# Cooling without heat

1. Dec 10, 2016

### NickPerry

ok, we have a really efficient way to make heat (adding energy into a system) all we have to do is pass a current through a high resistance wire, boom, close to %100 heat generation.

however, from what I can tell there is no way to create coolness (take energy away from a system) like that.

we have:
Phase change: (requires a lot of energy, generates a lot of heat that needs to be transferred else where)
peltier effect: (requires there to be a temperature differential to already exist)
sterling engine: (See peltier effect)

and on the fringe we have
%230 efficient LED (made in the MIT lab) which uses power + some heat to make light, but still takes power

and I think the closest we have is an Optical rectenna which takes visible and infrared wavelengths and turns it into power, however, it only works with RF waves, not particle movement.

is there a way to simply absorb particle movements and convert it straight into electricity like some ultra-small piezo generator? where it would generate power from a room simply by sucking the heat out of it & without needing a place to dump any excess heat.

2. Dec 10, 2016

### NickPerry

of course right after I post this I find the answer I'm looking for.
apparently it sort-of exists, and it's called a phonovoltaic (https://en.wikipedia.org/wiki/Phonovoltaic) which converts the lattice vibrations into energy, but apparently it only works in high energy environments, in a narrow band... but it's a good starting point.

3. Dec 11, 2016

### Drakkith

Staff Emeritus
Hmm... I'm not super familiar with this area, but I don't think so. This sounds sort of like Maxwell's[/PLAIN] [Broken] Demon. You certainly wouldn't be able to convert all of the thermal energy into electricity, but perhaps you can convert some of it. No matter what you do you will have "excess heat" that needs to be removed or dealt with. The phonovoltaic cell runs into the problem that high energy phonons get converted into multiple low energy phonons, lowering the efficiency. In fact, the pV cell is limited to a maximum efficiency approaching the Carnot limit.

Last edited by a moderator: May 8, 2017
4. Dec 11, 2016

### Staff: Mentor

Well, air conditioners run about 300% efficiency, so I'd say that's better!

5. Jan 5, 2017

### NickPerry

wow, I should probably check this forum more often, Thank you for the answers (although they are perhaps not what I want to hear :p)

"The phonovoltaic cell runs into the problem that high energy phonons get converted into multiple low energy phonons, lowering the efficiency. In fact, the pV cell is limited to a maximum efficiency approaching the Carnot limit."

That is very unfortunate.. but doesn't Carnot's limit basically state that the effect would be limited to the temperature differential? but since we aren't using a temperature differential would that not mean that does not apply?

"Well, air conditioners run about 300% efficiency, so I'd say that's better! "

HA! yeah, gotta love that marketing wank :p (but I must say that I haven't heard companies advertise those kinds of figures in a while now)

6. Jan 5, 2017

### Drakkith

Staff Emeritus
I confess I do not know.

7. Jan 5, 2017

### Staff: Mentor

No, they advertise COP or SEER...which people often understand even less. But my point was that your opening post implied to me that cooling can't be done as efficiently as heating, which isn't true. In terms of output vs input, cooling is much better than heating.

If what you are after is just solid state cooling, regardless of efficiency, try thermoelectric (peltier) devices.

8. Jan 5, 2017

### NickPerry

My apologies, I probably shouldn't have used the word 'efficiency' and the only reason I did is because if you have an air conditioner inside a room with no way for it to vent out, the amount of heat it outputs would be greater than the amount it can cool.

what sparked this question was the fact I was trying to think of a way to cool down components on a Venus rover where everything is fairly hot, and to try and pump out hot air of a standard air conditioner system doesn't strike me as the best way to go about it. rather it would be better if you could make a sealed compartment with something to cool the air (a peltier wouldn't really work because any heat-sink designed to whisk away the hot side would work in reverse, heating up the peltier as a whole instead. perhaps if I used a series of progressively cooler chambers..)
and that got me trying to think of other methods, hence this question.