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B.1
Radiative Properties of Porous Structures and Materials
Radiatively porous materials find applications in
filament-wound structures, ablative coatings for spacecraft atmospheric entry,
porous media combustion systems, packed and pebble beds for combustion and
nuclear reactors, and others.
With the exception of porous media used as absorbers from a
very-high-temperature external radiation source or for internal combustion or
nuclear applications, most radiative transfer porous media analyses require
knowledge of the radiative properties dominated by wavelengths in the infrared
region of the spectrum. Internal medium temperatures are limited by the material
properties of the porous medium, and for applications where bed temperatures are
of the order of 1500K or below, the important radiative transfer will be at
wavelengths of 2 mm and greater. For solar collectors or reentry ablation
materials, the effective incident energy distribution is from very high
temperature sources (up to 15,000 K in some reentry cases), and the important
incident radiation is at short wavelengths. In such a case, the spectral
dependence of the radiative properties must be considered.
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