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Unformatted text preview:  Textbook Table of Contents  Study Guide 10.7 Flow Measurement and Control by Weirs 689 1
≈H
3 h
H
2 V1 Nappe
Ventilation 1 Y Weir
(a) H
yc
V1
Weir Y L Fig. 10.16 Flow over wide, wellventilated weirs: (a) sharpcrested;
(b) broadcrested. (b) A very complete discussion of weirs, including other designs such as the polygonal
“Crump” weir and various contracting flumes, is given in the text by Ackers et al. [19].
See Prob. 10.122. Analysis of SharpCrested Weirs It is possible to analyze weir flow by inviscid potential theory with an unknown (but
solvable) free surface, as in Fig. P8.71. Here, however, we simply use onedimensionalflow theory plus dimensional analysis to develop suitable weir flowrate correlations.
A very early theoretical approach is credited to J. Weisbach in 1855. The velocity
head at any point 2 above the weir crest is assumed to equal the total head upstream;
i.e., Bernoulli’s equation is used with no losses:
V2
2
2g H h V2
1
2g H or V2(h) 2gh V2
1 where h is the vertical distance down to point 2, as shown in Fig. 10.16a. If we accept
for the moment, without...
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 Spring '08
 Sakar

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