Long shot - WTB Stirling Cycle Cryocooler

[MarioMaster]

I know there are some people here who might be able to get me something like this, I'm looking for a stirling cycle cryocooler capable of reaching about -200°C or any other refrigeration system capable of reaching such low temperatures.

Thanks for looking

[DMills]

What heat load?

I **Might** know where there is a helium compressor and used cryopump head, but at only -200C you may be better with something simpler (Read cheaper, lower maintenance and less power intensive).

The cryopumps are not good for high thermal loads, being really designed as UHV sorbitron pumps.

Regards, Dan.

[MarioMaster]

Great, more heat load is good but I don't need anything huge - my main problem is that as a college student I don't have a ton of money.

My goal is to be able to condense nitrogen.

[DMills]

A cryopump is the wrong weapon for this.

Why not use the N2 as a working fluid directly?

Compressors capable oh handling dry nitrogen are no big deal (Air is mostly N2 after all), and a couple of stages (which could all be run off the same pump with a bit of lateral thinking) will get you there

Start at a few hundred PSI and cool to ambient with a blown heat exchanger (the compressor will have an interstage intercooler in all probability anyway), then cool the high pressure gas further using a domestic freezer type arrangement or big water cooled peltier stack, should get you a few hundred PSI at -25C or so.

Next comes the clever pipework and insulating foam bit:

Expand most of the feed gas which will cool the expansion chamber and couple the cooled expansion chamber to cool the remaining high pressure gas, the exhaust from the chamber should be used to intercool the -20C feed gas, rather then wasting the cold gas.

Repeat a few times and you will have liquid N2.

Now, pertinent question: Why bother making LN2? The stuff is a few cents a litre to just buy.

And a safety warning: LN2 boils at a LOWER temperature then LO2 does, so if you use dry air as a feedstock (or leave a dewar of LN2 open to the air) you can end up with LO2 instead, which has really nasty explosive potential.
You DONT want liquid oxygen where you think you have liquid nitrogen!

Regards, Dan.

[MarioMaster]

Right, I would need to separate any other gasses from the air before trying to liquify it. I mainly want to do this as a proof of concept, the direct expansion method doesn't seem very efficient. I don't know of any local places where I can buy liquid nitrogen and I just like the idea of making it myself as a project in cryogenics.

I currently study HVAC/R and this sort of stuff is interesting to me.

[mixedgas]

Some how my reply post did not make it, so lets try again. If you cannot get Ln2, try a Joule Thompson cooler. Just have some one who is competent check the high pressure plumbing if you make one. 2500 PSI is a terrible thing when it gets loose. On a home made project scale of 1 to 10 with 10 being a Farnsworth Fusor or a Copper Bromide laser, a JT cooler is a 3 or 4.

But I agree with D Mills, a cryo cooler, is a tough solution, not to mention they are pretty much obsolete except for high vacuum systems, The main user, Uncle Sam, probably has room temperature sensors by now.

USED Ln2 Dewers are cheap. Ln2, from a bulk source, costs less then quality beer.

Ok, if you really want a cryofluid of sorts. although not a really cold one, PM me and I'll walk you through making one with less then 20$ of materials. Problem is it is flammable.

A quick check shows you have 4 possible ln2 vendors within 20 minutes of you.


From a patent search:

This invention is directed to a valve on a cryostat.

Simon cooling occurs in a high pressure gas tank when gas is discharged from the tank. The remaining gas in the tank does work on the gas being expelled, to decrease the temperature of the gas remaining in the tank. R. W. Stuart U.S. Pat. No.3,593,537 describes a Simon cooler.

A Joule Thomson cooler is one where a pre-cooled gas is expanded out of a nozzle at the cold point and the cold exhaust gas passes over the incoming higher pressure gas to provide the precooling. An example of a Joule Thomson cryostat is shownin J. S. Buller et al, U.S. Pat. No. 3,640,091.

In the prior art, high pressure gas bottles have been used to supply refrigerant gas to a Joule Thomson cryostat, as in Wurtz U.S. Pat. No. 3,095,711, but the advantage of employing both cooldown methods in combination only occurs for quickcooldown situations where the structures are close-coupled.


SUMMARY

Steve

[Stoney3K]

...On a home made project scale of 1 to 10 with 10 being a Farnsworth Fusor or a Copper Bromide laser, a JT cooler is a 3 or 4....

Would a Bussard-type Polywell be a 11, or a 12 in that case? It's basically a Farnsworth with larger vacuum chamber, lots of magnets and other cool bits...

Ok, if you really want a cryofluid of sorts. although not a really cold one, PM me and I'll walk you through making one with less then 20$ of materials. Problem is it is flammable.

Get a propane tank filled at your local gas supply store? Guess that WOULD be the simplest way to go, but I'm not sure what temperatures the TS will need. -200C won't really cut it with gases like that.

[mixedgas]

Butane works great as a pseudo cold fluid. Really acts just like LN2, only not as cold.

Steve

[DMills]

Would a Bussard-type Polywell be a 11, or a 12 in that case? It's basically a Farnsworth with larger vacuum chamber, lots of magnets and other cool bits...

More like a 25 or so, the magnetics are seriously non trivial (especially as they have to be fabricated to not act as a virtual leak at 10-4 torr or so while also being rigid enough to survive the imposed forces).....

Regards, Dan.

[MarioMaster]

Thanks for the information Steve, I'll have a look into the stuff you mentioned. I can make phase cooling systems all day and I have a 2 stage cascade system that reaches -100F but it's not cold enough to condense nitrogen.

Again I mostly want to do this as a project and proof of concept.