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  1. #1
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    Temperature after metering device



    I've asked around and had a look through a fair few text books and articles but can't seem to find an answer so here i go!

    Say for instance i have a split system that's metered at the outdoor unit to and cooling and sent to the evap. What should be the temperature of the expansion line? (Not sure what the techincal name is for it as i believe it wouldn't be a liquid line.)

    I've come across a fair few units that have only a very slight chill on this line at the outdoor unit. I would have thought because there is a much lower evaporating temp that the uninsulated line from the RMD + the stop valve assembly would have a nice chill to it.

    Only thing i can think of is because of the warmer outdoor ambient air and that there is not enough heat exchange surface available between short line between the RMD (Outdoor) to the stop valve that it can't absorb to much heat and get nice and cold as it never seems to be insulated.

    Any suggestions?



  2. #2
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    Re: Temperature after metering device

    There does not take place (a real) expansion in the "liquid line" - the pipe's diameter is not enough for it to start boiling. Capillary - the metering device - is placed in the outdoor unit in order to get rid of noice in a room being cooled.

  3. #3
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    Re: Temperature after metering device

    Thanks for the reply Yuri.

    So would it be correct to say that in the instant after the expansion device that the portion of liquid evaporates to cool the remaining liquid down to a colder temperature so immediately after the metering device it does not have the ability to absorb heat external to the system? That's why you do not get much temperature drop?

  4. #4
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    Re: Temperature after metering device

    Quote Originally Posted by mburns View Post
    Thanks for the reply Yuri.

    So would it be correct to say that in the instant after the expansion device that the portion of liquid evaporates to cool the remaining liquid down to a colder temperature so immediately after the metering device it does not have the ability to absorb heat external to the system? That's why you do not get much temperature drop?
    No.
    The temp is determined by pressure. You are presuming that the pressure at the exit of the expansion device is equal to that on some point in the evaporator.

  5. #5
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    Re: Temperature after metering device

    If it were possible to suddenly increase this pipe's diameter, then there would appear more (innner) space, the pressure would fall so as boiling would take place.
    But so as an AC is constructed, leaving the capillary the static pressure does not fall (it even should increase !) The pressure is constrained so far. Boiling is prevented constructionally to start here.

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