Cracking the Case: New Study Sheds More Light on the "Brazil Nut Effect"
upstart writes in with an IRC submission:
Cracking the case: New study sheds more light on the "Brazil nut effect":
Open a can of mixed nuts, and chances are you'll find a bunch of Brazil nuts topping the heap-whether that's a good or bad thing depends on how you feel about Brazil nuts.
[...] As I wrote at Gizmodo back in 2016, the primary mechanisms behind the Brazil nut effect are percolation and convection. Percolation causes smaller grains to move through larger grains to the bottom of the pile, while convection pushes the larger grains toward the top. Complicating matters is gravity, pulling down on every grain, as well as the fact that every individual grain is jostling against all the others in the container, producing friction and mechanical energy (lost as heat).
[...] The Manchester team placed a mixture of peanuts and Brazil nuts inside a shearbox, with the Brazil nuts initially at the bottom. They placed the shearbox inside a CT machine and conducted 181 scans as the shear box shook up the mixed nuts, with one shear cycle between each scan, to create the time-lapse video.
As expected, over time, the peanuts in the mix percolated down, while several larger Brazil nuts gradually rose upward. The Manchester team found it took about 70 shear cycles for the first Brazil nut to reach the top 10 percent of the bed of mixed nuts. Two more reached the same point after 150 shear cycles, while the rest of the Brazil nuts remained trapped at the bottom.
It turns out that the orientation of a given Brazil nut in the mix is the key to that upward movement. The nuts typically start out in a horizontal position, and they won't begin to rise to the top until they rotate toward the vertical axis. Once a Brazil nut reaches the surface, it will revert back to the horizontal position.
Also see the story at University of Manchester.
Journal Reference:
Parmesh Gajjar, Chris G. Johnson, James Carr, et al. Size segregation of irregular granular materials captured by time-resolved 3D imaging [open], Scientific Reports (DOI: 10.1038/s41598-021-87280-1)
Read more of this story at SoylentNews.