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Homework Help: Turbine efficiency

  1. Sep 10, 2011 #1
    1. The problem statement, all variables and given/known data
    I have attached the question. I'm not really sure how to do this one


    2. Relevant equations
    power = work done/time


    3. The attempt at a solution
    Is the turbine efficiency simply the power generation (750kW) divided by the mechanical output (800kW) which is so 750/800 x 100 = 93.75% efficiency?

    and then there's the combined turbine generator efficiency. How do you do that?
     

    Attached Files:

  2. jcsd
  3. Sep 10, 2011 #2
    Re: efficiency

    No it's not what you think.
     
  4. Sep 10, 2011 #3
    Re: efficiency

    You have been given rate of mass flow, height of water(70m). Calculate gravitational energy being converted (mgh).It gives potential energy converted per second.
     
  5. Sep 10, 2011 #4
    Re: efficiency

    so i simply do 1500(9.81)(70) = 1030050 J/s ? then what
     
  6. Sep 10, 2011 #5
    Re: efficiency

    Then you know the mechanical power output of turbine.Remember the power from potential energy can only be used by turbine and not by generator.
    ((800kW)/(1030050))*100
    Is efficiency of turbine.
     
  7. Sep 10, 2011 #6
    Re: efficiency

    I think answer's coming out to be 77.66% for turbine efficiency if you do the calculations.
     
  8. Sep 10, 2011 #7
    Re: efficiency

    ohh I get it, because j/s is watts - power. okay so then what is the electric power generation and the combined turbine-generator efficiency. is it simply (750000/1030050) x 100?
     
  9. Sep 10, 2011 #8
    Re: efficiency

    No.Just apply unitary method.
    800kW of mechanical output gives 750kW of electrical output.
    1W of mechanical output gives (750/800)W. ---equation (1)
    (kW get cancelled.You can Multiply 1W to both sides)
    We know efficiency of turbine as 77.66%.
    This means that when 100W of energy is inputted to turbine 77.66W of energy is it's mechanical output.
    Now multiply 77.6 to equation (1). answer is on right hand side-((750/800)*77.6).It comes around 72.81%
     
  10. Sep 10, 2011 #9
    Re: efficiency

    Ahh okkay thank you i get it now
     
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