Net emission coefficient of air thermal plasmas

Abstract

We have calculated the net emission coefficient of air plasmas at atmospheric pressure in the temperature range between 300 and 40 000 K, in the assumption of local thermodynamic equilibrium and isothermal plasmas. This calculation takes into account the radiation due to the atomic continuum, the molecular continuum, the molecular bands (several systems for O2, N2, NO and N2+) and the atomic lines. Special attention has been devoted in this paper to the description of the molecular bands radiation. The results show that in the high temperature range where molecules are dissociated, the radiation properties of air plasmas are mainly due to those of nitrogen plasmas, the resonance atomic lines playing an important role in spite of their strong self-absorption. At low temperature (T<6000 K) the role of the molecular bands of oxygen (O2) and NO is predominant.

Radiative emission from air thermal plasmas with vapour of Cu or W

“…These coefficients largely determine axial plasma temperatures above 8 000 K. To account for a balance between emission and absorption at lower temperatures with steep gradients, the method of net emission coefficients is not valid. Furthermore, molecules at lower temperatures are not fully dissociated and play an important role which increases with the plasma pressure [9,10]. Even though the use of the net emission coefficients cannot precisely account for an absorption in the outer part of the arc with steep temperature gradient, it is widely used in complex computations of a plasma flow.…”

Recent work on sprite spectrum in Taiwan

“…where G(v) and F v (J) are fitted using Klein-Dunham polynomial expansions for the specified vibrational quantum number v and the specified rotational quantum number J of the energy level (Lofthus and Krupenie 1977 (Herzberg 1950;Krupenie 1972;Naghizadeh-Kashani et al 2002), and N 2 LBH (NIST Chemistry WebBook).…”

Basic knowledge on radiative and transport properties to begin in thermal plasmas modelling

“…[41][42][43][44] The treatment of the lines is thus a complex and long step since they are numerous in thermal plasmas (15150 lines for SF 6 47 as examples. In this case, we need more than 300000 wavelengths to obtain a fine and correct description of the spectra (between 1 and 3 million wavelengths are needed if the molecular bands have to be considered; 37,48,49 the spectral resolution of the absorption coefficient cannot be taken as constant and depends on the nature of the species mixed in the plasmas (from 10 −3 nm to 10 −1 nm for SF 6 -C 2 F 4 plasmas; 48 the lines' profiles must be calculated on spectral ranges being more than 100 times the half width at half maximum. To determine the spectral absorption coefficient, it is thus necessary to know the population of the emitting levels (upper level), the transition probabilities or the oscillator strengths of each line transition, the electronic structures of the atoms (energy levels, degeneracies, quantum numbers.…”