A novel process for preparing molten salt/expanded graphite composite phase change blocks with good uniformity and small volume expansion

Herein a novel process was explored for preparing molten salt/expanded graphite (EG) composite phase change material (PCM) blocks, which involves mixing a solid molten salt with EG thoroughly, compressing the mixture into a block with a designed shape and then heating the block to a temperature above the melting point of the molten salt followed by cooling. An MgCl2-KCl eutectic salt was used as the PCM, and its EG-based composite PCM block was prepared by this process, in which the optimal mass fraction of the eutectic was determined to be around 85%. The microstructure of the MgCl2-KCl/EG composite PCM block containing 85% the eutectic shows a uniform distribution of the molten salt. The composite PCM block has a melting point of 424.14 degrees C and a solidification point of 418.39 degrees C, and its latent heat values are 161.37 J/g for melting and 160.28 J/g for solidification. Compared with the eutectic salt, the composite PCM block exhibits a reduction in supercooling by 3.7 degrees C and an enhancement in thermal conductivity by 11-fold. It has been verified that the composite PCM block possesses excellent thermal reliability. Furthermore, the composite PCM block has been compared with the one prepared by the conventional method (first adsorption and then compression). It is found that the composite PCM block fabricated by the novel process exhibits better uniformity and smaller volume expansion than the one obtained from the conventional method. The MgCl2-KCl/EG composite block shows great promise in high temperature thermal energy storage systems, and this novel process is very suitable for preparing molten salt/EG composite PCM blocks.