Modelling of flowing film concentrators

Majunder, Arun Kumar. (2003). Modelling of flowing film concentrators PhD Thesis, Julius Kruttschnitt Mineral Research Centre, The University of Queensland.

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Author Majunder, Arun Kumar.
Thesis Title Modelling of flowing film concentrators
School, Centre or Institute Julius Kruttschnitt Mineral Research Centre
Institution The University of Queensland
Publication date 2003
Thesis type PhD Thesis
Supervisor Dr Geoff J. Lyman
Dr Peter N. Holtham
Total pages 218
Collection year 2003
Language eng
Subjects L
290702 Mineral Processing
640300 First Stage Treatment of Ores and Minerals
Formatted abstract

Most particle separators in mineral processing involve particle motion through water, and separation between particles of differing size and density takes place as a result of the interplay of body forces (gravitation or centrifugal), drag forces and particle inertia. One of the simplest separators is the sluice, in which separation takes place in a flowing film a few millimetres thick. In the sluice flow, the particles are suspended by the turbulent eddies, and motion relative to the fluid takes place in the so-called hindered settling mode.

The mineral processing research community has devoted enormous efforts to the modelling of mineral separators over the last half century. While many efforts have been made to use only fundamental physics as a basis for the models, fluid flow patterns in separators are complex and the motion of particle swarms through fluids is difficult to describe. Even though computer codes for computational fluid dynamics are now very powerful, a reliable means of calculating the hindered settling velocity of a specific particle type within a polydisperse and polydense particle mixture has proved to be elusive. It is however an absolutely fundamental prerequisite to almost all model structures.

In an effort to test the extent to which fundamental fluid mechanics can provide a prediction of particle separation, a study on a simple parallel-sided sluice has been carried out using glass bead and ilmenite mixtures at various particle concentrations and flow rates. Great care was taken to devise a flow splitter at the end of the sluice that permitted accurate measurement of the fluid flow profile and collection of slurry samples, allowing evaluation of the particle species concentration profiles. Moderately narrow size distributions of particles were used (0.090 to 0.18 mm). Ilmenite and glass beads were separated magnetically for analysis.

The actual particle separation taking place was compared to predictions made by first describing the fluid flow by a modified 'law of the wall' model. The hydrostatic pressure variation in the flow was taken into account and the eddy viscosity was calculated from a mixing length expression incorporating Van Driest's damping function. Using an average density and viscosity provides an explicit expression for the velocity gradient that can be numerically integrated for the flow profile.

The particle concentration distributions were then modelled with Hunt's sediment transport model assuming the particle eddy diffusion coefficient to be the same as that for the water. Hindered settling velocities of the particles were calculated using either Richardson-Zaki factors (the same for all particles) or from Brauer and Thiele's formula which takes the particle size and density distributions and solids volumetric concentration into account.

The flow profile predictions were quite accurate for water and slurry, considering the unavoidable presence of waves on the surface of the flow and the fact that the flow splitter does generate a back-pressure.

The resulting predictions of particle separation are shown to be a strong function of the settling velocities of the particles used. However, considering the limitations of using the present model and the errors associated with the experimental data, the predicted data are close to the actual data. Recommendations have been made suggesting improvements to the present model, which can form the basis for future work in this direction.

Keyword Fluid dynamics

Document type: Thesis
Collection: UQ Theses (RHD) - UQ staff and students only
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Created: Fri, 24 Aug 2007, 18:09:36 EST