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Last year I completed an Honours year in Applied Mathematics at the University
of Melbourne. My project was on the segregation of granular materials in a
rotating drum. If a horizontal cylinder is approximately half-filled with two
granular materials and rotated at a constant rate, the materials may mix or they
may segregate, either radially, where a core rich in one material is seen, or
axially, where alternating bands that are rich in one or the other of the
granular materials appear along the length of the drum.
Confused? Yeah, so was I (a little), so I decided to make a rotating apparatus
out of LEGO to show the actual segregation.
First off, here’s a picture of the initial system (as close to well-mixed as I
could get. The point being, that these particular granular materials (sugar and
100s & 1000s) cannot be mixed.)
The cylinder begins spinning:
A band rich in 100s & 1000s can be seen:
Eventually, more bands appear:
The long-term behavious is that some bands will thicken, whereas others will
become thinner and/or disappear completely.
Finally, some pictures of the apparatus:
and the gearing required if using an old-style 9v motor:
If you’d like to construct a similar apparatus at home, my suggestion would be
to remove the  as it creates a fair bit of friction. Also,
attach the prongs on the rotors to the lid of the cylinder (this particular
cylinder was apparently custom-made). These problems became apparent after most
of the above pictures were taken, when I was trying to get some video of the
apparatus in action.
Yes, there is a video, but it is currently way too big to share on the internet.
Sorry about that.
Anyway, the full Brickshelf folder can be found
here.
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