Instructables

Homemade Liquid Nitrogen Generator using Joule Thomson Effect

video Homemade Liquid Nitrogen Generator using Joule Thomson Effect
Step by step guide to building your own liquid nitrogen generator. Using easily obtained materials you can liquefy nitrogen or air. The unit cools  to -320F in under 50 minutes. Production is about 350 cc/hr. A full tutorial and plans are at http://homemadeliquidnitrogen.com

If you like the extreme cold, you might like the extreme hot. Here is a video of an induction heater
http://www.youtube.com/watch?v=Q6Zrnv4OtbU
You can view a complete tutorial on building one at http://inductionheatertutorial.com
en2oh7 months ago
What do you think about design? These turbines are pretty simple. Air under pressure at right angles to the turbine axis of rotation. Would there be much to be gained by actually giving the turbine "work" to do ie coupling a second turbine to the driven blades to act as a simple compressor for return flow vs just having the jet of gas spin the single turbine itself without a specific useful load.

By the way, although you have a very high pressure gas with up to 4 SCFM air flow, what volume through put do you really get through the throttle? It can't be anywhere near 4 CFM, right? What is the throttle diameter? Is it a capillary tube of X length and Y ID or is it a dimple pinch off of the high pressure line? I'd really be interested in the actual measured flow at the JT throttle.
imsmooth (author) 7 months ago

Turbulence is good

Teflon was expensive even when bought from china

Copper refrigerator tubing is a better conductor

You need good insulation to prevent heat loss through your stainless steel tubing

Also this. Will increase the cooling time because of the higher heat capacity of the metal. You could also use an outer copper tube which is easier to bend

1/2 will give you little room and the outflow resistance will be too high

You also need space for your fittings. Use bigger diameter

You need to think through how you will bend and creat a coaxial helix

Let me know how you plan to do that

en2oh imsmooth7 months ago

I could go to 3/4" on the corrugated stainless. As far as bending the corrugated pipe, that will be easy. It's designed to coil. The copper will be bent with a harbor freight planetary bending tool. It would be nice to orient it coaxially, but I don't think that will matter too much. I'd like to find 24" Sono Tube, but that is tricky around here. I might look at a plastic system to cover the SS vacuum flask. Your bottom siphon arrangement to remove the LN2 is likely pressure driven. That's how we would transfer from our 30l dewars to out working vessels.

I don't think it will be possible for me to get a 200BAR compressor, but I might try a 10-20BAR compressor with 10+SCFM Volume.

imsmooth (author)  en2oh7 months ago
Sounds good
If you build it I would like to include the cool down data for comparison
en2oh imsmooth7 months ago

have you looked at make shift turbo expanders as a means to improve efficiency? Would putting a dental turbine cartridge (<$20 on ebay for ceramic bearing version rated at more than 100,000 RPM) at the JT throttle add to the workload of the expanding gas?

imsmooth (author)  en2oh7 months ago

I've definitely thought about turbo expanders, but I don't have a CNC to make my own and I did not know where to get a small one cheap enough. If you found one that cheap it is worth a try as long as it can withstand the pressure. Turbo expanders are way more efficient.

I see the turbine cartridges on Ebay. Did you see a housing for them? It would not be hard for me to test one and measure the temperature drop.

en2oh7 months ago

check out the Kleemenko mixed gas refrigerant cycle. It's a variation n the JT cycle but recently has been applied to desktop liquid nitrogen production.

The patent is by a guy named William A Little from Stanford Univeristy.

imsmooth (author)  en2oh7 months ago
I've heard about it and know someone who said he
Was going to try it

I didn't feel like dealing with refrigerants
en2oh7 months ago

here is a link to the corrugated stainless steel.

http://t.homedepot.com/p/HOME-FLEX-1-2-in-x-25-ft-CSST-Corrugated-Stainless-Steel-Tubing-11-00525/203073939/

en2oh7 months ago

I'm looking at sourcing items for this. I think I'll use corrugated stainless steel 1/2" for the counter current tube. $40 for 25'. $125 for 75'. I suspect that's cheaper than the teflon you used and being corrugated, will create lots of turbulence in the assembly. Since the pressures will be lower, I'm looking at 1/4" copper coil for the working pressure line. Conduction will be better than SS.

Thoughts?

en2oh7 months ago

very nice project. What is the minimum high pressure gas volume required to make this practical? It looks like you've based this on 4 SCFM AT 2500psi + but what lower limit in terms of compressor capacity would be practical?

en2oh en2oh7 months ago

yes, it's a balance. I'd love to build one. I've been thinking about a Stirling Cooler but this could be a more efficient means of producing volume. I wonder if the regenerative coil was pre charged (ie put some liquid nitrogen into the collection reservoir to start), if this might speed things along considerably. Have you tried this?

imsmooth (author)  en2oh7 months ago
Yes I've tried it because I made a pressure swing adsorber
It does nothing for speed
en2oh imsmooth7 months ago

I'm not sure how the PSA relates to my question. I would think that if the system is precooled to near liquid N2 temperatures, production would have to start more quickly. By precooling, I mean the receiver AND the counter current coil.

I've also thought about using a closed pump system, with helium as the working fluid. For an expansion chamber, I thought I'd use a copper dome sitting on top of a Dewar flask. I would hope that the expanding helium gas would result in liquification of gasses on the other side of the copper dome.

Any thoughts?

imsmooth (author)  en2oh7 months ago

I misread your question. I thought you were talking about N2, not liquid nitrogen. Yes, precooling would reduce the time. Once cooled, you are only limited by the flow rate. Getting the LN2 into the reservoir may be a little tricky because it is sealed in the insulated tower. You would have to pipe it backwards through the drain tubing.

I thought about a closed system. Remember that helium has a low inversion temperature (-222C), so in order to get cooling from JT expansion you have to be below it. N2 and O2 's inversion temperatures are well above ambient temperature. Stirling coolers don't use JT expansion; they derive the temperature drop from the expanding gas doing work on a piston.

Have you read my tutorial at http://homemadeliquidnitrogen.com ?

en2oh imsmooth7 months ago

yes I did. I was a physical chemist many, many years ago. Thermodynamics was our bread and butter but years in medicine have dulled the sharp edge, considerably :)

You might be interested in this paper. https://tu-dresden.de/die_tu_dresden/fakultaeten/f...

It actually examines the role of formal precooling in terms of efficiency. It also points out the difference between condensing mixed gases vs solitary gases. Very interesting.

I wish I could justify a 3K psi compressor. I wonder if I could rent ;)

imsmooth (author) 7 months ago

I have not tried lower pressures. The reason is that you get a temperature drop of about 1/4 degree Centigrade for every atmosphere of pressure. 200 atmospheres gives you a gradient of 50C driving the temperature down, which reduces the time for cool-down. In my case, the cool-down time to -320F is about 45 minutes. There is no reason you can't use a much lower pressure. You can use 20-30 atmospheres from a standard compressor, but you will have to wait much longer to get to the desired temperature. You can reduce the time by using a much smaller reservoir and/or a higher flow rate. I used 1 liter. If you use 750 ml you will reduce the time by a factor of 0.75.

en2oh imsmooth7 months ago

I don't think my question was clear. At what VOLUME of gas flow, in cubic feet per minute, does this ffect operate over? It clearly works at 3500PSI @4 SCFM, but what about .5 SCFM OR 0.05 SCFM.

imsmooth (author)  en2oh7 months ago

Are you thinking about making a generator?

imsmooth (author)  en2oh7 months ago

The flow rate will contribute to the cool-down time. Higher flow rates result in faster cool-down until an upper limit is reached. Higher flow rates are also directly linked to the production rate. So, you can use a lower flow rate but you will have to wait longer to reach -320F and you will have to wait longer for collecting the liquified product.

SpectrHz10 months ago

This is an excellent guide you have there, very concise and explains things well. I definitely know what my next project is going to be! Thank you very much for your posting :)

chernani10 months ago
you boss
FrankenPC10 months ago

Brilliant. All made to scare the cat. Your job is done here :D

Question, can you use liquid nitrogen in the pre-cooler to greatly increase the efficiency? Maybe use ice water to make the first batch, then dump the water and use your own captured liquid nitrogen to accelerate the process?

imsmooth (author)  FrankenPC10 months ago

Not necessary. Once the tower coils are cooled enough, you don't even need the ice bath. I suspect that it will take more LN2 to cool the pre-cooler than what you will make from it.

LeZombieHunter10 months ago
Time to execute my plans for world domination O_o