A synergistic improvement in heat storage rate and capacity of nano-enhanced phase change materials

Abstract

The efficient utilization of the latent heat thermal energy storage (LHTES) system is mainly limited by its underperforming heat storage rate and capacity. Recently, scholars utilized nanoparticles to enhance the thermal conductivity of phase change materials (PCMs). Nevertheless, simultaneous enhancements of thermal conduction and phase change enthalpy have not been realized, much less considering the convective heat transfer. In this study, we selected octadecylamine (ODA) as the PCM; multiwall carbon nanotubes (MWCNTs) were ultrasonically dispersed into the ODA to obtain the uniform-mixed nano-enhanced PCMs (NePCMs). The results show that MWCNTs are conducive to strengthening thermal conduction. Besides, the fusion enthalpy of ODA@0.05 (containing 0.05 wt% of MWCNTs) is 6.45% higher than the pure ODA. However, the addition of MWCNTs improves the viscosities of liquid NePCMs in a non-linear trend, which weakens the convective heat transfer. Considering both heat storage rate and heat storage capacity, we find that the heat storage power of the ODA@0.05 is 22.38% higher than that of the pure ODA. Besides, the heat release power is 14.00% higher than the pure ODA. Consequently, we acquired the composite ODA with fast heat storage/release power and large heat storage capacity, which is an excellent candidate for the LHTES system. This paper sheds some light on the rational utilization of nano-additives to avoid the abuse of nanoparticles.