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Thermodynamics-psychrometry question, mixing two streams of warm moist air

  1. Jul 17, 2011 #1
    1. The problem statement, all variables and given/known data

    I'm trying to determine how to go about attacking this problem that I'm doing to

    I have 2 streams of air mixing, and I'm trying to find the temperature and relative humidity of the third stream.

    Stream 1: 2bar, 20C, 40%rh, and 1kg/s
    Stream 2: 1bar, 20C, 4kg/s

    So I know I can find all my values for the first stream, but the second stream doesn't give me enough to find it on the psychometric charts.




    2. Relevant equations

    m=mass of mixture
    ma=mass air
    mv=mass vapour
    h=enthalpy of mixture
    ha= enthalpy dry air
    hv=enthalpy of water

    Mass Balance
    m1+m2=m3
    ma1+ma2=ma3
    mv1+mv2=mv3
    m=ma+mv


    Energy balance
    m1h1+m2h2=m3h3 and all variations of this with the contents of the air


    phi1=rh=Pv1/Pg1

    where phi is the relative humity
    Pv1 is the partial pressure of water
    Pg1 is the saturation pressure of water at the given temperature

    w=mv/ma for all values.

    energy=mc(delta)T

    where c is the constant used to determine this (name escaping me right now) (units of kj/kg.C)


    3. The attempt at a solution


    I got my values for state one, I've tried energy balance and mass balance, but I end up with more variables than equations and I've been confusing myself all day trying to do this. I can't find ANY question in over 3 books that excludes all data about state three other than the mass flow rate, and excludes the data required from the second stream of air.
     
  2. jcsd
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