Development of a geometric flight unloading model for flighted rotary dryers

Flighted rotary dryers are used extensively in industrial applications for the drying of granular materials, and the understanding of the unloading characteristics of the flights within these units is critical to understanding their behaviour. This paper presents the development of a geometrical derived model for the unloading profile of a generic two-section flight. This model is then validated using experimental data from a flight unloading apparatus. The model is shown to be able to accurately reproduce the observed unloading profiles, however the results are shown to be highly sensitive to the material surface angle used in the model. High-speed photography is used to observe the surface of the granular material during unloading and measurements of key properties are made. Observation of these high-speed images shows that the unloading of the flight is discontinuous, and that there are significant fluctuations in the behaviour of the discharging solids.