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Thread: Superheat

  1. #1
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    Superheat

    Will superheat go up or down on a capillary tube system, when the evaporator stays at a steady heat load and the condenser is suddenly cooled by a spray of water and why?

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    It will go up.

    Because the amount of refrigerant being fed to the evap will be less.
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    Beenthere, I was under the impression (perhaps wrongly) that a captube is a fixed orifice device. If so, how is less refrigerant delivered?

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    They require X pressure difference across them to maintain the flow rate.

    As the condensers pressure drops, the PD across the cap tube drops. feeding less refrigerant through the cap tube.
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  5. #5
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    Picture a garden hose sprayer nozzle set at one particular flow rate.

    What is the spray flow like at 80 psi?

    And compare that to 40 psi.

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    THANKS

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    Thread Starter

    cornfused

    Thanks guys for your reply, best wishes.

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    Wouldn't the suction drop off almost as rapidly as the head pressure?



  9. #9
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    Quote Originally Posted by jpsmith1cm View Post
    Wouldn't the suction drop off almost as rapidly as the head pressure?
    was that rhetorical? Yes it does with a piston system....maybe not so much with TXV.

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    The OP's question was about a cap tube system. Effectively a fixed metering device.

    Not entirely rhetorical, just trying to evoke thought.

    BT said that flow rate drops as head pressure drops, but the suction pressure is going to drop, too, so does the flow rate really change significantly?



  11. #11
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    He asked if superheat would increase and that is a definate Yes.

    I also see your point to get us thinking the logical way while working with fixed bore systems.

    Both sides act together equally.

  12. #12
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    Quote Originally Posted by jpsmith1cm View Post
    The OP's question was about a cap tube system. Effectively a fixed metering device.

    Not entirely rhetorical, just trying to evoke thought.

    BT said that flow rate drops as head pressure drops, but the suction pressure is going to drop, too, so does the flow rate really change significantly?
    Yes it does.

    The vapor pressure dropping, means the compressor is not able to draw as much refrigerant back. So flow rate has/does drop significantly. Which is why the SH increases.
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  13. #13
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    Quote Originally Posted by jpsmith1cm View Post
    The OP's question was about a cap tube system. Effectively a fixed metering device.

    Not entirely rhetorical, just trying to evoke thought.

    BT said that flow rate drops as head pressure drops, but the suction pressure is going to drop, too, so does the flow rate really change significantly?
    Yes its fixed AND yes its a metering device. Not simple at all IMO
    A cap tube running refrigerant is in no way like a hose with water.
    The flow rate will increase with more subcooling but is counteracted by the lower pressure in the system. There are two phases of refrigerant at a point in a cap tube and flow is slowed at this point. If I had to guess if the SH will change really depends how the system is designed. One system maybe another maybe not.
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