Three-dimensional modelling of a dc arc plasma in a twin-torch system

A three-dimensional steady-state arc model has been developed for simulating the behaviour of a twin-torch plasma system operating in an atmospheric argon environment. The governing equations for plasma flow, electric and magnetic fields are solved in a Cartesian coordinate system with suitable domain size and appropriate boundary conditions. Radiation from the arc is accounted for using the concept of net emission coefficient. Results over the current range 300-900 A suggest that the two arc columns attached, respectively, to anode and cathode are coupled by a thin tissue-like conducting layer with a thickness in the range 3-6 mm, serving as a critical part of the current path. Lorentz force resulting from the arc's current interacting with its own magnetic field plays a decisive role in bending the two arc columns and shaping the coupling zone. Turbulence is introduced to account for the effect resulting from instability of the coupling zone as observed in experiment and its effectiveness is analysed in detail using different length scale parameters. Suggestions to further improve the model are proposed.