Experimental study of sedimentation of concentrated mono-disperse suspensions: Determination of sedimentation modes

• We used a LIF technique to investigate sedimentation of mono-sized suspensions.
• Interface velocities and sediment compacity have been determined.
• Different sedimentation modes have been recognized from experimental data.
• We show that the use of Richardson and Zaki law can predict these modes.
• Change in suspension particle size leads to different sediment processes.

The goal of this paper was to experimentally investigate sedimentation of concentrated suspensions of mono-sized particles at low Reynolds number. Experiments were carried out with polymethylmethacrylate (PMMA) spheres of three different radii suspended in a fluid of matched refraction index. Laser Induced Fluorescence technique was used to determine the spatio-temporal evolution of particle concentration and displacement of sedimentation fronts. It was mainly possible to recognize the existence of specific modes that govern the sedimentation process when particle radius is changed. As a consequence, the maximum packing concentration of the sediment was found to be a decreasing function of particle radius and observed results were found to be well correlated with the corresponding Richardson and Zaki flux function.

This figure shows the vertical evolution of particle concentration versus non-dimensional time (particle radius: 37.7 μm, initial concentration: 0.30 and Re = 2 × 10− 6). The open circles correspond to the top interface velocity calculated from the R–Z law. The inset represents the ϕ(z,t) 3D-plot.Figure optionsDownload as PowerPoint slide