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  1. #51
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    Re: Getting Colder, need advice



    Hi,
    I've got the latest version up and running. It seems to pull it done to temp fairly fast.
    Although, when it gets about 85 deg. in the shop it seems to struggle / runs longer to keep it at temp.
    Would this be a condensor issue, as not large enough or needs more air flow?

    i got my new/final container for the coil that i'm working on, i'll pulling the system apart again to get it installed.
    hopefully the last time.


    thanks for your help with all the feed back.

    i'll post more as it gets closer to finished.


    thanks.
    Mvtop
    Last edited by mvtop; 02-06-2009 at 07:45 PM. Reason: submitted to soon



  2. #52
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    Re: Getting Colder, need advice

    Mvtop - we did'nt really get down to the cause of the very low SX on your last set of data i.e. 1psi instead of 7 psi as noted earlier - maybe a gas leak? Also what mods are you making with the coil etc.

    From your earlier data the condenser may be a little small for a hot day but that will probably be on a startup issue only - have to wait to see the latest data to see what you have done.

    Keep going.

    Chef

  3. #53
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    Re: Getting Colder, need advice

    Quote Originally Posted by Chef View Post
    Mvtop - we did'nt really get down to the cause of the very low SX on your last set of data i.e. 1psi instead of 7 psi as noted earlier - maybe a gas leak? Also what mods are you making with the coil etc.

    From your earlier data the condenser may be a little small for a hot day but that will probably be on a startup issue only - have to wait to see the latest data to see what you have done.

    Keep going.

    Chef
    Hey Chef,
    I do think there could of been a small leak, since the numbers were so different from where they started.
    And I had a few flare fittings installed to make dismanteling easier. They can be tricky to keep the leaks away.

    as to what mods, i did add the loop to the coil so gravitiy wouldn't drain any ref. into the compressor during off times, as Gary mentioned. And moved the return to the top of the coil and the supply to the bottom as recomended. Also, i did soft solder and wrap the cap. tube to the coil return and insulated well.

    for the mods of the new coil, it will be made of stainless steel, not as good as the aluminum i have now, but it's work better overall for my design.
    I plan to make a tighter wrap this time and remove all gaps between container and coil, solder/braze the coil to the container to help with heat transfer.
    It will hold and cool 2 gallons instead of 3 gallons. I"m not sure how much smaller the coil will be in terms of volume compared to what i have now. i'll know in a day or so as i get closer to finishing the coil. i was going to try to stay fairly close to the volume i have now so we can stick with the same length cap tube. I have a 39" .040 cap tube. I remeasured it when i had it apart again. I think I said I was using a 32".

    Is there any way to estimate the length of cap tube I might need if the volume of the coil is reduced by x%?
    I was using trail and error before. I don't think i can lengthen the cap. tube by x% the same as what i reduced the size of the coil.
    I really won't know what the volume of the new coil will be until i'm done with it. It might be close enough to what we have now. that's what i'm shooting for.

    I'll have some pics as I progress with this.

    Again, thank you all for your comments / feed back.

    Mvtop

  4. #54
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    Re: Getting Colder, need advice

    Quote Originally Posted by mvtop View Post
    Hey Chef,
    Is there any way to estimate the length of cap tube I might need if the volume of the coil is reduced by x%?
    I was using trail and error before. I don't think i can lengthen the cap. tube by x% the same as what i reduced the size of the coil.
    Mvtop
    The length of the cap tube is related to the compressor mass flow rate and the condensing and evaporating temperatures (and hence pressures) - so as these have not been altered (much) then the tube length will stay the same.

    However if you change the coil size by a lot then evap temps and pressures will change a little. In your case it is not so critical as you are running your cap tube with a sonic output and so changes in the evap pressure wont affect the flow rate in the tube.

    It will affect the suction conditions though and as you have a smaller coil size the pressure will drop a little so the mass flow will drop a little too and you will have less charge in the system.

    It all depends on how much you reduce the coil size, the smaller the coil the smaller the heat transefer area and so to get the same heat flow the temperature differance will need to greater, this in turn forces the suction pressure down. As you are using a HBP compressure you dont really want to push it down too far?

    Chef

  5. #55
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    Re: Getting Colder, need advice

    Hey,
    Happy Holidays.
    It's been awhile since I’ve posted on this project, mainly becasue it's working fairly well and i've been off on other tangents.

    I thought about putting this as a separate post, but i think there’s some history here that's relevant to the story line and instead of covering it all again, I’m just adding to the already long post.

    Gary,
    I would like to improve the performance of the cool down time. And as you mentioned, cap tube systems are designed for pulldown speed.

    Quote Originally Posted by Gary View Post
    Let's keep in mind that cap tube systems are not designed for pulldown speed. We plug them in, they pull down to the desired temp and remain very near that temp for the remainder of their useful lives. If we are designing for pulldown, we need a TXV.


    So I’m taking your suggestion Gary about using a TXV in my system. As you know, this is not your typical out of the box project. I'm ready to put this project back on the workbench again.

    So my questions relate to how to go about sizing / set up a TXV for my setup and what would be needed in addition to what i have. Which is basically a compressor, accumulator, condenser, and homemade evap.


    Again, thank you all for your posts and suggestions.
    mvtop

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