Brazil nut effect
The Brazil nut effect or muesli effect occurs in mixed granular media . After shaking a package containing particles of different sizes several times, the largest ones are on top.
The term comes from everyday life: If you open a pack of muesli or mixed nuts , the largest nuts are usually on top. Since the thickest pieces in the cereal in the United States often Brazil nuts (ger .: brazil nuts are), this is a phenomenon referred to as granular convection. In technical terms, it is a question of segregation or segregation.
The cause of the segregation of the differently sized components is the transport. The shaking movement briefly creates cavities into which the smaller components of the muesli prefer to slide. The larger ones don't fit in, so they effectively “wander” up the longer you shake.
The exact routes taken by the nuts depend on their density , shape, surface texture and external movement. So it can also be that the big nuts are on the bottom. One then speaks of the reverse Brazil nut effect .
The Brazil nut effect not only plays a role in muesli, but is also important for the dynamics of all granular media and thus in geophysics and geotechnical engineering in relation to sandy and gravelly soils. The Brazil nut effect is the functional principle of the avalanche airbag .
literature
- Andrea Naica-Loebell: Big nuts are on top . Telepolis , November 25, 2001
- HJ Schlichting, V. Nordmeier, D. Jungmann: The big ones always end up on top . (PDF; 61 kB) University of GH Essen
- Troy Shinbrot, Fernando J. Muzzio: Reverse Buoyancy in Shaken Granular Beds . In: Phys. Rev. Lett. , 81, 1998, pp. 4365-4368 (English)
- Daniel C. Hong, Paul V. Quinn, Stefan Luding: The Reverse Brazil Nut Problem: Competition between Percolation and Condensation . (English) arxiv : cond-mat / 0010459
- Reto U. Schneider : A tough nut to crack . In: NZZ Folio , 09/2010
- Physics Experiment: Muesli on the Moon. science.orf.at, April 16, 2013
