A novel population balance model (PBM) in which particle collision frequency function was determined through the coupling of the discrete element method with computational fluid dynamics was proposed to investigate the mechanisms of granule growth and breakage in fluidized bed granulation. The collision analysis revealed that the collision frequency function of one particle C(t) can be derived using the Froude number. In addition, the results indicated that the two-interparticle collision frequency function C-i,C- j(t) is equal to the one-particle collision frequency function C(t). The particle size distribution calculated using the PBM agrees extremely well with the actual values obtained through experiments at an actual production scale. This PBM can also predict the particle size distribution under various operating conditions. (C) 2019 Elsevier B.V. All rights reserved.