Two-temperature transport coefficients of SF₆-N₂ plasma

Sulfur hexafluoride (SF₆) is widely adopted in electric power industry, especially in high-voltage circuit breakers and gas-insulated switchgear. However, the use of SF₆ is limited by its high liquidation temperature and high global warming potential. Recently, research shows SF₆-N₂ mixture, which shows environmental friendliness and good electrical properties, may be a feasible substitute for pure SF₆. This paper is devoted to the calculation of and transport coefficients of SF₆-N₂ mixture under both LTE (local thermodynamic equilibrium) and non-LTE condition. The two-temperature mass action law was used to determine the composition. The transport coefficients were calculated by classical Chapman-Enskog method simplified by Devoto. The thermophysical properties are presented for electron temperatures of 300-40000K, ratios of electron to heavy species temperature of 1-10 and N₂ mole fraction of 0%-100% at atmospheric pressure. The ionization processes under both LTE and non-LTE have been discussed. The results show that deviations from local thermodynamic equilibrium significantly affect the properties of SF₆-N₂ plasma, especially before the plasma is fully ionized. The different influence of N₂ on properties for SF₆-N₂ plasma in and out of LTE has been found. The results will serve as reliable reference data for computational simulation of the behavior of SF₆-N₂ plasmas.