Elemental demixing in inductively coupled air plasma torches at high pressures

We present and analyze detailed numerical simulations of high-pressure inductively coupled air plasma flows using two different mathematical formulations: an extended chemical non-equilibrium formalism including finite-rate chemistry and a form of the equations valid in the limit of local thermodynamic equilibrium and accounting for the demixing of chemical elements. Simulations at various operating pressures indicate that significant demixing of oxygen and nitrogen occurs, regardless of the degree of nonequilibrium in the plasma. Ideally, this effect should therefore be taken into account when the results of tests of thermal protection materials for (re-)entry spacecraft in inductively coupled plasma wind tunnels are processed. As the operating pressure is increased, chemistry becomes increasingly fast and the nonequilibrium results correctly approach the results obtained assuming local thermodynamic equilibrium, supporting the validity of the proposed local equilibrium formulation.