Thermodynamic optimization method for lead-bismuth coupled supercritical carbon dioxide brayton cycle system

Abstract

This invention discloses a thermodynamic optimization method for a lead-bismuth stack coupled supercritical carbon dioxide Brayton cycle system. The method includes seven steps: 1. Initialization of the Brayton cycle system's thermodynamic parameters; 2. Dividing the Brayton cycle system into different modules; 3. Calculating the supercritical carbon dioxide thermodynamic parameters of the hot-end module; 4. Calculating the supercritical carbon dioxide thermodynamic parameters of the cold-end module; 5. Calculating the supercritical carbon dioxide thermodynamic parameters of the regenerator module; 6. Optimizing the Brayton cycle system configuration; 7. Calculating the optimal configuration thermodynamic parameters of the Brayton cycle system. This invention enables the coordinated calculation and optimization of the configuration, parameters, and stress of a lead-bismuth stack coupled supercritical carbon dioxide Brayton cycle system, significantly shortening the design cycle and improving the thermal efficiency and operational reliability of the system.

Description

Technical Field

[0001] This invention belongs to the field of nuclear energy development and new energy technology, specifically relating to a thermodynamic optimization method for a lead-bismuth coupled supercritical carbon dioxide Brayton cycle system. Background Technology

[0002] Supercritical carbon dioxide Brayton cycle systems use supercritical carbon dioxide as the working fluid, converting heat energy from a heat source into turbine work. Supercritical fluids possess both the high density of liquids and the low viscosity of gases, which helps reduce device size, increase the working capacity per unit volume of working fluid, and reduce flow losses. Compared to other supercritical fluids, supercritical carbon dioxide has the advantage of a critical temperature close to room temperature. Therefore, when using room temperature air as a coolant, the system's minimum operating temperature is maintained near the critical point, which is beneficial for reducing compressor size and power consumption. In fourth-generation nuclear reactors, liquid metal fast reactors are one of the most promising technological routes, including lead-bismuth cooled fast reactors, sodium-cooled fast reactors, and lead-cooled fast reactors. Among them, lead-bismuth cooled fast reactors have advantages such as compact core structure and high-quality heat source. They use liquid metal as the primary coolant, transferring heat to the secondary working fluid via an intermediate heat exchanger to drive the turbine and generate electricity. Currently, some research has been conducted on supercritical carbon dioxide Brayton cycle systems in fields such as solar energy and waste heat utilization. However, research on the thermo-mechanical coupling design of such systems at the printed circuit board heat exchanger level is still relatively lacking, especially when using small lead-bismuth cooled fast reactors as the heat source. Therefore, there is an urgent need to develop a method suitable for lead-bismuth coupled supercritical carbon dioxide Brayton cycle systems to achieve the selection and parameter optimization of the thermo-mechanical coupling configuration of the printed circuit board heat exchanger, and then reduce the impact of thermal stress by adjusting temperature parameters. Summary of the Invention

[0003] In order to overcome the problems existing in the prior art, the purpose of this invention is to provide a thermal optimization method for a lead-bismuth coupled supercritical carbon dioxide Brayton cycle system. This invention can realize the configuration selection and parameter optimization of the printed circuit board heat exchanger of the lead-bismuth stack coupled supercritical carbon dioxide Brayton cycle system, and then reduce thermal stress by changing the temperature parameters.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A thermodynamic optimization method for a lead-bismuth coupled supercritical carbon dioxide Brayton cycle system includes the following steps: Step 1: Initialize the thermodynamic parameters of the Brayton cycle system: Define the parameters required for thermodynamic optimization of the Brayton cycle system, including: 1) Standard parameters: the highest and lowest operating temperatures of supercritical carbon dioxide in the Brayton cycle system, the highest and lowest operating pressures of supercritical carbon dioxide in the Brayton cycle system, the temperature pinch point of the heat exchanger, the isentropic efficiency of the supercritical carbon dioxide compressor and turbine, and the temperature difference limit of the heat exchanger; 2) Core heat source parameters: core inlet temperature, core outlet temperature, and core power; 3) Physical properties of supercritical carbon dioxide and lead-bismuth; 4) Parameters to be optimized: the high-temperature side temperature drop of the supercritical carbon dioxide heat exchanger, and the integer variable value that determines the configuration of the Brayton cycle system; Set the initial values ​​of the above parameters using the heuristic optimizer algorithm of the Julia language; Among them, selecting the high-temperature side temperature drop of the supercritical carbon dioxide heat exchanger as the parameter to be optimized can ensure that when using a core heat source with a higher or lower temperature, the temperature change range of each heat exchanger is at the same level, without significant differences, and it is not necessary to frequently change the optimization range for different calculation objects, thus improving the universality of the program code; Step 2: Divide the Brayton cycle system into different modules: This invention adopts the hyperstructure optimization concept to reduce the amount of program code and increase its readability and reusability. The Brayton cycle system is divided into three different modules consisting of turbines and compressors of different numbers and connection methods, as well as printed circuit board heat exchangers. These modules include a hot-end module, a cold-end module, and a regenerator module. The hot-end module consists of turbines and printed circuit board heat exchangers, the cold-end module consists of compressors and printed circuit board heat exchangers, and the regenerator module consists of printed circuit board heat exchangers. Each module has a different configuration due to the different number and connection methods of its internal components. At this time, the complex connection relationship inside the Brayton cycle system is transformed into a combination selection between simple modules. The different configurations of the three modules are encoded separately, and the combination of the different codes of the three modules is an integer variable that determines the configuration of the Brayton cycle system. Step 3: Calculate the thermodynamic parameters of the supercritical carbon dioxide in the hot-end module: Select the configuration of the hot-end module, and input the highest temperature and pressure values ​​of the supercritical carbon dioxide operating in the Brayton cycle system set in Step 1, as well as the isentropic efficiency of the supercritical carbon dioxide turbine. Calculate the pressure ratio from the highest and lowest pressure values ​​of the supercritical carbon dioxide operating in the Brayton cycle system set in Step 1. The supercritical carbon dioxide thermodynamic parameters at the hot-end module outlet are calculated using the turbine equations. Step 4: Calculate the thermodynamic parameters of the supercritical carbon dioxide in the cold-end module: Select the configuration of the cold-end module, and input the lowest temperature and lowest pressure values ​​of the supercritical carbon dioxide operating in the Brayton cycle system set in Step 1, as well as the isentropic efficiency of the supercritical carbon dioxide compressor. Calculate the pressure ratio from the highest and lowest pressure values ​​of the supercritical carbon dioxide operating in the Brayton cycle system set in Step 1. The thermodynamic parameters of supercritical carbon dioxide at the outlet of the cold end module are calculated using the compressor equations. Step 5: Calculate the supercritical carbon dioxide thermodynamic parameters of the regenerator module: Select the regenerator module configuration based on the combination of the hot-end module configuration and the cold-end module configuration selected in Steps 3 and 4 respectively, and determine the integer variable values ​​of the Brayton cycle system; take the heat exchanger temperature pinch point value set in Step 1, the temperature drop value of the high-temperature side of the supercritical carbon dioxide heat exchanger to be optimized, the supercritical carbon dioxide thermodynamic parameters at the outlet of the hot-end module obtained in Step 3, and the supercritical carbon dioxide thermodynamic parameters at the outlet of the cold-end module obtained in Step 4 as known inputs, and calculate the supercritical carbon dioxide thermodynamic parameters of the remaining part of the Brayton cycle system using the heat exchanger equations. Step 6: Brayton Cycle System Configuration Optimization: Based on the parameters and calculation results set in Steps 1-5, the thermal efficiency value of the Brayton cycle system is obtained according to the thermal efficiency calculation formula, and then passed to the outer nested heuristic optimizer. Considering the influence of thermal stress on the regenerator module in the Brayton cycle system, a temperature difference constraint is added to it. Through iterative calculation, the temperature drop value of the high-temperature side of the supercritical carbon dioxide heat exchanger and the integer variable value that determines the configuration of the Brayton cycle system are adjusted to find the optimal parameter settings and optimal configuration of the Brayton cycle system. Step 7: Calculation of thermodynamic parameters for the optimal configuration of the Brayton cycle system: Based on the optimal configuration of the Brayton cycle system obtained in Step 6, output it to COMSOL for thermodynamic calculation. Determine whether the output result of the thermodynamic calculation meets the temperature difference limit of the regenerator module in the Brayton cycle system. If it meets the requirement, the calculation ends; otherwise, modify the geometric parameters of the printed circuit board heat exchanger in the Brayton system and recalculate until the calculation result meets the requirement.

[0005] In step 3, if the thermodynamic parameters of the supercritical carbon dioxide working fluid at the turbine inlet and the pressure ratio in the Brayton cycle system loop are known, the thermodynamic parameters of the supercritical carbon dioxide at the hot-end module outlet can be obtained through the isentropic expansion process, and the thermodynamic state of the supercritical carbon dioxide at the hot-end module outlet can be determined. The equilibrium equation is as follows: In the formula: The subscript 3 represents the turbine inlet; The subscript 4 represents the endpoint of isentropic expansion; This represents the entropy of supercritical carbon dioxide at the turbine inlet. ; This represents the entropy of supercritical carbon dioxide at the turbine outlet during the isentropic expansion process. ; The pressure of supercritical carbon dioxide at the turbine inlet, Pa; The pressure of supercritical carbon dioxide at the turbine outlet, Pa; The temperature of supercritical carbon dioxide at the turbine inlet, K; The temperature of supercritical carbon dioxide at the turbine outlet during the isentropic expansion process is K; The pressure ratio is the ratio of the maximum pressure to the minimum pressure. The thermodynamic parameters of supercritical carbon dioxide at the outlet of the hot-end module in the isentropic expansion process, calculated by equation (1), can be used to determine the thermodynamic state of supercritical carbon dioxide at the outlet of the hot-end module in the actual process, based on the isentropic efficiency of supercritical carbon dioxide permeability. The equilibrium equation is as follows: In the formula: The subscript 3 represents the turbine inlet; The subscript 4 represents the endpoint of isentropic expansion; The subscript 4' represents the actual expansion endpoint; The subscript "turbine" indicates a turbine. This refers to the specific enthalpy of supercritical carbon dioxide at the turbine inlet. ; This represents the specific enthalpy of supercritical carbon dioxide at the turbine outlet during the isentropic expansion process. ; This represents the specific enthalpy of supercritical carbon dioxide at the turbine outlet during the actual expansion process. ; The pressure of supercritical carbon dioxide at the turbine inlet, Pa; The pressure of supercritical carbon dioxide at the turbine outlet, Pa; The temperature of supercritical carbon dioxide at the turbine inlet, K; The temperature of supercritical carbon dioxide at the turbine outlet during the isentropic expansion process is K; Let K be the temperature of supercritical carbon dioxide at the turbine outlet during the actual expansion process; To improve entropy efficiency; The turbine equations are formed by equations (1) and (2) above.

[0006] In step 4, if the supercritical carbon dioxide thermodynamic parameters at the compressor inlet and the pressure ratio in the Brayton cycle system loop are known, the supercritical carbon dioxide thermodynamic parameters at the cold-end module outlet can be obtained through the isentropic compression process, and the supercritical carbon dioxide thermodynamic state at the cold-end module outlet can be determined. The equilibrium equation is as follows: In the formula: Subscript 1 represents the compressor inlet; The subscript 2 represents the endpoint of isentropic compression; This represents the entropy of supercritical carbon dioxide at the compressor inlet. ; This represents the entropy of supercritical carbon dioxide at the compressor outlet during the isentropic compression process. ; The pressure of supercritical carbon dioxide at the compressor inlet is given in Pa. The pressure of supercritical carbon dioxide at the compressor outlet, in Pa; The temperature of supercritical carbon dioxide at the compressor inlet, in K; The temperature of supercritical carbon dioxide at the compressor outlet during the isentropic compression process is K; The pressure ratio is the ratio of the maximum pressure to the minimum pressure. The thermodynamic parameters of supercritical carbon dioxide at the outlet of the cold-end module in the isentropic compression process, calculated by equation (3), can be used to determine the thermodynamic state of supercritical carbon dioxide at the outlet of the cold-end module in the actual process, based on the isentropic efficiency of the supercritical carbon dioxide compressor. The equilibrium equation is as follows: In the formula: Subscript 1 represents the compressor inlet; The subscript 2 represents the endpoint of isentropic compression; The subscript 2' represents the actual end point of compression; The subscript "compressor" indicates a compressor. This refers to the specific enthalpy of supercritical carbon dioxide at the compressor inlet. ; This refers to the specific enthalpy of supercritical carbon dioxide at the compressor outlet during the isentropic compression process. ; This represents the specific enthalpy of supercritical carbon dioxide at the compressor outlet during the actual compression process. ; The pressure of supercritical carbon dioxide at the compressor inlet is given in Pa. The pressure of supercritical carbon dioxide at the compressor outlet, in Pa; The temperature of supercritical carbon dioxide at the compressor inlet, in K; The temperature of supercritical carbon dioxide at the compressor outlet during the isentropic compression process is K; The temperature of supercritical carbon dioxide at the compressor outlet during the actual compression process, in K; The compressor has isentropic efficiency; The above equations (3) and (4) together constitute the compressor equation set.

[0007] In step 5, the printed circuit board heat exchanger that makes up the regenerator module has four ports, namely the inlet and outlet of the two types of fluids on the hot and cold sides. Usually, the thermodynamic state of the fluids at two of the ports is known. To solve the thermodynamic state of the entire printed circuit board heat exchanger, the thermodynamic calculation of the regenerator module requires a set of heat exchanger equations including the following equations (5), (6), (7) and (8): Use the temperature pinch point value allowed by the technical specifications of the printed circuit board heat exchanger as the constraint for the equation or inequality: Enthalpy balance equation for supercritical carbon dioxide working fluid: mass conservation equation: In the formula: The superscript "hot" indicates a hot fluid; The superscript "cool" indicates a cold fluid; The subscript "in" indicates the fluid inlet; The subscript "out" indicates the fluid outlet; The minimum temperature pinch value, K; The inlet temperature of the hot fluid is K; The outlet temperature of the hot fluid, in K; The inlet temperature of the cold fluid is K; The outlet temperature of the cold fluid, in K; Specific enthalpy of the heat fluid inlet. ; Specific enthalpy of the hot fluid outlet. ; For the specific enthalpy of the cold fluid inlet, ; For the specific enthalpy of the cold fluid outlet, ; The inlet pressure of the hot fluid is Pa; The outlet pressure of the hot fluid is Pa; The inlet pressure of the cold fluid is Pa; The outlet pressure of the cold fluid is in Pa. This refers to the mass flow rate of the hot fluid. ; This refers to the mass flow rate of the cold fluid. ; For a printed circuit board heat exchanger with internal node divisions, the equations are as follows: In the formula: The superscript "hot" indicates a hot fluid; The superscript "cool" indicates a cold fluid; The subscript i represents a heat exchanger node, and there are a total of n nodes; For nodes Temperature of the hot fluid, K. ; For nodes Temperature of the cold fluid, K. ; For nodes Specific enthalpy of the heat fluid , ; For nodes Specific enthalpy of cold fluid , ; For nodes The pressure of the hot fluid, Pa. ; For nodes The pressure of the cold fluid, Pa, ; For nodes Mass flow rate of the hot fluid. , ; For nodes Mass flow rate of the cold fluid , ; The minimum temperature pinch value is K.

[0008] The thermodynamic parameters of supercritical carbon dioxide required for calculation in step 5 include the temperature, pressure, and specific enthalpy of supercritical carbon dioxide.

[0009] The thermal efficiency value of the Brayton cycle system in step 6 is calculated from the net output power of the turbine and compressor. For the compressor, the formula for calculating the net output power is as follows: For a turbine, the formula for calculating net output power is as follows: In the formula: Subscript 1 represents the compressor inlet; The subscript 2' represents the actual end point of compression; The subscript 3 represents the turbine inlet; The subscript 4' represents the actual expansion endpoint; The subscript "compressor" indicates a compressor. The subscript "turbine" indicates a turbine. This refers to the net output power of the compressor. ; For the turbine's net output power, ; This refers to the specific enthalpy of supercritical carbon dioxide at the compressor inlet. ; This represents the specific enthalpy of supercritical carbon dioxide at the compressor outlet during the actual compression process. ; This refers to the specific enthalpy of supercritical carbon dioxide at the turbine inlet. ; This represents the specific enthalpy of supercritical carbon dioxide at the turbine outlet during the actual expansion process. ; The formula for calculating thermal efficiency is as follows: In the formula: The subscript "compressor" indicates a compressor. The subscript "turbine" indicates a turbine. This refers to the net output power of the compressor. ; For the turbine's net output power, ; For system thermal efficiency; For core power, .

[0010] In step 6, the temperature difference constraint for the regenerator module in the Brayton cycle system is added by adding a temperature difference inequality constraint to the heat exchanger equation set required for the thermodynamic calculation of the regenerator module in step 5. The temperature difference inequality constraint is as follows: In the formula: The superscript "hot" indicates a hot fluid; The superscript "cool" indicates a cold fluid; The subscript "in" indicates the fluid inlet; The subscript "out" indicates the fluid outlet; The inlet temperature of the hot fluid is K; The outlet temperature of the hot fluid, in K; The inlet temperature of the cold fluid is K; The outlet temperature of the cold fluid, in K; K is the temperature difference limit.

[0011] Compared with the prior art, the present invention has the following advantages: 1. Integrated parameter optimization and optimal configuration selection. This invention integrates configuration selection and parameter optimization within the same framework. Through an outer nested heuristic optimizer, it automatically seeks the optimal configuration and parameters, thus avoiding the local optima problem caused by "determining the configuration first and then adjusting the parameters".

[0012] 2. Modular modeling provides strong scalability. Each module (hot end, cold end, regenerator) is modeled independently, and the configuration can be flexibly combined or replaced according to actual needs, providing good engineering adaptability and scalability.

[0013] 3. Thermo-coupling design balances thermal efficiency and thermal stress. This invention selects the optimal configuration through COMSOL thermo-simulation, which effectively reduces thermal stress while improving system efficiency, significantly enhancing equipment lifespan and operational safety. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of a thermodynamic optimization method for a lead-bismuth coupled supercritical carbon dioxide Brayton cycle system provided in a specific embodiment of the present invention.

[0015] Figure 2 It shows a schematic diagram of the turbine and compressor structure, as well as a temperature entropy diagram.

[0016] Figure 3 This is a schematic diagram of the hot-end module.

[0017] Figure 4 This is a schematic diagram of the cold-end module.

[0018] Figure 5 This is a schematic diagram of the regenerator module.

[0019] Figure 6 The curves represent the process of optimizing the system's highest thermal efficiency under different temperature differential constraints.

[0020] Figure 7 It is a curve showing the change of system parameters during the optimization process of the temperature difference limiting system.

[0021] Figure 8 This is a schematic diagram of the configuration and parameters of the SCO2 Brayton cycle system under an 85K temperature difference limit. Detailed Implementation

[0022] This invention provides a thermodynamic optimization method for a lead-bismuth coupled supercritical carbon dioxide Brayton cycle system. The specific implementation of this invention will be described in detail below with reference to the accompanying drawings and examples.

[0023] like Figure 1 As shown, this invention provides a thermodynamic optimization method for a lead-bismuth coupled supercritical carbon dioxide Brayton cycle system, comprising the following seven steps: 1. Initialization of the thermodynamic parameters of the Brayton cycle system; 2. Dividing the Brayton cycle system into different modules; 3. Calculating the supercritical carbon dioxide thermodynamic parameters of the hot-end module; 4. Calculating the supercritical carbon dioxide thermodynamic parameters of the cold-end module; 5. Calculating the supercritical carbon dioxide thermodynamic parameters of the regenerator module; 6. Optimizing the configuration of the Brayton cycle system; 7. Calculating the thermodynamic parameters of the optimal configuration of the Brayton cycle system.

[0024] Step 1: Initialize the thermodynamic parameters of the Brayton cycle system: Define the parameters required for thermodynamic optimization of the Brayton cycle system, including: 1) Standard parameters: the highest and lowest operating temperatures of supercritical carbon dioxide in the Brayton cycle system, the highest and lowest operating pressures of supercritical carbon dioxide in the Brayton cycle system, the temperature pinch point of the heat exchanger, the isentropic efficiency of the supercritical carbon dioxide compressor and turbine, and the temperature difference limit of the heat exchanger; 2) Core heat source parameters: core inlet temperature, core outlet temperature, and core power; 3) Physical properties of supercritical carbon dioxide and lead-bismuth; 4) Parameters to be optimized: the high-temperature side temperature drop of the supercritical carbon dioxide heat exchanger, and the integer variable value that determines the configuration of the Brayton cycle system; Set the initial values ​​of the above parameters using the heuristic optimizer algorithm of the Julia language; Among them, selecting the high-temperature side temperature drop of the supercritical carbon dioxide heat exchanger as the parameter to be optimized can ensure that when using a core heat source with a higher or lower temperature, the temperature change range of each heat exchanger is at the same level, without significant differences, and it is not necessary to frequently change the optimization range for different calculation objects, thus improving the universality of the program code; Step 2: Divide the Brayton cycle system into different modules: This invention adopts the hyperstructure optimization concept to reduce the amount of program code and increase its readability and reusability. The Brayton cycle system is divided into three different modules consisting of turbines and compressors of different numbers and connection methods, as well as printed circuit board heat exchangers. These modules include a hot-end module, a cold-end module, and a regenerator module. The hot-end module consists of turbines and printed circuit board heat exchangers, the cold-end module consists of compressors and printed circuit board heat exchangers, and the regenerator module consists of printed circuit board heat exchangers. Each module has a different configuration due to the different number and connection methods of its internal components. At this time, the complex connection relationship inside the Brayton cycle system is transformed into a combination selection between simple modules. The different configurations of the three modules are encoded separately, and the combination of the different codes of the three modules is an integer variable that determines the configuration of the Brayton cycle system. Step 3: Calculate the thermodynamic parameters of the supercritical carbon dioxide in the hot-end module: Based on the specific operating conditions of the selected example, choose the configuration of the hot-end module. Input the highest temperature and pressure values ​​of the supercritical carbon dioxide in the Brayton cycle system set in Step 1, as well as the isentropic efficiency of the supercritical carbon dioxide turbine, as known quantities. Obtain the pressure ratio from the highest and lowest pressure values ​​of the supercritical carbon dioxide in the Brayton cycle system set in Step 1. The supercritical carbon dioxide thermodynamic parameters at the hot-end module outlet are calculated using the turbine equations. Step 4: Calculate the thermodynamic parameters of the supercritical carbon dioxide in the cold-end module: Based on the specific operating conditions of the selected example, choose the configuration of the cold-end module. Input the lowest temperature and lowest pressure values ​​of the supercritical carbon dioxide operating in the Brayton cycle system set in Step 1, as well as the isentropic efficiency of the supercritical carbon dioxide compressor, as known quantities. Obtain the pressure ratio from the highest and lowest pressure values ​​of the supercritical carbon dioxide operating in the Brayton cycle system set in Step 1. The thermodynamic parameters of supercritical carbon dioxide at the outlet of the cold end module are calculated using the compressor equations. Step 5: Calculate the supercritical carbon dioxide thermodynamic parameters of the regenerator module: Based on the combination of the hot-end module configuration and the cold-end module configuration determined in Steps 3 and 4 according to the specific operating conditions of the selected example, select the regenerator module configuration and determine the integer variable values ​​of the Brayton cycle system; use the heat exchanger temperature pinch point value set in Step 1, the supercritical carbon dioxide heat exchanger high-temperature side temperature drop value to be optimized, the supercritical carbon dioxide thermodynamic parameters at the outlet of the hot-end module obtained in Step 3, and the supercritical carbon dioxide thermodynamic parameters at the outlet of the cold-end module obtained in Step 4 as known inputs, and calculate the supercritical carbon dioxide thermodynamic parameters of the remaining part of the Brayton cycle system using the heat exchanger equations. Step 6: Brayton Cycle System Configuration Optimization: Based on the parameters and calculation results set in Steps 1-5, the thermal efficiency value of the Brayton cycle system is obtained according to the thermal efficiency calculation formula, and then passed to the outer nested heuristic optimizer. Considering the influence of thermal stress on the regenerator module in the Brayton cycle system during the operation of the selected instance, a temperature difference limit is added to it. Through iterative calculation, the temperature drop on the high-temperature side of the supercritical carbon dioxide heat exchanger and the integer variable value that determines the configuration of the Brayton cycle system are adjusted to find the optimal parameter settings and optimal configuration of the Brayton cycle system. Step 7: Calculation of optimal thermodynamic parameters for the Brayton cycle system: Based on the optimal configuration of the Brayton cycle system obtained in Step 6, output it to COMSOL for thermodynamic calculation. Determine whether the output of the thermodynamic calculation meets the temperature difference limit of the regenerator module in the Brayton cycle system. If it meets the requirement, the calculation ends; otherwise, without affecting the economic efficiency and safety of the selected instance, modify the geometric parameters of the printed circuit board heat exchanger in the Brayton system and recalculate until the calculation result meets the requirements.

[0025] The schematic diagrams and temperature entropy diagrams for the turbine of the hot-end module and the compressor of the cold-end module in step 2 are as follows: Figure 2 As shown, in this example, Figure 2In the diagram, 1 represents the compressor inlet, 2 represents the isentropic compression endpoint, 2' represents the actual compression endpoint, 3 represents the turbine inlet, 4 represents the isentropic expansion endpoint, and 4' represents the actual expansion endpoint. The process from 1 to 2 is the isentropic compression process, from 1 to 2' is the actual compression process, from 3 to 4 is the isentropic expansion process, and from 3 to 4' is the actual expansion process. In step 2, based on the specific research requirements of this example, the hot-end module is divided into different configurations consisting of printed circuit board heat exchangers and turbines with different numbers and connection methods. These include simple heating configurations, reheat configurations, high-low temperature parallel configurations, high-temperature reheat-low-temperature parallel configurations, and high-temperature-low-temperature reheat parallel configurations, such as... Figure 3 As shown; the cold-end module is divided into different configurations consisting of printed circuit board heat exchangers and compressors with varying numbers and connection methods, including simple cooling configuration, simple interstage cooling configuration, recompression configuration, and recompression interstage cooling configuration, such as... Figure 4 As shown, the regenerator modules are divided into different configurations consisting of printed circuit board heat exchangers of varying numbers and connection methods, including single-regenerator, double-regenerator, triple-regenerator, and quadruple-regenerator configurations, such as... Figure 5 As shown, the configuration of the regenerator module is determined based on different combinations of hot-end and cold-end modules.

[0026] In step 3, if the thermodynamic parameters of the supercritical carbon dioxide working fluid at the turbine inlet and the pressure ratio in the Brayton cycle system loop are known, the thermodynamic parameters of the working fluid at the hot-end module outlet can be obtained through the isentropic expansion process, and the thermodynamic state of the working fluid at the hot-end module outlet can be determined. The equilibrium equation is as follows: In the formula: Subscripts 3 and 4 represent Figure 2 The corresponding position in the middle; This represents the entropy of supercritical carbon dioxide at the turbine inlet. ; This represents the entropy of supercritical carbon dioxide at the turbine outlet during the isentropic expansion process. ; The pressure of supercritical carbon dioxide at the turbine inlet, Pa; The pressure of supercritical carbon dioxide at the turbine outlet, Pa; The temperature of supercritical carbon dioxide at the turbine inlet, K; The temperature of supercritical carbon dioxide at the turbine outlet during the isentropic expansion process is K; The pressure ratio is the ratio of the maximum pressure to the minimum pressure. The thermodynamic parameters of the working fluid at the outlet of the hot-end module in the isentropic expansion process, calculated by equation (1), can be used to determine the thermodynamic state of the working fluid at the outlet of the hot-end module in the actual process, based on the isentropic efficiency of supercritical carbon dioxide permeation. The equilibrium equation is as follows: In the formula: The subscripts 3, 4, and 4' represent Figure 2 The corresponding position in the middle; The subscript "turbine" indicates a turbine. This refers to the specific enthalpy of supercritical carbon dioxide at the turbine inlet. ; This represents the specific enthalpy of supercritical carbon dioxide at the turbine outlet during the isentropic expansion process. ; This represents the specific enthalpy of supercritical carbon dioxide at the turbine outlet during the actual expansion process. ; The pressure of supercritical carbon dioxide at the turbine inlet, Pa; The pressure of supercritical carbon dioxide at the turbine outlet, Pa; The temperature of supercritical carbon dioxide at the turbine inlet, K; The temperature of supercritical carbon dioxide at the turbine outlet during the isentropic expansion process is K; Let K be the temperature of supercritical carbon dioxide at the turbine outlet during the actual expansion process; To improve entropy efficiency; The turbine equations are formed by equations (1) and (2) above.

[0027] In step 4, if the thermodynamic parameters of the working fluid at the compressor inlet and the pressure ratio in the Brayton cycle system loop are known, the thermodynamic parameters of the working fluid at the cold-end module outlet can be obtained through the isentropic compression process, and the thermodynamic state of the working fluid at the cold-end module outlet can be determined. The equilibrium equation is as follows: In the formula: Subscripts 1 and 2 represent Figure 2 The corresponding position in the middle; This represents the entropy of supercritical carbon dioxide at the compressor inlet. ; This represents the entropy of supercritical carbon dioxide at the compressor outlet during the isentropic compression process. ; The pressure of supercritical carbon dioxide at the compressor inlet is given in Pa. The pressure of supercritical carbon dioxide at the compressor outlet, in Pa; The temperature of supercritical carbon dioxide at the compressor inlet, in K; The temperature of supercritical carbon dioxide at the compressor outlet during the isentropic compression process is K; The pressure ratio is the ratio of the maximum pressure to the minimum pressure. The thermodynamic parameters of the working fluid at the outlet of the cold-end module in the isentropic compression process, calculated by equation (3), can be used to determine the thermodynamic state of the working fluid at the outlet of the cold-end module in the actual process, based on the isentropic efficiency of the supercritical carbon dioxide compressor. The equilibrium equation is as follows: In the formula: The subscripts 1, 2, 2' represent Figure 2 The corresponding position in the middle; The subscript "compressor" indicates a compressor. This refers to the specific enthalpy of supercritical carbon dioxide at the compressor inlet. ; This refers to the specific enthalpy of supercritical carbon dioxide at the compressor outlet during the isentropic compression process. ; This represents the specific enthalpy of supercritical carbon dioxide at the compressor outlet during the actual compression process. ; The pressure of supercritical carbon dioxide at the compressor inlet is given in Pa. The pressure of supercritical carbon dioxide at the compressor outlet, in Pa; The temperature of supercritical carbon dioxide at the compressor inlet, in K; The temperature of supercritical carbon dioxide at the compressor outlet during the isentropic compression process is K; The temperature of supercritical carbon dioxide at the compressor outlet during the actual compression process, in K; The compressor has isentropic efficiency; The above equations (3) and (4) together constitute the compressor equation set.

[0028] In step 5, the printed circuit board heat exchanger that makes up the regenerator module has four ports, namely the inlet and outlet of the two types of fluids on the hot and cold sides. Usually, the thermodynamic state of two of the ports is known. To solve the thermodynamic state of the entire printed circuit board heat exchanger, the thermodynamic calculation model of the regenerator module needs to include the following set of heat exchanger equations: (5), (6), (7) and (8). Use the minimum temperature pinch point value allowed by the technical specifications of the printed circuit board heat exchanger as the constraint for the equation or inequality: Enthalpy balance equation for supercritical carbon dioxide working fluid: mass conservation equation: In the formula: The superscript "hot" indicates a hot fluid; The superscript "cool" indicates a cold fluid; The subscript "in" indicates the fluid inlet; The subscript "out" indicates the fluid outlet; The minimum temperature pinch value, K; The inlet temperature of the hot fluid is K; The outlet temperature of the hot fluid, in K; The inlet temperature of the cold fluid is K; The outlet temperature of the cold fluid, in K; Specific enthalpy of the heat fluid inlet. ; Specific enthalpy of the hot fluid outlet. ; For the specific enthalpy of the cold fluid inlet, ; For the specific enthalpy of the cold fluid outlet, ; The inlet pressure of the hot fluid is Pa; The outlet pressure of the hot fluid is Pa; The inlet pressure of the cold fluid is Pa; The outlet pressure of the cold fluid is in Pa. This refers to the mass flow rate of the hot fluid. ; This refers to the mass flow rate of the cold fluid. ; For heat exchangers with internal node divisions, the calculation formula is as follows: In the formula: The superscript "hot" indicates a hot fluid; The superscript "cool" indicates a cold fluid; The subscript i represents a heat exchanger node, and there are a total of n nodes; For nodes Temperature of the hot fluid, K. ; For nodes Temperature of the cold fluid, K. ; For nodes Specific enthalpy of the heat fluid , ; For nodes Specific enthalpy of cold fluid , ; For nodes The pressure of the hot fluid, Pa. ; For nodes The pressure of the cold fluid, Pa, ; For nodes Mass flow rate of the hot fluid. , ; For nodes Mass flow rate of the cold fluid , ; The minimum temperature pinch value is K.

[0029] The thermodynamic parameters of supercritical carbon dioxide required for calculation in step 5 include the temperature, pressure, and specific enthalpy of supercritical carbon dioxide.

[0030] The thermal efficiency value of the Brayton cycle system in step 6 is calculated from the net output power of the turbine and compressor. For the compressor, the formula for calculating the net output power is as follows: For a turbine, the formula for calculating net output power is as follows: In the formula: The subscripts 1', 2', 3', and 4' represent Figure 2 The corresponding position in the middle; The subscript "compressor" indicates a compressor. The subscript "turbine" indicates a turbine. This refers to the net output power of the compressor. ; For the turbine's net output power, ; This refers to the specific enthalpy of supercritical carbon dioxide at the compressor inlet. ; This represents the specific enthalpy of supercritical carbon dioxide at the compressor outlet during the actual compression process. ; This refers to the specific enthalpy of supercritical carbon dioxide at the turbine inlet. ; This represents the specific enthalpy of supercritical carbon dioxide at the turbine outlet during the actual expansion process. ; The formula for calculating thermal efficiency is as follows: In the formula: The subscript "compressor" indicates a compressor. The subscript "turbine" indicates a turbine. This refers to the net output power of the compressor. ; For the turbine's net output power, ; For system thermal efficiency; For core power, ; System parameter configuration optimization was performed on a small lead-bismuth reactor. Initial parameters included a core power of 125 MW, a core inlet temperature of 973.15 K, a core outlet temperature of 923.15 K, an isentropic efficiency of 83% for the supercritical carbon dioxide compressor, an isentropic efficiency of 87% for the supercritical carbon dioxide turbine, and a temperature pinch-out value of 10 K for the heat exchanger. Given the highest and lowest pressures and temperatures of the supercritical carbon dioxide system and the temperature drop on the high-temperature side of the heat exchanger, the calculated thermal efficiency variation curve is shown below. Figure 6As shown, the optimal system thermal efficiency value The ratio is 36.35%, the minimum temperature of the supercritical carbon dioxide cycle is 305K, the minimum pressure is 7.72MPa, and the pressure ratio is 3.1; in the "optimal configuration", the hot end module configuration is "reheat configuration", the cold end module configuration is "recompression interstage cooling configuration", and the regenerator module configuration is "recompression double regeneration configuration".

[0031] In step 6, the temperature difference constraint for the regenerator module in the Brayton cycle system is added by adding a temperature difference inequality constraint to the heat exchanger equations required for the thermodynamic calculation of the regenerator module in step 5. The temperature difference inequality constraint is as follows: In the formula: The superscript "hot" indicates a hot fluid; The superscript "cool" indicates a cold fluid; The subscript "in" indicates the fluid inlet; The subscript "out" indicates the fluid outlet; The inlet temperature of the hot fluid is K; The outlet temperature of the hot fluid, in K; The inlet temperature of the cold fluid is K; The outlet temperature of the cold fluid, in K; Due to temperature difference limitations, K; Based on thermal simulation, the optimal configurations of the hot-end and cold-end modules of the Brayton cycle system are determined as follows, under different temperature differences between the regenerator modules: 1) Temperature difference limitation is unlimited: reheat configuration + recompression interstage cooling configuration; 2) Temperature difference limit of 75K: reheat configuration + recompression interstage cooling configuration; 3) Temperature difference limit is 65K: reheat configuration + recompression configuration; 4) Temperature difference limit is 55K: reheat configuration + simple cooling configuration; 5) Temperature difference limit of 45K: reheat configuration + simple cooling configuration; 6) Temperature difference limit of 35K: reheat configuration + simple cooling configuration; 7) Temperature difference limit is 25K: simple heating configuration + simple cooling configuration; The changes in system parameters with variations in the temperature difference limitation of the regenerator module in the Brayton cycle system and the optimal configuration of the Brayton cycle system are as follows: Figure 7As shown, the optimal configurations of the hot-end and cold-end modules of the Brayton cycle system change under the constraint of temperature difference. When the temperature difference is limited to 85K~65K, the system parameters remain basically unchanged, while the configuration changes actively; this process is called the "configuration change" process. When the temperature difference is limited to 65K to 25K, the configuration remains basically unchanged, while the system's maximum operating pressure decreases and the minimum operating temperature increases; this process is called the "parameter change" process. Figure 6 The system thermal efficiency variation curve under temperature difference constraints shows that the decrease in system thermal efficiency is not significant during the "configuration change" process, but it decreases significantly during the "parameter change" process. Therefore, the optimal configuration during the "configuration change" stage is selected for arranging the supercritical carbon dioxide Brayton cycle system. Taking an 85K temperature difference constraint as an example, the configuration and parameters of the SCO2 Brayton cycle system are as follows: Figure 8 As shown in the figure. The hot-end module of the Brayton cycle system adopts a "reheat configuration", the cold-end module adopts a "recompression interstage cooling configuration", and the regenerator module adopts a "dual regenerator configuration".

[0032] The above description is a further detailed explanation of the present invention in conjunction with specific preferred embodiments. It should not be considered that the specific embodiments of the present invention are limited to this. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the scope of patent protection determined by the submitted claims.

Claims

1. A thermodynamic optimization method for a lead-bismuth coupled supercritical carbon dioxide Brayton cycle system, characterized in that: Includes the following steps: Step 1: Initialize the thermodynamic parameters of the Brayton cycle system: Define the parameters required for thermodynamic optimization of the Brayton cycle system, including: 1) Standard parameters: the highest and lowest operating temperatures of supercritical carbon dioxide in the Brayton cycle system, the highest and lowest operating pressures of supercritical carbon dioxide in the Brayton cycle system, the heat exchanger temperature pinch point, the isentropic efficiency of the supercritical carbon dioxide compressor and turbine, and the heat exchanger temperature difference limit; 2) Core heat source parameters: core inlet temperature, core outlet temperature, and core power; 3) Physical properties of supercritical carbon dioxide and lead-bismuth; 4) Parameters to be optimized: the high-temperature side temperature drop of the supercritical carbon dioxide heat exchanger, and the integer variable values ​​that determine the configuration of the Brayton cycle system; Set the initial values ​​of the above parameters using the heuristic optimizer algorithm in the Julia language. Step 2: Divide the Brayton cycle system into different modules: Divide the Brayton cycle system into three modules, including a hot-end module, a cold-end module, and a regenerator module. The hot-end module consists of a turbine and a printed circuit board heat exchanger, the cold-end module consists of a compressor and a printed circuit board heat exchanger, and the regenerator module consists of a printed circuit board heat exchanger. Since the number and connection methods of the components within the three modules are different, they also have different configurations. The different configurations of the three modules are encoded separately, and the combination of the different codes of the three modules is an integer variable that determines the configuration of the Brayton cycle system. Step 3: Calculate the thermodynamic parameters of the supercritical carbon dioxide in the hot-end module: Select the configuration of the hot-end module, and input the highest temperature and pressure values ​​of the supercritical carbon dioxide operating in the Brayton cycle system set in Step 1, as well as the isentropic efficiency of the supercritical carbon dioxide turbine. Calculate the pressure ratio from the highest and lowest pressure values ​​of the supercritical carbon dioxide operating in the Brayton cycle system set in Step 1. The supercritical carbon dioxide thermodynamic parameters at the hot-end module outlet are calculated using the turbine equations. Step 4: Calculate the thermodynamic parameters of the supercritical carbon dioxide in the cold-end module: Select the configuration of the cold-end module, and input the lowest temperature and lowest pressure values ​​of the supercritical carbon dioxide operating in the Brayton cycle system set in Step 1, as well as the isentropic efficiency of the supercritical carbon dioxide compressor. Calculate the pressure ratio from the highest and lowest pressure values ​​of the supercritical carbon dioxide operating in the Brayton cycle system set in Step 1. The thermodynamic parameters of supercritical carbon dioxide at the outlet of the cold end module are calculated using the compressor equations. Step 5: Calculate the supercritical carbon dioxide thermodynamic parameters of the regenerator module: Select the regenerator module configuration based on the combination of the hot-end module configuration and the cold-end module configuration selected in Steps 3 and 4 respectively, and determine the integer variable values ​​of the Brayton cycle system; take the heat exchanger temperature pinch point value set in Step 1, the temperature drop value of the high-temperature side of the supercritical carbon dioxide heat exchanger to be optimized, the supercritical carbon dioxide thermodynamic parameters at the outlet of the hot-end module obtained in Step 3, and the supercritical carbon dioxide thermodynamic parameters at the outlet of the cold-end module obtained in Step 4 as known inputs, and calculate the supercritical carbon dioxide thermodynamic parameters of the remaining part of the Brayton cycle system using the heat exchanger equations. Step 6: Brayton Cycle System Configuration Optimization: Based on the parameters and calculation results set in Steps 1-5, the thermal efficiency value of the Brayton cycle system is obtained according to the thermal efficiency calculation formula. Then, it is passed to the outer nested heuristic optimizer, and a temperature difference limit is added to the regenerator module in the Brayton cycle system. Through iterative calculation, the high-temperature side temperature drop of the supercritical carbon dioxide heat exchanger and the integer variable value that determines the configuration of the Brayton cycle system are adjusted to find the optimal parameter settings and optimal configuration of the Brayton cycle system. Step 7: Calculation of thermodynamic parameters for the optimal configuration of the Brayton cycle system: Based on the optimal configuration of the Brayton cycle system obtained in Step 6, output it to COMSOL for thermodynamic calculation. Determine whether the output result of the thermodynamic calculation meets the temperature difference limit of the regenerator module in the Brayton cycle system. If it meets the requirement, the calculation ends; otherwise, modify the geometric parameters of the printed circuit board heat exchanger in the Brayton system and recalculate until the calculation result meets the requirement.

2. The thermodynamic optimization method for a lead-bismuth coupled supercritical carbon dioxide Brayton cycle system as described in claim 1, characterized in that: In step 3, if the thermodynamic parameters of the supercritical carbon dioxide working fluid at the turbine inlet and the pressure ratio in the Brayton cycle system loop are known, the thermodynamic parameters of the supercritical carbon dioxide at the hot-end module outlet are obtained through an isentropic expansion process, and the thermodynamic state of the supercritical carbon dioxide at the hot-end module outlet is determined. The equilibrium equation is as follows: In the formula: The subscript 3 represents the turbine inlet; The subscript 4 represents the endpoint of isentropic expansion; This represents the entropy of supercritical carbon dioxide at the turbine inlet. ; This represents the entropy of supercritical carbon dioxide at the turbine outlet during the isentropic expansion process. ; The pressure of supercritical carbon dioxide at the turbine inlet, Pa; The pressure of supercritical carbon dioxide at the turbine outlet, Pa; The temperature of supercritical carbon dioxide at the turbine inlet, K; The temperature of supercritical carbon dioxide at the turbine outlet during the isentropic expansion process is K; The pressure ratio is the ratio of the maximum pressure to the minimum pressure. The thermodynamic parameters of supercritical carbon dioxide at the outlet of the hot-end module in the isentropic expansion process are calculated using equation (1). Based on the isentropic efficiency of supercritical carbon dioxide permeability, the thermodynamic state of supercritical carbon dioxide at the outlet of the hot-end module in the actual process is obtained, and its equilibrium equation is as follows: In the formula: The subscript 4' represents the actual expansion endpoint; The subscript "turbine" indicates a turbine. This refers to the specific enthalpy of supercritical carbon dioxide at the turbine inlet. ; This represents the specific enthalpy of supercritical carbon dioxide at the turbine outlet during the isentropic expansion process. ; This represents the specific enthalpy of supercritical carbon dioxide at the turbine outlet during the actual expansion process. ; Let K be the temperature of supercritical carbon dioxide at the turbine outlet during the actual expansion process; To improve entropy efficiency; The turbine equations are formed by equations (1) and (2) above.

3. The thermodynamic optimization method for a lead-bismuth coupled supercritical carbon dioxide Brayton cycle system as described in claim 1, characterized in that: In step 4, if the thermodynamic parameters of the supercritical carbon dioxide working fluid at the compressor inlet and the pressure ratio in the Brayton cycle system loop are known, the thermodynamic parameters of the supercritical carbon dioxide at the cold-end module outlet are obtained through the isentropic compression process, and the thermodynamic state of the supercritical carbon dioxide at the cold-end module outlet is determined. The equilibrium equation is as follows: In the formula: Subscript 1 represents the compressor inlet; The subscript 2 represents the endpoint of isentropic compression; This represents the entropy of supercritical carbon dioxide at the compressor inlet. ; This represents the entropy of supercritical carbon dioxide at the compressor outlet during the isentropic compression process. ; The pressure of supercritical carbon dioxide at the compressor inlet is given in Pa. The pressure of supercritical carbon dioxide at the compressor outlet, in Pa; The temperature of supercritical carbon dioxide at the compressor inlet, in K; The temperature of supercritical carbon dioxide at the compressor outlet during the isentropic compression process is K; The pressure ratio is the ratio of the maximum pressure to the minimum pressure. The thermodynamic parameters of supercritical carbon dioxide at the outlet of the cold-end module in the isentropic compression process, calculated by equation (3), are used to determine the thermodynamic state of supercritical carbon dioxide at the outlet of the cold-end module in the actual process, based on the isentropic efficiency of the supercritical carbon dioxide compressor. The equilibrium equation is as follows: In the formula: The subscript 2' represents the actual end point of compression; The subscript "compressor" indicates a compressor. This refers to the specific enthalpy of supercritical carbon dioxide at the compressor inlet. ; This refers to the specific enthalpy of supercritical carbon dioxide at the compressor outlet during the isentropic compression process. ; This represents the specific enthalpy of supercritical carbon dioxide at the compressor outlet during the actual compression process. ; The temperature of supercritical carbon dioxide at the compressor outlet during the actual compression process, in K; The compressor has isentropic efficiency; The above equations (3) and (4) together constitute the compressor equation set.

4. The thermodynamic optimization method for a lead-bismuth coupled supercritical carbon dioxide Brayton cycle system as described in claim 1, characterized in that: In step 5, the printed circuit board heat exchanger that makes up the regenerator module has four ports, namely the inlet and outlet of the two types of fluids on the hot and cold sides. Usually, the thermodynamic state of the fluids at two of the ports is known. To solve the thermodynamic state of the entire printed circuit board heat exchanger, the thermodynamic calculation of the regenerator module requires a set of heat exchanger equations including the following equations (5), (6), (7) and (8): Use the temperature pinch point value allowed by the technical specifications of the printed circuit board heat exchanger as the constraint for the equation or inequality: Enthalpy balance equation for supercritical carbon dioxide working fluid: mass conservation equation: In the formula: The superscript "hot" indicates a hot fluid; The superscript "cool" indicates a cold fluid; The subscript "in" indicates the fluid inlet; The subscript "out" indicates the fluid outlet; The minimum temperature pinch value, K; The inlet temperature of the hot fluid is K; The outlet temperature of the hot fluid, in K; The inlet temperature of the cold fluid is K; The outlet temperature of the cold fluid, in K; Specific enthalpy of the heat fluid inlet. ; Specific enthalpy of the hot fluid outlet. ; For the specific enthalpy of the cold fluid inlet, ; For the specific enthalpy of the cold fluid outlet, ; The inlet pressure of the hot fluid is Pa; The outlet pressure of the hot fluid is in Pa. The inlet pressure of the cold fluid is Pa; The outlet pressure of the cold fluid is Pa; This refers to the mass flow rate of the hot fluid. ; This refers to the mass flow rate of the cold fluid. ; For a printed circuit board heat exchanger with internal node divisions, the equations are as follows: In the formula: Subscript i This represents a heat exchanger node, with a total of n nodes; For nodes Temperature of the hot fluid, K. ; For nodes Temperature of the cold fluid, K. ; For nodes Specific enthalpy of the heat fluid , ; For nodes Specific enthalpy of cold fluid , ; For nodes The pressure of the hot fluid, Pa, ; For nodes The pressure of the cold fluid, Pa, ; For nodes Mass flow rate of the hot fluid. , ; For nodes Mass flow rate of the cold fluid , .

5. The thermodynamic optimization method for a lead-bismuth coupled supercritical carbon dioxide Brayton cycle system as described in claim 1, characterized in that: The thermodynamic parameters of supercritical carbon dioxide required for calculation in step 5 include the temperature, pressure, and specific enthalpy of supercritical carbon dioxide.

6. The thermodynamic optimization method for a lead-bismuth coupled supercritical carbon dioxide Brayton cycle system as described in claim 1, characterized in that: The thermal efficiency value of the Brayton cycle system in step 6 is calculated from the net output power of the turbine and compressor. For the compressor, the formula for calculating the net output power is as follows: For a turbine, the net output power is calculated using the following formula: In the formula: Subscript 1 represents the compressor inlet; The subscript 2' represents the actual end point of compression; The subscript 3 represents the turbine inlet; The subscript 4' represents the actual expansion endpoint; The subscript "compressor" indicates a compressor. The subscript "turbine" indicates a turbine. This refers to the net output power of the compressor. ; For the turbine's net output power, ; This refers to the specific enthalpy of supercritical carbon dioxide at the compressor inlet. ; This represents the specific enthalpy of supercritical carbon dioxide at the compressor outlet during the actual compression process. ; This refers to the specific enthalpy of supercritical carbon dioxide at the turbine inlet. ; This represents the specific enthalpy of supercritical carbon dioxide at the turbine outlet during the actual expansion process. ; The formula for calculating thermal efficiency is as follows: In the formula: For system thermal efficiency; For core power, .

7. The thermodynamic optimization method for a lead-bismuth coupled supercritical carbon dioxide Brayton cycle system as described in claim 1, characterized in that: In step 6, the temperature difference constraint for the regenerator module in the Brayton cycle system is added by adding a temperature difference inequality constraint to the heat exchanger equation set required for the thermodynamic calculation of the regenerator module in step 5. The temperature difference inequality constraint is as follows: In the formula: The superscript "hot" indicates a hot fluid; The superscript "cool" indicates a cold fluid; The subscript "in" indicates the fluid inlet; The subscript "out" indicates the fluid outlet; The inlet temperature of the hot fluid is K; The outlet temperature of the hot fluid, in K; The inlet temperature of the cold fluid is K; The outlet temperature of the cold fluid, in K; K is the temperature difference limit.

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