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Homework Help: Fluid systems centrifugal pumps

  1. Oct 12, 2008 #1
    1. The problem statement, all variables and given/known data
    Hi guys, Ive been working on some problems at uni to try and get to know this subject better and i have been unable to answer a question.

    the impellar of a centrifugel pump has the following configaration,
    diameter 254 (hence r2=127) blade exit angle (Beta) 32degrees, effective outlet area=0.017m^2, Speed (N)=1450 rpm (hence omega =151.84 rad/s). the diameter of the suction and delivery openings are 150mm and 125mm. delivery rate is 30.8l/s, pressure heads at suction and delivery are 4.5m and 13.5 m below and above respectively(atmospheric), pump motor is 8.28Kw. Alpha 1 is 90 degrees due to shockless entry and the actual tangential velocity at impeller outlet is 0.7 of the ideal. Determine
    1. the overall efficency
    2. the hydraulic efficency based on the actual tangentail velocity at blade outlet.


    2. Relevant equations
    I have used for the hydraulic efficency
    actual head developed by pump/theoretical head developed by impleller.

    vbar^2/2g energy loss in impeller
    (u2*vbart2)/g ideal head
    ideal head-energy loss = actual


    3. The attempt at a solution
    i have for my values
    u2=19.28
    vbarn2=2.27
    vbart2=15.64 15.64x0.7=10.95
    vbar2=15.77

    when i calculate for the hydraulic efficency i get 71% when the answer is 80% and i cant seem to get far enough in the first part to get an answer for it, but the correct answer for part one is 66%.
     
  2. jcsd
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