Time Dependent 3-D Modelling of Inductively Coupled Plasma Torches

The aim of this work is to investigate by means of a 3-D time-dependent numerical model the behaviour of inductively coupled plasma torches operating at atmospheric pressure, using customized CFD commercial code FLUENT. Unsteady flow and energy equations are solved for an Ar optically thin plasma under conditions of laminar flow and LTE, while the electromagnetic field equations are solved in their vector potential form, taking into account the actual shape of the helicoidal induction coil. Simulations are performed over a network cluster of double processor calculators in order to use the full capabilities of the 3-D modelling in a time-dependent framework. Due to the large memory and computational power granted by parallel processing, the gas injection section of an industrial TEKNA PL-35 plasma torch is included in the model without geometry simplifications, refining the mesh at the injection points, in order to perform a more realistic simulation of the inlet region of the discharge. Unsteady effects that may arise in the plasma in particular operating conditions are investigated, including the ignition transient with tungsten wire and the dynamic effects arising due to the swirl component of the gas injection, in order to better understand the plasma discharge behaviour during operation, overcoming the limitation of steady state codes. Moreover, non conventional configurations of gas injection in the plasma torch, such as reverse-vortex stabilization, are investigated in the framework of this model.