Practical guide
Fluids Mechanics III
Module Code (FMAPRA3)
Department of Mechanical and Industrial
Engineering
Compiled by Mr. S Nginda
IMPORTANT INFORMATION:
This practical guide contains important information
about your practical
FMAPRA3
1. EXECUTION OF THE EXPERIMENTS
Each experiment presented in this practical guide is performed according the
schedule provided. The order of performance of each experiment is followed
unless specified otherwise by the laboratory instructor. In order that the
laboratory session is conducted in the most meaningful manner possible, it is
imperative that each student read, study and understand the experiment to be
conducted prior to coming to the lab.
Students will be divided into groups to perform the experiment. Each group is
required to work together throughout the practical session. But, each student
must do his or her own analysis and compile individual report. Students must
come to the lab at their registered schedule.
An attendance register is circulated, and it is the responsibility of the student to
sign it at each lab session. The lab instructor is not expected to remember if the
student attended the practical session. Any student who arrives late (at the
discretion of the instructor) to the laboratory will be deducted 15% on the
laboratory report. Students arriving 30 minutes after the start of the
experiment is considered absent.
2. LABORATORY REPORT
Each student will submit a complete written report covering each experiment
performed. The report is to be individual own work. The report will be written
in the third person, past tense (for procedures executed, data taken, and results
obtained), and should be self-sufficient. In other words, the reader should not
need to consult the references in order to understand the report. Correct English
and spelling should be used. The reports are practice for writing technical
reports similar to those, which are required by engineers engaged in industry
and engineering practices.
The report must be typed using a word processor. All pages, equation, figures,
graphs and tables must be numbered. Figures, tables and graphs must have
titles. Thy must be neat and clear.
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3. SPECIFICATIONS
In order to observe the accepted rules of good writing form, the following
specifications for the general makeup of the report are required:
1.
2.
3.
4.
5.
Use A4 white paper.
Write the report with a word processor.
Consistent fonts and presentation for every section of the report.
Use one side of the paper only.
Create all drawings and figures using computer drawing and plotting
programs. Scanned images are allowed where appropriate.
6. Use the same font font style on drawings and graphs as used in the text.
Graphs axes should be clearly labelled, including units where appropriate.
4. REPORT OUTLINE
1. Title page: must include lab title, date performed, student names,
student number and submitting date.
2. Aim of the practical: state the objective clearly.
3. Apparatus: draw the apparatus used and clearly label it.
4. Procedure: write the procedure in your own words. And it must be
written in the third person, past tense. Note that it is unacceptable to
simply use or copy the procedural instruction from the practical
guide.
5. Data sheet: tabulate the experimental data.
6. Results: answer all questions posed in practical guide. All observed and
calculated data should be tabulated when possible. Heading and
subheadings identifying items of data or sets of data should be used
a) Sample calculations: show a sample of a complete calculation.
b) Graphs: plot graphs using word processor with all the titles.
7. Discussion and conclusion: most important section of the entire
report. It should be a complete discussion of the results obtained. Part
of this discussion should deal with the accuracy of the results.
8. References: publication or other authorities which help explain the
experiment, calculate results, explain errors, draw conclusion etc.,
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should be acknowledged. References should be arranged in
alphabetical order according to the last name of the author, or the last
name of the first-named author for papers with more than one author.
9. Appendices: materials that support the report but are not essential to
the reader’s understanding of it are included here.
5. SUBMISSION
Students must submit their report on or before the date stated on
MYUNISA. Students submitting late reports are not accepted resulting in
a zero mark for the practical.
6. CONTACT PERSON
Mr. S. Nginda
Telephone number: 011 471 3293
Email: nginds@unisa.ac.za
Contact Times
09H00 TO 14H00 (Monday to Friday.)
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EXPERIMENT 1
IMPACT OF JET
1. AIM
1.1 To investigate the impact and reaction force produced by a jet of fluid
against a surface.
2. APPARATUS
Diameter of the nozzle is 6mm.
Distance to target:
Flat surface 20mm
Conical and hemispherical surface 37.7mm.
Angled surface 15mm
3. PROCEDURE
3.1 Preparation
Mount the apparatus on the hydraulic bench and connect a soft rubber or
plastic hose from the outlet of the test bench to the inlet of the apparatus.
3.3 Measurements
a. Remove the winged nuts on the top of the tank and take out the
removable lid. Screw any of the targets onto the end of the weight
holder. Replace the lid and tighten the winged nuts.
b. Note the position of the needle on the weight holder and place 50g on
to the weight holder.
c. Start the pump and slowly open the inlet until the jet of water from the
orifice just starts to lift the weight holder.
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d. Install the overflow pipe supplied with hydraulic bench into the drain
plug of measurement basin of the bench. Record the time required to
collect 2l of water in the basin and calculate the flow rate.
e. Repeat steps b to d with increasing amount of weight on the weight
holder.
f. Repeat steps a to e with each of the different target surfaces.
3.4 CALCULATIONS
I.
Using the measure data, calculate the jet velocity and the impact
momentum for each set of target surface and flow rate data.
II.
Use the weight data for each set to calculate the reaction force R
exerted by the jet.
III.
Plot a graph of reaction force against impact momentum for each
target surface. Determine the slope of each graph and compere the
slope value with the theoretical values of 1, 0.2929,2 and cos2α for
the target surfaces.
Conical surface
The deflection angle is α = 450.
Hemispherical
The deflection angle is α = 1800.
Angled Surface
The deflection angle is α = 450 and 1350
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EXPERIMENT 2
FLOW THROUGH AN ORIFICE
1. AIM
To investigate and demonstrate the phenomena of fluid through an orifice.
2. APPARATUS
3. PROCEDURE
3.1 Preparation
a. Mount the apparatus on the hydraulic test bench and connect
a soft or plastic hose from the outlet of the bench to the inlet
of the apparatus.
b. Screw any of the orifices into the orifice holder. It is
recommended to start with the square edge orifice.
c. Close the outlet valve and close the inlet valve partially and
start the pump. Slowly open the inlet valve to allow water into
the tank until the level reaches the level of the outlet
overflow.
d. Adjust the level with the inlet and outlet valves so that water
just flows into the outlet. This level represents a head of
250mm.
3.2 Measurement of the jet exit velocity
I.
In this practical, the method of trajectory is used to determine
the velocity of the water jet. The water jet follows a parabolic
trajectory.
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Cv 
II.
Record the X coordinate on the coordinate grid where the
water jet first crosses an X gridline. Record the Y coordinate
of the jet at that point.
III.
Repeat step 1 at 20 mm intervals of the X coordinate.
IV.
Plot the Y coordinate against the X coordinate to obtain the
trajectory of the jet.
V.
Plot Y against the X coordinate and obtain the slope m of
the straight line. Calculate the coefficient of velocity from:
1
m2 h
Parabolic trajectory is related by:
v
g  x2
2 y
The actual velocity:
v act  Cv  2  g  h
The coefficient
of velocity:
Cv 
x2
4 y h
3.3 Measurement of discharge coefficient.
I.
To determine the discharge coefficient it is necessary to
measure the water flow rate from the orifice.
II.
Insert the supplied length of PVC pipe into the outlet of the
Standard Hydraulic Test bench, and allow water from the jet
to accumulate in the basin.
III.
Use a stopwatch and record the level of water in the basin at
time zero. Measure the time
elapsed to add 2 litres of
water to the basin. Calculate the flow rate from the volume
and elapsed time.
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IV.
Calculate the coefficient of discharge from Equation 6 and
from that result calculate the
coefficient of contraction
Cc.
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EXPERIMENT 3
ENERGY LOSSES IN BENDS AND FITTINGS
1. AIM
To measure pressure losses due to friction and turbulence when a fluid (water)
flows through bends and fittings.
2. APPARATUS
3. PROCEDURE
3.1 Preparation
a) Install the apparatus onto the hydraulic bench. Connect the
water outlet of the hydraulic bench to the inlet of the
apparatus with a soft rubber or plastic hose, using a hose
clamp.
b) Open the inlet and outlet valves very slightly and start the
pump.
c) Set the water flow rate through the rotameter at about 10l per
min.
d) Open the air vent and top bleed valves. Water will flow
through the manometer tubes and back to the basin through
the bleed valve. If all tubes are not filled, slowly increase flow
rate.
e) When there are no more air bubbles at the vent, close the air
vent valve and the top bleed valve.
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f) Close the inlet and outlet valves and Open the bottom bleed
valve and the air vent valve. Air will enter the tubes and the
water columns will decrease. When the lowest reading on the
scale is reached, close the air vent valve. The manometer is
now ready for measurement.
3.2 Measurements and calculations
To measure the pressure drop across the fittings on the bench, open the inlet
and outlet valves slowly to increase the flow rate until readings can be taken
from the scale for all manometer tubes.
I.
Record the height of the water column at each pressure tap.
II.
Slowly increase the flow rate and repeat step I.
III.
Repeat step I and II at different flow rate until the level in the
first manometer tube reaches the maximum reading.
IV.
Calculate the pressure difference across each bend, fitting and
expansion/ contraction for each flow rate value from:
V.
For each resistance element, plot the pressure difference
against the square of the flow velocity and determine the K
factor from the graph inside diameter of all fittings on the
apparatus is 20 mm. compare K factors against those listed in
table below.
VI.
Use the measured pressure drop values and the flow rate to
calculate the K factor for the fittings under test. Compare the K
values with the approximate values in table below.
P1 – P2 =   g  h
Where: P1 = pressure upstream of the element
P2 = pressure downstream of the element
P1 – P2 = pressure difference
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g = gravity acceleration
h = height difference (m)
Fitting
K factor
900 long radius elbow
0.6 – 0.8
450 elbow
0.3
450 T piece
0.375
900 square elbow
1.2
900 square T piece
1.2 – 1.8
Pressure loss also occurs when flow is forced through a sudden expansion or
a sudden contraction in the flow area. In this case, the K factor depends on
the area ratio of the pipe before and after the change. Typical K values for
sudden expansion/ contraction ratios are shown in the table below.
The expansion pipe is 30mm
Area ratio of expansion/ contraction K factor
0
0.5
0.04
0.45
0.16
0.38
0.36
0.28
0.64
0.14
1.0
0
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