Shroud gas effects on plasma characteristics of thermal plasma jetsat atmospheric conditions

摘要

Summary form only given. High-enthalpy and high-speed plasmaflames ejected from nontransferred dc plasma torches have been widelyused for material processings such as plasma spray coating and plasmasynthesis. The plasma flow is produced by the arc-gas interactionsbetween the cathode and anode inside the torch and expands as a jetthrough the nozzle into the air in the case of atmospheric conditions.The entrainment of surrounding air into the plasma flame, which reducesthe quality of materials processed, is undesirable for the efficientmaterial processings. This can be avoided by generating the plasma jetsin the low pressure environment or by flowing the shroud gas around thejet flame. The torch operation with the shroud gas is simpler and moreeconomic than the case of low pressure environment. In this work, shroudgas effects on the plasma how at atmospheric conditions are investigatedby a numerical analysis for finding the mole fraction of entrained airand the distributions of temperature and velocity components of plasmajets. Typical assumption of a steady state, axisymmetry, localthermodynamic equilibrium and optically-thin plasma is adopted in atwo-dimensional magnetohydrodynamic modeling of thermal plasma flow fromthe dc plasma torch. A control volume method and a modified SIMPLER(Semi-Implicit Method for Pressure Linked Equation Revised) algorithmare used for solving the governing equations, i.e., conservationequations for mass, momentum, energy, and mass fraction together withthe standard k-ε model for the flow turbulence