NaCl-KCl-CaCl2 molten salts for high temperature heat storage: Experimental and deep learning molecular dynamics simulation study

Abstract

The thermal energy storage system based on molten salts plays a crucial role in renewable energy utilization and power grid regulation system. This article investigates NaCl-KCl-CaCl₂ molten salts for high temperature heat storage by experimental measurement and deep learning molecular dynamics simulations. The phase transition, thermal stability, and thermophysical properties of NaCl-KCl-CaCl₂ were experimental analyzed, and the results indicate that it has high enthalpy of 251.37 J/g, with observable evaporation at temperatures above 1103 K. An accurate deep potential model was further trained based on ab initio molecular dynamics data, achieving a root mean square error of 0.50 meV/atom for energy and 15.31 meV/Å for force, and the experimental and computational results for density and viscosity have discrepancies of less than 5 %. Based on experimental and simulation data, correlation equations for thermophysical properties of NaCl-KCl-CaCl₂ were conducted, and thermal performance changes with temperature were further explained from the perspective of structural changes. As the temperature rises, all ionic pairs transfer to lower coordination numbers and disperse into smaller clusters, which results in the decreases of density, thermal conductivity and viscosity, and the stability of molten salt gradually decreases as the energy barriers for ion pairs dropping.