Non-isothermal crystallization behavior of molten salt-based nanofluids

Molten salts are promising phase change materials for high-temperature thermal energy storage. Mixing molten salts with nanoparticles is attracting much attention to enhance thermal performance. However, the solid-liquid phase transition mechanism of molten salt mixing with nanoparticles has not been revealed. Therefore, this study focuses on the non-isothermal crystallization behavior of solar salt (SS) and two solar salt-based nanofluids (Ag-SS and SiO 2 -SS). Firstly, SS, Ag-SS and SiO 2 -SS samples were prepared and characterized. Secondly, based on the DSC test results, the kinetic characteristics of the samples under different cooling rates were analyzed by the Jeziorny-modified Avrami equation and the combined model of Avrami and Ozawa. Then, the activation energy was calculated, and the phase diagram analysis was introduced to analyze the crystallization process. Finally, the topological evolution of crystals obtained from the visual experiments was discussed. The results showed that the latent heat of solar salt slightly reduced when mixing with 0.5 wt% SiO 2 nanoparticles but hardly changed with 0.5 wt% Ag nanoparticles. The crystallization of solar salt slowed down about 8 % after adding 0.5 wt% Ag nanoparticles but hardly changed with 0.5 wt% SiO 2 nanoparticles. The Jeziorny-modified Avrami equation can describe the first crystallization stage of the samples, while it was not for the second stage due to the eutectic transition. Adding Ag and SiO 2 nanoparticles would change the topological evolution of solid-liquid crystals. During the first crystallization phase, SS showed mainly epitaxial crystals with strong main stems, Ag-SS lots of acicular crystals, and SiO 2 -SS snowflake crystals with well-developed lateral branches.