Nature of convection-stabilized DC arcs in dual-flow nozzlegeometry. II. Optical diagnostics and theory

For pt.I see ibid., vol.18, no.1, p.91-101, 1990. A supersonic flow field with a 5.5-cm-long and ≈2.2-mm-thick cylindrical arc plasma column was observed with a four-mirror Schlieren optical system in dual-flow nozzle geometries. For both the orifice-type nozzle and the two dimensional convergent-divergent nozzle, the arc current was varied from 45 to 110 A. The optical cold-flow-plasma boundary displayed a sharp and laminar character in both nozzles, and a sharply defined, almost-constant-diameter, quiet arc is observed between the nozzles. Downstream of the nozzle throat the arc expands and assumes a conical shape. In this region, the fringe formation inside the arc is still clear, which is an indication of the laminar nature of the plasma. However, the arc boundary is not as distinct. A cooler arc is observed downstream of the nozzle throat. Using the experimentally determined axial static pressure and cold-flow mass flux rate distributions of pt.I and the channel-flow model with constant arc temperature, the energy integral was solved for the arc radius as a function of the axial distance. From this, the arc electric field strength, voltage, resistance, and power were determined, and the total heat transfer was related to the arc power. Good agreement between the calculated values and experimental data was observed