Numerical Modeling of Non-equilibrium Oxygen Induction Plasmas under Atmospheric Pressure

Thermal plasmas have simply been used as a high temperature source. This indicates that thermal plasmas may have more capabilities in material processing, if thermal plasmas are utilized effectively as chemically reactive gases. Therefore, characteristics of thermal plasmas with chemically reactive gas should be investigated. The purpose of this work is to develop chemically non-equilibrium modeling of induction thermal plasmas. A nonequilibrium modeling of oxygen induction thermal plasmas was performed without chemical equilibrium assumptions. The fields of flow, temperature, and concentration in the induction thermal plasma were calculated by solving the two-dimensional continuity, momentum, energy, and species conservation equations coupled with the Maxwell's equations. Chemical reactions of the dissociation and recombination as well as the ionization were taken into account in this modeling. The transport properties were estimated using Chapman-Enskog method with higher order of Sonine polynomial expansion with collision integrals at each of the calculation step. The degree of dissociation with the non-equilibrium model is only 60-70 % of the fully equilibrium degree of dissociation at the high temperature region of oxygen plasmas. Moreover, the degree of ionization is 80 % of the fully equilibrium degree of ionization. Oxygen atom and ion can be found near the torch wall where the temperature is relatively low. Oxygen induction plasmas can not be treated as equilibrium, even though oxygen has low dissociation energy of 494 kJ/mol. The non-equilibrium modeling with the finite chemical reaction demonstrates the following results compared with the LTE model; Wider area of high temperature region. Lower maximum-temperature. Stronger recirculation inside and above the induction coil. Wider area of oxygen atom existence. Lower maximum-concentration of oxygen atom. Peak position of Lorentz force shifts to the torch wall. As a result, a deviation from the LTE assumption is not negligible in oxygen induction plasmas under atmospheric pressure.