Reverse and intermediate segregation of large beads in dry granular media

Area of Science:

• Granular physics
• Particle dynamics
• Material science

Background:

• Granular materials display complex behaviors, including particle segregation based on size.
• Understanding segregation mechanisms is crucial for industrial processes involving granular flows.

Purpose of the Study:

• To investigate the influence of particle size ratio on segregation patterns in granular flows.
• To identify conditions leading to both normal and reverse segregation.

Main Methods:

• Experiments were conducted using mixtures of two types of glass beads.
• Shearing was performed in chute flow, a half-filled rotating drum, and a funnel-formed pile.
• Precise measurements tracked the location of segregated beads.

Main Results:

• Small size ratios resulted in large beads segregating at the surface (normal segregation).
• High size ratios (above 5) induced reverse segregation, with large beads moving deeper.
• An intermediate segregation level was observed for both high and very small size ratios, with location evolving continuously with size ratio.

Conclusions:

• Particle size ratio is a critical factor determining segregation patterns in granular flows.
• Reverse segregation occurs at high size ratios due to the balance between particle mass and geometric effects.
• The location of segregated particles is not solely at the surface but can be at intermediate depths.