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  1. #1
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    Question collecting oil in evaporator



    Hello everybody,
    In chiller with water cooled condenser, compressor oil is collecting into the evaporator. How can we send this oil to the compressor carter? Isthere any solution without changing evaporator?

    Thanks for your helps....

    Aygul



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    Wink Re: collecting oil in evaporator

    Quote Originally Posted by Aygul
    In chiller with water cooled condenser, compressor oil is collecting into the evaporator. How can we send this oil to the compressor carter? Isthere any solution without changing evaporator?
    What the size(TR) of chiller?
    Check the gas it will be short. for temporary solutions

    Is there any unloading system in compressor?

    If yes than unload the compressor all the oil in evaporator will move to compressor.this is temporary solution.

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    Re: collecting oil in evaporator

    Hi aygul.

    There are a few solutions.
    You can install an oil sepatator after the compressor.
    You can add a U oil trap on the outlet of the evaporator.
    You can add a little R12 to the refrigerant, it will help oil ruturning.

    Also, check that the TEV is not too open, (superheat too low).

    Can you give some more details of the chiller?

    Chemi

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    Re: collecting oil in evaporator

    Quote Originally Posted by aygul
    Hello everybody,
    In chiller with water cooled condenser, compressor oil is collecting into the evaporator. How can we send this oil to the compressor carter? Isthere any solution without changing evaporator?

    Thanks for your helps....

    Aygul
    Hi...is it the case that as oil has collected in the evaporator that someone has been topping up the compressor sump...oil bound evaporator followed by loss of refrigeration effect...loss of suction superheat...I have found that after rectifying the root cause of this type of problem it is reasonably easy to return the oil to the compressor sump where it can be drained to the correct level by running the compressor at full load conditions.There are various reasons to cause oil migration to the evaporator but as other site members have already requested it is necessary to know the details of the unit and a rundown on the present running conditions......best of luck...maybe you could post some details...in any case...the answer is.. no ...you would not have to change the evaporator

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    Re: collecting oil in evaporator

    Is this a new unit and was the problem there since the beginning or is it an old unit which gives just recently problems?
    Own design?
    Did someone changed something?
    Did you serviced always this unit?
    Is there a partial load system on the unit?
    Enough gas in the system?
    Not too high fluctuations in condensing pressure?
    What is the superheat?
    Furthet the same questions as Marc, shell and tube or plate HE and TEV or flooded?
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: collecting oil in evaporator

    Thanks all the answers...

    evaporator is shell and tube type-refrigerant goes through tubes and water goes outside the tubes. Refrigerant is R22, i thing there is enough refrigerant in the system... there is no unloading... there is screw compressor in the system...
    superheat aproximatelly 3 C... tev adjustment is 20 open tours (totally 40 tours)
    I thing i increased superheat closing tev...
    For oil return problem refrigerant velocity is important, when we increase superheat, can we supply to increase refrigerant velocity? or how much can i add R12 into the system?...

    Compressor has oil seperator, can i add additional oil seperator into the system?

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    Re: collecting oil in evaporator

    You're sure the screw has no partial load system (slide on the intake)
    You must be sure and not guess if there is enough refrigerant in the system.
    What about the answers on the other questions we - Chemi,Tejbir, Marc and I - posed you? We need correct answers and no guesses before we hurther can help you.

    A TEV with 20 opening rotations on the spindle doesn't say anything. We need real measured temperature and pressure values.

    You have to know what you're doing if you add R12 in the system, there is no rule to determine the quantity.

    Adding a second oil separator won't help you if the original one had functioned before very well. Is the present one working fine for the moment?

    You see, still too many questions before we can help.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: collecting oil in evaporator

    Quote Originally Posted by aygul
    Thanks all the answers...

    evaporator is shell and tube type-refrigerant goes through tubes and water goes outside the tubes. Refrigerant is R22, i thing there is enough refrigerant in the system... there is no unloading... there is screw compressor in the system...
    superheat aproximatelly 3 C... tev adjustment is 20 open tours (totally 40 tours)
    I thing i increased superheat closing tev...
    For oil return problem refrigerant velocity is important, when we increase superheat, can we supply to increase refrigerant velocity? or how much can i add R12 into the system?...

    Compressor has oil seperator, can i add additional oil seperator into the system?
    If there is a screw compressor in the system then what type of oil sump and pump is fitted or is there no oil pump at all????..if it was say a Dunham bush horizontal then there are several oil sump and pump configurations.....oil recovery on that type of screw is carried out by adjusting the discharge superheat to a minimum of 18 degrees .....any lower and the oil seperator mesh will not trap entrained oil and you will empty your sump into the system....I have seen 30 gallons of oil dissapear in about one minute due to this problem.......need much more detail yet.....what sort of screw is it etc?????

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    Re: collecting oil in evaporator

    Yes aygul, go and get all the details. I know its Sunday so first thing tomorow.

    Could the present oil saparator is blocked?
    Is there a sight glass in the oil returning line?

    Chemi

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    Re: collecting oil in evaporator

    Hi Marc..still havnt seen a real explanation of the system...sump etc....if this is a large screw then suction superheat may be fairly irrelevant(depending on the unit configuration) apart from indicating the oil bound evaporator problem.....some large screws with liquid injection require the adjustment of discharge superheat and the suction superheat falls wherever it falls...large screws can put up with a little liquid but some cant cope with a low discharge superheat and will dump their oil if it isd too low.....we really need to know the size of the oil sump...the lubricationcircuit as in the type of seperator etc...best regards ..

  11. #11
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    Re: collecting oil in evaporator

    I haven't heard anyone mention the flow through the chiller You need to determine if proper flow by taking a pressure drop across the chiller barrol and then get mfg specs if it is the currect drop ,then you can determine if the barrol is dirty or you have a strainer restriction or a bad pump If this is a 10*f chiller barrel and you are getting full flow then the heat exchanger in probably dirty.

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    Re: collecting oil in evaporator

    [We really need to know what the cause of the problem is, to be more epecific ]
    Hi again...I see where you are coming from and have to agree with what you say...I think we are both looking at the problem from different directions...I have fairly extensive large screw experience including dozens of teardowns and am looking at this problem from a "first impressions" point of view...however the machine may be of the PD (entrained oil) type for all I know...thats why I thought more info would be useful...there are such a wide variety of things that could cause this it is essential to have as much info as possible....have to agree with you about machine logging....it can be a real pain....some of the government sites that I visit have at the least a daily log of all relevent info for each machine.....some have several logs during each day.....it is a pain for the guy who has to do the logging but absolutely invaluable when it comes to a problem such as this current one. best regards etc

  13. #13
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    Re: collecting oil in evaporator

    Some symptoms of an oil-logged evaporator include:
    Noisy compressor;
    Low oil level in the sight glass on the compressorís crankcase;
    TXV has a hard time controlling superheat (hunting);
    Low evaporator and compressor superheat; and
    Warmer-than-normal chiller temperatures with loss of capacity.
    Here is a more-detailed look at those symptoms.
    Noisy compressor: The compressor may be noisy because of the lack of oil. Metallic sounds may be heard due to the lack of lubrication or because parts are out of tolerance from excessive wear. Oil is a sound deadener as well as a lubricant.
    Low oil level in compressorís sight glass: Because a lot of the oil is in the evaporator, the crankcase will be low on oil. In fact, all of the systemís components (excluding the compressor) may have too much oil. This would cause a low oil level in the compressorís crankcase sight glass.
    Many times, a compressor that is flooding with refrigerant will turn into an oil pumper. The crankcase will foam from the liquid refrigerant flashing in it. Small oil droplets entrained in the oil will be pumped through the compressor. This will oil log many components in the system.
    The velocity of the refrigerant traveling through the lines will try to return the oil from the system to the crankcase. Even an oil separator in the compressorís discharge line may have a hard time keeping up with excess oil in circulation. Oil will continue to get into the system if the flooding is not remedied.
    TXV has a hard time controlling superheat: The TXV will also see too much oil passing through it. The evaporatorís tailpipe will be oil logged and the inside of the tubes will be coated with oil. The remote bulb of the TXV at the evaporator outlet will have a hard time sensing a true evaporator outlet temperature because of the reduced heat transfer through the line. The TXV will hunt.
    As a result, constant superheat will not be maintained. The TXV remote bulb may sense a warmer-than-normal temperature from the oil insulating the inside of the line. This could make the TXV run a low superheat and flood or slug the compressor with refrigerant. Often the sight glass in the liquid line will be discolored with a yellow or brown tint from refrigerant and oil flowing through it.
    Low compressor superheat: If the TXV is running low superheat, this will cause the compressor superheat to run lower.
    Warmer then normal chilled water temperatures with capacity losses: Because of the reduced heat transfer in both the condenser and evaporator (caused by excess oil coating the inner tubing), capacity will be decreased. The compressor will run longer trying to maintain the set temperature.
    Evaporator temperatures and pressures may run low because of the reduced heat transfer from the oil insulating the evaporator tubes, reduced chill water flow or a low load.
    This will cause reduced mass flow ratesand oil has a tendency to accumulate in the coldest part of the system(Evap)
    If a chillers SST is 38*f and the chiller is rated at 10 degrees a normal cooler aproach is around 16*f entering (54*f on) and about 7*f leaving (44*f) water temperature.

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    Re: collecting oil in evaporator

    And is there a sump actually in the compressor....is it open drive or semihermetic...has it got a seperate oil sump or combined sump and seperator...are there oil sight glasses fitted...best info would be oem and model...if not a package then the oem and model of the screw compressor...information is all :-)

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