A two-temperature, axi-symmetric, chemical non-equilibrium model has been developed for an oxygen-plasma cutting torch in two dimensions to obtain distributions of different plasma quantities inside the torch. Apart from mass, momentum and potential conservation equations, separate energy balance equations are considered for electrons and heavy particles. The κ–ε model has been used to account for turbulence. Non-equilibrium properties required for fluid dynamic simulations are obtained from a non-equilibrium property code that includes chemical non-equilibrium. The results show distributions of temperature, velocity, pressure, potential, current density and different species densities inside the plasma torch for an arc current of 200 A. Plasma pressure inside the torch varies from several atmospheres to near-atmospheric pressure. It has been observed that the electron and the heavy particle temperatures differ less near the axis of the torch and appreciably near the wall. Interesting features, observed for other investigated quantities, found consistent with the recent experimental observations are discussed.

Thermodynamic and transport properties are computed for a 17 species model of nitrogen-oxygen plasma under different degrees of thermal non-equilibrium, pressures and volume ratios of component gases. In the computation electron temperatures range from 300 to 45,000 K, mole fractions range from 0.8 to 0.2, pressures range from 0.1 atmosphere to 5 atmospheres, and thermal nonequilibrium parameters (T e /T h ) range from 1 to 20. It is assumed that all the electrons follow a temperature T e and the rest of the species in the plasma follow a temperature T h . Compositions are calculated using the two temperature Saha equation derived by van de Sanden et al. Updated energy level data from National Institute of Standards and Technology (NIST) and recently compiled collision integrals by Capitelli et al., have been used to obtain thermodynamic and transport properties. In the local thermodynamic equilibrium (LTE) regime, the results are compared with published data and an overall good agreement is observed.

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This paper presents an experimental approach to identify the sources of instabilities in arc plasma devices. The phenomena of demixing in arcs have been utilized to explore the characteristics of different instabilities. Problems in explaining the observed behavior with our current understanding of the phenomena are discussed. Hydrogen is used as a secondary gas with argon as the primary plasma gas for this study. Results indicate that the observed behavior such as steady, takeover, and restrike modes of instabilities in arcs may essentially originate from the thin boundary layer over the anode wall primarily at the location of the anodic arc root. The bulk core flow apparently does not play any significant role in such instabilities. Arc currents rather than flow rates control the behavior of the instabilities in frequency space. Bifurcation of the system behavior and evidence for the existence of quadratic zones in flow space of binary gas mixtures separating steady and unsteady behavior are discussed.

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Thermodynamic and transport properties of two-temperature oxygen plasmas are presented. Variation of species densities, mass densities, specific heat, enthalpy, viscosity, thermal conductivity, collision frequency and electrical conductivity as a function of temperature, pressure and different degree of temperature non-equilibrium are computed. Reactional, electronic and heavy particle components of the total thermal conductivity are discussed. To meet practical needs of fluid-dynamic simulations, temperatures included in the computation range from 300 K to 45,000 K, the ratio of electron temperature (T e ) to the heavy particle temperature (T h ) ranges from 1 to 30 and the pressure ranges from 0.1 to 7 atmospheres. Results obtained for thermodynamic equilibrium (T e = T h ) under atmospheric pressure are compared with published results obtained for similar conditions. Observed overall agreement is reasonable. Slight deviations in some properties may be attributed to the values used for collision integral data and for the two temperature formulations used. An approach for computing properties under chemical nonequilibrium and associated deviations from two-temperature results under similar conditions are discussed.

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Fluctuations in arc plasma devices are extremely important for any technological application in thermal plasma. The origin of such fluctuations remains unexplained. This paper presents a theory for observed fluctuations in atmospheric pressure arc plasma devices. A qualitative explanation for observed behavior on atmospheric pressure arc plasma fluctuations, reported in the literature, can be obtained from the theory. The potential of the theory is demonstrated through comparison of theoretical predictions with reported experimental observations.