Comparisons of Two Models of DC Arc Plasma Torch

The hypothesis of Local Thermal Equilibrium (LTE) in thermal plasma has been widely accepted. Most of the simulation models for the arc plasma torch are based on the hypothesis of LTE and its results indicate a good validity to mimic the pattern of plasma flow inside plasma torch. However, due to the LTE hypothesis, the electrical conductivity near the electrodes is significantly low because of the lower gas temperature. Consequently, it is difficult for the flow of electrical current to pass through the electrodes. Therefore, a key subject for a model depending on the LTE assumption is to deal with the low electrical conductivity near the electrodes. In this study, two models, determining the electrical conductivity at the vicinity of electrode boundary using two different assumptions, were employed to calculate the flow patterns inside a non-transferred DC arc plasma torch. The comparison of the gas temperature, velocity, voltage drop and the location of attachment between the two models were carried out. The results indicate that plasma arc inside the plasma torch fluctuates simulated by both of the two models. It seems that the model can obtain comparable accuracy if the plasma gas electrical conductivity is determined by nominal electron temperature.