For the first time, scientists have captured the complex dynamics of particle movement in particulate materials, helping to explain why larger Brazil nuts are often seen in mixed nuts on top of all other nuts. These findings may have a crucial impact on industries in pharmaceuticals and mining that often struggle with this phenomenon.
Many people have this experience: dip their hands into a bag of mixed nuts, only to find Brazil nuts on the top. This effect is also easily observed on the cereal box, with larger items rising to the top. In layman's terms, this phenomenon of particles being isolated by size is called the "Brazil Nut Effect" and has a huge impact on the industry, because uneven mixing can seriously reduce product quality.
Now, for the first time, scientists at the University of Manchester have used time-resolved 3D imaging technology to show how Brazilian nuts rise up in a pile of nuts. This work shows the importance of particle shape in the removal process. A common difficulty in studying granular materials is tracking what happens to particles on the inside of the stack, which are not easily visible. The new study, published in the journal Scientific Reports, has made a critical breakthrough in our understanding by leveraging advanced imaging technology at the new National Laboratory X-ray Computed Tomography Research Facility (NXCT), located at the Henry Reus Institute.
Regius Professor Philip Withers said. "In this work, we tracked the movement of Brazilian nuts and peanuts through time-lapse X-ray computed tomography as the packaging is stirred repeatedly. This gives us the first view of the Brazilian nuts moving to the top through peanuts."
The team took this unique imaging experiment with video, showing the spatiotemporal evolution of the nut mixture in 3D. Peanuts were seen oozing downwards, while three larger Brazil nuts were seen rising upwards. The first Brazil nut reaches 10% of the bed height after 70 shear cycles, and the other two Brazil nuts reach this height after 150 shear cycles. The rest of the Brazil nuts seemed to be trapped at the bottom and did not rise up.
The study's lead author Dr. Parmesh Gajjar added. "The key is that the direction of the Brazilian nuts is the key to their upward movement. We found that the Brazilian nuts initially started horizontally, but did not start to rise until they first rotated fully toward the vertical axis. Once they reached the surface, they returned to a flat direction.
" Our study highlighted the important role of particle shape and direction in separation. Furthermore, this ability to track motion in 3D will pave the way for new experimental research to isolate the mixture and will open the door to more realistic simulations and powerful predictive models. This will allow us to better design industrial equipment, minimizing dimensional isolation, thus making the mixture more even. This is crucial for many industries, such as ensuring even distribution of active ingredients in tablets, and in food processing, mining and construction industries. "
