Thermophysical property and micro-structure of the molten NaCl-KCl-CaCl2 salt at high temperature by FPMD simulation

Abstract

The lack of thermophysical property data and kinetic characteristics parameter for the molten NaCl-KCl-CaCl₂ (NKC) salt over 873K limit its practical application in thermal energy storage systems. In order to solve this problem, the thermophysical properties and structural characteristics of the NKC molten salts were investigated using the first-principles molecular dynamics (FPMD) simulations coupling experiment test at 873−1173 K. The results show that the simulated specific heat capacity within the temperature range of 873 K–1173 K is in good agreement with the experimental values. Compared with the experimental values, the simulated density of the NKC molten salt has a maximum error of no more than 3.26 %. The viscosity values (1.26−2.13 cP) at the temperature range of 1073 K–1173 K were supplemented, and these values are consistent with the theoretically calculated values. The self-diffusion coefficients of each ion show the pattern of D_Na⁺>D_K⁺>D_Cl^‒>D_Ca²⁺. The causes of the changes in the thermophysical properties of the molten salts were also elaborated from the perspective of structural changes. With the increase in temperature, the high-coordination structure decreases and the low-coordination structure increases. The overall structure of the molten salt becomes loose, which leads to a decrease in density and viscosity. Ca−Cl shows a distorted octahedral configuration. It provides insights into the application of NKC in molten salt energy storage.