Computational analysis of the influence of a substrate, solid shield and gas shroud on the flow field of a plasma jet

A computational analysis has been carried out to simulate the interaction of a plasma jet with physical barriers using a CFD code. A simplified model based on energy conservation and wall functions is used to predict the effect of a substrate, solid shield and gas shroud on the temperature and velocity profiles of the plasma jet. It is found that the substrate has a substantial effect on the last 20 mm of the jet. The axial velocity slows markedly and there is a pronounced rise in temperature radially, which is partly due to the conversion of kinetic to thermal energy. Both the solid shield and gas shroud are predicted to provide a considerable improvement in the quality of the plasma, primarily by suppressing the entrainment of air into the jet. The high-temperature, high-velocity zone extends towards the substrate and broadens in the radial directions. This increase in the uniformity of the plasma jet is expected to provide major benefits in coating quality, materials and energy efficiency.