Can one stack Peltiers to 70 °K?

I don't know about the peltiers but you can get low temps by blowing off compressed CO2 or N2 through a needle office into some felt via a needle valve.

First thing to watch: the absolute temperature range your peltiers operate on. My guess: not lower than minus 20 degrees C, not (much) higher than 100 degrees. Keep it cool, but not with peltiers :-)

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Gerard Bok

On a sunny day (Sun, 12 Sep 2010 12:09:08 GMT) it happened snipped-for-privacy@zonnet.nl (Gerard Bok) wrote in :

Hi Gerard, I found this link

that has 3 Peltiers stacked, and reaches -55 °C. He warns that below that the Pelties can get damaged, but I am not sure if it is because of temperature, or because of too much power.

I also found this link, and they claim to have one for a customer do to 145 °K

After all it depends on the junction of 2 metals, so if those stay intact, then it should work?

On a sunny day (Sun, 12 Sep 2010 20:02:10 +0800) it happened "Dennis" wrote in :

OK, I will look into that too. I got really nice ice forming sometimes on my car at the pump (ran on LPG, (liquified gas).

As a rule of thumb a peltier generates as much heat as it transfers. If the coldest one transports 5W, the next will have to deal with 10W, then 20W, then 40W and finnaly 80W. IF a peltier could work at such low temperatures.

Perhaps you can find a cryogenic cooler on Ebay. The coolant may be very nasty stuff though.

--
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nico@nctdevpuntnl (punt=.)
--------------------------------------------------------------

If LN2 is _really_ a problem (shouldn't be within reach of civilization), then why not get ahold of a cryocooler?

Best regards, Spehro Pefhany

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Don't take the hot side over 100C - don't ask me how I know that the peltiers fall apart.

On a sunny day (Mon, 13 Sep 2010 09:14:24 +0800) it happened "Dennis" wrote in :

I was sort of planning to connect the hot side to the biggest CPU cooler I could find :-) Also to have the stack upside down, so heat rises, and does not heat up the cold part.

On a sunny day (Mon, 13 Sep 2010 00:22:31 -0400) it happened Phil Hobbs wrote in :

says they have reached 145 K.

Nico Coesel schrieb:

Hello,

that is why they build pyramid stacks: one in the coldest layer, then two, then four, then eight and finally sixteen. Together 31 Peltiers. Of course you need a good thermal connection between any two layers, but this connection should be isolated from the surrounding air. But the question remains, is it possible to reach even 70 K this way?

Bye

As far as I know: Peltier as a technology, works on many metals and over their usable temperature range (appart from dissipation issues.)

The commercial 'Peltier coolers' with delta T of 30 degrees C in a single unit are stacked semiconductor devices. Hence, the semiconductor temperature range.

--
Kind regards,
Gerard Bok

There are no minority carriers in Peltiers, because there is no PN junction--just separate P-type and N-type bars with metal on both ends. Thus there should be no carrier freeze-out issues. FETs work down to 4K.

Cheers

Phil Hobbs

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Democrats are best served up prepared as a hash Otherwise the dogs will refuse to eat them :)

Who'd want to email a cowardly little blowhard like you?

No, for you it's Google Groups. *snicker*

Well, I don't know from Peltiers, but if I was faced with this, I'd stack up banks of thermocouples on some kind of ceramic matrix. AFAIK, thermocouples don't care how cold they get. ;-)

Good Luck! Rich

could find :-)

cold part.

Heat doesn't rise. Heat goes in all directions.

_Warm air_ floats on top of _less warm air_, but I doubt if you'll have a lot of air convection in your setup. ;-)

If cooling is the issue, gin up a couple of heat pipes. ;-)

Good Luck! Rich

On a sunny day (Tue, 14 Sep 2010 13:39:26 -0700) it happened Rich Grise wrote in :

could find :-)

cold part.

Now if you want to pick nits, OK.

Of course the warm air going upards (these things dissipate a lot) to the hot side makes a huge difference.

Na, too complicated. I found small sterlingcoolers are the perfect thing, but the prices are insane, like 10,000 $ up

Now there is a way to make a lot of money (200$ parts I guess). I think cellphone towers have these, to cool superconducting bandpass filters, so I should look for a surplus cellphone tower, also IR missile tech uses it, so maybe a duff US missile, LOL. None on ebay so far.

Yea, if you find one (cheap [used] sterlingcooler) let me know. I spend hours googling..

Actually most cryocoolers do not use Sterling engines. Cost a lot less that way.

At standard pressure oxygen freezes at LN2 temperatures.