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.

Saturday, September 8, 2012

CryoBUG Enclosure Arrived

Front Panel Express came through with flying colors. Everything looked great and was packaged very well for shipment. They offer a very complete enclosure service, including all the hardware (screws, nuts, brackets) required to complete the assembly. And by using their free software (Windows, Mac, Linux) it is relatively easy to create whatever you want.

And here it is assembled with one side panel removed (this was just a test assembly to make sure everything lined up properly). By the way that really slick looking handle on top, I got from Halder. It's made by a German company called Rohde, and boy do they know how to make a robust, yet beautiful flip-up handle.

I'll have more pictures later when I start doing the final assembly with all the refrigeration components.

In the meantime I was able to get the Cold Head welded to the mounting base, and polyurethane foam insulate the interior space. A special thanks goes out to Randy at Randy's Design & Machine for cleaning up the messy cut I made when I modified the original piece. And also to Mike from M&T Systems for doing such an excellent job on welding it all together.

I would also like to acknowledge the donation of the original unmodified Cold Head from back in 2009, although they will remain nameless since I'm not sure if they wish to be known.

It's good to have gotten to this point, because now I feel like a kid with a really cool Erector Set. You know the deluxe one with all the motors and gears. So basically I just need to bolt all the pieces together, wire it up, charge it, and press GO!

Wednesday, September 5, 2012

CryoBUG Demo Unit Design in Process

Well sometime later today I hope to receive my enclosure from Front Panel Express in Washington. I am having mixed feelings of excitement and anxiety in anticipation of seeing what I have been working on come into reality. I just hope that I didn't make any major blunders in my enclosure layout.

Here's a look at some of my virtual piping design work...
Top View of basic piping (click on image to enlarge)

In the meantime there has been good progress made on fabrication of the Cold Head assembly that will be used on this initial pre-production CryoBUG demonstration unit.

Below can be seen the connection side of the actual "Cold Head" itself. The final (evaporator) cap tube is tightly coiled around the suction return line, and although it can not be seen in this image, enters on the left side, and then continues down into the copper head below. the stainless steel tubing is the thermowell used for measuring the temperature of the copper head, through use of a thermocouple probe.

To mount the Cold Head to the CryoBug, I am using a conflat half nipple which will be welded on to the Cold Head back side pictured above. Because of concerns about possible thermal conduction from the cold feed and return connections on the inside to the outer 2" stainless steel tubing of the half nipple, a copper tube was bonded to the inside which will eventually be connected to the air cooled condenser liquid line. It is hoped that this will maintain close to ambient temperature on the 2" tubing, extending back into the conflat mounting flange, and thereby avoid condensation or ice up problems on these parts.

The Inside of space will be insulated with an expanding polyurethane foam, same as to be used for insulating the HX Stack.

Here is a shot of the complete Cold Head assembly prior to be welded together...

For future versions, I have some redesign ideas that may alleviate the thermal conduction problems, as well as simplify the overall design. This particular Cold Head that I am using was designed for a specific application by a 3rd party, and has been greatly modified to suit my purposes. The price was right (as in "free"), so I really can't complain too much.

In my next post I will be showing images of my enclosure panels when they arrive, and an initial pre-fitting to render the complete enclosure.