Directional Spectral Emittance of a Packed Bed: Correlation Between Theoretical Prediction and Experimental Data

Abstract

Directional spectral emittance of an absorbing and scattering isothermal system of packed spheres is predicted by a radiative model based on the discrete ordinates method. Radiative properties for the bed of packed opaque spheres are obtained using geometric optics laws corrected with a scaling factor to take into account the dependent scattering. This model requires the knowledge of several parameters. Particle diameter and porosity can be easily obtained, but particle hemispherical spectral reflectivity is very difficult to obtain a priori. This particle reflectivity is determined by an identification method (Gauss method of linearization) applied to bidirectional spectral reflectance data obtained from an experimental device using a Fourier transform infrared spectrometer. Directional spectral emittance is measured using a direct radiometric technique that has been recently proposed. For a system of packed opaque spheres at high temperature, good agreement is observed between experimental results of directional spectral and computed theoretical data.

Experimental Determination of the Extinction Coefficient for a Packed-Bed Particulate Medium

“…Previous pertinent studies include the experimental characterization of radiative properties of dispersed media [8], the experimental determination of the extinction coefficient of packed beds [9][10][11][12] and liquid suspensions [13], and the development of an experimental system for measuring the scattering albedo, extinction, and scattering coefficients, phase function, and asymmetry factor of particulates in the infrared [14]. The basic approach for the experimental determination of β λ consists in measuring the attenuation of a light beam and solving Eq.…”

Thermal Radiative Properties of Complex Media: Theoretical Prediction Versus Experimental Identification

“…A possible issue consists of simultaneously heating with equal power incident fluxes both sides of a thin sample, by using lasers or arc lamps. This was adopted by Lopes et al [83,84] in the facility shown on Figure 5.…”

Determination of thermal radiative properties of packed-bed media containing a mixture of polydispersed particles

“…In a following study, it was shown experimentally that adding large (>100 μm) semi-transparent SiO 2 particles can significantly reduce the optical thickness, and consequently, enhance the radiative heat transfer within the packedbed [7]. Previous pertinent studies of the radiative properties in particulate media include a review of experimental work up to 1991 and scattering analysis of collimated radiation [8], experimental characterization of radiative properties of disperse systems [9], experimental determination of the extinction coefficient of packed-beds [10][11][12][13] and dense media [14,15], and Monte Carlobased determination of radiative characteristics of packed beds of large particles [16][17][18].…”