A multi-scale modeling approach is presented in which discrete element method (DEM) and population balance (PB) models are combined via a compartment model (CM) to account for flow heterogeneity in a particle mixer-coater. Using this approach, the mixer is decomposed into bed and spray regions, and particle trajectories taken from the DEM model are used to generate an intermediate sub-CM that matches the residence time distributions of particles in these regions. A system of PB models is then generated from the CM. The CM presents as implified, but still accurate description of the particle residence times in the regions of the mixer. A case study of a simple top spray coating system shows the method is 80% faster than using DEM alone with 13% of the error of using PB alone. Approaches to estimating the minimum DEM simulation time are also presented. (C) 2011 Elsevier Ltd. All rights reserved.