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What is the exit steam velocity?

  1. May 5, 2016 #1
    1. The problem statement, all variables and given/known data
    Steam, at 15 bar and 280oC, enters a nozzle with an initial velocity of 125 m/s. The steam enthalpy at the exit section is 2800 kJ/kg and the heat loss is 25 kJ/kg. What is the exit steam velocity?.

    2. Relevant equations
    1)Qin - Qout = m [h2-h1+((c22-c12))/2]
    2)h = Pv + u
    3)A1c1/ρ1 = A2c2/ρ2
    3. The attempt at a solution
    0-25k = m((2800-h1)+-125^2/2)

    Steam is not an ideal gas so I can't use Pv=mRT. I have two unknowns and I don't know where to start. I hope you can help.
     
  2. jcsd
  3. May 5, 2016 #2
    For steam at 15 bar and 280 C, from your steam tables, what is the specific volume and the specific enthalpy?
     
  4. May 5, 2016 #3

    SteamKing

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    1. What's the enthalpy of the steam in the nozzle inlet?
    2. What have you done with the heat loss of 25 kJ/kg which occurs while the steam passes thru the nozzle?
     
  5. May 5, 2016 #4
    Thanks for letting me pay attention to the tables.
    h1=2789.88
    v=0.132
    Now if I can only get the area I can use m= A*c1/ρ1 to get m and then substitute in 1 to get c2.
     
  6. May 5, 2016 #5
    You don't need to determine m or A, because you are going to solving the problem per unit mass. The 25 kJ/kg is already per unit mass. So the m should not be in your equation.
     
  7. May 5, 2016 #6
    O.k thanks a lot
     
  8. May 5, 2016 #7
    I solved it . Thank you anyway
     
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