Thermodynamic modeling and experimental verification of a NaNO3–KNO3–LiNO3–Ca(NO3)2 system for solar thermal energy storage

Abstract

A quaternary system, NaNO₃–KNO₃–LiNO₃–Ca(NO₃)₂, was predicted using the extended symmetric Kohler model to be a molten mixture with a low melting point that can be used as a heat storage and transfer fluid in concentrating solar power. The predicted eutectic temperature and composition of this system are 98.30 °C and 9.5 mol% NaNO₃, 52.8 mol% KNO₃, 27.6 mol% LiNO₃ and 10.1 mol% Ca(NO₃)₂. Differential scanning calorimetry and thermogravimetric analysis were used to measure the predicted eutectic mixture. The results showed that the salt mixture has a low melting point of 95.96 °C, which coincides with the predicted eutectic temperature (98.30 °C), a moderate heat of fusion of 64.88 J g⁻¹, and a thermal stability temperature of 450 °C. Therefore, this quaternary eutectic salt is suitable for use as a heat storage and transfer medium in solar thermal power plants.