Thermodynamic investigation of the Ca(NO3)2–NaNO3–KNO3 system for solar thermal energy storage

• Published in: Thermochimica acta Vol. 688; p. 178608
• Main Authors: Wang, Juntao, Xu, Fang, Hu, Yonghong, Chen, Zhiyuan, Mao, Caixia
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.06.2020
• Subjects: Concentrated solar power; Heat storage; Molten salt; Thermodynamic modeling; Concentrated solar power; Thermodynamic modeling; Heat storage; Molten salt
• ISSN: 0040-6031; 1872-762X
• DOI: 10.1016/j.tca.2020.178608

•The phase diagram of the Ca(NO3)2–NaNO3–KNO3 system is predicted.•The predicted ternary mixture is 32.4 % Ca(NO3)2–12.4 % NaNO3–55.2 % KNO3.•The predicted melting point of this system and that determined experimentally are in excellent agreement.•The predicted ternary mixture has a lower melting point. To eliminate the differences in the mixture with the lowest liquidus temperature of the ternary system Ca(NO3)2–NaNO3–KNO3 reported in the literature, a conformal ionic solution (CIS) model was selected to predict the phase diagram of this system. The predicted results show that there exists one mixture with the lowest liquidus temperature being 116.5 °C, and the compositions are 32.4 mol.% Ca(NO3)2+12.4 mol.% NaNO3+55.2 mol.% KNO3, respectively. Then, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) measurements of the predicted mixture were conducted. The results showed that this salt mixture has a low melting point of 115.6±0.1 °C, which coincides with the melting temperature of the predicted mixture (116.5 °C), and the thermal stability temperature is 500±1 °C. This predicted ternary salt mixture can be seen as a viable thermal energy storage medium for solar plants.