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Radial granular segregation under chaotic flow in two-dimensional tumblers
Stephen E Cisar1, Paul B Umbanhowar, Julio M Ottino
1Department of Chemical and Biological Engineering, Northwestern University, Evanston, Illinois 60208, USA.
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|February 7, 2007
Summary
Granular materials segregate into stable patterns when rotated in polygonal tumblers. Particle flow dynamics, influenced by container shape and fill fraction, dictate pattern formation, revealing key mixing and segregation forces.
Area of Science:
- Physics
- Materials Science
- Fluid Dynamics
Background:
- Granular materials exhibit complex behaviors when subjected to external forces.
- Radial segregation in rotating systems is a phenomenon influenced by particle properties and container geometry.
- Understanding pattern formation in granular flows is crucial for various industrial and scientific applications.
Purpose of the Study:
- To investigate the radial segregation patterns in granular materials within rotating polygonal tumblers.
- To explore the influence of flow dynamics, fill fraction, and container shape on pattern formation.
- To model and understand the underlying mechanisms driving segregation and mixing.
Main Methods:
- Experimental observation of granular material segregation in quasi-two-dimensional polygonal tumblers.
- Computational simulations using a simple model to reproduce experimental segregation patterns.
- Analysis of velocity fields using Poincaré plots to identify Kolmogorov-Arnol'd-Moser (KAM) regions.
Main Results:
- Granular materials composed of two distinct particle subclasses segregate into stable, radially symmetric lobed patterns.
- Segregation patterns are highly sensitive to time-periodic flow, which depends on fill fraction and container shape.
- Simulations successfully reproduced observed segregation patterns, with KAM regions attracting smaller, denser particles.
Conclusions:
- The spatial symmetries of segregation patterns mirror those of KAM regions in the flow model.
- A key role is played by the competition between radial segregation forces (percolation, buoyancy) and chaotic mixing.
- This study provides insights into the fundamental physics governing granular segregation and mixing dynamics.
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