MODELLING BASIC PHENOMENA OF HEAT GENERATION AND TRANSFER IN INDUCTIVELY-COUPLED PLASMA TORCHES FOR VARIOUS GEOMETRICAL CONFIGURATIONS

The aim of the work is to investigate the basic phenomena of heat generation and transfer in inductively-coupled RF plasma torches working at atmospheric pressure. Many fundamental works on the subject [1,2] propose a detailed treatment of the electromagnetic, temperature and velocity fields inside the torch. In the present work, in order to highlight the effects due to the distribution of the electromagnetic and temperature fields when separated from the effect of the complex behaviour of the fluid circulation, simplified slab and cylindric geometries for the cross section of the torch have been considered. The mathematical model takes into account heat conduction and convection, using a simplified expression for the velocity field; a two-dimensional treatment of the electromagnetic field is employed. The results presented refer to torch working near the minimum plasma sustaining power and well above threshold, showing temperature and power density distributions; comparisons between results obtained using the exact two-dimensional treatment for the electromagnetic field and a simplified one-dimensional approach are presented. A simple model is also presented explaining why the transverse temperature profile tends to change its shape in order to induce an increase of the mean power along the axial coordinate when the mean plasma temperature decreases.