Effect of fiber orientation on thermal radiation in fibrous media

Abstract

A radiation model is developed to evaluate the effect of fiber orientation on the radiative heat transfer through fibrous media between parallel planar diffuse boundaries. Fibers in the medium can be oriented in any given polar and azimuthal directions. Pertinent parameters in the model are the absorption ratio and the backscatter factor, which characterize the effect of the absorption coefficient and the amount of backscattered radiation, respectively. The analysis reveals that the polar orientation of the fibers strongly affects both the backscatter factor and radiative heat transfer. Radiative heat transfer is, however, independent of the azimuthal direction of the fibers. For fibers oriented parallel to the boundaries, backscattering of radiation is highest which results in minimum radiative heat transfer. If the fibers are oriented perpendicular to the boundaries, there is no backscattering of radiation and radiative heat transfer is affected only by the absorption coefficient. This then results in the highest radiative heat transfer.