Transient Radiative Heat Transfer from a Plasma Produced by a Capillary Discharge

Abstract

The objective of this work is to develop a better understanding of the transient behavior of radiative heat transfer from a plasma. The plasma generation occurred within a 3.2-mm-diam and 26-mm-long polyethylene capillary. Because of its high temperature and high pressure, the plasma evolved from the capillary into an ambient air environment as an underexpanded supersonic jet that interacted with a stagnation plate. Various diagnostic techniques were used. They include heat flux and pressure gauges mounted on the stagnation plate, heat flux gauges and silicon photodiodes mounted below the plasma jet, as well as current transducers interfaced with the electrical circuit. The heat flux gauges were manufactured via sputtering and calibrated using a standard convection oven. 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 row of heat flux gauges mounted below the plasma provided an assessment of the fraction of the radiative heat flux transmitted by the fused-silica window. The results show that the peak of emitted radiant flux occurs immediately after the peak of the discharge of electrical energy, which usually occurred a relatively long time prior to arrival of the precursor shock on the stagnation plate.