Nonequilibrium effects in supersonic induction plasma

Abstract

Supersonic plasma jets find applications in plasma chemistry and plasma processing, metallurgy, experimental physics, and space technology. Usually the plasma in these jets deviates from chemical and thermal equilibrium. To optimize the industrial process detailed study of nonequilibrium effects in supersonic flow is required. In the article we apply numerical simulation to study the supersonically accelerated argon plasma flow downstream of the induction plasma torch. We compare the jets exhausting from two different convergent-divergent nozzles by means of a two-temperature model. The results show that the axial electron number density is rather convective flux controlled than recombination-ionization reaction controlled in both cases. However, the recombination resulting in electron gas heating is more essential in the jet flowing from the nozzle with a higher outlet Mach number. The composition of the jet exhausting from the nozzle with a lower outlet Mach number remains almost unchanged (“frozen”) until the end of the first expansion zone. These results confirm that the chamber pressure and the nozzle design changing leads to the induction plasma jets with different chemical conditions. For low-pressure supersonic plasma, these conditions vary from frozen to recombining. The conclusion is that depending on the industrial process, one can choose the proper torch nozzle geometry to have nonequilibrium plasma with the required properties.