Molecular insights into thermal conductivity enhancement and interfacial heat transfer of molten salt/porous ceramic skeleton composite phase change materials

Abstract

Molten salt has been considered as one of the most promising candidate materials for thermal energy storage (TES) systems owing to its remarkable energy density and consistent thermal performance. These properties render it particularly advantageous for the applications in concentrated solar power (CSP) and industrial process heat utilization. Nonetheless, their practical applications still face nonnegligible challenges such as the low thermal conductivity and risk of leakage. Packing molten salts into porous skeletons could be an effective way for addressing these issues. In the present work, the heat transfer characteristics of a composite phase change material (CPCM) consisting of binary chloride salt and a porous ceramic skeleton, are investigated at the microscale level using molecular dynamics (MD) simulations. Simulation results indicate that the integration of a porous SiC skeleton can substantially enhance the thermal conductivity of binary molten salt NaCl/KCl. At the temperature of 1000 K, a notable enhancement of 625.74 % in thermal conductivity has been observed. Moreover, the underlying mechanism of heat conduction enhancement has been revealed from the microscopic perspective. The results demonstrate that auxiliary thermal conductivity paths and interfacial heat transfer play primary roles in determining the thermal conductivity of CPCMs. The method of surface charge modification can effectively improve the interfacial heat transfer and the reason can be attributed to the additional thermal conductivity paths and the large number of particles involved in the interfacial heat transfer. The results gained in this work may provide insights into the heat transfer mechanism of composite molten salt/porous skeleton as well as practical guidance for designing CPCM for thermal storage applications.