Interfacial Characteristics Research Of Solid-liquid Phase Change Base On Lattice Boltzmann Method

The problem of solid-liquid phase change in porous media has been existed widely in nature and many industrial fields.The solid-liquid phase change material has been widely used as a storage material.However,it is not a single pure substance in the practical application.During the process,the phase change temperature is not a certain value but a temperature range.At this time,there is a solid and liquid phase coexistence region(mushy region).The existence and properties of mushy region have an important influence on the phase change process.It is of great significance to study the flow and heat and mass transfer mechanism of solid-liquid phase change to explore the development,migration and to study heat and mass transfer characteristics of mushy region.Based on the analysis of the physical characteristics,this paper presents a two region composite model "Multiphase flow-porous",which is that the low liquid rate of mushy region uses Brinkmann-Forchheimer-Darcy porous medium seepage flow model near the solid and the high liquid rate of mushy region adopt the multiphase flow the model.As the solid-liquid phase change is a nonlinear problem.In order to obtain the influence of the skeleton on the solid-liquid phase change and the local flow heat transfer and the effect on the mushy region,this paper has established the mathematical model of REV and pore scale based on the enthalpy method.The lattice-Boltzmann method(LBM)is used to solve the problem by choosing the appropriate model,the equilibrium distribution function and the source term.The REV and pore scale of LBM model for the solid-liquid phase change mushy region have been established.And then,the validity and the accuracy of the model have been verified by a series of numerical experiments.In this paper,the solid-liquid phase change process in the square cavity is studied,numerical simulation of solid liquid phase change process without porous skeleton,the factors(Pr ?Ra ?Ste)affecting the development,migration and internal flow and heat transferin mushy region were discussed and analyzed.The result of the solid liquid phase change process without the skeleton is showed that : 1)the thickness of mushy region is directly related to the phase change temperature radius of the mushy region.The smaller the phase change temperature radius of the mushy region is,the thinner the mushy region thickness is.2)mushy region constant and high-low liquid fraction area of demarcation point,phase change materials and the structure of mushy region have a close relationship with each other.The dimensionless parameters(Pr ?Ra ?Ste)of phase change materials have obvious influence on the mushy region and the phase change process.Under the condition of low Pr number,the multi vortex structure will occur in the early stage of the phase change process,which will affect the mushy region shape and migration;The numerical value of Ra affects the natural convection intensity in the liquid phase region and the mushy region and affects the shape of the mushy region and the internal heat transfer flow.With the increase of Ra value,the melting rate increases,the mushy region becomes thinner,and the heat transfer ability of the hot wall surface is enhanced;The value of Ste affects the rate of melting.The thickness of mushy region increases with the increasing Ste number of mushy region.The corresponding speed increases with the increasing Ste number.The smaller the Ste number is,the higher heat storage capacity in the process of phase change is.Based on the previous analysis,the influence of the skeleton on the solid-liquid phase change process is analyzed.The effects of the framework on the characteristics of the mushy region and the flow and heat transfer in the whole process have been analyzed on the REV scale.The results showed that: 1)with increasing the skeleton of the Darcy number or reducing porosity,flow effects of the corresponding liquid region and the mushy region is more obvious.The thickness of mushy region is thin and its shape is more bent.The porosity reduces the heat transfer ability of the system,on the other hand,increasing the volume of phase change materials can increase the quantity of heat storage.2)adding the skeleton does not necessarily mean that thermal storage of skeleton is stronger.On the same condition,the mushy region boundary curvature smaller.On quasi steady state,the larger volume of unmelting stage keeps larger.The influence of the skeleton on the local details of the flow and heat transfer in the process of phase change was studied on the pore scale.The result shows that: 1)due to the influence of edge and skeleton in the mushy region,eddy current generated in the local council during the transformation process.2)there are consistent conclusions under the influence of pore size and REV scale in the process of phase change.High thermal conductivity has certain promotion effect on the heat transfer characteristics of the whole system.However,with the enhancement of thermal conductivity of the skeleton,its promotion effect gradually weakened.