Hydrated salts/expanded graphite composite with high thermal conductivity as a shape-stabilized phase change material for thermal energy storage

A novel shape-stabilized phase change material (PCM) was developed by impregnation of hydrated salts into expanded graphite (EG) and further coated with paraffin wax. It was displayed by scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FT-IR) measurements that the hydrated salts were filled into pores or adhered onto the flakes of EG by physical interactions, including capillary forces and surface tension. It was revealed from differential scanning calorimetry (DSC) analysis that phase segregation was inhibited and subcooling weakened in the coated composite PCM. The melting and freezing enthalpy of the coated composite PCM can reach 172.3 kJ/kg at 32.05 °C and 140.8 kJ/kg at 17.11 °C, respectively. Also, the results of thermal gravimetric analysis (TG) suggested that the coated composite PCM had good thermal stability in the working temperature range from 25 to 50 °C. Furthermore, the enthalpy loss of melting and freezing was negligible after 100 cycles, indicating its good thermal reliabilities. The thermal conductivity of the coated composite PCM can be as high as 3.643 W/(m K). According to the obtained results, the coated hydrated salts/EG composite PCM enjoys high latent heat, good thermal reliability and high thermal conductivity. Apart from its favorable thermal properties, the cost of the coated hydrated salts/EG composite PCM was quite low, making it promising for low temperature thermal energy storage applications.