Method and system for improving transient heat exchange calculation performance of spiral tube direct-current evaporator

Abstract

The invention discloses a method and system for improving transient heat exchange calculation performance of a spiral tube direct-current evaporator, and relates to the field of program design of pebble-bed high-temperature gas cooled reactor steam generators, and the method comprises the following steps: determining grid division and related constitutive equations of a heat component of a spiral tube steam generator; different grid heat exchange and pressure drop calculation modes are determined according to different working conditions; adopting a convection-diffusion term full implicit difference algorithm and a flow heat full coupling algorithm to optimize the transient heat exchange calculation performance of the spiral tube steam generator; on the basis of a fixed grid, a gas content movable boundary model is used for carrying out grid division on the control bodies under the three conditions again, and the heat exchange coefficient and the pressure drop parameter of each thermal component control body are calculated; setting boundary conditions, calculating the heat exchange coefficient of the next time step, and solving the heat exchange amount and the pressure drop parameter of the steam generator. The critical positions of the gas containing rates x = 0 and x = 1 serve as moving boundaries, heat exchange is recalculated for the transition grids from the single phase to the two phases, and the problem that a single moving boundary method is difficult to program in a system program is solved.

Description

Technical Field

[0001] The invention relates to the technical field of pebble bed type high temperature gas-cooled reactor steam generator program design, in particular to a method and a system for improving the transient heat exchange calculation performance of a spiral tube direct current evaporator. Background Art

[0002] As one of the indispensable components in a nuclear reactor, the safety of the steam generator is of great significance to the safe operation of a nuclear power plant. In a high-temperature gas-cooled reactor, the working fluid of the primary circuit is helium, and the working fluid of the secondary circuit is water. The steam generator adopts a spiral tube direct-flow steam generator, which has a higher thermal efficiency than the traditional nuclear reactor steam generator. By conducting transient analysis on the steam generator, the thermal-hydraulic characteristics of the steam generator under accident conditions can be obtained, providing safety assurance for the design and operation of the steam generator.

[0003] At present, many studies on the thermal-hydraulic characteristics of steam generators have been carried out at home and abroad. These include using the TRACE program to analyze the temperature field of the spiral tube steam generator in the high-temperature gas-cooled reactor and evaluate the influence of the number of nodes on the calculation; the ONCES program for the thermal-hydraulic design and performance analysis of the spiral tube steam generator developed using the homogeneous flow model and the movable boundary method; the system program TASS / SMR developed for the safety analysis of advanced integrated reactors; the two-dimensional program based on the secondary development of the CFD software Fluent uses an axisymmetric two-dimensional model to numerically simulate the spiral tube steam generator; the four-equation drift flow model is used as the calculation model of the two-phase flow, and the fixed boundary modeling method is adopted; the dynamic simulation program TH-OTSG is developed by discretizing the basic equation group with staggered grids, full implicit, and second-order upwind schemes; the transient response characteristics under different disturbances and the thermal-hydraulic analysis program STAGS for steam generator systems with a wide range of applications are carried out to study the response characteristics of the key thermal parameters of the steam generator when the shell and tube side inlet parameters are disturbed.

[0004] However, the above studies all focus more on the computational accuracy of the thermal-hydraulic analysis program, without considering the problems of short computational time step and low computational efficiency caused by the different thermodynamic response rates on the helium side and the water side. For example, the thermal safety program developed using the traditional semi-implicit numerical solution method often reduces the time step due to the Courant criterion, thereby reducing the computational efficiency of the steam generator thermal-hydraulic program.

[0005] In addition, in the spiral tube steam generator, after being heated by the secondary helium loop, the heat exchange modes with the wall include subcooled water convection, saturated boiling and superheated steam convection. The heat transfer coefficients of each mode are very different, and two different heat transfer modes may appear in the fixed grid. If only one of the modes is selected for heat transfer calculation, it will cause calculation errors in the heat transfer amount. At the same time, if the heat transfer mode of the grid changes, the change of the differential equation will artificially cause the discontinuity of the solution. The drastic change of heat caused by the change of the heat transfer mode in this fixed grid will lead to the oscillation problem of the direct current steam generator simulation. At present, there are two methods for heat transfer calculation of direct current steam generators, one is the fixed grid method and the other is the moving boundary method. The fixed grid method refers to dividing the system into multiple grids before calculation, and the grid remains unchanged during the transient calculation process, and the conservation equation is used to calculate the thermodynamic state of the fluid. The fixed grid method is suitable for system analysis programs, but it will cause discontinuity of the solution. The discontinuity can be reduced by increasing the number of grids and reducing the time, but it will reduce the calculation efficiency. In the moving boundary method, the grid boundary changes with the heat transfer mode, so the grid interface is a continuous function of time, avoiding sudden jumps in the calculation results. At the same time, the moving boundary method can reduce the number of grids and improve calculation efficiency, but the moving boundary method is not suitable for system analysis programs.

[0006] Therefore, the patent of this invention will be based on the homogeneous flow hydraulic model, use the convection-diffusion term implicit difference format algorithm to solve the basic conservation equations, use the flow-heat full coupling algorithm to solve the heat conduction process of the heat transfer tube, and use the moving boundary method based on the fixed grid improvement to develop a method to improve the transient heat exchange calculation performance of the spiral tube steam generator in the thermal-hydraulic program of the pebble bed high-temperature gas-cooled reactor. Summary of the invention

[0007] In view of the above-mentioned problems, the present invention is proposed.

[0008] Therefore, the technical problem solved by the present invention is: how to effectively improve the transient heat exchange calculation performance of the spiral tube direct current evaporator, especially the calculation accuracy and efficiency under different working conditions.

[0009] In order to solve the above technical problems, the present invention provides the following technical solution: a method for improving the transient heat exchange calculation performance of a spiral tube direct current evaporator, which comprises the following steps:

[0010] According to the control volume division method of the steam generator hydraulic components, the fixed grid method is used to determine the grid division and related constitutive equations of the thermal components of the spiral tube steam generator.

[0011] Determine the heat transfer and pressure drop calculation modes of different grids for cold water convection, saturated boiling and superheated steam conditions;

[0012] The transient heat transfer calculation performance of the spiral tube steam generator in the thermal hydraulic program of the pebble bed high temperature gas-cooled reactor is optimized by using the full implicit difference algorithm of convection-diffusion terms and the full fluid-heat coupling algorithm.

[0013] Based on the fixed grid, the control volume of the three cases of cold water convection, saturated boiling and superheated steam is meshed again using the gas content movable boundary model, and the heat transfer coefficient and pressure drop parameters of each thermal component control volume are recalculated;

[0014] Set boundary conditions, calculate the heat transfer coefficient of each grid in the next time step, and finally obtain the heat transfer and pressure drop parameters of the steam generator at each moment.

[0015] As a preferred solution of the method for improving the transient heat exchange calculation performance of the spiral tube direct current evaporator described in the present invention, wherein: the control body division method according to the steam generator hydraulic component includes that under the normal operation and safety accident conditions of the high-temperature gas-cooled reactor, the helium maintains a single-phase state without phase change, and the working medium water commonly used in the secondary circuit of the high-temperature gas-cooled reactor, in the spiral tube steam generator, changes from subcooling to two-phase and then to superheated steam, and is modeled based on the homogeneous flow model;

[0016] The homogeneous flow model regards the fluid as a uniform mixed flow of gas phase and liquid phase. The two phases are in a state of thermodynamic equilibrium and have the same velocity and temperature. The basic equation constructed is consistent with the conservation equation of single-phase fluid. The homogeneous flow model is used to simulate the primary and secondary sides of the high-temperature gas-cooled reactor steam generator.

[0017] Based on the one-dimensional flow of the coolant in the channel and combined with the three conservation equations of the single-phase flow model, the basic conservation equation of the hydraulic model is established. The mass conservation equation is expressed as:

[0018]

[0019] ρ=αρ g +(1-α)ρ f

[0020] Where A is the flow area, ρ is the density, t is the time, V is the flow velocity, z is the control volume length, α is the cavitation fraction, ρ g is the saturated gas density, ρ f is the saturated liquid density;

[0021] The energy conservation equation is expressed as:

[0022]

[0023] Where h is the specific enthalpy, g is the acceleration due to gravity, Q w is the thermal power, θ is the inclination angle, and P is the pressure;

[0024] The momentum conservation equation is expressed as:

[0025]

[0026] Where P is pressure, F w is the resistance along the way, F local is the local resistance;

[0027] The simulation of heat transfer from the steam generator heat transfer tube to the coolant uses the heat conduction model of the heat component to calculate the internal temperature distribution of the heat component and the convection heat transfer with the fluid on the boundary. The heat conduction model of the heat component is established using the one-dimensional unsteady-state heat conduction equation. The expression is:

[0028]

[0029] Where c is the specific heat capacity, T is the temperature, x is the distance, S is the heat source in the volume, A(x) is the area factor, and λ is the thermal conductivity;

[0030] The internal node method is used to perform radial meshing of the thermal component, the temperature node to be solved is located at the center of the grid, and the grid area is the control volume of the current point.

[0031] As a preferred scheme of the method for improving the transient heat exchange calculation performance of the spiral tube direct current evaporator described in the present invention, wherein: the determination of different grid heat exchange and pressure drop calculation modes is for cold water convection, saturated boiling and superheated steam conditions, and different grid heat exchange and pressure drop calculation modes are determined according to the gas content x, including the empirical relationship for the pressure drop inside and outside the spiral tube, the empirical relationship for the heat exchange inside the spiral tube, and the empirical relationship for the heat exchange outside the spiral tube.

[0032] As a preferred solution of the method for improving the transient heat transfer calculation performance of the spiral tube direct current evaporator described in the present invention, wherein: the use of the convection-diffusion term full implicit difference algorithm and the flow-heat full coupling algorithm to optimize the transient heat transfer calculation performance of the spiral tube steam generator in the thermal hydraulic program of the pebble bed high temperature gas-cooled reactor is to perform full implicit difference processing on the basic conservation equation of the single-phase flow model, and convert the differential equation into a difference equation;

[0033] The first-order upwind difference is used for the convection term of the basic conservation equation, and the first-order backward difference is used for the transient term. The expression is:

[0034]

[0035] Where H is the specific enthalpy of the control volume, the subscript o represents the control volume parameter, and the subscript x represents the takeover parameter.

[0036] As a preferred solution of the method for improving the transient heat transfer calculation performance of the spiral tube direct current evaporator described in the present invention, wherein: the use of the convection-diffusion term full implicit difference algorithm and the fluid-heat full coupling algorithm to optimize the transient heat transfer calculation performance of the spiral tube steam generator in the thermal hydraulic program of the pebble bed high temperature gas-cooled reactor also includes defining the mass conservation equation and the energy conservation equation in the control body, and the momentum conservation equation in the take-over pipe. For a reactor system containing N control bodies and J take-over pipes, the order of the formed differential equation group is N+2J, and the Newton iteration method is used to solve it, and the partial derivatives of each conservation equation with respect to the solution variable are derived, and the values ​​of each element in the Jacobian matrix are obtained. The full-pivot Gaussian elimination method is used to solve the linear equation group with the Jacobian matrix as the coefficient matrix;

[0037] The three major solution variables, namely, control volume pressure, takeover speed, and control volume specific enthalpy, are updated, and the inner iteration cycle is repeated until the Newton iteration method converges. The current variable value obtained is the thermal hydraulic calculation result at a new moment in the transient process, and the calculation of one time step is completed.

[0038] As a preferred solution of the method for improving the transient heat transfer calculation performance of the spiral tube direct current evaporator described in the present invention, wherein: the optimization of the transient heat transfer calculation performance of the spiral tube steam generator in the thermal hydraulic program of the pebble bed high temperature gas-cooled reactor by using the full implicit difference algorithm of the convection-diffusion term and the full coupling algorithm of the flow and heat also includes placing the one-dimensional non-steady-state heat conduction equation and the basic conservation equation of the hydraulic model of the fluids on both sides in the heat exchanger in the same set of equations for solving to form a high-order matrix;

[0039] The heat exchanger's hot component part is divided into only one grid in the radial direction, and the temperature is defined at the center of the grid. The convection boundary conditions on both sides are processed using the additional source term method, and the transient change term of the center temperature of the heat exchanger is backward differentiated. The expression is:

[0040]

[0041] Where V is the volume of the thermal component mesh control volume, is the primary side fluid temperature, is the secondary side fluid temperature, R1 is the total thermal resistance from the center of the thermal component to the primary side, and R2 is the total thermal resistance from the center of the thermal component to the primary side.

[0042] As a preferred solution of the method for improving the transient heat transfer calculation performance of the spiral tube direct current evaporator described in the present invention, wherein: the heat transfer coefficient and pressure drop parameter of each heat component control body are recalculated by using the fixed grid method after completing the calculation of one time step, and then using the gas content as the judgment basis, using the movable boundary model, re-gridding the control bodies of the three cases of cold water convection, saturated boiling and superheated steam to correct the heat transfer coefficient and pressure drop parameter of each heat component control body;

[0043] The judgment basis is that if the outlet is still supercooled water, the supercooled water heat exchange pressure drop calculation is performed; if the outlet is a two-phase mixture, it is necessary to calculate the boundary positions of the supercooled water and the two phases, and then calculate the heat exchange and pressure drop of the supercooled section and the two-phase section respectively; if the outlet is superheated steam, it is necessary to calculate the two boundary positions of the supercooled water, the two-phase section, and the superheated steam section, and then calculate the heat exchange and pressure drop of the supercooled section, the two-phase section, and the superheated steam section respectively; after one calculation is completed, the grid division is corrected and recalculated until the error is within an acceptable range and the calculation is completed.

[0044] Another object of the present invention is to provide a system for improving the transient heat transfer calculation performance of a spiral tube direct current evaporator, which can finely divide the grid of the steam generator thermal component by combining a fixed grid method and a movable boundary model of the gas content, and use a convection-diffusion term full implicit difference algorithm and a fluid-heat full coupling algorithm to optimize the thermal hydraulic parameters in the calculation process, thereby solving the problems in the existing methods of failing to accurately reflect the transient thermal changes under different working conditions when calculating the heat transfer coefficient and the pressure drop parameters, and the large errors in the calculation results, thereby achieving high-precision and high-efficiency transient heat exchange calculation problems.

[0045] In order to solve the above technical problems, the present invention provides the following technical solutions: a system for improving the transient heat transfer calculation performance of a spiral tube direct current evaporator, comprising: a fixed grid method module, a convection-diffusion term implicit difference algorithm module, a fluid-heat full coupling algorithm module, a gas content movable boundary model module, and a high-order matrix solution module;

[0046] The fixed grid method module uses the fixed grid method to accurately divide the control volume of the steam generator, generate grid calculation modes under different working conditions, and make corresponding adjustments according to the state of the steam;

[0047] The convection-diffusion term implicit difference algorithm module calculates the thermodynamic parameters of the control body by using the first-order upwind difference for the convection term and the first-order backward difference for the transient term;

[0048] The fluid-heat full coupling algorithm module defines the mass conservation equation and the energy conservation equation in the control body, and uses the full coupling algorithm to correlate the pressure, takeover speed, and specific enthalpy of the control body to form a differential equation group, which is solved by the Newton iteration method;

[0049] The gas content movable boundary model module is based on the fixed grid method, refines the grid division under three working conditions: cold water convection, saturated boiling and superheated steam, dynamically adjusts the grid division, and recalculates the heat transfer coefficient and pressure drop parameters of each thermal component control body;

[0050] The high-order matrix solution module solves the one-dimensional non-steady-state heat conduction equation and the basic conservation equations of the hydraulic model of the fluids on both sides in the same set of equations when processing the thermal hydraulic calculations of the heat exchanger. The convection boundary conditions are processed by solving the high-order matrix and the additional source term method to calculate the transient changes of the center temperature of the heat exchanger.

[0051] A computer device comprises a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the steps of the method for improving the transient heat exchange calculation performance of a spiral tube direct current evaporator are implemented as described above.

[0052] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the method for improving the transient heat exchange calculation performance of a spiral tube direct current evaporator as described above.

[0053] Beneficial effects of the present invention: The present invention uses the critical positions of gas content x=0 and x=1 as moving boundaries, and recalculates the heat exchange for the transition grid from single phase to two phases, which greatly simplifies the programming difficulty of the single moving boundary method in the system program, and effectively reduces the instability of the calculation results caused by the traditional fixed grid method, recalculates the heat exchange for the upper and lower areas of the moving boundary, improves the calculation accuracy of the coarse grid, and improves the calculation efficiency.

[0054] The water-side heat exchange logic determines the steam content x position based on the heat exchange amount, which simplifies the fixed grid water-side heat exchange mode determination process.

[0055] Re-dividing the moving boundary under the fixed grid can increase the continuity of the grid. The boundary position is corrected by calculating the steam content and heat transfer of the newly divided grid again, and the convergence standard is reached through repeated operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. Among them:

[0057] Figure 1An overall flow chart of a method for improving the transient heat transfer calculation performance of a spiral tube direct current evaporator provided in the first embodiment of the present invention;

[0058] Figure 2 A grid node division diagram of a heat component in a method for improving transient heat transfer calculation performance of a spiral tube direct current evaporator provided in a first embodiment of the present invention;

[0059] Figure 3 A differential grid schematic diagram of a method for improving the transient heat transfer calculation performance of a spiral tube direct current evaporator provided in the first embodiment of the present invention;

[0060] Figure 4 A flow chart of the moving boundary method in the method for improving the transient heat transfer calculation performance of a spiral tube direct current evaporator provided in the first embodiment of the present invention. DETAILED DESCRIPTION

[0061] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0062] Example 1, reference Figure 1 to Figure 3 According to one embodiment of the present invention, a method for improving the transient heat transfer calculation performance of a spiral tube direct current evaporator is provided, comprising:

[0063] S1. According to the control volume division method of the steam generator hydraulic components, the fixed grid method is used to determine the grid division and related constitutive equations of the thermal components of the spiral tube steam generator;

[0064] S2. Determine the heat transfer and pressure drop calculation modes for different grids for cold water convection, saturated boiling and superheated steam conditions;

[0065] S3, using the convection-diffusion implicit difference algorithm and the fluid-heat coupling algorithm to improve the calculation efficiency and ensure the stability of the fluid-heat coupling calculation in the heat exchanger under large time steps;

[0066] S4. Based on the fixed grid, the control bodies of the three cases of cold water convection, saturated boiling and superheated steam are meshed again using the air content movable boundary model, and the heat transfer coefficient and pressure drop parameters of each thermal component control body are recalculated;

[0067] S5. Set boundary conditions, repeat the above steps, calculate the heat transfer coefficient of each grid at the next time step, and finally obtain the heat transfer and pressure drop parameters of the steam generator at each moment.

[0068] Specifically, in step S1, the helium remains in a single-phase state during normal operation and safety accident conditions of the high-temperature gas-cooled reactor, and no phase change occurs. For the working fluid water commonly used in the secondary circuit of the high-temperature gas-cooled reactor, there is a state from supercooling to two-phase and then to superheated steam in the spiral tube steam generator. The present invention models it based on the homogeneous flow model. The assumption based on the homogeneous flow model is mainly to regard the fluid as a uniform mixed flow of gas phase and liquid phase. The two phases are in a state of thermodynamic equilibrium and have the same velocity and temperature. Therefore,

[0069] Its basic equation is completely consistent with the conservation equation of single-phase fluid in form, and a uniform homogeneous flow model is used to simulate the primary and secondary sides of the high-temperature gas-cooled reactor steam generator.

[0070] Based on the one-dimensional flow of coolant in the channel and combined with the three conservation equations of the single-phase flow model, the basic equations of the hydraulic model are established.

[0071] 1) Mass conservation equation

[0072]

[0073] Where: A is the flow area / m; ρ is the density / kg·m-3; t is the time / s; V is the flow velocity / m·s-1; z is the length of the control body / m. The first term is the mass transient change term, and the second term is the mass convection term.

[0074] For the working medium water in the secondary circuit, since it exists in a two-phase state, the density here refers to the uniformly mixed density of the two phases, which is obtained by weighted average of the gas phase cavitation fraction:

[0075] ρ=αρ g +(1-α)ρ f (2)

[0076] Where: α is the cavitation fraction; ρg is the saturated gas density / kg·m-3; ρf is the saturated liquid density / kg·m-3.

[0077] 2) Energy conservation equation

[0078]

[0079] In the formula: h is specific enthalpy / J·kg-1; T is temperature / K; g is gravitational acceleration / m·s-2; Qw is thermal power / W·m-1; θ is the inclination angle. The physical meanings of each term from left to right are energy transient change term, energy convection term, pressure-related term, gravitational work term, and heat source term.

[0080] 3) Momentum conservation equation

[0081]

[0082] Where: P is pressure / Pa; Fw is resistance along the way / Pa·m-1; Flocal is local resistance / Pa·m-1. The physical meanings of the terms from left to right in the equation are flow transient change term, convection term, static pressure drop term, gravity pressure drop term, friction pressure drop term and local pressure drop term.

[0083] like Figure 2 The simulation of heat transfer from the heat transfer pipe of the steam generator to the coolant uses the heat conduction model of the heat component to calculate the internal temperature distribution of the heat component and the convection heat exchange with the fluid on the boundary. The present invention uses a one-dimensional non-steady-state heat conduction equation to establish the heat conduction model of the heat component, and its general control equation is expressed as follows:

[0084]

[0085] Where: c is the specific heat capacity / J·kg-1·K-1; x is the distance / m; S is the internal heat source / W·m-3; A(x) is the area factor. The present invention adopts the internal node method to perform radial grid division on the thermal component, that is, the temperature node to be solved is located at the center of the grid, and the grid area is the control volume of the point, such as Figure 1 shown.

[0086] Specifically, in step S2, for cold water convection, saturated boiling and superheated steam conditions, the heat exchange and pressure drop calculation modes of different grids are determined according to the gas content x. The specific formula is as follows:

[0087] 1) Pressure drop in the tube

[0088] The single-phase friction pressure drop generally adopts the Darcy formula, that is,

[0089]

[0090] Where: f c is the single-phase friction factor in the spiral tube; G is the single-phase mass flow rate / kg·m -2 ·s -1 ; ρ is the density of single-phase fluid / kg·m -3 ; L is the channel length / m; D e is the equivalent diameter of the channel / m.

[0091] According to Ito's research, the friction factor relationship of single-phase laminar flow in spiral tube is:

[0092]

[0093] Where: f c is the single-phase friction factor in the spiral tube; f s,l is the friction pressure drop factor of single-phase laminar flow in straight tube; D e is the equivalent diameter of the channel / m; D is the outer diameter of the spiral tube; d is the inner diameter of the spiral tube.

[0094] The relationship between the friction factor of a single-phase laminar flow straight pipe is:

[0095] f s,l =64 / Re (8)

[0096] The empirical relationship of single-phase turbulent friction factor is:

[0097] f c =0.304 Re -0.25 +0.029(d / D) 0.5 (9)

[0098] Where: f c is the single-phase friction factor in the spiral tube; Re is the Reynolds number; D is the outer diameter of the spiral tube; d is the inner diameter of the spiral tube.

[0099] The critical Reynolds number relationship in the spiral tube is:

[0100] Re cr =2×10 4 (d / D) 0.32 (10)

[0101] Where: Re cr is the critical Reynolds number in the spiral tube; D is the outer diameter of the spiral tube; d is the inner diameter of the spiral tube.

[0102] The two-phase friction pressure drop in the spiral tube is calculated by the relationship proposed by Cioncilin:

[0103]

[0104] Where: f h is the friction factor between the two phases in the spiral tube; G is the mass flow rate / kg·m -2 ·s -1 ρ h is the density of the two-phase fluid / kg·m -3 ; L is the channel length / m; Re e is the Reynolds number under two-phase state; D is the outer diameter of the spiral tube; d is the inner diameter of the spiral tube; x is the gas content.

[0105] For the primary side external pressure drop, the widely accepted Gilli formula is used:

[0106]

[0107] 1) Heat exchange in tubes

[0108] When there is no phase change, the heat transfer coefficient of laminar flow is calculated using the relationship proposed by Rogers:

[0109]

[0110] The critical Reynolds number is calculated using equation (10). The turbulent heat transfer coefficient is calculated using the following equation:

[0111] Nu=0.023Re 0.85 Pr 0.4 (d / D) 0.1 (14)

[0112] When there is a phase change, the two-phase forced convection heat transfer coefficient is determined by the following formula:

[0113]

[0114] S and F are the fitting factor and Reynolds factor respectively, which are obtained from the experimental curves given in the literature.

[0115] The heat transfer coefficient of the liquid-deficient zone uses the Miropolskiy relationship:

[0116]

[0117] Where: G is mass flow rate / kg·m -2 ·s -1 ;μ g is the kinematic viscosity of the gas phase / kg·m -1 ·s -1 ; Pr w is the Prandtl number with the wall temperature as the qualitative temperature; ρ g and ρ f are the gas and liquid phase densities; x is the gas content.

[0118] 2) Heat exchange outside the tube

[0119] The heat transfer coefficient of the primary side outer tube flow is generally calculated using the Zhukaukas relationship. Zhukaukas can calculate the heat transfer coefficient of the outer tube flow within a wide range of parameters. The relationship is as follows:

[0120] 1≤Re≤5×10 2 :

[0121]

[0122] 5×10 2 ≤Re≤10 3 :

[0123]

[0124] 10 3 ≤Re≤2×10 5 :

[0125]

[0126] 2×10 5 ≤Re≤2×10 6 :

[0127]

[0128] In step S3, after determining the constitutive equation and the empirical relationship, it is necessary to improve the discrete calculation method to improve the transient heat transfer calculation performance of the spiral tube steam generator in the thermal hydraulic program of the pebble bed high temperature gas-cooled reactor. The specific processing method is as follows:

[0129] First, the three basic conservation equations of the single-phase flow model are fully implicitly differentiated to transform the differential equations into difference equations. In the differentiation process, the subscript o represents the control volume parameters, and the subscript x represents the takeover parameters, such as Figure 3 shown.

[0130] Among them, the convection terms of the three equations all use first-order upwind differences, and the transient terms use first-order backward differences, and the following difference equation expressions are obtained:

[0131]

[0132]

[0133] The mass conservation equation and energy conservation equation are defined on the control volume, and the momentum conservation equation is defined on the nozzle. For a reactor system containing N control volumes and J nozzles, the order of the differential equation system formed is N+2J, and it belongs to a nonlinear equation system. The present invention adopts the Newton iteration method to solve, and first generates the Jacobian matrix. The solution process of the Newton method can be expressed as:

[0134]

[0135] Note that the main variables to be solved in the equation group are the control volume pressure P, the control volume specific enthalpy h, and the flow rate V of the nozzle, so:

[0136] x k =[...P i-1 h i-1 V i-12 P i h i V i+12 P i+1 h i+1 ...] (twenty two)

[0137] Derive the partial derivatives of each conservation equation with respect to the solution variable, that is, obtain the value of each element in the Jacobian matrix. Next, solve the linear equations with the Jacobian matrix as the coefficient matrix. The present invention adopts the full-pivot Gaussian elimination method. Finally, the solution is obtained:

[0138] δx k =[...ΔP i-1 Δh i-1 ΔV i-12 ΔP i Δh i ΔV i+12 ΔP i+1 Δh i+1 ...] (twenty three)

[0139] Based on this, the three major solution variables of control body pressure, takeover speed, and control body specific enthalpy are updated, and other thermal hydraulic parameters of the coolant are also updated:

[0140]

[0141] This inner iteration cycle is repeated until the Newton iteration method converges. The variable value obtained at this time is the thermal-hydraulic calculation result at the new moment in the transient process, that is, the calculation of one time step is completed.

[0142] In order to ensure the stability of the fluid-heat coupling calculation in the heat exchanger under a large time step, the fluid-heat full coupling algorithm is adopted. That is, in the heat exchanger, the heat conduction equation of the thermal component and the three major hydraulic conservation equations of the fluid on both sides are placed in the same set of equations for solution, thereby forming a higher-order matrix.

[0143] To simplify the calculation, the heat exchanger's heat component is divided into only one grid in the radial direction, and the temperature is defined at the center of the grid. Since this unique grid is the boundary grid, the convection boundary conditions on both sides are processed using the additional source term method, and the transient change term of the center temperature of the heat exchanger is back-differentiated to obtain:

[0144]

[0145] In the formula: V is the volume of the thermal component grid control body / m3; Tf1 is the primary side fluid temperature / K; Tf2 is the secondary side fluid temperature / K; R1 is the total thermal resistance from the center of the thermal component to the primary side / K·W-1; R2 is the total thermal resistance from the center of the thermal component to the primary side / K·W-1.

[0146] The thermal resistance from the center of the thermal component to the fluid side consists of two parts, namely the thermal resistance of the thermal component's heat conduction and the thermal resistance of the convection heat transfer with the fluid. If the thermal component is in the shape of a plate, the total thermal resistance can be expressed as:

[0147]

[0148] Where: δ is the half thickness of the thermal component / m; A is the radial heat transfer area of ​​the thermal component / m2.

[0149] In general heat exchangers, the heat exchange components are concentric cylindrical. Taking the primary side as an example, assuming that the primary side is located inside the heat transfer tube, the total thermal resistance from the center of the heat component to the primary side can be expressed as:

[0150]

[0151] In the formula: do is the center diameter of the hot component / m; din is the inner diameter of the hot component / m; l is the axial heat exchange length of the hot component / m.

[0152] Therefore, equation (25) can be added to the nonlinear equation system based on the three major conservation equations of single-phase hydraulics, and the independent variables solved by the Jacobian matrix are transformed into:

[0153] δx k =[ΔP N Δh N ΔV J ΔT S ] (28)

[0154] Where: subscript N represents the hydraulic control body, subscript J represents the hydraulic pipe, and subscript S represents the thermal component control body in the heat exchanger. After the inner iteration loop converges, the thermal hydraulic parameters of the fluid and the node temperature of the thermal component of the heat exchanger can be obtained at the same time, which can ensure the stability of fluid-heat coupling.

[0155] Step S4, after the above fixed grid method completes the calculation of one time step, it is necessary to use the gas content as a judgment basis, adopt the movable boundary model, re-grid the control bodies of the three cases of cold water convection, saturated boiling and superheated steam, and recalculate the heat transfer coefficient and pressure drop parameters of each heat component control body. The specific method is as follows: Figure 4 As shown in the flow chart.

[0156] Example 2 is an embodiment of the present invention, which provides a system for improving the transient heat transfer calculation performance of a spiral tube direct current evaporator, including: a fixed grid method module, a convection-diffusion term implicit difference algorithm module, a fluid-heat full coupling algorithm module, a gas content movable boundary model module, and a high-order matrix solution module;

[0157] The fixed grid method module uses the fixed grid method to accurately divide the control volume of the steam generator, generate grid calculation modes under different working conditions, and make corresponding adjustments according to the state of the steam;

[0158] The convection-diffusion implicit difference algorithm module calculates the thermodynamic parameters of the control volume by using the first-order upwind difference for the convection term and the first-order backward difference for the transient term;

[0159] The fully coupled algorithm module for fluid and heat defines the mass conservation equation and the energy conservation equation in the control volume. The fully coupled algorithm is used to correlate the pressure, takeover speed, and specific enthalpy of the control volume to form a differential equation group, which is then solved by the Newton iteration method.

[0160] The gas content movable boundary model module is based on the fixed grid method, which refines the grid division under three working conditions: cold water convection, saturated boiling and superheated steam, dynamically adjusts the grid division, and recalculates the heat transfer coefficient and pressure drop parameters of each thermal component control body;

[0161] The high-order matrix solution module is used to solve the one-dimensional unsteady-state heat conduction equation and the basic conservation equations of the hydraulic model of the fluids on both sides in the same set of equations when processing the thermal hydraulic calculations of the heat exchanger. The convection boundary conditions are processed by solving the high-order matrix and the additional source term method to calculate the transient changes of the center temperature of the heat exchanger.

[0162] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc., which can store program code.

[0163] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in conjunction with such instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in conjunction with such instruction execution systems, devices or apparatuses.

[0164] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering or, if necessary, processing in another suitable manner, and then stored in a computer memory.

[0165] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0166] Embodiment 3: In this embodiment, in order to verify the beneficial effects of the present invention, scientific demonstration is carried out through economic benefit calculation and simulation experiments. This embodiment experiments the existing traditional method and the method of this embodiment respectively.

[0167] The present invention is based on the homogeneous flow hydraulic model, adopts the convection-diffusion term implicit difference format algorithm to solve the basic conservation equations, and adopts the fluid-heat full coupling algorithm to solve the heat conduction process of the heat transfer tube, so as to improve the calculation efficiency and ensure the stability of the fluid-heat coupling calculation in the heat exchanger under large time steps; the moving boundary method based on the fixed grid is used to determine the heat exchange mode of each grid, and the heat transfer coefficient and pressure drop of each grid are calculated for the supercooled water, two-phase evaporation, and superheated steam section conditions. Based on the fixed grid, the control body length of the evaporation section is re-gridified using the movable boundary model, and the heat transfer coefficients of the upper and lower heat components are recalculated. Set the boundary conditions, repeat the above steps, calculate the heat transfer coefficient of each grid in the next time step, and finally obtain the heat transfer of the steam generator at each moment. It not only ensures the heat exchange calculation accuracy of the spiral tube steam generator in the bed-type high-temperature gas-cooled reactor thermal hydraulic program, but also improves the solution speed of the reactor numerical calculation program.

[0168] like Figure 4As shown, the present invention first determines the state of the outlet by calculating the heat exchange of the spiral tube steam generator, and then determines and predicts the position of the secondary side from the subcooled water to the evaporation section and from the evaporation section to the superheated steam by the enthalpy rise. For the cold water convection, saturated boiling and superheated steam conditions, the heat exchange and pressure drop calculation modes of different grids are determined according to the gas content x. The specific formula is as follows:

[0169] Pressure drop in pipe

[0170] The single-phase friction pressure drop generally adopts the Darcy formula, that is,

[0171]

[0172] Where: f c is the single-phase friction factor in the spiral tube; G is the single-phase mass flow rate / kg·m -2 ·s -1 ; ρ is the density of single-phase fluid / kg·m -3 ; L is the channel length / m; D e is the equivalent diameter of the channel / m.

[0173] According to Ito's research, the friction factor relationship of single-phase laminar flow in spiral tube is:

[0174] f c =21.5f s,l De[1.56+log(De)] -5.73

[0175] 0.034<Re(d / D) 2 <300

[0176] 13.5<De<2000

[0177] Where: f c is the single-phase friction factor in the spiral tube; f s,l is the friction pressure drop factor of single-phase laminar flow in straight tube; D e is the equivalent diameter of the channel / m; D is the outer diameter of the spiral tube; d is the inner diameter of the spiral tube.

[0178] The relationship between the friction factor of a single-phase laminar flow straight pipe is:

[0179] f s,l =64 / Re

[0180] The empirical relationship of single-phase turbulent friction factor is:

[0181] f c =0.304Re -0 .25+0.029(d / D) 0.5

[0182] Where: fc is the single-phase friction factor in the spiral tube; Re is the Reynolds number; D is the outer diameter of the spiral tube; d is the inner diameter of the spiral tube.

[0183] The critical Reynolds number relationship in the spiral tube is:

[0184] Re cr =2×10 4 (d / D) 0.32

[0185] Where: Re cr is the critical Reynolds number in the spiral tube; D is the outer diameter of the spiral tube; d is the inner diameter of the spiral tube.

[0186] The two-phase friction pressure drop in the spiral tube is calculated by the relationship proposed by Cioncilin:

[0187]

[0188] 0<q<750,400<G<900

[0189] Where: f h is the friction factor between the two phases in the spiral tube; G is the mass flow rate / kg·m -2 ·s -1 ρ h is the density of the two-phase fluid / kg·m -3 ; L is the channel length / m; Re e is the Reynolds number under two-phase state; D is the outer diameter of the spiral tube; d is the inner diameter of the spiral tube; x is the gas content.

[0190] For the primary side external pressure drop, the widely accepted Gilli formula is used:

[0191]

[0192] C i =(cosβ) -1 (cosφ) 1.355

[0193]

[0194] Heat exchange in tube

[0195] When there is no phase change, the heat transfer coefficient of laminar flow is calculated using the relationship proposed by Rogers:

[0196] Nu=3.65+0.08[1+0.8(d / D) 0.9 Re a Pr 1 / 3 ]

[0197] a=0.5+0.2903(d / D)0.194

[0198] The heat transfer coefficient of turbulent flow is calculated by the following formula:

[0199] Nu=0.023Re 0.85 Pr 0.4 (d / D) 0.1

[0200] When there is a phase change, the two-phase forced convection heat transfer coefficient is determined by the following formula:

[0201]

[0202] S and F are the fitting factor and Reynolds factor respectively, which are obtained from the experimental curves given in the literature.

[0203] The heat transfer coefficient of the liquid-deficient zone uses the Miropolskiy relationship:

[0204]

[0205] Where: G is mass flow rate / kg·m -2 ·s -1 ;μ g is the kinematic viscosity of the gas phase / kg·m -1 ·s -1 ; Pr w is the Prandtl number with the wall temperature as the qualitative temperature; ρ g and ρ f are the gas and liquid phase densities; x is the gas content.

[0206] Heat exchange outside the tube

[0207] The heat transfer coefficient of the primary side outer tube flow is generally calculated using the Zhukaukas relationship. Zhukaukas can calculate the heat transfer coefficient of the outer tube flow within a wide range of parameters. The relationship is as follows:

[0208] 1≤Re≤5×10 2 :

[0209]

[0210] 5×10 2 ≤Re≤10 3 :

[0211]

[0212] 10 3 ≤Re≤2×10 5 :

[0213]

[0214] 2×10 5 ≤Re≤2×10 6 :

[0215]

[0216] After the calculation is completed, the newly calculated heat transfer is compared with the enthalpy rise of the critical position, and the boundary position is corrected again. Finally, when the set acceptable error is reached, the final heat transfer and pressure drop results are obtained. When performing the calculation, the convection-diffusion term implicit difference algorithm and the fluid-heat full coupling algorithm are used to improve the calculation efficiency and ensure the stability of the fluid-heat coupling calculation in the heat exchanger under large time steps.

[0217] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for improving the transient heat transfer calculation performance of a spiral tube direct current evaporator, characterized in that: include: According to the control volume division method of the steam generator hydraulic components, the fixed grid method is used to determine the grid division and related constitutive equations of the thermal components of the spiral tube steam generator. Determine the heat transfer and pressure drop calculation modes of different grids for cold water convection, saturated boiling and superheated steam conditions; The transient heat transfer calculation performance of the spiral tube steam generator in the thermal hydraulic program of the pebble bed high temperature gas-cooled reactor is optimized by using the full implicit difference algorithm of convection-diffusion terms and the full fluid-heat coupling algorithm. Based on the fixed grid, the control volume of the three cases of cold water convection, saturated boiling and superheated steam is meshed again using the gas content movable boundary model, and the heat transfer coefficient and pressure drop parameters of each thermal component control volume are recalculated; Set boundary conditions, calculate the heat transfer coefficient of each grid in the next time step, and finally obtain the heat transfer and pressure drop parameters of the steam generator at each moment.

2. The method for improving the transient heat transfer calculation performance of a spiral tube direct current evaporator according to claim 1, characterized in that: The control body division method of the steam generator hydraulic components includes that under normal operation and safety accident conditions of the high-temperature gas-cooled reactor, the helium remains in a single-phase state without phase change, and the working medium water commonly used in the secondary circuit of the high-temperature gas-cooled reactor changes from subcooling to two-phase and then to superheated steam in the spiral tube steam generator, and is modeled based on the homogeneous flow model; The homogeneous flow model regards the fluid as a uniform mixed flow of gas phase and liquid phase. The two phases are in a state of thermodynamic equilibrium and have the same velocity and temperature. The basic equation constructed is consistent with the conservation equation of single-phase fluid. The homogeneous flow model is used to simulate the primary and secondary sides of the high-temperature gas-cooled reactor steam generator. Based on the one-dimensional flow of the coolant in the channel and combined with the three conservation equations of the single-phase flow model, the basic conservation equation of the hydraulic model is established. The mass conservation equation is expressed as: p = ar g +(1-a)p f Where A is the flow area, ρ is the density, t is the time, V is the flow velocity, z is the control volume length, α is the cavitation fraction, ρ g is the saturated gas density, ρ f is the saturated liquid density; The energy conservation equation is expressed as: Where h is the specific enthalpy, g is the acceleration due to gravity, Q w is the thermal power, θ is the inclination angle, and P is the pressure; The momentum conservation equation is expressed as: Where P is pressure, F w is the resistance along the way, F local is the local resistance; The simulation of heat transfer from the steam generator heat transfer tube to the coolant uses the heat conduction model of the heat component to calculate the internal temperature distribution of the heat component and the convection heat transfer with the fluid on the boundary. The heat conduction model of the heat component is established using the one-dimensional unsteady-state heat conduction equation. The expression is: Where c is the specific heat capacity, T is the temperature, x is the distance, S is the heat source in the volume, A(x) is the area factor, and λ is the thermal conductivity; The internal node method is used to perform radial meshing of the thermal component, the temperature node to be solved is located at the center of the grid, and the grid area is the control volume of the current point.

3. The method for improving the transient heat transfer calculation performance of a spiral tube direct current evaporator according to claim 2, characterized in that: The determination of different grid heat exchange and pressure drop calculation modes is for cold water convection, saturated boiling and superheated steam conditions, and different grid heat exchange and pressure drop calculation modes are determined according to the gas content x, including the empirical relationship for the pressure drop inside and outside the spiral tube, the empirical relationship for the heat exchange inside the spiral tube, and the empirical relationship for the heat exchange outside the spiral tube.

4. The method for improving the transient heat transfer calculation performance of a spiral tube direct current evaporator according to claim 3, characterized in that: The method of optimizing the transient heat transfer calculation performance of the spiral tube steam generator in the thermal hydraulic program of the pebble bed high temperature gas-cooled reactor by using the convection-diffusion term full implicit difference algorithm and the fluid-heat full coupling algorithm is to perform full implicit difference processing on the basic conservation equation of the single-phase flow model and convert the differential equation into a difference equation; The first-order upwind difference is used for the convection term of the basic conservation equation, and the first-order backward difference is used for the transient term. The expression is: Where H is the specific enthalpy of the control volume, the subscript o represents the control volume parameter, and the subscript x represents the takeover parameter.

5. The method for improving the transient heat transfer calculation performance of a spiral tube direct current evaporator according to claim 4, characterized in that: The method of optimizing the transient heat transfer calculation performance of the spiral tube steam generator in the thermal hydraulic program of the pebble bed high temperature gas-cooled reactor by using the full implicit difference algorithm of convection-diffusion terms and the full coupling algorithm of fluid and heat also includes defining the mass conservation equation and the energy conservation equation in the control body, and defining the momentum conservation equation in the nozzle. For a reactor system including N control bodies and J nozzles, the order of the formed differential equation group is N+2J, and the Newton iteration method is used to solve the system, derive the partial derivative of each conservation equation with respect to the solution variable, obtain the value of each element in the Jacobian matrix, and use the full principal element Gaussian elimination method to solve the linear equation group with the Jacobian matrix as the coefficient matrix; The three major solution variables, namely, control volume pressure, takeover speed, and control volume specific enthalpy, are updated, and the inner iteration cycle is repeated until the Newton iteration method converges. The current variable value obtained is the thermal hydraulic calculation result at a new moment in the transient process, and the calculation of one time step is completed.

6. The method for improving the transient heat transfer calculation performance of a spiral tube direct current evaporator according to claim 5, characterized in that: The method of optimizing the transient heat transfer calculation performance of the spiral tube steam generator in the thermal hydraulic program of the pebble bed high temperature gas-cooled reactor by using the full implicit difference algorithm of convection-diffusion terms and the full coupling algorithm of fluid and heat also includes solving the basic conservation equations of the hydraulic model of the fluids on both sides of the one-dimensional non-steady-state heat conduction equation in the heat exchanger in the same set of equations to form a high-order matrix; The heat exchanger's hot component part is divided into only one grid in the radial direction, and the temperature is defined at the center of the grid. The convection boundary conditions on both sides are processed using the additional source term method, and the transient change term of the center temperature of the heat exchanger is backward differentiated. The expression is: Where V is the volume of the thermal component grid control volume, is the primary side fluid temperature, is the secondary side fluid temperature, R1 is the total thermal resistance from the center of the thermal component to the primary side, and R2 is the total thermal resistance from the center of the thermal component to the primary side.

7. The method for improving the transient heat transfer calculation performance of a spiral tube direct current evaporator according to claim 6, characterized in that: The recalculation of the heat transfer coefficient and pressure drop parameters of each heat component control body is to use the fixed grid method to complete the calculation of one time step, and then use the gas content as a judgment basis, adopt the movable boundary model, and re-grid the control bodies of the three cases of cold water convection, saturated boiling and superheated steam to correct the heat transfer coefficient and pressure drop parameters of each heat component control body; The judgment basis is that if the outlet is still supercooled water, the supercooled water heat exchange pressure drop calculation is performed; if the outlet is a two-phase mixture, it is necessary to calculate the boundary positions of the supercooled water and the two phases, and then calculate the heat exchange and pressure drop of the supercooled section and the two-phase section respectively; if the outlet is superheated steam, it is necessary to calculate the two boundary positions of the supercooled water, the two-phase section, and the superheated steam section, and then calculate the heat exchange and pressure drop of the supercooled section, the two-phase section, and the superheated steam section respectively; after one calculation is completed, the grid division is corrected and recalculated until the error is within an acceptable range and the calculation is completed.

8. A system using the method for improving the transient heat transfer calculation performance of a spiral tube direct current evaporator according to any one of claims 1 to 7, characterized in that: It includes fixed grid method module, convection-diffusion implicit difference algorithm module, flow-heat full coupling algorithm module, gas content movable boundary model module and high-order matrix solution module; The fixed grid method module uses the fixed grid method to accurately divide the control volume of the steam generator, generate grid calculation modes under different working conditions, and make corresponding adjustments according to the state of the steam; The convection-diffusion term implicit difference algorithm module calculates the thermodynamic parameters of the control body by using the first-order upwind difference for the convection term and the first-order backward difference for the transient term; The fluid-heat full coupling algorithm module defines the mass conservation equation and the energy conservation equation in the control body, and uses the full coupling algorithm to correlate the pressure, takeover speed, and specific enthalpy of the control body to form a differential equation group, which is solved by the Newton iteration method; The gas content movable boundary model module is based on the fixed grid method, refines the grid division under three working conditions: cold water convection, saturated boiling and superheated steam, dynamically adjusts the grid division, and recalculates the heat transfer coefficient and pressure drop parameters of each thermal component control body; The high-order matrix solution module solves the one-dimensional non-steady-state heat conduction equation and the basic conservation equations of the hydraulic model of the fluids on both sides in the same set of equations when processing the thermal hydraulic calculations of the heat exchanger. The convection boundary conditions are processed by solving the high-order matrix and the additional source term method to calculate the transient changes of the center temperature of the heat exchanger.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method for improving the transient heat exchange calculation performance of a spiral tube direct current evaporator according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for improving the transient heat exchange calculation performance of a spiral tube direct current evaporator as described in any one of claims 1 to 7 are implemented.

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