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Homework Help: Thermodynamics: entropy

  1. Feb 3, 2009 #1
    1. The problem statement, all variables and given/known data

    Steam enters a well-insulated turbine at 25 kg/s, 100 bar, 700 C and exits at 1 bar.

    a. What is the exit temperature if the turbine is reversible?

    b. How much power is produced if the turbine is reversible?

    c. If the turbine is only 80% efficient, how much power is produced?

    d. In this case, what is exit temperature?

    e. In this case, what is the rate of entropy generation?

    2. Relevant equations

    I'm not sure how to do the entropy balance. I can use the tables to find s1 and h1, but I dont think I can use anything else.

    3. The attempt at a solution

    a) Turbine means m1 = m2 = m where m is the mass flow rate

    Then m(s1-s2) + Q/T = 0 where Q = heat flow rate

    How do i get Q and T?

    b) W = m(h1-h2) where W = work flow rate

    c) W2 = 0.8(W)

    d) I can sole for the new mass flow rate m2 = W2/(h1-h2)

    Then use m2(s1-s2) + Q/T = 0 and solve for T?

  2. jcsd
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