Mixed Convection and Radiation Heat Transfer in Porous Media for Solar Thermal Applications

This chapter provides a guide on radiation convection coupling methodologies within the framework of porous solar receivers. Solid materials, contrarily to most gasses, are capable of absorbing light in the visible range. Electromagnetic waves in this spectral range propagate into the medium via the pores and interacts with the solid-gas interface at the pore boundaries. For this reason porous media can be used as efficient volumetric solar receivers. If high temperatures are involved, the solid matrix also emits thermal radiation allowing a "long-range" heat transport which substantially modies the temperature proles of the medium. Therefore, the influence of radiation on the heat transfer in a porous medium is of high importance for efficient energy applications. In this chapter the identification of effective radiative properties of the porous media and the most used numerical solution approaches of the radiative transfer equation are described. It also provides a short summary of the effect of radiation on heat transfer in porous media, as found in the literature, and describes the challenges associated with designing a porous medium volumetric solar absorber.