TRANSMITTANCE ENHANCEMENT OF PACKED-BED PARTICULATE MEDIA

• Published in: Experimental heat transfer 2008-01, Vol.21 (1), p.73-82
• Main Authors: Lipiński, W., Guillot, E., Olalde, G., Steinfeld, A.
• Format: Article
• Language: English
• Subjects: Applied sciences; Energy; Equipments, installations and applications; Exact sciences and technology; Natural energy; packed bed; radiation; Solar energy; Solar thermal conversion; spectroscopy; transmittance
• ISSN: 0891-6152; 1521-0480
• DOI: 10.1080/08916150701647843

The optical thickness of highly attenuating packed-bed particulate media can be significantly reduced and, consequently, the radiation heat transfer enhanced, by the addition of large (> 100μm) semi-transparent SiO 2 particles. The monochromatic transmittance of packed-bed mixtures of SiO 2 , ZnO, and C particles of various relative mass fractions is experimentally measured as a function of the packed-bed thickness using a He-Ne laser/fiber optic/spectrometer system. Two functions, one derived from the general solution of the equation of radiative transfer for an absorbing-scattering-non emitting medium, and a second one derived from Bouguer's law, were fitted to the experimental data and used to elucidate the effect of the incoming scattering and optical thickness on the medium transmittance. The augmenting contribution of the incoming scattering diminishes with increasing content of highly absorbing carbon particles, and, when it becomes negligible, the extinction coefficient is directly determined by applying Bouguer's law for attenuation of incident radiation along its path.