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Homework Help: Steam driven turbine: Heat, Power, evaporation

  1. Aug 3, 2011 #1
    1. The problem statement, all variables and given/known data

    A steam driven turbine generates 200 MW of mechanical power at tan eficiency of 32%. The temperature of the steam at the input is 500 C, and at the output it is 200C

    a: How much power is input as heat to run this turbine?

    b: How much power is lost in hear to the environment?

    c: What is the max ifficiency of any system used to do work with these input and output temps?

    d: If the waste hear is used to to evaporate water, how many kilograms of water can be evaporated in one hour?

    2. Relevant equations

    a: Qh = work/efficiency = 625MW

    b: Qh - Work = 425MW

    c: carnot engine: 1-(Tc/Th) = 1-(473/773) = .338

    d: Not sure: Q = mc(delta T)

    3. The attempt at a solution

    As you can see a, b, and c are figured out. I'm not sure how to approach d. No temp is given for the water, so I can't get delta T.
  2. jcsd
  3. Aug 3, 2011 #2


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    You have the waste heat being used to evaporate the water. So it is changing from a liquid to solid. So that waste heat will provide the latent heat to change the phase.

    (you can be more technical and have the latent heat + sensible heat, but as you said, you are not given a temperature so no ΔT - unless you assume an atmospheric temperature)

    EDIT:I meant liquid to gas not solid, my bad :redface:
    Last edited: Aug 3, 2011
  4. Aug 3, 2011 #3


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    If you are evaporating water, it is changing from a liquid to a gas, not a solid.
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