Study On Solid-liquid Phase Change Heat Transfer Characteristics Based On LBM Containing Complex Skeleto

Solid-liquid phase change materials mainly absorb and release heat through the transformation between solid and liquid phases,and have the advantages of a wide range of phase change temperatures,low cost,good thermal stability and large latent heat of phase change,etc.They are widely used in building envelopes,battery thermal management,aerospace thermal control and other fields.However,with the progress of science and technology,various fields have put forward higher requirements for the application of phase change materials,which have drawbacks such as low thermal conductivity.So how to strengthen the thermal performance of phase change materials has become an important issue and research hotspot.The filling of phase change materials with skeletons with high thermal conductivity can effectively solve this problem.In this thesis,the triply periodic minimal surfaces method is used to generate uniform Gyroid,Diamond,IWP and Primitive structures and combined composite structural skeletons.Using a two-region model of the solid-liquid phase change mushy zone,a three-dimensional lattice Boltzmann model and computational method for solid-liquid phase change with complex skeletons are established,and the heat transfer characteristics under various complex operating conditions are studied and analysed in depth based on the pore scale through high-performance GPU parallel computing.The effects of filling different structural skeletons and dimensionless parameters on the solid-liquid phase change flow and heat transfer characteristics were investigated and analysed.The results show that the filling of the four uniform TPMS skeletons can significantly increase the heat transfer rate inside the cavity compared to the cavity without skeleton.By comparing the solid-liquid phase change process of filling four different structures of TPMS skeleton cavities,it was found that when the porosity was 0.894,the phase change melting rate of four uniform TPMS skeleton cavities and the heating rate at the characteristic points were ranked as follows Gyroid>Diamond>Primitive>IWP.Under the same skeleton conditions,the higher the thermal conductivity ratio R_s,the higher the dimensionless temperature at the same location,and the faster the overall melting rate and temperature rise.The dimensionless parameters(Ra number,Ste number,Pr number)have a significant influence on the overall solid-liquid phase change process.The higher the Ra number,the faster the melting rate and the greater the width of the mushy zone,the stronger the natural convection inside the cavity and the shorter the time for the phase change material to melt completely.The higher the Ste number,the lower the latent heat of phase change,the faster the melting rate,the wider the mushy zone at the same moment and the faster the heating rate at the same location.The higher the Pr number,the wider the thickness of the mushy zone in the pre-melting and mid-melting,the faster the melting rate.The Diamond and Gyroid were combined horizontally and vertically to further investigate the influence of the skeletal properties of the composite structure on the solid-liquid phase change process.The results show that in the horizontal direction,compared with the DG skeleton,GD skeleton can make the heat transfer to the interior of the cavity fast,which increases the heating rate in the cavity,reduces the complete melting time and speeds up the overall heat transfer rate.In the vertical direction,the heat transfer rate of the DG skeleton is slightly faster than that of the GD skeleton,and the larger the volume of the Gyroid skeleton is when it is added to the cavity,the faster the overall melting rate and the better the temperature uniformity within the cavity.In the horizontal direction,the lower the porosity of the composite skeleton structure,the faster the temperature rise rate at the same location,the wider the mushy zone,the faster the overall melting rate.