[mousethatroared]

COP has to be compared at the same delta T. The COP of a loss less refrigerator is infinite at Delta T = 0

And you dont get to stack Peltiers to increase COP, only to increase delta T.

Still, Peltiers are super cool and I have some ideas for their use od they get slightly better. Advances are super welcome.

[jfengel]

The idea was just so astonishing that I ordered some from American Science and Surplus. I connected the leads to a battery and poof, one side got hot and the other got cold. Blew my mind.

I didn't actually have a use for it. It was just neat that it actually worked.

I understand the basic physics of it perfectly well. It's just one of those things where you expect basic physics to be overwhelmed by friction or something.

[BobbyTables2]

Had a similar experience myself.

The thinness of Peltier devices bothers me. Amazing temperature differences… without any room to insulate such!

[gsf_emergency_2]

I don't know how people can convince themselves that they can understand these effects.

Unusually effective heat insulation is exactly how they work. (This is tempered by eg radiative losses, so making them thicker doesn't work better.) placing poorer heat (vs electrical) insulators between peltier material is counterproductive, similar to using resistors to improve conduction between copper wires

Don't ask me for a better explanation :)

As to why COP or even Carnot efficiency hasn't been thrown out in favor of temp-difference independent efficiency metrics like exergy.

I can't tell you either

[BobbyTables2]

Indeed, but in practical use (like a mini refrigerator), one will want to insulate the hot and cold sides from each other.

If one makes the walls thick, then they end up with a hole for the Peltier device and somehow sandwich two heatsinks on the device while maintaining insulation around it.

Perhaps easier to deal with in CPU cooling and such since one side is simply smacked into the thing being cooled.

[mousethatroared]

What is exergy? The one time a mechanical engineering colleagues tried to explain it to me, he reached the wrong conclusion on the problem we were working on.

I haven't seen it in any physics thermodynamics book, and only mech eng. seem to know what it is, and then only in the US.

Faires (undergrad MIT Thermo book from the 50s) makes no mention of it as far as I can tell.

[mousethatroared]

@tlocke

But that isn't a mathematical expression. At best, it would appear to be energy * maximum_Carnot_efficiency (for heat engines anyway)

But it seems not to be adding very much, since Carnot efficiency depends on delta_(T). The OPs point that exergy doesn't depend on T is tautological since T has already been accounted for by the Carnot expression.

[tlocke]

Exergy is the amount of work that a system can potentially do. It was on my physics course in the UK I'm fairly sure.

[mousethatroared]

Careful! Wothout a heatsink they'll easily self destruct (solder on the PN junctions)

[lightedman]

They're already doing great. I have a portable neck AC unit that uses peltiers and it keeps my head and neck cool in otherwise nasty desert conditions when mining. Yes the radiative heating from the sun is still a bitch but a hat basically minimizes that, and also redirects the partially-chilled air more efficiently around my head and face.

The direct-contact neck cooling plates are an absolute lifesaver. Keep the sun off the back of your neck and chill one of the best heat sink locations exposed on your clothed body.

[exhilaration]

Sounds cool :-) I think we'd forgive you for providing a direct link to this product.

[nimos]

There's a bajillion of them around if you search "neck cooler" or similar. Very simple product sticking a few commodity items together. Some do only have fans though.

When I looked a while ago there wasn't really a clear winner or high quality unit. There is the "Coolify" series that are much more expensive but still somewhat middling reviews overall.

[lightedman]

No link, I have the Ranvoo Aice Lite. Couple hundred bucks on Amazon.

[GuB-42]

> Still, Peltiers are super cool

I'd say they are super hot, but it depends from which side you look at it.

[positron26]

One can only hope some kind of phonon diode material can exist that a slight voltage can overcome something so inescapable as entropy by providing it only lanes that suit us.