  A two-temperature thermal non-equilibrium model is developed and applied to
the three-dimensional and time-dependent simulation of the flow inside a DC arc
plasma torch. A detailed comparison of the results of the non-equilibrium model
with those of an equilibrium model is presented. The fluid and electromagnetic
equations in both models are approximated numerically in a fully-coupled
approach by a variational multi-scale finite element method. In contrast to the
equilibrium model, the non-equilibrium model did not need a separate
reattachment model to produce an arc reattachment process and to limit the
magnitude of the total voltage drop and arc length. The non-equilibrium results
show large non-equilibrium regions in the plasma - cold-flow interaction region
and close to the anode surface. Marked differences in the arc dynamics,
especially in the arc reattachment process, and in the magnitudes of the total
voltage drop and outlet temperatures and velocities between the models are
observed. The non-equilibrium results show improved agreement with experimental
observations.
