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Air-driven Brazil nut effect
M A Naylor1, Michael R Swift, P J King
1School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, England.
Summary
Vertical vibration causes large objects to rise in granular beds, known as the Brazil nut effect. Air movement significantly amplifies this effect in fine granular materials, revealing a connection to Chladni and Faraday
Area of Science:
- Physics
- Granular Mechanics
- Fluid Dynamics
Background:
- The Brazil nut effect describes the tendency of larger objects to rise in a granular mixture under vertical vibration.
- Interstitial air has been recently identified as a factor influencing the Brazil nut effect's dynamics.
- Previous studies by Chladni and Faraday noted phenomena related to fine granular beds and vibration.
Purpose of the Study:
- To investigate the mechanism behind the enhanced Brazil nut effect in fine granular beds due to air movement.
- To demonstrate the relationship between this enhanced effect and the piling of fine beds.
- To explore the role of air-particle interaction in vibration-induced granular phenomena.
Main Methods:
- Utilizing a porous-bottomed box to control and study air flow through a granular bed.
- Applying controlled vertical vibration to granular materials.
- Observing and analyzing the movement of larger objects within the granular bed and the behavior of fine particles.
Main Results:
- Vertical vibration induces significant air movement within fine granular beds.
- This induced air movement strongly enhances the Brazil nut effect, causing rapid rise of large objects.
- The observed phenomenon is directly linked to the air's interaction with fine particles, causing them to pile.
Conclusions:
- Air movement, driven by vertical vibration, is a primary driver of a strong Brazil nut effect in fine granular systems.
- The enhanced Brazil nut effect in fine granular beds is mechanistically related to air-particle interactions, akin to Chladni and Faraday's observations.
- Understanding these air-fluidized granular dynamics is crucial for various applications involving granular materials.