A numerical simulation method for filtering and purifying liquid metal impurities

Abstract

The application discloses a liquid metal impurity filtering and purifying numerical simulation calculation method, which comprises the following steps: establishing a geometric model of a hierarchical filtering screen fluid flow calculation domain; performing mesh division on the geometric model of the hierarchical filtering screen fluid flow calculation domain; calculating impurity particle force through an impurity particle force calculation model of liquid metal; calculating momentum convergence of the hierarchical filtering screen fluid flow calculation domain mesh, and obtaining fluid flow distribution in the hierarchical filtering screen fluid flow calculation domain; performing impurity particle contact and collision calculation according to an impurity particle contact calculation model of liquid metal; judging an impurity particle filtering state according to a screen boundary and an impurity particle motion state, and updating the calculation of the impurity particle distribution. The method can realize simultaneous simulation of important variables in the liquid metal impurity filtering and purifying process, and can provide accurate calculation data for liquid metal purification engineering design and filter model design in a liquid metal reactor.

Description

Technical Field

[0001] This invention belongs to the field of nuclear reactor thermal-hydraulic calculation technology, specifically relating to a numerical simulation calculation method for filtering and purifying liquid metal impurities. Background Technology

[0002] Filtration is one of the most suitable processes for purifying liquid metal coolants. During the circulation of liquid metal, undesirable impurities are continuously generated. Filtering these impurities helps maintain the liquid metal's good flow and heat transfer characteristics and reduces their adverse effects on the flow channels. Furthermore, impurity products formed in the liquid metal reactor can increase filter head loss, which must be considered in the performance evaluation and downstream effect analysis of liquid metal filters. Liquid metal filtration is a liquid-solid two-phase flow phenomenon, and its efficiency depends on numerous parameters, constants, or variables during operation. Simultaneously, the properties of the liquid metal (viscosity, density) and operating parameters (flow conditions, flow rate, temperature, pressure drop) influence the design of the filtration unit.

[0003] Due to the complexity of two-phase flows and limitations of experimental methods, research in this area has primarily focused on dilute phase flows with low particle concentrations. However, actual two-phase flows often involve high particle volume concentrations, especially in liquid metals due to their unique physicochemical properties, making it difficult to achieve satisfactory experimental results. Numerical simulation methods can simulate high-concentration solid-liquid two-phase flows, simulating impurity accumulation and clogging during impurity filtration and purification processes. Furthermore, it overcomes the drawback of long experimental cycles, making it a primary tool for studying two-phase flows and crucial for the purification engineering design and filter model design of liquid metal reactors. Summary of the Invention

[0004] In order to overcome the problems existing in the prior art, the purpose of this invention is to provide a numerical simulation calculation method for the filtration and purification of liquid metal impurities. This method can use computational fluid dynamics and discrete element methods to perform coupled calculations on the flow and heat transfer purification process of liquid metal in a graded filter screen and the filtration process of impurities in the graded filter screen.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] The method of this invention uses soft-sphere contact theory and collision model from computational fluid dynamics software and discrete element method software to simulate the filtration and purification phenomenon of liquid metal impurities. It calculates the forces acting on liquid metal impurity particles in a graded filter screen using a force calculation model for impurity particles. Based on these forces, it calculates the motion state of contact and collision between liquid metal impurity particles in the graded filter screen using a particle contact model. Simultaneously, it adds a momentum sink to the fluid flow calculation domain of the graded filter screen to calculate the flow distribution of liquid metal in the screen, thereby simulating the filtration and purification process of liquid metal impurities.

[0007] A numerical simulation calculation method for filtering and purifying liquid metal impurities includes the following steps:

[0008] Step 1: Establish the geometric model of the computational domain for fluid flow in the graded filtration screen for liquid metal impurities. This model includes three computational domain models for fluid flow in single-layer filter screens of the same size but different pore diameters. The specific steps are as follows:

[0009] Step 1-1: Use geometric modeling software to build the geometric model of the fluid flow calculation domain of the single-layer filter screen. Obtain the fluid flow channels before and after the single-layer filter screen through stretching. Considering the fluid flow channels at the filter holes of the single-layer filter screen, they are obtained by stretching according to the hole size. Combine the fluid flow channels before and after the single-layer filter screen to obtain the geometric model of the fluid flow calculation domain of the single-layer filter screen.

[0010] Step 1-2: Considering that liquid metal uses multi-layer filter screens to filter and purify impurities, in order to simplify the calculation, repeat step 1-1 to construct geometric models of the fluid flow calculation domain of single-layer filter screens with the same size but different pore sizes. By combining and connecting the geometric models of the fluid flow calculation domains of single-layer filter screens with different pore sizes, a geometric model of the fluid flow calculation domain of the graded filter screen is formed.

[0011] Step 2: Based on the geometric model of the computational domain of the graded filter screen fluid flow obtained in Step 1, mesh generation is performed. Specifically, structured mesh generation is performed using mesh generation software, the mesh at the filter screen pores is densified, the number of boundary layers of the wall mesh and the height of the first layer of the wall mesh are set, and the mesh model of the computational domain of the graded filter screen fluid flow is obtained.

[0012] Step 3: Perform basic physical field calculations for liquid metal within the mesh model of the fluid flow computational domain of the graded filter screen. Using the force calculation model for impurity particles in the liquid metal, calculate the forces acting on impurity particles within the fluid flow computational domain of the graded filter screen. The specific steps are as follows:

[0013] Step 3-1: Based on the calculation conditions, set the liquid metal temperature and velocity at the inlet of the fluid flow calculation domain of the staged filter screen, and the pressure at the outlet of the fluid domain; set the material properties, particle size, placement location, and rate of impurity particles; set the wall boundary conditions and material properties;

[0014] Step 3-2: Solve the mass, momentum, and energy equations for the liquid metal to obtain the velocity and temperature fields of the computational domain for the fluid flow in the staged filter screen. Considering the influence of impurity particles, an additional volume fraction term ε is added to the conservation equations. The mass and momentum conservation equations for the liquid metal are calculated as follows:

[0015]

[0016]

[0017] in:

[0018] ρ—fluid density, kg / m³ 3 ;

[0019] t — time, s;

[0020] u—fluid velocity, m / s;

[0021] g — acceleration due to gravity, m / s² 2 ;

[0022] μ—dynamic viscosity, Pa·s;

[0023] S – Momentum sink;

[0024] Step 3-3: Based on the velocity field and temperature field of the fluid flow calculation domain inside the fuel assembly, the distribution of impurity particles in the fluid flow calculation domain of the staged filter screen is calculated by using the force calculation model of impurity particles in liquid metal. Specifically, combining the fluid parameters and impurity particle motion parameters from the fluid flow calculation domain inside the fuel assembly, the free flow resistance of the impurity particles is calculated by the resistance calculation model, i.e., formula (3). At the same time, considering the lift generated by the impurity particles in the fluid, the lift of the impurity particles is calculated by combining the lift calculation model, i.e., formulas (4) and (5), with the fluid parameters. The force calculation model of the impurity particles is as follows:

[0025] F D =0.5C D ρA|ν f -ν p |(ν f -ν p (3)

[0026]

[0027]

[0028]

[0029]

[0030] in:

[0031] F D —Free flow resistance, N;

[0032] F saff — Saffmann lift, N;

[0033] F magn —Magnus lift, N;

[0034] C D —Free flow drag coefficient;

[0035] C L —Magnus lift-drag coefficient;

[0036] A – Projected area of ​​the particle, m 2 ;

[0037] Re – Reynolds number;

[0038] Re w —Rotational Reynolds number;

[0039] Re p —Particle Reynolds number;

[0040] ω c —The velocity gradient of the fluid;

[0041] ω p —The angular velocity of the particle;

[0042] d p —Particle size, in meters;

[0043] The forces acting on the impurity particles are solved by equations (1)-(5), and the displacement of the particles is obtained by Newton's second law. The forces acting on the impurity particles in the computational domain of the fluid flow of the graded filter screen are calculated.

[0044] Step 4: The force on the impurity particles calculated in Step 3 is used as the momentum sink in Equation (2) of Step 3-2. The fluid flow distribution in the calculation domain of the staged filter screen is calculated according to the momentum conservation equation:

[0045]

[0046] in:

[0047] V — Mesh cell volume, m3 ;

[0048] The momentum sink is the sum of the resistances of the fluid acting within the grid. By adding the momentum sink to the momentum conservation equation, the fluid flow distribution in the computational domain of the graded filter screen is calculated.

[0049] Step 5: Based on the fluid flow distribution in the calculation domain of the graded filter screen obtained in Step 4, add a liquid metal impurity particle contact calculation model, and perform impurity particle contact collision calculation within the fluid flow calculation domain of the graded filter screen. The specific steps are as follows:

[0050] Step 5-1: Represent the contact between particles and between particles and the boundary as vibrational motion, and perform calculations using the normal and tangential motion equations of the vibrational motion:

[0051]

[0052]

[0053]

[0054] in:

[0055] m i,j —Equivalent mass of particles i and j;

[0056] I i,j —Equivalent moment of inertia of particles i and j;

[0057] s — radius of rotation;

[0058] u n —The normal relative displacement of the particles;

[0059] u s —The relative tangential displacement of the particles;

[0060] θ — the rotation angle of the particle itself;

[0061] F n —The normal component of the external force acting on the particle;

[0062] F s —The tangential component of the external force acting on the particle;

[0063] M — the external torque acting on the particle;

[0064] K n —Normal elastic coefficient in the contact model;

[0065] K s —The tangential elastic coefficient in the contact model;

[0066] cn —Normal damping coefficient in the contact model;

[0067] c s —Tangential damping coefficient in the contact model;

[0068] Step 5-2: Considering the contact mode between impurity particles as soft particle contact, the forces and torques acting on the particles are calculated according to the liquid metal impurity particle contact calculation model as follows:

[0069]

[0070]

[0071] F t =-S t δ t (14)

[0072]

[0073] τ i =-μ r F n R i ω i (16)

[0074] in:

[0075] F n —Normal force;

[0076] F n d —Normal damping force;

[0077] F t — Tangential force;

[0078] F t d — Tangential damping force;

[0079] τ i —Torque of rolling friction contact surface;

[0080] E * —Equivalent Young's modulus

[0081] E i E j —Young's modulus of particle i and particle j;

[0082] ν i ν i —Poisson's ratio of particle i and particle j;

[0083] R * —Equivalent radius,

[0084] R i R j —Radii of particle i and particle j;

[0085] m * —Equivalent mass,

[0086] —The normal vector of the relative velocity;

[0087] β — coefficient

[0088] S n —Normal stiffness,

[0089] S t —Normal stiffness,

[0090] G * —Equivalent shear modulus,

[0091] G i G j —Particle shear modulus;

[0092] δ n —Normal overlap;

[0093] δ t —Tangential overlap;

[0094] μ r — Coefficient of rolling friction;

[0095] R i —The distance from the point of contact to the center of mass;

[0096] ω i —The unit angular velocity vector at the point of contact;

[0097] Based on the fluid flow distribution obtained in step 4, the collisions between impurity particles and between particles and boundaries within the fluid flow calculation domain of the graded filter screen are calculated. The motion state of the particles after contact and collision is calculated according to the liquid metal impurity particle contact calculation model and Newton's second law.

[0098] Step 6: Based on the particle contact calculation in the fluid flow calculation domain of the graded filter screen performed in Step 5, determine the filtration status of impurity particles and update the impurity particle distribution according to the filter screen boundary and the movement state of impurity particles. The specific steps are as follows:

[0099] Step 6-1: Based on the flow distribution and particle motion state in the fluid flow calculation domain of the graded filter screen, determine whether the impurity particles are in contact with the filter screen boundary. If they are in contact with the filter screen boundary, perform the impurity particle contact collision calculation in step 5 and update the motion state after the collision. If they are not in contact, they can directly pass through the filter screen to the next layer.

[0100] Step 6-2: Based on the distribution and movement of impurity particles, repeat step 6-1 to determine whether they have come into contact with the filter screen boundary. If the impurity particles pass through the first filter screen, they enter the next layer until all three filter screens have passed through. Otherwise, they will repeatedly collide in a certain layer until they accumulate and block the flow channel.

[0101] Step 6-3: Considering the special physical properties of liquid metal, it is necessary to select the corresponding thermophysical property relationship. Specifically, refer to the OECD / NEA to select the thermophysical property relationship of liquid metal. By continuously updating the flow distribution and impurity particle distribution information in the fluid flow calculation domain of the graded filter screen and judging the passage and accumulation of impurity particles, it is ensured that the heat transfer of liquid metal flow and impurity filtration and purification are consistent with the actual situation.

[0102] Preferably, the liquid metal is a liquid lead-bismuth alloy.

[0103] The present invention has the following beneficial effects:

[0104] 1) Since the method of the present invention calculates the force on the impurity particles by means of the force calculation model of the impurity particles in the fluid flow calculation domain of the graded filter screen based on the basic flow heat transfer physical field of liquid metal, and adds momentum sink to the momentum conservation equation to update the flow distribution of liquid metal accordingly; at the same time, it calculates the motion state of impurity particles after contact and collision according to the impurity particle contact calculation model, and updates the impurity particle distribution according to the filter screen boundary and the motion state of impurity particles, it can realize the coupled calculation of liquid metal impurity filtration and purification phenomenon and liquid metal flow heat transfer in the graded filter screen.

[0105] 2) Since the parameters of the impurity particle force calculation model and the impurity particle contact calculation model are independent in the method of the present invention, the coupling calculation method is simple and logical, and does not depend on the intermediate variables of the program calculation. Therefore, the model is independent, the method is highly versatile, and it can be adapted to different types of fluid dynamics calculation and analysis programs.

[0106] 3) Since the method of the present invention can simulate the filtration and purification process of impurities in liquid metal in a graded filter screen by calculation, and thus obtain the filtration state of impurity particles and the corresponding liquid metal flow distribution, the calculation method can simultaneously simulate various important variables in the impurity filtration and purification process, and can provide more accurate calculation data for purification engineering design and filter model design in liquid metal reactors. Attached Figure Description

[0107] Figure 1 The diagram shows a typical computational domain model for fluid flow in a liquid metal graded filter screen. (a), (b), and (c) are front views of the computational domains for fluid flow in single-layer filter screens with pore sizes of 500 μm, 300 μm, and 200 μm, respectively. (d) is a side view of the geometric model of the computational domains for fluid flow in single-layer filter screens with different pore sizes that are combined and connected.

[0108] Figure 2 A front view of the computational domain mesh for fluid flow in a graded filter screen.

[0109] Figure 3 This is a flowchart of the present invention. Detailed Implementation

[0110] The following combination Figure 3 The flowchart shown illustrates the calculation process of a typical liquid metal reactor staged filter screen, providing a more detailed description of the invention. The structure of the liquid metal reactor staged filter screen is also described below. Figure 1 As shown, the graded filter screen consists of three single-layer filter screens of the same size but different pore sizes. The pore sizes of the three filter screens are 500μm, 300μm and 200μm, respectively. A square with a side length of 5mm is selected as the cross-sectional size of the filter screen as a simplified calculation model.

[0111] This invention provides a numerical simulation calculation method for filtering and purifying liquid metal impurities, comprising the following steps:

[0112] Step 1: To perform numerical simulation calculations for the filtration and purification of liquid metal impurities, a geometric model of the computational domain for the fluid flow in the corresponding graded filter screen needs to be established first. For the flow of liquid metal in the graded filter screen, a geometric model of the computational domain for the fluid flow in the graded filter screen is established, representing the internal flow channels of the liquid metal within the filter screen. This model includes three computational domain models for the fluid flow of single-layer filter screens with the same size but different pore diameters. The specific steps are as follows:

[0113] Step 1-1: The liquid metal impurity filtration and purification device structure includes three filter screens with different pore sizes to intercept impurity particles and purify liquid metal. The flow channels of liquid metal in a single-layer filter screen include the front and back of the filter screen and the filter screen pores. First, it is necessary to construct the flow channels of the single-layer filter screen and then connect them in series according to the pore size to form a graded filter screen. Specifically, the fluid flow channels in front and back of the single-layer filter screen are obtained by stretching. Considering the fluid flow channels at the filter screen pores, they are obtained by stretching according to the pore size. By merging the front and back fluid flow channels, the geometric model of the fluid flow calculation domain of the single-layer filter screen can be obtained.

[0114] Steps 1-2: As Figure 1As shown in (a), (b), and (c), steps 1-1 are repeated to construct geometric models of the fluid flow computational domain for single-layer filter screens of the same size but different pore sizes. These geometric models are then combined and connected to form a geometric model of the fluid flow computational domain for a graded filter screen, as shown below. Figure 1 As shown in (d).

[0115] Step 2: Having obtained the geometric model of the computational domain for fluid flow in the graded filter screen in Step 1, it needs to be meshed to form a corresponding mesh model. Subsequent numerical simulations are based on this mesh model. Specifically, structured meshing is performed using meshing software, the mesh at the filter screen openings is refined, and the number of boundary layers and the height of the first layer on the wall are set to obtain the mesh model of the computational domain for fluid flow in the graded filter screen. Figure 2 As shown.

[0116] Step 3: After obtaining the mesh model of the fluid flow calculation domain of the graded filter screen in Step 2, basic physical field calculations can be performed on the liquid metal inside the graded filter screen. The basic physical fields provide the corresponding basic physical quantities such as temperature and flow velocity within the mesh of the fluid flow calculation domain of the graded filter screen. Substituting these basic physical quantities into the force calculation model of impurity particles in the liquid metal allows for the calculation of the forces acting on impurity particles within the fluid flow calculation domain of the graded filter screen. The specific steps are as follows:

[0117] Step 3-1: Based on the calculation conditions, set the liquid metal temperature and velocity at the inlet of the fluid flow calculation domain of the staged filter screen, and the pressure at the outlet of the fluid domain; set the material properties, particle size, placement location, and rate of impurity particles; set the wall boundary conditions and material properties;

[0118] Step 3-2: Solve the mass, momentum, and energy equations for the liquid metal to obtain the velocity and temperature fields of the computational domain for the fluid flow in the staged filter screen. Considering the influence of impurity particles, an additional volume fraction term ε is added to the conservation equations. The mass and momentum conservation equations for the liquid metal are calculated as follows:

[0119]

[0120]

[0121] in:

[0122] ρ—fluid density, kg / m³ 3 ;

[0123] t — time, s;

[0124] u—fluid velocity, m / s;

[0125] g — acceleration due to gravity, m / s² 2 ;

[0126] μ—dynamic viscosity, Pa·s;

[0127] S – Momentum sink;

[0128] Step 3-3: Based on the velocity field and temperature field of the fluid flow calculation domain inside the fuel assembly, the distribution of impurity particles in the fluid flow calculation domain of the staged filter screen is calculated by using the force calculation model of impurity particles in liquid metal. Specifically, combining the fluid parameters and impurity particle motion parameters from the fluid flow calculation domain inside the fuel assembly, the free flow resistance of the impurity particles is calculated by the resistance calculation model, i.e., formula (3). At the same time, considering the lift generated by the impurity particles in the fluid, the lift of the impurity particles is calculated by combining the lift calculation model, i.e., formulas (4) and (5), with the fluid parameters. The force calculation model of the impurity particles is as follows:

[0129] F D =0.5C D ρA|ν f -ν p |(ν f -ν p (3)

[0130]

[0131]

[0132]

[0133]

[0134] in:

[0135] F D —Free flow resistance, N;

[0136] F saff — Saffmann lift, N;

[0137] F magn —Magnus lift, N;

[0138] C D —Free flow drag coefficient;

[0139] Re – Reynolds number;

[0140] Re w —Rotational Reynolds number;

[0141] Re p —Particle Reynolds number;

[0142] ω c —The velocity gradient of the fluid;

[0143] ω p —The angular velocity of the particle;

[0144] d p —Particle size, in meters;

[0145] The forces acting on the impurity particles are solved by equations (1)-(5), and the displacement of the particles is obtained by Newton's second law. The forces acting on the impurity particles in the computational domain of the fluid flow of the graded filter screen are calculated.

[0146] Step 4: Based on the force on the impurity particles obtained in Step 3, the feedback influences the liquid metal flow in the calculation domain of the graded filter screen fluid flow, and the fluid flow distribution in the calculation domain of the graded filter screen fluid flow is calculated. Specifically, the force on the impurity particles calculated in Step 3 is used as the momentum sink in Equation (2) of Step 3-2, and the fluid flow distribution in the calculation domain of the graded filter screen fluid flow is calculated according to the momentum conservation equation:

[0147]

[0148] in:

[0149] V — Mesh cell volume, m 3 ;

[0150] The momentum sink is the sum of the resistances of the fluid acting within the grid. By adding the momentum sink to the momentum conservation equation, the fluid flow distribution in the computational domain of the graded filter screen is calculated.

[0151] Step 5: Based on the fluid flow distribution in the fluid flow calculation domain of the graded filter screen obtained in Step 4, in order to calculate and update the contact and collision motion of impurity particles in the fluid flow calculation domain of the graded filter screen, a liquid metal impurity particle contact calculation model is added. The contact and collision calculation of impurity particles is then performed in the fluid flow calculation domain of the graded filter screen. The specific steps are as follows:

[0152] Step 5-1: Represent the contact between particles and between particles and the boundary as vibrational motion, and perform calculations using the normal and tangential motion equations of the vibrational motion:

[0153]

[0154]

[0155]

[0156] in:

[0157] m i,j—Equivalent mass of particles i and j;

[0158] I i,j —Equivalent moment of inertia of particles i and j;

[0159] s — radius of rotation;

[0160] u n —The normal relative displacement of the particles;

[0161] u s —The relative tangential displacement of the particles;

[0162] θ — the rotation angle of the particle itself;

[0163] F n —The normal component of the external force acting on the particle;

[0164] F s —The tangential component of the external force acting on the particle;

[0165] M — the external torque acting on the particle;

[0166] K n —Normal elastic coefficient in the contact model;

[0167] K s —The tangential elastic coefficient in the contact model;

[0168] c n —Normal damping coefficient in the contact model;

[0169] c s —Tangential damping coefficient in the contact model;

[0170] Step 5-2: Considering the contact mode between impurity particles as soft particle contact, the forces and torques acting on the particles are calculated based on the contact model between liquid metal impurity particles as follows:

[0171]

[0172]

[0173] F t =-S t δ t (14)

[0174]

[0175] τ i =-μ r F n R i ω i (16)

[0176] in:

[0177] F n —Normal force;

[0178] F n d —Normal damping force;

[0179] F t — Tangential force;

[0180] F t d — Tangential damping force;

[0181] τ i —Torque of rolling friction contact surface;

[0182] E * —Equivalent Young's modulus

[0183] E i E j —Young's modulus of particle i and particle j;

[0184] ν i ν i —Poisson's ratio of particle i and particle j;

[0185] R * —Equivalent radius,

[0186] R i R j —Radii of particle i and particle j;

[0187] m * —Equivalent mass,

[0188] —The normal vector of the relative velocity;

[0189] β — coefficient

[0190] S n —Normal stiffness,

[0191] S t —Normal stiffness,

[0192] G * —Equivalent shear modulus,

[0193] G i G j—Particle shear modulus;

[0194] δ n —Normal overlap;

[0195] δ t —Tangential overlap;

[0196] μ r — Coefficient of rolling friction;

[0197] R i —The distance from the point of contact to the center of mass;

[0198] ω i —The unit angular velocity vector at the point of contact;

[0199] Based on the fluid flow distribution obtained in step 4, the collisions between impurity particles and between particles and boundaries within the fluid flow calculation domain of the graded filter screen are calculated. The motion state of the particles after contact and collision is calculated according to the liquid metal impurity particle contact calculation model and Newton's second law.

[0200] Step 6: Using the particle contact calculation in the fluid flow calculation domain of the graded filter screen obtained in Step 5, determine the filtration state of the impurity particles based on the filter screen boundary and the movement state of the impurity particles, and update the impurity particle distribution. The specific steps are as follows:

[0201] Step 6-1: Based on the flow distribution and particle motion state in the fluid flow calculation domain of the graded filter screen, determine whether the impurity particles are in contact with the filter screen boundary. Specifically, if they are in contact with the filter screen boundary, perform the impurity particle contact collision calculation in step 5 and update the motion state after the collision. If they are not in contact, they directly pass through the filter screen to the next layer.

[0202] Step 6-2: Based on the distribution and movement of impurity particles, repeat step 6-1 to determine whether they have come into contact with the filter screen boundary. Specifically, if the impurity particles pass through the first filter screen, they will enter the next layer until all three filter screens have passed through. Otherwise, they will repeatedly collide in a certain layer until they accumulate and block the flow channel.

[0203] Step 6-3: Considering the special physical properties of liquid metal, it is necessary to select the corresponding thermophysical property relationship. Specifically, refer to the OECD / NEA to select the thermophysical property relationship of liquid metal. By continuously updating the flow distribution and impurity particle distribution information in the fluid flow calculation domain of the graded filter screen and judging the passage and accumulation of impurity particles, it is ensured that the heat transfer of liquid metal flow and impurity filtration and purification are consistent with the actual situation.

Claims

1. A numerical simulation calculation method for filtering and purifying liquid metal impurities, characterized in that: Includes the following steps: Step 1: Establish a geometric model of the computational domain for fluid flow in a graded filter screen for liquid metal impurities. This model includes three computational domain models for fluid flow in a single-layer filter screen with the same size but different pore diameters. Step 2: Based on the geometric model of the computational domain of the graded filter screen fluid flow obtained in Step 1, mesh generation is performed. Specifically, structured mesh generation is performed using mesh generation software, the mesh at the filter screen pores is densified, the number of boundary layers of the wall mesh and the height of the first layer of the wall mesh are set, and the mesh model of the computational domain of the graded filter screen fluid flow is obtained. Step 3: Perform basic physical field calculations for liquid metal within the mesh model of the fluid flow computational domain of the graded filter screen. Calculate the forces acting on impurity particles in the fluid flow computational domain of the graded filter screen using the force calculation model for impurity particles in the liquid metal. Specific steps are as follows: Step 3-1: Based on the calculation conditions, set the liquid metal temperature and velocity at the inlet of the fluid flow calculation domain of the staged filter screen, and the pressure at the outlet of the fluid domain; set the material properties, particle size, placement location, and rate of impurity particles; set the wall boundary conditions and material properties; Step 3-2: Solve the mass, momentum, and energy equations for the liquid metal to obtain the velocity and temperature fields of the computational domain for the fluid flow in the staged filter screen. Considering the influence of impurity particles, an additional volume fraction term ε is added to the conservation equations. The mass and momentum conservation equations for the liquid metal are calculated as follows: in: ρ—fluid density, kg / m³ 3 ; t — time, s; u—fluid velocity, m / s; g — acceleration due to gravity, m / s² 2 ; μ—dynamic viscosity, Pa·s; S – Momentum sink; Step 3-3: Based on the velocity field and temperature field of the fluid flow calculation domain inside the fuel assembly, the distribution of impurity particles in the fluid flow calculation domain of the staged filter screen is calculated by using the force calculation model of impurity particles in liquid metal. Specifically, combining the fluid parameters and impurity particle motion parameters from the fluid flow calculation domain inside the fuel assembly, the free flow resistance of the impurity particles is calculated by the resistance calculation model, i.e., formula (3). At the same time, considering the lift generated by the impurity particles in the fluid, the lift of the impurity particles is calculated by combining the lift calculation model, i.e., formulas (4) and (5), with the fluid parameters. The force calculation model of the impurity particles is as follows: F D =0.5C D pA|n f -n p |(n f -n p ) (3) in: F D —Free flow resistance, N; F saff — Saffmann lift, N; F magn —Magnus lift, N; C D —Free flow drag coefficient; C L —Magnus lift-drag coefficient; A – Projected area of ​​the particle, m 2 ; Re – Reynolds number; Re w —Rotational Reynolds number; Re p —Particle Reynolds number; ω c —The velocity gradient of the fluid; ω p —The angular velocity of the particle; d p —Particle size, in meters; The forces acting on the impurity particles are solved by equations (1)-(5), and the displacement of the particles is obtained by Newton's second law. The forces acting on the impurity particles in the computational domain of the fluid flow of the graded filter screen are calculated. Step 4: The force on the impurity particles calculated in Step 3 is used as the momentum sink in Equation (2) of Step 3-2. The fluid flow distribution in the calculation domain of the staged filter screen is calculated according to the momentum conservation equation: in: V — Mesh cell volume, m 3 ; The momentum sink is the sum of the resistances of the fluid acting within the grid. By adding the momentum sink to the momentum conservation equation, the fluid flow distribution in the computational domain of the staged filter screen is calculated. Step 5: Based on the fluid flow distribution in the fluid flow calculation domain of the graded filter screen obtained in Step 4, add a liquid metal impurity particle contact calculation model, and perform impurity particle contact collision calculation within the fluid flow calculation domain of the graded filter screen. Step 6: Using the particle contact calculation in the fluid flow calculation domain of the graded filter screen performed in Step 5, determine the filtration status of impurity particles and update the impurity particle distribution based on the filter screen boundary and the movement state of impurity particles.

2. The numerical simulation calculation method for filtering and purifying liquid metal impurities according to claim 1, characterized in that: Step 1 is as follows: Step 1-1: Use geometric modeling software to build the geometric model of the fluid flow calculation domain of the single-layer filter screen. Obtain the fluid flow channels before and after the single-layer filter screen through stretching. Considering the fluid flow channels at the filter holes of the single-layer filter screen, they are obtained by stretching according to the hole size. Combine the fluid flow channels before and after the single-layer filter screen to obtain the geometric model of the fluid flow calculation domain of the single-layer filter screen. Step 1-2: Considering that liquid metal uses multi-layer filter screens to filter and purify impurities, in order to simplify the calculation, repeat step 1-1 to construct geometric models of the fluid flow calculation domain of single-layer filter screens with the same size but different pore sizes. By combining and connecting the geometric models of the fluid flow calculation domains of single-layer filter screens with different pore sizes, a geometric model of the fluid flow calculation domain of the graded filter screen is formed.

3. The numerical simulation calculation method for filtering and purifying liquid metal impurities according to claim 1, characterized in that: Step 5 is as follows: Step 5-1: Represent the contact between particles and between particles and the boundary as vibrational motion, and perform calculations using the normal and tangential motion equations of the vibrational motion: in: m i,j —Equivalent mass of particles i and j; I i,j —Equivalent moment of inertia of particles i and j; s — radius of rotation; u n —The normal relative displacement of the particles; u s —The relative tangential displacement of the particles; θ — the rotation angle of the particle itself; F n —The normal component of the external force acting on the particle; F s —The tangential component of the external force acting on the particle; M — the external torque acting on the particle; K n —Normal elastic coefficient in the contact model; K s —The tangential elastic coefficient in the contact model; c n —The normal damping coefficient in the contact model; c s —Tangential damping coefficient in the contact model; Step 5-2: Considering the contact mode between impurity particles as soft particle contact, the forces and torques acting on the particles are calculated according to the liquid metal impurity particle contact calculation model as follows: F t =-S t d t (14) t i =-μ r F n R i oh i (16) in: F n —Normal force; —Normal damping force; F t — Tangential force; F t d — Tangential damping force; τ i —Torque of rolling friction contact surface; E * —Equivalent Young's modulus E i E j —Young's modulus of particle i and particle j; ν i ν i —Poisson's ratio of particle i and particle j; R * —Equivalent radius, R i R j —Radii of particle i and particle j; m * —Equivalent mass, —The normal vector of the relative velocity; β — coefficient S n —Normal stiffness, S t —Normal stiffness, G * —Equivalent shear modulus G i G j —Particle shear modulus; δ n —Normal overlap; δ t —Tangential overlap; μ r — Coefficient of rolling friction; R i —The distance from the point of contact to the center of mass; ω i —The unit angular velocity vector at the point of contact; Based on the fluid flow distribution obtained in step 4, the collisions between impurity particles and between particles and boundaries within the fluid flow calculation domain of the graded filter screen are calculated. The motion state of the particles after contact and collision is calculated according to the liquid metal impurity particle contact calculation model and Newton's second law.

4. The numerical simulation calculation method for filtering and purifying liquid metal impurities according to claim 1, characterized in that: Step 6 is as follows: Step 6-1: Based on the flow distribution and particle motion state in the fluid flow calculation domain of the graded filter screen, determine whether the impurity particles are in contact with the filter screen boundary. If they are in contact with the filter screen boundary, perform the impurity particle contact collision calculation in step 5 and update the motion state after the collision. If they are not in contact, they can directly pass through the filter screen to the next layer. Step 6-2: Based on the distribution and movement of impurity particles, repeat step 6-1 to determine whether they have come into contact with the filter screen boundary. If the impurity particles pass through the first filter screen, they enter the next layer until all three filter screens have passed through. Otherwise, they will repeatedly collide in a certain layer until they accumulate and block the flow channel. Step 6-3: Considering the special physical properties of liquid metal, it is necessary to select the corresponding thermophysical property relationship. Specifically, refer to the OECD / NEA to select the thermophysical property relationship of liquid metal. By continuously updating the flow distribution and impurity particle distribution information in the fluid flow calculation domain of the graded filter screen and judging the passage and accumulation of impurity particles, it is ensured that the heat transfer of liquid metal flow and impurity filtration and purification are consistent with the actual situation.

5. The numerical simulation calculation method for filtering and purifying liquid metal impurities according to claim 1, characterized in that: The liquid metal is a liquid lead-bismuth alloy.

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