Two-temperature chemical equilibrium modeling of nitrogen DC plasma torch with cascaded anode

Abstract Compared to conventional plasma torch, the plasma torch with cascaded anode allows a reduction of the anode surface and a prolongation of the arc column, which improves the stability and specific enthalpy of the plasma jet. A two-dimensional (2D) hydrodynamic model with thermal nonequilibrium and chemical equilibrium is developed to investigate the arc characteristics of a cascaded-anode nitrogen DC plasma torch. The model calculates the current density, the density and temperature of heavy species and electrons, and the flow velocity in the nitrogen plasma torch. It is found that the deviations from the local thermodynamic equilibrium state occur in the fringes of the arc. Moreover, in the central region of arc, e, N + and N are the dominant species, however, at the edge of the arc, N and N 2 appear to be the dominant species. In the nitrogen plasma torch, the density of N 2 + ions is much lower than the density of N + ions. The gas flow velocity reaches a maximum in the constrictor of the plasma torch and decrease in the diverging section of the plasma torch. In this work, a thorough investigation of the arc characteristics of a cascaded-anode nitrogen DC plasma torch has been carried out. The model is employed to investigate the influence of the gas flow rate on the plasma flow velocity and the differences in the flow and temperature fields in a ‘cascade torch’ compared to that for a ‘standard DC torch’.