Basic properties of eutectic chloride salts NaCl-KCl-ZnCl2 and NaCl-KCl-MgCl2 as HTFs and thermal storage media measured using simultaneous DSC-TGA

Concentrated solar power (CSP) technologies tend to work at high temperatures for better energy efficiency, which need high temperature heat transfer fluids (HTF) and thermal storage. A good HTF should have low melting point and be thermally stable at high temperatures. A thermal storage medium needs a high heat capacity in order to store more energy in per unit of mass or volume. The objective of this work is to study the basic thermophysical properties of several eutectic molten salts for HTF and thermal storage media, which can work at upper limit temperatures of 850 °C. The eutectic salts are mixtures by NaCl-KCl-ZnCl2, and by NaCl-KCl-MgCl2, respectively. The heat capacity, melting point, and heat of fusion of the eutectic salts at different temperatures were measured using Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analysis (TGA) simultaneously. Details of the measurements and obtained experience of operating the equipment are provided in the work. For each of the eutectic salts multiple samples were tested to check repeatability and to minimize random errors. In theoretical analysis, mixing rules from literature was used to estimate the heat capacity of the new HTFs, which showed good agreement with experimental data.