Thermal conductivity in molten alkali halides: composition dependence in mixtures of (Na–K)Cl

Abstract

The thermal conductivities of molten (Na–K)Cl systems have been evaluated using equilibrium molecular dynamics simulation within the framework of Fumi–Tosi potential models. An expression for the thermal conductivity of binary ionic mixtures was derived from the phenomenological equations between flux densities and their conjugate forces in the related transport processes. Each transport coefficient was evaluated using the Green–Kubo formula. The statistical errors of thermal conductivity evaluated using six kinds of the coefficients in these mixtures were estimated to be ca. 7–12%, depending on composition, which is comparable with the case for single molten NaCl evaluated using three kinds of the coefficients. The calculation results for the equimolar mixture show that the thermal conductivity depends strongly on density, but only weakly on temperature. Furthermore, all the calculated thermal conductivities of the mixtures scale with m ^− 1/2 (N/V)^2/3, where m is the average ionic mass and N/V is the number density. These results regarding temperature and density dependencies and scaling with m ^− 1/2 (N/V)^2/3 are common to the previous results for a series of single molten alkali halides.