Countercurrent condensation loop

[imsmooth]

I will be attempting to make liquid nitrogen from air. Part of the process involves passing air compressed to 200 atm through a coil and rapidly expanding it. The expanded air that does not form liquid from the rapid cooling will pass back over the condensor coils in a counter-current fashion to precool the compressed air. Of course, this countercurrent system will be insulated from the surroundings.

My question is this: how long should should I make the countercurrent coil for it to be effective? I know I will transfer more heat with a longer coil, but there has to be a point of diminsishing returns. There are many variables so I think this comes down to experience. Does anyone have any idea?

I am planning on something between 8-16 feet for the coil.

 

[Chestermiller]

Have you had any courses in fluid mechanics and heat transfer? You can calculated all this. See Transport Phenomena by Bird, Stewart, and Lightfoot. You might also find an engineering handbook such as the Chemical Engineer's Handbook useful. The details of the complete methodology are a little too extensive to explain here. Basically, you need to learn how to design a heat exchanger.