Ab-initio molecular dynamics study on thermal property of NaCl–CaCl₂ molten salt for high-temperature heat transfer and storage

NaCl–CaCl₂ molten salt is considered as a promising high-temperature heat transfer and storage fluid for advanced nuclear power plants and concentrating solar power plants in the field of renewable energy utilization. However, the comprehensive physical properties and their microscopic mechanisms for the molten NaCl–CaCl₂ are failed to be measured accurately due to the extremely measuring condition. In this work, the ab-initio molecular dynamics simulation is used to investigate its microstructures and thermophysical properties for entire operating temperatures. It reveals that ion clusters are formed in terms of three for face-sharing, two for edge-sharing, and one for corner-sharing Cl⁻ ions between the coordination shells of two neighboring cations. The coordination numbers of Na⁺-Cl^- and Ca²⁺-Cl^- ion pairs decrease from 5.88 to 6.46 at 783 K to 5.33 and 6.02 at 1173 K respectively. Meanwhile, the reliable and meaningful values of densities, ion self-diffusion coefficients, viscosities, and thermal conductivities were evaluated from 783 to 1173 K. It suggests that the distances and interactions between ions pairs determine thermodynamic properties directly. The ab-initio molecular dynamics simulation is proved to be an effective way to obtain the essential data for the designs of heat transfer and thermal energy storage systems in practical applications.