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Friday, December 2, 2011

CryoBUG starts a new life...

It's been about a year (maybe more) since I worked on this project. And I had almost resigned myself to leaving this path unfinished. But with Winter approaching and my pond project nearing completion, I found myself having a renewed interest in making this mini AutoC a reality. So with that in mind, here are some pics of my newest Heat Exchanger (HX) Stack design...

5200 Btu/Hr Rotary Compressor and CryoBUG HXC Stack
HXC Stack (Bottom View)

This new design is based upon the work of Andrija Fuderer which was patented in the later part of 1965 (Patent #3203194). His approach was extremely simple as compared to ultra low temperature autocascade refrigeration systems in use today. However over the years I've really begun to embrace the idea of "simpler is better". And unlike Fuderer's time, I can take full advantage of technology that did not exist in 1965. Thus making this simple design into something more reliable and that can realistically work without the inherent oil freeze-up problems that could have plagued his system.

HXC Stack (Top View)
So as can be seen when looking into the inside of the HX stack, a coalescing oil separator is being used as the refrigerant phase separator. It will also still serve it's original function, that being to separate oil from the refrigerant stream, and then return it back to the compressor. However unlike the normal position, that being inline with the hot discharge gases leaving the compressor, this one will be seeing much colder temperatures (-35°C).

The oil I'll be using has a pour point of -46°C, but due to the influence of the refrigerants that it'll be mixed with, the actual temperature should be lower.

The small coil on top is a dummy evaporator, being made from about 6 feet of 1/4" OD copper tubing. It's mass is probably fairly close to the cold head I eventually want to chill, so it'll be a good first test to see what happens. My target temperature is -150°C, and I plan to do this with an all HFC refrigerant charge plus a little Argon.

Stay tuned for more info as the project continues...

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