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Vapor Fraction

  1. Sep 10, 2014 #1
    Long time lurker, 1st time poster.

    I need a sanity check that I am solving this problem correctly.

    I have a pipe with a combination of gas and liquid flowing through it, the density of the gas (ρg) is 5.5kg/m^3, the density of the liquid (ρL) is 435 kg/m^3.

    I have a vapor fraction (vf) of 0.92
    I also have a flow rate of 5000kg/hr.

    The combined density ρc = ρg*vf + ρL(1-vf) = 5.5*0.92 + 435*0.08 = 5.06+34.8=39.86 kg/m^3.

    Is the combined density per the method shown above, or do I use the volume flow rate Q to determine the combined density.

    flow of liquid = 5000*0.08 = 400kg/hr
    flow of gas = 5000*0.92 =4600 kg/hr
    dividing by densitys to get volume flow,
    Q liquid = 0.091 m^3/hr
    Q gas = 836.36 m^3/hr

    Combined volumetric flow = 836.36+0.091 = 836.451 m^3/hr
    As total mass flow is 5000 kg/hr.
    Density is mass/vol
    Combined density = 5000/836.451 = 5.98 kg/M^3.

    Any advice would be welcomed.

  2. jcsd
  3. Sep 10, 2014 #2
    in the first method, you assume that the vapor fraction is a volume fraction. In the second approach, you assume that it is a mass fraction.

    Does 0.92 mean that 92% of the volume is gas or does it mean that 92% of the mass is gas?
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