PHYSICS NEWS UPDATE

The American Institute of Physics Bulletin of Physics News

Number 772 April 5, 2006 by Phillip F. Schewe, Ben Stein, and
Davide Castelvecchi

LIQUID FLOWING UPHILL; MIGHT BE USED TO COOL CHIPS. In a phenomenon
known as the "Leidenfrost effect," water droplets can perform a
dance in which they glide in random directions on a cushion of vapor
that forms between the droplets and a hot surface. Now, a
US-Australia collaboration (Heiner Linke, University of Oregon,
linke@uoregon.edu) shows that these droplets can be steered in a
selected direction by placing them on a sawtooth-shaped surface.
Heating the surface to temperatures above the boiling point of water
creates a cushion of vapor on which the droplet floats. The
researchers think that the jagged sawtooth surface, acting as a sort
of ratchet, redirects the flow of vapor, creating a force that moves
the droplet in a preferred direction. The droplets travel rapidly
over distances of up to a meter and can even be made to move up
inclines. This striking method for pumping a liquid occurs for many
different liquids (including nitrogen, acetone, methanol, ethanol
and water) over a wide temperature range (from - 196 to + 151 C).
A practical application of this phenomenon might be to cool off hot
computer processors. In a concept the researchers plan to test,
waste heat in a computer would activate a pump moving a stream of
liquid past the processor to cool it off. Such a pump for coolants
would need no additional power, have no moving parts, and would
spring into action only when needed, when the processor gets warm.
(Linke et al., Physical Review Letters, upcoming; extensive visuals
and explanations at http://www.uoregon.edu/~linke/dropletmovies/ )