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nanotimes News in Brief

Engineering // The World’s Smallest Steam Engine

W

hat would be a case for the repair shop for a car engine is completely normal for a micro

engine. If it sputters, this is caused by the thermal motions of the smallest particles, which interfere with its running. Researchers at the University of Stutt- gart and Max Planck Institute for Intelligent Sys- tems (both in Germany) have now observed this with a heat engine on the micrometre scale.

“We’ve developed the world’s smallest steam engine, or to be more precise the smallest Stirling engine, and found that the machine really does perform work,” says Clemens Bechinger. “This was not ne- cessarily to be expected, because the machine is so small that its motion is hindered by microscopic pro- cesses which are of no consequence in the macro- world.” The disturbances cause the micromachine to run rough and, in a sense, sputter.

“We successfully decreased the size of the essential parts of a heat engine, such as the working gas and piston, to only a few micrometres and then assem- bled them to a machine,“ says Valentin Blickle. The working gas in the Stuttgart-based experiment thus no longer consists of countless molecules, but of only one individual plastic bead measuring a mere three micrometres (3,000nm) which floats in water. Since the colloid particle is around 10,000 times larger than an atom, researchers can observe its motion directly in a microscope.

The physicists replaced the piston, which moves periodically up and down in a cylinder, by a focused laser beam whose intensity is periodically varied. The optical forces of the laser limit the motion of the pla- stic particle to a greater and a lesser degree, like the compression and expansion of the gas in the cylinder of a large heat engine. The particle then does work on the optical laser field. In order for the contribu- tions to the work not to cancel each other out during compression and expansion, these must take place at different temperatures. This is done by heating the system from the outside during the expansion pro- cess, just like the boiler of a steam engine.

The researchers replaced the coal fire of an old- fashioned steam engine with a further laser beam that heats the water suddenly, but also lets it cool down as soon as it is switched off.

Valentin Blickle and Clemens Bechinger: Realization of a micrometre-sized stochastic heat engine, In: Nature Physics, December 11, 2011; DOI:10.1038/NPHYS2163: http://dx.doi.org/10.1038/NPHYS2163

http://www.mpg.de/4691201/smallest_steam_engine

11-11/12 :: November/December 2011