Ed Sirett wrote:

On Fri, 07 Jan 2005 15:42:35 +0000, Grunff wrote:

Markus Splenius wrote:
With the same frivolity as "Has anyone ever built a dalek", I wonder
if any of you have thought about making liquid nitrogen at home.

I always liked cryogenics as a kid :-)

Of course anything is possible - it's just a matter of cost! :-)


It's very, very difficult to do on any kind of DIY budget :-)

I would think you would need at least a scuba bottle compressor.
You then need a longish length of very very small gauge metal tube
(probably less than 0.5mm ID). This you coil so it fits into a very
very small thermos flask.

The output of the scuba receiver (already cooled to ambient) compressed at
about 200 bar goes into the fine tube the air escaping from the open end
of the is cool this pre-cools the compressed air coming down the fine tube
until the stuff coming out is so cold it's liquid.

I've done this at college with a 200 bar bottle of nitrogen as the source.
This made about a thimble full in 5 minutes. The flask part being the size
of a thimble so it might only work on that scale. 8-(

I expect there are some nasty gotchas like having to get rid of all the
water and CO2 from the air before compression? 8-(

Not really, any water in LN2 freezes so cold it sublimates away. CO2
freezes solid and in some situations can by seen as a frost on the walls
of the Dewar or rolling around on the bottom as nodules.

Peter
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