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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I did leave out the heat sink that would cool the compressed gas, so it was colder during expansion. Linde compressed his gas to 3000 psi. I have not looked at thermodynamics for some time, but I came across these equations:
Using air with a gamma of 1.4, am I correct that going from 200 atm to 1 atm should drop the temperature as such:
T2/T1 = (1/200)^(0.286) T2/T1 = 0.22
T2 = (298K)(0.22) T2 = 65K
So, it seems that a compressor that gives me 200 atm (3000 psi) should be able to do it as long as I can get rid of enough of the heat from the compressed gas. Does this seem reasonable?
What you were describing, Marko, with the Stirling engine using helium is how the Cryocooler systems work. I've seen some for sale, but they are over $1000.
Registered Member #2939
Joined: Fri Jun 25 2010, 04:25AM
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Posts: 615
The wikipedia article on the Joule-Thompson effect has some good information. You don't have to go to 200bar to get this to work, but lower pressures will be less effective. One thing I have read (can't recall where) is that the counter-current heat exchanger needs to be as efficient as possible i.e. long and well insulated.
Using a piston for expansion is even more effective as this removes energy from the gas, which can be mechanically returned to the compressor. Getting a piston seal to work at LN2 temps could be interesting.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Do large industrial gas suppliers use ultra high speed turbines to lower the atmospheric temp effciently for high volume operation? It seems like that what was on TV somewhere...
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
2Spoons wrote ...
Using a piston for expansion is even more effective as this removes energy from the gas, which can be mechanically returned to the compressor. Getting a piston seal to work at LN2 temps could be interesting.
I've read about all of this. I don't plan on fabricating my own compressor, so I doubt I will be able to get the expanding gas to do any work. I will probably be stuck with a standard expansion valve. I need to find a compressor that goes close to 200 bar and is oil-free so it does not freeze at the low temperatures. Anyone have suggestions where I can get one?
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
Yup. I've been searching the internet and have seen paint-ball and scuba compressors and they are expensive. I saw something in california that is "for parts" that is cheap, but the shipping would be huge. I'm going to have to wait until something appears closer to me.
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Condesation/Fractional distillation of air
