Modelling and Comparison of Different Design Solutions for DC Transferred Arc Plasma Cutting Torches

The aim of this work is to investigate by means of a 2-D and 3-D FLUENT© based numerical model the behaviour of different types of transferred arc dual gas plasma torches used for cutting of metallic materials [1-8], putting into evidence the physical reasons for the industrial success of various design and process solutions appeared over the last years, such as: secondary gas swirl injections with different directions, various different approaches for the geometry of the plasma chamber, the effect of externally superimposed magnetic fields, the effect of different geometry for efficiently cooling the inner electrode region. Flow and heat transfer equations are solved with coupled electromagnetic ones, for a LTE optically thin plasma, while turbulence phenomena are taken into account by means of a k-ε RNG model [9-11]. Simulations include a prediction of the thermal behaviour of the solid components of the torch head, including electrode and its hafnium insert, thermal histories and trajectories of particles emitted from it under idealized conditions and the efficiency of nozzle and electrode cooling systems in various operating conditions including gas mixtures (O2/air, H35/N2, N2/N2). Radiation heat transfer to the surface of the components is included in the calculation using a customized Discrete Ordinate (DO) model. Simulations of one of the plasma torches here considered are also compared with experimental measurements in order to perform a validation of the model for what concerns pressure values in different regions of the device, regions of the device, nozzle temperature and gas mass flow rate during the working phase.