A computational fluid dynamic (CFD) model for the air reactor of chemical looping combustion (CLC) technology has been developed, with special focus on flow of clusters. To model effects of clusters on flow behavior of gas and particles in a riser of air reactor, the model of cluster structure-dependent (CSD) drag coefficient is proposed on the basis of the minimization of energy dissipation by heterogeneous drag (MEDHD). The momentum balances that characterize the clusters in the dense phase and dispersed particles in the dilute phase are proposed. The CSD drag coefficient model is incorporated into the two-fluid model. The distributions of concentration and velocity of particles are predicted in a riser of air reactor. The Ergun/Wen and Yu drag model underestimates the distribution of concentration of particles in the riser. Dynamic evolution of clusters is reproduced and the profile of concentration and solid fluxes is analyzed. Predictions using the CSD drag coefficient model are in agreement with experimental data published in the literature. The distributions of O-2 concentration and temperatures of gas phase and particles are predicted with CuO as oxygen carrier in the AR. (C) 2012 Elsevier B.V. All rights reserved.