Highly thermal conductive shape-stabilized composite phase change materials based on boron nitride and expanded graphite for solar thermal applications

Abstract

Phase change heat storage technology is a good way to solve the problem that the temperature of solar hot water outlet is affected by the time domain. A stearic acid (SA)-benzamide (BA) eutectic mixture is a potential phase change material (PCM), but it still has the disadvantages of low thermal conductivity and liquid leakage. In this work, a new high thermal conductive shape-stabilized composite PCM was prepared by adding boron nitride (BN) and expanded graphite (EG) to a melted SA-BA eutectic mixture using an ultrasonic and melt adsorption method, and its phase change temperature, latent heat, crystal structure, morphology, thermal conductivity, chemical stability, thermal stability, cycle stability and leakage characteristics were characterized. The results indicates that the addition of BN and EG significantly improved the thermal conductivity of the SA-BA eutectic mixture, and they efficiently adsorbed the melted SA-BA eutectic mixture. Besides, when the mass fractions of BN and EG are 15 wt% and 20 wt%, respectively, the 15BN20EG composite has almost no liquid phase leakage. When the melting enthalpy and temperature of 15BN20EG are 132.35 J g^-1 and 65.21 °C, respectively, the thermal conductivity of the 15BN20EG is 6.990 W m^-1 K^-1, which is 20.601 times that of the SA-BA eutectic mixture. Moreover, 15BN20EG shows good thermal stability after 100 cycles and good chemical stability below 100 °C. Therefore, the 15BN20EG composite is considered as a potential candidate for solar thermal applications.