Thursday, July 26, 2012

CryoBUG Accelerated Cool-Down (Turbo Charged)

Well it isn't actually Turbo Charged, but what I did is revert back to a higher flow in the final cap tube, and got a pretty phenomenal speedup in the cooling rate. Of course there was a small compromise, and that was a slight sacrifice in ultimate temperature, as well as a bit more work for the compressor (still quite comfortable for a R-410a compressor).

In my last test I was able to achieve a stable -156°C, but it took nearly 2-1/2 hours to get there (not exactly a speed demon). Anyway after going back over my notes on previous tests, I saw a rapid cool down in a test I blogged about on April 4th 2012. In this test I achieved nearly the same temperature, but in only 1-1/2 hours. The problem was that soon after it achieved this very cold evaporator temperature, it started to warm up. This was due to the R-600 (N-Butane) freezing in the final cap tube. At the time I only suspected this as a possible reason behind the warm up, and now I know this with absolute certainty.

So what was different? The final cap tube was much shorter, giving more flow to the evaporator. So yesterday I modified the cap tubes, making them both shorter, CT#1 only slightly, and CT#2 less than half the original length. I also added a bit more Argon to make up for what I knew would be a higher suction pressure, and thus a warmer evaporating environment (the extra Argon decreases the boiling point). And of course I was once again using R-600a (Iso-Butane) to avoid the freezing problem.

So here is a look at how the unit tested in this new configuration...
CryoBUG 7/25/2012 Test Chart
Note: If you forgot what the TC locations were, refer to this diagram: CryoBUG V5 Piping & TC Locations

Final compressor running pressures were 38/227 psig, and the Evap-In was -153°C, with an Evap-Out of -151.5°C. As can be seen, the cool down time was amazing! Hitting -100°C in about 19 minutes, and -150°C in barely over 50 minutes. This is nearly 3 times faster than the 7/24/2012 test run, and even faster than the April test using shorter cap tubes with R-600. Basically a "Guinness Book of World Records" moment for such a small AutoC.

All I can add at the moment, is that I am extremely happy with the progress I'm seeing in this prototype unit.


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