Abstract The flow of a bulk solid powder through a mass flow hopper-silo system is modelled using stress field theory. Two common models are presented, the Coulomb and the conical model. The assumption is made that the velocity field is inversely proportional to the square of the radial coordinate. This simplification allows us to derive expressions for the stress and velocity fields in the system. The ejection times and residence time distributions for the two models are presented and the differences between the two models are shown. In particular, we find that the predictions of the two models differ greatly which has important implications for discharge and mixing as the powder flows through the system. A sensitivity analysis is also performed on some of the modelling parameters which affect the predicted differences between the Coulomb and conical models. Much of this work is based on Nedderman (1992).