Preparation and enhanced thermal conductivity of molten salt nanofluids with nearly unaltered viscosity

In this work, a series of solar salt nano-fluids with 2.5 wt%, 3.5 wt%, 4.5 wt%, 5.0 wt% and 10.0 wt% MgO nanoparticles (∼60 nm, 18 W/m·K[24]) have been prepared and their thermal properties over 220 °C have been studied. The viscosity (η), density (ρ), specific heat capacity (cp) and thermal diffusivity (α) of the nano-fluids have been measured by rotary viscometer, Archimedean technique, differential scanning calorimeter (DSC) and laser flash analysis (LFA) respectively. The thermal conductivity (λ) is determined by ρ, cp and α. The results show that the viscosity and density of nano-fluids are about 5.1 cp∼2.4 cp and 1.96 g/cm3∼1.83 g/cm3 at 240 °C–380 °C which is close to that of solar salt fluid. The average cp of the fluids with nano-MgO from zero to 5.0 wt% is 1.442–1.613 J/(g·K), and the λ of fluids is 0.37–0.60 W/(m·K) at 375 °C. The enhancement of cp and λ of nano-fluids reaches 11.9% and 62.1%, which increases the Nusselt number with improved heat transfer performance. It is suggested that the nano-fluid with 5.0 wt% MgO in solar salt is a promising fluid for application of heat transfer and thermal storage in a CSP system.