Experimental Investigation and Thermodynamic Modeling of the NaCl-NaNO₃-Na₂SO₄ Ternary System

Abstract

Molten salts as heat transfer and storage materials have been used to nuclear energy and concentrated solar power(CSP) applications. In this work, the system of molten salt mixture based on thermodynamic principles was designed as thermal energy storage(TES) materials. The substitutional solution model can be employed to describe the Gibbs energies of all liquid phase. Thermodynamic model parameters for the NaCl-NaNO₃-Na₂SO₄ subsystems were conducted by thermodynamic evaluation and optimization based on experimental phase-equilibria data. Thus, a set of self-consistent thermodynamic database was eventually obtained to reliably calculate the whole phase diagram and thermodynamic properties for the NaCl-NaNO₃-Na₂SO₄ ternary system. The results manifest that the eutectic point of theternary system located at T=280 °C and x_NaCl=8.4%, ${x_{NaN{O_3}}}$ =86.3% and ${x_{N{a_2}S{O_4}}}$=5.3%. Moreover, the results predicted were verified experimentally using differential scanning calorimetry(DSC) and the agreement between the measured value[T=(287±2) °C] and predicted value(T=280 °C) was satisfactory. Thus, the thermodynamic calculation method will be used to design and develop novel molten salt mixture as thermal energy storage materials.