Some Q's about using propane, butane and isobutane as refrigerants

[Brettbeck]

Hmmm I thought the R600 was used as an auxillary cooler. You basically use a large R600 charge to max out the heat-dissipation abilities of your condenser and then evaporate off the R600 in an HX with the rest of the Autocascade charge, dropping it down below room temperature. Can't imagine R600 condensing before the condenser like you say and evaporating in the 200psi atmosphere of the highside with decent temps, but I'm no professional.

R600 could be used as an auxiliary HX, but R600a would be a much better choice. YOu don't really need one in a single stage though, it wouldn't benefit the performance much if at all.

If you have say an autocascade with r600a, r290, r744 or whatever, the discharge pressure will be quite high and so will the discharge temperature, so the condenser will have to remove more heat for the r290 to condense. If you look at the PT chart for r600a;




Basicly it will condense even if not much heat is being removed (e.g 15bar @ 85c), and once that condenses it will lower the condenser temperature, making it easier to condense the first stage refrigerant (such as r290), and once it enters the phase seperator you can be sure all the r290 has condensed. And of course the better seperation the more effective your 1st HX will be .

I hope this isn't straying too far away from the subject .