MODELING AND EXPERIMENTAL-STUDY OF A TRANSFERRED ARC STABILIZED WITH ARGON AND FLOWING IN A CONTROLLED-ATMOSPHERE CHAMBER FILLED WITH ARGON AT ATMOSPHERIC-PRESSURE

For a transferred arc with a flat anode working at atmospheric pressure in an argon atmosphere, the influence of the gas injector design close to the cathode tip has been systematically studied for arc currents below 300 A, gas flowrates between 5 and 60 slm, and anode-cathode distances between 10 and 46 mm. Two types of injector configurations have been studied: a cylindrical one with its wall parallel to the cathode axis and a conical one with the same cone angle as that of the cathode tip. The arc temperature was measured using the absolute intensity of ArI and ArII lines. Beside the voltage and arc current, the losses at the cathode and at the anode were continuously recorded An elliptic model was used to calculate the flow velocity, the temperature, and the current density close to the cathode and in the arc column. This model was either laminar or turbulent (K - epsilon), with the empirical constants being functions of the Reynolds number of turbulence. A cathode sheath with nonequilibrium conditions was used to obtain accurate cathode boundary conditions. Experiments and modeling have shown the benefits of using conical injectors which constrict drastically the plasma flow and enhance the gas velocity and the current density, thus increasing the heat flux to the anode. With the cylindrical injector, recirculations close to the cathode tip modify deeply its heating and reduce the plasma jet constriction: velocities and temperatures are lower when the recirculation velocity is higher. This results in lower heat fluxes to the anode compared to the conical injector.