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Start with two sealed boxes that are the same in every way. Then connect them by a tesla valve so that air could flow between them.

Over time through entropy would the one-way preferential flow of the tesla value create a pressure difference between the two boxes.

https://en.wikipedia.org/wiki/Tesla_valve

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  • $\begingroup$ You have an isolated system in which, as you describe it, the final entropy will be less than the initial entropy. What does the 2nd Law of Thermodynamics tell you as to whether this process is possible? $\endgroup$ – Chet Miller Feb 20 '16 at 15:57
  • $\begingroup$ Such a spontaneous differential would require selectively allowing high-energy particles to pass one way and not the other. A single particle is just as likely to get through the valve one way as it is to get through the other way; do you see any basis to contest this statement? $\endgroup$ – Asher Feb 21 '16 at 1:39
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My sense is they would come to the same pressure, because if there were any difference in pressure there would be a flow. Even if the resistance to flow is greater in one direction than the other, the difference in pressure would still lead to flow that would reduce the pressure difference.

Here's an electrical analogy:

enter image description here

Would the capacitor tend toward having a charge across it? I don't think so, if only for the simple reason that the charge could be drawn off and you'd have a never-ending battery :)

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  • $\begingroup$ The question seems to imply that, initially, the pressures in the two boxes are equal. So, since there is no driving force to begin with, no flow will occur in either direction. That seems to be consistent with your assessment, provided the battery has no initial voltage. Is my interpretation of your analog correct? $\endgroup$ – Chet Miller Feb 21 '16 at 0:21
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    $\begingroup$ @ChesterMiller: Right, I think that's what Joe was asking, and I think the electrical analog is the corresponding situation. If in Joe's boxes a pressure differential would develop, then you could have it drive a little motor in a tube going from one box to the other. Perpetual motion machine! $\endgroup$ – Mike Dunlavey Feb 21 '16 at 4:20
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Perhaps a more appropriate device to accomplish your goal would be realized after Maxwell's Demon. According to the wiki link you reference, Tesla's proposed device depends on the fluid having a viscous property, and so you would need the fluid to have at least some minimal bulk viscosity (not particle velocity). The construction of the element is such that viscous forces are asymmetric with the direction of fluid flow. Without appreciable differences of pressure in the two boxes, one would not expect to see a bulk velocity develop.

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