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Isentropic Specific Enthalpy HELP

  1. Aug 23, 2011 #1
    Hi guys,

    I'm struggling with some equations regarding the enthalpy change over a compressor in a vcc system.

    I'm currently working on a model for the whole system and I think I've got all equations except the one describing the enthalpy difference betweeen the inlet and outlet of the compressor.
    I can't really understand how to handle the isentropic specific enthalpy, hout,s, in the following equation:

    hout = (hout,s - hin)/ns + hin

    where ns is the isentropic efficiency

    I also know that ns = (Tout,s-Tin)/(Tout-Tin) (assuming constant specific heat)

    I would prefer the model to be as "general" as possible, meaning that I don't have to perform a bunch of experimental test to determine certain coefficients.

    I would greatly appreciate some help with how to calculate/estimate hout,s. I think that the value of hout,s depends on the suction pressure (?) so assuming a constant value (from example a table at some operating condition) isn't good enough for an accurate model? I mean that value of hout,s does change when the system moves from that particular condition, right?

    Thanks in advance,
    Last edited: Aug 23, 2011
  2. jcsd
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