Study of Phase-Transition Characteristics of New Composite Phase Change Materials of Capric Acid-Palmitic Acid/Expanded Graphite

A new composite phase change material of capric acid-palmitic acid/expanded graphite (CA-PA/EG) with the optimum mass ratio of EG equated to 8:1 was prepared by the physical adsorption method. It was observed that the eutectic point of CA-PA binary system was reached at 22.1 °C, and CA-PA was uniformly distributed into the pores of EG by physical interaction. The melting and freezing temperatures of CA-PA/EG obtained by differential scanning calorimeter (DSC) were 23.05 and 20.82 °C, respectively, while the corresponding latent heats were 139.7 and 131.8 J/g, respectively. It had good thermal and chemical stability, and there was almost no leakage of liquid binary phase change materials after 1000 melting-freezing cycles. According to the experimental results of the thermogravimetry (TG) analyzer as well as heat storage and release, CA-PA/EG has excellent thermal reliability and heat resistance and the high thermal conductivity of EG promotes the thermal energy storage and release rate of CA-PA. Thus, CA-PA/EG is suitable as a phase change energy storage material for building energy conservation.