Range and size increment of industrial applications regarding Circulating Fluidized Bed (CFB) technology raise numerous design and operating problems. Further insight into the governing and complex multiphase flow physics regarding CFB operation can be provided by CFD analysis. However, it has been proven during the recent years that multi-scale phenomena occurring in CFB reactors cannot be accurately reproduced by conventional accurately reproduced by conventional models. Such model sare unable to accurately predict the moemntum exchange between the co-existing phases (gas and inert material) when calculating the drag coefficient. The main reason is that gas-solid two-phase flow features spatiotemporal multi-scale structures, named clusters, as the heterogensous flow field is developing. Aiming to evaluate the particles tendnecy to aggregate in clusters and describe the effects of this complicated mechanism on the main characteristisc of the induced multiphase flow field, the advanced Energy Minimization Multi-Scale (EMMS) analysis is applied. The EMMS scheme comprises of a set of equalities, constraints and a minimization energy equation, solved for a number of volume fraction's and slip velocitiy's values, using the optimization software General Algebraic Modeling System (GAMS). (C) 2010 Elsevier Ltd. All rights reserved.