Temperature Profiles and Energy Balances for an Inductively Coupled Plasma Torch

Abstract

A mathematical model was developed to predict radial and axial temperature profiles in an induction-coupled plasma torch. The model employed temperature dependent physical properties and included radiation heat loss. Temperature fields based on the model were calculated for an atmospheric pressure argon plasma. Computed radial temperature profiles were in agreement with experimental profiles reported in the literature. The gas flow rate and flow pattern in the torch did not greatly affect the radial temperature profiles in the hottest region of the torch under ordinary operating conditions, also in agreement with experiment. A one-dimensional analysis was developed which predicted these hot-spot profiles accurately. The plasma model was also found to accurately predict distribution of energy losses from the plasma. Based on the equilibrium current density and temperature profiles provided by the model, the question of the existence of local thermodynamic equilibrium was re-examined. It was concluded that equilibrium is closely approached in the high-temperature central portion of the plasma, in agreement with previous investigators; however, nonequilibrium conditions can exist in the region of high temperature gradient at the plasma edge.