Abstract: As heat storage media, molten salt thermal storage materials have received considerable attention in the field of high-temperature thermal storage technology. Research and understanding of their thermodynamic properties are fundamental to advancing molten salt thermal storage materials. In this study, a high-temperature drop calorimeter was constructed for measuring and analyzing the thermodynamic properties of molten salt thermal storage materials in the temperature range of 400-1100K. The accuracy of the drop calorimeter was determined to be ±1% by measuring the enthalpy of the standard material of α-Al2O3. By measuring the enthalpy values of high-purity Sn before and after its solid-liquid phase transition, the measurement deviations for phase transition temperature and enthalpy were determined to be ±1.2% and ±1.3%, respectively. The enthalpy values of NaNO3, KNO3, and Solar Salt (60%NaNO3-40%KNO3) were measured by the drop calorimeter in the temperature range of 350-750 K. Polynomial equations for the enthalpy of both the solid and liquid phases were obtained through data fitting, and the phase transition temperatures and enthalpy values were calculated. The results of this study indicate that the drop calorimetry method can accurately measure the enthalpy, phase transition temperature, phase transition enthalpy, and other thermodynamic properties of molten salt thermal storage materials, providing a reliable calorimetric experimental method for their thermodynamic research.

Key words: Drop calorimetry, Solar molten salt, Potassium nitrate, Sodium nitrate, Phase transition enthalpy; Phase transition temperature, Enthalpy