Boundary effect on the drag force on a nonhomogeneous floc

Area of Science:

• Fluid dynamics
• Particle science
• Chemical engineering

Background:

• Understanding drag forces on flocs is crucial in various industrial processes.
• Nonhomogeneous floc structures present unique challenges compared to homogeneous ones.
• Boundary effects, like confinement in tubes, can significantly alter fluid flow patterns.

Purpose of the Study:

• To investigate the boundary effect on drag force for a spherical, nonhomogeneous floc.
• To simulate a two-layer floc structure with varying permeability to mimic porous nature.
• To analyze the influence of tube walls on floc behavior and drag coefficient.

Main Methods:

• Numerical simulations were employed to model a spherical floc at the centerline of a cylindrical tube.
• The floc's porous nature was simulated by adjusting the relative permeability of its inner and outer layers.
• Analysis focused on streamline compression, vorticity contours, and wake depression.

Main Results:

• Tube walls were observed to compress streamlines and vorticity contours, depressing the wake.
• Boundary effects were more pronounced for heterogeneous flocs than homogeneous ones.
• Floc heterogeneity caused deviations from Stokes-law-like correlations for the drag coefficient, influenced by permeability.

Conclusions:

• The heterogeneous structure of flocs significantly impacts their interaction with fluid flow and boundary effects.
• Tube walls reduce the deviation from Stokes law for heterogeneous flocs, particularly when average permeability is low.
• The study highlights the importance of considering floc structure and confinement in drag force calculations.