Numerical investigation on the flow characteristics of a reverse-polarity plasma torch by two-temperature thermal non-equilibrium modelling

A two-temperature (2T) thermal non-equilibrium model is developed to address the thermal non-equilibrium phenomenon that inevitably exists in the reverse-polarity plasma torch (RPT) and applied to numerically investigate the plasma flow characteristics inside and outside the RPT. Then, a detailed comparison of the results of the 2T model with those of the local thermal equilibrium (LTE) model is presented. Furthermore, the temperature of the plasma jet generated by a RPT and the RPT's voltage are experimentally measured to compare and validate the result obtained by different models. The differences of the measured excitation temperature and the arc voltage between the 2T model and experimental measurement are less than 13% and 8%, respectively, in all operating cases, validating the effectiveness of the 2T model. The LTE model overestimates the velocity and temperature distribution of the RPT and its plasma jet, showing that thermal non-equilibrium phenomena cannot be neglected in the numerical modelling of the RPT. Unlike other common hot cathode plasma torches, the thermal non-equilibrium phenomenon is found even in the arc core of the RPT, due to the strong cooling effect caused by the big gas flow rate.