Mean absorption coefficient of H₂O–air–MgCl₂/CaCl₂/NaCl thermal plasmas

Abstract

Under the local thermodynamic equilibrium hypothesis, the mean absorption coefficients (MACs) were calculated for H2O–air–MgCl2/CaCl2/NaCl thermal plasmas in a temperature range from 300 to 30 000 K and at atmospheric pressure. The MACs were computed under the hypothesis of isothermal plasmas which allows a good description of the radiation absorbed in cold regions. In this study, we took into account the absorption radiation resulting from the atomic continuum, molecular continuum, atomic lines and some molecular bands. Free–free transitions (bremsstrahlung) and free–bound (electron–ion recombination and electron attachment) or bound–free transitions in terms of absorption were considered for the calculation of atomic continuum. For bound–bound transitions, natural, resonance, van der Waals, Stark and Doppler effects were taken into account for the line broadenings while the escape factors were used to treat the self-absorption of the resonance lines. Molecular continuum was considered for the main molecules (H2, O2, N2, OH, NO, H2O, N2O, NO2, O3, NO3 and N2O5) whereas we studied only diatomic systems O2, N2, NO and for the absorption of molecular bands. The influence of the proportion of MgCl2, CaCl2 or NaCl in a water–air mixture was analysed as the effect of the strong self-absorbed resonance lines of the alkaline salts (Ca, Ca+, Na, Na+, Mg, Mg+, Cl and Cl+). Our results show that a low concentration of alkaline salts (less than 1% in molar proportions) in the plasma increased the MACs at low temperatures (T < 10 000 K) due to the resonance lines mainly localized in the near-UV and visible spectral regions in opposition to hydrogen, oxygen or nitrogen species for which 90% of them exist in ultraviolet. In addition to the atomic and molecular continuum, the absorption radiation of molecular bands is important at low temperatures.

On the Selection of Integration Intervals for the Calculation of Mean Absorption Coefficients

“…The optically thin limit is postulated to be 0.25. Additionally the selected values are close to a values for realistic MACs at atmospheric pressure [13]. The relatively small range (compared to variation of a real spectral absorption coefficient) is selected to make any shifts in the minimum of the norm DF m more visible.…”

“…Nordborg and Iordanidis [6] used the variation of the spectral absorption coefficient with temperature as the base for the band selection. Hannachi et al [13] grouped the absorption coefficient into bands based on the energies and important processes in the considered mixture, while Jan et al [14] based their band distribution on the variation of the absorption continuum. Reichert et al [9] successfully used 7-band MAC radiation model in commercial CFD program but unfortunately did not state the method they used for the band selection.…”

Enhancement of Laser-Induced Breakdown Spectroscopic Signals in a Liquid Jet with Glow Discharge

“…32 Among these four radiative processes, the radiative recombination process is the dominant mechanism contributing to the total continuum emission of laser-induced gas–liquid interface plasmas. 33,34 In brief, the recombination continuum intensity I rec can be written approximately as: 32 where n ion , n e , and T e are the ion density, electron density, and electron temperature, respectively.…”

Non-uniqueness of the multi-temperature law of mass action. Application to 2T plasma composition calculation by means of a collisional-radiative model

“…-first the associated thermodynamic properties (enthalpies and specific heat of electrons and heavy species); -then the transport coefficients: viscosity, electrical conductivity and the various contributions (translation, internal and reaction) to thermal conductivities related to electrons and heavy particles; -finally, the radiative properties such as the net emission coefficient [88][89][90] and mean absorption coefficients [91].…”