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Homework Help: Hydroelectric turbine. . . net head question.

  1. Jan 17, 2010 #1
    Sorry, not so much of a problem, more. . I need to understand.


    1. The problem statement, all variables and given/known data
    Finding the net head.

    This website (http://www.oregon.gov/ENERGY/RENEW/Hydro/Hydro_index.shtml [Broken]), says that the gross or "static" head is the vertical distance between the top of penstock and the point at which the water is discharged from the turbine. It then says "Net head is gross head minus the pressure or head losses due to friction and turbulence in the penstock." I am confused about this statement. How do I go about finding net or "dynamic" head?? If I know the pressure at the top of the penstock, and the pressure at the bottom, how do I apply this information?

    2. Relevant equations
    I'm not sure if any of these are relevant. . .

    P2-P1 = -y (Z2- Z1)
    (The pressure difference between two altitudese. . )

    dp= -y dz
    (Change in pressure as it is related to change in weight. . .)

    y= (density) (g)


    3. The attempt at a solution
    I'm very confused. . . I just need to understand the method of determining net head.

    Thank you in advance!
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Jan 17, 2010 #2

    PhanthomJay

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    Quoting from the article, "Net head is gross head minus the pressure or head losses due to friction and turbulence in the penstock. These head losses depend on the type, diameter, and length of the penstock piping, and the number of bends or elbows. So you need a lot more information to calculate it, and even then you'd have to probably get that info on losses from the manufacturer and some tables, or from experimental tests.
     
  4. Jan 17, 2010 #3
    Well I'm trying to accomplish my project in a theoretical sense. . .


    So I guess, assuming no losses due to the penstock (impossible, but I'm trying to simplify it for myself), how would the pressure be factored into the situation?
     
  5. Jan 17, 2010 #4

    PhanthomJay

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    Again, you'll have to consult the turbine manufacturer, who can calculate the potential power delivered by the turbine, based on head (vertical height of water from top of penstock to turbine) and flow rate. The term head is converted to pressure using p =water density (in pounds per cubic foot) times height (in feet), but the given equation factors that in.
     
  6. Jan 18, 2010 #5
    Thank you!

    You really cleared it up for me.
     
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