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Old 21st October 2020, 07:49 AM   #161
Gord_in_Toronto
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Originally Posted by Puppycow View Post
If anyone's interested the latest episode of the Skeptic's Guide to the Universe podcast has an interview with the lead author of this paper.

https://www.theskepticsguide.org/podcasts/episode-797

I can't tell you exactly where the interview starts but roughly halfway into the episode.

I still don't think I fully understand this thing, and it still sounds a bit "too good to be true" to me, but they ask him some questions.

The energy comes from ambient heat, so in that sense it isn't really "free energy". They ask him to respond to stuff that Feynman said too, and he has an answer.
I listened to that interview and did not find myself much wiser. If anyone can find a video of the device actually working and producing power, let me know. If it works perpetually, I'll become a believer. Otherwise, it just seems to be some sort of heat pump.

I'm a bit mystified that he thinks "the diode was discovered in the 1950s". Per Wikipedia - "The discovery of asymmetric electrical conduction across the contact between a crystalline mineral and a metal was made by German physicist Ferdinand Braun in 1874." Or, if you wish, the ". . . solid-state (semiconductor) diodes were developed separately, at approximately the same time, in the early 1900s solid-state (semiconductor) diodes were developed separately, at approximately the same time, in the early 1900s".

I'll leave it up to people more qualified than I to explain why the resistor cools down when it's not in the circuit!

Hey. I'd be happy to have my skepticism dissipated; after all, when I joine,d this was an educational forum.
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Old 21st October 2020, 06:29 PM   #162
Robin
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Originally Posted by Ziggurat View Post
There are still unstated parameters of the problem which matter (as I said, very easy to do). In particular, the sides aren’t in thermal equilibrium, but are they in pressure equilibrium? I will assume so, though that need not be the case.
I didn't state it but I didn't forget it. In the model I was considering the pressure on the left was also greater than that on the right. Hence my assumption that the sum or the average of the particles' velocities would point to the right for a time.

My other unstated assumption is that I am dealing with something close to an ideal gas, although I don't know if that is relevant.
Quote:
The temperature on the colder side will not overshoot the warmer side even temporarily.
As I said I will take your word for it. You are saying that if there was a thermometer near the left and a thermometer near the right and we were to graph the measurements, then the temperatures would approach each other but the lines never cross, right? The temperature on the right would never exceed that on the left.

I have to say it sounds implausible to me since it seems that the graph of pressure on each side would have stationary points and this would imply that the graph of temperature on each side would have stationary points, ie the higher temperature would start falling and then rising and the lower temperature would start rising and then falling, and afterwards the move to equilibrium, which seems to imply an overshoot.
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Last edited by Robin; 21st October 2020 at 06:54 PM.
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Old 21st October 2020, 11:50 PM   #163
Ziggurat
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Originally Posted by Robin View Post
I didn't state it but I didn't forget it. In the model I was considering the pressure on the left was also greater than that on the right. Hence my assumption that the sum or the average of the particles' velocities would point to the right for a time.
Then we are into more assumptions, like what the mean free path is. If it's very large, the two gasses will just pass through each other before equilibrating, with no oscillation. If it's very small, then mixing is slow, and the oscillation you would get would be from mechanical work the gasses do on each other, not heat flow.

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As I said I will take your word for it. You are saying that if there was a thermometer near the left and a thermometer near the right and we were to graph the measurements, then the temperatures would approach each other but the lines never cross, right? The temperature on the right would never exceed that on the left.
They might oscillate from mechanical work, but not from heat flow. If it helps, you can think of heat flow like an overdamped oscillator.
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Old 22nd October 2020, 02:58 AM   #164
Robin
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Originally Posted by Ziggurat View Post
Then we are into more assumptions, like what the mean free path is. If it's very large, the two gasses will just pass through each other before equilibrating, with no oscillation. If it's very small, then mixing is slow, and the oscillation you would get would be from mechanical work the gasses do on each other, not heat flow.
So, to clarify, when you said:

Originally Posted by Ziggurat
Entropy is maximized by definition when the temperatures are equal. If heat flows from lower temperature to higher temperature, then that automatically means that entropy decreased
You meant it to apply exclusively to cases where the change in temperature changes occur by heat flow strictly defined and not in general to systems where one part is becoming cooler while the rest is becoming warmer.

So my statement - that one part of the system might become cooler compared to the rest and entropy of the system as a whole might still be increasing - is quite correct.

I would also point out that in the system under discussion the heat does not flow (in the sense you are using the term) rather the graphene performs work on the circuit.
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Old 22nd October 2020, 08:39 AM   #165
Ziggurat
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Originally Posted by Robin View Post
So my statement - that one part of the system might become cooler compared to the rest and entropy of the system as a whole might still be increasing - is quite correct.
Yes. And I never said otherwise. My point wasn't that you were wrong, but that this doesn't apply here.

Quote:
I would also point out that in the system under discussion the heat does not flow (in the sense you are using the term) rather the graphene performs work on the circuit.
I don't think that's the case, though. I think it's correct to classify this as heat flow.

Let's look at a Carnot cycle heat engine as an example. We've got a gas in a cylinder at some temperature and pressure, and we allow the gas to expand, doing work on the cylinder in the process and cooling down. The gas did work, and lost energy.

Did it transfer heat, though? No. How do we know? Well, one way we know is by looking at the entropy of the gas. Did the entropy of the gas change? The answer is no, actually, the entropy of the gas did not change. How do we know? Well, the easiest test is simply that the process is reversible. But if you want to dive down into the gritty details, what happened is that when the gas expands against the cylinder, it exchanged kinetic entropy (lots of different possible velocities) for positional entropy (the larger volume means more possible locations).

In our graphene circuit, the graphene is losing energy. But is it maintaining its entropy in the process? I don't think it is. I see nowhere that the graphene can gain entropy to compensate for the entropy it's losing. So energy loss along with entropy loss means heat flowed out of it.
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