Sunday, January 15, 2012

CryoBUG charge tuning

For the time being I'm pretty happy with CryoBUG's hardware configuration, but I know there is more tweaking left to do with the refrigerant charge.

So with that in mind, today I ran a test with reduced R-23 and increased R-14 to get a better feel for what is really needed.

New Refrigerant Charge:
R-134a  125 Grams
R-23        40 Grams
R-14        55 Grams
Argon       8 Grams (+/- 1 Gram due to inaccuracy of the scale at these low readings)

B.P. = 250 psig

Here's a chart showing all the recorded temperature points during this test run.

Chart of CryoBUG 1/15/2012 Test Results

Notice the warm-up about 10 minutes into the run of what I call CC SUCT (Cascade Condenser Suction), and then it's turn-around about 20 minutes later. It has also been rather surprising how warm my Phase Separator operates with this new design, something that was quite unexpected, but seems to be a characteristic of this system. And although the BUG was still ramping down and getting colder, I decided to shut it down at 2 hours into the run. BTW for a better explanation of the plotted temperature points please refer to the following diagram.

CryoBUG Thermocouple Location & Identification Diagram

At the 2 hour mark I was seeing compressor pressures of 14/207 psig, and a compressor current draw of 2.58 amps. Evap-In was at -140°C and the Evap-Out was just a bit warmer at -138°C (apparently a flooded evaporator). Most likely these temps would have come down another 4-5 degrees in the next hour, but I'd seen all I needed to at this point and made the decision to terminate the test run.

So what are my feelings about the results of this enriched R-14 charge? Well as I kinda suspected, but wanted to confirm, additional R-14 is not beneficial to my goal of creating a stable -150°C unit. In fact it was most likely hampering me from seeing a lower evaporator temperature then what I did today. However the lesser amount of R-23 in my opinion did help out, and this I believe was reflected in much more stable pressures and temperatures this go around.

I think my next test will be to reduce the R-14, while leaving all the other refrigerants in the same proportions.


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