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Homework Help: Weir flow

  1. Oct 14, 2008 #1
    1. The problem statement, all variables and given/known data

    ok i have a problem, i did a experiment to find the weir flow. Using q= cd 2/3 b root (2g) x h^(3/2)

    I measured b the width of the weir and the height. i was asked to find out the discharge coefficient cd. what i did was add weight to an unknow mass. so the original mass mass flow was x then we added 2.5kg each time. so to find to the flow q i do x (unknow mass) /time. I know have two unknow variables x and cd, where cd isnt constant. so i cant equate two readings. is cd was constant then u could.

    2. Relevant equations
    q= cd 2/3 b root (2g) x h^(3/2)

    3. The attempt at a solution

    ive given up
  2. jcsd
  3. Oct 15, 2008 #2


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    Are not coefficients constants?
  4. Oct 16, 2008 #3
    i got it now, the coefficients aren't constant. the coefficient for the rectanglular flow is cd=0.611 +h/z. so i can get the mass. and for the triangular weir cd is 0.58. but because my results are wrong. i cant sub these values into the equation to get the original flow, then the mass.
  5. Oct 16, 2008 #4


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    It's been a long time since I worked these kinds of problems. From my old text it mentions that (note K=cd):
    Essentials of Engineering Fluid Mechanics by Reuben M. Olson
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