CIVL151 Fluid Mechanics
Lab 3 – Pipe Flow
Lab Manual
TA:
Xu Jie (Jessie)
E-mail:
xujiebox@ust.hk
Objective
To investigate the validity of Bernoulli’s equation as applied to the flow of water in a venturi
meter.
Related Concepts and Theories
1) Bernoulli’s Equation (Conservation of Energy)
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p1
2
v
p
v
 1  z1  2  2  z 2
 2g

2g
for ideal flow
2) Continuity Equation (Conservation of Mass)
v1 A1  v2 A2
for incompressible fluid
3) Energy Grade Line (total head) and Hydraulic Grade Line (piezometric head)
v2
EGL: 
z
 2g
p
HGL:
p

z
4) Reynolds Number
Reynolds Number (R) =
R < 2000
vD

Laminar Flow
2000 < R < 4000 Transition Flow
R > 4000
Turbulent Flow
Apparatus
Hydraulic bench, venturi meter, manometer tubes, total head probe (pitot tube), scaling board,
stop watch and thermometer
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Procedures
By using the adjustable feet, the apparatus is levelled on the hydraulic bench. After injecting
a small amount of wetting agent into the test section, the apparatus is connected to the bench,
ensuring that the test section has the 14o tapered duct converging in the direction of flow.
Carefully fill the apparatus manometer tubes with water to discharge all pockets of air from
the system and ensure all connecting pipes are free from air. Carefully adjust the inlet feed
and the flow control valves to the largest convenient difference between the highest and
lowest manometer levels. Note the scale reading of each manometer level, and make sure it is
in the measuring range of the scaling board.
Take at least three sets of readings of volume and time to find the flow rate using the
volumetric tank.
Insert the total head probe to position (1). For each position (1, 2, 3, 4, 5 and 6), record the
scale readings of piezometric head and total head.
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Repeat this for three different flow rates (fast, medium and slow).
Stop the inlet feed, drain off the apparatus, withdraw the total head probe, undo the couplings,
reverse the test sections and replace the couplings.
Repeat the above procedures.
Results and Calculations
For both the normal flow setup and the reversed flow setup:
1) Present the test results and calculations in a tabulated form, use g=9.81m/s2.
2) Calculate the theoretical flow rate (Qt) based on Bernoulli’s Equation and Continuity
Equation, compared with the measured flow rate (Qm), and calculate the discharge
coefficient (CD) for different test conditions.
3) Use the theoretical flow rate (Qt) to calculate the theoretical flow velocities (vt), calculate
the measured flow velocities (vm) using the measured flow rate (Qm), and calculate the
flow velocity (vb) from the measured total and piezometric heads based on Bernoulli’s
Equation. Plot the three flow velocities along the tube of different flow rates.
4) Plot the experimental EGLs and HGLs along the pipe of different flow rates.
5) Calculate the Reynolds number using the measured flow velocities (vm).
Discussions
Please discuss at least the following questions or issues (you may add more if you like):
1) State possible sources of error or inaccuracy in this experiment.
2) List out or suggest precautions that have been done or should be done in order to
minimise errors mentioned in part (1).
3) Discuss the validity of the Bernoulli’s equation in this experiment.
4) Compare the theoretical and experimental results, and discuss the reasons for these
discrepancies.
5) Describe the impact of reversing the venturi meter and explain why these occur.
6) Determine the flow type and describe the flow pattern.
Report Guidelines
1) Each sub-sub-group must write a report for the experiment.
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2) Reports should be submitted to the pigeon hole outside TA office (Rm2126) within 2
weeks after the day conducting experiment.
3) You are expected to include at least the following sections in your report:
a) Title page (with group number (e.g. 1A-G3C1), names and student numbers of
group members, and the date conducting experiment)
b) Introduction (e.g. What is this experiment about? What are the objectives of this
experiment? What have been done to achieve these objectives? Please state the
division of work in this section too.)
c) Background and Theories (Don’t just copy what you have in this manual. Please
elaborate and possibly derive the equations)
d) Apparatus
e) Procedures (in point form)
f) Results and Calculations
g) Discussions
h) Conclusion
i) References (if any)
4) Tentative marks allocation for the report:
Contents: 70% (25% for parts (b) to (e); 45% for parts (f) to (h))
Organisation, Format and Language: 30%
5) Reports must be typed and well-written. Poorly written reports will not be accepted.
6) Don’t copy reports from other groups. Zero marks will be given in case of plagiarism.
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