- In this study we develop a model for estimating particle friction against the wall of a jet mill nozzle. The computation is reduced to a definition of conventional force acting on particles in a polydispersed stream. It is assumed that energy losses due to friction are caused by multiple particle collisions against the nozzle walls. The proposed model is oriented to calculating jet mill nozzles and is much simpler than previously applied methods. A parametric study of the proposed model was carried out and the effect of particle friction on particle and gas velocities was derived.