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Homework Help: Steam engine problem

  1. May 22, 2008 #1
    1. The problem statement, all variables and given/known data

    If a steam engine operates at half of its theoretical maximum efficiency, and does work at a rate of W J/s, calculate how much heat is discharged per second.

    3. The attempt at a solution

    emax = W/QH (Carnot)

    emax = W/2QH

    --> QH = W/emax

    Wrong answer. What is my mistake?
  2. jcsd
  3. May 26, 2008 #2
    Theoretical max would be equal to 1, 50% would be the actual efficiency = .5 =W/QH=1/2. Heat discharged would be QL which equals QH-W. If the engine is operating at 50% efficiency, half the heat input will go to shaft work, the other half will be discharged. So this engine would discharge 1 J/s. BTW, theoretical max. for a heat engine is 1-TL/TH.
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