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Brazil-nut effect versus reverse Brazil-nut effect in a moderately dense granular fluid
1Departamento de Física, Universidad de Extremadura, E-06071 Badajoz, Spain. vicenteg@unex.es
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|October 15, 2008
Summary
Researchers derived a segregation criterion to explain the Brazil-nut effect (BNE) and reverse Brazil-nut effect (RBNE) transitions. System parameters like gravity and thermal gradients influence whether larger particles rise or fall in granular mixtures.
Area of Science:
- Granular physics
- Statistical mechanics
- Non-equilibrium systems
Background:
- The Brazil-nut effect (BNE) describes the tendency of larger particles to rise in a granular mixture under vibration.
- The reverse Brazil-nut effect (RBNE) is the opposite phenomenon, where larger particles sink.
- Existing theoretical models often simplify particle interactions or system conditions.
Purpose of the Study:
- To derive a segregation criterion for the transition between BNE and RBNE.
- To investigate the influence of various system parameters on segregation phenomena.
- To extend theoretical understanding beyond near-elastic collisions and dilute systems.
Main Methods:
- Utilized the inelastic Enskog kinetic equation to develop a segregation criterion.
- Incorporated the effects of thermal gradients and gravity.
- Analyzed systems at moderate densities, considering varying mass/size ratios and coefficients of restitution.
Main Results:
- A segregation criterion was derived, elucidating the BNE-RBNE transition.
- The phase diagrams for BNE-RBNE transitions are sensitive to the balance between gravity and thermal gradients.
- Collisional dissipation's influence on segregation is more pronounced when thermal gradients dominate over gravity.
Conclusions:
- The derived criterion provides a comprehensive framework for understanding granular segregation.
- It is possible to switch between BNE and RBNE by adjusting system parameters.
- The findings extend previous dilute-limit results and align with recent experimental observations.
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