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IamSmooth

Sat Sept 01 2012, 07:40PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

Has anyone here ever attempted to liquify any of the gases from air as a project? It seems to be a large industrial process, but I do not underestimate the creativity on this site.

I know I can liquify gases if I cool them in copper coils in liquid nitrogen. I want to take raw air, compress and expand it to liquify the gases. Can this be done as a DIY project?

Pinky's Brain

Sat Sept 01 2012, 08:38PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837

I haven't done it, but I have a website of someone who has using a cryogenic cooler he salvaged on the cheap from used equipment :

In theory a cryogenic cooler can be made with an ordinary refrigerator compressor using a mixed coolant (which can then be used to cool down the air so you can extract the components you want) but I don't think any hobbyist has done that yet, or at least no one has published the results to my knowledge.

Patrick

Sat Sept 01 2012, 10:47PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

well if you figure it out be sure to post here on 4hv.

Ive got a AIM9-M sidewinder missle that needs liquid argon or nitrogen, i keep it in my apartment just in case those Rusians pansies cuase any problems here in California.

2Spoons

Sun Sept 02 2012, 02:38AM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
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It should be possible. Look up Carl von Linde. All it really takes is a compressor and a lot of copper tubing. Not efficient but it works.

Microwatt

Sun Sept 02 2012, 05:20AM

Registered Member #3282 Joined: Wed Oct 06 2010, 05:01PM
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Do you think it might be possible to make lox using stacked airconditioners? lets say replacing the refridgerant with methane/ hydrogen?

Ash Small

Sun Sept 02 2012, 10:03AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Microwatt wrote ...

Do you think it might be possible to make lox using stacked airconditioners? lets say replacing the refridgerant with methane/ hydrogen?

I've read articles where hobbiests have stacked two refrigeration pumps to achieve cryogenic temperatures for cooling cold traps for vacuum systems but I don't have any links to hand.

klugesmith

Sun Sept 02 2012, 02:51PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

It's been done by hobbyists, as reported in classic Amateur Scientist columns in Scientific American. Was discussed here in summer of 2011. I weighed in on the basic approach:

and later with a thumbs-up when OP found an old book by Georges Claude online.

Go for it. Today, access to dry ice and junk fridges (for air compressor, tubes for counterflow heat exchanger, and flow restrictor/expansion valve) should make it much easier than it was in the 19th century.

Of course if you're willing to buy dry ice, why not LN2?

IamSmooth

Sun Sept 02 2012, 04:45PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

I'm going to start reading this. The history of science is always amazing.

I watched a youtube video where liquid nitrogen was turned solid by rapidly decreasing the pressure using a vacuum pump. I thought that this would cause the liquid to boil. Is this because the pressure is below the vapor pressure of the liquid, and the boiling liquid removes heat, causing the remaining liquid to solidify?

IamSmooth

Mon Sept 03 2012, 12:22AM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

So this is what I am thinking of doing after doing some more reading:

I can take N2 from a tank and pump it through a long conical coil going to the compressor. This simplifies things by eliminating the water vapor and containments that could clog the system. The output of the compressor is wound around the input coil to create a counter-current exchanger. The output goes to an insulated container to collect the gas.

This seems too simple to think that others have not done it here. Any thoughts? Am I missing something?

Marko

Mon Sept 03 2012, 11:20PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hey guys

I had an opportunity to witness a really old school air liquefier/fractional distiller used to produce LN2 on a college nearby - I't s a single stage unit, basically a huge stirling engine ran in reverse by a 11kW motor, ant the hot part of it is water cooled... liquified air contents are led to a separate tank where they are separated. The machine used helium as working gas.

Seeing that done, I don't see a reason why the same wouldn't be possible using a simple fridge-like closed loop cycle, with a suitably huge compressor.

Calculations show that helium needs to expand about 10 times from room temperature in order to reach LN temperatures. This makes it theoretically plausible even with a fridge compressor (which I've seen do 30-40 bar), through the overall fluid throughput in this case would likely be very low and losses may prevent any air liquefaction.

A while ago I suggested this could be done with a fridge compressor overdriven by a VFD - unless someone, of course, could get their hands on a better pump, like one of compressors from those large chest type freezers in supermarkets or a large air conditioning system.

There may of course be a bunch of other before-unseen problems... the cheap capillary valve commonly used in fridges may not work the same with helium as it does with freon, the gas may leak from the system and so on.

So this is what I am thinking of doing after doing some more reading:

I can take N2 from a tank and pump it through a long conical coil going to the compressor. This simplifies things by eliminating the water vapor and containments that could clog the system. The output of the compressor is wound around the input coil to create a counter-current exchanger. The output goes to an insulated container to collect the gas.

This seems too simple to think that others have not done it here. Any thoughts? Am I missing something?

Hmm, since this does not exactly make sense with the laws of thermodynamics, I presume you left out some sort of an heat sink somewhere? It may help if you drew up a diagram of some sort... I guess the idea may work to some extent, providing that you waste a large portion of nitrogen for cooling and release it into air (though I still suspect a simple water cooled coil would be superior).

Marko

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