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Coffee House => Coffee House Boards => CH / Science and Technology => Topic started by: asian1 on April 25, 2005, 12:35:13 PM
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Is it possible to scale up this motor for automotive / pump or other applications?
http://www.freerepublic.com/focus/f-news/1384325/posts
The motor works by shuffling atoms between two molten metal droplets in a carbon nanotube.
One droplet is even smaller than the other. When a small electric current is applied to the droplets, atoms slowly eek off the larger droplet and join the smaller one. The small droplet grows – but never gets as big as the other droplet – and eventually bumps into the large droplet. As they touch, the large droplet rapidly sops up the atoms it had previously sloughed off. This quick shift in energy produces a power stroke.
The technique exploits the fact that surface tension -- the tendency of atoms or molecules to resist separating -- becomes more important at small scales. Surface tension is the same thing that allows some insects to walk on water.
The motor, a surface-tension-driven nanoelectromechanical relaxation oscillator, was built by a team of researchers led by Alex Zettl at the University of California, Berkeley.
Although the amount of energy produced is small -- 20 microwatts -- it is quite impressive in relation to the tiny scale of the motor. The whole setup is less than 200 nanometers on a side, or hundreds of times smaller than the width of a human hair. If it could be scaled up to the size of an automobile engine, it would be 100 million times more powerful than a Toyota Camry’s 225 horsepower V6 engine, the researchers say.
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You can't scale it up, as the effect it relies upon is only significant on a small scale... you could however, put lots of them together to make a larger "motor", which would be quite similar to our own muscles... no information regarding the efficency though :-/
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You knew the first response would be from me, didn't you :-)?
No, this cannot be scaled up to the scale of automotive or pump devices. There are several reasons for this. One, the energy released with the 'stroke' of the small bubble dissipating into the big one cannot be effectively harvested as it is used almost exclusively to increase the surface area of the big droplet. If you hinder that growth, the small bubble won't disappear fully into the big one and your engine will experience 'knocking'.
One-and-a-half, if you put some sort of thin sheet across the bubbles to have that stretch and contract thus producing a voltage difference, the surface tension will immediately see to it that your precious bubbles become a thin smear. Or in other words, you create a capillary effect. The device works because it relies on surface tension producing bubbles. Anything interfering with that process ruins the engine.
Two, the researchers only gave numbers about the energy released from the disappearance of the small bubble. You don't get that energy for free. The big bubble decreases in size, requiring energy. Some energy---but not all---is returned as the small bubble grows. Only when the small bubble touches the big one is the energy balance completed and is the energy difference equalised with a big jolt. It is therefore not really an engine, but more a little device capable of producing pulses.
Three, simply making larger bubbles doesn't work, as the forces scale with the reciprocal of bubble size. Or, in layman's terms: the bigger the bubble, the less important the surface tension.
Four, this device would require materials of utmost purity (any contiminant would influence the surface tension and thus the properties of the pulse) and mechanical stability (these bubbles have almost nothing to hold on to). The shaking you'd get in a car would render the engine useless: all the droplets would be torn from their anchoring points.
Nice piece of nano-engineering, but for all intents and purposes, utterly useless.
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looks like you've burst that bubble!