Laboratory Experiment -Flow Over Weir PDF

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Summary

Laboratory Report 1 (Assessment 3 of 4).
Laboratory Practical Sheet
Experiment 1: Flow over a Rectangular Weir...

Description

School of Vocational Engineering, Health and Sciences Laboratory Report 1 (Assessment 3 of 4) Type of Assessment

Laboratory Experiment -Flow Over Weir

Course Title

Fluid Systems

RMIT Course Code

CIVE 1204

RMIT Program Code

Teacher’s Name (s)

Dr B. Richards

RMIT Group No.

Total Possible Marks

10

Marks Received

AD026

Group No: Student ID

Last name

First Name

1. Instructions to Students: 1. Follow Occupational Health & Safety (OHS) procedures and wear appropriate Personal Protective Equipment (PPE) while completing this assessment. 2.

3.

4. 5.

Students found in breach of assessment conditions can be charged with academic misconduct, have their results cancelled, be excluded from the program and receive other penalties. Penalties can also apply if a student’s assessment material is copied by others. Plagiarism is the presentation of the work, idea or creation of another person as though it is one’s own. It is a form of cheating and is a very serious academic offence that may lead to expulsion from the University. Plagiarised material can be drawn from, and presented in, written, graphic and visual form, including electronic data, and oral presentations. Plagiarism occurs when the origin of the material used is not appropriately cited. RMIT special consideration is to enable you to maintain your academic progress despite adverse circumstances. The process for special consideration can be found at http://www.rmit.edu.au/students/specialconsideration/online. Students with a disability or long-term medical or mental health condition can apply for adjustments to their study and assessment conditions (Reasonable Adjustments and Equitable Assessment Arrangements) by registering with the Disability Liaison Unit (DLU) at http://www1.rmit.edu.au/browse;ID=01daxmpd1vo4z. If you already registered with DLU and your study plan is approved, please inform your teacher if this assessment task is not adjusted in line with approved study plan.

Additional Instructions to Students: 1. Students are required to read and sign Safe Work Methods Statement (SWMS) form provided by the teacher before conducting the laboratory experiment. 2. Marks from this assessment will count towards 10% of the final grade.

Students’ Declaration: I have read and understood the instructions listed above. Students’ Signature:

1.

Date: 27/04/2021

CIVE1204 Laboratory Report

Fluid Systems Laboratory Practical Sheet Experiment 1: Flow over a Rectangular Weir

Contents Table of Figures ............................................................................................ 3 Introduction ................................................................................................... 4 Aim of Experiment ......................................................................................... 4 Equipment ..................................................................................................... 4 Background ................................................................................................... 5 Procedure...................................................................................................... 7 Results .......................................................................................................... 8 Data recorded ............................................................................................... 8 Computation of results .................................................................................. 8 Relationship between Log H and Log Q ....................................................... 9 Discussion ................................................................................................... 10 Conclusion .................................................................................................. 10 References .................................................................................................. 11 Virtual Laboratory Activity Information ........................................................ 11

CIVE1204 Laboratory Report

Table of Figures Figure 1. Lippe River, Weir. ............................................................ 4 Figure 2. Equipment used ............................................................... 5 Figure 2.1. Side view-Change in the shape of the NappeTop/Bottom contractions ................................................................. 5 Figure 3. Data recorded .................................................................. 8 Figure 3.1. Computation of results .................................................. 8

CIVE1204 Laboratory Report

Introduction

In the event of water streaming through an open channel flow, there can be barriers that limit and control the water. This barrier is known as a weir, where it acts as a channel that regulates the water flow and can increase or decrease the water intensity. Weirs are used worldwide, found in all environments that need water regulated or controlled. They can be found in rivers, drains, dams, lakes, reservoirs, and ponds. In smaller scaled scenarios, weir are called notches. Figure 1. Lippe River, Weir. https://damremoval.eu/portfolio/weir-1-lippe-river-germany/

Aim of Experiment The experiment was conducted to analyse and examine the notion of water flow over a rectangular weir. The objective by observing the functionality of the rectangular weir, the report aims to determine the value of the ‘Coefficient of Discharge’ for rectangular notch.

Equipment • • • • • • • • • • • • •

Hydraulic bench Rectangular notch Drain valve Point Gauge carrier Plunger Water splitter Screws Stopwatch Point gauge Stilling Baffle Delivery nozzle Rectangular notch Hydraulic bench

CIVE1204 Laboratory Report

Figure 2. Equipment used

Background The total theoretical flow rate(theoretical discharge-𝑄𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙) over a rectangular notch, may be determined using the following equation: Qtheoretical =

2 3

√2𝑔 𝑏𝐻 3/2

where; b= width of the notch, H= depth of water above the notch

Figure 2.1. Side view-Change in the shape of the Nappe-Top/Bottom contractions

CIVE1204 Laboratory Report

CIVE1204 Laboratory Report

Procedure 1. Prior to the commencement of the experiment; ensure all required personal projective equipment (PPE) has been used correctly. This ensures that the work environment is safe. 2. Proceed to then place the rectangular notch. 3. Secure the notch by using the screws. Then slide the stilling baffle in the slot. 4. Then observe and record the sill level. 5. Place the drainage valve in the hole. 6. Insert the water nozzle and then install the water splitter. The water splitter must be attached to the nozzle. 7. Start the pump and slowly open the inflow control valve, allowing the water level to steadily rise above the notch. 8. Position the vernier height gauge so that it sits in the centre of the rig. 9. Turn off the pump and close the inflow control valve until the water level exceeds the appropriate height (head over the crest is 0), also known as the datum. 10. As the water has reached the datum, record the height using the point gauge. 11. Place the point on the water's surface, only touching it, and record the height in the surface level segment using the point gauge. 12. Restart the pump and raise the inflow control valve. 13. Raise the drainage valve, so that the water level returns back to zero. 14. Turn off the drainage valve and use the stopwatch to time how long it takes for the water level to rise from zero to the appropriate level. The measurement instrument on the side of the rig can be used to check the water level. 15. Make sure the inflow control valve is turned off so that the required water level does not change 16. After the water level has reached the appropriate level, wait until it has stabilised, then use the point gauge to calculate the height and record it. 17. Repeat steps 9–13 for the remaining necessary water levels, keeping track of all times, volumes, and heights.

CIVE1204 Laboratory Report

Results

Data recorded Sill level (mm)

Surface level (mm)

Measuring Tank (l)

Time to fill seconds

115.5 115.5 115.5 115.5 115.5 115.5 115.5 115.5 115.5 115.5

56.5 61.5 66.5 71.5 76.5 81.5 86.5 91.5 96.5 101.5

35 35 25 25 15 15 15 5 5 5

38.25 45.29 34.81 44.61 30.84 39.73 45.82 21.31 25.47 52.71

Figure 3. Data recorded

Computation of results H = Sill – Surf level (m)

Flow rate Q x 10-3m3 / s

Log H

Log Q

0.059 0.054 0.049 0.044 0.039 0.034 0.029 0.024 0.019 0.014

0.915 0.73 0.718 0.560 0.486 0.378 0.327 0.235 0.196 0.095

-1.23 -1.27 -1.31 -1.36 -1.41 -1.47 -1.54 -1.62 -1.72 -1.85

-3.04 -3.11 -3.14 -3.25 -3.31 -3.42 -3.49 -3.63 -3.71 -4.02

Figure 3.1. Computation of results

CIVE1204 Laboratory Report

Relationship between Log H and Log Q Y = 1.50537x – 1.18707 -2

-1.8

-1.6

-1.4

Log H -1.2

-1

0 -0.8

-0.6

-0.4

-0.2

0 -0.5 -1 -1.5

-2.5

Log Q

-2

-3 -3.5 -4 -4.5

Figure 3.2. Relationship between Log H and Log Q

Observations ➢ The equation of best fit is y = 1.50537x – 1.18707. The line of best fit can be viewed in the plotted graph above in Figure 3.2. ➢ The y- intercept is -1.18707 ➢ The slope/gradient Is 1.50537 (n) ➢ log10k = −1.18707 ( log k = y-intercept )

Best line of fit −4−−1.18707 −1.85−0

= 1.53 ≈ 1.505

Determining Cd Using the equation;

2

( 3)(Cd)(√2(g))(b)

Width of the notch (b) = 0.03m 2 k = ( )(Cd)(√2(9.8))(0.03) 3 k = 0.088544(Cd ) Take log of 10 on both sides. 0.02925 = 0.088544(Cd) 𝐶𝑑 = 0.331 CIVE1204 Laboratory Report

Discussion The main goal of the experiment was to use the connection between the head of the notch and the discharge to calculate the coefficient of discharge for a rectangular weir. The experiment was repeated 12 times at various volumes to establish this. The data was recorded by repeating the experiment several times. In relation to Figure 3.1, the (H) was simply calculated by subtracting the Sill level from the surface level, and the (Q) flow rate was calculated using the formula Q=(V/T) *10-3. A graph with the line of best fit was generated using the data that was recorded, as shown in Figure 3.2. In addition, the gradient (n) was found to be 1.50537, and the y intercept was found to be -1.18707. This data was observed; analysing figure 3.2. In addition, the coefficient of discharge was determined using the formula and the above-mentioned values. Any potential causes of errors encountered during the experiment include operator error, equipment error, and failure to follow the steps carefully, all of which may lead to another error, which is why it is important to follow the appropriate steps. The most common type of error found was one caused by the operator, such as a slow reaction time. Using the stopwatch to record the time it takes for the water level to exceed the appropriate limit (start & stop) was an example of this that was discovered during the experiment. Another example is not reading the height from the Vernier Height Gauge to the exact measurement, which can be done with the operator at eye level. These errors must be minimised to allow for the most accurate reading, as removing them is incredibly difficult. These errors can affect the experiment's accuracy, resulting in incorrect results, so they should be held to a minimum.

Conclusion

In summary of the experiment, the objective of finding the relationship between the notch and coefficient of discharge was met. All procedures of this practise were followed and the results are final. This laboratory experiment was undertook virtually, consequently limiting the practical experience of the whole report. Ultimately, this makes it clear that the obtained findings and results would’ve be more sufficient if this experiment was acted upon properly (not virtual).

CIVE1204 Laboratory Report

References

➢ ➢ ➢ ➢ ➢

Dr. B Richards RMIT CANVAS Lecture slides / Tutorials https://www.engineeringexcelspreadsheets.com/2011/05/ http://h-hydro.com/New_Site/my-microhydro-site/

Virtual Laboratory Activity Information 1. Watch the following laboratory activity demonstrations (a and b) a.) https://www.youtube.com/watch?v=l8kDN0E4x-k b.) https://www.youtube.com/watch?v=cNuI0SCWN0M You are expected to take notes and provide comments regarding differences and similarities observed during both demonstrations (e.g. instrumentation used, etc) I realised that the experiments were very similar in that they both had the same goal of determining the discharge coefficient. It was the measurement instruments that differed between the two experiments in terms of variations. A hook gauge was used in experiment A, while a point gauge was used in experiment B. Furthermore, in experiment A, a rectangular notch was used instead of a vnotch, while in experiment B, a v-notch was used. These were the only distinctions discovered. 2. Observe the Laboratory activity shown in the following video c.) https://www.youtube.com/watch?v=tHqyOoahl0g You are expected to take notes and provide comments on differences and similarities observed among the 3 demonstrations you have watched so far. In terms of measuring the coefficient of discharge, the target was the same in video C. In comparison to the others, the experiment C was certainly more informative and clarified much more clearly, so the reader has a good understanding of what is going on and how to conduct the experiment. In addition, the causes of error were addressed in experiment C; for example, they went through the types of errors that may have occurred within the experiment, such as a human error. Observe the Laboratory activities shown (a, b, and c) and reply to questions 3 and 4. a.) https://www.youtube.com/watch?v=lafyQ4itD8g b.) https://www.youtube.com/watch?v=RbJ69dp96Vs c.) https://www.youtube.com/watch?v=HGQM913rI10 CIVE1204 Laboratory Report

3.) Cite possible source of errors that may result using the rigs shown in the following videos denoted as a, b and c. a.) In experiment A, the gentleman failed to insure that the Vernier Height Gauge was positioned in the centre of the hydraulic bunch. Another mistake that may have happened was that the gentlemen did not get in eye-level with the height calculation, so he was looking at it at an angle, resulting in inaccurate measurements.. Another error is human error, as slow reaction time will affect the stopwatch's (start/stop) time when calculating the water level hitting a certain level. However, by repeating the experiment three times and taking the average of the results, this error was reduced to a minimum. b.) In experiment B, the lady failed to insure that the rectangular notch was safely screwed in, allowing water to seep through. The measurement may be incorrect if it is not firmly attached. Another mistake is human error, which can affect the (start/stop) time of the stopwatch when calculating the water level approaching a certain level. c.) It's clear from experiment C that the hydraulic bench wasn't of the highest standard. The hydraulic bench's base didn't seem to be level, which could have potentially led to inaccuracy in the results because the measurements wouldn't be accurate because the base wasn't level. Furthermore, since the volume of this hydraulic bench had to be measured manually rather than using the scale on the side, human error could have easily occurred while taking measurements. Another mistake that may have happened was the gentleman's failure to measure the bucket's height using the ruler at eye level. Another mistake that could occur is if the valve isn't completely clean, causing the flow to be disrupted and unsteady, affecting the (Cd) calculations. 4.) What type of measuring device is being used in the video denoted c. How is the actual discharge measured in video C? The piezometer was used in video C as a measurement instrument. The water is first stored in the 'collecting tank' to determine the actual discharge. The inside measurements of the collecting tank are then determined. The valve is then removed, allowing the tank's water level to increaseUsing the stopwatch, the time it takes for the water to reach the necessary amount is registered. The actual discharge can be measured based on the time it takes for the water level to reach the appropriate water level. 5.) Watch the following videos. Explain what you would have done differently and why. https://www.youtube.com/watch?v=_U1z1oaq3DQ b. https://www.youtube.com/watch?v=r29fl7_Ku8k a.) The gentlemen in this video was seen reading the value at an angle. I would have done it slightly differently, allowing for an eye level measurement to improve the accuracy of the reading. b.) Following the video, I would have placed perforated plates in the centre of the hydraulic bench, allowing for a steadier flow after the water passes through the holes, resulting in more precise measurement using the Vernier Height Gauge. Activity: Carry out some desktop research and explain whether the farmer is taking the H measurement correctly. The farmer is not correctly calculating the H value. Calculating the difference between the surface and sill levels is a good idea. However, if you want to determine the H value, you must measure the height of the water in the centre, or where the flow is relatively constant, so you can get a more precise height calculation. The farmer is taking the measurement at the crest, where the water dips a little, and the water is splashing everywhere, making it difficult to read the measurement accurately.

CIVE1204 Laboratory Report...