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Saturday, October 20, 2012

CryoBUG in Standby

It's been a little while since my last post, so I thought it would be good to bring people up to date on what has been happening.
 
I charged the new demo unit with what I thought was the same charge as used in the breadboard prototype. But after doing a test run, I realized that there was something very wrong. Apparently my method of weighing in the various refrigerants was just not producing repeatable results. A lot of this can be blamed on the influence of the hose attachment between the refrigerant cylinders and the unit. Try as I might, it is virtually impossible to keep the weight and drag of the hose from offsetting the scale readings.
 
So I'm left with adding all the high boiling gases based on pressure. And for the R600a, which is charged in as a liquid, I will need to use a self sealing fitting in order to disconnect and weigh several times during the charging process for verification.
 
I also ran out of R600a, so I am patiently waiting for some more to arrive. Had to find another source, since my eBay connection ran out, and had a 2 month back order. As it turned out my new source is even cheaper.
 
My preliminary tests suggest that my ultimate temperature will not be as cold as achieved with the breadboard. Although I am still seeing fast cool downs into the -100 C range (18-19 minutes from warm start). However with the extra mass of the cold head, and some conduction into the vacuum flange, temperatures will most likely be in the mid -140's.
 
If all goes well, I should be testing again next week.
 

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