Method for solving Brayton cycle transient process of tower type solar supercritical carbon dioxide

Abstract

The invention discloses a method for solving a Brayton cycle transient process of tower type solar supercritical carbon dioxide, belongs to the technical field of transient analysis and calculation of a solar photo-thermal power generation system, and solves the problems that transient response of an integrated system is difficult to capture due to solar intermittency, transient maintenance is difficult due to physical property distortion of a supercritical CO2 critical point, and the transient response is difficult to capture. And existing steady-state / quasi-steady-state analysis neglects transient characteristics and lacks a multi-configuration Brayton cycle transient solving method. The method comprises the following steps: firstly, initializing an integrated system parameter and a Brayton cycle configuration, and then carrying out side-by-side iteration: dispersing a conservation equation of a molten salt side cold tank, a heat collector and the like, calculating the state of the conservation equation, and judging temperature convergence; and then the parameters of the intermediate heat exchanger are taken as boundaries, the CO2 side Brayton cycle equation is discretized to calculate the parameters, internal energy convergence is judged, and iteration is carried out until the final calculation time is reached. According to the method, the Brayton cycle transient process of the tower type solar supercritical CO2 is accurately captured, calculation is simplified, precision is guaranteed, and a multi-cycle configuration is supported.

Description

Technical Field

[0001] This invention relates to the field of transient analysis and calculation technology for solar thermal power generation systems, and in particular to a method for solving the transient process of a tower solar supercritical carbon dioxide Brayton cycle. Background Technology

[0002] Supercritical carbon dioxide Brayton cycle power generation technology is the most promising technical route for future concentrated solar thermal power generation systems. One of the problems with solar energy is its intermittency and fluctuation; therefore, conducting thermodynamic analysis research on integrated power generation systems that couple supercritical carbon dioxide Brayton cycle systems with tower solar power is of great significance for their safe and stable operation.

[0003] Thermodynamic analysis of supercritical carbon dioxide solar integrated power generation systems can be divided into three levels: design condition analysis, non-design condition analysis, and dynamic simulation. The goal of design condition analysis is to determine the cycle thermodynamic parameters and key performance parameters of critical components under given boundary conditions. Non-design condition analysis is based on the design condition results. Through design condition analysis, the performance and structural parameters of the cycle system and key components can be obtained, leading to the understanding of the operating characteristics of key components at non-design conditions, thus enabling the prediction of system performance under non-design conditions. However, both design and non-design condition analyses are developed based on steady-state / quasi-steady-state assumptions, neglecting the transient response characteristics of fluid flow and heat transfer processes during transient operation. Especially for solar thermal power integrated systems using a supercritical carbon dioxide Brayton cycle as the power conversion system, the carbon dioxide working fluid at the compressor inlet in the supercritical carbon dioxide cycle typically operates near the critical point. Due to the property distortion of the carbon dioxide working fluid near the critical point, maintaining the carbon dioxide working fluid in a supercritical state during transient operation becomes difficult. Predicting the response characteristics of tower solar integrated systems under various operating conditions through system analysis programs is a powerful tool for conducting research on the dynamic characteristics, safety analysis, and control strategies of integrated systems.

[0004] However, research shows that there are currently very few publicly available results and patents both domestically and internationally introducing numerical methods for solving the transient processes of supercritical carbon dioxide Brayton cycle coupled tower solar integrated power generation systems. Summary of the Invention

[0005] This invention proposes a method for solving the transient process of a supercritical carbon dioxide Brayton cycle in a tower solar system. The method first initializes the configuration and integrated system parameters of the supercritical carbon dioxide Brayton cycle, then iteratively solves the problem on each side: First, the mass / energy / momentum conservation equations on the molten salt side are discretized, and the convergence of the temperature change rate is determined using Gauss-Seidel iteration and the SIMPLE algorithm to obtain the heat transfer state of the molten salt flow. Then, using the high-pressure side outlet parameters of the intermediate heat exchanger as boundaries, the supercritical CO2 conservation equations on the Brayton cycle side are discretized, and the instantaneous pressure is calculated using CO2 fluid properties. Convergence is determined by the rate of change of internal energy to obtain the key parameters of the cycle. Finally, the fluid state of the entire system within each time step is obtained through iteration. This method addresses the problems of difficulty in capturing the transient response of the integrated system due to the intermittency of solar energy, difficulty in maintaining the transient state due to property distortion near the critical point of supercritical CO2, and the lack of transient solution methods adapted to multiple configurations of Brayton cycles in existing steady-state / quasi-steady-state analyses that ignore transient characteristics.

[0006] A method for solving the transient process of a supercritical carbon dioxide Brayton cycle in a tower solar cell includes the following steps: S1. Complete the initialization of the basic parameters of the integrated system, including the initial power of the solar collector, the fluid state and calculation time step of the molten salt channel on the solar molten salt side and the Brayton cycle working fluid channel; at the same time, complete the configuration initialization of the Brayton cycle according to the requirements. S2. First, discretize the mass and energy conservation equations of the molten salt inside the cold tank. Based on these discretized equations, calculate the temperature distribution of the cold tank control volume within the current system time step. Then, use a quasi-steady-state method to calculate the pressure distribution inside the cold tank. Finally, calculate the temperature change rate of the cold tank. If each node If the maximum value is greater than the specified value, the current cold tank iteration step is determined to be non-convergent, the cold tank temperature is updated, and S2 is re-executed; if the maximum value is less than the specified value, the cold tank calculation is determined to be convergent, and S3 is executed. S3. Based on the state of the cold tank after convergence and the boundary conditions such as solar irradiance and ambient temperature, update and calculate the instantaneous power of the collector. S4. First, discretize the mass, energy, and momentum conservation equations for the molten salt inside the collector. Based on these equations, calculate the temperature, velocity, and pressure distributions of the collector control volume within the current system time step. Simultaneously, using the updated collector power from S3 as a constraint, calculate the collector wall temperature distribution. Then, calculate the collector temperature change rate. If each node If the maximum value is greater than the specified value, the current collector iteration step calculation is determined to be non-convergent, the collector temperature is updated, and S4 is re-executed; if the maximum value is less than the specified value, the collector calculation is determined to be convergent, and S5 is executed. S5. First, determine the mass and energy conservation equation of the molten salt in the heat sink, and calculate the temperature distribution of the heat sink control volume within the current system time step based on this equation; then, use the quasi-steady-state method to calculate the pressure distribution inside the heat sink; finally, calculate the temperature change rate of the heat sink. If each node If the maximum value is greater than the specified value, the current hot tank iteration step is determined to be non-convergent, the hot tank temperature is updated, and S5 is re-executed; if each node If the maximum value is less than the specified value, the hot tank calculation is considered to have converged, and S6 is executed; S6. First, discretize the mass and energy conservation equations of supercritical carbon dioxide in the cycle and the momentum conservation equation of the nozzle. Then, use the high-pressure side outlet parameters of the intermediate heat exchanger in the previous system time step as boundary conditions, and calculate the mass, internal energy and flow rate of the control volume in the current Brayton side iteration step based on the discrete equations in S2. S7. Based on the enthalpy and specific volume of each node on the Brayton cycle side obtained in S6, and combined with the carbon dioxide fluid property package, calculate the instantaneous pressure within each node. S8. Based on the instantaneous pressure of the node obtained in S7, synchronously update the key circulation parameters of the Brayton cycle side pipe, including pressure, flow rate and enthalpy, to ensure that the pipe state matches the node state. S9. Calculate the rate of change of internal energy ΔU / U of each fluid node on the Brayton cycle side. If the maximum value of ΔU / U of each node is greater than the specified value, it is determined that the current iteration step on the Brayton side is not converged. The time step is halved and the calculation is returned to S6. If the maximum value of ΔU / U of each node is less than the specified value, it is determined that the current iteration step on the Brayton side is converged. Execute S10. S10. Check if the current cumulative calculation time on the Brayton side has reached a system time step. If it has, terminate the Brayton side calculation for the current round. If it has not, jump to S6 to continue the calculation for the next small time step. S11. First, discretize the mass, energy, and momentum conservation equations for the molten salt in the intermediate heat exchanger. Based on these equations, calculate the temperature, velocity, and pressure distributions of the intermediate heat exchanger control volume within the current system time step. Then, calculate the temperature change rate of the intermediate heat exchanger. If each node If the maximum value is greater than the specified value, it is determined that the current intermediate heat exchanger iteration step calculation has not converged. After updating the intermediate heat exchanger temperature, S11 is re-executed; if each node If the maximum value is less than the specified value, the intermediate heat exchanger calculation is considered to have converged, and S12 is executed; S12. Check whether the cumulative calculation time of the integrated system has reached the preset final calculation time. If it has, terminate the transient process calculation of the entire tower solar supercritical carbon dioxide Brayton cycle integrated system. If it has not, return to S2 to start the full process calculation of the next system time step.

[0007] Furthermore, in S2, S4, S5, and S11, the energy conservation equations for the discrete collectors, hot and cold storage tanks, and intermediate heat exchangers are presented using a first-order upwind finite difference scheme. Furthermore, in S4 and S11, the flow rates and pressures of the discrete heat collector and intermediate heat exchanger are solved using the SIMPLE algorithm to obtain the flow rate and pressure distributions for the next iteration step, while the pressure distribution of the cold and hot storage tanks is calculated using the quasi-steady-state form of the Bernoulli equation.

[0008] Furthermore, the feature is that the conservation equations for the mass, energy, and momentum of the molten salt in the solar collector are:

[0009]

[0010]

[0011] in, The flow rate of the solar collector is kg / s; Mass of the solar collector, kg; For collector pressure drop, Pa; This is the friction loss coefficient along the friction path; Density, kg / m³ 3 ; is the flow velocity, m / s; is the channel length, m; is the equivalent diameter, m; is the local loss coefficient; is the cross-sectional area, m². 2 ; represents height, in meters; ; represents the pressure drop provided by the pump, in Pa. The specific heat capacity of molten salt, ; Temperature, K; The convective heat transfer coefficient is... ; The enthalpy of the solar collector is expressed in kJ / kg. The energy conservation equation for the metal wall of the solar collector takes into account the received solar irradiance, heat loss between the collector and the external environment, and convective heat transfer from the internal fluid. The change in the average temperature of the solid metal is expressed as: .

[0012] in, T sr The average temperature of the metal wall surface, expressed in K; Q rec,inThe solar irradiance received by the collector is expressed in W. Q rec,loss Let W be the heat loss of the solar collector. The heat loss of the solar collector includes three components: reflection loss, radiation loss, and convection loss, expressed as:

[0013] in, ρ panel The reflectivity of the receiver panel; A rec For the receiver panel area, m 2 ; A ape The area of ​​the cavity is m. 2 ; ε w The receiver tube wall radiation coefficient is corrected by the correction factor; T air The ambient temperature is in K.

[0014] The conservation equations for the mass and energy of molten salt in hot and cold storage tanks are as follows:

[0015]

[0016] in, Flow rate, kg / s; Mass, kg; For pressure drop, Pa; This is the friction loss coefficient along the friction path; It is the specific heat capacity of molten salt. ; Temperature, K; The convective heat transfer coefficient is... ; The enthalpy value of the storage tank is expressed in kJ / kg. The pressure distribution in the storage tank is related to the external pump, and its expression is as follows:

[0017] in, This is the friction loss coefficient along the friction path; Density; kg / m³ 3 , The velocity is m / s; The length of the flow channel is in meters (m). The equivalent diameter is in meters (m). This is the local loss coefficient; m is the cross-sectional area. 2 ; Height, in meters (m); The pressure drop provided by the pump, in Pa; The conservation equations for the mass, energy, and momentum of the molten salt in the intermediate heat exchanger are as follows:

[0018]

[0019]

[0020]

[0021] in, Flow rate, kg / s; Mass, kg; For pressure drop, Pa; This is the friction loss coefficient along the friction path; Density, kg / m³ 3 , where is the flow velocity (m / s); is the channel length (m); is the equivalent diameter (m); is the local loss coefficient; is the cross-sectional area (m²). 2 ; Height, in meters (m); It is the specific heat capacity of molten salt. ; Temperature, K; The enthalpy of the solar collector is expressed in kJ / kg. In the intermediate heat exchanger, the energy transfer from the hot-side molten salt fluid to the cold-side CO2 fluid occurs sequentially through convective heat transfer between the molten salt fluid and the metal wall, heat conduction through the metal wall, and convective heat transfer between the CO2 fluid and the metal wall. The heat conduction process through the metal wall can be represented by a one-dimensional heat conduction equation without an internal heat source:

[0022] in, The density of the material is expressed in kg·m. -3 ; The specific heat capacity of the material is expressed in J·(kg·K). -1 ; Let K be the material temperature. Let the time to solve the problem be in seconds (s). Let W be the thermal conductivity of the material, expressed in W·(m·K). -1 .

[0023] The convective heat transfer process of a metal wall is represented as follows:

[0024]

[0025] in, The convective heat transfer coefficient is... ; Thermal power, W;T f,hot The temperature of the molten salt fluid; T w,hot This refers to the surface temperature of the molten salt side metal wall. T f,cold The temperature of the CO2 fluid; T w,cold This refers to the surface temperature of the metal wall on the CO2 side.

[0026] Furthermore, in S6, the mass and energy conservation equations for the discrete Brayton cycle-side supercritical carbon dioxide, as well as the momentum conservation equation for the tube, are solved using Gauss-Seidel iteration with respect to the Jacobian matrix. The solution yields the mass increment, energy increment, and flow rate increment at each node of the circulating fluid. This allows us to calculate the node's mass, energy, and the flow rate of the node in the next iteration step, as well as the mass increment, energy increment, and flow rate increment. The calculation is as follows:

[0027]

[0028]

[0029] in, For time step, For the number of nodes, For the number of units taken over, Let be the independent variable at the current moment. Indicates the current moment.

[0030] Furthermore, the energy conservation equation and mass conservation equation for carbon dioxide fluid are applied to the control volume to calculate the changes in its mass, internal energy, and pressure. The momentum conservation equation is applied to the nozzle to calculate the coolant flow rate into and out of the control volume. By combining the difference equations for mass conservation and energy conservation of all control volumes with the difference equation for momentum conservation of the nozzle, the following formula is obtained:

[0031] Expanding the first term on the right-hand side using a first-order Taylor series, substituting it into the above equation, and discretizing the time derivative on the left-hand side, yields the node's mass increment, energy increment, and inlet flow rate increment. .

[0032] Furthermore, the conservation equations for the mass, momentum, and energy of the carbon dioxide fluid are as follows:

[0033]

[0034]

[0035] in, Density; for Fluid flow rate; The fluid velocity; For pressure; Equivalent diameter; The coefficient of frictional resistance; It is the acceleration due to gravity; It is the internal energy of the fluid; This refers to the enthalpy of the fluid. As an internal heat source for the fluid, This represents the number of nodes that have received input to the current node. This represents the node height.

[0036] Furthermore, the feature is that in S2, S4, S5, S6 and S11, the pipes on the solar molten salt side and within the Brayton cycle are represented by nodes, and the fluid circulation system is spatially discretized using staggered grids, with momentum grid cells deviating from mass and energy grid cells by half a spatial increment.

[0037] Furthermore, the performance curves of the rotating machinery are used to interpolate and solve for the efficiency and pressure ratio of the rotating machinery. When solving in the transient analysis program, the rotating machinery is a nozzle and a node. The pressure rise or pressure drop calculated from the pressure ratio will act on the momentum equation of the inlet nozzle of the rotating machinery. The work done by the rotating shaft on the fluid inside the rotating machinery is added to the energy conservation equation of the fluid node of the rotating machinery in the form of a source term.

[0038] A computer device includes: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the above-described method for solving the transient process of supercritical carbon dioxide Brayton cycle in a tower solar cell.

[0039] The beneficial effects of this invention are as follows: This invention provides a method for solving the transient process of supercritical carbon dioxide Brayton cycle in a tower solar cell. Based on a homogeneous flow model, it combines the physical properties, friction, and heat transfer characteristics of supercritical carbon dioxide and molten salt (60% NaNO3-40% KNO3) to discretize the fundamental equations of supercritical carbon dioxide and molten salt in both time and space. Since supercritical carbon dioxide is essentially a single phase in the Brayton cycle, using a homogeneous flow model to calculate the fundamental fluid equations effectively reduces the number of fundamental equations and the required constitutive relations, simplifying the calculation steps and accurately capturing the state changes of supercritical carbon dioxide. Simultaneously, by employing varying time steps or adding a multiplication factor to the Jacobian matrix, the convergence of the method near the carbon dioxide critical point is significantly improved, effectively solving the numerical divergence problem that easily occurs in the transient solution of the Brayton cycle and the difficult problem of solving transient processes in rotating machinery. For the collector, after modeling, it is equivalent to a single... The root heat pipe not only ensures accurate capture of the details of the collector's state changes but also reduces computational costs and time. In the processing of rotating machinery, relying on the externally input rotating machinery performance curves to provide pressure ratio and efficiency, it can quickly and accurately simulate the transient operating state of rotating machinery and unify the basic equations of fluids inside rotating machinery with those inside ordinary pipes, becoming the key to realizing the calculation of transient processes of closed Brayton cycles. In addition, the accuracy of the method's correctness is further guaranteed by the accurate supercritical carbon dioxide and molten salt properties, heat transfer and friction relationships. The solution method on the Brayton side supports the parameterized encapsulation of Brayton cycles, and the dynamic configuration of the control unit can realize the rapid configuration of different cycle topologies such as simple cycles, regenerative cycles, and intercooled cycles. In summary, this invention, based on simplified fluid fundamental equations, a reasonable rotating machinery model, accurate physical properties and heat transfer friction relationships, and an effective numerical solution method, simplifies the solution process for transient processes in tower solar supercritical carbon dioxide Brayton cycles while ensuring computational accuracy. It enables the transient process solutions based on this method to accurately reflect the transient physical processes of tower solar supercritical carbon dioxide Brayton cycles and supports the construction of Brayton cycles with various configurations. It can be effectively used for accident analysis and control strategy research in tower solar supercritical carbon dioxide Brayton cycles. Attached Figure Description

[0040] Figure 1 A schematic diagram of a tower-type solar supercritical carbon dioxide Brayton cycle integrated system; Figure 2 This is a flowchart of a method for solving the transient process of a supercritical carbon dioxide Brayton cycle in a tower solar cell according to the present invention; Figure 3 Flowchart for the calculation of solar collector components; Figure 4 Flowchart for the calculation of intermediate heat exchanger components; Figure 5 A flowchart for the calculation of thermal storage tanks (including cold tanks and hot tanks); Figure 6 This is a discrete diagram of the flow channel in this invention.

[0041] Among them, 1 is the mirror field; 2 is the cold tank; 3 is the solar collector; 4 is the hot tank; 5 is the intermediate heat exchanger; 6 is the gas turbine; 7 is the compressor; 8 is the precooler; and 9 is the regenerator. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] First, the objects to which the method of the present invention is applied are as follows: Figure 1 As shown, Figure 1 This paper showcases the overall structural layout of a tower-type solar-coupled supercritical carbon dioxide Brayton cycle integrated system. At the system's initiation, a mirror field 1 reflects and focuses solar energy onto collector 3. Collector 3, acting as a heat pipe, receives heat energy and heats the molten salt working fluid within it. After receiving energy from the mirror field, the molten salt first enters a cold tank 2 for cryogenic storage, then flows to collector 3 to complete the heating process. The heated, high-temperature molten salt is stored in a hot tank 4, providing a high-temperature heat source for subsequent energy conversion stages. The core of the energy conversion occurs in the intermediate heat exchanger 5, where the high-temperature molten salt transfers heat energy to the supercritical carbon dioxide working fluid. On the Brayton cycle side, compressor 7 first compresses and pressurizes the carbon dioxide working fluid. The fluid then flows through a regenerator 9 to recover waste heat before entering the intermediate heat exchanger 5 to absorb heat energy from the molten salt. The high-temperature, high-pressure carbon dioxide drives turbine 6 to generate electricity, which is then cooled by a precooler 8 and returned to compressor 7, forming a complete closed-loop power cycle. The entire system adopts a modular design, supporting rapid configuration of different Brayton cycle topologies.

[0044] The system's energy transfer achieves closed-loop flow through three core paths: the molten salt circulation path begins in the cold tank 2, flows through the solar collector 3 to absorb solar energy and heat up before entering the hot tank 4, and finally transfers the heat energy to the carbon dioxide working fluid through the intermediate heat exchanger 5 and returns to the cold tank 2; the carbon dioxide circulation path begins in the compressor 7, is preheated by the regenerator 9, enters the intermediate heat exchanger 5 to absorb heat energy, drives the gas turbine 6 to generate electricity, and then returns to the compressor 7 after being cooled by the precooler 8; the heat transfer direction follows the conversion chain of "solar energy → molten salt collector → molten salt / carbon dioxide intermediate heat exchanger → mechanical energy gas turbine", in which the regenerator 9 and the precooler 8 undertake the key functions of waste heat recovery and working fluid cooling, respectively.

[0045] In terms of structural design, the piping system adopts Figure 6 The staggered grid discretization method shown deviates momentum grid cells from mass and energy grid cells by half a spatial increment to ensure transient solution accuracy. The high-pressure side outlet parameters of intermediate heat exchanger 5 are used as key boundary conditions to achieve dynamic coupling calculations of the molten salt cycle and the carbon dioxide Brayton cycle, supporting transient response analysis of the system under various operating conditions.

[0046] Accordingly, this invention provides a method for solving the transient process of a supercritical carbon dioxide Brayton cycle in a tower solar thermal system. First, the parameters of the tower solar thermal system are initialized, and the configuration of the Brayton cycle is initialized. Then, the temperature, flow rate, and pressure distribution of the cold tank are calculated, and the rate of temperature change of the cold tank is calculated. The calculation is compared with specified values. If the maximum rate of temperature change at each node of the cold tank is greater than the specified value, the current iteration step is considered non-convergent, the temperature is updated, and the mass, internal energy, and flow rate on the cold tank control body are recalculated. If the maximum rate of internal energy change at each fluid node of the cold tank is less than the specified value, the current Brayton iteration step is considered convergent. Then, the transient power of the solar collector is calculated. The transient temperature, flow rate, and pressure distribution of the solar collector are calculated, the wall temperature of the solar collector is calculated, and the rate of temperature change of the solar collector is calculated. The results are compared with specified values. If the maximum rate of temperature change at each node of the collector is greater than the specified value, the current iteration step is considered non-convergent, the temperature is updated, and the mass, internal energy, and flow rate on the collector control body are recalculated. If the maximum rate of internal energy change at each fluid node of the collector is less than the specified value, the current iteration step is considered convergent. Then, the transient temperature, flow rate, and pressure distribution of the hot tank are calculated, and the rate of temperature change of the hot tank is calculated. The values ​​are compared with specified values. If the maximum rate of temperature change at each node of the hot tank is greater than the specified value, the current iteration step is considered non-convergent. The temperature is updated, and the mass, internal energy, and flow rate at the nozzle of the hot tank control body are recalculated. If the maximum rate of internal energy change at each fluid node of the hot tank is less than the specified value, the current iteration step is considered convergent. Then, the high-pressure side parameters of the intermediate heat exchanger in the previous system time step are used as boundary values ​​to calculate the mass, internal energy, and flow rate at the nozzle of the control body in the current Brayton-side iteration step. The pressure, flow rate, and enthalpy parameters of the nozzle are updated. The flow rate at each fluid node is calculated. The rate of change of internal energy of the control volume nodes, ΔU / U, is calculated. If the maximum value of the rate of change of internal energy of each node on the Brayton side is greater than a specified value, the current iteration step on the Brayton side is considered non-convergent, the time step is halved, and the mass, internal energy, and flow rate on the pipes of the control volume on the Brayton side are recalculated. If the maximum value of the rate of change of internal energy of each fluid node on the Brayton side is less than a specified value, the current iteration step on the Brayton side is considered convergent. Then, it is determined whether the time on the Brayton side has reached the system time step. Then, the transient temperature, flow rate, and pressure distribution of the intermediate heat exchanger are calculated, and the rate of change of temperature of the intermediate heat exchanger is calculated. The temperature change rate of the intermediate heat exchanger is calculated by comparing it with the specified value. The results are compared with specified values. If the maximum rate of temperature change at each node of the intermediate heat exchanger is greater than the specified value, the current iteration step is considered non-convergent, the temperature is updated, and the mass, internal energy, and flow rate on the intermediate heat exchanger control body are recalculated. If the maximum rate of internal energy change at each fluid node of the intermediate heat exchanger is less than the specified value, the current iteration step is considered convergent. Finally, it is determined whether the final calculation time has been reached. Based on the above solution method, the flow state of the molten salt on the solar molten salt side, the operating state of the rotating machinery on the Brayton side, and the flow state of the coolant in the cycle can be obtained at each time step, thus forming the transient process of the tower solar supercritical carbon dioxide Brayton cycle.

[0047] This invention can accurately and effectively solve the transient processes of supercritical carbon dioxide Brayton cycles in tower solar cells with various configurations, and can be used for accident analysis and control strategy research of supercritical carbon dioxide Brayton cycles in tower solar cells.

[0048] Reference Figures 1-5 As shown, a method for solving the transient process of a supercritical carbon dioxide Brayton cycle in a tower solar cell includes the following steps: S1. Complete the initialization of the basic parameters of the integrated system, including the initial power of the solar collector, the fluid state and calculation time step of the molten salt channel on the solar molten salt side and the Brayton cycle working fluid channel; at the same time, complete the configuration initialization of the Brayton cycle according to the requirements. S2. First, discretize the mass and energy conservation equations of the molten salt inside the cold tank. Based on these discretized equations, calculate the temperature distribution of the cold tank control volume within the current system time step. Then, use a quasi-steady-state method to calculate the pressure distribution inside the cold tank. Finally, calculate the temperature change rate of the cold tank. If each node If the maximum value is greater than the specified value, the current cold tank iteration step is determined to be non-convergent, the cold tank temperature is updated, and S2 is re-executed; if the maximum value is less than the specified value, the cold tank calculation is determined to be convergent, and S3 is executed. S3. Based on the state of the cold tank after convergence and the boundary conditions such as solar irradiance and ambient temperature, update and calculate the instantaneous power of the collector. S4. First, discretize the mass, energy, and momentum conservation equations for the molten salt inside the collector. Based on these equations, calculate the temperature, velocity, and pressure distributions of the collector control volume within the current system time step. Simultaneously, using the updated collector power from S3 as a constraint, calculate the collector wall temperature distribution. Then, calculate the collector temperature change rate. If each node If the maximum value is greater than the specified value, the current collector iteration step calculation is determined to be non-convergent, the collector temperature is updated, and S4 is re-executed; if the maximum value is less than the specified value, the collector calculation is determined to be convergent, and S5 is executed. S5. First, determine the mass and energy conservation equation of the molten salt in the heat sink, and calculate the temperature distribution of the heat sink control volume within the current system time step based on this equation; then, use the quasi-steady-state method to calculate the pressure distribution inside the heat sink; finally, calculate the temperature change rate of the heat sink. If each node If the maximum value is greater than the specified value, the current hot tank iteration step is determined to be non-convergent, the hot tank temperature is updated, and S5 is re-executed; if each node If the maximum value is less than the specified value, the hot tank calculation is considered to have converged, and S6 is executed; S6. First, discretize the mass and energy conservation equations of supercritical carbon dioxide in the cycle and the momentum conservation equation of the nozzle. Then, use the high-pressure side outlet parameters of the intermediate heat exchanger in the previous system time step as boundary conditions, and calculate the mass, internal energy and flow rate of the control volume in the current Brayton side iteration step based on the discrete equations in S2. S7. Based on the enthalpy and specific volume of each node on the Brayton cycle side obtained in S6, and combined with the carbon dioxide fluid property package, calculate the instantaneous pressure within each node. S8. Based on the instantaneous pressure of the node obtained in S7, synchronously update the key circulation parameters of the Brayton cycle side pipe, including pressure, flow rate and enthalpy, to ensure that the pipe state matches the node state. S9. Calculate the rate of change of internal energy ΔU / U of each fluid node on the Brayton cycle side. If the maximum value of ΔU / U of each node is greater than the specified value, it is determined that the current iteration step on the Brayton side is not converged. The time step is halved and the calculation is returned to S6. If the maximum value of ΔU / U of each node is less than the specified value, it is determined that the current iteration step on the Brayton side is converged. Execute S10. S10. Check if the current cumulative calculation time on the Brayton side has reached a system time step. If it has, terminate the Brayton side calculation for the current round. If it has not, jump to S6 to continue the calculation for the next small time step. S11. First, discretize the mass, energy, and momentum conservation equations for the molten salt in the intermediate heat exchanger. Based on these equations, calculate the temperature, velocity, and pressure distributions of the intermediate heat exchanger control volume within the current system time step. Then, calculate the temperature change rate of the intermediate heat exchanger. If each node If the maximum value is greater than the specified value, it is determined that the current intermediate heat exchanger iteration step calculation has not converged. After updating the intermediate heat exchanger temperature, S11 is re-executed; if each node If the maximum value is less than the specified value, the intermediate heat exchanger calculation is considered to have converged, and S12 is executed; S12. Check whether the cumulative calculation time of the integrated system has reached the preset final calculation time. If it has, terminate the transient process calculation of the entire tower solar supercritical carbon dioxide Brayton cycle integrated system. If it has not, return to S2 to start the full process calculation of the next system time step.

[0049] Specifically, this embodiment first initializes the basic parameters of the integrated system and the Brayton cycle configuration, laying a precise initial foundation for solving the transient process of the supercritical carbon dioxide Brayton cycle in a tower solar system. This ensures that subsequent calculations can be tailored to different cycle topology requirements and avoids solution deviations caused by fuzzy initial parameters. Subsequently, discrete solutions are performed on the molten salt side cold tank, collector, and hot tank in a logical sequence. The temperature and velocity distribution of each component's control volume are obtained through discrete mass and energy conservation equations. The pressure distribution is calculated using a quasi-steady-state method, and convergence is judged by whether the maximum temperature change rate meets a specified value. If convergence fails, the temperature is updated and recalculated. This process effectively captures the transient state changes of molten salt as an energy buffer medium under intermittent and fluctuating solar energy, making up for the shortcomings of traditional steady-state / quasi-steady-state analysis that ignores the transient response characteristics of the molten salt side. In particular, the collector solution stage specifically calculates the wall temperature distribution with the updated instantaneous power as a constraint, further improving the accuracy of the description of the transient heat transfer relationship during the collector's reception of solar energy and heating of molten salt, ensuring dynamic matching between molten salt temperature changes and solar energy input. After the key components on the molten salt side converge, using the high-pressure side outlet parameters of the intermediate heat exchanger as the boundary, the mass and energy conservation equations for supercritical carbon dioxide on the Brayton cycle side and the momentum conservation equation for the nozzles are discretized. Combined with the carbon dioxide fluid properties package, the instantaneous pressure at the nodes is calculated, and key parameters such as pressure, flow rate, and enthalpy of the nozzles are updated synchronously. Then, the internal energy change rate at each fluid node is used... The convergence judgment and calculation adjustment are implemented. If convergence fails, the time step is halved and the solution is recalculated. This effectively addresses the difficulty in maintaining the transient state caused by the distortion of physical properties of supercritical carbon dioxide near the critical point, avoids the numerical divergence problem that easily occurs in the transient solution of Brayton cycle, and ensures the stable response calculation of key cycle parameters. At the same time, by checking whether the cumulative calculation time on the Brayton side reaches the system time step, the timing consistency between the transient solution of Brayton cycle and the state transfer on the molten salt side is ensured, and the timing misalignment of the calculations on both sides is avoided from affecting the overall transient accuracy. Finally, discrete solutions are performed on the molten salt side of the intermediate heat exchanger. The state of its control volume is obtained through discrete mass, energy and momentum conservation equations. Adjustments are made based on the convergence of the rate of temperature change. Then, the process is terminated based on the cumulative calculation time of the integrated system. This forms a complete logic of iterative and dynamic coupling on both sides: "solution of key components on the molten salt side - solution of the Brayton cycle on the Brayton side - coupling solution of the intermediate heat exchanger". This logic can obtain the fluid flow and heat transfer state of the collector, hot and cold storage tanks, intermediate heat exchanger and Brayton cycle within each time step, accurately reflecting the transient physical process of the tower solar supercritical carbon dioxide Brayton cycle integrated system.

[0050] Furthermore, in S2, S4, S5, and S11, the energy conservation equations for the discrete collectors, hot and cold storage tanks, and intermediate heat exchangers are presented using a first-order upwind finite difference scheme.

[0051] Specifically, this embodiment addresses the discrete problem of the energy conservation equation for key components (collectors, hot and cold storage tanks, and intermediate heat exchangers) on the molten salt side in the transient solution of the integrated system. The Gauss-Seidel iterative method is used in steps S2, S4, S5, and S11 to accurately obtain the temperature distribution for the next iteration step, providing core support for accurately describing the transient heat exchange process of molten salt within these components. The temperature calculation process explicitly associates the time step, spatial step, and the dimensions of the time and spatial nodes. Combining the Gaussian iterative formula (clearly defining the correspondence between the row and ordinate coordinates of the matrix) and the general expression of the Jacobian matrix (integrating the time step, the number of discrete nodes, and the current state quantity), a rigorous mathematical logic is provided for the discrete solution of the energy conservation equation. This avoids temperature deviations caused by a lack of clear parameter associations in the calculation method, ensuring consistency and traceability in temperature calculations for different components and at different iteration stages. This precise temperature distribution calculation can meticulously capture the transient thermal state changes of molten salt during low-temperature storage in the cold tank, the temperature rise of the collector after receiving solar energy, the high-temperature heat storage in the hot tank, and the heat transfer process between the intermediate heat exchanger and supercritical carbon dioxide. For example, the collector can more accurately match the dynamic response relationship between solar input power and molten salt temperature; the intermediate heat exchanger can optimize the heat exchange efficiency between molten salt and carbon dioxide based on accurate temperature data; and the cold and hot storage tanks can clearly reflect the real-time changes in heat storage capacity through temperature distribution. This provides a reliable molten salt-side thermal state basis for solving the Brayton cycle side with the high-pressure side outlet parameters of the intermediate heat exchanger as boundary conditions, avoiding a decrease in overall transient solution accuracy due to temperature calculation errors being transmitted to the cycle side. Simultaneously, the efficient convergence characteristics of the Gauss-Seidel iterative method, combined with the convergence judgment mechanism of the temperature change rate in the earlier steps, ensure both the accuracy requirements of temperature calculation and the speed of solving the energy conservation equation, ensuring efficient completion of the thermal state iteration of key components on the molten salt side within each system time step.

[0052] Furthermore, in S4 and S11, the flow rates and pressures of the discrete heat collector and intermediate heat exchanger are solved using the SIMPLE algorithm to obtain the flow rate and pressure distributions for the next iteration step, while the pressure distribution of the cold and hot storage tanks is calculated using the quasi-steady-state form of the Bernoulli equation.

[0053] Specifically, in this embodiment, differentiated and precise calculation methods are adopted for the flow velocity and pressure calculation of key components on the molten salt side, taking into account the functional characteristics and flow features of different components. In the calculations for the collector (S4) and the intermediate heat exchanger (S11), considering that these two types of components are the core of solar energy absorption and heat transfer on the molten salt side, and that the transient coupling relationship between the internal molten salt flow velocity and pressure directly affects the heat exchange efficiency and system stability, the SIMPLE algorithm is used to discretize and solve the flow velocity and pressure distribution. This algorithm can efficiently handle the mutual constraints between flow velocity and pressure in fluid flow, and gradually approximate the actual flow state through iteration, thereby accurately obtaining the flow velocity and pressure distribution for the next iteration step. This ensures that the flow parameters and heat exchange requirements are dynamically matched during the process of receiving solar energy heating in the collector and during the heat exchange between the molten salt and supercritical carbon dioxide in the intermediate heat exchanger, avoiding inaccurate heat exchange efficiency assessments due to deviations in flow velocity or pressure calculations. For hot and cold storage tanks, their core function is to store and buffer molten salt. The internal molten salt flow is relatively smooth, eliminating the need for complex transient pressure calculations. Therefore, a quasi-steady-state form of the Bernoulli equation is used to calculate the pressure distribution. This significantly simplifies the tank pressure calculation process while ensuring reliability, reducing unnecessary computational redundancy and improving the overall efficiency of molten salt side parameter calculations. This design, tailored to the characteristics of different components, ensures the accuracy of flow parameter calculations for key heat exchange components such as collectors and intermediate heat exchangers, providing a reliable foundation for subsequent temperature distribution calculations and heat transfer analysis. Furthermore, it optimizes computational efficiency by simplifying the pressure calculation process for hot and cold storage tanks.

[0054] Furthermore, the feature is that the conservation equations for the mass, energy, and momentum of the molten salt in the solar collector are:

[0055]

[0056]

[0057] in, The flow rate of the solar collector is kg / s; Mass of the solar collector, kg; For collector pressure drop, Pa; This is the friction loss coefficient along the friction path; Density, kg / m³ 3 ; is the flow velocity, m / s; is the channel length, m; is the equivalent diameter, m; is the local loss coefficient; is the cross-sectional area, m². 2 ; represents height, in meters; ; represents the pressure drop provided by the pump, in Pa. The specific heat capacity of molten salt, ; Temperature, K; The convective heat transfer coefficient is... ; The enthalpy of the solar collector is expressed in kJ / kg. The energy conservation equation for the metal wall of the solar collector takes into account the received solar irradiance, heat loss between the collector and the external environment, and convective heat transfer from the internal fluid. The change in the average temperature of the solid metal is expressed as: .

[0058] in, T sr The average temperature of the metal wall surface, expressed in K; Q rec,in The solar irradiance received by the collector is expressed in W. Q rec,loss Let W be the heat loss of the solar collector. The heat loss of the solar collector includes three components: reflection loss, radiation loss, and convection loss, expressed as:

[0059] in, ρ panel The reflectivity of the receiver panel; A rec For the receiver panel area, m 2 ; A ape The area of ​​the cavity is m. 2 ; ε w The receiver tube wall radiation coefficient is corrected by the correction factor; T air The ambient temperature is in K.

[0060] The conservation equations for the mass and energy of molten salt in hot and cold storage tanks are as follows:

[0061]

[0062] in, Flow rate, kg / s; Mass, kg; For pressure drop, Pa; This is the friction loss coefficient along the friction path; It is the specific heat capacity of molten salt. ; Temperature, K; The convective heat transfer coefficient is... ; The enthalpy value of the storage tank is expressed in kJ / kg. The pressure distribution in the storage tank is related to the external pump, and its expression is as follows:

[0063] in, This is the friction loss coefficient along the friction path; Density; kg / m³ 3 , The velocity is m / s; The length of the flow channel is in meters (m). The equivalent diameter is in meters (m). This is the local loss coefficient; m is the cross-sectional area. 2 ; Height, in meters (m); The pressure drop provided by the pump, in Pa; The conservation equations for the mass, energy, and momentum of the molten salt in the intermediate heat exchanger are as follows:

[0064]

[0065]

[0066]

[0067] in, Flow rate, kg / s; Mass, kg; For pressure drop, Pa; This is the friction loss coefficient along the friction path; Density, kg / m³ 3 , where is the flow velocity (m / s); is the channel length (m); is the equivalent diameter (m); is the local loss coefficient; is the cross-sectional area (m²). 2 ; Height, in meters (m); It is the specific heat capacity of molten salt. ; Temperature, K; The enthalpy of the solar collector is expressed in kJ / kg. In the intermediate heat exchanger, the energy transfer from the hot-side molten salt fluid to the cold-side CO2 fluid occurs sequentially through convective heat transfer between the molten salt fluid and the metal wall, heat conduction through the metal wall, and convective heat transfer between the CO2 fluid and the metal wall. The heat conduction process through the metal wall can be represented by a one-dimensional heat conduction equation without an internal heat source:

[0068] in, The density of the material is expressed in kg·m. -3 ; The specific heat capacity of the material is expressed in J·(kg·K). -1 ; Let K be the material temperature. Let the time to solve the problem be in seconds (s). Let W be the thermal conductivity of the material, expressed in W·(m·K). -1 .

[0069] The convective heat transfer process of a metal wall is represented as follows:

[0070]

[0071] in, The convective heat transfer coefficient is... ; Thermal power, W; T f,hot The temperature of the molten salt fluid; T w,hot This refers to the surface temperature of the molten salt side metal wall. T f,cold The temperature of the CO2 fluid; T w,cold This refers to the surface temperature of the metal wall on the CO2 side.

[0072] Specifically, this embodiment provides a rigorous mathematical model to accurately describe the flow, heat transfer, and energy conversion processes of molten salt in different components by explicitly providing the mass, energy, and momentum conservation equations for the molten salt in the collector, hot and cold storage tanks, and intermediate heat exchangers, as well as the relationship between heat transfer between the fluid and the metal wall and the expression for the temperature change of the metal solid. This ensures that the physical state changes of the molten salt in each component can be meticulously characterized through quantitative equations. For the collector, its molten salt conservation equations cover key parameters such as flow rate, mass, pressure drop, friction loss coefficient, density, flow velocity, specific heat capacity, and convective heat transfer coefficient. This comprehensively reflects the mass change, energy absorption and transfer, and pressure loss of the molten salt during the flow process after the collector receives solar energy. In particular, by introducing parameters such as convective heat transfer coefficient and collector enthalpy, the heat transfer relationship between the molten salt and the collector wall is accurately correlated, ensuring that the heat energy converted from solar energy can be accurately transferred to the molten salt. This provides a reliable equation basis for subsequent calculations of collector temperature distribution and wall temperature. For both hot and cold storage tanks, the molten salt mass and energy conservation equations also include core parameters such as flow rate, mass, and pressure drop. Furthermore, a specific expression for the tank pressure distribution related to the external pump is provided, clearly demonstrating the pump's impact on the molten salt pressure within the tank. This accurately calculates the storage state and pressure changes of the molten salt within the tank, adapting to the functional requirements of hot and cold storage tanks as molten salt buffer storage units and avoiding pressure calculation errors caused by neglecting the pump's role. For intermediate heat exchangers, the molten salt conservation equations not only comprehensively cover flow and energy-related parameters but also clarify the convective heat transfer process between the molten salt and the metal wall through heat transfer relationships. Combined with expressions for the temperature changes of the metal solid, this further connects the molten salt heat transfer with the temperature response of the metal structure, accurately reflecting the dynamic process of heat transfer from the molten salt to supercritical carbon dioxide within the intermediate heat exchanger, ensuring accurate and reliable quantitative calculations of heat transfer. Furthermore, the clear definition of each parameter in these equations (such as density, specific heat capacity, convective heat transfer coefficient, etc.) avoids transient solution errors caused by ambiguous parameter definitions or missing equations. This allows the calculation of each component on the molten salt side to be carried out based on a unified and complete mathematical logic, providing an accurate calculation basis for subsequent convergence judgment through temperature change rate, thereby ensuring the accuracy of transient process solution for the entire tower solar supercritical carbon dioxide Brayton cycle integrated system.

[0073] Furthermore, in S6, the mass and energy conservation equations for the discrete Brayton cycle-side supercritical carbon dioxide, as well as the momentum conservation equation for the tube, are solved using Gauss-Seidel iteration with respect to the Jacobian matrix. The solution yields the mass increment, energy increment, and flow rate increment at each node of the circulating fluid. This allows us to calculate the node's mass, energy, and the flow rate of the node in the next iteration step, as well as the mass increment, energy increment, and flow rate increment. The calculation is as follows:

[0074]

[0075]

[0076] in, For time step, For the number of nodes, For the number of units taken over, Let be the independent variable at the current moment. Indicates the current moment.

[0077] Specifically, in the core transient solution (S6) of the Brayton cycle side in this embodiment, the mass and energy conservation equations of supercritical carbon dioxide and the momentum conservation equation of the nozzles are discretized, and the Jacobian matrix is ​​solved using the Gauss-Seidel iterative method. This allows for the accurate acquisition of the mass increment, energy increment, and flow increment of each node in the circulating fluid, as well as the flow rate increment of each nozzle. This enables the reliable calculation of the node mass, energy, and flow rate of the next iteration step, providing crucial quantitative computational support for the refined analysis of the transient process on the Brayton cycle side. The calculation of mass increment, energy increment, and flow rate increment is clearly correlated with the time step, the number of nodes, the number of nozzles, and the independent variables at the current moment. The clear definition of these parameters provides a rigorous logical basis and traceability for the calculation process, avoiding deviations in incremental calculations caused by ambiguous parameter definitions or missing correlations. This ensures that the incremental results of each iteration step accurately reflect the transient change trend of supercritical carbon dioxide within the cycle. The application of the Gauss-Seidel iterative method can efficiently handle the convergence problem in the Jacobian matrix solution process. Even when faced with the characteristic of supercritical carbon dioxide's properties being easily distorted near the critical point, it can stably advance iterative calculations, reduce the risk of numerical divergence, and ensure the reliability of incremental results. Furthermore, obtaining the core parameters of the next iteration step indirectly through incremental calculation is more effective than direct calculation in capturing subtle transient changes in the mass, energy, and flow rate of supercritical carbon dioxide. For example, in the calculation of the inlet flow rate, the accuracy of the flow rate increment directly affects the fluid balance of the inflow and outflow control volumes, thereby ensuring the accuracy of subsequent node pressure calculations (S7) and inlet parameter updates (S8). This forms a coherent logical chain of "incremental solution - parameter update - convergence judgment," laying an important foundation for the accuracy and stability of the entire Brayton cycle transient solution, and ultimately contributing to the accurate representation of the transient physical processes of the tower solar supercritical carbon dioxide Brayton cycle integrated system.

[0078] Furthermore, the energy conservation equation and mass conservation equation for carbon dioxide fluid are applied to the control volume to calculate the changes in its mass, internal energy, and pressure. The momentum conservation equation is applied to the nozzle to calculate the coolant flow rate into and out of the control volume. By combining the difference equations for mass conservation and energy conservation of all control volumes with the difference equation for momentum conservation of the nozzle, the following formula is obtained:

[0079] Expanding the first term on the right-hand side using a first-order Taylor series, substituting it into the above equation, and discretizing the time derivative on the left-hand side, yields the node's mass increment, energy increment, and inlet flow rate increment. .

[0080] Specifically, in this embodiment, during the solution of transient parameters for supercritical carbon dioxide on the Brayton cycle side, the energy conservation equation and mass conservation equation of the carbon dioxide fluid are specifically applied to the control volume to accurately calculate the changes in mass, internal energy, and pressure of the control volume. Simultaneously, the momentum conservation equation is focused on the nozzle to solve for the coolant flow rates into and out of the control volume. This scenario-specific equation design perfectly matches the actual physical process of "control volume storage state change - nozzle flow transfer" within the supercritical carbon dioxide cycle, avoiding calculation deviations caused by confusion in equation application scenarios and laying a foundation for subsequent parameter solutions that conforms to physical laws. Furthermore, this embodiment combines the mass and energy conservation difference equations of all control volumes with the momentum conservation difference equation of the nozzle, breaking the limitations of solving each equation in isolation. This creates a tightly integrated calculation logic linking the state changes of the control volume with the flow transfer through the nozzle, ensuring that the mass, energy, and momentum balance relationships of the fluid within the cycle are uniformly satisfied and preventing transient process distortion caused by neglecting the overall coupling relationship in solving local equations. Furthermore, by performing a first-order Taylor series expansion on the first term of the simultaneous equations and discretizing the time derivative on the left side, the complex nonlinear equations are effectively transformed into precisely calculable increments in node mass, energy, and inlet flow rate. This preserves the physical essence of the equations while reducing the complexity of numerical solutions and avoiding computational instability issues that may arise from directly solving complex equations. These resulting increment parameters provide accurate data for updating node mass, energy, and inlet flow rate in subsequent iterations, supporting the Brayton cycle's convergence assessment based on the rate of change of internal energy, and ensuring accurate characterization of the transient response of supercritical carbon dioxide within the cycle.

[0081] Furthermore, the conservation equations for the mass, momentum, and energy of the carbon dioxide fluid are as follows:

[0082]

[0083]

[0084] in, Density; for Fluid flow rate; The fluid velocity; For pressure; Equivalent diameter; The coefficient of frictional resistance; It is the acceleration due to gravity; It is the internal energy of the fluid; This refers to the enthalpy of the fluid. As an internal heat source for the fluid, This represents the number of nodes that have received input to the current node. This represents the node height.

[0085] Specifically, this embodiment provides a complete and rigorous mathematical basis for accurately characterizing the transient flow and energy change process of supercritical carbon dioxide in the Brayton cycle by explicitly giving the mass, momentum, and energy conservation equations of the carbon dioxide fluid. The equations cover core parameters such as density, fluid flow rate, velocity, pressure, equivalent diameter, friction coefficient, gravitational acceleration, fluid internal energy, enthalpy, internal heat source, as well as the number of nodes flowing into the current node and node height. This comprehensively covers the key physical quantities of supercritical carbon dioxide during mass transfer, momentum transfer, and energy conversion within the cycle, ensuring that each physical process can be meticulously reflected through quantitative equations, and avoiding distortion of the description of the transient state of supercritical carbon dioxide due to missing parameters or incomplete equations. Among them, the mass conservation equation focuses on the dynamic relationship between density and fluid flow rate, accurately capturing the increase or decrease in carbon dioxide mass at different nodes within the cycle, providing a foundation for subsequent calculations of node mass increments; the momentum conservation equation, by integrating force parameters such as pressure, frictional resistance, and gravity, clearly characterizes the change in fluid velocity during flow, especially adapting to momentum fluctuations caused by changes in physical properties or pipe structure when supercritical carbon dioxide flows within the inlet, ensuring the accuracy of inlet flow rate calculations; the energy conservation equation, relying on parameters such as internal energy, enthalpy, and internal heat sources, fully presents the heat exchange between carbon dioxide and the molten salt side of the intermediate heat exchanger in the cycle, as well as the energy loss during its own flow, accurately reflecting the energy transfer and conversion paths. Simultaneously, the introduction of parameters such as "number of nodes flowing into the current node" and "node height" in the equations fully considers the influence of spatial differences in the location of different nodes within the cycle on the fluid state, making the solution process more closely resemble the spatial distribution characteristics of supercritical carbon dioxide in actual cycles, further improving the accuracy of calculations. The clarification of these conservation equations not only provides a unified calculation benchmark for the discrete equations of the S6 stage, solving for the mass increment, energy increment, and nozzle flow increment, but also lays a reliable foundation for the subsequent calculation of the instantaneous pressure of the node (S7) and the synchronous update of the key nozzle parameters (S8) by combining the carbon dioxide fluid property package. This effectively avoids calculation deviations caused by the ambiguity of the equation logic and ultimately ensures the accuracy of the transient solution of the entire Brayton cycle side.

[0086] Furthermore, the feature is that in S2, S4, S5, S6 and S11, the pipes on the solar molten salt side and within the Brayton cycle are represented by nodes, and the fluid circulation system is spatially discretized using staggered grids, with momentum grid cells deviating from mass and energy grid cells by half a spatial increment.

[0087] Specifically, in the core calculation steps (S2, S4, S5, S6, S11) of the solar molten salt side and the Brayton cycle side, the pipes on both sides are represented as nodes. This constructs a quantifiable and discretizable foundation for the continuous pipe system, allowing the flow and heat exchange process of molten salt and supercritical carbon dioxide within the pipes to be transformed into solving for specific nodes and the relationships between them. This provides a clear computational basis for the subsequent application of the mass, energy, and momentum conservation equations. Simultaneously, the fluid circulation system is spatially discretized using staggered grids, causing the momentum grid cells to deviate from the mass and energy grid cells by half a spatial increment. This grid design effectively avoids the pressure and velocity coupling calculation errors (such as numerical oscillation problems) that easily occur in traditional co-located grids. It is particularly suitable for the characteristics of supercritical carbon dioxide near the critical point, where its properties are sensitive and its flow velocity and pressure are prone to subtle fluctuations, as well as the requirement for precise matching of temperature and flow velocity distribution when molten salt flows within components such as collectors and intermediate heat exchangers. In the calculations of the S2 cold tank, the S4 collector flow heat transfer, the S5 hot tank storage process, the S6 Brayton cycle side supercritical carbon dioxide parameter solution, and the S11 intermediate heat exchanger coupled heat transfer, this staggered grid discretization method can ensure a more accurate spatial distribution of key parameters such as pressure, velocity, and temperature at each node. For example, when calculating the velocity and pressure of molten salt in the collector, it can avoid local parameter distortion caused by grid overlap. When solving for the carbon dioxide flow rate in the Brayton cycle side pipe, the reasonable grid misalignment can also make the calculation results of the momentum equation and the mass equation more consistent. Ultimately, this scientific discretization method provides reliable spatial discretization support for the efficient solution of the fluid conservation equations on both sides, ensuring that the parameter calculations on both the molten salt side and the Brayton cycle side have high spatial accuracy in each core step, reducing calculation errors caused by improper mesh design, and thus ensuring the accuracy of parameter transmission on both sides (such as the temperature and pressure of molten salt and carbon dioxide at the intermediate heat exchanger). This lays the foundation for the accurate characterization of fluid flow and heat transfer state during the transient process of the entire integrated system, making the basic data on which subsequent convergence judgments (such as the rate of temperature change and the rate of internal energy change) depend more reliable.

[0088] Furthermore, the performance curves of the rotating machinery are used to interpolate and solve for the efficiency and pressure ratio of the rotating machinery. When solving in the transient analysis program, the rotating machinery is a nozzle and a node. The pressure rise or pressure drop calculated from the pressure ratio will act on the momentum equation of the inlet nozzle of the rotating machinery. The work done by the rotating shaft on the fluid inside the rotating machinery is added to the energy conservation equation of the fluid node of the rotating machinery in the form of a source term.

[0089] Specifically, in processing rotating machinery (such as compressors and turbines) in a tower-type supercritical carbon dioxide Brayton cycle solar cell, this embodiment uses performance curve interpolation to solve for efficiency and pressure ratio. This allows for the rapid and accurate acquisition of core operating parameters of the rotating machinery under different transient conditions, avoiding computational redundancy and accuracy loss caused by directly establishing complex dynamic models. This approach meets the dual requirements of efficiency and accuracy for solving transient processes in integrated systems. In the transient analysis program, this embodiment equates the rotating machinery to a nozzle and a node. This simplified design not only maintains consistency with the "node-nozzle" discrete models of other components on the molten salt side and Brayton cycle side, achieving uniformity in the computational logic of the entire integrated system, but also effectively reduces the computational adaptation difficulty between different types of components, ensuring a smooth transient solution process. Meanwhile, the pressure rise or drop calculated from the pressure ratio directly acts on the momentum equation of the inlet nozzle of the rotating machinery, which can accurately reflect the driving or hindering effect of the rotating machinery on the fluid flow (such as the pressurization effect of the compressor and the pressure reduction work process of the gas turbine), avoiding the deviation in the calculation of fluid velocity and pressure inside the nozzle caused by ignoring this effect; and the work done by the rotating shaft on the fluid inside the rotating machinery is added to the energy conservation equation of the fluid node of the rotating machinery in the form of a source term, which can completely describe the energy transfer process between the rotating machinery and the fluid (such as the compressor consuming mechanical energy and converting it into fluid internal energy, and the gas turbine receiving fluid energy and converting it into mechanical energy), ensuring the strict adherence of the law of conservation of energy in transient solutions. This refined approach to processing rotating machinery not only accurately captures its dynamic operating characteristics in the cycle but also improves computational efficiency through reasonable simplification and model unification. It ensures that the transient response of the rotating machinery on the Brayton cycle side is highly matched with the transient process of the entire integrated system. This provides reliable rotating machinery-related data support for subsequent convergence assessment and updating of key cycle parameters through the rate of change of internal energy. Ultimately, it helps to accurately present the transient physical processes of the tower solar supercritical carbon dioxide Brayton cycle integrated system, providing a strong basis for the study of system dynamic characteristics, safety analysis, and control strategy design.

[0090] A computer device includes: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the above-described method for solving the transient process of supercritical carbon dioxide Brayton cycle in a tower solar cell.

[0091] Specifically, the computer device provided in this embodiment stores in its memory the computer program for solving the transient process of supercritical carbon dioxide Brayton cycle in a tower solar cell, as well as various key data required for the calculation process. These data include basic parameters of the integrated system (initial power of the collector, fluid state of the molten salt and working fluid channels, etc.), physical property data of molten salt and supercritical carbon dioxide, performance curves of rotating machinery, and parameters required for calculating the conservation equations of each component (such as friction loss coefficient, specific heat capacity, convective heat transfer coefficient, etc.). This provides stable data storage and retrieval support for the entire transient solution process, avoiding calculation interruptions or parameter deviations due to insufficient data storage or inconvenient retrieval. Meanwhile, the processor can efficiently execute computer programs in memory, accurately running all steps from initializing integrated system parameters, discretely solving the molten salt side cold tank / collector / heat tank / intermediate heat exchanger and judging the convergence of temperature change rate, to discretizing the supercritical carbon dioxide conservation equation on the Brayton cycle side, calculating instantaneous pressure at nodes, updating key parameters of the nozzles and verifying the convergence of internal energy change rate, and then interpolating the efficiency and pressure ratio of rotating machinery. This fully adapts to the complex needs of multi-stage iterative calculations and multi-parameter coupled analysis in transient solutions, avoiding solution delays or accuracy losses due to insufficient computing power. This hardware-software collaborative architecture transforms the aforementioned method for solving the transient process of a tower solar supercritical carbon dioxide Brayton cycle from a theoretical scheme into a practically operable analytical tool. It ensures stable and efficient acquisition of the fluid flow and heat transfer state of the integrated system within each time step, accurately reflecting the transient physical process of the system. This provides reliable equipment support for practical applications such as accident analysis and control strategy research of tower solar supercritical carbon dioxide Brayton cycles, facilitating the implementation of research related to the safe and stable operation of such integrated systems.

[0092] The following is a specific example: This invention provides a method for solving the transient process of a supercritical carbon dioxide Brayton cycle in a tower solar cell, comprising the following steps: S1. Initialize parameters such as collector power, molten salt flow channel on the solar molten salt side and fluid state of the Brayton cycle working fluid channel, and calculation time step; initialize the configuration of the Brayton cycle; S2. Mass and energy conservation equations for molten salt in discrete cold tanks; calculate the temperature distribution of the cold tank control volume within the current system time step. The conservation equations for the mass and energy of the molten salt in the storage tank are as follows:

[0093]

[0094] in, Flow rate, kg / s; Mass, kg; For pressure drop, Pa; This is the friction loss coefficient along the friction path; It is the specific heat capacity of molten salt. ; Temperature, K; The convective heat transfer coefficient is... ; The enthalpy value of the storage tank is expressed in kJ / kg. The pressure distribution in the storage tank is related to the external pump, and its expression is as follows:

[0095] in, This is the friction loss coefficient along the friction path; Density; kg / m³ 3 , The velocity is m / s; The length of the flow channel is in meters (m). The equivalent diameter is in meters (m). This is the local loss coefficient; m is the cross-sectional area. 2 ; Height, in meters (m); The pressure drop provided by the pump, in Pa; In the numerical calculation, the energy equation calculation is consistent with the S3 calculation, and the pressure solution is calculated using the quasi-steady-state Bernoulli equation; Calculate the temperature change rate of the cold tank If the node's If the maximum value is greater than the specified value, the current cold tank iteration step is considered non-convergent, the cold tank temperature is updated, and S2 is recalculated; if the values ​​of each node are not converged... If the maximum value is less than the specified value, the calculation of the current cold tank is considered to have converged, and the process proceeds to the next step. S3. Update the calculation of the solar collector's power; S4. Conservation equations for mass, energy, and momentum of molten salt in discrete collectors; calculate the temperature distribution, velocity distribution, and pressure distribution of the collector control volume within the current system time step; calculate the collector wall temperature distribution using collector power as a condition. The conservation equations for the mass, momentum, and energy of the molten salt in the solar collector are as follows:

[0096]

[0097]

[0098] in, The flow rate of the solar collector is kg / s; Mass of the solar collector, kg; For collector pressure drop, Pa; This is the friction loss coefficient along the friction path; For collector density; kg / m³ 3 , For the collector speed; The length of the flow channel is in meters (m). The equivalent diameter is in meters (m). The energy conservation equation for the metal wall of the solar collector takes into account the received solar irradiance, heat loss between the collector and the external environment, and convective heat transfer from the internal fluid. The change in the average temperature of the solid metal is expressed as: .

[0099] in, T sr The average temperature of the metal wall surface, expressed in K; Q rec,in The solar irradiance received by the collector is expressed in W. Q rec,loss Let W be the heat loss of the solar collector. The heat loss of the solar collector includes three components: reflection loss, radiation loss, and convection loss, expressed as:

[0100] in, ρ panel The reflectivity of the receiver panel; A rec For the receiver panel area, m 2 ; A ape The area of ​​the cavity is m. 2 ; ε w The receiver tube wall radiation coefficient is corrected by the correction factor; T air The ambient temperature is in K.

[0101] In numerical calculations, the pipes of the solar collector are represented by nodes. Spatially, the fluid circulation system is discretized using staggered grids, with momentum grid cells offset from mass and energy grid cells by half a spatial increment. Figure 6 The cross-mesh partitioning between two adjacent nodes K and L is given. A nozzle j connects nodes K and L. Energy and mass conservation equations are applied to the nodes to calculate changes in mass, internal energy, and pressure. Momentum conservation equation is applied to the nozzle to calculate the coolant flow rates into and out of the control volume, as shown in the figure (W). j-1 W j and W j+1 .

[0102] The momentum conservation equation and the mass conservation equation are solved using the SIMPLE algorithm; Calculate the temperature change rate of the solar collector If the node's If the maximum value is greater than the specified value, the current collector iteration step is considered non-convergent, the collector temperature is updated, and S4 is recalculated; if the values ​​of each node are not converged... If the maximum value is less than the specified value, the calculation of the current solar collector is considered to have converged, and the process proceeds to the next step. S5. Calculate the mass and energy conservation equations for the molten salt inside the heat sink; calculate the temperature distribution of the heat sink control volume within the current system time step; calculate the pressure distribution using the quasi-steady-state method; calculate the rate of change of the heat sink temperature. If the node's If the maximum value is greater than the specified value, the current hot tank iteration step is considered non-convergent, the hot tank temperature is updated, and S5 is recalculated; if the values ​​of each node are not converged... If the maximum value is less than the specified value, the calculation of the current hot tank is considered to have converged, and the process proceeds to the next step. The numerical calculation is consistent with S2; S6. The mass and energy conservation equations for supercritical carbon dioxide in the discrete Brayton cycle and the momentum conservation equation for the nozzle; the mass, internal energy and flow rate of the control volume in the current Brayton iteration step are calculated using the intermediate heat exchanger parameters of the previous time step as boundary conditions. The mass, momentum, and energy conservation equations for carbon dioxide fluid are as follows: (1) (2) (3) in: Density, kg / m³ 3 ; For area, m 2 ; The fluid flow rate is expressed in kg / s. The fluid velocity is expressed in m / s. Pressure, MPa; The equivalent diameter is in meters (m). The coefficient of frictional resistance; The acceleration due to gravity is m / s². 2 ; The fluid's internal energy is expressed in kJ / kg. The enthalpy of the fluid is expressed in kJ / kg. Internal heat source for the fluid, kW / kg; This represents the number of nodes that have received input to the current node. The node height; In numerical calculations, the pipes within a Brayton cycle are represented by nodes. Spatially, the fluid circulation system is discretized using staggered grids, with momentum grid cells offset from mass and energy grid cells by half a spatial increment. Figure 6 The cross-mesh partitioning between two adjacent nodes K and L is given. The connection between nodes K and L is pipe j. Energy and mass conservation equations are applied to the nodes to calculate changes in mass, internal energy, and pressure. Momentum conservation equations are applied to the pipes to calculate coolant flow rates into and out of the control volume, as shown in the figure as Wj-1, Wj, and Wj+1.

[0103] By combining the difference equations for the conservation of mass and energy at all nodes, and the difference equation for the conservation of momentum at the nozzle, we obtain the following form: (4) Expanding the first term on the right-hand side of equation (4) using a first-order Taylor series, we get: (5) Substituting formula (5) into formula (4), we get: (6) Discretizing the time derivative on the left side of equation (6), we get: (7) Substituting formula (7) into formula (6), we finally obtain: (8) in,

[0104]

[0105]

[0106] in, For time step, For the number of nodes, For the number of units taken over, The value of the independent variable at the current moment. Indicates the current moment.

[0107] The Gauss-Seidel iteration can be used to solve formula (8) to obtain the mass increment, energy increment and flow increment of each node of the circulating fluid, and thus calculate the mass, energy and flow of each node in the next iteration step.

[0108] S7. Calculate the instantaneous pressure within each node based on the enthalpy and specific volume of the carbon dioxide fluid properties package. S8. Update the pressure, flow rate, enthalpy, and other parameters of the connected pipe; S9. Calculate the rate of change of internal energy ΔU / U for each fluid node. If the maximum value of the rate of change of internal energy for each node is greater than the specified value, the current iteration step is considered to be non-convergent, the time step is halved, and the calculation is returned to step S6. If the maximum value of the rate of change of internal energy for each fluid node is less than the specified value, the current iteration step is considered to be convergent, and the calculation proceeds to the next step. S10. Determine whether the calculation time on the Brayton side has reached a system time step. If it has, terminate the calculation; if not, jump to step S6 to calculate the next time step.

[0109] S11. Discretize the mass, energy, and momentum conservation equations of the molten salt in the intermediate heat exchanger; calculate the temperature distribution, velocity distribution, and pressure distribution of the intermediate heat exchanger control volume within the current system time step; The conservation equations for the mass, energy, and momentum of the molten salt in the intermediate heat exchanger are as follows:

[0110]

[0111]

[0112]

[0113] in, Flow rate, kg / s; Mass, kg; For pressure drop, Pa; This is the friction loss coefficient along the friction path; Density, kg / m³ 3 , The velocity is m / s; The length of the flow channel is in meters (m). The equivalent diameter is in meters (m). is the local loss coefficient; is the cross-sectional area, m 2 ; Height, in meters (m); The pressure drop provided by the pump, in Pa; It is the specific heat capacity of molten salt. ; Temperature, K; The enthalpy of the solar collector is expressed in kJ / kg. In the intermediate heat exchanger, the energy transfer from the hot-side molten salt fluid to the cold-side CO2 fluid occurs sequentially through convective heat transfer between the molten salt fluid and the metal wall, heat conduction through the metal wall, and convective heat transfer between the CO2 fluid and the metal wall. The heat conduction process through the metal wall can be represented by a one-dimensional heat conduction equation without an internal heat source:

[0114] in, The density of the material is expressed in kg·m. -3 ; The specific heat capacity of the material is expressed in J·(kg·K). -1 ; Let K be the material temperature. Let the time to solve the problem be in seconds (s). Let W be the thermal conductivity of the material, expressed in W·(m·K). -1 .

[0115] The convective heat transfer process of a metal wall is represented as follows:

[0116]

[0117] in, The convective heat transfer coefficient is... ; Thermal power, W; T f,hot The temperature of the molten salt fluid; T w,hot This refers to the surface temperature of the molten salt side metal wall. T f,cold The temperature of the CO2 fluid; T w,cold This refers to the surface temperature of the metal wall on the CO2 side.

[0118] Numerical calculations are consistent with S3, and the mass and momentum conservation equations are solved using the SIMPLE algorithm. Calculate the temperature change rate of the intermediate heat exchanger If the node's If the maximum value is greater than the specified value, the current intermediate heat exchanger iteration step is considered non-convergent, the intermediate heat exchanger temperature is updated, and S11 is recalculated; if the values ​​of each node are not converged... If the maximum value is less than the specified value, the calculation of the current intermediate heat exchanger is considered to have converged, and the process proceeds to the next step. S12. Determine whether the final calculation time has been reached. If it has, terminate the calculation. If it has not, jump to step S2 to calculate the next time step.

[0119] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0120] The numerical solution methods for the momentum and mass conservation equations of the solar energy side components, such as the collector and intermediate heat exchanger, are all solved using the publicly available SIMPLE algorithm.

[0121] The supercritical carbon dioxide heat transfer calculations used the publicly available Gnielinski relation, and the friction relation used the publicly available Zigrang-Sylvester relation.

[0122] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for solving the transient process of a supercritical carbon dioxide Brayton cycle in a tower solar cell, characterized in that, Includes the following steps: S1. Complete the initialization of the basic parameters of the integrated system, including the initial power of the solar collector, the fluid state and calculation time step of the molten salt channel on the solar molten salt side and the Brayton cycle working fluid channel; at the same time, complete the configuration initialization of the Brayton cycle according to the requirements. S2. First, discretize the mass and energy conservation equations of the molten salt inside the cold tank. Based on these discretized equations, calculate the temperature distribution of the cold tank control volume within the current system time step. Then, use a quasi-steady-state method to calculate the pressure distribution inside the cold tank. Finally, calculate the temperature change rate of the cold tank. If each node If the maximum value is greater than the specified value, the current cold tank iteration step is determined to be non-convergent, the cold tank temperature is updated, and S2 is re-executed; if the maximum value is less than the specified value, the cold tank calculation is determined to be convergent, and S3 is executed. S3. Based on the state of the cold tank after convergence and the boundary conditions such as solar irradiance and ambient temperature, update and calculate the instantaneous power of the collector. S4. First, discretize the mass, energy, and momentum conservation equations for the molten salt inside the collector. Based on these equations, calculate the temperature, velocity, and pressure distributions of the collector control volume within the current system time step. Simultaneously, using the updated collector power from S3 as a constraint, calculate the collector wall temperature distribution. Then, calculate the collector temperature change rate. If each node If the maximum value is greater than the specified value, the current collector iteration step calculation is determined to be non-convergent, the collector temperature is updated, and S4 is re-executed; if the maximum value is less than the specified value, the collector calculation is determined to be convergent, and S5 is executed. S5. First, determine the mass and energy conservation equation of the molten salt in the heat sink, and calculate the temperature distribution of the heat sink control volume within the current system time step based on this equation; then, use the quasi-steady-state method to calculate the pressure distribution inside the heat sink; finally, calculate the temperature change rate of the heat sink. If each node If the maximum value is greater than the specified value, the current hot tank iteration step is determined to be non-convergent, the hot tank temperature is updated, and S5 is re-executed; if each node If the maximum value is less than the specified value, the hot tank calculation is considered to have converged, and S6 is executed; S6. First, discretize the mass and energy conservation equations of supercritical carbon dioxide in the cycle and the momentum conservation equation of the nozzle. Then, use the high-pressure side outlet parameters of the intermediate heat exchanger in the previous system time step as boundary conditions, and calculate the mass, internal energy and flow rate of the control volume in the current Brayton side iteration step based on the discrete equations in S2. S7. Based on the enthalpy and specific volume of each node on the Brayton cycle side obtained in S6, and combined with the carbon dioxide fluid property package, calculate the instantaneous pressure within each node. S8. Based on the instantaneous pressure of the node obtained in S7, synchronously update the key circulation parameters of the Brayton cycle side pipe, including pressure, flow rate and enthalpy, to ensure that the pipe state matches the node state. S9. Calculate the rate of change of internal energy ΔU / U at each fluid node on the Brayton cycle side. If the maximum value of ΔU / U at each node is greater than the specified value, it is determined that the current iteration step on the Brayton side is not converged. The time step is halved and the calculation is returned to S6 for recalculation. If the maximum value of ΔU / U at each node is less than the specified value, then the current Brayton iteration step is determined to be converged, and S10 is executed; S10. Check if the current cumulative calculation time on the Brayton side has reached a system time step. If it has, terminate the Brayton side calculation for the current round. If it has not, jump to S6 to continue the calculation for the next small time step. S11. First, discretize the mass, energy, and momentum conservation equations for the molten salt in the intermediate heat exchanger. Based on these equations, calculate the temperature, velocity, and pressure distributions of the intermediate heat exchanger control volume within the current system time step. Then, calculate the temperature change rate of the intermediate heat exchanger. If each node If the maximum value is greater than the specified value, it is determined that the current intermediate heat exchanger iteration step calculation has not converged. After updating the intermediate heat exchanger temperature, S11 is re-executed; if each node If the maximum value is less than the specified value, the intermediate heat exchanger calculation is considered to have converged, and S12 is executed; S12. Check whether the cumulative calculation time of the integrated system has reached the preset final calculation time. If it has, terminate the transient process calculation of the entire tower solar supercritical carbon dioxide Brayton cycle integrated system. If it has not, return to S2 to start the full process calculation of the next system time step.

2. The method for solving the transient process of a tower solar supercritical carbon dioxide Brayton cycle according to claim 1, characterized in that, In S2, S4, S5, and S11, the energy conservation equations for the discrete solar collectors, hot and cold storage tanks, and intermediate heat exchangers use a first-order upwind difference scheme.

3. The method for solving the transient process of a tower solar supercritical carbon dioxide Brayton cycle according to claim 1, characterized in that, In S4 and S11, the flow rates and pressures of the discrete heat collector and intermediate heat exchanger are solved using the SIMPLE algorithm to obtain the flow rate and pressure distributions for the next iteration step. The pressure distribution of the cold and hot storage tanks is calculated using the quasi-steady-state form of the Bernoulli equation.

4. A method for solving the transient process of a tower solar supercritical carbon dioxide Brayton cycle according to any one of claims 2 or 3, characterized in that, The conservation equations for the mass, energy, and momentum of the molten salt in the solar collector are as follows: in, The flow rate of the solar collector is kg / s; Mass of the solar collector, kg; For collector pressure drop, Pa; This is the friction loss coefficient along the friction path; Density, kg / m3; The velocity is m / s; The length of the flow channel is in meters (m). The equivalent diameter is in meters (m). This is the local loss coefficient; m is the cross-sectional area. 2 ; Height, in meters (m); The pressure drop provided by the pump, in Pa; The specific heat capacity of molten salt, ; Temperature, K; The convective heat transfer coefficient is... ; Let be the enthalpy of the solar collector, kJ / kg; the energy conservation equation for the metal wall of the solar collector considers the received solar irradiance, heat loss between the collector and the external environment, and convective heat transfer from the internal fluid. The change in the average temperature of the solid metal is expressed as: in, T sr The average temperature of the metal wall surface, expressed in K; Q rec,in The solar irradiance received by the collector is expressed in W. Q rec,loss The heat loss of the solar collector, W, includes three components: reflection loss, radiation loss, and convection loss, and is expressed as: in, ρ panel The reflectivity of the receiver panel; A rec For the receiver panel area, m 2 ; A ape The area of ​​the cavity is m. 2 ; ε w The receiver tube wall radiation coefficient is corrected by the correction factor; T air For ambient temperature, K, The conservation equations for the mass and energy of molten salt in hot and cold storage tanks are as follows: in, Flow rate, kg / s; Mass, kg; This is the friction loss coefficient along the friction path; It is the specific heat capacity of molten salt. ; Temperature, K; The convective heat transfer coefficient is... ; The enthalpy value of the storage tank is expressed in kJ / kg. The pressure distribution in the storage tank is related to the external pump, and its expression is as follows: in, This is the friction loss coefficient along the friction path; Density; kg / m³ 3 , The velocity is m / s; The length of the flow channel is in meters (m). The equivalent diameter is in meters (m). This is the local loss coefficient; m is the cross-sectional area. 2 ; Height, in meters (m); The pressure drop provided by the pump, in Pa; The conservation equations for the mass, energy, and momentum of the molten salt in the intermediate heat exchanger are as follows: in, Flow rate, kg / s; Mass, kg; For pressure drop, Pa; This is the friction loss coefficient along the friction path; Density, kg / m³ 3 , The velocity is m / s; The length of the flow channel is in meters (m). The equivalent diameter is in meters (m). This is the local loss coefficient; m is the cross-sectional area. 2 ; Height, in meters (m); It is the specific heat capacity of molten salt. ; Temperature, K; The enthalpy of the solar collector is expressed in kJ / kg. The energy transfer from the hot-side molten salt fluid to the cold-side CO2 fluid in the intermediate heat exchanger occurs sequentially through convective heat transfer between the molten salt fluid and the metal wall, heat conduction through the metal wall, and convective heat transfer between the CO2 fluid and the metal wall. The heat conduction process through the metal wall can be represented by a one-dimensional heat conduction equation without an internal heat source. in, For material density, kg‧m -3 ; The specific heat capacity of the material is expressed in J (kg·K). -1 ; Let K be the material temperature. Let the time to solve the problem be in seconds (s). Let W be the thermal conductivity of the material, expressed in W·(m·K). -1 , The convective heat transfer process of a metal wall is represented as follows: in, The convective heat transfer coefficient is... ; Thermal power, W; T f,hot The temperature of the molten salt fluid; T w,hot This refers to the surface temperature of the metal wall on the molten salt side. T f,cold The temperature of the CO2 fluid; T w,cold This refers to the surface temperature of the metal wall on the CO2 side.

5. The method for solving the transient process of a tower solar supercritical carbon dioxide Brayton cycle according to claim 1, characterized in that, In S6, the mass and energy conservation equations for the discrete Brayton cycle-side supercritical carbon dioxide, as well as the momentum conservation equation for the nozzle, are solved using Gauss-Seidel iteration with respect to the Jacobian matrix. The solution yields the mass increment, energy increment, and flow rate increment at each node of the circulating fluid. This allows us to calculate the node's mass, energy, and the flow rate of the node in the next iteration step, as well as the mass increment, energy increment, and flow rate increment. The calculation is as follows: in, For time step, For the number of nodes, For the number of units taken over, Let be the independent variable at the current moment. Indicates the current moment.

6. The method for solving the transient process of a tower solar supercritical carbon dioxide Brayton cycle according to claim 5, characterized in that, The energy and mass conservation equations for carbon dioxide fluid are applied to the control volume to calculate changes in its mass, internal energy, and pressure. The momentum conservation equation is applied to the nozzle to calculate the coolant flow rates into and out of the control volume. The difference equations for mass and energy conservation of all control volumes, along with the difference equation for momentum conservation of the nozzle, are combined to obtain the following formula: Expanding the first term on the right-hand side using a first-order Taylor series, substituting it into the above equation, and discretizing the time derivative on the left-hand side, yields the node's mass increment, energy increment, and inlet flow rate increment. .

7. The method for solving the transient process of a tower solar supercritical carbon dioxide Brayton cycle according to claim 6, characterized in that, The mass, momentum, and energy conservation equations for carbon dioxide fluid are as follows: in, Density; for Fluid flow rate; The fluid velocity; For pressure; Equivalent diameter; The coefficient of frictional resistance; It is the acceleration due to gravity; It is the internal energy of the fluid; This refers to the enthalpy of the fluid. As an internal heat source for the fluid, This represents the number of nodes that have received input to the current node. This represents the node height.

8. The method for solving the transient process of a tower solar supercritical carbon dioxide Brayton cycle according to any one of claims 7, characterized in that, In S2, S4, S5, S6 and S11, the pipes on the solar molten salt side and within the Brayton cycle are represented by nodes. The fluid circulation system is spatially discretized using staggered grids, with momentum grid cells offset from mass and energy grid cells by half a spatial increment.

9. The method for solving the transient process of a tower solar supercritical carbon dioxide Brayton cycle according to claim 1, characterized in that, The efficiency and pressure ratio of the rotating machinery are solved by interpolation using the performance curve of the rotating machinery. When solving in the transient analysis program, the rotating machinery is a nozzle and a node. The pressure rise or pressure drop calculated from the pressure ratio will act on the momentum equation of the inlet nozzle of the rotating machinery. The work done by the rotating shaft on the fluid inside the rotating machinery is added to the energy conservation equation of the fluid node of the rotating machinery in the form of a source term.

10. A computer device, characterized in that, include: The method for solving the transient process of supercritical carbon dioxide Brayton cycle in a tower solar cell, as described in any one of claims 1-9, includes a memory, a processor, and a computer program stored in the memory and executable on the processor.

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