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Homework Help: Pelton wheel's theoretical speed for max efficiency

  1. Jul 21, 2013 #1
    1. The problem statement, all variables and given/known data

    A Pelton wheel is driven by five identical jets. The runner has a diameter of 3,8 m, fixed in a horizontal position. The head from reservoir level to nozzles is 350 m and the efficiency of power transmission through the pipeline and nozzles is 90%. The relative velocity decreases by 8% as the water traverses the bucket surfaces which deflect the jet at an angle of 162°. The coefficient of velocity for the jets is 0,97 (Cv) and the discharge is 25920 m[itex]^{3}[/itex]/hour.
    Calculate the following:
    a) The velocity of water entering the buckets
    b) The theoretical wheel speed in r/min for maximum efficiency (u = 0,5 V)

    2. Relevant equations

    For a: [itex]V = Cv\sqrt{2g×h}[/itex] where h = Height×90%

    For b: [itex]U = \frac{\pi×D×N}{60}[/itex]

    3. The attempt at a solution

    a) [itex]V = Cv\sqrt{2g×h} = 0,97×\sqrt{2(9,81)×315} = 76,256 m/s[/itex]

    b) [itex]U = 0.5V = \frac{\pi×D×N}{60}[/itex]
    I'm confused as to whether I must use V from (a) or if I must calc a new V where h = H for max efficiency?
    Last edited: Jul 21, 2013
  2. jcsd
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