In dried fruit mixes, Brazil nuts tend to come to the fore, but why? (Photo: Getty Images via BBC)
Have you noticed that when you shake a package of dried fruits, the Brazil nuts (or Brazil nuts, as it’s known overseas), usually larger, tend to rise to the top?
If not, run the test.
The same effect is observed in any granular material, such as various breakfast cereals (granola, for example). When moving, larger particles tend to come up to the surface.
This phenomenon is generally known as the “Brazil Nut Effect” or “Brazil Nut Effect” and has major implications for sectors where an uneven mix can significantly affect product quality, such as the pharmaceutical and mining industries.
But for the first time, scientists in the United Kingdom have been able to capture the complex dynamics of particle motion in granular materials, helping to unravel this physical “puzzle”.
Researchers at the University of Manchester (England) used 3D time-lapse images to show how Brazil nuts rise to the surface in a mixture of dried fruits.
“In this work, we followed the movement of Brazil nuts and peanuts via a time-lapse computerized tomography (CT) X-ray while the package was repeatedly shaken,” said Professor Philip Withers de Regius, co-author of the study. the top “.
A common challenge when analyzing granular materials is to monitor what happens to the particles within a pile, which are not easily visible.
Scientists noticed that peanuts go to the bottom, while three larger Brazilian kernels rise when the package is shaken. The first nut reaches the first 10% of base height after 70 shearing cycles (application of a perpendicular force to the longitudinal axis of the body), with the other two Brazilian nuts reaching this height after 150 shearing cycles. The remaining chestnuts are stuck to the bottom and do not rise up. (watching video)
Parmesh Gajjar, lead author of the study, adds the following: “Crucially, the direction of the Brazil nuts is the key to their upward movement. We found that the Brazil nuts initially start out horizontally, but do not start rising until they have rotated enough towards the vertical axis. To the surface, they return to the flat direction. “
In other words, when the sachet is shaken, the smaller dried fruits bump into the sides of the larger sacs, which increases the likelihood of the larger fruits turning around. When the Brazil nuts point up, more space is freed for the smaller dried fruits to fall off the sides. The downward flow of the smallest and then the largest forces ascends to the top.
Hence, when you get to supermarket shelves, the packaging is already shaken enough that all Brazil nuts are on top.
“Our study highlights the important role of particle shape and orientation in separation. Additionally, this ability to track 3D motion will pave the way for further experimental studies to separate mixtures and open the door to more realistic simulations and predictive models. Strong.”
According to Jaggar, this discovery could be in the interest of many sectors, such as the pharmaceutical industry and mining.
“This will allow us to better design industrial equipment to reduce separation by volume to a minimum, resulting in more regular mixtures. This is critical for many industries, for example ensuring the uniform distribution of the active ingredients in medicinal tablets, but also in the treatment of Food, mining and construction. “
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