Method and device for simulating phase transition water hammer in nuclear power plant pipeline

Abstract

This invention discloses a simulation method and apparatus for phase change water hammer in nuclear power plant pipelines. The method includes the following steps: First, establishing a computational domain model of the nuclear power plant pipeline; then, meshing the computational domain model to generate a grid; setting boundary conditions based on the water hammer phenomenon, including inlet boundary conditions, outlet boundary conditions, and wall boundary conditions; establishing a Lee-HTC hybrid model; finally, based on the grid and boundary conditions, using the SST k-ω turbulence model, the VOF multiphase flow model, and the established Lee-HTC hybrid model, simulating the phase change water hammer phenomenon and obtaining simulation results. This invention combines the advantages of the Lee model and the HTC model, simultaneously considering heat and mass transfer at the two-phase interface and phase change within the liquid, thus expanding the applicability of traditional condensation models and achieving accurate simulation and analysis of the water hammer effect in complex phase change processes such as flash evaporation and condensation.

Description

Technical Field

[0001] This invention relates to the field of multiphase flow simulation technology, specifically to a method and apparatus for simulating phase change water hammer in nuclear power plant pipelines. Background Technology

[0002] Water hammer is a non-steady-state flow phenomenon that occurs in liquid flow. When a liquid suddenly stops or changes velocity in a pipe, it causes a rapid change in pressure within the pipe, generating a shock wave. This shock wave effect is known as water hammer. Water hammer can occur in many facilities in daily life, such as domestic water supply systems and steam pipes in thermal power plants. Especially in large industrial pipeline systems, due to the high fluid velocity and large flow rate, the destructive impact of water hammer can be greater. Based on the different mechanisms that trigger water hammer, it can be divided into two categories: water hammer caused by the sudden cessation of single-phase flow and water hammer caused by condensation phase change. Single-phase water hammer often occurs in water supply plant pipeline systems. Condensation water hammer refers to the instantaneous pressure pulsation and impact force generated in pipeline systems due to the interaction between steam and condensate. It is commonly seen in the hot gas defrosting process in the refrigeration industry and in the pressurized water reactor supply water pipes and evaporators of nuclear power plants. Condensation water hammer is a common and dangerous form of water hammer; it not only damages pipes and equipment but also threatens personnel safety. The mechanism of water hammer in condensation is complex, involving multiple physical processes such as multiphase flow, phase change, heat transfer, and mass transfer. It is difficult to model and solve, making accurate prediction and control a challenging task. Currently, computational fluid dynamics (CFD) has become one of the effective methods for analyzing and predicting water hammer in condensation. However, traditional condensation models such as the Lee model do not perform well in simulating condensation phenomena. The HTC model, based on surface renewal theory, only considers the heat and mass transfer processes at the phase change interface, making it difficult to describe the flash evaporation process inside the liquid and to simulate the water hammer effect during cavitation collapse.

[0003] Existing patent CN111695242A discloses a numerical simulation method for steam condensation in wet saturated flue gas. This method simplifies the condensation process of wet saturated flue gas into a steam condensation process containing a large amount of non-condensable gases. It performs geometric modeling and meshing of the heat transfer flow field, uses a phase change coefficient model combined with a multiphase flow model for numerical calculation, sets non-condensable flue gas as the main phase, and adds mass and energy source terms to the governing equations by importing a self-developed UDF program to realize the mass and energy transfer between phases due to phase change. This simulates the steam condensation process in wet saturated flue gas and analyzes the distribution of flue gas velocity and mass fraction under turbulent conditions. This method is used to achieve faster and more effective numerical prediction of the steam condensation heat transfer process in wet saturated flue gas, but it is not suitable for solving the water hammer effect in complex phase change processes involving flashing and cavitation collapse.

[0004] Existing literature 2, "Numerical Simulation of Steam Condensation and Flow in Horizontal Tubes," numerically simulates the steam condensation and flow process within the 100mm inlet section of the heat exchange tubes in a horizontal tube falling film evaporator in a seawater desalination plant. The VOF method is used to trace the phase interface, and the Lee model and CSF model are used to handle the condensation source term and surface tension, respectively. The influence of the heat transfer temperature difference between the tube wall and the steam, and the inlet steam mass flow rate on the tube heat flux density and average heat transfer coefficient is analyzed. The two-phase distribution inside the tube is observed; no complete liquid film forms around the tube wall, and the steam can directly contact the wall surface for condensation and heat release. The thickness of the temperature boundary layer at the tube wall is 20-30 μm. The axial and radial velocity distributions of the steam under different heat transfer temperature differences are analyzed.

[0005] In summary, none of the existing literature mentioned above has solved the problem of the inability to accurately predict and analyze the water hammer effect in complex phase transition processes involving flash evaporation and cavitation collapse in the current technology. Summary of the Invention

[0006] Based on the above-mentioned technical problems, this invention proposes a simulation method and device for phase change water hammer in nuclear power plant pipelines, which solves the problem that the existing technology cannot accurately predict and analyze the water hammer effect in complex phase change processes including flashing and cavitation collapse.

[0007] To achieve the above objectives, this invention proposes a simulation method for phase change water hammer in nuclear power plant pipelines.

[0008] A method for simulating phase change water hammer in nuclear power plant pipelines includes:

[0009] Establish a computational domain model for nuclear power plant piping;

[0010] The computational domain model is meshed to generate a mesh;

[0011] Boundary conditions are set based on the water hammer phenomenon. The boundary conditions include inlet boundary conditions, outlet boundary conditions, and wall boundary conditions.

[0012] Establish a Lee-HTC hybrid model;

[0013] Based on the grid and boundary conditions, the phase change water hammer phenomenon was simulated using the SST k-ω turbulence model, the VOF multiphase flow model, and the established Lee-HTC mixing model, and the simulation results were obtained.

[0014] Furthermore, it also includes: evaluating the Lee-HTC hybrid model based on simulation results.

[0015] Furthermore, the computational domain model is meshed to generate a mesh, including:

[0016] Simulations were performed using multiple sets of initial grids of different sizes to obtain the temperature and vapor-liquid mass transfer rate of the flow field corresponding to the initial grids of different sizes, and to verify the grid independence.

[0017] The size of the mesh is determined based on the mesh independence verification results, and the computational domain model is meshed using the size.

[0018] Establishing the Lee-HTC hybrid model includes:

[0019] A Lee-HTC hybrid model is established using the first volume fraction equation, the mass conservation equation, the momentum conservation equation, and the energy conservation equation.

[0020] First volume fraction equation

[0021]

[0022] in, This represents the volume fraction of steam. It represents the liquid volume fraction;

[0023] mass conservation equation,

[0024]

[0025]

[0026] in, For vapor density, It is a velocity vector. For quality source items, For the density of the liquid, For time, The divergence of steam mass flux is represented by... The divergence representing the mass flux of a liquid;

[0027] Momentum conservation equation

[0028]

[0029] in, Let be the density of the fluid at the grid. Negative gradient pressure, The dynamic viscosity of the fluid. This represents the transpose operator. The vector of gravitational acceleration. The force acting on each unit volume of an object;

[0030] Energy conservation equation

[0031]

[0032] in, For temperature, For temperature gradient, express, Thermal conductivity, For specific heat capacity, This is an energy source term.

[0033] Furthermore, based on the grid and boundary conditions, the phase change water hammer phenomenon was simulated using the SST k-ω turbulence model, the VOF multiphase flow model, and the Lee-HTC mixing model. The simulation results include:

[0034] The turbulent kinetic energy and specific dissipation rate were determined based on the SST k-ω turbulence model.

[0035] Based on turbulent kinetic energy and specific dissipation rate, the energy source term of the Lee-HTC mixing model is determined;

[0036] Determine the mass source term of the Lee-HTC hybrid model based on the energy source term;

[0037] The liquid volume fraction was determined using the VOF multiphase flow model.

[0038] The simulation results are obtained by solving the first volume fraction equation, the mass conservation equation, the momentum conservation equation, and the energy conservation equation based on the liquid volume fraction, energy source term, and mass source term. The simulation results include the vapor volume fraction, temperature, pressure, and velocity.

[0039] Furthermore, the turbulent kinetic energy and specific dissipation rate are determined based on the SST k-ω turbulence model, including:

[0040] The turbulent kinetic energy and specific dissipation rate are determined based on the turbulent kinetic energy equation and specific dissipation rate equation in the SST k-ω turbulence model. (Turbulent kinetic energy equation...)

[0041]

[0042] in, For turbulent kinetic energy, Let be the density of the fluid at the grid. The velocity vector is the first One portion, Indicates azimuth coordinates. The term representing the generation of turbulent kinetic energy. For coefficients, To compare the dissipation rate, The dynamic viscosity of the fluid. For turbulent dynamic viscosity;

[0043] Specific dissipation rate equation ,

[0044] in, For specific dissipation rate, Turbulent kinematic viscosity ， It is a mixed function. , is a coefficient.

[0045] Furthermore, based on turbulent kinetic energy and specific dissipation rate, the energy source term of the Lee-HTC mixing model is determined, including:

[0046] Based on turbulent kinetic energy and specific dissipation rate, the dissipation rate is determined using Formula 1. Formula 1, ,in, For dissipation rate, The coefficients are constants.

[0047] Based on the turbulent kinetic energy and dissipation rate, the heat transfer coefficient in the Lee-HTC mixing model is determined using Equation 2. HTC Formula 2

[0048]

[0049] in, As a regulating factor, The thermal conductivity of the liquid is denoted as . is the specific heat capacity of the liquid. For the density of the liquid, For dissipation rate, The kinematic viscosity of the liquid. It is the Reynolds number;

[0050] Based on the heat transfer coefficient HTC The energy source term of the Lee-HTC hybrid model is determined using Formula 3.

[0051]

[0052] in, For energy source terms, For relaxation time, For the density of the liquid, For liquid temperature, The saturation temperature For latent heat of phase transition, HTC The heat transfer coefficient, For interface density.

[0053] Furthermore, the mass source terms of the Lee-HTC hybrid model are determined based on the energy source terms, including:

[0054] Based on the energy source term, the mass source term of the Lee-HTC hybrid model is determined using Formula 4. Formula 4... ,in, This is a quality source item.

[0055] Furthermore, the liquid volume fraction was determined using the VOF multiphase flow model, including:

[0056] The liquid volume fraction is determined based on the second volume fraction equation in the VOF multiphase flow model. (Second volume fraction equation) ,in, It represents the divergence of the liquid volume fraction.

[0057] Furthermore, the Lee-HTC hybrid model was evaluated based on the simulation results, including:

[0058] Based on the simulation results, vapor volume fraction cloud map, temperature cloud map, pressure change curve, mass transfer rate curve, and vapor-liquid mass transfer rate curve are generated.

[0059] The Lee-HTC mixing model was evaluated by combining vapor volume fraction cloud map, temperature cloud map, pressure change curve, mass transfer rate curve, and vapor-liquid mass transfer rate curve.

[0060] To achieve the same objective as the methods described above, this invention also proposes a simulation device for phase change water hammer in nuclear power plant pipelines, comprising:

[0061] The first module is used to build the computational domain model of the nuclear power plant's piping.

[0062] The meshing module is used to mesh the computational domain model and generate the mesh.

[0063] The setting module is used to set boundary conditions based on the water hammer phenomenon. The boundary conditions include inlet boundary conditions, outlet boundary conditions, and wall boundary conditions.

[0064] The second module is used to build the Lee-HTC hybrid model;

[0065] The simulation module is used to simulate phase change water hammer phenomena based on grids and boundary conditions, using the SST k-ω turbulence model, VOF multiphase flow model, and the established Lee-HTC mixing model, and obtain simulation results.

[0066] Furthermore, it also includes an evaluation module for evaluating the Lee-HTC hybrid model based on simulation results.

[0067] Furthermore, the modules are divided for:

[0068] Simulations were performed using multiple sets of initial grids of different sizes to obtain the temperature and vapor-liquid mass transfer rate of the flow field corresponding to the initial grids of different sizes, and to verify the grid independence.

[0069] The size of the mesh is determined based on the mesh independence verification results, and the computational domain model is meshed using the size.

[0070] Furthermore, the second module is used for:

[0071] A Lee-HTC hybrid model is established using the first volume fraction equation, the mass conservation equation, the momentum conservation equation, and the energy conservation equation.

[0072] First volume fraction equation

[0073]

[0074] in, This represents the volume fraction of steam. It represents the liquid volume fraction;

[0075] mass conservation equation,

[0076]

[0077]

[0078] in, For vapor density, It is a velocity vector. For quality source items, For the density of the liquid, For time, The divergence of steam mass flux is represented by... The divergence representing the mass flux of a liquid;

[0079] Momentum conservation equation

[0080]

[0081] in, Let be the density of the fluid at the grid. Negative gradient pressure, The dynamic viscosity of the fluid. This represents the transpose operator. The vector of gravitational acceleration. The force acting on each unit volume of an object;

[0082] Energy conservation equation

[0083]

[0084] in, For temperature, For temperature gradient, express, Thermal conductivity, For specific heat capacity, This is an energy source term.

[0085] Furthermore, the simulation module is used for:

[0086] The turbulent kinetic energy and specific dissipation rate were determined based on the SST k-ω turbulence model.

[0087] Based on turbulent kinetic energy and specific dissipation rate, the energy source term of the Lee-HTC mixing model is determined;

[0088] Determine the mass source term of the Lee-HTC hybrid model based on the energy source term;

[0089] The liquid volume fraction was determined using the VOF multiphase flow model.

[0090] The simulation results are obtained by solving the first volume fraction equation, the mass conservation equation, the momentum conservation equation, and the energy conservation equation based on the liquid volume fraction, energy source term, and mass source term. The simulation results include the vapor volume fraction, temperature, pressure, and velocity.

[0091] Furthermore, the turbulent kinetic energy and specific dissipation rate are determined based on the SST k-ω turbulence model, including:

[0092] The turbulent kinetic energy and specific dissipation rate are determined based on the turbulent kinetic energy equation and specific dissipation rate equation in the SST k-ω turbulence model. (Turbulent kinetic energy equation...)

[0093]

[0094] in, For turbulent kinetic energy, Let be the density of the fluid at the grid. The velocity vector is the first One portion, express, The term representing the generation of turbulent kinetic energy. For coefficients, To compare the dissipation rate, The dynamic viscosity of the fluid. For turbulent dynamic viscosity;

[0095] Specific dissipation rate equation ,

[0096] in, For specific dissipation rate, Turbulent kinematic viscosity ， It is a mixed function. , is a coefficient.

[0097] Furthermore, based on turbulent kinetic energy and specific dissipation rate, the energy source term of the Lee-HTC mixing model is determined, including:

[0098] Based on turbulent kinetic energy and specific dissipation rate, the dissipation rate is determined using Formula 1. Formula 1, ,in, For dissipation rate, The coefficients are constants.

[0099] Based on the turbulent kinetic energy and dissipation rate, the heat transfer coefficient in the Lee-HTC mixing model is determined using Equation 2. HTC Formula 2

[0100]

[0101] in, As a regulating factor, The thermal conductivity of the liquid is denoted as . is the specific heat capacity of the liquid. For the density of the liquid, For dissipation rate, The kinematic viscosity of the liquid. It is the Reynolds number;

[0102] Based on the heat transfer coefficient HTC The energy source term of the Lee-HTC hybrid model is determined using Formula 3.

[0103]

[0104] in, For energy source terms, For relaxation time, For the density of the liquid, For liquid temperature, The saturation temperature For latent heat of phase transition, HTC The heat transfer coefficient, For interface density.

[0105] Furthermore, the mass source terms of the Lee-HTC hybrid model are determined based on the energy source terms, including:

[0106] Based on the energy source term, the mass source term of the Lee-HTC hybrid model is determined using Formula 4. Formula 4... ,in, This is a quality source item.

[0107] Furthermore, the liquid volume fraction was determined using the VOF multiphase flow model, including:

[0108] The liquid volume fraction is determined based on the second volume fraction equation in the VOF multiphase flow model. (Second volume fraction equation) ,in, It represents the divergence of the liquid volume fraction.

[0109] Furthermore, the evaluation module is used for:

[0110] Based on the simulation results, vapor volume fraction cloud map, temperature cloud map, pressure change curve, mass transfer rate curve, and vapor-liquid mass transfer rate curve are generated.

[0111] The Lee-HTC mixing model was evaluated by combining vapor volume fraction cloud map, temperature cloud map, pressure change curve, mass transfer rate curve, and vapor-liquid mass transfer rate curve.

[0112] Based on the above technical solution, the present invention has at least the following beneficial effects:

[0113] 1. The Lee-HTC hybrid model established in this invention combines the advantages of the Lee model and the HTC model, and simultaneously considers the heat and mass transfer at the two-phase interface and the phase change inside the liquid. It can expand the applicability of the traditional condensation model and realize the accurate simulation and analysis of the water hammer effect in the complex phase change process of flash evaporation and condensation.

[0114] 2. This invention proposes to use the Lee model to determine the energy source term for liquid flash evaporation into vapor when the liquid temperature is greater than the saturation temperature, and to use the hybrid HTC model combining the Shen model and the HD model to determine the energy source term for vapor condensation into liquid when the liquid temperature is lower than the saturation temperature. This method and device can be applied to the simulation of two-phase flow water hammer phenomena that need to consider obvious flash evaporation and condensation effects, and can improve the accuracy of water hammer assessment and protection. Attached Figure Description

[0115] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0116] Figure 1 This is a flowchart illustrating a simulation method for phase change water hammer in a nuclear power plant pipeline according to an embodiment of the present invention.

[0117] Figure 2 This is a schematic diagram illustrating the condensation of flash steam from a power plant upon contact with subcooled water, according to one embodiment of the present invention.

[0118] Figure 3 This illustrates the temperature variations under different grid sizes in one embodiment of the present invention.

[0119] Figure 4 This is an example of the variation in liquid mass transfer rate under different grid sizes in one embodiment of the present invention;

[0120] Figure 5 This is a flowchart simulating the phase change water hammer phenomenon in one embodiment of the present invention;

[0121] Figure 6 This is a flowchart illustrating the determination of the energy source term in the Lee-HTC hybrid model based on turbulent kinetic energy and specific dissipation rate in one embodiment of the present invention.

[0122] Figure 7 In one embodiment of the present invention, the Lee-HTC hybrid model is used to simulate the temporal distribution characteristics of the vapor volume fraction cloud map during the vapor-liquid phase transition process;

[0123] Figure 8 In one embodiment of the present invention, the Lee-HTC hybrid model is used to simulate the temporal distribution characteristics of temperature cloud map during the vapor-liquid phase transition process;

[0124] Figure 9 In one embodiment of the present invention, the Lee-HTC mixing model is used to simulate the temporal distribution characteristics of pressure during a vapor-liquid phase transition.

[0125] Figure 10 In one embodiment of the present invention, the Lee-HTC mixing model is used to simulate the temporal distribution characteristics of mass transfer rate during vapor-liquid phase transition.

[0126] Figure 11 This is a schematic diagram of a simulation device for phase change water hammer in a nuclear power plant pipeline according to an embodiment of the present invention. Detailed Implementation

[0127] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0128] The present invention will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed by the present invention.

[0129] Example

[0130] To address the problem that existing technologies cannot accurately predict and analyze the water hammer effect in complex phase change processes involving flashing and cavitation collapse, this invention proposes a simulation method and apparatus for phase change water hammer in nuclear power plant pipelines.

[0131] Figure 1 A flowchart illustrating a phase change water hammer simulation process in a nuclear power plant pipeline according to an embodiment of the present invention is shown. The method mainly simulates the phase change water hammer phenomenon through the following steps.

[0132] S1, establish the computational domain model of the nuclear power plant pipeline.

[0133] After obtaining the nuclear power plant's pipeline information, a corresponding computational domain model is established based on this information. For example... Figure 2 The diagram illustrates the condensation of flash steam in a power plant upon encountering subcooled water in this embodiment. High-temperature water flows in from inlet 1 and undergoes flash evaporation after passing through high-pressure zone A to low-pressure zone B. The low-pressure zone is filled with low-temperature water flowing in from inlet 2. The steam generated by flash evaporation encounters the subcooled water in the pipe and undergoes a condensation reaction, resulting in a complex two-phase flow hammer effect in the pipe. The fluid in the pipe is discharged from outlet 3.

[0134] S2, performs mesh generation on the computational domain model.

[0135] Furthermore, the computational domain model is meshed to generate a mesh, including:

[0136] Simulations were conducted using multiple initial meshes of different sizes to obtain the temperature and vapor-liquid mass transfer rate of the flow field corresponding to each mesh size, and mesh independence was verified. Based on the results of the mesh independence verification, a reasonable mesh size was determined, and then the selected size was used to mesh the computational domain model.

[0137] In this embodiment, three different mesh sizes (10mm, 2.5mm, and 2mm) were used to verify mesh independence, and the 2.5mm mesh was ultimately selected for simulation. Figure 3 This embodiment illustrates the temperature variations in the flow field corresponding to different grid sizes. Figure 3 It can be observed that the overall temperature change for the three different grid sizes is a sudden drop followed by a rise. This is caused by the rapid leftward movement due to cavitation collapse after the cold water flows past the measuring point. Cavitation collapse refers to the gas voids formed during liquid flow. When the grid size is 2.5 mm and 2 mm, the temperature change curves coincide, and the time for temperature drop and rise is the same. Figure 4 The diagram illustrates the variation of liquid mass transfer rate in the flow field corresponding to different grid sizes in this embodiment. Figure 4 As can be seen, at 9s, the liquid mass transfer rate suddenly peaks due to the second cavitation collapse. Similarly, the peak times and amplitudes of the liquid mass transfer rates are the same for mesh sizes of 2.5mm and 2mm.

[0138] Combination Figure 3 and Figure 4It can be seen that the calculation results for mesh sizes of 2.5mm and 2mm are almost identical, indicating that the calculation results no longer change with mesh refinement, demonstrating good mesh independence. Since smaller mesh sizes result in denser meshes and higher calculation accuracy, but also increase computational complexity, and considering that the temperature and liquid mass transfer rate changes are almost identical for mesh sizes of 2.5mm and 2mm, this embodiment ultimately selected a mesh size of 2.5mm for dividing the computational domain. Mesh quality checks showed that after dividing the computational domain using this mesh size, all mesh elements had orthogonality greater than 0.15, aspect ratios less than 10, and smoothness less than 2.5, indicating good mesh quality.

[0139] In addition, to ensure computational accuracy and avoid divergence, this embodiment establishes a boundary layer mesh with a growth factor of 1.2, an outermost mesh size of 0.4 mm, and a total of 10 layers near the pipe wall in the computational domain model.

[0140] S3 sets boundary conditions based on the water hammer phenomenon. The boundary conditions include inlet boundary conditions, outlet boundary conditions, and wall boundary conditions.

[0141] The inlet boundary conditions include inlet temperature and inlet velocity under high-temperature conditions, and inlet temperature and inlet velocity under low-pressure conditions; the outlet boundary conditions include outlet pressure and reflux temperature; the wall boundary conditions are no-slip adiabatic boundary conditions, i.e., the temperature gradient is 0. In a specific embodiment of the present invention, the inlet temperature under high-temperature conditions is set to 420.35 K, and the inlet velocity is 2.0738 m / s; the inlet temperature under low-temperature conditions is set to 311.75 K, and the inlet velocity is 0.979 m / s; the outlet pressure boundary conditions are set to 0 Pa (gauge pressure), and the reflux temperature is set to 311.75 K; the wall boundary conditions are no-slip adiabatic boundary conditions.

[0142] S4, establish the Lee-HTC hybrid model.

[0143] This embodiment establishes a Lee-HTC hybrid model using the first volume fraction equation, the mass conservation equation, the momentum conservation equation, and the energy conservation equation. A mass source term is added to the conservation equations. and energy source items To better describe the heat and mass transfer phenomena between the vapor and liquid phases.

[0144] The first volume fraction equation is:

[0145]

[0146] in, This represents the volume fraction of steam. This represents the liquid volume fraction.

[0147] The mass conservation equation is,

[0148]

[0149]

[0150] in, For vapor density, It is a velocity vector. For quality source items, For the density of the liquid, For time, The divergence of steam mass flux is represented by... It represents the divergence of liquid mass flux.

[0151] The equation for the conservation of momentum is:

[0152]

[0153] in, Let be the density of the fluid at the grid. Negative gradient pressure, The dynamic viscosity of the fluid. This represents the transpose operator. The vector of gravitational acceleration. It is the force acting on each unit volume of the object.

[0154] The energy conservation equation is:

[0155]

[0156] in, For temperature, For temperature gradient, express, Thermal conductivity, For specific heat capacity, This is an energy source term.

[0157] S5, based on grid and boundary conditions, uses the SST k-ω turbulence model, VOF multiphase flow model and the established Lee-HTC mixing model to simulate the phase change water hammer phenomenon and obtain simulation results.

[0158] The traditional Lee model primarily calculates the energy source term using the following formula. This allows for the simulation of phase change water hammer phenomena.

[0159]

[0160] in, For relaxation time, It is the liquid volume fraction. For the density of the liquid, For liquid temperature, The saturation temperature This is the latent heat of phase transition.

[0161]

[0162] in, It is the adjustment coefficient. It represents the vapor phase volume fraction. Where is the density of the vapor phase. It is the diameter of the spherical vapor bubble. It is the liquid phase density. M It's the molecular weight. R It is the universal gas constant. L It is latent heat.

[0163] The traditional HTC model regarding heat transfer coefficient HTC The calculation method is as follows:

[0164]

[0165] Where C is the coefficient. For the thermal conductivity of liquid, For Prandtl numbers, For turbulent kinematic viscosity, This refers to the viscosity of the liquid.

[0166] Traditional Lee models simulate flash evaporation well but poorly condensation. Traditional HTC models, when calculating heat and mass transfer at the vapor-liquid interface, typically assume the phase change occurs only at the interface, considering only the heat and mass transfer processes at that point. However, flash evaporation occurs not only at the vapor-liquid interface but also within the liquid. Therefore, traditional Lee and HTC models cannot accurately predict and analyze water hammer effects in complex phase change processes involving flash evaporation and cavitation collapse.

[0167] This invention combines the advantages of the HTC model and the Lee model to simulate the phase change water hammer phenomenon, and can obtain ideal simulation results.

[0168] like Figure 5 The flowchart shown below illustrates the simulation results of phase change water hammer in this embodiment. Figure 5 As shown, the process mainly includes five steps, S501 to S505.

[0169] S501, determine the turbulent kinetic energy and specific dissipation rate according to the SST k-ω turbulence model.

[0170] The SST k-ω turbulence model consists of two main transport equations: the turbulent kinetic energy equation and the specific dissipation rate equation. In this embodiment, the two transport equations are used to determine the corresponding turbulent kinetic energy and specific dissipation rate, which are used to determine the energy source term of the Lee-HTC hybrid model.

[0171] The turbulent kinetic energy equation is as follows.

[0172]

[0173] in, For turbulent kinetic energy, Let be the density of the fluid at the grid. The velocity vector is the first One portion, Indicates azimuth coordinates. The term representing the generation of turbulent kinetic energy. For coefficients, To compare the dissipation rate, The dynamic viscosity of the fluid. This refers to the turbulent dynamic viscosity.

[0174] The specific dissipation rate equation is as follows:

[0175]

[0176]

[0177] in, For specific dissipation rate, Turbulent kinematic viscosity ， It is a mixed function. , is a coefficient.

[0178] The turbulent kinetic energy can be obtained by solving the above two equations and related parameter values. Sum of dissipation .

[0179] S502, based on turbulent kinetic energy and specific dissipation rate, determines the energy source term of the Lee-HTC mixing model.

[0180] Furthermore, such as Figure 6 As shown, the energy source term of the Lee-HTC mixing model is determined based on turbulent kinetic energy and specific dissipation rate, including sub-steps S5021 to S5023.

[0181] S5021, based on turbulent kinetic energy and specific dissipation rate, uses Formula 1 to determine the dissipation rate.

[0182] Formula 1, ,in, For dissipation rate, These are constant coefficients. Specifically, in this embodiment, The constant coefficient is taken as 0.09, based on the above determination. k and Substituting into Formula 1, the dissipation rate can be determined. .

[0183] S5022, based on turbulent kinetic energy and dissipation rate, the heat transfer coefficient in the Lee-HTC mixing model is determined using Equation 2. HTC .

[0184] Formula 2,

[0185]

[0186] in, As an adjustment factor, it is set to 0.075 in this embodiment. The thermal conductivity of the liquid is denoted as . is the specific heat capacity of the liquid. For the density of the liquid, For dissipation rate, The kinematic viscosity of the liquid. Let be the Reynolds number. Further, the Reynolds number... , R It is the universal gas constant.

[0187] As shown in Formula 2, the hybrid HTC model in this invention combines the Shen model and the HD model, and incorporates the turbulent Reynolds number. Re This serves as a condition to determine which HTC model to use in the current scenario. Furthermore, for the coefficient C in the traditional HTC model, this invention sets different values ​​for the model under different scenarios. At that time, the heat transfer coefficient was determined using the HD model. HTC The original coefficient C takes the value of 2. At that time, the heat transfer coefficient was determined using the Shen model. HTC The original coefficient C has a value of 1.407.

[0188] S5023, based on heat transfer coefficient HTC The energy source term of the Lee-HTC hybrid model is determined using Formula 3.

[0189] Formula 3,

[0190]

[0191] in, For energy source terms, For relaxation time, For the density of the liquid, For liquid temperature, The saturation temperature For latent heat of phase transition, HTC The heat transfer coefficient, The interface density. Further, the interface density... , This represents the gradient of liquid volume fraction.

[0192] Formula 3 above uses saturation temperature As the dividing value, it combines the method for determining the energy source term in the traditional Lee model with the heat transfer coefficient. HTC The energy source term was determined under the corresponding conditions. In this way. Specifically, Formula 3 above can be understood as, when the liquid temperature... At that time, the Lee model is used to determine the energy source term for liquid flash evaporation into vapor; when the liquid temperature... At that time, the hybrid HTC model is used to determine the energy source term for vapor condensation into liquid. It should be understood that when the liquid temperature... In this case, the presence of a vapor-liquid interface can be determined first by checking the liquid volume fraction. If the liquid volume fraction is between 0.0001 and 0.9999, it indicates the presence of vapor in the liquid, thus establishing a vapor-liquid interface. The Reynolds number can then be determined accordingly. Re Whether it is greater than 2500 depends on the heat transfer coefficient under the corresponding conditions. HTC The calculation method is determined HTC The method also identifies the energy source term for vapor condensation into liquid. This approach overcomes the shortcomings of the traditional Lee model (poor simulation of condensation) and the HTC model (poor simulation of flash evaporation).

[0193] S503, determine the mass source term of the Lee-HTC hybrid model based on the energy source term.

[0194] Specifically, according to the energy source item The quality source terms of the Lee-HTC hybrid model are determined using Formula 4. ,in, This is a quality source item.

[0195] S504, using the VOF multiphase flow model to determine the liquid volume fraction.

[0196] The VOF multiphase flow model is used to track the interface between two unmixed fluids, and the volume fraction equation is the core of the VOF model.

[0197] In this embodiment, the liquid volume fraction is determined according to the second volume fraction equation in the VOF multiphase flow model. The second volume fraction equation... ,in, This represents the gradient of liquid volume fraction.

[0198] S505, based on the liquid volume fraction, energy source term, and mass source term, combined with the first volume fraction equation, mass conservation equation, momentum conservation equation, and energy conservation equation, obtains simulation results. The simulation results include steam volume fraction, temperature, pressure, and velocity.

[0199] Furthermore, in another embodiment of the present invention, after performing steps S1 to S5, step S6 is further performed to evaluate the Lee-HTC hybrid model based on the simulation results.

[0200] Furthermore, the Lee-HTC hybrid model was evaluated based on the simulation results, including:

[0201] Based on the simulation results, vapor volume fraction contour maps, temperature contour maps, pressure change curves, mass transfer rate curves, and vapor-liquid mass transfer rate curves were generated. Subsequently, the Lee-HTC hybrid model was evaluated by combining the vapor volume fraction contour maps, temperature contour maps, pressure change curves, mass transfer rate curves, and vapor-liquid mass transfer rate curves.

[0202] like Figure 7 The diagram illustrates the temporal distribution characteristics of the vapor volume fraction cloud map during the vapor-liquid phase transition process simulated using the Lee-HTC hybrid model in this embodiment. Figure 8 The temporal distribution characteristics of the temperature cloud map are displayed. Figure 7 , Figure 8 The steam bubbles in the steam volume fraction cloud map and temperature cloud map shown are continuously increasing in size. Figure 10 The graph shows the mass transfer rate curve, which refers to the mass transfer rate of the liquid. Therefore, a value less than 0 indicates liquid evaporation, and a value greater than 0 indicates vapor liquefaction. Based on the above theory, combined with... Figure 10 From the total mass transfer rate curve 3, it can be seen that in the time period from 0.260968s to 0.355888s, the vapor-liquid mass transfer rate of flash evaporation is greater than that of condensation. On the other hand, through... Figure 10 As can be seen from the total mass transfer rate curve 3, in the time period from 0.355888s to 0.362954s, the vapor-liquid mass transfer rate of condensation is greater than that of flash evaporation. Figure 7 , Figure 8 The steam bubbles in the steam volume fraction and temperature cloud maps shown are continuously decreasing in size and eventually collapsing. That is, within the two time periods mentioned above, Figure 10 Changes in mass transfer rate and Figure 7 and Figure 8 The changes in steam bubbles in the steam volume fraction cloud map and temperature cloud map correspond to each other.

[0203] like Figure 9The temporal distribution characteristics of pressure from 0 to 0.45 s during the vapor-liquid phase transition simulated by the Lee-HTC mixing model are shown. Figure 9 As can be seen, the pressure remained essentially constant during the period from 0s to 0.260968s, indicating that the liquid was still in a high-pressure single-phase flow state during this stage. However, at 0.3s and 0.35s, two pressure spikes appeared, which are related to the liquid flashing into gas and undergoing cavitation collapse. Figure 10 The temporal distribution of mass transfer rate during the vapor-liquid phase transition process simulated by the Lee-HTC hybrid model is presented from 0 s to 0.45 s. Here, mass transfer rate 1 refers to the mass transfer rate when the liquid temperature within the grid is below the saturation temperature, and mass transfer rate 2 refers to the mass transfer rate when the liquid temperature within the grid is above the saturation temperature. The sum of the two represents the mass transfer rate of the entire flow field. Figure 10 During the period from 0s to 0.260968s, the mass transfer rate I is zero, indicating that no phase change occurred in the liquid during this stage. However, at 0.3s and 0.35s, the mass transfer rate I reaches two peaks, and the rate of increase is very rapid, which is consistent with... Figure 9 The two peaks in the pressure diagram correspond to each other. During the period of 0.4s–0.45s, the mass transfer rate (I) returns to zero, indicating that the bubbles have completely collapsed and no new bubbles are generated during this stage. The total mass transfer rate curve reflects the relative intensity of the evaporation and condensation processes throughout the flow field. From… Figure 10 It can be seen that the total mass transfer rate is positive around 0.3s and 0.35s, indicating that the condensation process dominates, while the evaporation process dominates at other time intervals. Combined with... Figures 7 to 10 As can be seen from the above analysis, the Lee-HTC hybrid model can simulate the scenario where flash evaporation and cavitation collapse occur simultaneously, and it has a good simulation effect.

[0204] Steps S1 to S5 above allow the Lee-HTC hybrid model to be embedded into the simulation program for numerical calculations via user-defined functions (UDFs). This definition process can be divided into the following five steps:

[0205] (a) Declare basic variables: m_s Average heat over time 、T_l Liquid phase temperature Saturation temperature rho_l Liquid density theCond_l Liquid thermal conductivity dissp_l Liquid dissipation rate specheat_l Latent heat of liquid phase HTC HTC coefficient ,ai Volume fraction Qtransfer Energy source item Re Reynolds number m_dot_l Liquid phase mass transfer rate m_dot_v Vapor phase mass transfer rate and pointer variables.

[0206] (ii) Define an adjustment function to calculate the gradient of the volume fraction in the VOF and store it in the user-defined module interface (UDMI).

[0207] (III) Define the energy function, obtain the liquid-vapor interface based on the initial variables, then calculate the liquid temperature, and determine whether the liquid temperature within the grid is greater than the saturation temperature. If the liquid temperature is greater than the saturation temperature, it indicates that the current effect is evaporation, and determine the energy source term at this time according to Formula 3. Qtransfer If the liquid temperature is less than or equal to the saturation temperature, it indicates a condensation effect. The liquid volume fraction is then determined to be between 0.0001 and 0.9999. If so, it indicates the presence of vapor in the liquid, indicating a vapor-liquid interface. The Reynolds number is then then determined. Re Whether it is greater than 2500 depends on the heat transfer coefficient under the corresponding conditions. HTC The calculation method is determined HTC Thus, the energy source term is determined. Qtransfer If the liquid volume fraction is not between 0.0001 and 0.9999, then Qtransfer =0. To make the calculation easier to converge, this embodiment utilizes the previous... Qtransfer Value and current Qtransfer The time-average heat m_s is calculated and stored as an energy source term.

[0208] (iv) Define the liquid function and calculate the liquid mass source term. Obtain the liquid temperature. If the liquid temperature is greater than or equal to the saturation temperature, it is evaporation. Then calculate the liquid mass change rate m_dot_l, store it in UDMI, and return it in m_dot_1 as the source term value. If the liquid temperature is less than the saturation temperature, it is condensation. Calculate m_1, store it in UDMI, and return m_1 as the source term value.

[0209] (v) Define the vapor phase function and calculate the steam mass source term. Obtain the liquid temperature. If the temperature is greater than or equal to the saturation temperature, it is evaporation. Calculate the steam mass source term generated by liquid evaporation, store it, and return m_dot_V. If the temperature is less than the saturation temperature, it is condensation. Calculate the decrease in steam mass caused by condensation, store it, and return m_v.

[0210] To achieve the same objective as the methods described above, this invention also proposes a simulation device for phase change water hammer in nuclear power plant pipelines.

[0211] like Figure 11The diagram shows a schematic of a simulation device for phase change water hammer in a nuclear power plant pipeline according to an embodiment of the present invention. Figure 11 As shown, the device includes a first establishment module 110, a division module 111, a setting module 112, a second establishment module 113, and a simulation module 114. The functions of each module will be described in detail below.

[0212] The first module 110 is used to establish the computational domain model of the nuclear power plant pipeline.

[0213] The meshing module 111 is used to mesh the computational domain model and generate a mesh.

[0214] Furthermore, module 111 is divided for:

[0215] Simulations were performed using multiple sets of initial grids of different sizes to obtain the temperature and vapor-liquid mass transfer rate of the flow field corresponding to the initial grids of different sizes, and to verify the grid independence.

[0216] The size of the mesh is determined based on the results of the mesh independence verification, and the computational domain model is meshed using the size.

[0217] Setting module 112 is used to set boundary conditions according to the water hammer phenomenon. The boundary conditions include inlet boundary conditions, outlet boundary conditions and wall boundary conditions.

[0218] The second module 113 is used to establish the Lee-HTC hybrid model.

[0219] Furthermore, the second module 113 is used for:

[0220] A Lee-HTC hybrid model is established using the first volume fraction equation, the mass conservation equation, the momentum conservation equation, and the energy conservation equation.

[0221] First volume fraction equation

[0222]

[0223] in, This represents the volume fraction of steam. This represents the liquid volume fraction.

[0224] mass conservation equation,

[0225]

[0226]

[0227] in, For vapor density, It is a velocity vector. For quality source items, For the density of the liquid, For time, The divergence of steam mass flux is represented by... It represents the divergence of liquid mass flux.

[0228] Momentum conservation equation

[0229]

[0230] in, Let be the density of the fluid at the grid. Negative gradient pressure, The dynamic viscosity of the fluid. This represents the transpose operator. The vector of gravitational acceleration. It is the force acting on each unit volume of the object.

[0231] Energy conservation equation

[0232]

[0233] in, For temperature, For temperature gradient, express, Thermal conductivity, For specific heat capacity, This is an energy source term.

[0234] Simulation module 114 is used to simulate phase change water hammer phenomena based on grids and boundary conditions, using the SST k-ω turbulence model, VOF multiphase flow model and the established Lee-HTC mixing model, and obtain simulation results.

[0235] Furthermore, the simulation module 114 is used for:

[0236] The turbulent kinetic energy and specific dissipation rate were determined based on the SST k-ω turbulence model.

[0237] Furthermore, the turbulent kinetic energy and specific dissipation rate are determined based on the SST k-ω turbulence model, including:

[0238] The turbulent kinetic energy and specific dissipation rate are determined based on the turbulent kinetic energy equation and specific dissipation rate equation in the SST k-ω turbulence model. (Turbulent kinetic energy equation...)

[0239]

[0240] in, For turbulent kinetic energy, Let be the density of the fluid at the grid. The velocity vector is the first One portion, Indicates azimuth coordinates. The term representing the generation of turbulent kinetic energy. For coefficients, To compare the dissipation rate, The dynamic viscosity of the fluid. This refers to the turbulent dynamic viscosity.

[0241] Specific dissipation rate equation ,

[0242] in, For specific dissipation rate, Turbulent kinematic viscosity ， It is a mixed function. , is a coefficient.

[0243] Based on turbulent kinetic energy and specific dissipation rate, the energy source term of the Lee-HTC mixing model is determined.

[0244] Furthermore, based on turbulent kinetic energy and specific dissipation rate, the energy source term of the Lee-HTC mixing model is determined, including:

[0245] Based on turbulent kinetic energy and specific dissipation rate, the dissipation rate is determined using Formula 1. Formula 1, ,in, For dissipation rate, These are constant coefficients.

[0246] Based on the turbulent kinetic energy and dissipation rate, the heat transfer coefficient in the Lee-HTC mixing model is determined using Equation 2. HTC Formula 2

[0247]

[0248] in, As a regulating factor, The thermal conductivity of the liquid is denoted as . is the specific heat capacity of the liquid. For the density of the liquid, For dissipation rate, The kinematic viscosity of the liquid. It is the Reynolds number.

[0249] Based on the heat transfer coefficient HTC The energy source term of the Lee-HTC hybrid model is determined using Formula 3.

[0250]

[0251] in, For energy source terms, For relaxation time, For the density of the liquid, For liquid temperature, The saturation temperature For latent heat of phase transition, HTC The heat transfer coefficient, For interface density.

[0252] Furthermore, the mass source terms of the Lee-HTC hybrid model are determined based on the energy source terms, including:

[0253] Based on the energy source term, the mass source term of the Lee-HTC hybrid model is determined using Formula 4. Formula 4... ,in, This is a quality source item.

[0254] The liquid volume fraction was determined using the VOF multiphase flow model.

[0255] Furthermore, the liquid volume fraction was determined using the VOF multiphase flow model, including:

[0256] The liquid volume fraction is determined based on the second volume fraction equation in the VOF multiphase flow model. (Second volume fraction equation) ,in, This represents the gradient of liquid volume fraction.

[0257] The simulation results are obtained by solving the first volume fraction equation, the mass conservation equation, the momentum conservation equation, and the energy conservation equation based on the liquid volume fraction, energy source term, and mass source term. The simulation results include the vapor volume fraction, temperature, pressure, and velocity.

[0258] Furthermore, it also includes: an evaluation module 115 for evaluating the Lee-HTC hybrid model based on simulation results.

[0259] Furthermore, the evaluation module 115 is used for:

[0260] Based on the simulation results, vapor volume fraction cloud map, temperature cloud map, pressure change curve, mass transfer rate curve, and vapor-liquid mass transfer rate curve are generated.

[0261] The Lee-HTC mixing model was evaluated by combining vapor volume fraction cloud map, temperature cloud map, pressure change curve, mass transfer rate curve, and vapor-liquid mass transfer rate curve.

[0262] It should be understood that the simulation device for phase change water hammer in nuclear power plant pipelines is described in the same way as the corresponding simulation method for phase change water hammer in nuclear power plant pipelines, so it will not be repeated in this embodiment. Furthermore, it is understood that the simulation method and device for phase change water hammer in nuclear power plant pipelines proposed in this invention can be applied to pipeline systems in nuclear power, chemical, and petroleum industries to predict water hammer hazards that may occur under complex operating conditions and guide engineering layout and operation.

[0263] In summary, as can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0264] 1. The Lee-HTC hybrid model established in this invention combines the advantages of the Lee model and the HTC model, and simultaneously considers the heat and mass transfer at the two-phase interface and the phase change inside the liquid. It can expand the applicability of the traditional condensation model and realize the accurate simulation and analysis of the water hammer effect in the complex phase change process of flash evaporation and condensation.

[0265] 2. This invention proposes to use the Lee model to determine the energy source term for liquid flash evaporation into vapor when the liquid temperature is greater than the saturation temperature, and to use the hybrid HTC model combining the Shen model and the HD model to determine the energy source term for vapor condensation into liquid when the liquid temperature is lower than the saturation temperature. This method and device can be applied to the simulation of two-phase flow water hammer phenomena that need to consider obvious flash evaporation and condensation effects, and can improve the accuracy of water hammer assessment and protection.

[0266] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0267] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0268] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus or device (such as a computer-based system, a processor-included system or other system that can fetch and execute instructions from, an instruction execution system, apparatus or device).

[0269] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0270] It should be noted that, in the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

Claims

1. A method for simulating phase change water hammer in nuclear power plant pipelines, characterized in that, include: Establish a computational domain model for nuclear power plant piping; The computational domain model is meshed to generate a mesh; Boundary conditions are set according to the water hammer phenomenon, including inlet boundary conditions, outlet boundary conditions, and wall boundary conditions. Establishing a Lee-HTC hybrid model includes: using the first volume fraction equation, the mass conservation equation, the momentum conservation equation, and the energy conservation equation to establish the Lee-HTC hybrid model. The first volume fraction equation... ， in, This represents the volume fraction of steam. The volume fraction of the liquid; the mass conservation equation, ， ， in, For vapor density, It is a velocity vector. For quality source items, For the density of the liquid, For time, The divergence of steam mass flux is represented by... The divergence representing the mass flux of the liquid; the momentum conservation equation. ， in, Let be the density of the fluid at the grid. Negative gradient pressure, The dynamic viscosity of the fluid. This represents the transpose operator. The vector of gravitational acceleration. The force acting on each unit volume of the object; the energy conservation equation, ， in, For temperature, For temperature gradient, express divergence, Thermal conductivity, For specific heat capacity, For energy source terms; Based on the aforementioned mesh and boundary conditions, the phase change water hammer phenomenon is simulated using the SST k-ω turbulence model, the VOF multiphase flow model, and the established Lee-HTC mixing model. The simulation results include: determining the turbulent kinetic energy and specific dissipation rate according to the SST k-ω turbulence model; determining the energy source term of the Lee-HTC mixing model based on the turbulent kinetic energy and specific dissipation rate; and determining the dissipation rate using Formula 1 based on the turbulent kinetic energy and specific dissipation rate. ,in, For dissipation rate, For constant coefficients, For turbulent kinetic energy, The specific dissipation rate is used; based on the turbulent kinetic energy and the dissipation rate, the heat transfer coefficient in the Lee-HTC mixing model is determined using Formula 2. HTC Formula 2, ， in, As a regulating factor, The thermal conductivity of the liquid is denoted as . is the specific heat capacity of the liquid. For the density of the liquid, For dissipation rate, The kinematic viscosity of the liquid. The Reynolds number; based on the stated heat transfer coefficient HTC The energy source term of the Lee-HTC hybrid model is determined using Formula 3. ， in, For energy source terms, For relaxation time, For the density of the liquid, For liquid temperature, The saturation temperature For latent heat of phase transition, HTC The heat transfer coefficient, For interface density.

2. The method according to claim 1, characterized in that, Also includes: The Lee-HTC hybrid model is evaluated based on the simulation results.

3. The method according to claim 1, characterized in that, The computational domain model is meshed to generate a mesh, including: Simulations were performed using multiple sets of initial grids of different sizes to obtain the temperature and vapor-liquid mass transfer rate of the flow field corresponding to the initial grids of different sizes, and to verify the grid independence. The size of the mesh is determined based on the results of the mesh independence verification, and the computational domain model is meshed using the size.

4. The method according to claim 1, characterized in that, Based on the aforementioned grid and boundary conditions, the phase change water hammer phenomenon was simulated using the SST k-ω turbulence model, the VOF multiphase flow model, and the Lee-HTC mixing model. The simulation results also include: The mass source term of the Lee-HTC hybrid model is determined based on the energy source term; The liquid volume fraction was determined using the VOF multiphase flow model. The simulation results are obtained by solving the liquid volume fraction, the energy source term, the mass source term, the first volume fraction equation, the mass conservation equation, the momentum conservation equation, and the energy conservation equation. The simulation results include the vapor volume fraction, temperature, pressure, and velocity.

5. The method according to claim 4, characterized in that, The turbulent kinetic energy and specific dissipation rate are determined based on the SST k-ω turbulence model, including: The turbulent kinetic energy and specific dissipation rate are determined based on the turbulent kinetic energy equation and specific dissipation rate equation in the SST k-ω turbulence model. The turbulent kinetic energy equation... ， in, For turbulent kinetic energy, Let be the density of the fluid at the grid. The velocity vector is the first One portion, Indicates azimuth coordinates. The term representing the generation of turbulent kinetic energy. For coefficients, To compare the dissipation rate, The dynamic viscosity of the fluid. For turbulent dynamic viscosity; The specific dissipation rate equation, , in, For specific dissipation rate, Turbulent kinematic viscosity ， It is a mixed function. , For coefficients, The dynamic viscosity of the fluid. This refers to the turbulent dynamic viscosity.

6. The method according to claim 4, characterized in that, The mass source term of the Lee-HTC hybrid model is determined based on the energy source term, including: Based on the energy source term, the mass source term of the Lee-HTC hybrid model is determined using Formula 4, where Formula 4 is... ,in, This is a quality source item.

7. The method according to claim 4, characterized in that, Determining the liquid volume fraction using the VOF multiphase flow model includes: The liquid volume fraction is determined according to the second volume fraction equation in the VOF multiphase flow model. ,in, This represents the gradient of liquid volume fraction.

8. The method according to claim 2, characterized in that, The Lee-HTC hybrid model is evaluated based on the simulation results, including: Based on the simulation results, steam volume fraction cloud map, temperature cloud map, pressure change curve, mass transfer rate curve, and vapor-liquid mass transfer rate curve are generated. The Lee-HTC mixing model is evaluated by combining the vapor volume fraction cloud map, the temperature cloud map, the pressure change curve, the mass transfer rate curve, and the vapor-liquid mass transfer rate curve.

9. A simulation device for phase change water hammer in nuclear power plant pipelines, characterized in that, include: The first module is used to build the computational domain model of the nuclear power plant's piping. The partitioning module is used to partition the computational domain model into a mesh and generate a mesh. The setting module is used to set boundary conditions according to the water hammer phenomenon. The boundary conditions include inlet boundary conditions, outlet boundary conditions and wall boundary conditions. The second module is used to establish the Lee-HTC hybrid model, including: establishing the Lee-HTC hybrid model using the first volume fraction equation, the mass conservation equation, the momentum conservation equation, and the energy conservation equation. The first volume fraction equation... ， in, This represents the volume fraction of steam. The volume fraction of the liquid; the mass conservation equation, ， ， in, For vapor density, It is a velocity vector. For quality source items, For the density of the liquid, For time, The divergence of steam mass flux is represented by... The divergence representing the mass flux of the liquid; the momentum conservation equation. ， in, Let be the density of the fluid at the grid. Negative gradient pressure, The dynamic viscosity of the fluid. This represents the transpose operator. The vector of gravitational acceleration. The force acting on each unit volume of the object; the energy conservation equation, ， in, For temperature, For temperature gradient, express divergence, Thermal conductivity, For specific heat capacity, For energy source terms; The simulation module is used to simulate phase change water hammer phenomena based on the grid and boundary conditions, using the SST k-ω turbulence model, the VOF multiphase flow model, and the established Lee-HTC mixing model, and to obtain simulation results, including: determining the turbulent kinetic energy and specific dissipation rate according to the SST k-ω turbulence model; determining the energy source term of the Lee-HTC mixing model based on the turbulent kinetic energy and the specific dissipation rate; and determining the dissipation rate using Formula 1 based on the turbulent kinetic energy and the specific dissipation rate. ,in, For dissipation rate, For constant coefficients, For turbulent kinetic energy, The specific dissipation rate is used; based on the turbulent kinetic energy and the dissipation rate, the heat transfer coefficient in the Lee-HTC mixing model is determined using Formula 2. HTC Formula 2, ， in, As a regulating factor, The thermal conductivity of the liquid is denoted as . is the specific heat capacity of the liquid. For the density of the liquid, For dissipation rate, The kinematic viscosity of the liquid. The Reynolds number; based on the stated heat transfer coefficient HTC The energy source term of the Lee-HTC hybrid model is determined using Formula 3. ， in, For energy source terms, For relaxation time, For the density of the liquid, For liquid temperature, The saturation temperature For latent heat of phase transition, HTC The heat transfer coefficient, For interface density.

10. The apparatus according to claim 9, characterized in that, Also includes: An evaluation module is used to evaluate the Lee-HTC hybrid model based on the simulation results.

11. The apparatus according to claim 10, characterized in that, The partitioning module is used for: Simulations were performed using multiple sets of initial grids of different sizes to obtain the temperature and vapor-liquid mass transfer rate of the flow field corresponding to the initial grids of different sizes, and to verify the grid independence. The size of the mesh is determined based on the results of the mesh independence verification, and the computational domain model is meshed using the size.

12. The apparatus according to claim 11, characterized in that, The simulation module is also used for: The mass source term of the Lee-HTC hybrid model is determined based on the energy source term; The liquid volume fraction was determined using the VOF multiphase flow model. The simulation results are obtained by solving the liquid volume fraction, the energy source term, the mass source term, the first volume fraction equation, the mass conservation equation, the momentum conservation equation, and the energy conservation equation. The simulation results include the vapor volume fraction, temperature, pressure, and velocity.

13. The apparatus according to claim 12, characterized in that, The turbulent kinetic energy and specific dissipation rate are determined based on the SST k-ω turbulence model, including: The turbulent kinetic energy and specific dissipation rate are determined based on the turbulent kinetic energy equation and specific dissipation rate equation in the SST k-ω turbulence model. The turbulent kinetic energy equation... ， in, For turbulent kinetic energy, Let be the density of the fluid at the grid. The velocity vector is the first One portion, Indicates azimuth coordinates. The term representing the generation of turbulent kinetic energy. For coefficients, To compare the dissipation rate, The dynamic viscosity of the fluid. For turbulent dynamic viscosity; The specific dissipation rate equation, , in, For specific dissipation rate, Turbulent kinematic viscosity ， It is a mixed function. , For coefficients, The dynamic viscosity of the fluid. This refers to the turbulent dynamic viscosity.

14. The apparatus according to claim 13, characterized in that, The mass source term of the Lee-HTC hybrid model is determined based on the energy source term, including: Based on the energy source term, the mass source term of the Lee-HTC hybrid model is determined using Formula 4, where Formula 4 is... ,in, This is a quality source item.

15. The apparatus according to claim 13, characterized in that, Determining the liquid volume fraction using the VOF multiphase flow model includes: The liquid volume fraction is determined according to the second volume fraction equation in the VOF multiphase flow model. ,in, It represents the divergence of the liquid volume fraction.

16. The apparatus according to claim 10, characterized in that, The evaluation module is used for: Based on the simulation results, steam volume fraction cloud map, temperature cloud map, pressure change curve, mass transfer rate curve, and vapor-liquid mass transfer rate curve are generated. The Lee-HTC mixing model is evaluated by combining the vapor volume fraction cloud map, the temperature cloud map, the pressure change curve, the mass transfer rate curve, and the vapor-liquid mass transfer rate curve.

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