Saturday, July 26, 2014

Ultra low-temperature cascade refrigeration system repair

I bought a -100*C refrigerated cold trap from a surplus sale, which was not operational.  In this video, I describe how the unit works after recharging its second stage with R1150 (ethylene) refrigerant.

Savant RVT4104 - (manual) http://phoenix.tuwien.ac.at/chemistry/Gebrauchsanweisungen/SAVANT%20Vapor%20Trap.pdf


16 comments:

  1. Thats a nice system you have there Ben, If you have problems with refrigerants again I would suggest retrofitting the R-502 with R-404A. it is a direct drop in. The R-13B1 can be replaced with R403B. I retrofitted a cascade system for Lockheed Martin a few years back and I happened to have some R-23 around the shop and used that in place of the R-502 with no issues except the cost of R-23 is about ten times that of R-404.

    When brazing on the system make sure to purge nitrogen through the system so you can avoid oxidation with in the system. And any time I do open a refrigeration system up I install a new liquid line filter dryer. Before you charge pull a good 400 micron vacuum and let it sit for 10 minutes and you will be ready to charge. I recommend pulling a deep vacuum with copper tubing, refrigeration hoses are pressure rated and have a tendency to permeate air through in a deep vacuum.

    It appears you have your leak fixed so you shouldn't have to open the system up again. I wouldn't be concerned about R-1150 or R-170 in a sealed system I have used propane in place of R-12 as a direct drop in to get my by in a bind. In fact R-1150 will preform better for you with lower discharge temperatures than any of the original refrigerants. If you have any more problems finding refrigerant or parts shoot me an email and I can get you taken care of.

    ReplyDelete
  2. Another great blog posting on this technology.
    One question I have is given the relative simplicity of these cascaded systems, do you think it might be possible to home brew one of these? I can see a major problem with reclaiming oil from the second compressor. That would be a critical issue to address in the ultralow temp evaporator side of things.

    Any thoughts?

    ReplyDelete
  3. Nitrous, yes, there are homebrew cascade systems. They are most often built by CPU overclockers, and there is a lot of banter on the forums, but not a whole lot of detail. Search for cascade cpu, and you'll find lots of long talky threads with a few bits of actionable details here and there.

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  4. Hi Ben,
    Quick update on the cryo front. I've got a cold trap on order and am thinking about changing gases. Ethylene seems available from our local Praxair distributor. Not sure of the price yet... But I wondered about using R404a as an alternative (readily sourced on eBay. The Labconco unit I got may not be a dual compressor type. The temperature limit isn't currently known. They have an ultra model that goes to -100C but this one might just stop at -50C or so.

    I'm concerned about refrigerant / compressor compatibility. I got this unit for $5.00 plus shipping ($60) so I don't think I can go wrong.

    Doug

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  5. Hi Ben,
    Just an update on the $5.00 Labcoco Centrivap cold trap. It actually works, more or less. It gets to -48C but not quite to the rated -50C. The refrigerant is R403b. I'm going to open it up and do a thorough cleaning. The ready light doesn't come on, but no surprise if -50C is the set point. I'm thinking of using this as a gas precooler for my sterling cooler. I was also thinking of chilling the hot end f the Cryocooler. Any idea how low you can safely go with a Cryocooler Stirling engine?

    Doug

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  6. hi dear ben ,

    ı am teknical services operators,

    are you help me ?

    low compresor = r407

    hıgh compresor = r508b+r170


    I can not find r170 :(

    which I use instead of gas ?

    r290 ??? is it ok. ??

    ReplyDelete
  7. The short answer to your question is "No"

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  8. full 508b use cascade system ??

    350 gr (r170) + 350 gr (r508b) = 700 gr addivite gas

    700 gr ( 508b) gaz ??

    ReplyDelete
  9. The ethylene gas is for the ultra low temperature. Without it, or something similar, you will not get to the temperature you want.

    Nitrous

    ReplyDelete
    Replies
    1. thanks nitrous ;

      Which gas are you advice substitude for 508b ?

      Delete
    2. thanks nitrous ;

      Which gas are you advice substitude for 508b ?

      Delete
  10. R508b is actually a replacement for R13 and R503. It's a very low temperature refrigerant. In a cascade system, you need to chose combinations of complimentary refrigerants to achieve the desired temperature. The very name "cascade" suggests that each gas takes the temperature down to a new level. sort of like going down stairs. This link might help you understand the refrigerants better. http://www.ior.org.uk/ior_/images/pdf/se/Datasheet%2014%20-%20Master%20Gas%20List.pdf

    ReplyDelete
    Replies
    1. hi dear nitrous

      r170 gas for altenatives gas ?? 508+??

      Delete
    2. hi dear nitrous

      r170 gas for altenatives gas ?? 508+??

      Delete
  11. I have a ultra low temperature freezer -86c. It has mix refrigerant. Do you know how to recharge a mix refrigerant freezer? It has one original manufacture connector.
    Here's all the info regarding its refrigerant. This is on a sticker on the side of the freezer. It looks like there's never been any tampering that would indicate modification

    REFRIGERANT
    Stage Type Oz. PSI
    1 R-134A 7.5 -
    1 R-404A 17 -
    2 R-404A 1.4 4
    2 R-508B 8.6 126

    ReplyDelete