Calculation of thermodynamic properties and transport coefficients for SF6-N2 mixtures in the temperature range 1,000?30,000 K

Abstract

We have computed the equilibrium composition, the transport coefficients (viscosity, electrical and thermal conductivities), the thermodynamic properties (Gibbs and Helmholtz potentials, entropy, enthalpy, specific heats), and the derived quantities (mass density, sound velocity) for SF6-N2 mixtures in conditions relevant to circuit-breaker arcs: temperatures between 1000 and 30,000 K, pressures in the range 1–10 atm. The validity of our computation has been checked by a detailed comparison of our results with those available in the literature concerning pure SF6 and pure N2. In SF6-N2 mixtures the chemical reactions (dissociation, ionization) have a strong influence on thermal conduction and heat capacities. The effect of SF6 on the properties of such mixtures is elucidated: in a mixture containing 40% SF6, the amplitude of the thermal conduction peak appearing around 7500 K is reduced by a factor of 4 relative to that of pure N2. The influence of pressure on the properties of the plasma between 1 and 10 atm is relatively low.