Molecular Dynamics Simulation of the Effects of Nitrite/Nitrate Equilibrium on the Structure and Properties of Kno2-Kno3-K2co3 Molten Salt Systems

Abstract

The nitrite/nitrate balance significantly affects the physical properties of molten salt systems. In this study, the effects of nitrite/nitrate equilibrium on the microstructure and physical properties of KNO2-KNO3-K2CO3 molten salt system with KNO2 concentrations ranging from 5.9 mol% to 45.9 mol% and temperatures from 673 K to 973 K were investigated by classical molecular dynamics simulation. The radial distribution function and coordination number results show that the cation-anion interaction is weakened with the increase of KNO2 concentration, while the cation-cation interaction is enhanced. The interaction between cations and carbonate ions is almost unaffected by the nitrate/nitrite ratio. According to the results of Potential of mean force, Cage correlation function and self-diffusion coefficient,  ion has the highest diffusivity and can promote the diffusion ability of the system. The density of the molten salt system decreased due to the conversion from nitric acid to nitrite. An interesting point is that the thermal conductivity at 45.9% KNO2 concentration shows a parabolic trend with temperature. The viscosity and specific heat of the mixed molten salts decreased with the increase of KNO2 concentration, and the viscosity difference decreased with the increase of temperature.

Keywords: Molten salt, Molecular dynamic, Concentrating solar power, Physical properties, Thermal energy storage