Gas emissivities and radiative transfer studies

Abstract

In Chapter 1 theoretical expressions are derived for the relations between gas absorptivities and emissivities for the limit of zero optical depth and for various models of vibration-rotation bands. Some of the band models for which useful results are obtained are bands with constant average absorption coefficients and well-defined widths, bands composed of non-overlapping spectral lines with dispersion or Doppler contour, and bands composed of randomly distributed lines with dispersion contour. The theoretical formulae are shown to provide a good correlation for the available experimental data on CO2, H2O, and CO. Representative estimates for the radiant energy emission from the combustion products formed by a burning ammonium perchlorate propellant grain are made in Chapter 2. The listed compilations of data may be used to estimate the radiant heat transfer to the burning propellant surface, as well as the radiant energy loss from the combustion products, since emission and absorption of radiation by the gases in the reaction zone are shown to be negligibly small. The study in Chapter 3 on radiant energy transfer from non-isothermal molecular emitters with non-overlapping dispersion lines complements earlier work done on overlapping lines and on randomly distributed dispersion lines. In addition to the transparent gas approximation for gases of small optical depth, a square root approximation is found to be valid for large optical depths, provided the temperature gradient in the slab of gas nearest to the observer is not too large. These approximations are used to derive explicit expressions for the radiant energy flux from two adjacent isothermal regions at different temperatures. In Chapter 4, the important equilibrium emission processes in a hydrogen plasma are investigated in the temperature range between 300°K and 10,000°K for pressures up to several hundred atmospheres. It is found that the pressure-induced spectrum of the H2 molecule makes an important emissivity contribution at the lower temperatures (below approximately 4500°K) whereas, at the higher temperatures, the bound-free and free-free transitions of the H ion and the continuum and line spectrum of the H atom are the most important contributors to the emissivity. The problems of the very broad wings of the Lyman a line and of the lowering of the ionization potentials by the fields of the plasma ions are considered.