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Thread: Liquid CO2

  1. #1
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    Liquid CO2



    Okay, I went to the gas distibutor and refilled my CO2 bottle. Now I'm going to build a block to run CO2 through, and see if I can get the -78F.



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    First it went great.. I had a minus78F to a minus 80F block (evaporator)... but then the ice (dry ice) started to build up in the evaporator, and as the evap pressure rose, so did the temp

    I tried restricting the outlet to reduce the formation of the ice (increase evap press.), but as I did so, the realized temperature increased also... at least I tried it

    Maybe I need a CO2 TEV

    Nice idea.... poor results.... I'll get some nitrogen, next.

    PS: Now I'm driving the overclockers crazy.
    Last edited by herefishy; 25-06-2003 at 01:16 AM.

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    Maybe I need a CO2 TEV
    It just may happen some day... Perhaps fortunately for us valve manufacturers, there aren't too many engineers excited about designing trans-critical refrigeration systems.
    Prof Sporlan

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    BTW, triple point for CO2, according to the ASHRAE Fundamentals Handbook, is -69.8F (60.4 psig). You'll have to keep your evap pressure/temperature above this point to prevent dry ice formation...
    Prof Sporlan

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    Liquid nitrogen would really open up things up to low temp refrigeration... Its triple point is -346F (1.82 psia) according to the ASHRAE Fundamentals Handbook.

    If you're really going to get serious, try liquid helium. -455.75F (0.704 psia) triple point. This ought to turn an Intel 8088 into a Cray computer...
    Last edited by Prof Sporlan; 25-06-2003 at 03:50 AM.
    Prof Sporlan

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    Cray computer LOL

  7. #7
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    Originally posted by Prof Sporlan
    BTW, triple point for CO2, according to the ASHRAE Fundamentals Handbook, is -69.8F (60.4 psig). You'll have to keep your evap pressure/temperature above this point to prevent dry ice formation...

    Hmmmmm, perhaps an EPR?

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    Simple CO2 phase diagram

    I am also tinkering with the idea of using CO2 in a cascade. The main problem is it's triple point of -56C/-78F. Staying above this point doesn't make sense; a cascade using R134a in the high stage and R507 (or maybe R410A) in the low stage should be able to reach those temperatures also.

    Thus, the question is: how to expand CO2 into an evaporator at 1-2 bara (15-30psia), without the dry ice blocking the expansion device? And then the second big problem: how to efficiently transfer the heat to the metal walls of the evaporator?

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    Hmmmmm, perhaps an EPR?
    Absolutely! Keep evaporator pressures on a CO2 system a comfortable distance above 60 psig, and you won't make dry ice. Not sure you will find many epr manufacturers who will readily warrant their products on such a system, though...
    Prof Sporlan

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    Thus, the question is: how to expand CO2 into an evaporator at 1-2 bara (15-30psia), without the dry ice blocking the expansion device?
    Unfortunately, when you expand liquid CO2 below triple point pressure (60.4 psig), you will make dry ice.

    And then the second big problem: how to efficiently transfer the heat to the metal walls of the evaporator?
    The Prof isn't an expert on CO2 refrigeration, but he sees significant problems attempting to evaporate CO2 in a refrigeration system below -70F. In his humble opinion, there are easier ways to design low temp cascade systems.
    Prof Sporlan

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    Originally posted by Prof Sporlan
    Not sure you will find many epr manufacturers who will readily warrant their products on such a system, though...
    Prof., should you know that I would never make such a claim (warranty)? If you wonder... NOT.

    Mind you, that I am merely expelling the CO2 to atmosphere. "Triple Point" is an interesting term, which I have never encountered before, though I believe the diagram submitted by DaBit explains it!

    Thanks, gentlemen.... I learned something (and I don't say that like I know anything)

    I'm considering the capability of the R-404a to reach near -60F, and the potential for the -67F of the CO2, in consideration of, I guess the enthalpy, and the amount of CO2 expended to handle the 120W +/- load. I will reference the appropriate information to to determine the difference in btu/lb of the CO2 vs. R-404A. I may actually be in the process of demonstrating the efficiency of mechanical compression cycle refrigeration?


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    There are two saturated states that are noteworthy. One is the critical point. Here, the liquid and vapor phases become indistiguishable. This is the point on top of the P-H dome.

    The triple point is the saturated state where the solid, liquid and vapor phases are in equilibrium. This is the "bottom" of the P-H dome.

    The bottom of the P-H dome for most substances used as refrigerants is at a very low pressure, and not even a concern for those designing vapor compression refrigeration units. CO2 is an exception.
    Prof Sporlan

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    Originally posted by Prof Sporlan
    [B]Unfortunately, when you expand liquid CO2 below triple point pressure (60.4 psig), you will make dry ice.


    I already was afraid of that. Physical laws cannot be broken.

    The Prof isn't an expert on CO2 refrigeration, but he sees significant problems attempting to evaporate CO2 in a refrigeration system below -70F. In his humble opinion, there are easier ways to design low temp cascade systems.
    Well, there are only a few reasons why 'we overclockers' consider using CO2: it is available to us, it is affordable, and it is doable to build a 2-stage cascade with it. Stuff like R508B is both not available and even if we could get it, it is extremely expensive.

    My preferred low-temp refrigerant for overclocking purposes is ethane. But I had a price quote of $185 excluding VAT, safety fees and transport fees for only 50g (~ 2oz) in a lecture bottle. But still, ethane has some nice properties.

  14. #14
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    Re: Liquid CO2

    Sorr I'm new.

    i need information on how to calculate a evaporator coil for a block ice machine

    Regards

    Jose

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    Re: Liquid CO2

    Quote Originally Posted by Prof Sporlan View Post

    If you're really going to get serious, try liquid helium. -455.75F (0.704 psia) triple point. This ought to turn an Intel 8088 into a Cray computer...
    If you use Helium remember to nail the compressor down,.

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