Elaborating the high thermal storage and conductivity of molten NaCl-KCl-NaF eutectic from microstructures by FPMD simulations

AUTHORS: Liu, MM; Li, XJ; Wang, Y; Xu, TR; Yan, LM; Tang, ZF
Ternary NaCl-KCl-NaF eutectic salt is a promising thermal storage and heat transfer medium for the application of high-temperature concentrated solar power due to the high energy density and thermal conductivity. However, the relationships between these properties and structures of NaCl-KCl-NaF eutectic cannot be well explained by experiments, and thus the first principles molecular dynamics (FPMD) simulations technique stands out. In the work, the initial models of molten NaCl-KCl-NaF are constructed based on experimental densities, the energy storage density and thermal conductivity are evaluated via FPMD simulations, and the origins of the two properties are explained from the microstructures of radial and angular distribution functions. It is concluded that the strong coordinated solvation shell of Na-F results in the high energy storage density. And the orientations of Cl-Cl-Cl bond angle are enlarged by addition of F anions, thereby enhancing the thermal diffusion coefficient. Finally, the viscosities of molten NaCl-KCl-NaF from 923 to 1323 K are predicted by FPMD based on the diffusion coefficient and solvodynamic mean radius, suggesting that some anions of KCl and NaF are exchanged with each other above 1123 K. Overall, these simulation results are helpful to understand the performance improvement of molten alkali halides, and to replenish and modify the molten salt database. (C) 2021 Elsevier B.V. All rights reserved.