Extending the kinetic theory-based thermal conductivity model to reciprocal molten salt mixtures with short-range ordering via the Modified Quasi-chemical Model in the Quadruplet Approximation

Molten salts are among the most promising materials for advanced energy systems in the renewable energy and nuclear fields, with thermal conductivity being a critical property that directly impacts the efficiency of heat transfer processes. However, reliable experimental data on the thermal conductivity for molten salt mixtures is scarce, requiring the use of atomistic simulations and robust theoretical frameworks to fill this gap. This study extends a previously developed kinetic theory-based model for common-anion molten salt mixtures to reciprocal molten salt mixtures (for example, LiF–KCl) as a function of temperature and composition. To account for the effects of first nearest neighbor short-range ordering between cations and anions, pair fractions in the Modified Quasi-chemical Model in the Quadruplet Approximation were employed. The current model fills an important gap in the modeling of thermal conductivity for reciprocal molten salt mixtures, since no existing model has accurately characterized their thermal conductivity. Predicted results were compared with various equilibrium molecular dynamics simulations performed in this work for solutions involving Li⁺, Na⁺, K⁺/F⁻, Cl⁻, as well as with existing experimental measurements. The model also predicted the thermal conductivity of reciprocal molten salt mixtures proposed in the literature as potential phase change materials. The current model demonstrated excellent predictive capability and accuracy of thermal conductivity for both monoatomic and polyatomic anion reciprocal molten salt mixtures, with an estimated error margin up to 20%. This advancement will significantly contribute to improving the statement of knowledge of reciprocal molten salt thermal conductivity and provide valuable tools for evaluating the thermal conductivity of molten salt mixtures in engineering applications.