Thermophysical properties of Ca(NO3)2-NaNO3-KNO3 mixtures for heat transfer and thermal storage

In this study calcium nitrate, sodium nitrate, and potassium nitrate were mixed to form cheap ternary molten salts based on different weight ratios. These molten salts can be used as both sensible heat storage materials and latent heat storage materials. In addition, they can be directly used as heat transfer fluids due to their low freezing temperatures. The results indicated that the mixture (Ca(NO3)2:NaNO3:KNO3 = 32:24:44 wt%) had the best performance for latent heat storage with its enthalpy of 67 J/g and melting point of about 80 °C. The specific heat capacity (1.7 J/(g °C) for the solid phase and 1.2 J/(g °C) for the liquid phase), viscosity (next to zero at 200 °C), thermal conductivity (about 1-3 W/(m K)), thermal decomposition, and cycle stability of the molten salts were measured by DSC, Malvern Kinexus Ultra+, a transient plane thermal conductivity meter, STA, and XRD, respectively. The thermophysical properties including the low manufacturing cost showed that the molten salts have great potential applications in thermal storage systems.