Investigation Of The Plasma-Electrodes Interfaces By Their Participation In The Simulation Region

A plasma torch has many applications and the understanding of the electrical and thermal phenomena that occur inside it is necessary to control its stability and extend its lifetime. Mumerical simulation can provide a powerful tool, however, the good simulation should be close to reality, and unrealistic boundary conditions should not be used in the modeling. In the most of performed studies so far, the simulation region contains only the space between the electrodes (plasma), and the unrealistic boundary conditions have been applied at the electrode surface. Taking such boundary conditions might produced inaccurate results. Certainly, the thermal and electrical properties are not only dependent on the plasma medium but also on the electrodes. In this study, in order to eliminate such boundary conditions, in addition to the plasma passage area, both electrodes are included in the simulation region. Three-dimensional, time-dependent and non-equilibrium simulation is performed and the plasma temperature distribution is predicted. The electric current path along the cathode-plasma-anode is determined without applying any unrealistic boundary conditions. In fact, the obtained result is in good agreement with the experiment. The electric current passes through the tapered section of the anode and this finding is well consistent with that of the eroded experimental sample. The heat transfer coefficient distribution at the anode surface is also obtained. The maximum heat transfer coefficient is about 1.6 x 10(4) W/(m(2) K) at the location of the arc attachment. A comparison with some conventional unrealistic boundary conditions indicates that some of them are inaccurate and need to be reviewed.