A numerical solution method for multiphase flow with coupled phase change component transport

Abstract

The present invention discloses a method for numerically solving multiphase flow with coupled phase-change component transport, which belongs to the field of multi-component multiphase flow. The phase change model is used to calculate the component states between multiple phases, the mass transfer rate between phases, the phase volume fraction, etc., which are coupled to the component transport equation to further solve the net mass transfer rate, the Schmidt number, and the multi-component diffusion effect; based on the estimation-correction iteration of pressure-velocity correction, a two-way coupled and highly coordinated solution algorithm is constructed. The present invention can handle the problems of temperature-density-mass transfer rate-pressure-velocity being difficult to couple and converge, as well as the inaccurate interface capture, and realize the calculation of non-steady, viscous, incompressible, and multi-dimensional heterogeneous and homogeneous multiphase flows. It has important engineering value and scientific significance for the research on the fields of high efficiency, integration, and safety of energy systems. The present invention can simulate complex scenarios, has high flexibility, scalability, and easy convergence, and realizes more accurate simulation.

Description

Technical Field

[0001] The invention belongs to the field of numerical solution of multi-component multi-phase flow, and specifically relates to a numerical solution method of multi-phase flow of coupled phase change component transport. Background Art

[0002] Multiphase flow is an important branch of fluid mechanics. It studies the interaction and change rules of substances (such as liquids, gases, solids) in two or more different physical states in the flow process. It has a wide range of applications in many industrial productions, such as petrochemicals, aerospace engineering, electric power, building energy conservation, and the electronics industry. Specifically, for example, leakage safety issues in projects such as liquid hydrogen refueling stations and liquefied natural gas stations, phase change evaporation processes in heat exchangers, thermal management of micro / nanoelectronic devices, and evaporation characteristics of nanofluid droplets.

[0003] The core essence of multiphase flow lies in describing and understanding the interactions between different phases, and how these interactions affect the overall flow behavior and transport characteristics. This includes the dynamic changes of the phase interface, the transfer of mass, momentum and energy between phases, and the instability and phase separation phenomena in multiphase flow. Therefore, the calculation of multiphase flow is a complex physical process in which the fluid flow and heat and mass transfer under multiple components and states are coupled. Conventional numerical calculation methods have a low degree of coupling, and it is difficult to guarantee the convergence and accuracy of the results. They cannot accurately describe complex multiphase flows, and cannot add source terms and key physical parameters suitable for actual working conditions based on complex scenarios. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the present invention proposes a multiphase flow numerical solution method for coupled phase change component transport in view of the heat and mass transfer of multiphase fluid phase change that is prevalent in the fields of industrial production and scientific research. In view of the closely coupled characteristics of heat transfer, mass transfer and flow process in multiphase flow problems, the calculation of interphase transfer rate, multicomponent diffusion, thermal diffusion and drag is placed before the solution steps of component equations and momentum equations, and these calculations are embedded in the estimation-correction iteration loop to ensure the consistency and accuracy of the calculation. Furthermore, before solving the algebraic equations related to velocity, pressure and temperature, the diffusion coefficient is updated to reflect the latest changes in the fluid state. It is particularly critical that the coupling mechanism of phase change and component transport is realized in the following way: in the estimation-correction iteration framework based on pressure-velocity correction, the latest density, temperature and mass fraction information of each component are used, and according to the specific algorithm of the phase change component transport model, the mass transfer intensity coefficient between each component, the volume fraction of the phase, the state of the phase, the mass transfer rate between the phases, and the multicomponent diffusion effect, thermal diffusion behavior and drag effect in the solution process are accurately calculated. Subsequently, these calculation results are used to analyze the phase change and component coupling processes to update the component volume fractions and temperature distribution, thereby constructing a bidirectionally coupled and highly coordinated solution algorithm.

[0005] The present invention solves the problem of difficult coupling of temperature-density-mass transfer rate-pressure-velocity under multiphase flow and multicomponent, avoids the instability or divergence phenomenon under such strong coupling calculation, can visualize parameters, can freely modify and add source terms and expand the model, and improves the turbulence of the fluid after phase change and the pulsating interaction of the phase interface. The present invention can assimilate real-time observation data with simulation results, dynamically adjust model parameters to make it closer to the actual situation, reduce the deviation between simulation results and actual situation, and expand the accuracy and application scenarios of phase change transport models. The present invention has the characteristics of high flexibility, scalability, easy convergence, and flexibility in improving the interphase mass and heat transfer mechanism, so as to achieve more accurate simulation.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A multiphase flow numerical solution method for coupled phase change component transport includes the following steps:

[0008] Step 1: Establish the unsteady, viscous, incompressible multi-dimensional Navier-Stokes governing equations;

[0009] Step 2: Establish a phase change model, and use the phase change model to determine the volume fraction of the phase, the state of the phase, the mass transfer intensity coefficient, the evaporation coefficient, the condensation coefficient, the interphase mass transfer rate, and the saturation temperature;

[0010] Step 3: The multidimensional Navier-Stokes control equations of step 1 and the phase change model of step 2 constitute a multidimensional coupled phase change component transport multiphase flow mathematical model. Combined with the initial conditions, boundary conditions and grid division, the multidimensional coupled phase change component transport multiphase flow mathematical model is numerically discretized to obtain a group of algebraic equations about density, velocity, component, temperature, phase volume fraction, diffusion coefficient, density, Schmidt number and interphase mass transfer rate, and the algebraic equations are linearized.

[0011] Step 4: Perform pressure-velocity bidirectional correction solution. The calculation of evaporation coefficient, condensation coefficient, mass transfer intensity coefficient, saturation temperature, latent heat, and net mass transfer rate is located before the construction of the multidimensional coupled phase change component transport multiphase flow mathematical model, and the estimation-correction iterative algorithm is used for multiple cycles to ensure convergence; before solving the multidimensional coupled phase change component transport multiphase flow mathematical model, the surface tension coefficient, density, dynamic viscosity, velocity, pressure, interface heat transfer source term, mass transfer intensity coefficient, phase volume fraction, and net mass transfer rate are updated.

[0012] The beneficial effects of the present invention compared with the prior art are:

[0013] 1. The present invention couples the phase change model with the component transport model into the Navier-Stokes equations, and establishes a multiphase flow mathematical model for coupled phase change component transport;

[0014] 2. The present invention adopts a step-by-step solution strategy, first solving the phase change process, and then adding the mass transfer rate as a source term to the component transport for solution, thereby reducing the difficulty of coupled solution and ensuring the accuracy of the calculation;

[0015] 3. The present invention can calculate heterogeneous or homogeneous materials such as multi-component, multi-phase, high temperature, low temperature, etc. by calibrating the phase change transport model parameters of evaporation coefficient, condensation coefficient, mass transfer intensity coefficient, diffusion coefficient (multi-component diffusion coefficient and thermal diffusion coefficient), surface tension coefficient and slip velocity;

[0016] 4. The present invention improves the turbulence of the fluid after phase change and the pulsating interaction of the phase interface, and expands the accuracy and application scenarios of the phase change transport model;

[0017] 5. The present invention realizes the coupling of phase change model and component transport, solves the problem of difficult coupling of temperature-density-mass transfer rate-pressure-velocity under multiphase flow and multicomponent, and avoids the instability or divergence under such strong coupling calculation.

[0018] In summary, the present invention can be used to simulate complex multiphase flow processes, predict flow behavior and transmission characteristics, and provide a more efficient and accurate simulation tool for industrial production and scientific research. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A flowchart of a multiphase flow numerical solution method for coupled phase change component transport according to the present invention;

[0020] Figure 2 Schematic diagram of phase change at the interface of the embodiment;

[0021] Figure 3 It is a geometric structure grid distribution diagram in the embodiment;

[0022] Figure 4 It is a schematic diagram of the force on the surface microelement;

[0023] Figure 5 Graph showing the distribution of hydrogen concentration of components in the embodiment. DETAILED DESCRIPTION

[0024] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and carefully in conjunction with the embodiments below, but the protection scope of the present invention is not limited to the following specific embodiments.

[0025] The present invention couples the phase change component transport model with the pressure correction method under the framework of the finite volume method, realizes the numerical solution of multiphase flow, and can handle the numerical simulation of unsteady, viscous, incompressible, and multi-dimensional multiphase flow.

[0026] like Figure 1 As shown, a multiphase flow numerical solution method for coupled phase change component transport of the present invention comprises the following steps:

[0027] Step 1: Establish the unsteady, viscous, incompressible multi-dimensional Navier-Stokes governing equations;

[0028] Step 2: Establish a phase change model, and use the phase change model to determine the volume fraction of the phase, the state of the phase, the mass transfer intensity coefficient, the evaporation coefficient, the condensation coefficient, the interphase mass transfer rate, and the saturation temperature;

[0029] Step 3: The multidimensional Navier-Stokes control equations of step 1 and the phase change model of step 2 constitute a multidimensional coupled phase change component transport multiphase flow mathematical model. Combined with initial conditions, boundary conditions and grid division, the multidimensional coupled phase change component transport multiphase flow mathematical model is numerically discretized to obtain a group of algebraic equations about density, velocity, component, temperature, phase volume fraction, diffusion coefficient, density, Schmidt number and interphase mass transfer rate, and the algebraic equations are linearized.

[0030] Step 4: perform pressure-velocity bidirectional correction solution; among them, the calculation of evaporation coefficient, condensation coefficient, mass transfer intensity coefficient, saturation temperature, latent heat, and net mass transfer rate is located before the construction of the multidimensional coupled phase change component transport multiphase flow mathematical model, and they are all cycled multiple times within the estimation-correction iterative algorithm to ensure convergence; in addition, the surface tension coefficient, density, dynamic viscosity, velocity, pressure, interface heat transfer source term, mass transfer intensity coefficient, phase volume fraction, and net mass transfer rate are updated before the multidimensional coupled phase change component transport multiphase flow mathematical model is solved.

[0031] Through the above four steps, a numerical solution method for multiphase flow with coupled phase change component transport is established.

[0032] Specifically, the multi-dimensional coupled phase change component transport multiphase flow mathematical model includes the following sub-models:

[0033] (I) The unsteady, viscous, incompressible multidimensional Navier-Stokes governing equations, which include density equations, velocity equations, component transport equations, mass equations, constitutive equations, and incompressible ideal gas state equations. The multidimensional Navier-Stokes equations reflect the basic laws of flow, heat, and mass transfer problems.

[0034] (ii) Phase change model, which is used to solve the component state and phase volume fraction between multiple phases. It can be used to simulate multiphase flow in which each phase moves at different speeds, but assumes local equilibrium on a short spatial length scale. By referring to the slip velocity, each phase can effectively move at different speeds. It can also be used to simulate a homogeneous multiphase model in which there is strong coupling and each phase moves at the same speed. Each phase (gas phase) can be simulated by solving the momentum, continuity and energy equations of the mixture, the volume fraction equation of the minor phase, and the algebraic expression of the relative velocity. , Liquid Phase or solid phase ). Control the volume fraction of each phase and , can take any value between 0 and 1, depending on the gas phase , Liquid Phase or solid phase The continuity equation of the mixture, the momentum equation of the mixture, the energy equation of the mixture, and the volume fraction equation of the minor phase are solved, and the algebraic expression of the relative velocity (if the phases move at different speeds) is also included. It has the advantages of accurate calculation, high efficiency, and saving of computing resources, and can well reproduce the main characteristics of evaporation and condensation.

[0035] The phase change model assumes that the mixture has 6 components, namely the first liquid phase, the second liquid phase, the first gas phase, the second gas phase, the third gas phase and the first solid phase. These 6 components are solved based on the mathematical model of the basic physical laws such as conservation of mass, conservation of momentum and conservation of energy, as well as physical parameters including saturation temperature, latent heat, interphase mass transfer rate, evaporation coefficient, condensation coefficient, etc. These parameters and equations together describe the changes in fluid mass, momentum and energy during the phase change process. For example, when simulating the boiling process, the first liquid phase is in a static equilibrium state at the beginning, with a uniform temperature distribution and specific components and volume fractions, while the volume fraction of the first gas phase is almost zero. When the saturation temperature is reached, the first liquid phase can be transformed into the first gas phase.

[0036] (III) Pressure-velocity equation: The pressure equation is derived from the continuity equation and the momentum equation. The pressure equation is derived from the density equation, the velocity equation and the ideal gas state equation. It is a transport equation about the pressure variable. Solving the pressure equation can obtain the latest pressure field. Since the pressure equation is corrected and updated so that the velocity field meets the continuity condition, it is ensured that the simulation of the flow field satisfies the conservation of mass and momentum at the same time. The present invention takes into account the change of density when deriving the pressure-velocity equation, so it can realize the numerical solution of multiphase flow.

[0037] In the step 3, when solving the numerical discretization process of the multi-phase flow mathematical model of multi-dimensional coupled phase change component transport, it is first necessary to clarify the initial conditions, boundary conditions and details of the grid division. The initial conditions set the spatial distribution state of each physical field (such as density, velocity, component, phase volume fraction, temperature and pressure) at the beginning of the simulation. The boundary conditions define the physical behavior at the edge of the model calculation domain, including velocity, temperature, pressure, component, phase volume fraction and dynamic behavior of the phase interface. Meshing is the process of discretizing the continuous calculation domain into a series of finite-sized, interconnected units such as hexahedrons, tetrahedrons, etc. The quality of the grid (such as density, orthogonality, smoothness) directly affects the accuracy and computational efficiency of the numerical solution. For multi-dimensional coupled phase change component transport problems, fine grids are usually required to capture subtle changes in the phase interface and rapidly changing regions of the component volume fraction. In addition, adaptive grids can also be used to dynamically adjust the grid density when necessary to improve the calculation accuracy.

[0038] Based on the above initial conditions, boundary conditions and grid division, the multi-dimensional coupled phase change component transport multiphase flow mathematical model is numerically discretized. This process usually involves converting continuous physical fields (such as density ,speed , components , phase volume fraction , net mass transfer rate ,temperature , dynamic viscosity , surface tension coefficient , diffusion coefficient and pressure ) are converted into numerical solutions at discrete points through the finite volume method, and a set of algebraic equations about these physical quantities are established on each grid element.

[0039] In the step 4, when constructing a multi-dimensional coupled phase change component transport multiphase flow model, a core step is to add the phase change model as a source term into the component transport equation through a mathematical equation. This process requires not only accurate evaporation coefficient, condensation coefficient and mass transfer intensity coefficient, but also careful consideration of the dynamic changes of net mass transfer rate and latent heat of evaporation. The calculation of these parameters needs to be placed in the solution process of component transport equation and energy equation in advance to ensure the logical coherence and accuracy of the physical process. In order to achieve this goal, the present invention designs an efficient prediction-correction iterative framework (such as pressure-velocity coupling iteration). Within this framework, the calculation of mass transfer intensity coefficient, determination of saturation temperature and estimation of latent heat of evaporation are all placed at the core of the iterative loop, and multiple iterations are performed until the preset convergence standard is reached. This multiple-cycle mechanism ensures the accuracy of the description of the phase change process, so that the model can capture the complex and subtle physical changes near the phase interface. At the same time, in order to further improve the accuracy of the numerical solution, a series of key parameters will be updated before solving the algebraic equations of key physical quantities such as velocity, component and temperature. These parameters include but are not limited to density (affected by temperature, pressure and phase change), multi-component diffusion coefficient (reflecting the strength of interaction between different components), thermal diffusion coefficient (describing the ability of heat to propagate in a medium) and phase volume fraction (directly reflecting the proportion of each phase in space). The real-time update of these parameters ensures that the physical parameters used to solve the algebraic equations are the latest and most accurate, thereby improving the stability and reliability of the entire numerical model. By tightly coupling the phase change model with the component transport equation, and performing multiple cycles within the estimation-correction iteration to ensure convergence, and updating the relevant parameters before solving the key physical quantities, a numerical model that can accurately describe the multi-dimensional coupled phase change component transport multiphase flow process is constructed.

[0040] Specifically, the step 4 includes:

[0041] Step 1: Accurately set the global time step to ensure steady progress and iterative convergence of the simulation. This time step is carefully considered after the phase change time step and the convection time step, and a smaller time step is taken to accurately capture the heat transfer and flow process.

[0042] Step 2: Discretize the complex partial differential equations in the momentum equation, continuity equation, and energy equation using the finite volume method. Integrate the conservation equations in each control volume to obtain discretized algebraic equations that can be solved iteratively.

[0043] Step 3: By solving the continuity equation and momentum equation, and combining the state equation to update the density value, the density change is expressed. Specifically, by iteratively solving these equations, the velocity field and pressure field of the fluid can be obtained.

[0044] Step 4: The temperature equation is a key variable in the energy solution equation. It participates in the calculation together with the phase change model. The temperature equation is discretized in space and time to form a series of algebraic equations. The discretized nonlinear equations are linearized, and the distribution of the temperature field is obtained by iteratively solving the linearized algebraic equations.

[0045] Step 5. Solve the multiphase mass transfer rate, component state and phase volume fraction based on the phase change model. It can be solved by the momentum, continuity and energy equations of the mixture, as well as physical parameters such as saturation temperature, latent heat, interphase mass transfer rate, mass transfer intensity coefficient, evaporation coefficient, condensation coefficient, etc. The volume fraction equation of the secondary phase and the algebraic expression of the relative velocity are used to simulate each phase (gas phase, liquid phase or solid phase). These parameters and equations together describe the changes in fluid mass, momentum and energy during the phase change process.

[0046] Step 6. Add the mass transfer rates of different phases and components as source terms to the multi-dimensional coupled phase change component transport multiphase flow mathematical model, solve it after discretization, introduce the interphase action model (such as the Syamlal-O'Brien model, the Wen-Yu model and the Gidaspow model) for the different drag forces between phase momentum, and obtain the multi-component field of different phases.

[0047] Step 7: Perform an iterative solution through pressure-velocity coupling to solve the pressure term in the discretized momentum equation, correct the pressure field through the continuity equation, and solve the momentum equation again to update the velocity field.

[0048] Step 8: Solve the problem through repeated iterations until the convergence criterion is met or the maximum number of prediction-correction iterations is reached.

[0049] Step 9: Determine whether convergence is reached (the residual value is below the set threshold or the monitored physical quantity no longer changes significantly) or the maximum number of estimation-correction iterations is reached, otherwise repeat steps 1 to 8.

[0050] Step 10: Update the volume fraction of each phase component.

[0051] Step 11: Determine whether the specified end time has been reached, otherwise repeat steps 1 to 10.

[0052] In the above process, the algebraic equations are first linearized. In this process, the coefficients in the algebraic equations are all the latest available values, aiming to effectively improve the convergence speed of the calculation. In view of the close coupling characteristics of heat transfer, mass transfer and flow process in multiphase flow problems, the present invention particularly places the calculation of interphase mass transfer rate, multi-component diffusion, thermal diffusion and drag before the solution steps of component equations and momentum equations, and these calculations are embedded in the estimation-correction iterative loop to ensure the consistency and accuracy of the calculation. Furthermore, before solving the algebraic equations related to velocity, pressure and temperature, the present invention updates the diffusion coefficient in time to reflect the latest changes in the fluid state. It is particularly critical that the coupling mechanism of phase change and component transport is realized in the following way: in the estimation-correction iterative framework based on pressure-velocity correction, using the latest density, temperature and mass fraction information of each component, according to the specific algorithm of the phase change component transport model, the mass transfer intensity coefficient between each component, the volume fraction of the phase, the state of the phase, the interphase mass transfer rate and the multi-component diffusion effect, thermal diffusion behavior and drag effect in the solution process are accurately calculated. Subsequently, these calculation results are used to analyze the phase change and component coupling processes to update the component volume fractions and temperature distribution, thereby constructing a bidirectionally coupled and highly coordinated solution algorithm.

[0053] Example

[0054] This example uses liquid hydrogen evaporation as the background for numerical calculation. Since liquid hydrogen has an extremely low temperature, it will quickly undergo a phase change and evaporate into hydrogen in the air, accompanied by the condensation of various components in the air (such as water vapor, nitrogen, and oxygen). At this time, the flow field formed is a complex mixture containing multiple phases and components.

[0055] This embodiment includes the following steps:

[0056] In step 1, the unsteady, viscous, incompressible multidimensional Navier-Stokes governing equations are established, where the general form of the governing equations is:

[0057] ;

[0058] in, is the density, is a universal variable, is the generalized diffusion coefficient, is the generalized source term, represents a velocity vector or tensor; Represents time, represents the divergence operator. The common variables are the variables to be determined, including components, temperature, density, velocity and pressure. The generalized diffusion coefficient includes dynamic viscosity, multi-component diffusion coefficient and thermal diffusion coefficient. The generalized source terms include heat transfer source terms and mass transfer rate source terms.

[0059] In step 2, a phase change model is established, and the volume fraction of the phase, the state of the phase, the mass transfer intensity coefficient, the evaporation coefficient, the condensation coefficient, the interphase mass transfer rate, and the saturation temperature are determined using the phase change model;

[0060] ;

[0061] ;

[0062] in, is the mass transfer rate from the condensed phase to the evaporated phase, is the condensation phase mass transfer intensity coefficient, is the volume fraction of the condensed phase, is the density of the condensed phase, is the condensation phase temperature, is the evaporation phase temperature, is the saturation temperature, is the mass transfer rate from the evaporating phase to the condensing phase, is the mass transfer intensity coefficient of the evaporation phase, is the volume fraction of the evaporated phase, is the density of the evaporated phase.

[0063] Figure 2 The schematic diagram of phase change at the interface of the embodiment is shown in FIG. The evaporation-condensation interface is the contact surface between the evaporation phase and the condensation phase. At the interface, the molecules of the evaporation phase and the condensation phase will exchange and interact with each other, resulting in various interface phenomena, such as surface tension and diffusion. The phase change at the evaporation-condensation interface is a complex and important physical process, which involves many aspects such as molecular motion, interface equilibrium, and heat transfer. Figure 2 As shown, the nature and process of phase change can be understood more intuitively. The upper part is the evaporation phase, and the lower part is the condensation phase. The condensation phase surface is represented by wavy lines to highlight the irregularity of the surface. , the arrow will point from the condensed phase surface to the evaporating phase, indicating the evaporation process of molecules escaping from the condensed phase into the evaporating phase. , the arrow will point from the surface of the evaporating phase to the condensing phase, indicating the condensation process of molecules from the evaporating phase into the condensing phase.

[0064] In step 3, the algebraic equations are linearized, including:

[0065] ;

[0066] in, It is a component The mass fraction in the evaporating phase, represents the velocity vector or tensor of the evaporating phase, It is a component The diffusion coefficient in the evaporating phase, is the turbulent viscosity, is the turbulent Schmidt number. is the rate generated from the dispersed phase plus the custom source term, is the thermal diffusivity, is the temperature, It is a component The mass transfer rate from the condensed phase to the evaporated phase, It is a component The mass transfer rate from the evaporating phase to the condensing phase, is the rate of a heterogeneous reaction.

[0067] Build a 3D geometric model and divide it into structured meshes. First, define the geometric model, including vertex coordinates, block definitions, mesh size divisions, and boundaries. Determine the coordinates of the geometric structure points. Then, generate faces through a series of points, and then generate mesh cells from these faces. Meshing is a crucial step in CFD (computational fluid dynamics) simulation, which directly affects the accuracy and efficiency of subsequent calculation results. Figure 3 This is the geometric structure grid distribution diagram in the embodiment. This embodiment performs grid division and generates a hexahedral calculation grid in a block manner. Adjust the parameters in the file to control the size, shape distribution and boundary type of the grid. Finally, the connection relationship of the grid is determined based on the subordinate adjacent relationship between the face and the grid unit. Figure 3 As shown, the grid division is regular and evenly distributed with clear boundaries.

[0068] Set initial parameters, boundary conditions and physical parameters. Set the liquid hydrogen leakage rate to 1 kg / s, define the boundaries with the custom boundary names in the grid definition file, and set the front, back, left, right, bottom, top and inlet interfaces. Set the physical parameters (density, viscosity, thermal conductivity, specific heat capacity, molar molecular mass, Prandtl number, etc.) of liquid hydrogen, hydrogen, water vapor, nitrogen and oxygen.

[0069] In step 4, the pressure-velocity bidirectional correction solution is performed, including:

[0070] like Figure 4 As shown in the figure, it is a schematic diagram of the force on the surface microelement, which shows in detail the force on the surface microelement at the interface between the two phases. In the surface environment, the surface tension of the fluid and the pressure difference ( ) reaches equilibrium.

[0071] ;

[0072] ;

[0073] in, is the surface tension, is the surface tension coefficient, is the normal vector, and They represent the side lengths of the surface elements, is the area of ​​the surface element, is the pressure drop, and are the pressures on both sides of the interface, and are the two radii of the surface element respectively.

[0074] Figure 4 It can be concluded that, assuming that the direction of the pressure drop is downward, the direction of the interfacial tension is correspondingly upward. The pressure drop at this interface is mainly affected by the surface tension and the curvature of the surface.

[0075] ;

[0076] in, is the volume fraction, is the normalized velocity vector, Net mass transfer rate.

[0077] ;

[0078] in, is the density, is the correction pressure, It's pressure. is the acceleration due to gravity, is the position vector of the mesh cell body center.

[0079] ;

[0080] ;

[0081] ;

[0082] ;

[0083] in, It represents the first Mutually, represents the number of phases in the multiphase. yes The volume fraction of the phase, is the dynamic viscosity, yes The dynamic viscosity of the phase, is the interface heat transfer source term, It is latent heat.

[0084] ;

[0085] ;

[0086] in, is the condensation coefficient, is the evaporation coefficient. is the molar mass, is the universal gas constant (8.314 ).

[0087] The above steps 1 to 11 are performed. Finally, a hydrogen component concentration distribution diagram of the flow field is calculated based on this embodiment.

[0088] Figure 5 The hydrogen concentration distribution diagram of the components in the embodiment is a complex multiphase flow process. The hydrogen concentration distribution diagram after the evaporation of liquid hydrogen can be simulated by the numerical solution method of the present invention. Figure 5 As shown in the figure, the continuous heat exchange between liquid hydrogen and the surrounding environment will quickly cause phase change and evaporate into hydrogen. The hydrogen cloud will continue to mix with the surrounding air. The diffusion of the hydrogen cloud is mainly affected by gravity and natural convection driven by the density difference between hydrogen and air. As the hydrogen cloud diffuses, a clear concentration gradient is formed.

[0089] Parts of the present invention that are not disclosed in detail belong to the common knowledge in the art.

[0090] Although the above describes the illustrative specific embodiments of the present invention to facilitate those skilled in the art to understand the present invention, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. A method for numerical solution of multiphase flow with coupled phase change component transport, characterized in that: The steps include: Step 1: Establish the unsteady, viscous, incompressible multi-dimensional Navier-Stokes governing equations; Step 2: Establish a phase change model, and use the phase change model to determine the volume fraction of the phase, the state of the phase, the mass transfer intensity coefficient, the evaporation coefficient, the condensation coefficient, the interphase mass transfer rate, and the saturation temperature; Step 3: The multidimensional Navier-Stokes control equations of step 1 and the phase change model of step 2 constitute a multidimensional coupled phase change component transport multiphase flow mathematical model. Combined with the initial conditions, boundary conditions and grid division, the multidimensional coupled phase change component transport multiphase flow mathematical model is numerically discretized to obtain a group of algebraic equations about density, velocity, component, temperature, phase volume fraction, diffusion coefficient, density, Schmidt number and interphase mass transfer rate, and the algebraic equations are linearized. Step 4: Perform pressure-velocity bidirectional correction solution. The calculation of evaporation coefficient, condensation coefficient, mass transfer intensity coefficient, saturation temperature, latent heat, and net mass transfer rate is located before the construction of the multidimensional coupled phase change component transport multiphase flow mathematical model, and the estimation-correction iterative algorithm is used for multiple cycles to ensure convergence; before solving the multidimensional coupled phase change component transport multiphase flow mathematical model, the surface tension coefficient, density, dynamic viscosity, velocity, pressure, interface heat transfer source term, mass transfer intensity coefficient, phase volume fraction, and net mass transfer rate are updated.

2. A multiphase flow numerical solution method for coupled phase change component transport according to claim 1, characterized in that: In the step 2, the phase change model is solved to calculate the multi-phase component state, interphase mass transfer rate and phase volume fraction according to the mass transfer intensity coefficient, evaporation coefficient, condensation coefficient, saturation temperature and fluid temperature.

3. A multiphase flow numerical solution method for coupled phase change component transport according to claim 1, characterized in that: In step 3, the multi-dimensional coupled phase change component transport multiphase flow mathematical model is: ； in, is the density of the evaporated phase, is the volume fraction of the evaporated phase, It is a component The mass fraction in the evaporating phase, represents the velocity vector or tensor of the evaporating phase, It is a component The diffusion coefficient in the evaporating phase, is the turbulent viscosity, is the turbulent Schmidt number; is the rate generated from the dispersed phase plus the custom source term, is the thermal diffusivity, is the temperature, It is a component The mass transfer rate from the condensed phase to the evaporated phase, It is a component The mass transfer rate from the evaporating phase to the condensing phase, is the heterogeneous reaction rate; Represents the divergence operator.

4. A multiphase flow numerical solution method for coupled phase change component transport according to claim 1, characterized in that: The fourth step comprises: Step 1: Accurately set the global time step; Step 2: discretize the momentum equation, continuity equation, and energy equation by using the finite volume method to obtain a set of algebraic equations to be solved iteratively; Step 3, solve the continuity equation and momentum equation, and update the density value in combination with the state equation to obtain the velocity field and pressure field of the fluid; Step 4: discretize the temperature equation in space and time to form a nonlinear equation; linearize the discretized nonlinear equation to obtain a linearized algebraic equation group; iteratively solve the linearized algebraic equation group to obtain the distribution of the temperature field; Step 5, solving the mass transfer rate, component state and phase volume fraction between multiple phases according to the phase change model; Step 6: Add the mass transfer rates of different phases and different components as source terms to the multi-dimensional coupled phase change component transport multiphase flow mathematical model, solve it after discretization, introduce the interphase action model for different drag forces of interphase momentum, and obtain the multi-component field of different phases; Step 7: Perform an iterative solution through pressure-velocity coupling to solve the pressure term in the discretized momentum equation, correct the pressure field through the continuity equation, and solve the momentum equation again to update the velocity field; Step 8, solving by repeated iterations until the convergence criterion is met or the maximum number of estimation-correction iterations is reached; Step 9: Determine whether convergence is reached, that is, the residual value reaches below the set threshold or the monitored physical quantity no longer changes significantly or reaches the maximum number of estimation-correction iterations, otherwise repeat steps 1 to 8; Step 10, updating the volume fraction of each phase component; Step 11: Determine whether the specified end time has been reached, otherwise repeat steps 1 to 10.

5. A multiphase flow numerical solution method for coupled phase change component transport according to claim 4, characterized in that: The solution in step 5 is achieved through the momentum equation, continuity equation and energy equation of the mixture as well as saturation temperature, latent heat, interphase mass transfer rate, mass transfer intensity coefficient, evaporation coefficient and condensation coefficient.

6. A multiphase flow numerical solution method for coupled phase change component transport according to claim 4, characterized in that: In step 6, the coupling mechanism of the multi-dimensional coupled phase change component transport multiphase flow mathematical model is realized in the following way: using the latest density, temperature and mass fraction of each component, according to the algorithm of the phase change component transport model and the multi-component diffusion effect, thermal diffusion behavior and drag influence in the solution process, the component volume fraction and temperature distribution are updated, and a bidirectional coupling and highly coordinated solution algorithm is constructed within the estimation-correction iterative framework based on pressure-velocity correction.

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