Numerical Simulation Of Paraffin Phase Change In Differentiated Porous Media Based On LBM

The problem of energy supply mismatch in time and space could be effectively solved by developing thermal energy storage technology and energy utilization efficiency could be improved.Solid-liquid metamaterials store thermal energy through latent heat and have greater energy storage density than sensible heat storage.Conventional phase change materials have low thermal conductivity,which is difficult to meet the requirements of industrial applications.Heat transfer performance can effectively enhanced by adding metal foam with high thermal conductivity into phase change materials.In this paper,four-parameter stochastic growth method(Quartet Structure Generation Set,QSGS)is used to build a physical model of porous media.The enthalpy-porosity model is adopted,and the fuzzy region during phase transition is regarded as porous media.Based on pore scale,lattice Boltzmann method(Lattice Boltzmann method,LBM)is used to numerical simulate the phase change heat transfer process of paraffin in a square cavity with skeleton.The main work contents and conclusions are as follows:(1)The uniform and heterogeneous physical models of porous media used in this paper are constructed by controlling structural parameters using QSGS method.Optimize the generation steps of QSGS method to improve the dead hole and accuracy problems.(2)A double-distribution lattice Boltzmann model based on enthalpy method is established to solve the solid-liquid phase change problem with skeleton.The model calculated results are compared with classical solutions in literature to verify the accuracy of solid-liquid variable problems and fluid-solid coupling problems on the basis of lattice independence verification.(3)The effects of dimensionless parameter Ra number,Pr number and Ste number on the melting process in a square cavity with skeleton are explored based on the established LBM model.The results show that with the increase of Ra number,the natural convection intensity increases.The melting rate increases in the middle and late melting process,and the inclination degree of the fuzzy region increases.With the increase of Pr number,the melting rate is accelerated.The flow state is vortex in a single pore in the early stage of melting,and it changes to circulation among multiple pores in the middle and late stage of melting.The larger the Pr number,the earlier the circulation appeared.The increase of Ste number leads to the decrease of latent heat absorption,the acceleration of melting rate,the decrease of inclination angle of fuzzy region and the thickening of fuzzy region.(4)The effect of the difference of porous media on the melting process is investigated and the dimensionless thermal storage power is proposed as an evaluation index.The results show that the melting rate increases and the dimensionless thermal storage power increases with the decrease of porosity.The lower the porosity,the higher the dimensionless heat storage power.Increasing the thermal conductivity ratio could improve the melting rate,but the improvement is limited.When the skeleton morphology does not change,the thermal conductivity ratio has little effect on the convective heat transfer intensity.Choosing the right direction growth probability could effectively improve the heat transfer rate.