Free Energy From Shaped Holes

Craig B

Penultimate Amazing
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This idea is a strange one. By making "funnel shaped holes" in gold foil it would be possible to create pressure differences that would enable energy to be produced with no input. Is the inventor's confidence that this device could be made to generate free energy misplaced? If not, why not? See http://revolution-green.com/
 
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phunk said:
Sounds like a variation of Maxwell's demon.
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That was my comment, but the inventor states that the demon is performing an action, and therefore uses energy, while the holes don't.
 
Why isn't the "pressure gradient" identified as doing work?

It is an open system...how the heck are air molecules supposed to build "pressure"?

Had it not been so long since I passed p chem I could probably make a decent pass at a mathematical proof of failure.



I thus came up with a perpetual motion machine
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...ok...
 
Diogenes said:
Why isn't the "pressure gradient" identified as doing work?

It is an open system...how the heck are air molecules supposed to build "pressure"?
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Lets be kind and say the gold leaf with the shaped holes is separating two halves of an enclosed vessel and pressure builds up in half of that vessel. Does that make it any better?
 
Craig B said:
Lets be kind and say the gold leaf with the shaped holes is separating two halves of an enclosed vessel and pressure builds up in half of that vessel. Does that make it any better?
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Not really, that "pressure builds up" part is the sticky bit. Unless there's some experimental data on that page that I missed. Do the experiment and see what happens, I suppose. No reason not to try even if you expect failure.
 
Diogenes said:
Not really, that "pressure builds up" part is the sticky bit. Unless there's some experimental data on that page that I missed. Do the experiment and see what happens, I suppose. No reason not to try even if you expect failure.
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I asked the proposer if he had done the experiment, but he put me off the idea a bit by stating
It needs a fab or MEMs lab and a few million financing. I haven’t got the money, so no I haven’t done it. It’s not a macroscopic scale, you see, it’s nanoengineering. Have you ever tried to achieve sub-micron accuracy? I can’t even measure that here.
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Craig B said:
I asked the proposer if he had done the experiment, but he put me off the idea a bit by stating
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Then I guess the math/model would need to be done so it could get funded, but...well I might be going out on a limb...it won't ever get funded as I'm pretty sure the math won't work. If there are "many" air molecules on one side they'll just go back through the hole rather than do work. If you had a membrane that only allowed air to pass in one direction you might have...something.
 
Diogenes said:
Then I guess the math/model would need to be done so it could get funded, but...well I might be going out on a limb...it won't ever get funded as I'm pretty sure the math won't work. If there are "many" air molecules on one side they'll just go back through the hole rather than do work. If you had a membrane that only allowed air to pass in one direction you might have...something.
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He seems to think that if it is more probable that molecules would pass in one direction than the other, then there would be a higher pressure in one half of the container.
 
First off, it's not a "million dollar project". If the idea were to work with 60 nanometer holes in ambient air, then it would also work with 600um holes in a vacuum chamber at 0.1 mbar. Which means you can make your Nobel-prize-winning, world-saving, thermodynamic-law-violating foil by placing a $200 vacuum pump and a $100 laser-drilling order.

Of course it doesn't work. The author's guesswork version of the gas dynamics is wrong.
 
Not being willing to spend the time required for a detailed analysis, my rough take is as follows. (You need to follow the link in the OP.)

Molecules approaching from the left will, for certain angles, be more likely to be guided throught the holes. However, the steeper the wall angles, the less likely it will be for molecules approaching at an angle off the perpendicular to reach the hole. They will rattle around in the well and then bounce out. For molecules approaching from the right, there is no enhancement for some angles, but also no shielding for others. I suspect that the two just happen to cancel out.

Also note that there is at least one case where the funnels do absolutely no good: perpendicular approach and 45 degree walls. Any molecule which bounces off a wall will do so at a 90 degree angle, then bounce a second time at 90 degrees and exit the funnel right back the way they came.
 
WhatRoughBeast said:
I suspect that the two just happen to cancel out.
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Yep. They're guaranteed to cancel out. Think of it as a mapping. Trajectory A approaching from the left, interacts with the wall, then results in trajectory B. A -> B. A subset of this mapping (A' -> B') represents passage through the wall. Physics is time-reversible, so running any trajectory backwards leaves you in the same map.... T(B) -> T(A) and T(B') -> T(A').

Think of the version from the right. C -> D, of which subset C', D' gets through the wall.

The crackpot claim is that there are more trajectories in A' than in C'. Every element of C' maps to a D'. But each D'---a trajectory leaving the wall and heading right---is the same thing as a T(A'), and each C' is a T(B'). Therefore the fraction of all trajectories that cross the wall heading left, is exactly the same as the fraction that cross the wall heading right.

That's a rough statement of Liouville's Theorem.
 
Craig B said:
Edd. Exactly. I hadn't thought of that. It's exactly the same principle, it seems to me.
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Well I didn't really get what he was getting at with the holes getting bigger and smaller but it seemed likely similar issues would crop up.
 
Posit there is a small preference (what-if).

As soon as a very small pressure differential (read that as molecule population imbalance) is in place, the slightly larger population side will have more encounters at the slightly lower rate of capture/passage, and the pressure would stabilize (transfer rate equal in both directions).

It would be interesting to see what the pressure differential would be given a specified passage direction preference, were such possible.
 
CNY_Dave said:
It would be interesting to see what the pressure differential would be given a specified passage direction preference, were such possible.
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Oh, you can most definitely create a passage direction preference through a barrier, and the pressure you create is directly related to the strength of that preference. We know it can be done, because it's done all the time. You are, quite literally, living proof: it's how cell walls operate.

But it costs either energy or entropy. You cannot do it for free, not even in principle. Ben's comment about time reversal symmetry is the easiest way to conceptualize that on a completely general level.
 
edd said:
Well I didn't really get what he was getting at with the holes getting bigger and smaller but it seemed likely similar issues would crop up.
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Yes. He's imagining the funnels are aligned such that molecules striking from the wider side will push the funnel open farther, allowing entry. But molecules striking from the narrow side will not do so. Hence the holes being bigger and smaller. This becomes the pawl from the ratchet
 
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