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Slow axial drift in three-dimensional granular tumbler flow
Zafir Zaman1, Umberto D'Ortona, Paul B Umbanhowar
1Department of Chemical & Biological Engineering, Northwestern University, Evanston, Illinois 60208, USA.
Summary
Particle flow in tumblers isn't purely radial. Experiments and simulations reveal particles drift along the axis of rotation, challenging previous models of particle dynamics in tumbling systems.
Area of Science:
- Physics of granular materials
- Computational fluid dynamics
- Chemical engineering
Background:
- Particle flow models in partially filled tumblers often neglect axial motion.
- Understanding particle dynamics is crucial for optimizing mixing and separation processes.
Purpose of the Study:
- To experimentally and computationally investigate the assumption of negligible axial particle flow in partially filled spherical and double cone tumblers.
- To quantify axial particle displacement and identify factors influencing this drift.
Main Methods:
- Experiments using spherical and double cone tumblers with colored particle tracers.
- Discrete element method (DEM) simulations to model particle flow.
- Tracking of millimeter-sized surface particles to measure axial displacements.
Main Results:
- Axial particle drift was observed in both tumbler geometries, contradicting the negligible flow assumption.
- Surface particles drifted towards the poles, while deeper particles moved towards the equator.
- Axial drift magnitude was 1-3% of the tumbler diameter per pass and varied with axial position, being zero at the equator.
Conclusions:
- The assumption of negligible axial particle flow is invalid for partially filled tumblers.
- Wall slope and equatorial diameter significantly influence axial drift.
- Normalized axial drift patterns are similar across different tumbler geometries, suggesting a universal behavior.
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