COMBINED CONDUCTION AND CORRELATED-RADIATION HEAT-TRANSFER IN PACKED-BEDS

A quasihomogeneous model for heat transfer in a plane-parallel packed bed of opaque spheres is presented. The proposed model takes into acco unt the variable porosity distribution within a packed bed and the cor related radiative properties of packed spheres having gray diffuse sur faces. On the basis of the proposed model, combined conductive and rad iative heat transfer through comparatively thin packed layers of cordi erite spheres or oxidized steel spheres are analyzed numerically and t he obtained results are compared with the experimental ones. Additiona lly, the adequacy of a simplified analytical formula for the total eff ective thermal conductivities of a packed bed is discussed. It is foun d that the detailed theoretical model accurately predicts the heat tra nsfer characteristics and the temperature profiles of the plane-parall el packed beds, and the predictions derived from the approximate formu la well-correlate with the present experimental data for the total eff ective thermal conductivities.