Radiative properties and radiative transfer in high pressure thermal air plasmas

The aim of this paper is to investigate radiative properties of thermal air plasmas in wide ranges of pressure and temperature, and to analyse the accuracy of some spectral and geometrical approximations in high-pressure radiative transfer applications. Comprehensive calculations of absorption spectra, including molecular, atomic and ionic line and continuum radiation, are presented and the dependence of these spectra on the pressure level is analysed. The high resolution spectra, in association with a rigorous ray-tracing method, are then used to study the accuracy of the P-1 and the simplified SP3 geometrical approximations in 1D axisymmetric geometries. Cylindrical plasma columns at uniform pressure and with a non-uniform pressure distribution are considered. The P-1 approximation provides acceptable results but the SP3 approximation is found to be more accurate. Concerning the spectral approximations, the use of band averaged Rosseland mean absorption coefficients yields volumetric radiative powers in fairly good agreement with line-by-line calculations.