1. Not finding help here? Sign up for a free 30min 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!

Power plant

  1. Sep 13, 2007 #1
    [SOLVED] Power plant

    Hi! Here i have a problem : A power plant generates 400 MW of electric power.It has an effieciency of 40%.
    a) At what rate does it dissipate heat?
    b)If the waste heat is carried away by a river, and the temperature rise of the river must not exceed 3°C, what flow rate is required in the river?


    Here is what i have tried:

    a)
    Pel=400 MW
    η=40%=0.4
    Pth=Pel/η=1000 MW

    b) Pwaste=W/t Q=W=m*c*ΔT m=ρ*V

    Pwaste=(ρ*V*c*ΔT)/t V/t= Volume Flow = V°= Pwaste/(ρ*c*ΔT)

    Pwaste= Pth-Pel=600 MW and then calculations

    I am not quite sure whether this way is correct or not.I will be happy if someone can tell me his opinion.
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Sep 14, 2007 #2
    Seems right to me, although there is at least one assumpution which is implied:
    1. All of the wasted energy is lost as heat.
    Fairly reasonable, there's bound to be some light and sound etc. but the vast majority will definitely be heat.

    I don't fully understand your notation for Pwaste, but it looks pretty good. I guess one assumes that the river isn't below 0 C, and you can look up the specific heat of water, so that's no biggy. Seems like you got it.
     
  4. Sep 15, 2007 #3
    Yeah , i think i got it! Thanks anyway :)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?