On Sat, 08 Jan 2005 01:45:11 +0000, Andrew Gabriel wrote:

In article ,
Grunff writes:
Andy Dingley wrote:

Don't forget that Ohnes liquified helium in 1911 and discovered
superconductivity almost immediately afterwards. Nitrogen was back in
the 1880's. Now how much technology did any lab have back then that
you can't reproduce in a half-decent modern home workshop ?

This is a fair point, but it would be quite a bit of work none the less.
Got any diagrams etc. of homebuilt kit?

ISTR it can be done with a compressor and pair of concentric
copper pipes. These are coiled up and inserted into a thermos or
dewer. Air is pumped down the central one which has an expansion
jet on the end which cools the air. The cool air is recovered
back up the outside one which further cools the air coming down
the central one, until eventually the air gets cold enough to
start liquifying when it leaves the expansion jet. At least,
this is my recollection of one way of doing it from O-level
physics.

There appear to be some details missing from this, like where
the heat gets dumped. Probably, the compressed air is cooled
back down to room temperature before it enters the coil to be
further cooled by the returning air. (It is not necessary to
send the same air round and round the system.)

Obviously, starting with air, you end up with liquified air
rather than nitrogen. The boiling points of nitrogen, oxygen
and argon are near enough you'll get them all ISTR.

This subject came up a few months back, as I was considering
trying to do this with a compressor from a freezer. I did
google around thinking there was probably a secret society of
low temperature hobbists out there doing this, but came up with
nothing, so if there is, they are very secret. I couldn't even
find a description of the process above which I recall from my
O-level physics lessons.


I don't know if you saw my post.
I'm fairly sure you'll need 200bar for the air.
The heat given off compressing air to that amount is huge.
And needs to be removed before the compressed air enter the low temp part.

I'm fairly sure the fridge kit is only good for a few bar output.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html