3-D Turbulent Modeling of an ICPT with Detailed Gas Injection Section

Summary form only given. The aim of this work is to investigate in a realistic manner the behaviour of inductively coupled plasma torches operating at atmospheric pressure, by means of an improved (time-dependent) turbulent version of the 3-D model based on customized CFD commercial code FLUENTcopy developed at the University of Bologna. The mathematical model is based on the hypothesis of optically thin Ar plasma under local thermodynamic equilibrium (LTE) condition and includes the coupled set of continuity, momentum, energy and turbulence transport equations for the plasma flow along with the vector potential equations for the electromagnetic field, taking into account the actual shape of the helicoidal induction coil. The standard Reynolds stress model is used to describe turbulence phenomena in the discharge. Unlike in the previously studied configurations with simplified gas inlet section, the use of a turbulent model is here necessary due to the high Reynolds numbers occurring near the gas injection regions as a consequence of the low argon viscosity value at ambient temperature and of the high gas injection velocity related to the small dimensions of the inlet zones. 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; the gas injection section of an industrial Tekna Plasma Systems Inc 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. In particular, special attention is devoted to the modelling of the actual inlet gas section, which is characterized by two different sets of 8 and 18 circumferentially distributed injection points with a diameter of 0.8 mm for the tangential plasma gas and the axial sheath gas, respectively. A carrier gas introduced axially by means of an injection probe i- also considered. Modelling results for plasma temperature distribution are compared with experimental ones obtained by an enthalpy probe system developed at the University of Milan and conclusions are drawn on non-axisymmetric behaviour of the discharge in various operating conditions