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Brazil Nut Effect and Granular Materials

Strange effects of granular fluids

A few strange granular effects - poaring mixtures of different granules into a hele shaw cell. to see various sorting effects. Also shaking balls in rice.

If you shake a box of mixed nuts the larger nuts tend to rise to the top, it would be nice to do some experiments to explain this.

Apparently it is because when you shake a granular substance you get a convection current because the particles at the bottom have more energy - so they are further apart so are in bulk less dense, so they rise up, and then fall down at the sides. The particles are too big to fit down any holes that are made by shaking, or down the downward convection currents - I think we need to do some experiments/ research.

Risk Assessment
Date risk assesment last checked: 
Tue, 08/01/2013
Risk assesment checked by: 
Date risk assesment double checked: 
Sun, 20/01/2013
Risk assesment double-checked by: 
Richard H
Risk Assessment: 

Looking at granular materials, slope of repose, etc. by pouring granular materials around and between two pieces of perspex (Hele-Shaw cell)


1. The cell may fall on demonstrator or member of the public.

2. Nuts can trigger very severe allergic reactions in some individuals.

Control Measure:

1. Ensure cell is held in such a way that it cannot fall over.

2. Any demonstrations involving nuts must be fully enclosed in a robust container, with the lid fixed down such that it cannot be opened accidentally.

In case of accident:

If nuts are spilt they must be completely cleared up immediately and safely disposed of.

Call first aider in case of injury.

Note: Some schools have a "no nuts on site" policy, if thinking of running this experiment in a school check with a member of staff whether this applies.