Sunday, February 5, 2012

CryoBUG 2-stage results mixed

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Well I tried converting the unit to a 2-stage AutoC design as shown in my recent V2 piping diagram, but I can't say I was really very impressed by the test results. First off, not having an auxiliary condenser preceding the 1st phase separator, makes Cascade Condenser #1's output tend to follow the evaporation temperature of the first refrigerant only (R-134a). So in other words, there doesn't seem to be much if any of the other refrigerants mixing with the R-134a, and this yields a rather warm 2nd phase separator as a result. And without any R-134a in this 2nd separation point, plus the fact that the temperature is too warm to condense the R-23, the system kinda stalls out.

So I changed out the R-134a for R-507 in the hopes that with a lower boiling point, the 2nd phase sep would come down into a more favorable range for condensing the R-23. End result was some improvement, but not nearly enough to really get the system running optimally.

Now the logical conclusion that I came to, would be to add another heat exchanger (HX) preceding the 1st phase separator, thus giving the unit an auxiliary condenser. This approach would most likely have a very high probability of success. However I'm trying to keep this unit as simple, and as small as possible. Adding yet another HX just doesn't fit into this plan.

So I think I'll be going back to the Version 1 layout, but based on some things I saw in my V2 tests, I think I'll be upping the flow for both the phase separator and evaporator cap tubes.

New cap tubing is on order, and hopefully we'll be seeing a retest in about week. I will also be doing a complete oil change to low temperature PVE, and might play around a little bit more with using R-507 as my first refrigerant instead of the R-134a (or perhaps in combination with it).


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