An adaptive discretization for population balance equations is presented. The method is combined with the multiphase CFD code STAR-CCM+ of CD-adapco. In order to account for the multidisperse nature of the flow the dispersed phase is split into M size groups; from the modelling point of view each group is a separate phase in every aspect but the name. The groups move with their own velocities and exchange mass, momentum, and energy with other groups and with the continuous phase. Size of a group is not prescribed a priori, but calculated from an additional scalar equation. A special procedure is designed to ensure that at each point all groups have the same volume fractions. As the particle sizes change due to coagulation and breakup, the discretization of the phase space adjusts itself to the new size distribution. Few groups suffice to predict the mean characteristics of the flow.