AXIAL AND RADIAL HEAT-TRANSPORT IN A HIGH-TEMPERATURE SF6 ARC

Measured radial temperature profiles and electric fields in high-current (1-17 kA), supersonic (Mach 1.5) SF6 interrupter arcs are used to evaluate the axial (enthalpy and kinetic energy flux) and radial (conduction and radiation) components of the energy balance. The input power in the 20 mm upstream arc section considered varies from 0.5 to 6 MW and the copper impurity concentration from <or=2 to 20% in this current range. Axial losses are a maximum of 75% of the input at 9 kA. A significant fraction of the input at 17 kA is lost by optically-thin impurity line radiation. At 1 kA only 20% of the input can be attributed to convection and only approximately 1% to laminar thermal conduction. The low-current temperature profiles are characteristic of radiation-loss-dominated arcs. Evaluation of the effective radiation conductivity yields repeatable peaks at 13500 and 18500K corresponding to maximum emission of S and F atomic resonance line radiation. Resonance radiation escaping from the arc core is absorbed in the thermal zone by molecular species.