Cold air - Vortex tube.

[DaveH]

Thanks Arvid,
I'll need to sit and read them
I made mine about 1994 I didn't have quite so much access to information then. So mine was more guess work than any thing else. Like Tom said it "eats" the air.
Now there are commercial ones about so, me being me I thought I might copy one of those - I'm not proud

These commercial ones seem to do the job - I think

DaveH