typodupeerror

## Heat Engines Shrunk By Seven Orders of Magnitude168

KentuckyFC writes "The vast majority of motors that power our planes, trains, and automobiles are heat engines. They rely on the rapid expansion of gas as it heats up to generate movement. But attempts to shrink them by any significant amount have mostly ended in failure. Today, the smallest heat engines have a volume of some 10^7 cubic micrometers. Now group of Dutch engineers has built a heat engine that is seven orders of magnitude smaller than this. The engine consists of a piezoelectric bar that expands and contracts in the normal piezoelectric way. However it also heats up and cools at the same time causing a thermal expansion and contraction, which lags the piezoelectric displacement. By carefully choosing the frequency of the driving AC current, the Dutch team found a resonant effect in which the thermal expansion and contraction amplifies the mechanical motion, making it a true heat engine. Operating the thermodynamic cycle in reverse turns the device into a heat pump or refrigerator. The total volume of the device is just 0.5 cubic micrometres."
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## Heat Engines Shrunk By Seven Orders of Magnitude

• #### Re:what is a cubic micrometer (Score:5, Informative)

on Friday January 22, 2010 @10:47AM (#30860012) Journal
You know how big a millimeter is, right? A micrometer is one thousandth the length of a millimeter.

A cubic micrometer is the volume occupied by a cube one micrometer on each side.

10^7 cubic micrometers would fill a cube about one-fifth of a millimeter on a side. Smaller than a pinhead.
• #### Re:what is a cubic micrometer (Score:5, Informative)

on Friday January 22, 2010 @10:51AM (#30860074)

Fun fact - Wolfram Alpha can serve as your 'self-checkout line' for things like this.
http://www.wolframalpha.com/input/?i=1+cubic+micrometer [wolframalpha.com]

Here's a bit of scale - a cubic micrometer is about the same size as a calibration bead for microscopy. A red blood cell is about 8 micrometers across. http://learn.genetics.utah.edu/content/begin/cells/scale/ [utah.edu] Or, there's this video showing the "powers of ten" (also its title...): http://www.youtube.com/watch?v=A2cmlhfdxuY [youtube.com]

Also, chemists work at these dimensions, too! (So do biologists. And others.) :*P Don't snub the other disciplines!!! Or I'll weep. And not gently, nor to a guitar.

• #### Re:Heat engine != internal combustion engine (Score:1, Informative)

by Anonymous Coward on Friday January 22, 2010 @10:57AM (#30860150)

Because the researchers can't say spent their grants to make a piece of metal that vibrates a little more then the last piece of vibrating metal. By comparing this to one of the greatest and most useful inventions of all time and then saying they shrunk it 7 orders of magnitude really makes for a great press release, at least on /.

• #### Re:Heat engine != internal combustion engine (Score:5, Informative)

on Friday January 22, 2010 @11:03AM (#30860220) Homepage Journal

Somehow "heat engine" directly translates into "internal combustion engine" for me.

why emphasize that it is a heat engine?

Because they figure it's mostly usefull as a heat pump, not as a mechanical actuator.

• #### Re:what is a cubic micrometer (Score:4, Informative)

on Friday January 22, 2010 @11:03AM (#30860234)

about one-fifth of a millimeter on a side

That's about the thickness of a sheet of paper. (Round here, and probably in a lot of the world, the thickness and density of paper is specified, for instance "160 g/m^2, 200 micrometres".)

• #### Re:Heat engine != internal combustion engine (Score:4, Informative)

on Friday January 22, 2010 @11:15AM (#30860368) Homepage

The internal combustion engine is only one class of heat engines. The Sterling Engine and the External Combustion Engine (used in old steam locomotives) are also heat engines. Heat engines use heat to create power either by taking advantage of temperature differences or the expansion of heated air.

• #### Re:Reeedeeeculous (Score:3, Informative)

on Friday January 22, 2010 @11:20AM (#30860436)

So as you shrink things, pretty soon, you can't start a fire. The fire loses heat over its surface area faster than itrs volume can generate it.
Which is why you don't see flames smaller than a certain, much larger than micrometer, size.

So if I'm understanding this argument correctly, the limitation can also be understood in terms of the time window available in which to extract the energy decreases, as the engine scales down. At a material level, the heat dissipation has a limit as well -- for conduction, it can't be any faster than the speed of sound (within the material comprising the engine).

While we don't have any information on the frequency at which the piezo engine operates, it could be very high, allowing for nearly instant energy extraction. We could possibly be approaching the limit at which the two limitations compete.

• #### Re:Heat engine != internal combustion engine (Score:5, Informative)

on Friday January 22, 2010 @11:28AM (#30860560) Homepage Journal

Somehow "heat engine" directly translates into "internal combustion engine" for me.

A steam engine is an external combustion engine, yet is is still a heat engine. The thing with this teensy engine is that it reuses waste heat rather than throwing it away, making it far more efficient than your ordinary electric motor.

As a side note, the difference between a motor and an engine is that a motor rotates, an engine reciprocates. You can indeed have an electric engine (theyre usually called "solenoids") and a gasoline motor (Mazda had "rotary engines" back in the '70s; they were actually gasoline motors.)

• #### Re:Heat engine != internal combustion engine (Score:3, Informative)

<yttriumox@Nospam.gmail.com> on Friday January 22, 2010 @11:58AM (#30860900) Homepage Journal

Mazda had "rotary engines" back in the '70s; they were actually gasoline motors.

Had? Wouldn't "have had ... since [wikipedia.org]" be more accurate? (oh, and it's since 1963 [wikipedia.org], so the '60s...)

• #### Re:what is a cubic micrometer (Score:3, Informative)

<mdmadph@noSPam.gmail.com> on Friday January 22, 2010 @12:26PM (#30861262) Homepage

That's "U.S. Customary [wikipedia.org]" assloads, Loyalist swine.

• #### Re:Nanites are in luck (Score:3, Informative)

on Friday January 22, 2010 @12:57PM (#30861616)
"peddle" - no I don't think they need to sell stuff.
• #### Re:Heat engine != internal combustion engine (Score:5, Informative)

on Friday January 22, 2010 @03:15PM (#30862946)

As a side note, the difference between a motor and an engine is that a motor rotates, an engine reciprocates.

Huh. I didn't know that.

Not surprising that you didn't know that, since it isn't true.
An engine is a machine that does work using a source of energy like the coiled rope of a catapult or the tank of gas for your internal combustion engine.
A motor is an engine that moves something, like, say, a motorcycle.

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