Hindered Stokesian Settling of Discs and Rods

Area of Science:

• Fluid Dynamics
• Particle Science
• Rheology

Background:

• Sedimentation of particles in fluids is crucial in various industrial and natural processes.
• Hindered settling, a reduction in settling velocity with increased particle concentration, is a known phenomenon for spheres.
• The behavior of non-spherical particles, like discs and rods, under hindered settling conditions is less understood.

Purpose of the Study:

• To measure and analyze the hindered settling velocities of disc and rod suspensions.
• To compare the hindering effects of discs and rods with those of spheres.
• To develop a predictive model for hindered settling applicable to non-spherical, axisymmetric particles.

Main Methods:

• Experimental measurements of mean settling velocities for disc and rod suspensions.
• Investigation across various particle aspect ratios and solid volume fractions.
• Analysis of settling data in the Stokes flow regime.

Main Results:

• Both discs and rods demonstrate hindered settling, with velocities decreasing as solid volume fraction increases.
• Discs and rods exhibit less hindering compared to spheres at equivalent interparticle separations.
• Settling data for all tested shapes collapse onto sphere data when scaled by a factor dependent on relative particle volume.

Conclusions:

• Hindered settling in non-spherical particles is predominantly influenced by particle volume, not just orientation.
• A universal scaling law based on particle volume can predict hindered settling for various axisymmetric shapes.
• This finding simplifies the prediction of sedimentation behavior for complex particle suspensions.