Understanding plasma fluid dynamics inside plasma torches through advanced modeling

The aim of this paper is to investigate the behavior of different types of transferred-arc dual-gas plasma torches used for the cutting of metallic materials by means of a 2-D FLUENT-based numerical model, putting into evidence the physical reasons for the industrial success of various design and process solutions appeared over the last years, such as the following: vented-nozzle technology, various different approaches for the geometry of the plasma chamber, the effect of externally superimposed magnetic fields, and secondary-gas-swirl injections with different directions. Flow and heat-transfer equations are solved with coupled electromagnetic ones for local-thermodynamic-equilibrium optically thin plasma, whereas turbulence phenomena are taken into account by means of a k-epsilon realizable model. The simulations include a prediction of the thermal behavior of the solid components of the torch head, including electrode and hafnium insert, and the efficiency of nozzle- and electrode-cooling systems in various operating conditions, including gas mixtures (O-2/air, H35/N-2, and N-2/N-2). Radiation is included in the calculation of heat transfer to the surfaces of the components, using a customized discrete-ordinate model. Results have been analyzed with respect to plasma behavior, and conclusions have been drawn, concerning the powerfulness of numerical simulation as a tool for cutting torch design.