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posted by
martyb
on Tuesday February 19 2019, @08:27PM
from the does-it-also-make-the-room-darker? dept.
from the does-it-also-make-the-room-darker? dept.
Researchers at the University of Michigan ran a light emitting diode (LED) with electrodes reversed in order to cool another device mere nanometers away. The approach could lead to new solid-state cooling technology for future microprocessors, which will have so many transistors packed into a small space that current methods can’t remove heat quickly enough.
This could turn out to be important for future smartphones and other computers. With more computing power in smaller and smaller devices, removing the heat from the microprocessor is beginning to limit how much power can be squeezed into a given space.
https://www.rtoz.org/2019/02/18/running-an-led-in-reverse-could-cool-future-computers/
[How does this compare to a Peltier device?
--Ed.]
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Running an LED in Reverse Could Cool Future Computers
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I'm mentally OVERDRAWN! What's that SIGNPOST up ahead? Where's ROD
STERLING when you really need him?
(Score: 5, Informative) by Immerman on Tuesday February 19 2019, @09:27PM (10 children)
It's unlikely to function as heat-pump though. More likely the light-emitting junction, in reverse polarity, becomes a photon-absorbing junction, converting infrared photons to electricity rather than the other way around.
Basically, it transforms thermal radiation into electricity, it doesn't have anything to do with mechanical heat, and thus is not bound by the usual thermodynamic limitations.
(Score: 4, Touché) by Anonymous Coward on Tuesday February 19 2019, @10:05PM (7 children)
The great thing about being able to convert heat into electricity with no thermodynamic losses is that you can apply some electric power, let the power dissipate to heat, convert the heat back into electricity and feed it back into the power supply. Then you disconnect the 'bootstrap' power, and let your perpetual motion machine run forever mining bitcoin.
Another useful feature of direct conversion of heat into electricity is that you can make an air con unit that not only cools your house, but also powers the rest of your house. You could even make money by feeding it back to the grid.
(Score: 2) by c0lo on Tuesday February 19 2019, @10:24PM (6 children)
Even more, you do it in perpetuity.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by JoeMerchant on Tuesday February 19 2019, @10:58PM (1 child)
Unfortunately, free market commercial demands for cheap energy means that we'll all freeze to death with all this heat converted to electricity...
I think the "infrared photon converted directly to electricity" is missing something, somewhere - probably one of those laws of thermodynamics having to do with entropy...
🌻🌻 [google.com]
(Score: 3, Informative) by c0lo on Tuesday February 19 2019, @11:27PM
1. if you want to cool the junction faster than the heat diffusion, you can but you'll need to "evacuate" the electrons promoted (by IR absorption) into the conduction band before they recombine and give you the absorbed heat back. Which means you'll need to maintain the reverse polarity on the diode, and this doesn't energetically come for free. The good thing in this 'thermal pump' setup - you are going to produce the extra heat in some other place, where you may be able to dissipate easier.
2. if you think, a photoelectric element is doing the light to electrical energy conversion without applying a reverse potential (and IR is light). But in this case, the junction is highly doped and the produced electrons/holes move under the gradient of charge concentration by thermal diffusion. If you make the junction thin enough, more charge carriers will reach the collecting electrodes (and "find it easier to travel" to the opposite side of the junction using the external circuit) than they recombine and you will have an electric current. However, you can't use this arrangement to cool (i.e. extract energy) faster than thermal diffusion - because the thermal diffusion of charge carriers that is the very engine which powers the PV element.
Now, the consequence of the above: you need the junction to be "hotter" than the outside circuit, otherwise the PV element will never generate electrical power (will simply act as a resistor).
In both cases, the laws of entropy are already at work.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 3, Funny) by pipedwho on Tuesday February 19 2019, @11:40PM (3 children)
I wanted to add more, but as my house started to runaway towards zero Kelvin, my fingers were freezing and slowing down too much to continue. I was posting from my phone, and I can’t be arsed porting my password manager across, so posted as AC in my ice cold A/C, while feeding AC back to the grid.
(Score: 2) by c0lo on Wednesday February 20 2019, @02:24AM (2 children)
Sucks to be so greedy, ain't it?
If you would only export half of it and use the other half to heat your home, you wouldn't become super-conductive.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by pipedwho on Wednesday February 20 2019, @02:53AM (1 child)
Not greedy as such. Just forgot the thermostat and without the laws of thermodynamics to asympote it towards an energy equilibrium it got out of hand. Barely made it to the off switch before I was too frozen to move.
(Score: 1) by anubi on Wednesday February 20 2019, @03:52AM
Carnot is a bitch when it comes any useful energy from heat differentials.
"Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
(Score: 4, Informative) by c0lo on Tuesday February 19 2019, @10:22PM
That's exactly how it functions. Otherwise you'd be able to extract the energy from a low temperature (say, 60C) and use it to heat water to boiling point without consuming extra work.
Don't forget that the difference in electrical potential (otherwise know as voltage) is defined as 'the work necessary to transport a unit of electrical charge between the two potentials'.
To evacuate the electron with higher energy resulted from the absorption of the photon, you need to maintain the reverse voltage applied on the diode - otherwise the electron will recombine with the hole it left behind. So, having displaced the electron, as soon as it reaches the collecting electrode and neutralizes some charge there, you'll have to put the extra work to restore the voltage. And, believe it or not, you aren't going to obtain a unitary efficiency in restoring that voltage.
Nothing escapes thermodynamic laws (which are just the macroscopic average expression of 'the energy always flow from high towards low".
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by JoeMerchant on Tuesday February 19 2019, @11:03PM
Last time I looked into it, everything is bound by the usual thermodynamic limitations. You can shuffle things around, but once entropy has increased there's no decreasing it in the big picture. Entropy can be decreased in a localized part of a system, but only by increasing entropy (usually including some bonus entropy, but at least as much as was decreased) somewhere else in the system.
Unless Maxwell's Demon is real...
🌻🌻 [google.com]