Improvements of radiative transfer calculation for SF6 thermal plasmas

We present a comparison between an exact calculation of radiative transfer in SF6 thermal plasma based on a fine description of the spectrum with 300 000 spectral points for each temperature value, for simplified conditions (1D and 2D geometries with imposed symmetrical temperature profiles and Local Thermodynamic Equilibrium) and two kinds of approximated calculations. The first is the classical Net Emission Coefficient largely used in arc modelling. The second one is based on a very simplified spectral description with only seven intervals assuming a grey body condition within each interval and using the Planck and the Rosseland averaging for deducing the mean absorption coefficient. At high temperature the use of the Rosseland averaging is not satisfactory. The other two approximated methods (Net emission and the Planck averaging) are acceptable but the radiative flux is in general not very accurate. The radiative transfer calculation can be improved following three ways: a better knowledge of the basic processes and in particular of the absorption coefficients for diatomic and polyatomic molecules; the use of different definitions of mean absorption coefficients (Planck averaging at high temperature and mean natural value at low temperature); a careful choice of the spectral intervals.