Mechanism of Specific Heat Capacity Enhancement of Molten Salts Based Nanofluids for Thermal Energy Storage - A Molecular Study

Molten salts have been widely used for thermal energy storage in the field of solar plants and waste heat recovery. It is reported that adding nanoparticles could enhance the specific heat capacity of molten salts. One explanation is that there is a solid-like structure formed in the molten salts which leads to the enhancement. However, the underlying mechanism from molecular scale is still not clear. In this paper, KCl is chosen as the molten salt since K and Cl ions have the same charges and also the very close molar mass. SiO2 is selected as the nanoparticles. The intermolecular potential is modified in three different patterns to study the relationship between the force fields and the enhancement of specific heat capacity. A distinctive structural arrangement of K+ and Cl-ions is observed around the nanoparticles. The structure characteristics are analyzed using cross correlation covariance. It is found that, with the cross correlation covariance less than −0.041, specific heat capacity is significantly enhanced, which indicates that a separation of K+ and Cl-ions happens around nanoparticles. This finding proves from molecular scale that the enhancement of specific heat capacity is contributed by a solid-like layer around the nanoparticles. This paper provides a new approach to study the mechanism of specific heat capacity enhancement of molten salts based nanofluids.