The idea of harvesting energy from graphene is controversial because it refutes physicist Richard Feynman’s well-known assertion that the thermal motion of atoms, known as Brownian motion, cannot do work. Thibado’s team found that at room temperature the thermal motion of graphene does in fact induce an alternating current (AC) in a circuit, an achievement thought to be impossible.
Even more, the result is essentially claiming to violate the Second Law Of Thermodynamics. HN should be flagging this sort of crank claim.
“According to Kumar, the graphene and circuit share a symbiotic relationship. Though the thermal environment is performing work on the load resistor, the graphene and circuit are at the same temperature and heat does not flow between the two.
That’s an important distinction, said Thibado, because a temperature difference between the graphene and circuit, in a circuit producing power, would contradict the second law of thermodynamics. “This means that the second law of thermodynamics is not violated, nor is there any need to argue that ‘Maxwell’s Demon’ is separating hot and cold electrons,” Thibado said.”
Anyway, if you see the animation in the video, they are trying to makes a device that use this effect to collect the charge in a capacitor and then release the energy in a resistor, and that proposed device breaks the second law, in particular is more clear with this version https://en.wikipedia.org/wiki/Second_law_of_thermodynamics#P...
How so? Isn't it just converting the effect of thermal energy to electric energy? Presumably, there is no Brownian motion at absolute zero, and the actual output would drop well above that temperature.
A direct conversion of thermal energy into electric energy would cool down the entire system. Since electric energy carries no entropy, this would reduce the overall entropy of the system. This is forbidden by the second law of thermodynamics.
If treated as a closed system, the claim would indeed be violating the second law of thermodynamics. If it's treated as an open system, then well yeah... the "limitless" energy is actually coming from outside the boundaries of the system, which they conveniently neglect to track. No magic to be had here, but a cool way to convert energy...
I just skimmed the paper. Right in the end of the discussion, the authors write:
Our model provides a rigorous demonstration that continuous thermal power can be supplied by a Brownian particle at a single temperature while in thermodynamic equilibrium, provided the same amount of power is continuously dissipated in a resistor. Here coupling to the circuit allows electrical work to be carried out on the load resistor without violating the second law of thermodynamics.
I don't find this very clear at all, but it appears to contradict the claim that the setup could be used for energy harvesting.
If this work as described in the press article, it breaks the second law of thermodynamics, in spite they claim it doesn't. It's based in a research article published in 2020, so if they didn't win the Nobel price 2021, it's pretty clear that it does not "generates clean limitless power".
The idea is that at room temperature, the Brownian motion moves the graphene, and that generates a small current in the circuit, so the circuits absorbs some energy from the environment. But there is electric noise in the circuit, and that noise makes the graphene move as a motor and release some energy to the environment. One of the consequence of the second law is that if all the circuit and environment are at the same temperature, the energy absorbed an the energy released are equal, so the net effect is zero.
Now if you look at the resistance, the noise in the circuit makes it release some energy as heat, but the Brownian motion of makes it generate some noise. Again, one of the consequence of the second law is that if all the circuit and environment are at the same temperature, the energy absorbed an the energy released are equal, so the net effect is zero.
And now, considering the diodes, ..., the second law ..., so the net effect is zero.
And now, considering the wires (wires are small resistances), ..., the second law ..., so the net effect is zero.
And now, considering the mechanical support of the circuit (small devices are weird), ..., the second law ..., so the net effect is zero.
The problem is that in spite what the article says, a consequence of the Second Law of Thermodynamics is that if all the device is at the same temperature it's not possible to "generates clean limitless power".
The graphene isn't pulled taut like a sheet pulled flat, but slightly loose, like a sheet slightly drooping, and the graphene naturally buckles and deforms.
Imagine air molecules colliding with the sheet causing buckles to form, invert, or flatten out, with the deformation popping up nearby.
Each time it buckles, a tiny current is generated. If it buckles in one direction, current goes one way, if it buckles in the other direction, current goes the other way.
Because of quantum effects - brownian motion - no collisions have to occur, the heat going into the graphene sheet itself is enough to chaotically produce buckling, with a direct transformation of mechanical energy deformation to electricity.
Heat storage is really easy. It'll be interesting to see how efficiency scales, in practice. If it exceeds modern thermoelectric performance, it's got a future, but this might get really high efficiency. The limit is the effective surface area of the graphene.
Because it's solid state, it makes low temperature / shallow geothermal much more feasible.
No gradient needed is the revolutionary phenomena here. It's a solid state quantum motion based electricity generator. The higher the temperature, the more rapid the brownian motion, the more power is produced.
What I don't understand is what would happen if you put a bunch of these inside a highly insulated really hot cavity. The paper suggests that it doesn't cool down while generating current, but that it cools while no current is being drawn. Is that just a "wtf, nature?!" thing or is something being missed?
I really think you are misreading the paper. They are specifically calling out that they aren't claiming to be Maxwell's demon and they the system quickly reaches equilibrium and the power drops to zero.
Nope, the quantum dynamics of individual atoms of carbon cause the buckling, no gradient needed. It doesn't make macro sense. I'm leaving the door all the way open for some alternative explanation, but so far the science seems solid. It needs to be replicated and scaled up.
The weird bit is the cooling while not passing current. Does the system as a whole have a tendency to cool, and why does removing energy as electricity not cool it down? Is the quantum buckling effectively separated from the heat of the system? Particles are weird.
I guess I'm confused about the source of the buckling, then. Is it directly caused by air molecules colliding with the graphene?
If that's the case, then by definition, as current is produced, energy is taken from the collisions mechanically, and temperature would decrease. Thibado says that when current is not flowing the resistor cools down, and implies that when current is flowing, it doesn't heat up.
>>“People may think that current flowing in a resistor causes it to heat up, but the Brownian current does not. In fact, if no current was flowing, the resistor would cool down,” Thibado explained. “What we did was reroute the current in the circuit and transform it into something useful.”
If current is produced and the system isn't extracting heat (cooling) then the energy has to come from somewhere, right? That's why I was assuming they were talking about the Brownian motion of the graphene itself. If it's just the graphene, the system would work in a vacuum. If it's air molecules then Thibado has to be wrong, or the quote was sloppy or out of context.
The buckling is caused by hits of the air molecules, sound waves transmitted by the support, photons that hit the surface (probably very small at room temperature), and any other stuff ...
The idea is that the resistor acts as a small generator that produces a current that is electric notice. This transform some mechanical energy into electricity, and in a magical universe it would cool down the resistor.
The problem is that the rest of the circuit is also producing electric noise. So the small current of the noise of the rest of the circuit goes to the resistor and is dissipated as heat and warms the resistor.
If you live in a magical word, you can magically turn off the noise of the rest of the circuit, but in the real word that is impossible and both effect cancel and the resistor keeps it's temperature.
This is pretty standard theory, but perhaps it's not the best way to explain it.
My guess is that the important result of the research paper is that the spectrum of the noise of the part of the circuit with the graphene is different of the spectrum of the noise of the resistor. It's interesting, but it does not break the current laws of Physics.
>>> What we did was reroute the current in the circuit and transform it into something useful
That's a direct jump into the "totally wrong or Nobel price" category. That's a claim that breaks the Second Law, so they are totally wrong or they get a Nobel price, there is no middle ground. (Sometimes the Nobel committee takes a few year to assign the price, but a result like this would cause immediately a huge discussion in the Physic community, like the discovery of the Higgs boson or LIGO.)
Graphene buckles, that is in theory its lowest energy state is not flat as a sheet. This is part of the original thermodynamic arguments against graphene's existence that were disproved by finding it. I think the Mermin-Wagner theorem used to be invoked.
Very curious to learn more about the underlying research. My understanding is that this would be the first example device which can extract thermal energy from Brownian motion without a temperature gradient.
That this is even thermodynamically possible is an exciting development, would be interesting to see if it's possible to scale up the results at all.
Given that the latest version of Chrome is 98.0.4758, if yours is reporting a strange version number like that then it could well fall outside the bounds of whatever check they put in.
In Javascript, "99" > "10000000" === true. Naive user agent parsing libraries will fall for this problem while they're trying to block out known bad browsers.
Hard to tell what shitty browser detection they use that doesn't turn the version number into a number before comparising the two, but this is why both Chrome and Firefox are hesitant about releasing version 100 of their browser.
Even more, the result is essentially claiming to violate the Second Law Of Thermodynamics. HN should be flagging this sort of crank claim.