Gravity mass powder flow through conical hoppers ‐ Part I: A mathematical model predicting the radial velocity profiles of free‐flowing granular systems as a function of cohesion and adhesion properties

Abstract

AbstractIt has been demonstrated that the concentration, velocity profiles, and residence time distribution (RTD) of a binary powder mixture flowing under gravity‐driven conditions can be evaluated via near‐infrared spectroscopy (NIRS). Contrary to a classical fluid flow profile, a granular flow profile was proven to be a function of cohesion and adhesion powder mixture properties. The present work aimed to develop a semi‐empirical equation inspired by the radial flow profile equation used for classical fluids. It achieves this by introducing the effect of powder friction properties as internal (particle‐particle) and external (particle‐hopper wall) friction angles. The developed equation shows good agreement with the experimental results using various hopper angles and two types of free‐flowing granular systems. The knowledge gained from the developed equation is intended to predict flow behaviour in conical hoppers as a function of flowing powder adhesion and cohesion parameters. Combining such knowledge with residence time distribution and the radial concentration profiles would make it possible to evaluate the expected extent of segregation, which could lead to prohibitive deviations in the production of pharmaceutical solid dosage forms.