Monday, January 23, 2012

CryoBUG completed tuning for V1

Version 1 of CryoBUG has now officially completed it's tuning phase experiments.

In this go around, I accomplished what I consider to be a very stable "sub -140°C" unit charge, which is one where the pressures and temperatures are stable, without making wild excursions as seen in some of the previous tests. Although -150°C is the goal for this unit, the reality of achieving this with my very simple hardware is probably not realistic. At least not in what I consider to be a stable and reliable production ready version. So with that in mind, here is the charge that seems to work well for the -140°C regime.

110 Grams R-134a
60 Grams R-23
40 Grams R-14
8 Grams Argon

BP = 235 psig

Here is the 2nd day's confirmation test run with this charge (for TC locations, reference: V1 Diagram)...

Chart of CryoBUG 1/23/2012 Test Results

Within 1 hour the evaporator was down to -131°C. And when it finally stabilized after running four and half hours,  it achieved an ultimate temperature of -143.5°C, and running pressures of 5/205 psig. Temperatures only varied by +/- 0.5° worst case, and the suction pressure variance was only +/- 0.5 psi.

The unusually low suction pressure is the result of only running with the original #1 cap tube coming off of the phase separator (I have the extra parallel cap tube that was added later capped off for this test). My gut feeling tells me the system would benefit from more flow, but not so much if the added flow is to cap tube #1 like it used to be. I think it's time to add some active feed going directly to the top of what is now the Auxiliary Condenser, thus making it into a Cascade Condenser (see proposed Version 2 system diagram below). My thoughts are that this will allow for better separation and utilization of the R-23.

So in essence what I'll be doing, is to add another Phase Separator before the original Auxiliary Condenser, and another cap tube feeding from it to the end of this HX (this HX becomes Cascade Condenser #1). I believe this will be a far more effective way to add additional cap tube flow to the system, while enhancing separation of the R-23 from the R-14, and insuring good oil return back to the compressor. This should also yield a system that is better suited for -150°C temperatures, although still retaining a simple design.

Hopefully I'll get a chance to test out this theory over the next couple of days or weeks.


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