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Unformatted text preview: ). Finally, the flow rate follows
from widechannel critical flow, Eq. (10.32):
1
3 3
gyc Broadcrested theory: q 2
3 V2
1
2g 2g H 3/2 (10.54) Again we may usually neglect the upstream velocity head V 2/(2g). The coefficient
1
1/ 3 0.577 is about right, but experimental data are preferred. Experimental Weir
Discharge Coefficients Theoretical weirflow formulas may be modified experimentally as follows. Eliminate
the numerical coefficients 2 and 2, for which there is much sentimental attachment
3
in the literature, and reduce the formula to
Qweir Cdb gH V2
1
2g 3/2 gH3/2 Cdb (10.55) where b is the crest width and Cd is a dimensionless, experimentally determined weir
discharge coefficient which may vary with the weir geometry, Reynolds number, and
Weber number. Many data for many different weirs have been reported in the literature, as detailed in Ref. 19.
An accurate ( 2 percent) composite correlation for wide ventilated sharp crests is
recommended as follows [19]:
Wide sharpcrested weir: Cd 0.564 0.0846 H
Y for H
Y 2 (10.56) The Reynolds numbers V1H/ for these data varied from 1 E4 to 2 E6, but the formula
should app...
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 Spring '08
 Sakar

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