Material Dependence of Plasma Radiation Produced by a Capillary Discharge

Abstract

An experimental investigation has been conducted on the radiative heat transfer from an electrothermal‐ chemical plasma jet. The plasma jet was initiated by a 3.6-mg thin metallic wire within a 3.2 mm diameter and 26 mm long capillary. During the discharge of the 0.6 kJ of electrical energy, the plasma evolved from the capillary into an ambient air environment as an underexpanded supersonic jet that interacted with a stagnation plate. The effect of capillary and trigger wire materials on the radiative heat transfer between the plasma jet and stagnation plate was investigated. Experiments were conducted with nine different combinations of capillary and wire materials. Various diagnostic techniques were used, including heat flux and pressure gauges mounted on the stagnation plate, as well as a high-resolution charge-coupled device camera for flow visualization. A fused-silica window, placed about 1 mm above the gauges, ensured that only the radiative heat flux transmitted by the window was deduced. The results show that appreciable differences are present among the capillary and wire combinations, with a polycarbonate capillary and copper wire yielding the largest energy deposition in the substrate, whereas Teflon ® ‐nickel yielded the lowest. Nomenclature c p = specific heat, J/kg · K Iav = mean value of current, A Ipot = ionization potential, eV k = conductivity, W/m · K qmax = peak heat flux, W/m 2 q �� = heat flux, W/m 2