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Heat Engines Shrunk By Seven Orders of Magnitude
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."
Great, let's make this 500 times bigger and power my car!
Great! When can I get these built into my CPUs?
When our name is on the back of your car, we're behind you all the way!
a micro SUV
Its a heat engine but it does not use gas, so maybe this could be the engine for a train of nano bots! Or we can use them to cool our CPUs. Interesting indeed, now we need to find an use for it
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Can the physics gurus please put cubic micrometers in perspective for us common mortals? Is that as big as a grain of rice or a head of a pin?
10^7 micrometers is.... a spehrical cow? a toaster?
Can it be used for other things?
How many beer cans fit in a 0.5 micrometers refrigerator?
This is a great invention, but how can it be used in a meaningful way? It is so small that it produces a very minimal amount of horsepower, which is not useful for any actual way.
Somehow "heat engine" directly translates into "internal combustion engine" for me. But this piece uses electricity, exactly how useful is that? This is bound to be less efficient than to use the electricity to just power an ordinary electric motor. I suppose scaling a motor down to that size might be kinda difficult, though, if that was the point, why emphasize that it is a heat engine?
Peltier diode?
Finally my plan for steampunk (almost)nanobots can come to fruition! Those millions in grant money to the blacksmith have finally paid off.
...with that UFO crash in Holland two years ago.
I guess the Logopolians will have to spend even more time doing base block calculations to prevent the heat death of the universe.....
Tsukasa: All I really want, is to be left alone...
Apparently there are 0.001mm^2 engines already!
Sometimes I despair about the level of scientific knowledge imparted to today's youth.
There is NO WAY to make a heat engine of any efficiency smaller than a few cc's.
It's the basic SCALING LAW that Galilleo figured out like 600 years ago.
As you make things smaller, their volume, which is their abilitry to burn fuel, goes down as the CUBE of its linear dimension.
But its surface area, which is how it loses heat, only goes down as the square.
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.
Even for non-flame sources, the exact same rules apply. So you can't make a heat engine of any usable efficiency below a certain size. Model-airplane engines of 1cc capacity are about the lower practical limit. Anything smaller and you have trouble getting it to light off and even if it does, the heat quickly dissipates.
So just on general principles, one can guess that this touted device has vanishingly small efficiency.
And no, no "but we can INSULATE it" or "the RULES are DIFFERENT down there".
Surely thermoelectric semi-conductors would do the trick?
They may not be very efficient, but I'd suspect you could make them fairly small if you utilized modern chip technology.
The total volume of the device is just 0.5 cubic micrometres.
I know I parked my car around here somewhere. Anyone see it?
Who would win this election: Andrew Weiner vs Andrew Weiner's weiner.
So thats like much smaller than a womp rat!
I will not be pushed, filed, stamped, indexed, briefed, debriefed or numbered. My life is my own.
when i saw the title i said "wow". then i read the summary, and i said "wow" again. that makes it a double-wow.
In Soviet Russia, engine...does not heat you. :(
Not only is 10 million much easier to understand than 10^7, but 0.01 cubic millimeters is a MUCH more common number, and measurement.
Not exactly hidden information either.
Now they don't have to peddle to work each day. The nanites can make a cool ride with one of these motors.
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I agree that using cubic micrometers is nowhere near intuitive.
1 um (replace "u" with the Greek letter "mu" please) is 1e-6 metres.
So, 1 cubic um is 1e-18 cubic metres. So, the smallest conventional heat engines are 1e7 of these 1e-18 cubic metres, or 1e-11 cubic metres.
Not that intuitive either. So we'll use cubic mm.
1mm is 1e-3 metres, so 1 cubic mm is 1e-9 cubic metres.
Something that's 1e-11 cubic m (1e7 cubic um) is 1e-2 cubic mm. So, it's 1% of 1 cubic millimetre.
That's pretty small.
404555974007725459910684486621289147856453481154 in hex is "You sank my Battleship?"
[GPG key in journal]
if this is useful. I've seen micro rotary and piston engine. They suffer from two problems. One is heat loss due to high surface area to volume ratio (heat leaks away before work can be extracted), and the other is charge (fuel/air) leakage. This appears to solve the leakage problem buy not using combustion. Good job!
..for the endonucleic transgenesis procedure?
According to TFA:
"Today's macroscopic heat engines are clearly more efficient than biological ones. "
Come to think of it, why (after all these millions of years), didn't evolution reach this stage?
I read the attached paper on arxiv, and from what I could tell, they passed a DC current through the thing, which caused the small engine beam to expand, causing it to heat up and move the mass. The piezoelectric effect causes the resistance in the small engine beam to change, which causes the beam to cool down and move the mass back with help from the larger spring beam. Rinse, repeat. Effectively a thermoelectric buzzer. The buzzing of this particular device was measured to be about 1.255 MHz at a DC current of 1.045 mA.
Unlike what the Technology Review article says, the paper shows no application of an AC current to get the thing vibrating. In fact, the measured voltage is alternating because the resistance is alternating. The current remains the same. There is no complicated application of a DC current and an AC current. There's just an applied DC current.
Am I understanding the paper correctly?
Towards the Singularity.
Mmm, piezo...
If the solenoid is electrically driven, is it really an engine by the definition above (reciprocating)?
I mean sure, the piston reciprocates, but not as part of power generation like in an ICE. I suppose the object being physically acted upon would see the solenoid piston as the source of power.
It seems that viewing a solenoid as an engine means that electricity is the fuel, and my mind is choking on that.
Is electricity as "fuel" to a solenoid as electric engine a valid analogy?
Am I on the right track here, or simply out to lunch?
While that's certainly interesting, wouldn't you just use an electric motor anywhere electricity was available?
Oh, wait. It's use as a heat pump at that size is notable, but as a motor:
> It's future as a motor is less clear. It's relatively straightforward to make
> electrostatic motors that work on this scale and we've looked at plans to
> build electric motors on the quantum scale.
(-1: Post disagrees with my already-settled worldview) is not a valid mod option.
... they passed a DC current through the thing, which caused the small engine beam to expand, causing it to heat up and move the mass. The piezoelectric effect causes the resistance in the small engine beam to change, which causes the beam to cool down and move the mass back with help from the larger spring beam. Rinse, repeat. Effectively a thermoelectric buzzer. ... Am I understanding the paper correctly?
As far as you went.
But the alternating heating/cooling doesn't have to come from current through the material. It could come from alternating heating/cooling of its environment, for instance. Like by periodically-varying temperature changes in a fluid or high-intensity illumination.
Thermoacoustic machinery operates by using very high intensity sound - high enough that it makes major periodic temperature changes in the working fluid due to compression and rarefaction. This is used to build heat engines and heat pumps, sometimes with no moving parts but a gas. And it can operate at small scales and high frequencies.
It will be interesting to see if arrays of devices using this technology can make a better electrical interface for pulling power out of or putting it into a thermoacoustic device than piezoelectric devices working just on mechanical coupling to the motion of the working fluid.
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