Comparative determination of actual thermal plasma characteristics by modeling and measurements for a nontransferred plasma torch with hollow electrodes

Summary form only given, as follows. Thermal plasma characteristics of a nontransferred plasma torch with hollow electrodes are numerically and experimentally investigated in the atmospheric condition, and a more accurate determination method of their actual distributions is suggested by comparison between numerical modeling and experiments. The plasma torch designed and fabricated consists of a cylindrical cathode with one end closed, a cylindrical anode, and a vortex chamber connecting the two electrodes. Air is used as arc gas, and a solenoid coil mounted around the cathode produces magnetic fields for reducing its erosion by arc root rotation. The arc voltages are measured by varying operating and geometrical conditions, and the thermal efficiency of a plasma torch is obtained by measuring the flow rate and temperature rise of the electrode coolant. In the numerical analysis, typical assumptions of steady state, axisymmetry, local thermodynamic equilibrium and optically thin plasma are adopted in a two-dimensional MHD modeling of thermal plasma. A control volume method and a modified SIMPLER algorithm are used for solving governing equations of mass, momentum, energy along with the equations describing the K-/spl epsiv/ model for turbulent effects and the current continuity for arc discharge. Spatial distributions of temperature and velocity of the thermal plasma are calculated inside the torch by varying its operating conditions. Thereafter, the profiles of temperature and velocity at the torch exit are modified by comparison of net powers of the plasma torch between a numerically calculated one and an experimentally measured one as a product of thermal efficiency and input power of the torch. By this comparative method, the temperature and velocity distributions of thermal plasma outside the torch can be finally determined to give more actual values of thermal plasma properties.