Analytical and experimental investigations of radiative emission from media containing molecular gases and scattering particles
Walters, Donald Verne
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Permalink
https://hdl.handle.net/2142/21466
Description
Title
Analytical and experimental investigations of radiative emission from media containing molecular gases and scattering particles
Author(s)
Walters, Donald Verne
Issue Date
1990
Doctoral Committee Chair(s)
Buckius, Richard O.
Department of Study
Mechanical Science and Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Mechanical
Language
eng
Abstract
This work has focussed on developing solutions and obtaining verifying data for the emission from media containing real gases and scattering particles. The photon path length approach to solving the radiative transfer equation allows the interaction between the spectrally dependent absorption and emission of gases and the redirection of energy that scattering induces to be quantified in a rigorous manner. Solutions for geometries other than the simple layer and for nonhomogeneous media are lacking, however.
As a first step, then, the photon path length approach is formulated for a multidimensional, homogeneous medium. Rather than solving the resultant equations analytically. Monte Carlo algorithms for effecting the solutions are detailed. Emitted fluxes from multidimensional gas-particle media are computed to serve as a benchmark values. In order to extend the analysis to media with reflecting boundaries, arbitrary scattering phase functions, nonisothermality, and nonhomogeneity, the concept of the emission path is introduced. The emission path can be viewed as an extension of the line-of-sight to reflecting, scattering media and allows the rigorous incorporation of length-dependent gas-band models. An approximate method of accurately obtaining the emission from a multidimensional gas-particle medium is also desirable. The mean emission length is developed as a fundamentally valid characteristic length in scattering media. When applied to radiative transfer calculations, the mean emission length approach generally provides superior accuracy and computational efficiency as compared to similar calculations involving mean gas absorption coefficients.
Experimentally, measurements of the emitted energy from a high-temperature mixture of a real gas and scattering particles are important as verifying data for the analyses described above. Such data for a layer of CO$\sb2$ gas and Al$\sb2$O$\sb3$ particles are presented. A range of particle optical depths and mixture temperatures is investigated, and the normal, spectral intensity emitted from the mixture is measured in the spectral region encompassing the 4.3 $\mu$m CO$\sb2$ band. The interaction between the gas and particles is evidenced by CO$\sb2$ band structure changes, which are dependent upon the value of the particle extinction coefficient. Comparisons of the measured band intensities to values obtained using the emission path analysis indicate excellent agreement in most cases.
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