Fabrication and thermal properties of capric–stearic acid eutectic/nano-SiO2 phase change material with expanded graphite and CuO for thermal energy storage

With the booming development of energy storage technology, phase change materials (PCMs) provide more possibilities for building energy efficiency. In this paper, binary eutectic mixture of capric acid (CA) and stearic acid (SA) is PCM, nano silica (SiO2) is used as the nano-enhancer, and expanded graphite (EG) and nano CuO are used as the thermal conductivity enhancers. Different mass fractions of composite phase change materials (CPCMs) are prepared by melt impregnation method. The structure, thermal properties, stability, thermal conductivity properties, thermal storage/release properties and temperature response properties of the CPCMs are characterized. Results show the prepared CA-SA/SiO2/EG(CPCM5) melts at 30.62 °C and solidifies at 25.29 °C with latent heat of 156.50 J/g and 144.20 J/g, respectively, and CA-SA/SiO2/CuO(CPCM8) melts at 29.09 °C and solidifies at 25.30 °C with latent heat of 152.60 J/g and 140.70 J/g, respectively. The latent heats of melting are higher than the theoretical latent heat due to the enhancement of the nano SiO2. Good compatibility is observed between CA-SA, SiO2, CuO and EG. The thermal conductivity of CPCM8 and CPCM5 are 0.287 and 0.929 W/(m·K), respectively, and CPCM5 has better thermal storage/release and temperature response characteristics. Moreover, CPCM5 does not decompose at 100.00 °C, and shows good stability after 200 cycles of heating and cooling. Therefore, the composite has great potential for application in the field of building energy efficiency.