The effective medium model of perfusive particles has been used to modify the dispersion coefficient of a packed bed to account for intraparticle velocity and internal structure of the perfusive particles. In this model, the diffusivity factor has been derived by solving the steady-state diffusion equation in the three regions (that is, external, envelope, and internal regions) of the effective medium model and proved experimentally. The diffusivity factor is incorporated with hydrodynamic parameters obtained earlier to modify the dispersion coefficient of bed packed with perfusive particles. It was found that the diffusivity factor is independent of perfusive particle shape. Also. it was found that the uniformity of perfusive particles is not a necessary condition, once average accessible porosity is considered instead of actual porosity. Finally, it was shown that a significant error would be introduced to predict the performance of bed packed with perfusive particles of the effect of perfusive phenomena on the dispersion coefficient of a packed bed were not considered. (c) 2005 American Institute of Chemical Engineers.