Study On The Characteristics Of Solid-Liquid Phase Transition Process With Framework Based Three-Dimensional Pore Scale

Phase change energy storage materials have the characteristics of large energy storage density,small operating temperature change range,and solid-liquid-solid periodic storage and release of energy when heated.They have been applied to many fields such as building energy conservation,battery thermal management,and solar power generation.However,most phase change materials have a small thermal conductivity,which greatly affects their speed during heat storage and heat release.Therefore,it is of great significance to improve the thermal conductivity of phase change energy storage materials.The addition of framework materials with high thermal conductivity to the phase change energy storage materials provides an effective way to solve the problem of phase change materialsIn this paper,the three-dimensional lattice Boltzmann method(LBM)is used.On the basis of the analysis of the solid liquid phase transition process,the development and evolution of the phase interface,and the theory of porous media seepage and multiphase flow,a two region model is established to describe the mushy region.The mathematical model is verified,and the results are in good agreement with the classical literatureBased on the two region model,the melting and heat storage process of pure phase change material in the cavity is simulated.The results show that:1)with the increase of the dimensionless parameter Ra number,the thermal buoyancy caused by the natural convection in the cavity increases,the paste area bends,and the shape of narrow top and wide bottom appears,the melting rate of the phase change material increases;2)with the increase of the Ste number,the natural convection heat transfer ability of the phase change material in the cavity increases,and the melting rate increases at the same time;3)With the increase of the transformation temperature radius,the paste area becomes thicker and the melting rate of the phase change material becomes slower.However,the temperature radius of phase change ?R has little effect on the heat transfer of phase change materials in the cavityBased on the analysis of the melting and heat storage of pure phase change materials,the uniform and non-uniform physical models of solid skeleton are generated by TPMS.The physical models of solid skeleton are added to the phase change materials.The influence of skeleton on the process of solid-liquid phase change and the development and evolution of mushy area is analyzed based on the pore scale.The results show that:1)the higher the thermal conductivity of the skeleton,the greater the influence on the melting and heat storage of PCM.When the thermal conductivity ratio is 10,50 and 100,the melting time is shortened by 12%,28%and 31%respectively;2)The lower the porosity of the porous media composite,the higher the effective thermal conductivity of the composite phase change material,and the higher the melting and heat storage rate.When the porosity is 0.95,0.90 and 0.85,the melting time is shortened by 13%,18%and 24%,respectively.The homogeneity of the phase change temperature field is also increased,but the addition of the skeleton weakens the natural convection of the phase change material to a certain extent;3)The addition of heterogeneous porous media not only accelerates the melting rate,but also makes the temperature field in the cavity more uniform.