UNIVERSITI TEKNOLOGI MARAFAKULTI KEJURUTERAAN KIMIATHERMOFLUIDS LABORATORY(CGE 536)NAME: MOHD ZAIDI BIN MOHD RADZALI(2014678172) AMIRA BINTI KORMAIN(2014851022) NURULTHAQIFAH BINTI BAHARUM(2014870248) FARHAN HAIRI BIN KASIM(2014204678)EXPERIMENT: FLOW OVER WEIRSDATE PERFORMED: 10/04/2015SEMESTER: 3PROGRAMME/ CODE: EH243GROUP: 8

NoTitleAllocated Marks %Marks

1Abstract/ Summary5

2Introduction5

3Aims/ Objectives5

4Theory5

5Apparatus5

6Procedure10

7Result10

8Calculations10

9Discussion20

10Conclusions10

11Recommendations5

12References5

13Appendices5

TOTAL100

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TABLE OF CONTENTS

No.TitlePage No.

1.Abstract1

2.Introduction2

3.Objectives2

4.Theory2

5.Apparatus5

6.Procedure6

7.Results8

8.Sample Calculations12

9.Discussion14

10.Conclusion16

11.Recommendation16

12.References17

13.Appendices17

ABSTRACTThe experiment was conducted to observe the flow characteristics of a regular notch and v-notch and determine the discharge of fluid flow. The experiment started by levelling the weir apparatus on the hydraulic bench and the rectangular notch weir installed. The flow control was slowly opened until the water level is even with the crest of the weir and then allowed to stabilize. With a vernier gauge positioned, the water was channelled and adjusted to obtain head (H). After the water stabilized, head reading was taken for every increase of 1cm. The procedure was repeated for different flow rates. Then, the experiment was repeated for v-notch replacing the regular one. The v-notch was found to have higher flow rate compared to regular notch for the discharge coefficient. The Cd for regular notch is 0.9155 while Cd for v-notch is 2.869.

1.0 INTRODUCTIONWeirs are structures that consist of an obstacle such as a dam placed across the open channel with a specialty shaped opening, also known as notch1. The weirs will results the water level, or head, in dam to increase. As the water level increase, the flow rate over a weir also increases. The function of weirs is to measure the flow rates in open channels and rivers. When we use term weirs, sometimes we will refer to the whole complex structure and sometimes will refer to the notch only2. There are various types of weirs that used worldwide. The common weirs constructed are the rectangular notch, the triangular notch or v-notch and the broad-crested weirs. Weirs with sharp-crested usually has sharp edge and constructed from thin metal plates. Weirs with broad-crested has blunt edge and made of wide timber or concrete1. Rectangular notch and triangular or v-notch are often used in water supply, wastewater and sewage systems. For broad-crested notch, it can be observed in dam spillways where the broad-crested can be found under water surface of the stream. Other types of weirs that available are the trapezoidal (Cipolletti) weirs, Sutro (proportional) weirs and compound weirs1.

2.0 OBJECTIVESTo observe the flow characteristics over a rectangular notch and v-notch and to determine the discharge of the fluid flow.

3.0 THEORYIn this experiment, we are using two types of notch, rectangular notch and v-notch. The method of calculating the discharge coefficients of the fluid flow is different when using different type of notch.1) Rectangular notchA rectangular notch which is a thin metal plate with sharp edge is installed in a weir channel shown in figure below.

Figure 3.1: Rectangular notch

Where:Qt = volume flow rate (m/s)H = height above notch base (m)b = width of rectangular notch (m)Cd = the discharge coefficientg = gravity (9.81 m/s2)

The discharge from a rectangular notch will be considered less from theoretical analysis due to curvature effects. A coefficient of discharge, Cd, is therefore introduced so that

2) Triangular notch (v-notch)

Figure 3.2: Triangular notch

Where:Qt = volume flow rate (m3/s)H = height above notch base = v-notch angle Cd = the discharge coefficient

A discharge coefficient for v-notch is introduced, so that

V-notch is more reliable because at low flow rates, it get much more accurate measurement compared to rectangular notch.

4.0 APPARATUS

Figure 4.1: The Hydraulic Bench

Figure 4.2: The Upper Part of the Hydraulic Bench

Figure 4.3: Rectangular Notch and V-Notch

5.0 PROCEDURESGeneral Start-Up Procedures1. Make sure the hydraulic bench pump is securely connected.2. Ensure the collection tank drain valve is left open to allow discharge back into sump tank.3. Set up the flow over weirs apparatus on the hydraulic bench.4. Ensure thumb nuts are securing the rectangular notch weir plate is fully secured.Note: Weirs notch have sharp edges. Take safety precautions while installing and changing weirs notch.

General Shut-Down Procedures1. Shut hydraulic bench flow control valve and close water supply.2. Empty the residue water from channel and sump tank by ensuring the drain tank valve is left open.Experiment: Flow Characteristics over Weirs1. The weir apparatus is levelled on the hydraulic bench and the rectangular notch weir is installed.2. The hydraulic bench flow control is slowly opened to admit water to the channel until the water discharges over the weir plate. Ensure that the water level is even with the crest of the weir.3. The flow control valve is closed and the water level is allowed to stabilize.4. The Vernier Gauge is set to a datum reading using the top block. The gauge is positioned about half way between the notch plate and stilling plate.5. The water is admitted to the channel. The water flow is adjusted by using the hydraulic bench flow control valve to obtain heads (H).6. The water flow condition is waited to be stabilized, take heads reading in every increasing of about 1 cm.7. Step 4 and 5 is repeated for different flow rate.8. The readings of volume and time are taken using the volumetric tank to determine the flow rate.9. Repeat the experiment by replacing the notch with V-notch.10. The results are recorded in the tables.

6.0 RESULTSRectangular NotchVolume = 3L = 0.003 m3 B = 0.03 m

Height, H (m)Time (s)Average Time (s)Flowrate, Q (m3/s)Log HLog QQ2/3CdH/B

T1T2T3

0.0139363637.008.11 x 10-5-2.000-4.0911.874 x 10-30.91550.333

0.0218161717.001.76 x 10-4-1.699-3.7543.141 x 10-30.70250.667

0.038121210.672.81 x 10-4-1.523-3.5514.290 x 10-30.61051.000

0.046655.675.29 x 10-4-1.398-3.2776.541 x 10-30.74641.333

0.055544.336.93 x 10-4-1.301-3.1597.831 x 10-30.69971.667

0.063333.339.01 x 10-4-1.221-3.0459.329 x 10-30.69202.000

Figure 6.1: A graph of log Q against log H for rectangular notch

Figure 6.2: A graph of Q2/3 against H for rectangular notch

Figure 6.3: A graph of Q against H3/2 for rectangular notch

Figure 6.4: A graph of Cd against H for rectangular notch

V-NotchVolume = 3L = 0.003 m3

Height, H (m)Time (s)Average Time (s)Flowrate, Q (m3/s)Q2/5Cd

T1T2T3

0.01043464444.36.78 x 10-50.02152.869

0.02017151616.01.88 x 10-40.03231.406

0.0308898.333.60 x 10-40.04190.977

0.0404444.007.50 x 10-40.05620.992

0.0434343.678.18 x 10-40.05820.904

Figure 6.5: A graph of Q2/5 against H for V-notch

Figure 6.6: A graph of Q against H5/2 for V-notch

7.0 SAMPLE CALCULATIONS

Average time, T

Flowrate, Q

H/B

Coefficient of discharge, Cda. Rectangular Notch

b. V-notch

2.869

Based on graph Q against H3/2 for rectangular notch, the equation obtained is:y = 0.0002x 0.0001m = Cd x K = 0.0002Cd = 0.0002 K = 0.0002 w

= 2.258 x 10-3

Based on graph of Q against H5/2 for V-notch, the equation obtained is:y = 0.0002x 0.0002m = Cd x K = 0.0002Cd = 0.0002 K = 0.0002 H5/2 (tan )

= 8.466 x 10-5

8.0 DISCUSSIONSAll of the data are recorded in the results section. The coefficient of discharge, Cd, for both notch were calculated and determined. Graphs of Q versus H3/2 or H5/2, log Q against log H and Cd against H were all plotted. The coefficient of discharge, Cd, is an experimental correction factor which must be applied to the theoretical discharge value to obtain the actual discharge. Because real flows do not meet all the assumptions listed above, the actual flow will generally be less than the theoretically predicted flow.

Below is how we can obtain the value of Cd,

Based on the results obtained, the Cd for rectangular notch is 0.9155 and for V notch is 2.869. From dimensional analysis and experiments, the average value of Cd for a rectangular weir is 0.622, and the value of Cd for a V-notch weir 0.58 to 0.61.

For this experiment, the Cd value for both notch are not constant. Since Cd is not a constant, a functional relationship needed to be created:Qactual = a * HnWhere a and n are constants

In order to find the value of a and n, a power fit or trend line in Excel needed to be used.

Figure 8.1: A graph of Q against H3/2 for rectangular notch

Figure 8.2: A graph of Q against H5/2 for V-notchBased on both graphs above, the value of a and n for rectangular notch is 7 and 1.36999 respectively. As for V notch, the value of a is 7 and the value of n is 1.6219. The experiment did not produce the exact resuls as the theory maybe due to human careless mistakes. However, the coefficient of discharge can still be determined eventhough there is a slight difference between the theory.

9.0 CONCLUSIONSIn the nutshell, the objectives of the experiment to demonstrate the flow characteristics over rectangular notch and V-notch and the determination of the discharge coefficients are achieved. Through the experiment, the discharge coefficients are been able to determine. The V-notch has the higher flow rate compared to the rectangular notch even though at first the V-notch takes longer time. The discharged coefficients for both notches were obtained from the results and calculations where the Cd for rectangular notch is 0.9155 whilst the Cd for V-notch is 2.869. Due to some mistakes during conducting the experiment, the results produced may not be the exact results as the theory. On the contrary, the coefficient of the discharge can still be gained since there is only small difference between the experiment results and the theory.

10.0 RECOMMENDATIONS1. Ensure that the weir plate is tightly bolted onto the hydraulic bench to prevent water from leaking through and affect the reading.2. Let the water level stabilize for a minute after adjusting the flow rate because the it takes a while before the water reaches its supposed water level.3. Take a higher volume reading for calculating the flow rate especially higher ones to obtain more accurate results.4. Ensure that the vernier gauge rod is exactly at water surface level at the start before increasing the height to minimize errors.

11.0 REFERENCES1. Retrieved 14th April 2015 from http://www.engineeringtoolbox.com/weirs-flow-rate-d_592.html2. Retrieved 14th April 2015 from http://www.hubbardbrook.org/w6_tour/weir-stop/weirwork.htm3. Retrieved 14th April 2015 from www.codecogs.com4. Retrieved 14th April 2015 from saba.kntu.ac.ir5. Retrieved 14th April 2015 from www.cussons.myzen.co.uk6. Retrieved 14th April 2015 from www.efm.leeds.ac.uk

12.0 APPENDICES