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Thermo, heat transfer rate, power plant

  1. Mar 23, 2013 #1
    1. The problem statement, all variables and given/known data
    A power plant generates 1300MW and operates at 315 °C a 20°C heat sink is available.
    what is the minimum rate at which heat must be discarded?

    2. Relevant equations
    not really sure how to begin this one, have a feeling it is related to dq=Tds at constant pressure giving (dq/dT)p=T(dS/dT)p=(dH/dT)p=Cp but that seems to go no where. tried relating it to Enthalpy Changes along the path from 315->100 then condense to liquid water and go 100->20 but none of these seem to use the power out put. honestly completely lost on this one.

    3. The attempt at a solution
  2. jcsd
  3. Mar 23, 2013 #2


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    Gold Member

    Hi, Confusedby. Welcome to PF!

    This looks like a basic heat engine problem. Have you studied the concept of efficiency of a heat engine and how the second law implies a maximum possible efficiency for given hot and cold reservoir temperatures?
  4. Mar 24, 2013 #3
    Thank You

    Well I feel a little silly, for some reason "maximum Thermal efficiency" became "maximum residual heat". If I were to use this arrangement:
    (W/e)-W=q residual. were e is the efficiency and W is the work. it should give the minimal heat flow if I assume Carnot Efficiency correct?
  5. Mar 24, 2013 #4


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    Yes. q is the heat discarded rather than the rate at which heat is discarded. But if you let W be the work done each second, then q will be the heat discarded each second.
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