Effects of Solid Shield and Shroud on Plasma Jet Flame in APS Process

Gas entrainment occurs in atmospheric plasma spray (APS) after plasma jet flows into the cold surroundings, resulting in rapid decaying of speed and unwanted oxidation. Installing a solid shield or inserting a gas shroud at the end of the nozzle may be helpful to reduce air entrainment. Effects of solid shield and inert gas shroud on plasma jet are investigated numerically. It is found that solid shield and gas shroud will expand high temperature field of plasma jet in both axial and radial direction, consequently, enabling a thorough reaction of oxygen content for virtually oxygen free plasma jet. The mass fraction of the O2 gas in the plasma flow outside the shield decreases with the increase of the inert gas velocity, which maintains nearly zero in the solid shield. Inert gas velocity and its injection angle turn out to be important factors to offset the negative effects of solid shield on the main flow. It is demonstrated that the flow field is less affected when the inert gas is axially injected with the inlet velocity of 150m/s. Ar is more appropriate than N2 as an inert gas, which is mainly attributed to its physical properties.