Comment by plebianRube
4 years ago
I would read the article, it is easy to read and accessible.
Here's the meat though.
"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.
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."
A circuit producing power without a temperature difference contradicts the second law of thermodynamics, which is what Thibado is claiming to have done.
Hard to see how this works when Brownian ratchets don't.
Also: "Léon Brillouin in 1950 discussed an electrical circuit analogue that uses a rectifier (such as a diode) instead of a ratchet. The idea was the diode would rectify the Johnson noise thermal current fluctuations produced by the resistor, generating a direct current which could be used to perform work. In the detailed analysis it was shown that the thermal fluctuations within the diode generate an electromotive force that cancels the voltage from rectified current fluctuations. Therefore, just as with the ratchet, the circuit will produce no useful energy if all the components are at thermal equilibrium (at the same temperature); a DC current will be produced only when the diode is at a lower temperature than the resistor."
https://en.wikipedia.org/wiki/Brownian_ratchet
But if the diode at a lower temperature than the resistor can generate current, then the current should raise the temperature of the resistor, meaning that it will stay running.
That seems unlikely, as I understand thermodynamics. Can anyone explain?
Current in a resistor will raise the resistor's temperature.
Current in a diode also raises the diode's temperature.
It takes work to keep the diode at a lower temp.
The diode won't be at a lower temperature for very long.
AC, eh?
680kHz perhaps?
The first thing they should do it hook up this radio frequency “AC” to a speaker and see if it sounds like country music or traffic reports.
AC in a high impedance circuit is practically unavoidable, graphene or not.
This is pretty meaningless argument though. Ok, maybe it does not contradict the second law of thermodynamics. It still contradicts the conservation of energy though, and that's what matters!
(It also does not contradict law of conservation of momentum, Boltzmann law, and San Francisco parking rules. Who cares?)
The abstract doesn't appear to me to say anything about violating known physical law.
They are claiming it all works as theory predicts, I think.
What is missing for me is an explanation why this is in fact interesting to a layperson.
"At room temperature, micron-sized sheets of freestanding graphene are in constant motion, even in the presence of an applied bias voltage. We quantify the out-of-plane movement by collecting the displacement current using a nearby small-area metal electrode and present an Ito-Langevin model for the motion coupled to a circuit containing diodes. Numerical simulations show that the system reaches thermal equilibrium and the average rates of heat and work provided by stochastic thermodynamics tend quickly to zero. However, there is power dissipated by the load resistor, and its time average is exactly equal to the power supplied by the thermal bath."
I guess it sounds like they are saying the graphene is all wibbly-wobbly at room temperature, and applying a kind of damping mechanism temporarily produces power. Very temporarily.
I'm not quite sure why this should or should not be possible. If they say it's initially not at equilibrium though, that means they aren't suggesting new physics, right?
Thanks