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Abstract
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.
ACKNOWLEDGMENT
This study was performed within the framework of the EU research project SOLZINC. Funding by the European Community's Research Directorate (contract ENK6-CT2001-00512), the Swiss State Secretariat for Education and Research (SER), and the Swiss Federal Office of Energy (BFE) is gratefully acknowledged. We thank T. Osinga, D. Wuillemin, and R. Garcia for technical support in preparation of the experimental set-up.
Notes
1The error values of the parameters A 1, A 2, A 3, and B represent the formal standard deviations of the fit.