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 U.S.-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 degrees Celsius). 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
Contact Heiner Linke, University of Oregon, linke@uoregon.edu
See Heiner Linke's Web site for extensive visuals, movies, and explanations