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EXPT.No.7-C 1
HYDHYDRAULICS LABORATORY
Experiment No.7-CDetermination of the Coefficient of Discharge
over a Triangular Weir
Triangular or V-notch weirs are the most accurate open channel constrictions formeasuring discharge. The discharge of a V-notch weir increases more rapidly with thehead than in the case of a horizontal crested weir (rectangular or trapezoidal), so for thesame maximum capacity, it can measure much smaller discharges, compared to arectangular weir.
The general equation to compute the theoretical discharge in a v-notch weir includingeffect of approach;
()
where: - interior angle of the weirH - head over the weirQ - discharge
To calculate the actual discharge we introduce a coefficient of discharge, Cd, which
accounts for losses at the edges of the weir and contractions in the area of flow, giving:
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EXPT.No.7-C 2
HYDHYDRAULICS LABORATORY
I. Experiment Objectives
- To observed the characteristics of open-channel flow over a triangular weir.- To determine value of the discharge coefficient for triangular weir.
II. Materials and Apparatuses Required
The apparatuses necessary to perform this experiment are the following:
- Tilting Flume Apparatus- Calibrated Bucket- Stopwatch- Metric Scale- Triangular Weir
III. Procedures
a) Attach the triangular weir to the channel (Flume).b) Measure the interior angle of the triangular weir.c) Turn on the pump and open the control valve until water discharges over the
weir.d) Regulate the flow to maintain a water level in the flow channel so that the weir is
filled to the highest possible level without overflowing the channel.e) Allow a steady flow to develop throughout the entire circuit.f) Measure the height of the water level above the top of the weir as an H to start
the analysis.g) Measure the flow rate with a stopwatch and calibrated bucket.h) For each set of measurements, measure the flow rate at least three times and
take the average.i) Reduce the approach, repeat step e to step h by using different flow rate of
water, which can be done by adjusting the water supply. Measure and record theH and the time to fill a certain volume of water in the bucket.
j) Compute for the theoretical discharge using the equation;
()
k) Calculate the actual discharge by volumetric method using the formula;
l) Determine the coefficient of discharge of a v-notch weir:
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EXPT.No.7-C 3
HYDHYDRAULICS LABORATORY
IV. Laboratory Data
TRIAL
ACTUAL DISCHARGE THEORETICAL DISCHARGECOEFFICIENT OF
DISCHARGEVOLUME
(m3)
TIME
(sec)Qa H (m) Qt Cd Cd (AVERAGE)
1
2
3
COEFFICIENT OF DISCHARGE, Cd
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EXPT.No.7-C 4
HYDHYDRAULICS LABORATORY
V. Observations
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VI. Conclusions
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