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Thread: Oil viscosity

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    Oil viscosity



    Am currently doing my level 2 diploma in refrigeration and air conditioning and I had a question in my test which was to do with oil viscosity. It was- What is the oil viscosity of oil at -20 in a freezer. The answers were- ISO15,ISO32,ISO68,ISO120. If anyone can help it would be great. Thanks, Liam.



  2. #2
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    Re: Oil viscosity

    These test questions are written by idiots, the oil will be whatever viscosity the compressor manufacturer recommends, most common would be ISO32 in hermetic and scroll comps, the bigger semi hermetics sometimes use ISO68 (also would depend on refrigerant type)

    The actual viscosity of the oil in the evaporator will be difficult to work out as it will be diluted by the liquid refrigerant.

    This is my take on it anyway
    Last edited by monkey spanners; 26-01-2013 at 07:40 PM. Reason: duh brain
    Mostly found in Oxfordshire, UK :)

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    Re: Oil viscosity

    Hi Liam.
    Monkey has a good point.
    Basically the oil viscosity is measured at 40c with the ISO being the industry standard for those grades.

    What you are asking is not a simple case of saying well therefore a 68 oil would be double or half the viscosity.

    There are numerous things to concider, such as operating pressures temperature and what refrigerant is within the system.

    The attached may help?
    Grizzly


    Attachment 9968

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    Re: Oil viscosity

    Thanks for the help, much appreciated. I agree, some of the questions am getting are an absolute joke.

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    Re: Oil viscosity

    I once put some 3gs oil which is ISO32 in a small jar and left in the freezer overnight and it was like honey by the morning, didn't taste as nice though.

    Still got to get answers right to past test so guess doesn't matter if stupid questions so long as you know the answer (and the correct answer!)
    Last edited by monkey spanners; 26-01-2013 at 07:41 PM. Reason: not telling
    Mostly found in Oxfordshire, UK :)

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    Re: Oil viscosity

    Question is probably trying test your in-depth knowledge not just general knowledge. Viscosity at -20 would relate the pour point temp of an oil, which is to be considered in a refrigeration system for oil return, some oils freeze/ go gluggy other stay fluid at -20.

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