Mixing effects of Ar-H/sub 2/ on the plasma characteristics of non-transferred DC plasma torches in the practical geometries

Abstract

Summary form only given. Non-transferred DC plasma torches have been widely used as clean heat sources for material processings such as plasma spraying and synthesis. High enthalpy and high-speed plasma flames have given good processing efficiencies in the practical thermal plasma applications, especially in the plasma spray coating systems. Experiments indicate that an addition of hydrogen gas, which has a high specific heat and a low plasma density, to a primary argon gas greatly affects the arc power and plasma characteristics. In this study, mixing effects of Ar-H/sub 2/ on plasma characteristics in the non-transferred DC plasma torches at atmospheric condition are investigated by analyzing the voltage-current characteristics of are discharge and the distributions of plasma flow field. Typical assumptions of steady state, axisymmetry, local thermodynamic equilibrium (LTE) and optically thin plasma are adopted in a 2-D magnetohydrodynamic (MHD) modeling of thermal plasma with a special treatment of electrical conductivity at low temperature. In order to reflect the geometrical shapes of the torch, the numerical calculations are performed in the body-fitted nonorthogonal coordinate system with covariant velocity components using Karki's (1986) modified SIMPLER algorithm.