Method for converting thermal energy into mechanical work

Abstract

The invention relates to methods for converting thermal energy into mechanical work and can be used in energy engineering and power plants. The present method includes the adiabatic compression of a working fluid which is subsequently heated and directed into a thermally insulated de Laval nozzle, after which the working fluid is interacted with a flow of a cooling fluid and then directed onto the working blades of a turbine to perform mechanical work, after which the spent working fluid is removed for preparation for a repeat cycle, wherein, at the exit from the thermally insulated de Laval nozzle, the working fluid travelling at supersonic speed in a saturated vapour state enters a thermally insulated channel having a uniform cross-section, a wall of which is formed by the flow of a cooling fluid, and interacts with the cooling fluid, resulting in the subsequent partial condensation of the working fluid. The resulting liquid and vapour parts of the flow, in the state of a saturated liquid and a saturated vapour, are separated, then the vapour part is directed onto the working blades of an impulse steam turbine and the liquid part is directed onto the working blades of a hydraulic turbine. After being spent in the turbines, the working fluid is removed for preparation for a repeat cycle, wherein the cooling fluid is cooled to its initial temperature, transmitting heat to an external source, and is subsequently supplied to the inlet of the thermally insulated uniform cross-section channel. The method makes it possible to increase significantly the efficiency of devices operating on the basis of the claimed method (i.e. to increase energy conversion efficiency).

Description

[0001] A method of converting thermal energy into mechanical work

[0002] The invention relates to methods for converting thermal energy into mechanical work and can be used in energy and power plants, for example, in transport vehicles as an engine, in particular using low-temperature thermal energy sources.

[0003] A well-known method for converting thermal energy into mechanical energy operates according to the thermodynamic Rankine cycle [1], in which the working fluid undergoes a liquid-vapor phase transition (evaporation), adiabatic expansion of the vapor with the performance of work, and a reverse vapor-liquid phase transition (condensation). The efficiency of this method depends largely on the magnitude of the heat drop (pressure and temperature), i.e., achieving significant efficiency values ​​requires large pressure and temperature differences.

[0004] A known method for generating mechanical work involves the use of a cryogenic gas turbine [2], in which the liquid working fluid is split into two streams and sent through two pipelines. One stream, through one pipeline, is directed to heating, evaporation, and adiabatic expansion in the gas turbine, producing work, while the other is throttled into a receiver, from where the cooled liquid is sent to condense the exhaust steam in the gas turbine and the steam generated by throttling.

[0005] A disadvantage of this method is that it does not maintain a heat energy balance, as the heat capacity of the cooled liquid is not sufficient to condense all the resulting steam, making the method ineffective.

[0006] A known method of operating a turbo-installation [3] involves feeding a hot liquid working fluid into a nozzle, in which the working fluid boils in an adiabatic process, passing into a state of wet steam, and acquires supersonic speed, then at the exit from the nozzle it enters a mixing chamber, where it interacts with a cooling liquid, as a result of which it completely condenses to obtain a drop-liquid jet, which is then fed to the blades of a hydraulic turbine.

[0007] A disadvantage of this method is that the boiling (expansion) of the working fluid occurs adiabatically, which requires the use of large heat differentials at a relatively low efficiency, as is the case with the method of converting thermal energy into mechanical energy operating on the thermodynamic Rankine cycle. Thus, based on the results of the conducted analysis of information known from the prior art, it was determined that the method closest in terms of the set of common technical features to the claimed method of converting thermal energy into mechanical work is the method mentioned above with reference to the source of information [3].

[0008] The technical objective of the invention is to develop a method for converting thermal energy into mechanical work, which will increase the efficiency of converting thermal energy into mechanical work, i.e., to obtain high efficiency of devices operating according to the claimed method, in particular, using low-temperature thermal energy sources.

[0009] The stated problem is solved, and the claimed technical results are achieved, by the claimed method for converting thermal energy into mechanical work. This method involves adiabatic compression of the working fluid, followed by heating and directing the working fluid into a thermally insulated Laval nozzle, followed by interaction with a coolant flow. The working fluid is then directed toward the turbine blades, performing mechanical work. The spent working fluid is then withdrawn for preparation for a repeated cycle. At the outlet of the thermally insulated Laval nozzle, the working fluid, in a saturated vapor state, enters a thermally insulated channel of constant cross-section, in which at least one wall is formed by a coolant flow. The channel interacts with the coolant, resulting in partial condensation of the working fluid.The resulting liquid and vapor portions of the flow, in a saturated liquid and saturated vapor state, are separated, with the vapor portion subsequently directed to the blades of an active steam turbine, and the liquid portion to the blades of a hydroturbine. After processing in the turbines, the working fluid is withdrawn to prepare for a repeat cycle. The coolant is cooled to its original temperature, transferring heat to an external source, and is then fed to the inlet of a thermally insulated channel of constant cross-section.

[0010] The combination of features proposed in the claimed invention makes it possible to increase the efficiency of converting thermal energy into mechanical work of devices operating according to the claimed method.

[0011] In preferred forms of implementation of the claimed method for converting thermal energy into mechanical work, at the outlet of a heat-insulated channel of constant cross-section, a flow consisting of a liquid and steam part is directed into a diffuser channel, in which the flow is decelerated with subsequent complete condensation of the steam part, while the resulting liquid, which is under high pressure, is directed into a hydro-steam turbine.

[0012] In preferred embodiments of the claimed method for converting thermal energy into mechanical work, the coolant is cooled by means of a vapor-compression refrigeration unit equipped with a hydro-steam turbine, followed by heat transfer from the coolant to the working fluid, wherein the coolant is cooled below the ambient temperature.

[0013] The proposed method for converting thermal energy into mechanical work is implemented as follows. The working fluid, pre-compressed adiabatically and heated to a dry saturated vapor state at initial pressure and temperature values ​​determined depending on the temperature of the external heat source (to ensure heat transfer from the external source to the working fluid, the initial working fluid temperature must be 3-6 degrees lower than the external source temperature), is directed into a thermally insulated Laval nozzle. In the thermally insulated Laval nozzle, the working fluid expands, cools, and becomes saturated. It accelerates to supersonic speed and is directed into a thermally insulated channel of constant cross-section, where it interacts with a flow of coolant homogeneous with the working fluid. At least one wall of the thermally insulated channel of constant cross-section is formed by the flow of coolant.In this case, the coolant mass flow rate and temperature at the inlet of a thermally insulated channel of constant cross-section are set such that, as a result of heat and mass exchange between the working fluid and the coolant flow, the resulting liquid and vapor portions of the flow (two-phase flow) exit the thermally insulated channel at equilibrium—i.e., in a state of saturated liquid and saturated vapor. The interaction of the coolant and the working fluid is accompanied by partial condensation of the working fluid, which leads to a decrease in flow density and, consequently, to an increase in supersonic flow velocity and a decrease in static pressure and temperature.Thus, when moving through a thermally insulated channel of constant cross-section, the enthalpy of the working fluid is expended on increasing the kinetic energy of the flow and heating the coolant, while the entropy of the working fluid decreases. This allows for the subsequent compression of the working fluid to its initial pressure to expend less work than it would produce on the turbine rotor. It should be noted that since the velocity of the condensing working fluid is greater than the velocity of the coolant, according to the law of conservation of momentum, the momentum of the liquid portion of the flow (the mixture of coolant and working fluid condensate) will increase, and, accordingly, its kinetic energy will increase.

[0014] At the outlet of a thermally insulated channel of constant cross-section, the resulting liquid (coolant and working fluid condensate) and vapor (gaseous working fluid) portions of the flow, which are in the saturated liquid and saturated vapor states, are separated. The vapor portion of the flow is directed to the rotor blades of an active steam turbine, while the liquid portion of the flow is directed to a hydraulic turbine, whose operation is directed, for example, to drive a compressor compressing the working fluid and to drive a coolant pump.

[0015] The coolant, after separating the working fluid condensate, is then sent to a heat exchanger for cooling to its initial temperature before entering a thermally insulated channel of constant cross-section, transferring heat to an external source. The coolant is then pumped to the inlet of the thermally insulated channel of constant cross-section. After being processed in the turbines, both parts of the working fluid (steam and condensate) are directed and compressed to the initial pressure in a compressor, such as a liquid-ring compressor. Since the enthalpy of the working fluid, which is in a wet vapor state after compression, is lower than the initial pressure, the working fluid is heated in a heat exchanger to its initial state of dry saturated vapor and sent to a thermally insulated Laval nozzle. The cycle then repeats.

[0016] The above-mentioned other features and advantages of the claimed method for converting thermal energy into mechanical work will be further examined in more detail using examples of some preferred, but non-limiting, forms of implementation with references to the positions of the figures of the drawings, which schematically represent:

[0017] Fig. 1 - schematic representation of a device for converting thermal energy into mechanical work according to variant 1;

[0018] Fig. 2 - schematic representation of a device for converting thermal energy into mechanical work according to variants 2 and 3.

[0019] Fig. 3, 4 - schematic representation of devices for converting thermal energy into mechanical work, made with two compressors according to variants 1, 2 and 3.

[0020] The claimed method for converting thermal energy into mechanical energy is implemented on a device schematically shown in Figure 1 in the following manner. Coolant, located in a cooled receiver 1 and pre-cooled (cooling is carried out with heat transfer to an external source) to a predetermined temperature, is fed by pump 2 to a swirling device 3 of a nozzle apparatus. The coolant then enters a heat-insulated channel 4 of constant cross-section, which is, for example, a heat-insulated cylindrical channel of constant cross-section, with the subsequent formation of an annular flow 5. In the case where the heat-insulated channel 4 of constant cross-section is, for example, a heat-insulated flat arcuate channel of constant cross-section, then device 3 is not used.After the formation of a stable annular flow 5 of the cooling liquid, the working fluid, pre-compressed in the compressor 18 and heated in the heated receiver 19, is directed into the heat-insulated Laval nozzle 7. At the outlet of the heat-insulated Laval nozzle 7, namely at the outlet of its diffuser part, the working fluid at a supersonic speed in a state of saturated vapor enters the heat-insulated cylindrical channel 4, the walls of which are formed by the annular flow 5 of the cooling liquid. When the working fluid passes through the heat-insulated cylindrical channel 4, interaction with the flow 5 of the cooling liquid occurs, followed by partial condensation of the working fluid, which is accompanied by an increase in speed, a drop in temperature and static pressure.At the outlet of the heat-insulated cylindrical channel 4, the resulting liquid (coolant and condensate of the working fluid) and vapor (gaseous working fluid) portions of the flow are separated, and then directed: the vapor portion of the flow to the rotor blades of the active steam turbine 8, connected by a power take-off shaft to the electric generator 9, and the liquid portion to the annular diffuser channel 10. In channel 10, as a result of the flow deceleration, its static pressure increases, and then the liquid portion of the flow is directed to the blades of the hydraulic turbine 12 after passing first through the conoidal nozzle 11, where the reverse process occurs - a drop in pressure and an increase in speed. From the casing of the hydraulic turbine 12, the liquid portion of the flow enters the separating receiver 13.In receiver 13, the liquid is separated into its initial components: a mass equal to the mass of the cooling liquid is sent to cooled receiver 1, and a mass equal to the mass of the working fluid condensate is sent through dispenser 14 by pump 15 to mixer 16, where it is mixed with the steam (gaseous working fluid) portion of the flow, which is supplied from the casing of steam turbine 8 by gas blower 17. From mixer 16, the working fluid in the state of wet steam is sent to compressor 18, made, for example, of the liquid-ring type, and adiabatically compressed to the initial pressure, then sent to heated receiver 19, where it is isobarically and isothermally heated to the initial state of dry saturated steam and fed into a heat-insulated Laval nozzle. Then the cycle is repeated.

[0021] The claimed method for converting thermal energy into mechanical work is implemented using a device schematically shown in Figure 2 as follows. Coolant from cooled receiver 1, pre-cooled to a predetermined temperature, is fed by pump 2 to swirling device 3 of the nozzle apparatus. The coolant then enters a heat-insulated cylindrical channel 4 of constant cross-section, which is, for example, a heat-insulated cylindrical channel of constant cross-section, followed by the formation of an annular flow 5. In the case where the heat-insulated channel 4 of constant cross-section is, for example, a heat-insulated flat arcuate channel of constant cross-section, device 3 is not used. After the formation of a stable annular flow 5 of coolant, the working fluid, pre-compressed in compressor 18 and heated in heated receiver 19, is directed into heat-insulated Laval nozzle 7.At the outlet of the thermally insulated Laval nozzle 7, namely at the outlet of its diffuser section, the working fluid enters at supersonic speed in a saturated vapor state into the thermally insulated cylindrical channel 4, the walls of which are formed by an annular flow 5 of coolant. As the working fluid passes through the thermally insulated cylindrical channel 4, it interacts with the coolant flow 5, resulting in partial condensation of the working fluid, which is accompanied by an increase in velocity and a drop in temperature and static pressure. At the outlet of the thermally insulated cylindrical channel 4, the resulting liquid (coolant and working fluid condensate) and vapor (gaseous working fluid) portions of the flow are directed into the annular diffuser channel 10. In channel 10, as a result of flow deceleration, an increase in static pressure occurs, and, as a consequence, complete condensation of the vapor portion of the flow.The resulting liquid, consisting of a cooling liquid and a condensate of the working fluid and under high pressure, is sent to a hydro-steam turbine 12.

[0022] From the casing of the hydro-steam turbine 12, the resulting wet steam, consisting of a cooling liquid, condensate of the working fluid and the steam part of the working fluid, enters the separating receiver 13. In the receiver 13, the liquid is separated into the initial components: a mass equal to the mass of the cooling liquid is sent to the cooled receiver 1, and a mass equal to the mass of the condensate of the working fluid is sent through the dispenser 14 by the pump 15 to the mixer 16, where it is mixed with the steam part of the working fluid, which is fed through the separator 20 by the gas blower 17. From the mixer 16, the working fluid in the state of wet steam is sent and adiabatically compressed in the compressor 18 and then sent to the heated receiver 19, where it is isobarically and isothermally heated to the initial state of dry saturated steam and fed to the heat-insulated Laval nozzle. Then the cycle is repeated.

[0023] In contrast to the embodiments of the claimed method described above, in which the heat during cooling of the coolant in receiver 1 is transferred directly to an external source (to the environment), in the third embodiment a vapor-compression refrigeration unit (heat pump) is used to cool the coolant. The vapor-compression refrigeration unit consists of an evaporator 21, in which the heat removed from the coolant is absorbed during evaporation of the refrigerant, a compressor 22, in which the refrigerant is compressed to the condensation pressure, a condenser 23, which is located in receiver 19 and is designed to condense the refrigerant vapor with the transfer of the condensation heat to the working fluid, and a hydro-steam turbine 24, in which the refrigerant, performing work, is cooled, and in the state of highly humid vapor is directed to evaporator 21. In this case, the coolant is cooled to a temperature below the ambient temperature.

[0024] Figures 3 and 44 show schematic representations of devices constructed with two compressors for converting thermal energy into mechanical work according to the claimed method, variants 1, 2, and 3. The difference between the method implemented on the devices schematically shown in Figs. 1 and 2 is as follows: the working fluid in the state of dry saturated steam from the heated receiver 19 is sent to the high-pressure compressor 6, where the working fluid is pre-compressed and then sent to the heat-insulated Laval nozzle 7.

[0025] It should be noted that the shape of the insulated duct 4 with a constant cross-section and the use of two compressors 6, 18 do not affect the technical result achieved, and therefore, the effectiveness of the claimed method. Below is an evaluation of the effectiveness of the claimed method using a device designed with two compressors.

[0026] We will evaluate the effectiveness of the proposed method using two laws:

[0027] 1. The law of conservation of momentum in the form of the equation of momentum for the flow: (1) where F is the cross-sectional area of ​​the flow (for a cylindrical channel F=const) - static pressure, density and velocity of the working fluid in the inlet and outlet sections of a heat-insulated cylindrical channel of constant cross-section (hereinafter referred to as the channel), respectively.

[0028] 2. The law of conservation of energy in the form of the first law of thermodynamics for an energetically isolated flow (i.e. the heat content equation): (2) where, is the kinetic energy and enthalpy of the flow at the input and output cross-section of the channel, respectively.

[0029] The working fluid, which is in the state of dry saturated steam, and the cooling liquid enter the channel in the form of cocurrent flows with different speeds and temperatures at the same static pressure Pi. The flow parameters of the working fluid in the inlet section of the channel speed, density r enthalpy entropy

[0030] For simplicity, we will assume that the mass flow rate of the working fluid and coolant is equal to

[0031] Then the kinetic energy of the working fluid in the inlet section of the channel:

[0032] Cross-sectional area of ​​the working fluid steam flow:

[0033] At the flow rate of the coolant, its kinetic energy equals:

[0034] In the outlet section of the channel, the velocity of the steam (gaseous working fluid) part of the flow is determined from equation (1): i

[0035] - mass flow rate of steam (dryness level) in this section of the channel: X

[0036] - kinetic energy of the steam part of the flow: 2

[0037] - enthalpy of the working fluid in this section: 2p T

[0038] - entropy of the working fluid in this section: Where, - the enthalpy and entropy of the saturated vapor and liquid in the outlet section of the channel. The velocity of the liquid portion of the flow, consisting of the coolant and the condensate of the working fluid, in the outlet section of the channel is determined by its momentum, equal to the sum of the momentum of the coolant flow and the total momentum condensate of the working fluid, which can be determined with sufficient accuracy by the method of graphical integration: then the kinetic energy of the liquid part of the flow in the outlet section of the channel:

[0039] Since the temperature of the liquid part of the flow in the outlet section of the channel will be equal to the temperature of the steam part of the flow (heat and mass transfer will cease), then the enthalpy and entropy the liquid part of the flow will be equal to the enthalpy and entropy of the saturated liquid at the pressure in the outlet section of the channel Pg and the heat content equation (2) can be written as

[0040] From the equation we determine the enthalpy of the cooling liquid in the inlet section of the channel:

[0041] Based on the enthalpy value of the cooling liquid determined in this way in the inlet section of the channel and the pressure known in this section, its temperature and entropy

[0042] The difference in enthalpy of the coolant in the control sections is equal to the amount of heat removed from the working fluid when moving through the channel and, accordingly, the same amount of heat must be removed from the coolant to return it to its original state.

[0043] The technical work performed by the flow on the turbine is equal to the sum of the kinetic energies of the parts of the flow in the outlet section of the channel: L

[0044] The work of returning to the initial state consists of the work of adiabatic (isentropic) compression:

[0045] - working fluid to the initial pressure P

[0046] - the working fluid to pressure P to ensure a given speed

[0047] - coolant from pressure P to pressure to ensure the specified speed - in the case of using a heat pump that transfers heat from the coolant to the working fluid, the work of its drive is defined as the difference between the work of adiabatic compression of the evaporated refrigerant from the evaporation pressure to the condensation pressure and the work performed by the refrigerant during the adiabatic expansion of the condensate to the evaporation pressure in the hydrosteam turbine.

[0048] A quantitative calculation carried out using the described method without taking friction into account using the thermophys program for determining the thermophysical parameters of liquid and steam, carried out using an example where the working fluid and coolant are water vapor and water, the mass flow rate of the working fluid is 1.0 kg / sec, the coolant is 4.0 kg / sec, the pressure and temperature in the inlet section of the channel: , in the outlet section of the channel: speeds in the inlet section of the channel: working fluid, cooling liquids , gave the following results:

[0049] - technical work of turbines

[0050] - work to return to the original state:

[0051] - useful work: J / sec;

[0052] - the amount of heat that must be supplied to the working fluid after its compression from

[0053] - the amount of heat released into the environment:

[0054] - the difference between the amount of heat supplied and removed: we get

[0055] The efficiency of the claimed method of converting thermal energy into mechanical work will be:

[0056] Table 1 provides the efficiency values ​​for devices operating using the claimed method and methods described in prototypes at the same heat transfer rate. The efficiency of an ideal Carnot cycle at this heat transfer rate is 19.55%.

[0057] Thus, the claimed method of converting thermal energy into mechanical work significantly improves the efficiency of devices operating according to the claimed method. Sources of information:

[0058] 1. Kirillin V.A., Sychev V.V., Sheindlin A.E. Technical thermodynamics. - M.: Energoatomizdat, 1983. - P. 295-301;

[0059] 2. Patent RU 2131045, priority 06 / 16 / 1997;

[0060] 3. USSR Author's Certificate 397667, priority 13.05.1971.

Claims

Invention formula 1. A method for converting thermal energy into mechanical work, including adiabatic compression of the working fluid with subsequent heating and directing the working fluid into a heat-insulated Laval nozzle, followed by interaction with a flow of coolant, and then directing the working fluid onto the turbine blades with the performance of mechanical work, after which the spent working fluid is removed to prepare for a repeated cycle, characterized in that at the outlet of the heat-insulated Laval nozzle, the working fluid at a supersonic speed in a state of saturated vapor enters a heat-insulated channel of constant cross-section, in which at least one wall is formed by a flow of coolant, interacts with the coolant with subsequent partial condensation of the working fluid, wherein the resulting liquid and vapor parts of the flow, which are in a state of saturated liquid and saturated vapor,separated with subsequent direction of the steam part to the working blades of the active steam turbine, and the liquid part to the working blades of the hydraulic turbine, after working in the turbines, the working fluid is removed to prepare for a repeated cycle, while the cooling liquid is cooled to the initial temperature, transferring heat to an external source, with subsequent supply to the input of a heat-insulated channel of constant cross-section.

2. The method of claim 1, characterized in that at the outlet of a heat-insulated channel of constant cross-section, a flow consisting of a liquid and steam part is directed into a diffuser channel, in which the flow is slowed down with subsequent complete condensation of the steam part, while the resulting liquid, which is under high pressure, is directed into a hydro-steam turbine.

3. The method according to paragraph 1, characterized in that the coolant is cooled by means of a vapor-compression refrigeration unit equipped with a hydro-steam turbine, with subsequent transfer of heat from the coolant to the working fluid, wherein the coolant is cooled below the ambient temperature.

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