Effect of expanded graphite size on performances of modified CaCl2·6H2O phase change material for cold energy storage

The effect of expanded graphite (EG) size on thermal performances of PCM has been little discussed although many EG-based PCMs were investigated. Here, three different sizes of EGs (50, 80, 100 mesh) were adopted as supporting materials to prepare their respective composite PCMs (CPCMs). Form-stability, thermal conductivity and phase change behavior of CPCM were systematically discussed. Results indicated that the shape-stabilized effect and the adsorptive rate of EG-50 for modified CaCl2·6H2O PCM were superior to that of EG-80 and EG-100, which originated from its larger proportions of micropores, larger specific area and pore volume respectively. The results of pore structure analysis and SEM confirmed that the pore structures of three kinds of EGs were occupied by modified CaCl2·6H2O PCM. CPCM with EG-50 possessed a higher thermal conductivity and latent heat than that of the other two with EG-80 and EG-100 respectively, which were due to the low interfacial thermal resistance and the small confinement effects in EG-50 respectively. The addition of EG could suppress the supercooling degree of modified CaCl2·6H2O PCM. This work will provide insights into the enhanced thermal performance for shape-stabilized CPCMs by introducing carbon-based supporting materials with appropriate size.