Study On Phase Change Heat Transfer And Flow Characteristics Of Porous Media Based On LBM

The problem of thermal management of electronic components is becoming more and more serious.Strengthening micro-scale heat transfer can effectively solve the current problem.Phase change heat pipe is the use of internal working medium gas and liquid phase to transfer heat,its heat transfer efficiency is much higher than the traditional materials,with good thermal conductivity,good isotherm,reversible heat flow direction,good heat exchange effect and other advantages.It is of great value in engineering application and scientific research to study the temperature change of working medium in heat pipe under different conditions.Experimental research can not timely and accurately control the temperature change of working medium in heat pipe,and the existing macro numerical model can not simulate the heat transfer process of micro scale heat pipe.Lattice Boltzmann method is a new fluid system modeling and simulation method.This method has a history of more than thirty years.The most important characteristic of this method is that it can deal with complex boundary naturally without the need for the transformation of computational grid.It has been widely used in the problems of gas-liquid phase change and fluid flow in porous media.In this thesis,the heat transfer of heat pipes is studied by means of a numerical model of vapor-liquid phase variation based on mesoscopic lattice Boltzmann method.Specific research contents include:First of all,A two-phase flow model based on lattice Boltzmann method was established by introducing a new form of particle interaction force and an exact difference method.This method can effectively improve the accuracy and stability of numerical calculation,and reduce the non-physical dependence of calculation results on relaxation time.At the same time,this thesis also introduces the interparticle interaction force and combines it with the energy equation model to form a new double distribution function model.Secondly,according to previous studies on porous media,the relationship between porosity,pore size,permeability,flow resistance and capillary force,copper powder with particle size of 100 μm～150 μm is selected as porous media material,and a new generation method of porous media is proposed,porous media with different porosity can be obtained by random function.Combined with the DDF model,the variation of working fluid temperature with time,the influence of different heat source temperature on heat transfer of heat pipe and the influence of different porosity on heat transfer of heat pipe were obtained.Finally,the higher the heat source temperature is,the lower the cold source temperature is,the better the heat transfer effect is.Small vortexes appear in fluid flow in porous media,and more vortexes appear in fluid flow in porous media with 46% and 56%porosity.When the porosity of porous medium in heat pipe is 56%,heat transfer effect of heat pipe is the best.This study opens up a new research idea for numerical simulation of vapor-liquid phase change in micro scale heat pipe,illustrates the change of working medium in heat pipe,reveals the influence of temperature and porosity on heat transfer,and provides an important theoretical basis for improving heat transfer efficiency by changing temperature and porosity.