Measured Radiation Heat Flux to a Probe in a NASA Ames Arc Jet

Abstract

Radiation from inside the arc heater, incident on an optical probe in the arc-heated stream, is measured to quantify radiative heating of material samples from that region. The spectral distribution in the wavelength range from 250 to 950 nm is measured with a fiber-coupled spectrometer. Total radiation measurements are made with temperature-compensated thermopile sensors, their wavelength range only being limited by the sapphire window transmission cutoff below 160 nm and above . Four arc-heater conditions with bulk enthalpies between 8 and are investigated using the 152-mm (6-in.)-diameter nozzle of the Interaction Heating Facility at NASA Ames Research Center. For two conditions, additional measurements are conducted with the 330-mm (13-in.)-diameter nozzle, yielding a different distance to the arc heater inside. The spectra are dominated by continuum emission with contributions from bound-bound emission, predominantly from nitrogen and oxygen atoms. Total radiation heat fluxes between 8 and are measured at a distance of 76 mm (3 in.) to the 6-inch-nozzle exit plane, accounting for up to 1.5% of the total heat flux on a hemispheric calorimeter or 2.7% on a flat face geometry. Although stronger than anticipated, these values are still considered negligible as a heat load.