The Three-dimensional Lattice Boltzmann Model For Interfacial Characteristics Of Phase Change In A Porous Medium Cavity

The solid-liquid phase change technology has extensive application value in energy efficient utilization and effective thermal management.For example,adding a phase change material layer to a building maintenance structure increases the thermal inertia of the building maintenance structure,and the addition of shaped phase change materials to precision components can effectively increase the heat dissipation capability of the components.In-depth study of the evolution law of the phase change process and the law of migration and change in the mushy zone have important influence on the actual production process;the influence rule of the skeleton characteristics on the low-temperature solid-liquid phase change materials is discussed,and it is the practical application of the phase change technology.According to the evolution law of phase transition and the basic principle of solid-liquid interface migration,the theory(the porous media seepage theory and multiphase flow theory)analysis and numerical simulation methods are combined to establish the phase transition material paste zone heat transfer.The region where the low-liquid-rate region of the mushy zone exhibits percolation in the porous medium is modeled by the extended Darcy model.In the high-liquid-rate region of the mushy zone,the solid-liquid two-phase flow model was used to simulate the solid particle suspension flow in the liquid phase change material.The two-region model of solid-liquid phase transition was modeled using the double distribution function(DDF)model in lattice Boltzmann(LBM).In the LBM model of the temperature distribution function and velocity distribution function,the D2Q9(two-dimensional working condition)lattice discrete velocity model is used,and the three-dimensional working condition simulation uses the D3Q19 velocity discrete model;then the temperature equilibrium distribution function of the solid region is used to establish therelaxation The size of the the relaxation time is used to achieve the fluid-structure interaction problem of the model.The buoy lift term is added to the flow equation(N-S equation)to realize the coupling of flow and temperature.Based on the two-region model of solid-liquid phase change established in this paper,the phase-change heat and mass transfer process of phase-change materials in a closed-cell cavity was studied from the perspective of pore size.1)The analysis of the dividing line between the high and low liquid content ratios in the two-region model can well divide the high and low liquid content areas of the two-area model;2)The increase of the Prandtl number makes the diffusion process of the change process more obvious,which accelerates the initial melting speed of the phase transformation and reduces the melting rate of the phase change in the quasi-steady state phase;3)The change of the Rayleigh number changes the intensity of the natural convection heat transfer in the cavity.And with the increase of Rayleigh number,the thickness of the mushy zone becomes more pronounced in narrow and wide patterns on the mushy zone;4)With the increase of Stefan number,the sensible heat transfer effect in the three-dimensional cavity becomes more obvious,resulting in many different sizes eddies.The eddy currents suppress the progress of heat exchange and the thickness of the mushy zone becomes thicker and thicker.Combined with quartet structure generation set(QSGS)to generate real porous media models filling the cavity with different porosity(? =0.7,? = 0.8 and ? = 0.9)and with different thermal conductivities(? =5,? =10,? =20).1)Generating a random framework through quartet structure generation set,its random characteristics make the thickness of the mushy zone increase significantly,and its seepage characteristics with the skeleton is obvious;2)the porosity of the skeleton influences the heat transfer and flow of the phase change.The larger the flow vortices,the larger the size of the three-dimensional cavities,the smaller the size of the flow vortices.3)The increase in the ratio of the heat transfer coefficient of the skeletal layer can significantly promote the phase transformation during the initial phase of the transformation,and gradually merge the local small-flow vortices in the three-dimensional cavity into a flow vortex,speeding up the phase transition process.