A New Ternary Chloride Eutectic Mixture and its Thermo-physical Properties for Solar Thermal Energy Storage

Abstract

In order to meet the needs of solar energy storage over 550°C, the eutectic point and composition of a new ternary salt mixture consisted of NaCl, CaCl2 and MgCl2 was predicted from calculated phase diagram and that was also validated by differential scanning calorimetry (DSC). The lowest eutectic temperature predicted by the phase diagram was 424.05°C. The actual eutectic point was confirmed 424°C but with different composition compared with the predicted eutectic point. Besides, this new eutectic salt mixture (named SYSU-C4) was prepared by static melting method and its thermo-physical properties were also measured. Heat capacity, density and viscosity of SYSU-C4 were respectively determined by DSC, Archimedes and vibration-rotation methods. Heat capacity of this molten salt was calculated from DSC curve in the reference of sapphire standard material, the average value of solid salt was 0.83 J/g K and the liquid salt was 1.19 J/g K. Density of molten salt decreased linearly from 2.5 g/cm3 to 1.9 g/cm3 with increasing in the temperature range from 500°C to 750°C. Viscosity of the eutectic salt mixture also decreased from 4.0 cp to 3.0 cp as the temperature increased. Meanwhile, mass loss curves under isothermal conditions were determined and the result showed that the thermal stability of this new eutectic salt was excellent under 700°C.