Measurement of the Basic Properties of Ternary Eutectic Chloride Salts Used as High Temperature Heat Transfer Fluids and Thermal Storage Media

Concentrated solar power (CSP) technologies tend to work at more and more high temperatures, which correspondingly need a high temperature heat transfer fluid (HTF) to transmit the heat from solar concentrator to power plant. The objective of this work is to study heat capacities of a HTF which can work at upper limit temperature of around 850 °C. The ideal HTF should have low melting temperature and be thermally stable at high temperatures. High specific heat capacity is also favorable. The eutectic ternary salt mixtures studied in this work are formed by NaCl, KCl and ZnCl₂. The heat capacity, heat of fusion, and melting temperatures of three salt mixtures were measured by using Differential Scanning Calorimetry (DSC)/Thermal Gravimetric Analysis (TGA) simultaneously. The accuracy of the measurements was validated by measuring three metals, Indium, Tin, and Zinc, which have standard reference data. Each of the three eutectic mixtures by NaCl-KCl-ZnCl₂ ternary system had 10 to 11 samples tested for heat of fusion, the melting point, and heat capacity. Mixing rule from literature was used to estimate the heat capacity of the new HTF, which showed very good agreement to experimental data.