Shroud gas effects on plasma characteristics of thermal plasma jets at atmospheric conditions

Abstract

Summary form only given. High-enthalpy and high-speed plasma flames ejected from nontransferred dc plasma torches have been widely used for material processings such as plasma spray coating and plasma synthesis. The plasma flow is produced by the arc-gas interactions between the cathode and anode inside the torch and expands as a jet through the nozzle into the air in the case of atmospheric conditions. The entrainment of surrounding air into the plasma flame, which reduces the quality of materials processed, is undesirable for the efficient material processings. This can be avoided by generating the plasma jets in the low pressure environment or by flowing the shroud gas around the jet flame. The torch operation with the shroud gas is simpler and more economic than the case of low pressure environment. In this work, shroud gas effects on the plasma how at atmospheric conditions are investigated by a numerical analysis for finding the mole fraction of entrained air and the distributions of temperature and velocity components of plasma jets. Typical assumption of a steady state, axisymmetry, local thermodynamic equilibrium and optically-thin plasma is adopted in a two-dimensional magnetohydrodynamic modeling of thermal plasma flow from the dc plasma torch. A control volume method and a modified SIMPLER (Semi-Implicit Method for Pressure Linked Equation Revised) algorithm are used for solving the governing equations, i.e., conservation equations for mass, momentum, energy, and mass fraction together with the standard k-/spl epsiv/ model for the flow turbulence.