Characterisation and Prediction of Powder Flow

Publication Reference: 
Author Last Name: 
Drs Geldart/Woodcock
Report Type: 
Research Area: 
Powder Flow
Publication Year: 
Publication Month: 
United Kingdom

This report covers research under the auspices cf IFPRI during the period January - December 1987 following the appointment of Hr. M.C. Turner to a Research Assistantship.

The foremost objective of the research is to elucidate the fundamental description and mechanisms of granular flow using both computer simulation and experimental methods. We aim to properly understand and formally describe the diversity of flax behaviour commonly observed in processes such as fluidisation of povters and flow from hoppers.

A generalised three-dimensional computer simulations program has Seen developed, ab initio, specifically designed to integrate the equations-of-motion of colloidal-like interacting spheres under gravitational flow on an inclined plane. The technique uses the general methodology of previous studies of dense suspensions under shear flow but incorporates numerous features essential to granular flow such as boundary friction and an interparticulate coefficier: of restitution to achieve steady-state conditions.

A novel feature of the simulations is the use of "gravitational units" whereby the gravitational constant g sets tie time and energy scales. With this approach we expect to gain s overview of the different regimes of behaviour (e.g. Geldart-types X, B, C, D, etc.) found for different powders on real laboratory of engineering time scales. The basic initial computer program is now 13 'production' and preliminary results are reported.

Laboratory experiments are being carried out alongside the simulations to investigate the flow behaviour of well-characterised (spherical, monodisperse) powders under gravitational: steady-shear flow. An experimental rig comprising a rotating bed, with the provision for a fluidisation flow field, has been constructed E d is operational. Preliminary experiments are reported, for larger particles (> 5~) and no gas field, to resemble the initial simulation conditions as closely as possible.

Both the simulations and the experimental studies are being extended to investigate the effects of a cohesive inter particle potential, which becomes important for fine powder when it is large compared to gmo, the gravitational energy, and t'L2 hydrodynamic flow field where aeration plays an important role.