Chippla Vandu (M.Sc.), Dr. Jürg Ellenberger and Prof. R. Krishna

Van 't Hoff Institute for Molecular Sciences

University of Amsterdam, The Netherlands

Under the influence of vibrations, a mixture of granular materials tends to segregate. Depending on the selected vibration parameters, such as the vibration amplitude and frequency, larger particles are often observed to rise to the top of the mixture as shown in the figure below. This peculiar behavior is known as the Brazil Nut Effect (BNE). The term 'Brazil Nut Effect' stems from the fact that in a container consisting of a mixture of different sized nuts, the largest nuts, often the brazil nuts, always seem to rise to the top. Have a look at these movies.

Before vibration	After vibration

Under certain vibration conditions, the Reverse Brazil Nut Effect (RBNE) is observed. Here, larger particles tend to settle at the bottom of the mixture with smaller particles rising to the top.

Granular segregation is an interesting phenomenon and the dynamics of granular materials are central to many industrial processes. More often than we may think, we do encounter granular segregation. For instance, when a pack of muesli is shaken, the larger particles end up on top of the smaller ones.

Despite the large amount of research work dedicated to understanding the Brazil Nut Effect, there is still no generally acceptable explanation in the scientific community as to how it occurs.

Our research work is focused on understanding the effect of vibrations on granular segregation, utilizing a wide range of particles. From such study, we hope to proffer explanations as to why and under what conditions the Brazil Nut and Reverse Brazil Nut Effects happen.

Next: Experimental Setup