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Thread: r12 walk in

  1. #92
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    Quote Originally Posted by ICanHas View Post
    Does it work like a common two phase cycle or more like a closed loop air liquefication plant that uses sequential comression/expansion gas cooling to liquefy? What's the overall COP like at -150C?
    The overall COP... I haven't the slightest. I wouldn't expect it to be good. 3 horse scroll to cool 5 cubic feet with something like 80% "on time". The rest... tbh I don't have the vocabulary to answer that question. I turn wrenches

    Think about it like this: 5 different gases all mixed, all go through one air cooled condenser. liquid drops out but not everything condenses. in the receiver you take liquid from the bottom and use it to cool a heat exchanger (cascade condenser). the vapor from the top of that first receiver goes through the other side of the cascade condenser, more gas is condensed, there's another receiver, followed by another cascade condenser, and on and on until what's left is partially condensed (saturated vapor maybe) R-740 (argon). That goes through the last capillary tube and cools the wall of the cabinet. Follow the suction line back to the compressor and you have argon, then it picks up the refrigerant from that last heat exchanger, then the next, and so on, until when it gets back to the compressor inlet it's once again a mixture of 5 different gases.

    They're touchy bastards, but they can be fun at times...

  2. #93
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    Quote Originally Posted by cmclifton View Post
    The overall COP... I haven't the slightest. I wouldn't expect it to be good. 3 horse scroll to cool 5 cubic feet with something like 80% "on time". The rest... tbh I don't have the vocabulary to answer that question. I turn wrenches

    Think about it like this: 5 different gases all mixed, all go through one air cooled condenser. liquid drops out but not everything condenses. in the receiver you take liquid from the bottom and use it to cool a heat exchanger (cascade condenser). the vapor from the top of that first receiver goes through the other side of the cascade condenser, more gas is condensed, there's another receiver, followed by another cascade condenser, and on and on until what's left is partially condensed (saturated vapor maybe) R-740 (argon). That goes through the last capillary tube and cools the wall of the cabinet. Follow the suction line back to the compressor and you have argon, then it picks up the refrigerant from that last heat exchanger, then the next, and so on, until when it gets back to the compressor inlet it's once again a mixture of 5 different gases.

    They're touchy bastards, but they can be fun at times...
    How do you avoid oil logging or keep any from getting into -150C portion? I can't think of oil that will stay thin at that temperature. Are the heat exchangers layered so you sort of have -150C portion encased in prior evaporator so you essentially have a -150C box within a -86C box? I kind of want a ULT box to take apart

  3. #94
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    Quote Originally Posted by ICanHas View Post
    How do you avoid oil logging or keep any from getting into -150C portion? I can't think of oil that will stay thin at that temperature. Are the heat exchangers layered so you sort of have -150C portion encased in prior evaporator so you essentially have a -150C box within a -86C box? I kind of want a ULT box to take apart
    Coalescing oil separators, and just the simple fact that there's no oil left in the stream by the time you get past the last receiver and heat exchanger. The argon doesn't carry the oil the way the other refrigerants do, so by the time you get to the end, all the oil has dropped out with the liquid refrigerants, which will then act as solvents in the suction line with that super cold argon keeping them liquified until you get further down stream and things start warming up again...

    edit: sorry I totally missed the second half of that question. They're not layered like that. The various capillary tubes and little receivers are all hidden away inside the walls, foamed in place where you can never get to them... The cabinet itself isn't much different from a typical -86 cabinet.
    Last edited by cmclifton; 06-20-2014 at 01:01 AM.

  4. #95
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    Quote Originally Posted by cmclifton View Post
    that argon does get somewhat condensed.
    That's probably why they use argon instead of something like nitrogen. It is there to keep the pressures up, and if they can get a bit of work out of it, then that would be a bonus !

    If there was another gas that would give them more cooling, like neon or whatever, I'm sure they would have chosen that.

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