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Liquid nitrogen generator, N2 gas generator

  1. Jun 3, 2014 #1
    I thought some of you engineers would be interested in reading my web tutorials. I have written some extensive tutorials on the theory and building of a homemade N2 gas generator. It takes regular air, and using pressure swing adsorption, concentrates the N2 up to 99%. This is here.

    I then use this to supply the N2 for my homemade liquid nitrogen generator. I can liquefy N2 in my garage without any fancy, high-tech equipment. This tutorial is here.

    What I'd really like to do is fabricate a small turbo expander, but I think I would need a CNC to do it correctly. Anyway, my generator produces about 300-350 cc/hr of LN2.
  2. jcsd
  3. Jun 5, 2014 #2


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    Impressive! Wish I was as good with lathes & stuff.

    How do you get it below the JT Inversion Temp. the very first time? When you've no LN2 to cool the gas against?
  4. Jun 5, 2014 #3
    The inversion temperature for N2 and O2 is well above room temperature unlike Helium. I would love to make a turbo expander if anyone has some useful information or references.
  5. Jun 5, 2014 #4


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    Ah. So you could liquify any gases except those two I guess.
  6. Jun 5, 2014 #5


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    Industrial turbo expanders are intricate & carefully designed, but for a home brew I wonder if a piston like engine would work?

    Essentially you want to take out work, somehow?
  7. Dec 10, 2014 #6
    This is a really interesting project. Congratulations on your success.

    It would be impractical for me to attempt this at the moment but it is definitely going on my list of projects to attempt in the future. For now I will limit myself to the theory.

    That compressor is a beast. The temperature change appears to be linear with respect to the pressure drop so I wonder whether a higher volume flow rate at lower pressure would also work. If the mass flow rate is kept constant could the pressure be reduced?

    I'm not sure how that would alter the efficiency of the heat exchanger.

    How much ice does it consume?

    p.s. While reading through your tutorial I noticed that you sometimes switch between units while the values remain the same. For example on http://homemadeliquidnitrogen.com/ you talk about a 1/4 degree Fahrenheit temperature drop for each atmosphere of pressure drop. However, on http://homemadeliquidnitrogen.com/compressor.html this becomes a 0.25C temperature drop.
  8. Dec 11, 2014 #7


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    If AHS wasn't covering my oxygen generators, I'd be actively seeking you out right now. The portable unit cost over $5,000. It's exactly the same as your machine in principle, except it spits the nitrogen out and releases the remainder (98+% oxygen) into my nose. Top speed is 3 litres/minute on constant flow or up to 6L/m on pulse (demand regulator). The plug-in home unit is constant only and goes up to 10.
  9. Dec 12, 2014 #8
    I'm glad you all find this interesting. This took a lot of research and work. Figuring out the baffle section was also trial and error, and some consultation with an engineer at Air Products. I fixed the 1/4 F / 1/4 C typo. I believe it is 1/4 C all around. I am sure a lower pressure with a higher mass flow rate will work. One just has to make sure more heat leaves the system than seeps back into it. If I was running experiments for a mass-marketed product I would a high-flow rate compressor running at a few hundred psi. I am guessing that if you don't have really high flows the gradient will be too low, and you will have a very, very long cool-down.

    The unit consumes almost no ice. The ice-bath takes some of the heat out. A lot of heat comes out on the compressor-side when the coils get cooled by a fan.

    If anyone is interested, I built a highly accurate cryogenic thermometer for this stuff. It is accurate to tenths of a degree (F and C). You can see it at http://homemadeliquidnitrogen.com/crybaby.

    Maybe some of you can use it for your experiments.
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