Degree Name

Doctor of Philosophy


Department of Mechanical Engineering


The gravity flow of bulk solids from mass flow bins and hoppers is a subject of considerable practical and theoretical interest Many published papers have brought greater understanding of the flowrate of coarse particles. Research on finer materials was insufficient due to imprecise predictions of the air pressure gradient at the hopper outlet, which is a very important factor in predicting the flowrate of the fine particles.

The work in this thesis develops theoretical models for predicting the interstitial air pressure gradient and for predicting the flowrate of bulk solids from conical mass flow bins. The theoretical models are based on the continuum mechanics theory. The boundary conditions follow air pressure and bulk density continuity in a vertical direction. A close agreement between theoretical results and experimental results was obtained for predicting both flowrate and air pressure distribution. Both theoretical and experimental results indicate that the flowrate of free flowing bulk solids increases rapidly at first and then more gradually as the particle permeability constant increases.

The use of 'permeability' enables the theories developed to be applied in describing the flow behaviour of both coarse and fine particle mixtures as well as composite particle size-distributed bulk solids. The use of consolidation-related bulk density and permeability enables the theoretical models to be applied to both compressible and incompressible materials.

Results of both theoretical and experimental work on the effect of material surcharge level on the flowrate indicate that for fine materials this effect is significant.

Based on the original theoretical model, simplified expressions for predicting the dynamic deaeration coefficient Kdea and a simplified flowrate model are presented.

Finally, the study is extended to examine, theoretically and experimentally, the use of standpipes attached at the hopper outlet to increase the limiting gravitational flowrate.