Analysis of the volumetric phenomenon in porous beds subject to irradiation

This work examines the volumetric effect of convection within a packed bed in the presence of collimated irradiation. Using a modified P-1 approximation incorporating a local thermal nonequilibrium (LTNE) model, the energy transportation through convection and thermal conduction, and collimated and diffuse radiative transfer are investigated. The impact of pertinent parameters such as porosity phi, pore diameter d(p), and optical thickness tau on the volumetric effect are analyzed. In addition, the mechanisms of how the volumetric effect impacts LTNE and radiative heat loss are revealed. The effect of the volumetric heat transfer coefficient h(v), the fluid flow velocity u, and the ratio of solid to fluid thermal conductivities zeta versus the volumetric effect are systematically analyzed and displayed through a number of contour maps to assess the efficiency eta. Our analysis shows that enhancing the volumetric effect and extending the thickness of the porous medium improves the efficiency eta.