Characterization and thermal properties of a shape-stable Na2CO3-K2CO3/coal fly ash/expanded graphite composite phase change materials for high-temperature thermal energy storage

Abstract

A shape-stable Na2CO3-K2CO3/coal fly ash (CFA)/expanded graphite (EG) composite phase change material (PCM) for high-temperature thermal energy storage was developed successfully. Five samples with EG contents of 0, 1.5, 3, 4.5 and 6 wt.% were prepared. The micro structure, thermal conductivity, chemical compatibility, specific heat capacity and latent heat of the prepared shape-stable PCMs (SSPCMs) were investigated. After adding EG to the composites, the overall morphology was changed, and the pores of the composites expanded, making the surface area and pore size increase. The specific heat capacity and the latent heat of SSPCMs decreased slightly with EG content, while the thermal conductivity of SSPCM increased with EG content. The thermal conductivity of the SSPCM containing 6 wt.% EG was 3.182 W/(m·K), which was 183% higher than that of the SSPCM without EG. The heat storage density of the SSPCM containing 6 wt.% still reached 972.4 J/g, only 5% lower than that of the SSPCM without EG. Furthermore, the thermal conductivities of SSPCMs were calculated theoretically, and the experimental results were consistent with the theoretical calculations of the quadratic parallel model. Overall, the SSPCM containing 6 wt.% EG had excellent thermal storage property and thermal conductivity.