Half a croissant, on a plate, with a sign in front of it saying '50c'
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Brownian pump or wing

Energy from still air
  [vote for,

If one way valves are made smaller than 1 micron they can be opened and closed by microscopic fluid movements called brownian motion. This can be used to move a fluid from low pressure to a slightly higher pressure using the internal energy of the fluid i.e. by cooling it. By using sheets covered with these valves and stacking them together a fluid can be pumped. Once the fluid is moving energy can be extracted from it using a turbine and generator. Electrical energy can be produced from still air at room temperature simply by cooling the surrounding environment. As the valves get smaller brownian motion gets more and more violent so there can be a greater pressure difference between the sheets. The ultimate brownian pump consists of valves which just let a single molecule through at a time, one single sheet is then required. The device can also be thought of as a brownian wing. Air striking one side of the wing bounces off applying pressure, but some of the air striking the other side passes through this generates lift without the wing moving.
philg, Jan 30 2004

Maxwell's Demon http://members.iglo...apers/DemonEnv.html
//For decades, the demon defied scientific understanding. Attempts to explain why the demon could not defeat the Second Law all turned out to be flawed. It wasn't until the 1980s that Charles Bennett of IBM showed definitively that the demon could not succeed.// [Worldgineer, Oct 17 2004, last modified Oct 21 2004]

Maxwell's Demon http://users.ntsour...s/demon/dpaper.html
There are some good examples of this exact idea here. [Worldgineer, Oct 17 2004, last modified Oct 21 2004]

Maxwell's Demon Kitchen Friend http://www.halfbake..._20Kitchen_20Friend
Other useful ways to use the demon. [Worldgineer, Oct 17 2004]

(?) Maxwell Game http://cougar.slvhs...ctures/maxwell.html
Like this game, but you're trying to get all of the molecules on one side. I made it to 44/16. [Worldgineer, Oct 17 2004, last modified Oct 21 2004]

Brownian Motors http://hcs.harvard....002/nagiel11-13.pdf
PDF file [half, Oct 17 2004, last modified Oct 21 2004]


       Does this mean self-polishing shoes ?
normzone, Jan 30 2004

       I just figured out what's wrong with this: the air isn't still.   

       (thinking further) There's gotta be something else... help me out here?
galukalock, Jan 30 2004

       If the valves could be made speed sensitive, this could work as an air conditioner. Fast moving molecules would be allowed to leave the room and slow moving molecules would be allowed to enter the room.
GenYus, Jan 30 2004

       Note that:
1) Your doors cannot be much larger than an air molecule, or or on average there will be air molecules striking the other side, keeping the door closed.
2) The mass of your doors will have to be small compared to the mass of an air molecule and the hinges must be nearly frictionless, or the collision of an air molecule against the door will not open it.
3) Even with these two requirements satisfied, I'm not convinced you'd be able to have the door open and close before any molecules escape.

       This being said, what you've rediscovered is the only example of a decreasing entropy system I've ever heard of - my thermodynamics professor mentioned such a theory back in college and I don't remember if/why he said it was impossible.
Worldgineer, Jan 30 2004

       Worldgineer, you beat me to those points as I was typing. Think of a pool-ball analogy. If your door is similar in size to the air molecule, hitting it with an air molecule will be an almost complete energy transfer, i.e. the air molecule will come to a near-stop, the door will swing open. The door will then hit its stop, bounce back, hit the air molecule and the energy will be back where it started. This would be much like those swinging-balls-on-a-string executive desk toys. In theory, the concept is good, but putting it into practice would be nearly impossible.
Freefall, Jan 30 2004

       I seem to recall some recent experiment where they did in fact achieve it, but explained it away as a localized effect.
theircompetitor, Jan 30 2004

       The valves of a brownian pump can be as large as 1 micron as 1 micron sized dust particles can be moved by brownian motion. That is larger than the transistor on the chip of this PC. Maxwell's demon and the brownian pump are the same device trying to do two different things. Maxwell is trying to break the second law of thermodynamics and I am trying to clean cheap energy. The difference being I am allowed an open system and increase entropy somewhere else.
philg, Feb 05 2004

       Where does this "cheap energy" come from?
Worldgineer, Feb 05 2004

       The energy comes from cooling the gas. If the device was deep in interstellar space it would cool down until the gas froze and it would stop working. On earth it will just cool whatever it was in contact with.
philg, Feb 06 2004

       How to create a powerful single molecule Brownian Pump. Cover one side of a thin sheet of material with a layer which is say positively charged. Make nanometre sized holes in the sheet, One way of doing this would be to to fire heavy ions through the sheet. Expose the material to a detergent like molecule which would cover one side with a monomolecular layer. The surface is now covered in tiny strings the negative ends stick to the surface and the positive ends stick up in the air. Around the holes the positive ends will be pushed inwards creating a wigwam like structures over the holes.Molecules trying to get through the holes from above the layer will push the ends together and be blocked. Molecules trying to get through the hole from below will push the ends appart and get through. Therefore the surface is covered in single molecule one way valves. As point out by worldgineer the molecules need to be heavy enough to deflect the detergent molecules. A heavy gas such as Xenon or a hydro-carbon gas would be most effective.
philg, Feb 06 2004

       philg, a molecule trying to get through one of your valves would have to have enough energy not only to push against the valve's mass, but to push against the molecules that are hitting the valve from the other side and pushing it closed. Since you've already said the other side has a higher pressure (if it didn't, the whole exercise would be pointless) this will not work.   

       Brownian motion is not magically different from what we normally call "pressure." If a gas is under higher pressure, it's got more randomly moving molecules per unit of space, that's all. It doesn't matter whether your valves are molecule-sized or door-sized - if there is higher pressure, that is, more collisions per unit of area, on one side then the valve will not open toward that side.
hob, Feb 06 2004

       hob at normal atmospheric pressure molecules only occupy only thousandth of the available volume( which is why a liquid or solid is a 1,000 times as dense as a gas. Therefore at the moment that the molecule hits the lower side of the valve the chances are that if the valve is about the same size as the molecule. Another molecule will not be hitting it from above. So that if say the the high pressure is twice the low pressure 998 times out of a thousand molecules will not be hitting the valve from both sides at the same time. So the molecule from the lower pressure volume will usually pass to the high pressure volume. This effect also works at larger scales because statistically small pressure variations are going to occur but in this case the difference in pressure between the two regions can only be small therefore I have proposed to boost the pressure by using multiple layers of one way valves each increasing the pressure by a small amout until a useful pressure difference is obtained.
philg, Feb 07 2004

       I'm still not convinced...   

       a) It takes the valve a non-zero amount of time to swing open, during which time it can be knocked shut.   

       b) Once the valve is open, what's going to shut it?   

       c) In fact, why wouldn't it just fly apart on its own, when your little strings have identical positive charges on their ends?   

       d) As Freefall said, a fast-moving gas molecule hitting an obstacle, even if it hits hard enough to open the valve, is more likely to stop or bounce back than to go on through.
hob, Feb 10 2004


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