Finding Weir Flow with Unknown Variables

[sharp910sh]

Homework Statement

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 isn't constant. so i can't equate two readings. is cd was constant then u could.

Homework Equations

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

The Attempt at a Solution

ive given up

 

[dlgoff]

Are not coefficients constants?

 

[sharp910sh]

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 can't sub these values into the equation to get the original flow, then the mass.

 

[dlgoff]

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