8/2/2019 Study of a rectangular notch

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Name of the experiment: Study of a rectangular notch.

Objectives:

1. To calculate Qt and Qa.2.

To find mean co-efficient of discharge.

3. To plot Qa vs H3/2 in a graph.4. To calculate Cd from graph.5. To plot Qa vs H.6. To plot Cd vs H.

Apparatus: bucket, stop watch, meter scale, slide calipers, rectangular notch, hydraulic bench.

Theory:

an expression for the theoretical discharge can be derived by

Qt = 2/3 LH3/2

But actual discharge is not the same as the theoretical discharge. The expression for the

theoretical discharge is Qa=2/3Cd LH3/2

We can find actual discharge from the experiment by

Qa = Q/t

Co-efficient of discharge

Cd = Qa/Qt

Procedure:

1. The length of the notch was measured.2. Supply valve is opened. The crest level is determined when the discharge passing over

the crest is reduced and the water just touches the crest.

3. The discharge is increased by regulating the supply valve. When the discharge becomesteady measured the head over the crest.

4. The initial water level of the measuring tank is taken and started the stop watch. Recordthe rise in water level for a suitable time period.

5. Further increase the discharge and repeat step 3 and 4.

8/2/2019 Study of a rectangular notch

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Observation:

Obsno:

DischargeQ c.c

t sec Qa=Q/t

m3/s

Initialh1

mm

Finalh2

mm

H=(h1-h2)

m

H3/2

Qt Cd=Qa/Qt

MeanCd

1 420 1.43 2.9410-4 100 69 0.031 5.4610

-3 4.8410

-4 0.61

2 400 1.8 2.22

10-4

100 75 0.025 3.95

10-3

3.50

10-4

0.63

3 410 2.27 1.81

10-4

100 80 0.020 2.83

10-3

2.51

10-4

0.72 0.69

4 390 3.00 1.3

10-4

100 84 0.016 2.02

10-3

1.79

10-4

0.73

5 402 4.02 1

10-4

100 87 0.013 1.48

10-3

1.31

10-4

0.76

Calculation:

L=30mm

Qt1= 2/3 LH3/2 = 4.8410-4 m3/s

Qt2= 2/3 LH3/2 = 3.5010-4 m3/s

Qt3= 2/3 LH3/2 = 2.5110-4 m3/s

Qt4 = 2/3 LH3/2

= 1.7910-4

m3

/s

Qt5 = 2/3 LH3/2 = 1.3110-4 m3/s

Precaution:

1. The flow must be steady.2. The over head tank must be kept full. Alternatively, a pump can be used for supplying

water to the tank.

3. Special care must be taken when measuring the crest level. 4. A large measuring tank for collecting water must be used.

Discussion: