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Homework Help: Help with mass flow rate of turbine?

  1. Jan 15, 2016 #1
    1. The problem statement, all variables and given/known data
    An turbine expands air at 1300 kPa and 500oC to 100 kPa and 127oC. Air enters the turbine through a 0.2-m2 opening with an average velocity of 50 m/s, and exhausts through a 1-m2 opening. Determine (a) the mass flow rate of air through the turbine

    2. Relevant equations
    m dot = (1/v)(V)(A)

    3. The attempt at a solution

    I use PV=RT to get specific volume. (.287 * 773)/1300 = .17065 m^3/kg
    I then plug it in to the formula for mass flow rate which is (1/.17065)(50)(.2) = 58.6 kg/s
    the problem is that the answer is suppose to be 46.9 kg/s but I can see anything Ive done wrong. can someone help??
  2. jcsd
  3. Jan 15, 2016 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    Did you check what happens at the exhaust end? The air has expanded after going thru the turbine.
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