The Numerical Analysis of the Three Differently Modified Ar-H₂ Atmospheric Plasma Spray Torches Toward Oxidation Control of Spraying Metal Particles

The modeling and numerical simulation of plasma jet dynamics inside and outside the modified Ar-H₂ air plasma spray torches were carried out. The simulation was made for three different anode nozzle configurations geometrically modified with the internal powder injector to generate ultra-high temperature oxide-free molten metal droplets. The effects of various working conditions, including nozzle geometry, and hydrogen mass flow rates on the plasma jet temperatures, the corresponding flow fields, and plasma compositions were examined. It was found that adding a diverging section or a converging section inside the torch has a major effect on the plasma jet temperature, velocity, and overall mixing of atmospheric oxygen into the plasma jet. Thus, the shape change of the internal torch section can play a major role in regulating the plasma jet characteristics that consequently control particle oxidation. Furthermore, the compositions of plasma jets were also simulated to examine the evolution of the oxygen along the plasma jet axis. The experimental results were used for the model validations and to investigate the spray distance-dependent oxygen content in plasma jets. The reaction between O₂ and H₂ is modeled, and it was recognized that an increment in H₂ significantly increases the oxygen consumption in the formation of water vapor in the near spray distances, and higher H₂ contents would effectively control the oxidation of spraying particles along using divergent nozzle design.