Effect of fumed silica additive on supercooling, thermal reliability and thermal stability of Na2HPO4·12H2O as inorganic PCM

Novel composites phase change material (PCM) formed by immersing disodium hydrogen phosphate dodecahydrate (DHPD) in fumed silica (FS) is developed. The influences of porous media structure, distribution uniformity and thermal conductivity of heat transfer medium that affect the supercooling of DHPD were experimentally investigated. The results revealed that the equally distributed FS in the composites PCM was helpful to prevent dehydration of DHPD. The addition of FS with porous structure in DHPD could reduce its supercooling degree from 14.4 °C to 4.1 °C. Moreover, the phase change temperature of DHPD/FS composites PCM basically remain the same after 50 times heating-cooling cycle test, showing excellent thermal stability of the as-prepared PCM. The phase change temperature of DHPD/FS composites PCM is 33.99 °C and phase change latent heat of 211.8 J/g were obtained with 2 wt% FS added in DHPD, with perfect thermal stability, which proved DHPD/FS a promising PCM for thermal energy storage.