Select your localized edition:

Close ×

More Ways to Connect

Discover one of our 28 local entrepreneurial communities »

Be the first to know as we launch in new countries and markets around the globe.

Interested in bringing MIT Technology Review to your local market?

MIT Technology ReviewMIT Technology Review - logo

 

Unsupported browser: Your browser does not meet modern web standards. See how it scores »

{ action.text }

In 1939, the Japanese researcher Yositisi Oyama, showed that a rotating drum half-filled with beads of different sizes causes the beads to demix forming into various patterns of segregation. This is a potentially interesting way to separate such mixtures. This and other work kickstarted an entirely new field focused on the strange behaviour of granular fluids.

Now, Frank Rietz and Ralf Stannarius at the Department of Nonlinear Phenomena at the University of Magdeburg in Germany have found a curious corollary to this work.

Instead of a rotating drum, they confine their mixture of small and large beads to a flat box which they then set rotating at slow speed so inertial effects are minimised. And instead of half filling the box, they almost totally fill it with beads.

You might imagine that the beads would jam, preventing any separation but what actually happens is quite extraordinary. Above some filling threshold, the bead separation flow begins to show a rich pattern of convection.

All this is beautifully filmed and explained in a fluid dynamics video which is well worth looking at (if only to see how scientific publication is changing.)

Rietz and Stannarius say they have been unable to explain these patterns using the known mechanisms of granular convection. So they’re left with a puzzle: how do these patterns emerge?

The answer may be of more than passing interest to earth scientists since similar convection patterns emerge on large scale in Earth’s atmosphere. Whether there is any link, however, has yet to be established.

An interesting puzzle for fluid dynamicists with a few hours to spare.

Ref: arxiv.org/abs/0910.4897: Convection Rolls in a Rotating Box Filled with Beads

3 comments. Share your thoughts »

Tagged: Materials

Reprints and Permissions | Send feedback to the editor

From the Archives

Close

Introducing MIT Technology Review Insider.

Already a Magazine subscriber?

You're automatically an Insider. It's easy to activate or upgrade your account.

Activate Your Account

Become an Insider

It's the new way to subscribe. Get even more of the tech news, research, and discoveries you crave.

Sign Up

Learn More

Find out why MIT Technology Review Insider is for you and explore your options.

Show Me