Monday, September 24, 2012

CryoBUG Demo Unit Assembly Completed

I've been pretty busy over the last couple of weeks taking all the individual pieces that make up a CryoBUG, and bringing it all together into a complete package. A lot of planning had to be done in process, in order to adapt the conceptualized drawings into reality. But I think in the end it all went very well, and stayed fairly close to what I had originally envisioned.

The HX Stack stayed pretty true to the original design as used in the final prototype shown here. So at least this didn't require a lot of rethinking, but it did get housed in an entirely different way (see overhead view below).

CryoBUG (Overhead View) Almost ready to be foam insulated
A full complement of thermocouples were also installed, so as to get a good comparison to the prototype test data. This may very well reveal differences brought about by the new Cold Head being used in this demo unit. And I will also be doing a full capacity curve by applying heat directly to the face of the Cold Head via an attached power resistor. So it will be nice to see how all the different stages handle the extra heat.

Since I thought many of you would be interested in seeing the expanding foam insulation being applied to the HX Stack, I have also included a video showing the entire event. Due to me being the cameraman and having to deal with the actual foaming process, sometimes the framing is less then desirable, often times cutting off my head.

Note: In this video I mention 8 minutes elapsing, in reality it was 8 seconds

After the foam insulation was completed, and all the excess was trimmed away, the next step required installation of the air cooled condenser, which resides in the upper most section of the enclosure.

HX Stack foamed, now ready for installation of condenser
Unfortunately I had a slight mishap when I drilled through the condenser's fins to allow the lift handle support post to pass through. I nicked the copper tubing causing a small leak. It didn't look bad at first, but after applying some heat and brazing rod, it kinda got a bit ugly. Luckily it all gets covered up by the top grill and handle, so it shouldn't be too noticeable.

The main problem that caused this, is that the threaded support post really needs to be reduced in diameter. At it's present size, it's just too close for comfort to fit between the two copper tubes passing on either side of it. Something I'll have to remember if I ever build another one of these again.

-- With the air cooled condenser in place and plumbed, the main assembly is done --

Next I secured the top panel, put the unit on a vaccum pump, and when it reached a pressure of 78 microns, I put in a very simple preliminary test charge made up from some reclaimed HCFC refrigerants, including Ethane (no R-14 or Argon). Basically I just wanted to confirm that everything worked. And for this go around, I wasn't shooting for anywhere near -150°C, which is the ultimate target temperature for CryoBUG.

It was nice to see the white snowy stuff appear soon after start-up. Also it looked like the liquid line bonding inside the 2" SST tubing was doing a good job of keeping water from condensing on the outside, which was the intended purpose.

Red = Cold Head Temperature, Green = Set Point Temperature for Relay Activation
With the initial test charge, the unit got down to -77°C pretty quickly, but soon after, it leveled off around -80°C. Which is about as good as it gets without any R-14 or Argon. The main thing, is that I was able to verify that all systems are a go and ready to be recharged with the real hydrocarbon juice.

The custom controller board also appeared to be working correctly, and even detected a low pressure fault soon after start-up when my initial refrigerant charge was a bit weak. This resulted in a system shutdown, followed by a red LED lighting up in the compressor symbol and the On-Off switch's LED illumination flashing red (see video below).

Here is a view of the controller board mounted behind the front panel. The long green terminal block is where all the safeties are plugged in (LPCO, HPCO, HTCO).

Controller Board glowing blue, a sign that it is active
And in case you noticed, I still need to clamp the bottom of that discharge vibration eliminator.

On the news front, my brother has been working on a new version of the test software that I use for logging multiple temperature points from thermocouples. I can hardly wait to set everything up and see how it all goes with a "real" refrigerant charge in use. It should be exciting.


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