10.Flow Over Weir

UNIVERSITI MALAYSIA PAHANG FACULTY OF CIVIL ENGINEERING AND ENVIRONMENTAL HYDRAULIC & HYDROLOGY LABORATORY FLOW OVER WEIR SUBJECT CODE EXPERIMENT TITLE DATE OF EXPERIMENT GROUP NUMBER & SECTION GROUP MEMBER NAME & ID NUMBER

LECTURER/PERSON IN CHARGE MARKS

REMARKS

DAA 3911 FLOW OVER WEIR 10/01/2011 GROUP 11 SECTION 25 & 26 AHMAD MUSTAQIM BIN MOHAMED RADZI 1. RAZIN BARWIN BINTI ABDUL SAMAD 2. MOHD.AIZAD BIN JOHARI 3. AMIRUDDIN BIN ROZLAN 4. MOHD ZAHARIN BIN TARUDIN 5. YANG WENBIAO 6.

AA09194 AA09195 AA09197 AA09198 AA10183 AA09202

ENDORESMENT

TABLE OF CONTENT Title

Page

1.

Introduction

2

2.

Principle

2-3

3.

Objective

3

4.

Apparatus

3

5.

Procedure

4

6.

Result

5-7

7.

Discussion/Analysis

8

8.

Conclusion

9-10

9.

References & Appendices

11

2

INTRODUCTION As the depth of flow above the base of a notch is related to the volume flow rate through it, the notch forms a useful flow measurement device. The classical results for flow over notches are obtained by application of the Bernoulli equation, from a point well upstream to a point just above the notch.

PRINCIPLE This approach requires a number of very substantial assumptions and it yields the following results: For rectangular notch Q = 2/3 Cd b√2g h⅔ Where: Cd

= unloading coefficient

b

= width of the neckline or the width of the wier

h

= height of the load or the height of the water on the crest or wier threshold

For the V-shape weir Q = 8/15 Cd √2g tan θ/2 h5/2 Where: Cd

= unloading coefficient

θ/2

= the vertex semi-angle or the neckline

h

= the load height

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The coefficient Cd is required to accommodate the effects of the simplified assumptions in the theory. These can be rearranged to give: For rectangular notch: Cd =

3Q 2b √2g H3/2

For Vee notch: Cd =

3Q 8 tan θ/2√2g H5/2

OBJECTIVE i)

To determine the characteristics of open-channel flow over, a rectangular notch and then a triangular (Vee) notch

ii)

To determine the values of the discharge coefficient, Cd for both notches

APPARATUS i)

Set of flow over weir apparatus

ii)

Hydraulic Bench

iii)

Stop watch

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PROCEDURE

Put the weir into the Hydraulic Bench, and then adjust the hook right to the bottom of the weir.

Set and immobilize the nonius of the caliber to zero

Then, flow the water to the channel until it unloads through the weir

Adjust the flow of the water and stabilize it. Next, point the hook until the edge of its touch the water surface and take a reading of the nonius

Let the water flow and measure the value of the load height using the scale in the volumetric tank and the chronometer

Repeat above procedure but with different height of water

The same procedure are done to rectangular and vee weir

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RESULT Rectangular Weir Volume

Time

Flow

Height

Log

Log

m3

s

m

Q

h

0.005

5.8

m3/s(Q) 0.00086

0.056

-3.0645

-1.2518

0.0302

0.005

6.1

0.051

-3.0862

-1.2924

0.0287

0.005

9.2

0.043

-3.2652

-1.3665

0.0190

0.005

10.1

0.038

-3.3054

-1.4202

0.0173

0.005

21.1

0.029

-3.6253

-1.5376

0.0083

Cd

2 0.00082 0 0.00054 3 0.00049 5 0.00023 7

Cd

Q theoretical 0.001162 0.001105 0.000732 0.000666 0.000319

Vee Weir Volume

Time

Flow

Height

Log

Log

m3

s

m

Q

h

0.005

16.9

m3/s(Q) 0.000295

0.035

-3.5289

-1.4559

0.005

14.8

0.033

-3.4713

-1.4814

0.005

16.5

0.031

-3.5186

-1.5086

0.005

22.7

0.025

-3.6570

-1.6021

0.005

52.2

0.020

-4.0186

-1.6990

9 0.000337 8 0.000303 0 0.000220 3 0.000095 8

6

Q theoretical

0.00140 0 0.00159 9 0.00143 4 0.00104 3 0.00045 3

0.0000592 0.0000676 0.0000606 0.0000441 0.0000191

CALCULATION Q = AV For rectangular weir:

For vee weir:

A = bh

A = (½) bh X 2

b = 0.03m

b = 0.08m

h = 0.082m

h = 0.04m

= 0.00246m3

= 0.0032 m3

Example: For rectangular notch: Cd =

3Q

.

2b √2g H3/2 =

3(0.000862) 2(0.03) (√2 x 9.81) (0.082) 3/2

= 0.0302

For Vee notch: Cd =

3Q 8 tan θ/2√2g H5/2

=

3(0.0002959) 8 tan 90/2√2 x 9.81 x (0.04) 5/2

= 0.001400

For rectangular notch: 7

Q = 2/3 Cd b √ 2 g h 2/3 = 2/3 (0.0302) (0.03) √ 2 (9.81) (0.082) 2/3 = 0.001162 m3/s

For Vee notch: Q = 8/15 Cd√ 2 g tan ǿ/2 h 5/2 = 8/15 (0.001400) √ 2 (9.81) tan 90/2 (0.04)5/2 = 0.0000592 m3/s

DISCUSSION/ANALYSIS 8

The experiment objective is to establish the relationship between head over the weir and discharge for a sharp crested weir. In this experiment, we can prove the objective. The head over weir directly relation with the discharge of water. If the head over the weir is high, the discharges of water also increase. If the specific energy increases, the discharge also increases. It’s maybe because when the discharge of water is high, the water friction at the sharp crested weir is high and that why the head of over weir is also high. A uniform flow may theoretically be steady or unsteady, depending on whether or not the depth changes with time. An open channel is conduit in which water flows with a free surface. The classification of open channel flow is made according to the change in flow respect to time and space. Open channel flow is uniform if the depth of flow is the same at every section of the channel. A uniform flow may theoretically be steady or unsteady, depending on whether or not the depth changes with time. The establishment of unsteady uniform flow requires that the water surface fluctuate with time while remaining parallel to the channel bottom. Since it is impossible for this condition to occur within a channel, steady uniform flows are the fundamental type of flow treated in open channel hydraulics.

CONCLUSION 9

For the overall experiment we do this experiment well and most achieve the objective this experiment. From our results, the value of the theoretical and experiment is have a different. Form overall results we get, the value of theory is more than experiment value. But we feel so good cause achieve the objective this test (determine the value of the discharge coefficient and determine the characteristic of open-channel flow over) well. This experiment is very important to know the direction and also the flow rate of the water. This experiment also to known the head of the pressure at the high of head (always use in construction dam). This test also important to known the area around the damn can happen the flooding in several years.

1)90 ° V-Notch Weir - The 90 ° V-notch weir, in figure, is most accurate when measuring discharges of less than 500 gpm. The maximum discharge that can be accurately measured is approximately 5,000 gpm. The sides of the notch are inclined outwardly at 45 ° from the vertical.

2) Rectangular-Notch Weir - The rectangular-notch weir is illustrated in figure. This is the oldest type of weir now in use. Its simple construction makes it the most popular. The

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discharge equation for the rectangular-notch weir is gives discharge values for rectangular-weir notch lengths of up to 4 feet and depths of flow or head of up to 1.5 feet.

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REFERENCES & APPENDICES http://www.aquatext.com/calcs/weir%20flow.htm http://www.buffer.forestry.iastate.edu/Virtual_Risdal_Tour/Site_12/stop_12.htm http://www.cee.mtu.edu/~dwatkins/ce3600_labs/weir.pdf http://chl.erdc.usace.army.mil/chl.aspx?p=s&a=PUBLICATIONS!419 From books: •

Engineering Laboratory Manual: Hydraulic& Hydrology Laboratory: Flow Over Weir

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