Experimental Study On Thermophysical Properties Enhancement And Corrosion Behavior Of Mixed Molten Salt

Molten salt at high temperature is a molten inorganic substance composed of anions and cations.It has been widely used in the heat transfer and storage process of solar thermal power generation owing to the advantages of low viscosity,low vapor pressure and wide operating temperature range.The sCO2 Brayton cycle has been proposed to be utilized as the back-end power cycle in the new generation of concentrated solar energy system in order to improve the power generation efficiency,which requires molten salt to be suitable for higher temperature conditions.At present,the large-scale commercial solar salt and Hitec mixed nitrate keep a thermal stability of about 600? which will not work normally as a heat storage medium in higher temperature.Therefore,KCl-MgCl2(0.625-0.375wt%)and Li2CO3-Na2CO3-K2CO3(32.1-33.4-34.5wt%),two kinds of molten salts systems with excellent performance at high temperature,are selected in this paper to carry out experimental researches on the thermophysical strengthening and corrosion characteristics of molten salt.The target molten salts are prepared by the melting method in this paper.Three nanometer materials of 1%wt SiO2(15nm),Al2O3(30nm),and MWCNT(15nm)are added into the base salts and the molten salt nanofluids were prepared by two-step method.Differential scanning calorimetry(DSC)was used to measure the melting point,latent heat,and specific heat capacity of the nanometer molten salts.The experimental results showed that the addition of nanoparticles improves the heat storage performance of the molten salts.Scanning electron microscopy(SEM)observation and Energy Dispersive Spectroscopy(EDS)were performed on the micromorphology of the nanometer molten salt composite,and needle-like,cluster-like,and layered nanostructures were observed in the SiO2,Al2O3,and MWCNT nanometer molten salt composites.Therefore,this paper concludes that these special nanostructures are an important reason for the enhancement of heat storage performance.304,316L,321,and 310S four types of stainless steel were selected to conduct experimental research on the corrosion characteristics of binary chloride salt KCl-MgCl2(0.625-0.375wt%).The experimental conditions of contacting air and isolating air were designed respectively to simulate the actual working conditions of molten salt as much as possible and the external temperature was selected to be 550.650,and750? for short-term and long-term corrosion experiments.The experimental results show that the corrosion rate increases with the increasing temperature,and external air is an important factor that accelerating corrosion.Intergranular corrosion and pinhole corrosion can be observed on the surface of the stainless steel.The corrosion products of the four alloys show different morphologies.The EDS elemental analysis of the corrosion resistance showed that the corrosion resistance of 316L and 310S was better than that of 321 and 304 and the binary chloride KCl-MgCl2 has a strong corrosion.