Thermal Properties of SiO2 Nanoparticle-Enhanced NaNO3–KNO3 Eutectic Molten Salt

Abstract This study provides a thermophysical property metrology of a nitrate-based eutectic molten salt (NEMS) enhanced by silica nanoparticles. The improvement of molten salt thermal properties can benefit fluid transport and energy storage in concentrating solar power plants and molten salt reactors. The thermal behavior and heat transfer mechanisms of the system were investigated through experimental characterization of thermal conductivity, specific heat capacity, and thermal diffusivity. Silica (SiO2) nanoparticles were added into NaNO3–KNO3 binary eutectic molten salt at 60:40 ratio. Thermal conductivity measured by a needle probe confirmed the thermal conductivity increase by nanoparticles from room temperature to the liquid eutectic phase. We demonstrate that thermal conductivity nearly doubled with 0.5 wt % silica nanoparticle concentration at molten temperatures, with a five times increase upon solidification to room temperature. Specific heat measurements also confirmed that the addition of 1.0 wt % SiO2 nanoparticles increased the molten salt's heat capacity with reductions of latent heat of fusion. Changes in specific heat were also found to be linked to nanoparticle concentration, dispersion, and interfacial configuration affecting thermal transport. The enhancement mechanism is suggested by dendrite precipitate formation around nanoparticles, which increase the effective solid–liquid interface area and induce localized changes in interfacial thermal resistance. The resulting interfacial modifications enhance thermal energy storage capacity by altering local heat transfer dynamics. These variations influence not only heat transfer but also the system's heat capacity for thermal energy storage.