Design and thermal properties of a novel ternary chloride eutectics for high-temperature solar energy storage

Abstract

A new ternary chloride salt mixture, named SYSU-4, was developed composed of NaCl, CaCl2 and MgCl2 to meet the needs of solar energy storage over 550°C. The eutectic point and composition of SYSU-4 was predicted from the calculated phase diagram and also validated by differential scanning calorimetry (DSC). SYSU-4 was prepared experimentally by static melting method and its thermo-physical properties including heat capacity, density and viscosity at high temperature were measured, which were determined by DSC, Archimedes and vibration–rotation methods, respectively. According to the calculated ternary phase diagram, the lowest eutectic temperature was 424.05°C, in good agreement with experimental results of 424°C measured by DSC. Heat capacity of SYSU-C4 was averaged as 0.83 and 1.19J/gK for solid and liquid phase, respectively referred to sapphire standard material. Density of SYSU-C4 decreased linearly from 2.5g/cm3 to 1.9g/cm3 with the increase of temperature from 500 to 750°C. Viscosity of SYSU-C4 also decreased from 4.0cp to 3.0cp as the temperature increased. Negligible changes on the melting and freezing points of SYSU-C4 in 50 thermal cycles at 370–550°C indicates excellent thermal cycling stability. Moreover, the thermal stability of SYSU-C4 was excellent under 700°C. The developed ternary chloride salt mixture SYSU-4 can be a promising eutectic mixture for high-temperature solar thermal energy storage.