Shape effect of Al2O3 nanoparticles on the thermophysical properties and viscosity of molten salt nanofluids for TES application at CSP plants

Two Al2O3 based nanofluids have been developed to increase the thermophysical properties of the molten salts used for thermal energy storage application at concentrated solar power plants. A novel simple dry preparation method by using a physical shaking technique was demonstrated in the present research work. A good dispersion of 1 wt% Al2O3 nanomaterials with different shapes (nanospheres and nanorod) in the base eutectic salt, i.e. 51 wt% NaNO3-49 wt% KNO3, was achieved by a shaking time of 15 min. Two different shaped Al2O3 nanomaterials, i.e. nanoparticles (Al2O3-NPs) and nanorods (Al2O3 -NRs), have been used to prepare the nanofluids. Their stability and thermophysical properties have been studied by means of TGA, DSC, LFA, Rheometry and Dilatometry. The main aim of the present study is to investigate the nanoparticle shape effects on the enhancement of the thermophysical properties of the base inorganic salt. The Al2O3-NPs based nanofluid (Al2O3 NPs-nanofluid) and Al2O3-NRs based nanofluid (Al2O3-NFts-nanofluid) show enhancements of the specific heat capacity (C-p) in solid and liquid states of -3% and -6%, respectively. The thermal conductivity analysis demonstrates enhancements of 12% and 20% in solid states and 16% and 12% in liquid state for Al2O3-NPs-nofluid and Al2O3-NRs-nanofluid, respectively. The viscosity increases of 25% and 37% were observed for Al2O3-NPs-nanofluid and Al2O3-NRs-nanofluid, respectively.