Finite Element Modeling of the Arc Reattachment Process in DC Plasma Torches

Summary form only given. Progress has been achieved in the simulation of the arc dynamics inside plasma torches, but the realistic modeling of the arc reattachment process is still an unsolved problem. To mimic the physical reattachment process, a model faces the questions of where and how to introduce the new attachment. In this paper we present a reattachment model that answers the above questions as follows: a new attachment is formed at the location where the local electric field exceeds a certain pre-specified value; there, a high electrical conductivity channel along the direction normal to the anode is introduced, inducing the formation of a new attachment. This model has been implemented in our multiscale finite elements code for the simulation of a commercial plasma spray torch operating with Ar-He under different operating conditions. While the calculated reattachment frequencies and arc lengths agree with our experimental observations, the total voltage drops exceed those measured. This finding, added to the apparent lack of a well defined cold boundary layer around the arc, points towards the importance of non-equilibrium effects inside the torch.