Scientists create world's smallest steam engine

Scientists create world's smallest steam engine

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News & Events - Engineering News

December 14, 2011

German scientists said recently they had created the world's smallest steam engine.

A team of scientists from Stuttgart University and the Max Planck Institute for Intelligent Systems affirmed they had engineered a micro-sized engine that could be instrumental in the development of small heat engines that are ultra-efficient. The engineers tweaked the design of standard engineers while crafting their miniature version, The Engineer reports.

A gas-filled cylinder is alternately heated and cooled in a typical Sterling engine, a design that causes the gas to expand and contract. By oscillating between heat and cold, the engine then powers pistons, which in turn can perform a desired task such as turning a wheel.

To design the miniaturized version of the engine, an observable plastic bead takes the place of the working gas. The bead, which measures three micrometers, floats in water, according to Stuttgart University researcher Valentin Blickle. Physicists working on the project then moved to substitute the Sterling engine's pistons with a focused laser beam with variable intensity.

"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 assembled them to a machine," Blickle said in a statement.

The researchers noted that the small-scale engine functions like its progenitor, with the fluctuating strength of the laser beam limiting the motion of the plastic bead. The functioning of the bead imitates that of the Sterling engine's expanding and contracting gas.

"This is quite similar to a weight which loses energy when you let it drop in a gravitational field," Stuttgart University professor Clemens Bechinger said. "In our case, the energy of the particle at a given position inside the laser trap is proportional to the laser intensity. So, when you reduce the laser intensity, the particle loses energy."

By effectively replacing pistons with laser beams, the engineers were able to create a functioning steam engine visible through the lens of a microscope. Bechinger asserted the breakthrough illustrates how lasers can be used to produce steam engines as effective as conventional models, CNN reports.

"Instead of pistons that were common at that time, we use laser beams," Bechinger affirmed. "For the first time, we have [built] a steam engine out of laser beams that is as effective as classical ones."

Blickle said that although the team's version of the steam engine is far less complex than a typical model, their basic functioning is aligned. By reducing the intensity of the laser beams in their microscopic model, the scientists were able to compress the gas particles; on the other hand, increasing laser intensity resulted in the reverse effect.

"If we change the temperature in the right rhythm, we operate like a large steam engine," according to Bechinger. "Our experiments offer a rare insight into the conversion of thermal to mechanical energy on a microscopic level, and pave the way for the design of future micromechanical machines. Although our machine does not provide any useful work as yet, there are no thermodynamic obstacles, in principle, which prohibit this in small dimensions."

The scientists' work was published this week in Nature Physics.


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