Thermophysical Characterization and Molecular Dynamics Simulation of Low Melting Nitrate Molten Salts for Concentrating Solar Power

Aiming at the problem of pipeline blockage in concentrated solar power (CSP) systems caused by the high freezing point of commercial nitrate molten salts, Na-K-Ca ternary (NKC) and Li-Na-K-Ca quaternary (LNKC-1) low-melting nitrate molten salts were prepared from nitrate raw materials related to salt lake resources. Their thermophysical properties were systematically tested, and the microstructure-property relationship was analyzed by molecular dynamics simulation under NPT ensemble. Results showed NKC had a melting point of 119.54℃ and decomposition temperature of 534.66℃, while LNKC-1 was 117.32℃ and 579.94℃, with a broader operating temperature range. Their average specific heat capacities were 1.035 and 1.041 J·g-1·℃-1 at 150~450℃, with viscosities of 1.8 and 2.3 mPa·s at 500℃, and the sharp rise in viscosity below 200℃ was the main performance shortcoming. Simulations confirmed the molten salts had a short-range ordered and long-range disordered structure, metal cations coordinated with O in NO₃⁻, and the anion-cation interaction strength followed Ca2+>Li+>Na+>K+, with the evolution of microstructure highly consistent with the change of macroscopic thermophysical properties. This study provides experimental and theoretical basis for the design of low-melting molten salts for CSP, and a new direction for the high-value utilization of lithium, potassium and calcium resources in western China’s salt lakes.