Experimental And Numerical Simulation Of Phase Change Process And Heat Transfer Behavior Of Paraffin-based Composites

The use of energy is the foundation of human life.However,the wide application of the fossil energy will bring pollution and damage to the environment.And clean,renewable energy sources such as solar energy may face some problems.One of them is the storage of the energy.The phase change material can transport energy in time or space by melting or solidifying.In order to optimize the design and improve the performance of the material in the application,the phase change process of paraffin-based phase change materials was explored in this thesis.(1)Paraffin was taken as the research object,and the numerical model was established.By comparing the experimental results with the numerical simulation results,the parameters and model configuration in the simulation were adjusted.And the process of paraffin melting was analyzed based on the results.(2)In order to improve the thermal conductivity,expanded graphite(EG)was added to the system.In order to discuss the influence of EG on the thermal conductivity of this system,a geometric model of EG micropores was constructed based on the microstructure of EG.This model had obvious anisotropy.In the simulation calculation,paraffin/EG based on this geometric structure also had anisotropic thermal conductivity.However,as the number of pores increased,this anisotropy was weakened and finally changed to isotropy,which was observed in the actual experiments.The theoretical thermal conductivity obtained in the theoretical calculation is relatively close to the maximum thermal conductivity measured in the actual experiment.(3)Finally,the influence of the mass fraction between EG and ethylene-vinyl acetate copolymer(EVA)in paraffin/EG/EVA composite on the heat storage performance of the system was investigated.When the mass fraction of the paraffin was fixed,the samples with high EVA mass fraction had low thermal conductivity and viscosity.In the melting/solidification experiments of the composite,it was found that samples with low EVA mass fraction had higher heat storage efficiency than samples with high EVA mass fraction.By analyzing the results of numerical simulations,in samples with high EVA mass fraction,the natural convection was higher than the samples with low EVA mass fraction.However,due to the influence of thermal conductivity,the samples with low EVA mass fraction melted faster and had the better heat storage properties than the samples with high EVA mass fraction.The results of the numerical simulation confirmed the experimental results.