In particle bed comminution energy is dissipated by several microprocesses which accompany the flow of particles, their compaction, and breakage. It is unknown how much energy is associated with each microprocess and what the ratios are between the energies dissipated by the different microprocesses. Based on an experimental study, a model has been developed to calculate a critical compaction velocity and the energy dissipated by flow losses. The critical compaction velocity describes the probability of the deaeration of a particle bed. Since the flow losses consume less than 0.1% of the total energy input this microprocess can be considered negligible compared others. (C) 2014 Elsevier B.V. All rights reserved.