Scientists Create World's Smallest Steam Engine

First time accepted submitter Virtucon writes "German physicists say they've built a heat engine measuring only a few micrometers across which works as well as a normal-sized version — although it sputters, they admit. Researchers at the University of Stuttgart and the Max Planck Institute for Intelligent Systems say that the engine does basically work, meaning there's nothing, in principle, to prevent the construction of highly efficient, small heat engines."

Another write up

[PerlJedi]

I also found this story here: http://www.sciencedaily.com/releases/2011/12/111211134002.htm [sciencedaily.com]

impressively small

[Trepidity]

Afaik, even considerably larger miniature heat engines have significant problems, which are only recently being solved, but most of the existing research is on things more in the millimeter to centimeter range. I suppose micrometer engines might face different problems entirely, but quite impressive.

For example, a discussion of difficulties in building a miniaturized combustion-based heat engine:

The problem being faced by micro-miniature heat engines is that, as the size is reduced, the surface-area-to-volume ratio of the combustor begins to dominate the combustion process. Both the chemical reactivity of the wall and the heat transfer to the wall affect the radical recombination and generation rates of the reactants. If important radicals such as hydroxyl or methyl are destroyed at or near the wall too quickly, the combustion process can be quenched. The thermal and chemical quenching pathways are strongly coupled, so that very small changes in temperature or chemical activity of the wall can lead to significant changes in radical concentration near the wall, making gas phase combustion using air as the oxidant difficult to sustain below a critical length scale (i.e. quenching distance) of a few millimeters (Kuo, 1986).

Source: This paper (PDF, 2005) [illinois.edu]

And a working-in-simulation model of a 65 x 22 cm Stirling engine: from a 2008 paper [doi.org]

Re:How Efficient?

[Anonymous Coward]

It's hidden at the end of the article:

"Although our machine does not provide any useful work as yet..."

Efficiency = Power Out / Heat In = 0/Heat In = 0%

Re:No engineers involved in this job

[vlm]

From the Wikipedia article, a Sterling Engine can be a steam engine

Incorrect. Not even close. Stirling engines basically rely on the expansion and contraction of a gas at different temperatures, usually by moving the gas between hot and cold areas using some displacer gadget, and usually a heat regen unit it between to increase efficiency. The resulting pressure variations in the overall system, make the typical crankshaft arrangement rotate.

Steamies more or less work like a simple air engine, here's an intense pressure on one side of a piston and open to the air or to a vacuum on the other, now reverse the valves in time with the crank and off you go. Not entirely unlike a 2-cycle IC engine, although stereotypically ICs cylinders are almost all single acting and steamies are stereotypically mostly double acting (like having two pistons in one cylinder, back to back in opposite directions, sorta kinda). You can condense the steam outside the cylinder to make a vacuum but its considered extremely bad form to condense inside the cylinder, hydro-lock and kaboom are inevitable... which is why steam locomotives put on such a show with open cylinder drain valves when starting up, start up with those drains closed on a cold cylinder, the cylinder fills with condensed water, and bang it shatters open once it hydrolocks. Once the cylinder is hotter than boiling water its all good and they close the cylinder drains.

Note that you can play word games. Instead of providing heat to one side of a very low power stirling using an electric heater, you could sit it atop a hot steam radiator, making it "steam powered stirling". Or you could even pipe raw heating steam around the hot cylinder as a heat source, instead of a flame or electric heating element. Or, you could play games and an electrically heated stirling got its electricity from a steam turbine at the local nuke plant, so its technically a steam powered stirling, or more accurately a nuclear powered stirling. Possibly, instead of using air or helium in your Stirling like a normal engineer, you could use steam of various levels of superheat, so you could have 400 degree steam in the "hot" side and 300 degree steam in the "cold" side. But thats just playing word games to obfuscate the actual thermodynamics of the situation.