Novel MgCl2-KCl/expanded graphite/graphite paper composite phase change blocks with high thermal conductivity and large latent heat

Abstract

Herein a novel composite phase change material (PCM) block consisting of a molten salt, expanded graphite (EG) and graphite paper (GP) has been developed via a mixing-compression-heating process. The effects of the addition amount of GP and the compression degree on the composition and thermal characteristics of the obtained MgCl2-KCl/EG/GP composite blocks have been investigated. An increase in the amount of GP leads to a linear increase in thermal conductivity for the composite blocks, while a decrease in latent heat appears as the GP/EG mass ratio is more than 0.88. As the packing density of EG is increased from 200 to 320 kg/m3, the thermal conductivity of the MgCl2-KCl/EG composite blocks increases gradually, while their latent heat increases first and then decreases as the EG packing density is more than 280 kg/m3. The MgCl2-KCl/EG/GP composite phase change block prepared at the GP/EG mass ratio of 0.84 and the EG packing density of 280 kg/m3 exhibits an enthalpy per unit volume of 205.35 MJ/m3, showing a decrease by only 1.27% as compared with that of the MgCl2-KCl/EG one, while its thermal conductivity is as high as 12.76 W/m K, 2.08 times that of the MgCl2-KCl/EG one. 1000 heating–cooling cycles verify that the MgCl2-KCl/EG/GP composite phase change block possesses good thermal reliability. The MgCl2-KCl/EG/GP composite phase change block show great potentials in practical applications.