A numerical model for thermal processes in an electrode submitted to an arc in air and its experimental verification

The energy transferred to the electrodes, based on the determination of the liquid and vapor quantities created by the arc root, is evaluated by numerical computation and compared with measurements. With the help of a high-speed laser cinematography technique, the authors confirmed the assumption of a concentrated and quasi-circular arc root in air at atmospheric pressure, so an axial symmetry is adopted in the numerical model for both arc root and electrode. This modeling takes into account the huge power focused onto a small area of the electrode surface, producing intense surface heating, liquefaction, evaporation, and subsequent crater formation. This is a typical ablation problem with moving boundaries, and a method is presented here which overcomes the difficulties related to state changes and the ablation problem. The model is used to account for the results obtained with an original experimental device designed to obtain directly the amount of liquid and vapor formed, and finally, to provide a good approximation of the energy brought by the arc to the electrodes