Faculty of civil engineering
Department of Civil Engineering
FLUID MECHANICS AND HYDRAULICS LAB (CE 354)
Name: Marwan Mohammad Al-Rababah
ID: 139518
Experiment № 3
Name of experiment: Impact of a jet.
Date of Submission: November 18th, 2021
Objectives:
The objective of this experiment is to investigate the reaction forces produced
by the change in momentum of a fluid flow when a jet of water strikes a flat
plate (90˚),120˚-plate or a hemispherical cup (180°) surface, and to compare
the results from this experiment with the computed forces by applying the
momentum equation.
Theory:
The velocity of the water (v) leaving the nozzle with the cross-sectional area
(A) can be calculated by:
v = Q/A
(1)
in which Q is the flow rate.
Applying the energy equation between the nozzle exit point and the surface of
the deflector shows that the magnitude of the flow velocity does not change as
the water flows around the deflector; only the direction of the flow changes.
Applying the momentum equation to a control volume encompassing the
deflected flow results in:
Fy = ρQv(cosϴ +1)
(2)
where:
Fy: force exerted by the deflector on the fluid
ρ: fluid density
ϴ: 180- α, where α a is the flow deflection angle
Examples of flow deflection angles for flat, 120˚-plate and hemispherical
deflectors. The first image shows a 90-degree flow deflection for a flat
deflector and the second image shows a 180-degree flow deflection for a
hemispherical deflector.
The figure below shows Examples of flow deflection angles for flat, 120˚-plate
and hemispherical deflectors
From equilibrium of forces in a vertical direction, Fy is balanced by the
applied weight on the weight pan, W (W = mg, where m is the applied mass),
i.e., Fy = W. Therefore:
W = ρQv(cosϴ +1)
(3)
Since Q = vA, this equation can be written as:
W = ρAv2(cosϴ +1)
(4)
procedure:
1. Uncover the transparent cylinder by removing the top plate through
releasing the knurled nuts and screw the flat plate onto the end of the shaft.
2. Connect the inlet tube to the quick-release connector on the bench.
3. Level the impact of jet apparatus by making the water bubble at the center
and then adjust the pointer level to coincide to datum drawn on the weight
pan (level gauge).
4. Ensure the weight shaft is free to move by oscillating it against the spring to
minimize the effect of friction.
5. Place a weight on the weight pan (start at 30-g), switch the pump on and
then allow flow rate to increase/decrease gradually by operating the control
valve on the bench until the weight pan returned to its original level gauge.
6. Measure the flow rate by recording the time required to collect a certain
amount of water in hydraulic bench tank.
7. Repeat with additional masses on the weight pan (Table 1).
8. After finishing with the flat plate, remove it and replace it with 120° plate
and repeat the above procedure for weights shown in Table 1, and
9. Finally, repeat the same procedure with the hemispherical plate and for
weights shown in Table 1.
10. Close the control valve and switch off the pump.
Data:
• Nozzle diameter, d = 8-mm
• Nozzle area, A = ∏/4 *d2 = ∏/4 *(8*10-3)2
=5.03*10-5
• Density of water, 𝜌 = 1000 kg/m3
• Collected Volume in the tank= 5 liters
=5*10-3 m3
Table 1:
Time
(Sec.)
39
33
30
28
25
22
20
19
41
38
32
29
26
23
21
19
43
37
33
29
25
23
22
20
Plate
Flat Plate
Weight
(g)
30
40
50
60
70
80
100
120
40
60
80
100
120
140
160
180
50
70
100
120
150
180
200
220
Hemispherical plate 120o-plate
Test
No.
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Calculations:
Table 2 :
Flowrate.
𝑄=
Test
No.
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
ꓯ
𝑡
(m3/sec)
Mass
flow
rate
𝑚° = 𝜌𝑤 𝑄
(kg/sec)
0.000128
0.000152
0.000167
0.000179
0.0002
0.000227
0.00025
0.000263
0.000122
0.000132
0.000156
0.000172
0.000192
0.000217
0.000238
0.000263
0.000116
0.000135
0.000152
0.000172
0.0002
0.000217
0.000227
0.00025
0.128
0.152
0.167
0.179
0.200
0.227
0.250
0.263
0.122
0.132
0.156
0.172
0.192
0.217
0.238
0.263
0.116
0.135
0.152
0.172
0.200
0.217
0.227
0.250
Nozzle Momentum Mass
inlet
force,
weight,
velocity,
RZ
=mg
𝑢𝑜
(N)
(N)
=
𝑄
𝐴𝑛𝑜𝑧𝑧𝑙𝑒
(m/sec)
2.419
2.859
3.145
3.369
3.774
4.288
4.717
4.965
2.301
2.483
2.948
3.253
3.628
4.102
4.492
4.965
2.194
2.550
2.859
3.253
3.774
4.102
4.288
4.717
0.310
0.433
0.524
0.602
0.755
0.975
1.179
1.307
0.421
0.490
0.691
0.841
1.047
1.338
1.604
1.960
0.510
0.689
0.866
1.122
1.509
1.783
1.949
2.358
0.294
0.392
0.491
0.589
0.687
0.785
0.981
1.177
0.392
0.589
0.785
0.981
1.177
1.373
1.570
1.766
0.491
0.687
0.981
1.177
1.472
1.766
1.962
2.158
Flat Plate
𝑹𝒁 = 𝒎𝒐 𝒖°
120o-plate
𝑹𝒁
= 𝟏. 𝟓 𝒎𝒐 𝒖°
Hemispherical
plate
𝑹𝒁 = 𝟐 𝒎𝒐 𝒖°
Discussion:
● the results would have been more accurate if the deflectors were closer to
the nozzle because this distance is theoretically neglected, but it affects the
results experimentally.
● An error shows in the readings due to instrument manufacturing, which is
called constant error, and due to human inaccuracy in measuring time and
water volume, which is called random error.
● The most significant error which caused the difference between theoretical
and experimental results is the random error