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Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hi everyone
Recently I've ran into some very interesting articles describing cryocoolers that could be constructed out of readily available air conditioner parts and yet provide lowtemperatures approaching those required for air liquefaction, and I thought it may be interesting for some of you:
I was interested in possibility of using these for cooling power mosfets, but there seems to exist a possibility that they could be used for production of liquid air as well. The standard mixture of gases used seems to be nitrogen, methane and ethane. The system uses a recuperating heat exchanger which generally seems to be built into the main cryostat along with most other elements, apart the compressor and aftercooler.
1. While it may be fairly easy for most people here to get methane and nitrogen, but bottled pure ethane would be fairly exotic, apart from some likely expensive scientific supply. Would any other gas make a good supstitute? One could combine natural gas and nitrogen, for example. Propane/butane is also sometimes added to the mixture, though those generally have fairly high boiling points.
2. Is it possible to adapt a system like this for air liquefaction, even though it uses nitrogen in the loop? Would increased pressure help gain lower temperatures? Or perhaps adding some extra gas with low J/T cooling transition temperature (Hydrogen??)
3. Is it necessary to have a valve regulator, compared to a simple capillary tube, and what would be it's disadvantages?
4. I'd like to learn some basic theory regarding the choice of gases and their ratios, based on their Joule thompson coefficient curves and boiling points?
Registered Member #3272
Joined: Mon Oct 04 2010, 11:40PM
Location: Beaverton, OR
Posts: 101
A friend and I picked up a couple helium compressors for cryo pumps to give this a try... someday... CTI makes a more generic cold head in place of the cryopumps the compressors usually are hooked to.
But, really, LN2 is quite cheap, I picked up 50 liters this last summer for $80. With a good dewar that will last quite a while. My guess one of those chillers would create LN2 at a significantly higher price than getting it commercially.
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Mixed Gas Joule-Thomson Cryocoolers
