And I got to thinking that we still have some hot water systems around which would make a good container for the regenerative cooler. With a chest freezer and some bits and bobs this is pretty achievable. I think the only really difficult part is the hardcore compressor, they seem to be 1.5-4k on gumtree.
At the bottom of the instructable he also talks about a 2 stage pressure swing absorber which produces pure n2 gas, which would be quite a handy resource to have in general even before liquefaction.
So, who likes this idea? If I can get some co conspirators I’m happy to look into it seriously
2.7Mpa or 391psi 27atmospheres max pressure. For a cheap (oil free) compressor that isn’t too bad. I’m not sure what minimum pressure is needed for the system to work…
and after actually looking we have the answer “This is the most expensive component. I used a RIX oil-free SA-3E. This delivers 3 SCFM @ 3500psi (230 ATM). I modified the motor and pulleys to deliver 4 SCFM. A higher flow gives you a faster cool-down and production rate. The high pressure allows you to have a larger temperature drop when you throttle the gas to a lower pressure. You can use a regular refrigerator compressor, but you will be waiting a long time to drop 400 degrees Fahrenheit from the ambient temperature to -320F if you only have 40 ATM of pressure.
My compressor allows me to get to -320F in 45 minutes. I am guessing that a standard compressor at 40 ATM will take 6 times longer, or 4 1/2 hours. Of course, if the flow rate is less then you have to add more time.”
So these little fridge compressors will take 7 hours to get to -320F. A few of them in parallel might improve the flow rate therefore increase cooling and production rate to something comparable for a fraction of the cost. what do you think @devians
@Hally, those compressors aren’t oil free, the compressor sits in the oil for lubrication. However with an oil seperator on the output I can’t imagine it being too hard to get around that anyway. I’ve got a compressor from a small portable airconditioner that may have a decent flow?
Tesla500 on Youtube started making an air liquefier however he hasn’t been at it for some time. Someone mentioned in the comments on the video, that the lower pressure gives a lower temperature differential hence the heat exchanger has to be more efficient or larger to achieve the same result.
If anyone was eager to get machining, some stages in the high pressure compressors available just use a lubricated rod in a very tight bore, like the Shoebox compressor. Something like that could also be doable to bring the high side pressure up a bit.
@Hally, I think we could definitely pair some together to up a flow. Do you have prices for the ones you linked?
I’m not really sure what the more important factor is, the psi or the flow rate. IE could you get similar results with a one tenth the pressure but ten times the flow rate?
I did have a look at the shoebox style high pressure setups, but I discounted them because their output flow rate is really really small?
@Thermoelectric do you know what the numbers are on your air conditioner compressor?
The original plans (http://homemadeliquidnitrogen.com/compressor.html) for the design give a formula for temperature drop, with it solely relying on pressure. With refrigeration compressors we’ll still only get maybe a 10C drop, but will have more chilled gas. If the heat exchanger is efficient enough it should work if we had the volume.
The reason I mentioned the Shoebox is as that’s a pretty similar concept to how SCUBA compressors get their high pressure. For our purposes it is small however something could be made with either a higher speed or bigger piston to boost the pressure, giving a better final temp drop.
The compressor I’ve got is just a little thing, not sure on volume, would be similar pressure to the fridge compressors. Thinking it’s about 0.65 horsepower. The fridge compressors are maybe 0.1-0.2HP.
To make liquid nitrogen, you primarily need pressure ( to squeeze the gas
into a liquid ), but in an open-loop system there are evaporation losses
due to environmental heat absorbtion, and the volume that evaporates is
substantial… so you’ll also need a relatively large volume to overcome
these losses, or you end up not reaching “critical” … the point at which
the volume of liquid produced exceeds the losses in the system.
