Development of molten nitrate salt based nanofluids for thermal energy storage application: High thermal performance and long storage components life-time

The use of thermal energy storage (TES) for electricity production at concentrated solar power (CSP) plants has provided several important benefits, like lower environmental impact and higher dispatchability, compared to other methods. Many investigations have been focused on the enhancement of thermophysical properties of molten salts (TES material for CSP) by the addition of minor percentage of nanoparticles. In the present work, two nanofluids were developed based on the binary eutectic mixture of NaNO3 and KNO3 (mole ratio of 55:45) as base fluid with by addition of a small amount (1wt.%) of commercial Al2O3 and SiO2 nanoparticles. The thermophysical properties of the developed nanofluids have been investigated in terms of enhancement of their heat capacity and thermal conductivity. Firstly, an effective dry method is proposed and validated for the preparation of molten salt based nanofluids. The obtained nanofluids were characterized by different techniques such as scanning electron microscopy (SEM) and X-ray powder diffraction (XRPD). Secondly, their thermophysical properties have been investigated by means of differential scanning calorimetry (DSC) and laser flash apparatus (LFA). The developed nanofluids present significant enhancements of the specific heat capacity and thermal conductivity as compared to the base fluid ones. Finally, immersion corrosion tests were conducted under atmospheric conditions for carbon steel (CS) A516.Gr70 in contact with nanofluids at 390 °C, for exposure times of 250, 500, 1000 and 1500 hours. Carbon steel samples were analysed by means of SEM-EDX (surface and cross section), XRD and mass variation. Regarding the corrosion study, the oxidation was determined as the main mechanism of carbon steel degradation upon direct contact with molten nitrate salt. It was found that adding 1%wt of Al2O3 or SiO2 nanoparticles decreases the corrosion layer thickness more than twice as compared to the pure salt.The use of thermal energy storage (TES) for electricity production at concentrated solar power (CSP) plants has provided several important benefits, like lower environmental impact and higher dispatchability, compared to other methods. Many investigations have been focused on the enhancement of thermophysical properties of molten salts (TES material for CSP) by the addition of minor percentage of nanoparticles. In the present work, two nanofluids were developed based on the binary eutectic mixture of NaNO3 and KNO3 (mole ratio of 55:45) as base fluid with by addition of a small amount (1wt.%) of commercial Al2O3 and SiO2 nanoparticles. The thermophysical properties of the developed nanofluids have been investigated in terms of enhancement of their heat capacity and thermal conductivity. Firstly, an effective dry method is proposed and validated for the preparation of molten salt based nanofluids. The obtained nanofluids were characterized by different techniques such as scanning electron microscopy (SEM) ...