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Homework Help: Thermodynamics on steady state

  1. Jun 7, 2012 #1
    1. The problem statement, all variables and given/known data
    At steady state, a stream of liquid water at 20C, 1bar is mixed with a stream of ethylene glycol (M=62.07 g/mol) to form a refrigerant mixture that is 50% glycol by mass. The water molar flow rate is 4.2 kmol/min. The density of ethylene glycol is 1.115 times that of water.


    a) the molar flow rate, in kmol/min, and volumetric flow rate, in m3/min, of the entering
    ethylene glycol.

    2. Relevant equations

    m1 + m2 = m3

    m1h1 + m2h2 = m3h3

    3. The attempt at a solution

    Firstly, I do not know whether is there a leaving flow on the ethylene glycol there that make it to have the m3 flow rate to exist.

    If I assume there is a flow rate exit there,

    Vf = 0.001002 m^3/kg
    Density of water = 1/0.001002
    = 998 kg/m^3
    Density of ethylene = 1.115 x 998
    = 1112.77kg/m^3

    Mw = 18.015 kg/kmol
    Volume flow rate of water = 18.015(4.2)(0.001002)
    = 0.07581 m^3/min

    0.07581 + m2 = m3

    If I assume that the mass flow rate for the exit one is m3 = 0.5m2

    The answer turns out to be negative, which i dont think is correct
  2. jcsd
  3. Jun 8, 2012 #2

    rude man

    User Avatar
    Homework Helper
    Gold Member

    questions for you:

    what is the mass flow of the water?
    therefore, what is the mass flow of the ethylene glycol?
    therefore, what is the volumetric flow of ethylene glycol?
    and finally the molar flow of the ethylene glycol?
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