MEASUREMENTS OF TOTAL RADIANT INTENSITY OF AIR

The radiant intensity of high-temperature air plasmas was measured in the reflected shock region of a 12-in.-diam, arc-heated shock tube by utilizing a windowless cavity gage configuration. Measurements were made at gas pathlengths between 3 and 12 cm with ρ/ρ0 = 0.03 and T = 10,000 °-16,000°K utilizing newly developed transient heat-transfer gages. These gages overcome the difficulties experienced with thin-film and pyroelectric gages in the adverse environment characteristic of a total radiation measurement. Results are given for the total (windowless) intensity and for that transmitted by a quartz window (λ > 160 nm). These results are compared with theoretical predictions obtained by a spectral evaluation of the radiant energy transport equation. The theory predicts approximately equal contributions from both continuum and atomic line radiation and also that about one-half the total intensity is located at wavelengths below 120 nm. The comparison shows that the experimental results agree with the theoretical predictions at the lower temperatures, but fall below by about a factor of 2 at the higher temperatures. A similar comparison of the theory against the reported results of several other spectrally integrated air radiation measurements also shows general agreement to within a factor of 2. © 1969 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.