Two-temperature transport coefficients of SF6–N2 plasma

Abstract

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 300–40 000 K, 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.