Thursday, January 23, 2014

CryoSPRITE is about to be born

Because of the success I've had with the CryoBUG platform, and seeing a need for something even smaller, I've begun work on a new development unit code named CryoSPRITE. Currently the rough dimensions for this unit look to be a 7" x 7" footprint x 12" tall. It is hoped that it'll be able to do a solid -140°C at 20 watts of heat load, and be light enough to easily carry around by one person. The application is the same as CryoBUG, doing water vapor cryopumping for small vacuum systems, or imaging detector cooling. But the idea behind this project is to make it a better fit for very tight spaces, which will help in many existing applications.

Aspen Original Series Compressor
(Shown with its DC Controller)
The first order of business was to find an extremely small compressor. And that was done thanks to Aspen Compressor, utilizing one of their Q-Series Rotaries. The new Q-Series takes the place of their original compressor line (shown in the image on the left). And because this compressor series is so new, they didn't have one available for shipment until the end of this month. So now here I am anxiously awaiting its arrival, like a kid waiting for Christmas to finally get here. Link to: Q-Series Compressor Dimensional Drawing
Photo Courtesy "Honey I Shrunk The Kids" © Disney Studios

The next thing on my list, was a very tiny air cooled condenser to go with the small compressor I had ordered. This was not something I could readily find for sale off the shelf, or at least not in a quantity one buy. So I needed to take something larger and shrink it down to size.

Now unfortunately I don't have access to a Shrink Ray Gun, other wise this would have been the perfect solution, and a done deal. In fact this would have solved everything by simply placing my existing CryoBUG unit under the ray, and reducing it down to just under 1/2 its original size. Hmmm... I wonder if I could rent one of these?

Custom Air Cooled Condenser with Fan
Anyway I had to do it the hard way and chop up a bigger air cooled condenser (actually it was a left over window AC evaporator from one of my earlier projects).  Although it was a bit of a challenge, I was able to fabricate a fairly decent miniature condenser, that was just slightly larger then the 120 mm muffin fan that I would use to cool it.

With the fan and the compressor both running off of 24 VDC, and combining this with a switching power supply having a wide voltage range, a more universal power input should now be possible (90-250 VAC 50/60 Hz).

CryoSPRITE Prototype HX Stack
Continuing to go down the list of parts needed for my miniature chiller, the next item was a autocascade Heat Exchanger (HX) stack. And as you probably guessed, this also needed to be much smaller then anything I've ever built before (still no Shrink Ray Gun in sight). So I had to design and build something from scratch that was of an appropriate size to match up with the Aspen compressor's throughput.

This actually was easier for me to do then modifying the air cooled condenser. Which had involved some very tricky bending of the copper tubing return loops.

What's left?

I'll be fabricating a small combination evaporator/heater assembly to run heat load tests. And of course I'll need to put all these pieces together, leak check, charge refrigerants, and then power it all up for the first time.

Stay tuned for more to come.


Roland van Hall said...

Hello Michael, with interest I've been reading your article about the Cryosprite. I'm using a two stage compressor system I've built myself to generate -85C which I use to measure physical properties of diesel.

Your system however is very small and I like the principle it is based upon. The relative low pressures make it more reliable. Best thing I like is the energy efficiency though!

I would like to built a similar system for testing, however I can not trace the length of the capilaries captube #1 and #2. Can you tell us what capilary size you're using and the length of each?

Anonymous said...

Ronald use the Contact Me button at the bottom of the page, and I'll respond to your question via email.


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