Evaluation of thermal physical properties of molten nitrate salts with low melting temperature

NaNO3-KNO3 (60-40 wt%, Solar salt) has been used as medium for TES and HTF in the CSP system. One of the key challenges using Solar salt is its high melting temperature, which may freeze and block the pipeline. In this work, a novel eutectic nitrate molten salt of the LiNO3-NaNO3-KNO3-CsNO3 system with low melting temperature of 368 K is designed using Calphad method. Its thermal physical properties, as well as that of Solar salt, LiNO3-NaNO3-KNO3, NaNO3-KNO3-CsNO3, NaNO3-KNO3-Ca(NO3)2, and LiNO3-NaNO3-KNO3-CsNO3-Ca(NO3)2 molten salts are comprehensively determined and evaluated for better understanding their thermal storage and heat transfer performances, such as the melting temperature, thermal stability, specific heat capacity, thermal diffusivity, density and viscosity. The energy storage capacities and figures of merit of the six molten nitrate salts are calculated based on their thermophysical properties to evaluate their TES and HTF performances. This work not only provides the basic engineering data for CSP system, but is useful for choosing media of TES and HTF.