Numerical solutions were obtained by the relaxation method to the combined conduction and radiation heat transfer equation in the cubic (ε = o.476) and orthorhombic (ε=O.395) lattice models of spheres, respectively. The calculated results are shown in chart as k_e/k_f vs. k_s/k_f (=10^-310⁴) with parameter of h_rD_p/k_s (-0-1). Effective thermal conductivities were experimentally determined and found in good agreement with the theory. The formula for radiation heat transfer coefficient h_r is also presented.