CN-120373186-B - High-density ratio two-phase boiling heat transfer simulation method based on lattice Boltzmann algorithm

CN120373186BCN 120373186 BCN120373186 BCN 120373186BCN-120373186-B

Abstract

The invention discloses a large density ratio two-phase boiling heat transfer simulation method based on a lattice Boltzmann algorithm, which comprises the steps of solving corresponding pseudo potential according to density and a corresponding non-ideal state equation, calculating various forces in a multiphase system, calculating source items in a gas-liquid phase model, calculating relaxation factors corresponding to different moments in a multiphase flow field and a temperature field according to entropy stability conditions and fluid specific properties, substituting evolution equations of the multiphase flow field and the temperature field according to the calculated evolution equations, executing collision and migration according to the evolution equations, calculating macroscopic physical quantities such as density, speed, temperature and the like at each lattice point according to density and temperature distribution functions, and judging whether iteration is ended or not. The invention can effectively improve the two-phase density ratio in the simulation of the gas-liquid boiling problem, realize the simulation of the phase change conversion process of water and water vapor under the real condition, and solve the simulation problem of complex multiphase flow heat transfer.

Inventors

XU BINJIE
WANG YIQIAN
LU PENG
Lv Zongze
ZHAO NING
ZHU CHUNLING
ZHU GUANGQING
HOU FEI

Assignees

中国矿业大学

Dates

Publication Date: 20260512
Application Date: 20250409

Claims (7)

1. A lattice boltzmann algorithm-based high density ratio two-phase boiling heat transfer simulation method, which is characterized by comprising the following steps: S1, according to density Solving corresponding pseudo potential with corresponding non-ideal state equation Calculating inter-particle interactions in a multiphase system And gravity force Solving a source term in the gas-liquid phase change model according to the speed and the temperature of the flow field Calculating relaxation matrixes corresponding to different moments in the multiphase flow field and the temperature field according to the entropy stability condition and the fluid self attribute And ; S2, relaxing the matrix And Interaction force between particles Gravity force Source item Respectively substitutes into density distribution functions And a temperature distribution function Performing collision and migration in the evolution equation of (2) to obtain a density distribution function and a temperature distribution function; s3, calculating macroscopic physical quantities including density, speed and temperature at each grid point according to the density distribution function and the temperature distribution function, and judging whether iteration is finished or not; In step S1, the source term is calculated using the following formula : ; Wherein the method comprises the steps of Is the thermal conductivity of the material, Is the specific heat capacity of the glass, Is a constant produced by the lattice boltzmann method, Is the density of the fluid which is to be measured, As a gradient of the temperature of the liquid, To determine the partial conductance of the state equation to temperature under the condition of fixed density, For the pressure to be found by the non-ideal state equation, Is the speed.
2. The method for simulating boiling heat transfer in a large density ratio and two phases based on the lattice Boltzmann algorithm according to claim 1, wherein in step S1, the method is based on density Solving corresponding pseudo potential with corresponding non-ideal state equation : ; Wherein c is the lattice velocity, P is the pressure obtained by the non-ideal state equation, Is the speed of sound of the lattice, Is the fluid density, x is at the current position, t is the current time, and G is the interaction force strength.
3. The lattice boltzmann algorithm-based high density ratio two-phase boiling heat transfer simulation method according to claim 1 or 2, wherein the non-ideal state equation includes a van der waals equation, a Peng-Robinson equation, a Carnahan-Starling equation, and a piecewise linear equation.
4. The method for simulating boiling heat transfer in two phases with a large density ratio based on the lattice Boltzmann algorithm according to claim 1, wherein in step S1, the inter-particle interaction force is calculated using the following formula : ; Wherein, the For adjusting parameters for adjusting mechanical stability conditions, G is the interaction force strength, x is the current position, t is the current time, Represented as discrete speeds in the i-direction, For the time step size of the time step, As the weight coefficient of the light-emitting diode, Is a pseudo potential.
5. The lattice boltzmann algorithm-based high density ratio two-phase boiling heat transfer simulation method according to claim 1, wherein in step S1, a relaxation matrix of a flow field is expressed as follows: ; Wherein the method comprises the steps of To correspond to the viscosity coefficient Is used for the relaxation factor of (a), The specific formulas of the adopted entropy stabilizing operators are as follows: ; Wherein the method comprises the steps of Is a correlation matrix Is the inverse of the (a) and (b), Relaxation parameter Coefficient of viscosity Related to each other, the relationship between the two is ; Is a cut-out of the density distribution function and M and n are integers, and the value ranges are 0,1 and 2, which correspond to the second-order moment, the third-order moment and the fourth-order moment respectively; And Respectively shearing and deviation of a high-order moment and a balance state of the high-order moment, wherein superscript eq represents a balance state function, and i represents an i direction; the relaxation matrix of the temperature field is expressed as follows: 。
6. the method for simulating boiling heat transfer in two phases with a large density ratio based on the lattice boltzmann algorithm according to claim 1, wherein in step S3, the flow field density at each lattice point is calculated from a density distribution function and a temperature distribution function Speed and velocity of Temperature T: ; Wherein, the In order to achieve a density of the particles, And Representing the density and temperature distribution functions respectively, Is an integer of the number of the times, Q is the number of discrete speeds, Represented as discrete speeds in the i-direction, For speed, F is the sum of forces to which it is subjected, including inter-density interaction forces And gravity force G is gravitational acceleration.
7. The method for simulating boiling heat transfer in a large density ratio and two phases based on the lattice boltzmann algorithm according to claim 1, wherein in step S3, it is judged whether the density change of the flow field is smaller than that Or if the preset maximum calculation step number is reached, stopping iteration if the preset maximum calculation step number is reached, otherwise, returning to the step S1 to enter the next iteration.

Description

High-density ratio two-phase boiling heat transfer simulation method based on lattice Boltzmann algorithm Technical Field The invention relates to the technical field of multiphase flow heat transfer analysis, in particular to a high-density ratio two-phase boiling heat transfer simulation method based on a lattice Boltzmann algorithm. Background Due to the extremely high heat exchange efficiency, boiling flow heat transfer has found wide application in various heat dissipating systems and industries, such as nuclear power reactor cooling, chip cooling in computer data centers, avionics cooling, satellite electronics cooling, and cooling of various other advanced electronics. However, in practical applications, there are still some limitations on boiling heat transfer, for example, once nuclear boiling changes to film boiling occur, boiling heat transfer efficiency may drop sharply, and equipment operation safety may be compromised, and serious economic loss and casualties may also be caused. Therefore, the deep exploration of boiling heat transfer mechanism is of great significance. However, it is not an easy matter to study such a complex multiphase flow heat transfer system because of the complex variety of motion changes at the multiphase interface due to the generation, growth, incorporation, etc. of the internal bubble nuclei, and these processes typically occur in smaller temporal and spatial dimensions. In addition, since the dynamic behavior of bubbles in the liquid is complex and rich, it is still extremely difficult to observe the whole process of bubble growth and obtain detailed information of multiphase flow fields through experimental means. And experiments also make it difficult to perform decoupling studies on different variables. It is therefore highly desirable to develop a robust and accurate two-phase boiling heat transfer numerical simulation method to capture such a complex multiphase flow heat transfer phenomenon. Traditional macroscopic computational fluid mechanics methods require the simulation of boiling heat transfer by means of additional models and artificial placement of initial nucleation points, and thus cannot explore the bubble nucleation mechanism in depth. Different from the traditional computational fluid dynamics method, the lattice Boltzmann method can be based on a mesoscopic physical basis to establish different models to realize simulation of complex multiphase heat transfer phenomena of physical natural combination of micro-scale and macro-scale such as phase interface breaking, merging and large deformation. The invention with the publication number of CN118673830A discloses a method for freely setting initial nucleation points based on a pseudo-potential lattice Boltzmann model in a boiling process, which is based on the boiling simulation of a flat and uniform wall surface and comprises the following steps of (1) determining characteristic lattice points and corresponding wetting parameters in a range of the lattice points of the wall surface according to the number of the nucleation points and the wetting property of the nucleation points, (2) obtaining parameters of other lattice points through interpolation among the characteristic lattice points, initializing the wetting parameters of the lattice points of the wall surface, keeping unchanged in an initial certain time step, and (3) updating the wetting parameters of the lattice points of the wall surface according to the expected setting form and the wetting property requirement after the setting is carried out in a certain time step. The invention does not depend on the stimulus of factors such as temperature, surface structure and the like to activate nucleation points, can set the quantity, distribution and wetting property of the nucleation points, and can conveniently control the wetting state of the wall surface according to a desired format after nucleation. But limited by numerical stability, the current multi-phase lattice boltzmann method still has difficulty in handling the simulation of the high density to two-phase boiling problem. In recent years, many scholars have proposed methods of expanding the calculation template of the interaction force, increasing the transition width of the interface, and the like to expand the density ratio in the gas-liquid phase simulation. However, the density ratio which can be simulated by the methods is still difficult to reach more than 1000 and is far less than the two-phase boiling density ratio taking water as a medium under the real condition. Therefore, the multiphase lattice Boltzmann method is further developed to simulate the boiling heat transfer phenomenon under the real condition, the influence rule of different factors such as surface wettability, surface structure and surface materials on the boiling heat transfer is explored, the boiling heat transfer mechanism is revealed, the application efficiency and the application range of the boiling hea