Physics – Optics
Scientific paper
Jan 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt........55h&link_type=abstract
Thesis (PH.D.)--THE UNIVERSITY OF TEXAS AT AUSTIN, 1993.Source: Dissertation Abstracts International, Volume: 54-12, Section: B,
Physics
Optics
Porous Ceramics, Ceramics
Scientific paper
Applications for reticulated porous ceramics are being rapidly developed in advanced energy systems, such as advanced porous combustion burners and volumetric absorbers in solar thermal receivers/reactors. Knowledge of the thermal radiative properties of reticulated porous ceramics is critical for accurate radiative modelling in anticipated high-temperature applications of future advanced energy systems. Two types of reticulated porous ceramics, partially -stabilized zirconia and oxide-bonded silicon carbide, were investigated to determine spectral absorption coefficients, spectral scattering coefficients, and spectral phase function characteristics. The investigation was limited to wavelengths of 0.3-5.0mum and material categories of 10 ppi (pores/inch), 20 ppi, and 65 ppi zirconia and silicon carbide. A new inverse analysis technique was developed using higher-order discrete ordinates radiative models to simultaneously derive absorption and scattering coefficients, and phase function properties from external reflectance and transmittance measurements on test samples of multiple thicknesses. The technique consisted of a non-linear, least-squares optimization process to minimize a multi -variable objective function using a modified Levenberg -Marquardt algorithm, active set strategy and special numerical optimization techniques to incorporate constraint conditions. Spectral absorption and scattering coefficients were recovered by inverse analysis of reflectance/transmittance test data for two different two-parameter phase functions: one based on the physical structure of the materials and the second a modified Henyey-Greenstein phase function. The physically-based phase function had scattering characteristics in common with the well-known Delta-Eddington phase function. The reflectance and transmittance test data were generally well predicted by both phase functions, and their corresponding absorption and scattering coefficients, in the discrete ordinates radiative models. Spectral absorption and scattering coefficients were established for each material and material category. Higher ppi-rated material categories were discovered to have higher absorption and scattering coefficients because of larger number densities of absorption and scattering sites. Partially -stabilized zirconia was discovered to have highly spectrally -dependent radiative properties, while oxide-bonded silicon carbide was found to have slowly-varying radiative properties with wavelength. Extinction coefficients for both materials correlated well with theoretical extinction coefficient models based on geometric optics theory.
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