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stacking peltiers

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Microwatt

Wed Sept 19 2012, 05:58PM

Registered Member #3282 Joined: Wed Oct 06 2010, 05:01PM
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Posts: 224

Has anybody heard of reaching cryogenic temperatures with a stack of PT junctions. Maybe the top one smaller than the lower pile. each separated by 1/4 inch aluminum plate. waste heat can be removed by a very large aluminum plate and a bag of ice.

Conundrum

Wed Sept 19 2012, 06:33PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

Have heard of it, you run into diminshing returns without water cooling though.
The problem is for n stages you need to dump n+n watts of heat.
The thermal capacity drops with each stage as well, so you may have to insulate around each step in the pyramid with silicone or another themal insulator.

I'd also put sensors on each stage to detect thermal runaway before it causes fried junctions.

Looked into this for testing a 212K SC pellet but the problem is that this is really cold. 212K is >40 degrees lower than the temperature of a domestic freezer.
So assuming an optimistic 10C per stage you'd need at least 6 stages with the bottom Peltier being a behemoth.

AndrewM

Wed Sept 19 2012, 08:40PM

Registered Member #49 Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362

I've done a watercooled 4 layer stack before. As said, the diminishing returns kill you.

IIRC to pump 1W it takes 4W+ near the maximum deltaT... so each stage has to be 5x larger than the one after it.

My "coldest" stage was only a .5"x.5" (4x4 junction) module but the hottest module was huge, 3"x3". Water cooling was easily effective and the cold stage got VERY cold (cold enough to freeze your finger right to it).

I may have made a thread on it at the time... that would have been 2004ish so it'd be in the archives, if anywhere.

2Spoons

Wed Sept 19 2012, 10:42PM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
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Posts: 615

AndrewM wrote ...

IIRC to pump 1W it takes 4W+ near the maximum deltaT... so each stage has to be 5x larger than the one after it.

Its actually a lot worse than that. It takes ~4W to pump 1W with NO deltaT. As deltaT increases the performance worsens until max deltaT is reached, at which point no heat is pumped at all.

Patrick

Wed Sept 19 2012, 11:01PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Does the AIM 9X sidewinder use peltiers? in know the airforce and navy wanted to get rid of the cryo nitrogen/argon bottles for cooling the "M"...

Dragon64

Wed Sept 19 2012, 11:47PM

Registered Member #1438 Joined: Sat Apr 12 2008, 12:57AM
Location: Canada
Posts: 218

Not the cleanliest setup, I've managed to get about -45.1ÂºC with a dual stacked peltier in an ice bath. (Picture bellow)

Tecdouble

Though the top peltier is nearly the same size as the lower, the top is running at about half the power the bottom is running at. With a triple peltier setup, I've actually seen the temperature become higher then that of the dual peltiers but I'm guessing it's due to the fact that I haven't got a peltier powerful enough to dissipate the heat of the two on top and only adding heat to the system.

Though I've seen websites selling prearranged pyramid peltiers and some patents on cascade peltier arrangements.

Patent

Abstract

Selling

(I can't really say much about the seller because I've never bought any cascade peltiers before)

Adam Munich

Thu Sept 20 2012, 01:04AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

^^ I've done the same thing before, but better.

1) Paint the top peltier matte black.
2) Find a small plastic transparent box, like a mineral specimen box and glue a tiny shard of felt to one wall.
3) Drop some methanol on that felt.
4) Put a piece of thorium, americium etc on the peltier and place the box over it.

Cloud chamber

Microwatt

Thu Sept 20 2012, 03:15AM

Registered Member #3282 Joined: Wed Oct 06 2010, 05:01PM
Location:
Posts: 224

the question is can you reach liquid h2 temperatures with a stack of peltiers and a big bath of ln2

2Spoons

Thu Sept 20 2012, 04:04AM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

The problem with that is that peltiers use semiconductors, and as they get colder the resistance goes up (less thermal energy means fewer current carriers), so the I2R self heating goes up, and the heat pumping ability gets worse.

So the short answer is most likely 'no'.

IntraWinding

Thu Sept 20 2012, 01:18PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

I had a good look at stacked Peltiers once with the idea of using one to cool a vacuum cold trap without the hassle of finding liquid nitrogen or dry ice (people online always seem to be able to get this easily, but I can't).

It seemed to me Marlow was way ahead of other suppliers on products and technical information. I think they even had a piece of free downloadable software for calculating optimal stacks at one time.

Looking now I can see they have a range of 2, 3 and 4 stage modules on page 2 here:

And here's loads of technical stuff to read:

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