What would it take to build a cryogenic cooler?

[Shingoshi]

This was an answer to the questions listed below. But my response will show the direction I'm taking in the planning of this project. So it really needs to be here as well.

1,2)This is kind of andvanced stuff but anyway. You don't look for a refridgerant that does not condense in room temperature. You can do this with every rifridgerant. You just "get rid of" the gas superheating (cooling the gas, so it gets closer to condensing temperature at the spesific pressure).

3) Usually the first compressor (that sucks superheated gas from the evaporator) is close to 3 times larger than the sencond compressor. This is due to the lower spesific volume on the gass after the intercooler.

4) The difference between cascade and traditional two-stage system is that you just have one refridgerant in a two stage system. (The same refridgerant runs through the entire system). In a cascade you can have the same refridgerant, but they run in a independent loop that heat exchange (The 1st. stage is condensing against the 2. stage evaporator).

5) You chose refridgerant based on the pressure and temperature you want the system to have. Things like oil blend capability, and oil types is also a factor. The critical pressure/temp (the maximum pressure that a refridgerant can have in order to condens/evaporate) is a major factor.

6) Nitrogen has an extremely low critical point. (34bar/-147c) But this is not what you want to consentrate on.

Hope this helps!

1+2.) Let's concentrate on R-744 as my baseline for this discussion. I need to look at how much pressure I need to get the condensation point low enough to work with. I need to take the time to convert bar to psi to see what I'm working with here. My main concern is that I don't want too much pressure inside my gas coolers. Specifically because they weren't designed for this (They're actually very large 32"x12"x3" Turbocharger Intercoolers). So I don't want the pressure inside of them to be higher than say 200psi. I want to use my smaller compressors to bump the pressure up from there.

3.) My two compressor sizes are 19.6cc and 7.75cc respectively for the Matsushi+a (York) and Rechi. That's about a 2.5x difference between them.

4.) I have a total of six compressors. Two York and four Rechi. See my link I posted above to see them together. I want to use the two York (Panasonic/Matsu) compressors in tandem/parallel for my first stage. I simply want to use them to provide for the system's volume/load capacity. I then want to divide the four Rechi compressors into two separate tandem/parallel groups. The first tandem group will be used to bump the pressure of the refrigerant up coming from the gas coolers. The second tandem group will be used to subcool the refrigerant leaving the first group, passing the heat back to the outbound refrigerant.

So there will be two completely separate refrigerant loops in the system. The first loop will have the combination of both the York and Rechi compressors. This loop will likely have R-744 as the main refrigerant. The Yorks will be (first-stage) before the gas cooler, and the Rechis will be (second-stage) after the gas cooler. The second independent loop will have only the last two Rechi compressors to provide the subcooling. The subcooling loop will likely have R-600a as the refrigerant. The two loops (main flow and subcooling) will run in counterflow. The inside subcooling Rechi loop is moving refrigerant in the opposite direction against the main incoming refrigerant loop. Instead of the subcooling loop having it's own condenser, it will use a heat-exchanger to cool the subcooling refrigerant with the refrigerant coming from the evaporator of the main loop. This will also be done with the two Rechi compressors in the second stage.

I'll leave 4+5 alone for now.

Thanks for your time!
Shingoshi