Numerical study on solidification heat transfer of spherical composite phase change capsule with high thermal conductivity

This study explores numerically the solidification of a spherical composite phase change capsule (PCC) with high thermal conductivity, in which expanded graphite (EG) is added into the high-density polyethylene (HDPE)/paraffin shape-stabilized phase change material (SSPCM). The mathematical model is solved numerically by the apparent heat capacity method. In the simulations, the volume change of paraffin during phase transformation and the distribution of cavities arising from the manufacturing process are considered. As an important thermophysical property of the HDPE/paraffin/EG material, the effective thermal conductivity is determined based on fractal theory, the laws of minimal thermal resistance and specific equivalent thermal conductivity. The model is validated by comparison with similar available models and the agreement is found to be satisfactory. The influence of several significant parameters on the heat transfer process is analyzed, such as the content of EG, volume change of the PCM, etc. The results show that the volume change of paraffin has a great impact on the heat transfer process during the later stages. A certain amount of EG addition can effectively improve the heat transfer characteristics of the phase change capsule, including the moving rate of the phase interface and instantaneous release rate of heat flux.