lower temperature is governed by the Second Law of Thermodynamics and the maximum possible efficiency is the Carnot efficiency which is 1−T2/T1 where T1 and T2 are absolute temperatures of the heat source (e.g. the temperature of incoming water) and heat sink (i.e. the temperature in the condensing process 5-7) respectively. For the general conditions given in
An isentropic or expander efficiencies of 80% or more are achievable for organic fluids such as R-245fa. Because these fluids become drier as expansion proceeds, the expansion process can proceed to temperatures near ambient without the fluid becoming two-phase. This avoids the complications of and the reductions in expander efficiency of operation in the two phase region. Therefore utilizing this type of fluid leads to a high cycle efficiency. Suitable fluids include organic ammonia, benzene, butane, isobutane, carbon tetrachloride, HCFC 123, HCFC 134a, propane, R-245fa, R-245ca, toluene, or any other suitable fluid.
Not wishing to be bound by theory, the inventors have found that a formula for the theoretical efficiency η for this type of cycle may be derived, as:
Where Tc is the temperature at which the cycle rejects heat (i.e. T7 as shown in
The above formula for cycle efficiency assumes a perfectly isentropic (i.e., reversible) expansion process (i.e. process 2-5 as shown in
The isentropic efficiency ηisent for any gas expansion process, may be defined as the actual enthalpy change divided by ideal enthalpy change possible in the process and applies to reversible, adiabatic processes.
Ideally, the total amount of heat available for recovery, represented as a temperature difference, is (Tout′−Tout). However, this whole amount may not available due to imperfect heat exchanger efficiencies. In such cases, the actual heat recovered is may represented by the difference between Tout″ and Tout, given by (Tout″−Tout) where
Therefore k is a proportionality factor, where 0<k<1, which accounts for less-than-perfect heat recovery in an actual heat exchanger.
Taking into account the isentropic expansion efficiency ηisent and the heat recovery factor k, the cycle efficiency η may be calculated as:
where
F=((1−k)+kηisent).
Note that for the special case k=1 and ηisent=1, the above efficiency formula reduces to that derived in the case of perfect expansion efficiency and heat recovery.
As will be understood by those skilled in the art, the above described heat engines may be modified to employ and of the devices or techniques described herein. For example, the heating process 1-2 may include the injection of quantity of working fluid into a chamber (e.g. of a piston), and the introduction of energy (e.g. via concentrated solar energy directed through a transparent window in the chamber) to the quantity of working fluid to vaporize the fluid, as described in detail above.
Although in the examples above, 50% of the working fluid was diverted to bypass the second expander 204, any other suitable bypass ratio may be used. In some embodiments, the bypass ratio may be adjust to improve or maximize one or more operating parameters of the cycle (e.g. net cycle efficiency, work output, etc.). In various embodiments, one or more of these operating parameters may be monitored via a suitable sensor, and the bypass ratio adjusted based on the sensor measurement (e.g. using a servo loop in real time).
In some embodiments, heat engine 200 may be modified to include one or more additional components. For example, referring to
The calculated efficiency the heat engine 200 depicted in
Generally the incorporation of both feed water heating and recuperation after final expansion has result in a significant practical cycle efficiency improvement. Note that cycle efficiencies of greater than 17%, e.g., up to about 24% or more may be achieved. In some embodiments, the efficiency may approach the theoretical Carnot efficiency (equal to 1−T2/T7). In some embodiments, the cycle efficiency may be in the range of about 15% to about 25%.
Referring to
As will be evident to one skilled in the art, any number of additional heat expanders may be included in a similar fashion, each capable of extracting mechanical work Flow splitters positioned between some or all of the expanders to allow extraction of working fluid to be used for feed fluid heating.
The calculated efficiency the heat engine 200 depicted in
Generally the incorporation of both feed water heating and recuperation after final expansion has resulted in a significant practical cycle efficiency improvement. Note that cycle efficiencies of greater than 17%, e.g., up to about 24% or more may be achieved. In some embodiments, the efficiency may approach the theoretical Carnot efficiency (equal to 1−T2/T7). In some embodiments, the cycle efficiency may be in the range of about 15% to about 25%.
Referring to
As will be understood by one skilled in the art, an increased amount of mechanical work extracted from the diverted fluid will lead to a decreased cycle efficiency for heat engine 200. Referring to
Although
Referring to
In some embodiments, the first working fluid of the upper cycle has a relatively high boiling point, while the second working fluid of the lower cycle has a relatively low boiling point. For example, the first working fluid may be pressurized water/steam, while the second working fluid is a low boiling point fluid, e.g. an organic fluid such as HCFC 123 or HCFC 134a. In other embodiments, the organic working fluid may include organic ammonia, benzene, butane, isobutane, carbon tetrachloride, propane, R-245fa, R-245ca, toluene, or any other suitable fluid. Accordingly, the lower cycle is able to operate efficiently using the relatively low temperature heat rejected from the upper cycle.
Considering first the upper cycle, in process 5-1, a liquid pump 150 isentropically compresses the water working fluid to upper working pressure. In process 1-2, a heat exchanger 135 transfers heat from a primary heat source to the compressed water working fluid. As shown, the heat source is waste heat from a coal power station at 140 degrees C., which heats the compressed working fluid from a temperature of about 32 degrees C. to a temperature of 120 degrees C.
In process 2-3 the heated working fluid undergoes isentropic (reversible, adiabatic) expansion in an expander 136, and is cooled to a temperature of 102 degrees C. As shown, expander 136 is a reciprocating piston expander. However, in other embodiments, other suitable expanders may be used, e.g. a turbine expander.
In process 3-4 heat is recovered from the expanded water vapor exhausted from the expander and transferred to the HCFC 123 working fluid of the lower cycle using a heat exchanger 151. In process 4-5 the water vapor working fluid exiting the heat exchanger 151 is condensed back tot the liquid state using a steam vapor condenser 137. Note that, in some embodiments, the heat rejected during this process may also be transferred to heat the lower cycle working fluid. The condensed water working fluid is then recirculated to the pump 150 to begin the cycle anew.
Considering the lower cycle, this cycle of the heat engine operates as a conventional trilateral flash cycle on the HCFC 123 working fluid. In process 6-7 a liquid pump 150 isentropically compresses the HCFC 123 working fluid to upper working pressure. In process, 7-8, the pressurized HCFC 12 working fluid is heated to a temperature of 82 degrees C. in heat exchanger 151 using heat rejected from the upper cycle.
In process 8-9 the heated HCFC 123 working fluid undergoes isentropic (reversible, adiabatic) expansion in an expander 139, and is cooled to a temperature of about 40 degrees C. As shown, expander 139 is a reciprocating piston expander. However, in other embodiments, other suitable expanders may be used, e.g. a turbine expander.
In process, 9-6 the expanded working fluid exhausted from the expander 139 is condensed in fluid condenser 140, rejecting heat into the surrounding environment. Note that in some embodiments, the heat rejected by the lower cycle may be used to drive a tertiary cycle, etc.
As shown, all of the mechanical output of both types of expanders, upper water/vapor based expander 136 and lower low boiling point organic based expander 139 is integrated into a common shaft 152 which is then used to turn a single alternator 153 to generate electrical energy.
In embodiments described herein, two trilateral flash cycles, the upper one using water and the lower using a working fluid with a lower boiling point, are cascaded for purposes of achieving higher efficiency. In a typical example, recovery useful energy from the waste heat of a coal power plant stack gas, input and output parameters were as follows:
Therefore useful power generation from waste heat may be carried out using low grade heat sources, utilizing the proposed cascaded thermodynamic cycle
While in both exemplary cycles described above the working fluid was heated into the wet vapor region, in other embodiments, the working fluid in one or more cycle may be heated to a supercritical fluid state.
As will be understood by those skilled in the art, the above described heat engine may be modified to employ and of the devices or techniques described herein. For example, the heating processes may include the injection of quantity of working fluid into a chamber (e.g. of a piston), and the introduction of energy (e.g. via concentrated solar energy directed through a transparent window in the chamber) to the quantity of working fluid to vaporize the fluid, as described in detail above. Any of the cycles may include multiple expanders and/or bypass preheating devices and techniques described herein
Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.
This application is related to U.S. Provisional Application Ser. No. 60/719,327, entitled “PIEZOELECTRIC SELECTABLY ROTATABLE BEARING,” filed on Sep. 21, 2005, Application Ser. No. 60/719,328, entitled “SOLAR HEAT ENGINE SYSTEM,” filed on Sep. 21, 2005, U.S. application Ser. No. 11/512,568, entitled “SOLAR HEAT ENGINE SYSTEM,” filed on Aug. 30, 2006, and application Ser. No. 12/246,127, entitled “HEAT ENGINE IMPROVEMENTS,” filed on Oct. 6, 2008 each of which are herein incorporated by reference in its entirety.
