1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    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.
    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
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted