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Weir flow

by sharp910sh
Tags: flow, weir
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sharp910sh
#1
Oct14-08, 03:35 PM
P: 8
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
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dlgoff
#2
Oct15-08, 06:01 PM
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P: 2,701
Are not coefficients constants?
sharp910sh
#3
Oct16-08, 02:33 AM
P: 8
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.

dlgoff
#4
Oct16-08, 06:17 PM
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P: 2,701
Weir flow

It's been a long time since I worked these kinds of problems. From my old text it mentions that (note K=cd):
Numerous values for K (or a similar coefficient) have been published in hydraulic liteature, and a rational analysis by von Mises indicated K to have the form
K=0.611 + 0.075 H/Z
Essentials of Engineering Fluid Mechanics by Reuben M. Olson


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