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  1. #1
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    Flooded Water Cooled Screw Chiller



    Hi everyone

    I'm developing a water-cooled screw chiller with a flooded evaporator. it is a 180-ton cooling capacity with the refrigerant R-22. I managed to build a test loop in order to examine the chiller behavior in different situations. the pressures and outlet/ inlet temperatures are satisfying. but some of the results seem quite unusual. anyone's help will be appreciated.

    1- Although a refrigerant distributor has been managed in the bottom of the evaporator, the level of the boiling refrigerant is uneven. the level approximately is 5 cm (2inch) higher beneath the suction area rather than the middle section of the evaporator. I have no idea if it is normal or not. (As it is an experimental project I installed two sight glasses in different places)

    2- how much boiling foam on the top of the refrigerant in the evaporator using R-22 is acceptable?

    formation of foam in the evaporator may indicate that the oil has escaped to the evaporator.
    An oil recovery system has been managed in the evaporator to suck the accumulated oil back to the compressor. (also an oil separator in the discharge line is installed)

    the oil level in the compressor top-level sight glass is always at its top point when running. although the compressor manufacturer manual mentions when the compressor is working, the oil level should be maintained somewhere in the middle of the top-level sight glass.
    at our start-up process, I mistakenly charged 2 more liters of oil in the oil separator. (assuming the flooded chiller needs more oil). after 2 or 3 hours of working, I drained it out.

    So the question is if the oil level in the compressor is at its top-level and oil recovery is sucking back the oil to the compressor, what is this foam?

    I'm going to attach some close shot photos of the foam from the evaporator sight glass. it may help you to understand more about the foam that I'm saying and its quality.

    Thanks in advance for your help.
    Attached Images Attached Images
    Last edited by NaderAttar; 22-09-2021 at 07:22 AM. Reason: miss-spelling



  2. #2
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    Re: Flooded Water Cooled Screw Chiller

    That is an excellent piece of engineering! Would the foam be caused by the liquid boiling off, not necessarily oil carry over? What metering device are you using and are your flow rates close to design? Someone with more knowledge than me will hopefully be along shortly
    Mostly found in the southern part of this green and pleasant land.

  3. #3
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    Re: Flooded Water Cooled Screw Chiller

    Quote Originally Posted by NaderAttar View Post
    Hi everyone

    I'm developing a water-cooled screw chiller with a flooded evaporator. it is a 180-ton cooling capacity with the refrigerant R-22. I managed to build a test loop in order to examine the chiller behavior in different situations. the pressures and outlet/ inlet temperatures are satisfying. but some of the results seem quite unusual. anyone's help will be appreciated.

    1- Although a refrigerant distributor has been managed in the bottom of the evaporator, the level of the boiling refrigerant is uneven. the level approximately is 5 cm (2inch) higher beneath the suction area rather than the middle section of the evaporator. I have no idea if it is normal or not. (As it is an experimental project I installed two sight glasses in different places)

    This would be normal, as gas flow is towards the suction port. to balance it, maybe add a suction port on either end so that you have 3 suction ports leading to the main suction

    2- how much boiling foam on the top of the refrigerant in the evaporator using R-22 is acceptable?

    Depends, if the system has been calculated to run at 0C suction, 40C discharge with 20C water inlet temperature, but in the initial stages you run with 30C water inlet there will a lot of boiling/foaming until the system reaches design specifications.


    formation of foam in the evaporator may indicate that the oil has escaped to the evaporator.
    An oil recovery system has been managed in the evaporator to suck the accumulated oil back to the compressor. (also an oil separator in the discharge line is installed)

    oil may be causing the "foaming" effect on top, would be interested in seeing more pictures


    the oil level in the compressor top-level sight glass is always at its top point when running. although the compressor manufacturer manual mentions when the compressor is working, the oil level should be maintained somewhere in the middle of the top-level sight glass.
    at our start-up process, I mistakenly charged 2 more liters of oil in the oil separator. (assuming the flooded chiller needs more oil). after 2 or 3 hours of working, I drained it out.

    So the question is if the oil level in the compressor is at its top-level and oil recovery is sucking back the oil to the compressor, what is this foam?

    Been quite some years since I worked with R-22, so I hope I have my numbers correct.
    R-22 can "absorb" 15-20% of it's weight in oil before the oil starts separating. So if you have 100kg of R-22, theoretically, you can add 20 liter/kg of oil and it will be a balanced mixture. Oil is lighter than R-22 and if there is to much oil in the chiller it will start to for a oil rich layer on top of the liquid. what you may be experiencing with the foaming, is that a small amount of oil is mixed in the R-22 and that is what is causing the foaming.


    I'm going to attach some close shot photos of the foam from the evaporator sight glass. it may help you to understand more about the foam that I'm saying and its quality.

    Thanks in advance for your help.

    My replies in Red inside the quoted text
    -Cheers-

    Tycho

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    Re: Flooded Water Cooled Screw Chiller

    I like how compact the unit is, most flooded chillers have a surge drum on top, and it seems like you have place for one if you make the control cabinets smaller, or are able to place them somewhere else

    Screenshot_34.jpg

    Looking forward to hearing more about your testing
    -Cheers-

    Tycho

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    Re: Flooded Water Cooled Screw Chiller

    thanks so much Tycho for your reply.

    the system is designed for air conditioning purposes, and when the system comes to a steady-state operation the foam on top becomes lesser, but I think it is still too much.

    the top half of the evaporator shell is left empty and there is a moist eliminator beneath the suction port, so there is no need for a surge drum. controlling the superheat assures that no liquid will enter the compressor.

    thanks again for sharing your experience with me
    Last edited by NaderAttar; 22-09-2021 at 08:10 PM.

  6. #6
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    Re: Flooded Water Cooled Screw Chiller

    Quote Originally Posted by al View Post
    That is an excellent piece of engineering! Would the foam be caused by the liquid boiling off, not necessarily oil carry over? What metering device are you using and are your flow rates close to design? Someone with more knowledge than me will hopefully be along shortly
    thanks al,
    no matter how good an oil separator is, a small amount of oil will find its way to the evaporator, so there is oil in the evaporator for sure, but I'm not sure about the amount of it.

    I'm using a flow transmitter sending a signal to a motorized butterfly valve to control the flow and the returning chilled water temperature. also, a frequency inverter drive is connected to the evaporator pump so I can keep the flow rate constantly.

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