Convective Sedimentation of Colloidal Particles in a Bowl

Area of Science:

• Fluid dynamics
• Colloidal science
• Sedimentation processes

Background:

• Colloidal dispersions are often modeled as continuous fluids.
• Gravitational sedimentation is a key process in many scientific fields.
• Cellular convection can influence particle transport.

Purpose of the Study:

• To investigate cellular convection during gravitational sedimentation.
• To model this phenomenon in a specific geometry: a hemispherical bowl with a cylindrical shaft.
• To understand the impact of convection on sedimentation rates.

Main Methods:

• Utilized a physical model treating colloidal dispersion as a fluid continuum.
• Adapted the stream-function-vorticity form of Navier-Stokes equations for axial symmetry.
• Coupled hydrodynamic equations with mass balance for binary diffusion under gravity.
• Employed finite-element software to solve governing equations for coupled flow.

Main Results:

• Observed the development of a rapidly intensifying horizontal toroidal vortex near the bowl's axis.
• Characterized the vortex by downward flow along the bowl's curved surface and upward flow near the axis.
• Demonstrated that this large-scale cellular convection significantly enhances sedimentation rates.

Conclusions:

• Cellular convection, driven by a toroidal vortex, plays a crucial role in gravitational sedimentation.
• The specific geometry of the hemispherical bowl with a cylindrical shaft promotes this convective enhancement.
• Findings contribute to understanding particle transport and settling in complex fluid systems.