Can one stack Peltiers to 70 °K?

No it doesn't. O2 liquifies at 90K (will just do it in liquid argon). Solidifies at 54K. If you have any solid oxygen component in LN2 then it is as ozone which is a much darker blue and tends to detonate unpleasantly when it thaws. It sometimes happens if you have a wide cold finger dewar open to air and kept topped up for a very long time.

One of the more spectacular and somewhat dangerous pyrotechnicians doing the UK science lecture circuit had/has his own LOX still made out of copper pipe. No reputable supplier will sell him LOX because of the things he does with it. eg Rich tea biscuit + LOX + match. Most chemistry and physics departments have bulk LN2 freely available. Price is similar to beer which makes complex arrays of Peltiers redundant.

The lecturer was John Salthouse and his last touring version was called "Son et Lumiere" an abridged version of some of the more spectacular stunts online at (LOX + biscuit is 13-18s in, LOX+cotton wool 24-34s) :

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Music is annoying - original sound track is very loud in parts - actual lecture disturbs dust from the roof and on occasions ceiling panels.

There are other more complete versions on Utube, but technical quality and audience noise is poor. There is also an official BBC version where in the later takes he is sporting a plaster on the forehead after scaling one of the bending an iron bar detonations up a bit too far.

Anyway you will struggle to get things much below dry ice temperatures with any realistic Peltier based cooling. Great for having no moving parts but you have to shift a lot of I^2R heat from the hot side.

Regards, Martin Brown

Reply to
Martin Brown
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Lovely!

And there's the old classic,

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Tim

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Reply to
Tim Williams

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I recall seeing Col Shaw at Nottingham University in the early 70s

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Dirk

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Reply to
Dirk Bruere at NeoPax

^ ^ ^ ^ ^

Chloride?

Dry ice + acetone is also a cheap, well known laboratory refrigerant.

Tim

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Reply to
Tim Williams

On a sunny day (Thu, 16 Sep 2010 23:10:04 -0400) it happened Phil Hobbs wrote in :

What I have come up so far is this: SC-UD08 cooler, for ~750 $:

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this can do 15W @ -100 °C. Then a three stage Peltier to get 82 °C extra, an other 150 $ Still < 1000 $.

The catch is in that they do not want you to heat the cold side of the SC-UD08 (see manual). Well, switching it on step by step and keep Peltier power below 15 W COULD work. What do you think?

Reply to
Jan Panteltje

SC-UD08 (see manual).

work.

I'm sure you meant "it"!

John

Reply to
John Larkin

This is water ice and CaCl2. YCLIU.

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

Or even just a CO2 fire extinguisher

But you can't get any colder than dry ice (with C02), which is ok for many, and most others are satisfied with liquid nitrogen which is still fairly cheap.

running compressed air (or nitrogen in a closed loop) through a regular air compressor and small aperatiure might be a solution too. it's just a mechanical heat pump with air (or N2) as the working fluid.

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??pun u?op ?o?? s?u??????
Reply to
Jasen Betts

On a sunny day (Sun, 12 Sep 2010 11:03:24 GMT) it happened Jan Panteltje wrote in :

This project is now moving forward. The stacking of Peltiers causes too many problems, already theoretically, and the price of suitable cryocoolers that go to that low temperature directly is around 10.000$. But I managed to score a used superconducting cellphone tower filter with such a cryocooler and drive electronics build in, for much much less.

Now we shall finally be able to cool those sensors to get the noise down:-) And a lot of other cool (pun intended) experiments.

Stuff may take some time to arrive, customs, shipping...

Cool PICs? hehe

Reply to
Jan Panteltje

Now that it's too late to make a difference, did anyone in this thread suggest immersion in liquid nitrogen? It's commonly done in the IR imaging world for prototyping, and I know of at least one commercial product that had a spout on top for LN2.

(I worked for an IR imaging company for years, and it took me several of them to understand that a "pour fill" dewar was not a dewar flask that was manufactured by a broke guy named Phillip, but instead was a dewar flask with evaporative cooling).

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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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Reply to
Tim Wescott

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