Three-dimensional modeling of arc root rotation by external magnetic field in non-transferred thermal plasma torches

Summary form only given, as follows. A three-dimensional (3-D) numerical model has been developed to investigate the arc root rotation induced by an external magnetic field and its influences on the thermal plasma characteristics in the non-transferred arc plasma torches. A two-dimensional (2-D) numerical code package, DCPTUN (DC Plasma Torch in UNstructured Grid System) which was previously developed in the authors´ laboratory, has been extended to this 3-D model including the 3-D and transient natures of arc plasma in the atmospheric condition. The 3-D distributions of electric current are obtained from a current continuity equation along with the generalized Ohm´s law, while the magnetic fields induced by the arc, superimposed on the external field applied by permanent magnets or solenoid coils, are calculated by vector potential equations. The interactions between the arc and plasma flow are described in the framework of magnetohydrodynameic (MHD) equations in conjunction with the K-epsilon turbulence model. As a result of calculations, the angular velocity of arc root around the electrode surface and the distributions of the plasma temperature and flow fields inside the plasma torch are presented for the various operation conditions in the two kinds of plasma torches with rod-type and hollow-type electrodes, respectively. Calculated results show that the external magnetic field forces the arc attachment to rotate around the electrode surface, and that the rotating arc spreads its heat fluxes over a wider range of the electrode surface, which is expected to get less damage by reduced erosion. The temperature and velocity distributions at the torch exit are also appeared to be broaden by the arc root rotation.