JET IMPACT
FACULTY OF PETROLEUM AND RENEWABLE ENERGY ENGINEERING
UNIVERSITI TEKNOLOGI MALAYSIA
FLUID MECHANICS LABORATORY
TITLE OF EXPERIMENT
JET IMPACT (E3)
Name Bong Woei Shen (A13KP0021)
Kumaresan a/l Sinathurai (A13KP0038)
Ahmed Gamal Mahmoud Moteir (A12KE4016)
Group / Section2/Section 11
SupervisorAssociate Professor Issham bin Ismail
Date of Experiment 3 March 2014
Date of Submission9 March 2014
Marks obtained (%)
TECHNICIANS:
1. EN. MAHMOOD RASIDON
2. PN. ZAIMARHAMAH ZAINUDDIN
1.0Objective
The objective of this experiment is to measure the force exerted
by a fluid jet impinging upon a flat plate or a hemispherical
surface and to compare the results with the theoretical
values.2.0Introduction
Water jet from a small opening, with a high velocity, when
exerted on a surface of plate will produce force that gives power
to move a system. The principle of jet impact is the basis for the
understanding of liquid flow in turbines. This principle is used in
designing impulse turbines. In these turbines part of the fluid
energy is transformed into kinetic energy in a nozzle ( or a set of
nozzles) which issues a jet of fluid at high speed. The jet strikes
the moving blades, mounted on the turbine wheel, producing the
force required to drive it.3.0Theory
A jet of fluid when impinging upon a flat or a curved surface
generates a force due to change of momentum of the fluid according
to Newtons second law of motion. For example, when water of a
velocity is forced out from a jet nozzle with diameter d on a
plate, the rate of change of momentum produced and its magnitude is
the same with the force exerted on the surface of the plate to
support the water jet.
Force= Rate of momentum change of water jet
= (mass of fluid/time) x change of velocityThe force (F)
generated by a jet of water as it strikes depends on the shape of
the plate surface, e.g. flat plate or a curved (hemispherical)
surface.
Diagrams 1-2 show a jet of fluid issuing from a nozzle of
diameter d, and moving vertically upward with velocity v and
strikes a stationary surface. The jet is deflected by the vane
through an angle and the fluid leaves the vane with velocity vThe
force generated is
(1)
where,
Fth= Theoretical force exerted on the plate (Newton)
a= Cross-sectional area of nozzle (m2)
= Density of water (kg/m3)
Angle of water flow after impact on the plate surface
v= Velocity of water jet before impact on the plate surface
v= Velocity of water jet after impact on the plate surface
For flat plate (diagram 1) , = 90o, therefore cos = 0 , so
(2)
For hemispherical plate (diagram 2), = 180o, therefore cos = -1,
So
(3)4.0ApparatusThe apparatus consists of an upward discharging
jet surrounded by a clear Plexiglas tube
provided with levelling screws. The plate located directly over
the jet is mounted on a
stainless steel spindle, which passes through the top plate of
the apparatus. A weight pan
is mounted on the upper end of this spindle Water is supplied
from the lab faucet (supply
valve) to the inlet of the apparatus via a hose. Water flowing
through the nozzle strikes
the flat plate and deflects from the flat plate and falls to the
base of the clear Plexiglas
tube where it exit and drain in the sink.
5.0Experimental Procedure
Notice:-
The weight cannot be reentered to make up the total required
weight
1. Be sure the flat or hemispherical plates are fixed. (please
be careful, do not turn it too tight since it would be difficult to
open)
2. 700g was the standard weight for each plate apparatus.
Weights were put on the spring plat. Standard weight for both
plates must be similar.
3. Standard indicator was adjusted to be level with the position
of the plate containing the weight as standard mark. (zero velocity
of water, V = 0)
4. The water control valve was sure to be closed (clockwise).
Both switches of the pump were turn on and water control valve was
opened slowly (anticlockwise) until maximum.
5. The plate with standard weight height will increase above
standard mark. More weights were added until it returns to the
standard mark. The total maximum weight for the first reading of
the load is taken.
6. The valve of the water tank is closed (clockwise). Time
started to be taken as the volumes at 2 liter until it reached 7
liter. 5 liter of water was accumulated.
7. The total weight load was reduced; the plate will rise above
the standard mark. The flow of water jet was reduced slowly
(clockwise) until the plate apparatus returns to the standard mark
level. Step 6 was repeated. 8. Step 7 and 6 was repeated for next
readings until the last total weight load is the same with the
standard weight load
9. Control valve was closed (clockwise) and the pumps were
switched off after the experiment was finished. The equipments were
cleaned and dry.
6.0Experimental data and analysisWater density, = 1000
kg/m3Water velocity of the jet by the nozzle with diameter d = 5
mm
where
V= Water velocity (m/s)
Q= Volumetric flow rate of water
A= Area of nozzle with diameter d (m2)
Hence, the force measured is
RESULTS
Flat plateStandard Weight= 700 (g) Maximum Weight= 1300
(g)Weight
Load (Gram)Actual Weight
(Gram)Fmea(Newton)Time
(Second)Q
(L/S)V
(m/s)Fth(Newton)Log VLog FmeaPercentage of relative error
13006005.8914.380.34817.676.131.2470.77012.07
12005004.9016.160.30915.744.861.1970.6900.82
11004003.9218.710.26713.603.631.1340.5937.99
10003002.9421.310.23511.972.811.0780.4684.63
9002001.9628.100.1789.121.630.9600.29220.25
8001000.9842.780.1175.960.700.775-0.00940.00
70000-000000
Hemispherical plate Standard Weight= 700 (g) Maximum Weight=
1700 (g)Weight
Load (Gram)Actual Weight
(Gram)Fmea(Newton)Time
(Second)Q
(L/S)V
(m/s)Fth(Newton)Log VLog FmeaPercentage of relative error
170010009.8113.380.37419.0514.251.2800.99231.16
16009008.8314.30.35017.8312.481.2510.94629.25
15008007.8515.360.32616.6010.821.2200.89527.45
14007006.8716.660.30015.289.171.1840.83725.08
13006005.8917.560.28514.518.271.1620.77028.78
12005004.9119.470.25713.096.731.1170.69127.04
11004003.9221.750.23011.715.381.0690.59327.14
10003002.94323.150.21611.004.751.0410.46938.04
9002001.96225.700.1959.933.870.9970.29349.30
8001000.98128.630.1758.913.120.950-0.00868.56
70000-000000
Note: (1) Nozzle size, d = 5 mm(2) Actual Weight = Load Weight
Standard Weight
7.0 RESULT AND DISCUSSION
Calculation for each data for both flat and hemisphere plate is
same. Then we take the calculation for first data of each plate as
example.
For Flat Plate,Actual weight =Maximum weight (g) Standard weight
(g)
=1400 g - 800 g
=600 g
Fmeasured =weight (g) / (1000g/kg) x 9.81 m/s2
=(600/1000) kg x 9.81 m/s2
=5.886 N
Flow rate, Q =Volume (L)/Time (s)
=5 L/14.13 s
=0.35386 L/s
Velocity, v =(Q/1000)/A
=0.35386 L/s x 1 m3/103 L [(/4) x (5/1000)2] m2
=18.02179 m/s
Ftheory
=AV2
=1000 kg/m3 x [(/4) x (5/1000)2] m2 x (18.02179 m/s)2
=1000 kg/m3 x 0.00001963 m2 x 324.785 m2/s2
=6.3771 N
Log V
=log (18.02179)
=1.256Log Fmeasured =log (5.886)
=0.770Percentage of relative error, % = (Fmea Fth) / Fth x
100%
= (5.886 6.3771) / 6.3771 x 100%
= 7.70%
For Hemisphere Plate,Actual weight =Maximum weight (g) Standard
weight (g)
=1700 g - 800 g
=900 g
Fmeasured =weight (g) / (1000g/kg) x 9.81 m/s2
=(900/1000) kg x 9.81 m/s2
=8.829 N
Flow rate, Q =Volume (L) / Time (s)
=5L / 15.90s
=0.31447 L/s
Velocity, V =(Q/1000)/A
=0.31447 L/s x 1 m3/103 L [(/4) x (5/1000)2] m2
=16.01559 m/s
Ftheory
=2AV2
=2 x 1000 kg/m3 x [(/4) x (5/1000)2] m2 x (16.01559 m/s)2
=10.0727 N
Log V
=log (16.01559)
=1.205Log Fmeasured =log (8.829)
=0.946Percentage of relative error, % = (Fmea Fth) / Fth x
100%
= (8.829 10.0727) / 10.0727 x 100%
= 12.35%
A.Estimate the slope of the graph for each plate and compare
with the theoretical value as shown in eq. 1 and eq. 2,
respectively. Comment on the difference.The slope of the graph 1
for flat plate is a linear graph. By logging both side of the
theoretical equation for flat plate we are able to get:
=(av2 (1)
Log =Log (av2
=Log ( + Log a + Log v2
Log =2Log v + A
(2),
Where A is constant, A= Log ( + Log a
While the slope of graph 2 for hemispherical plate is also a
linear graph. By logging both side of the theoretical equation for
hemispherical plate we are able to get:
=2(av2 (1)
Log =Log 2(av2
=Log 2 + Log ( + Log a + Log v2
Log =2Log v + B
. (2)
Where B is constant, B= Log 2 + Log ( + Log a (The same goes to
.)The slope of Fmea on flat plate is 2.2718 while its Fth is
1.9977. The differences of slope is only 0.2741, and slightly
deviated from the theoretical value but still result can be
considered acceptable. The difference might be caused by the height
between the nozzle and the vane due to the change of vanes as all
vanes do not have equal heights. As for hemispherical plate, the
Fmea slope is 2.2989 while its Fth 1.9976. The difference is also
0.301 thus3 can be considered acceptable. The difference might be
cause by error such as bubbles present in the water can be a reason
to get inaccurate readings as well.A. Estimate the y-intercept
ratio of hemispherical to flat plate and compare with the
theoretical ratio, as deduced from eq. 1 and eq. 2. Comment on the
difference.
Y- Intercept ratio of hemispherical plate to flat plate
Ratio = -1.8142/-2.029 = 0.8236 (Fmean)Ratio= -1.4037/1.7044 =
0.8236 (Ftheory)The ratio of y-intercept of hemispherical to flat
plate for () is 0.8236 : 1 while the ratio of y-intercept of
hemispherical to flat plate for( is 0.8236 : 1. Both values for
gradient and y-intercept for both graphs are identical, thus the
result obtained is near to the theoretical value. So, the data that
we calculated and recorded can be considered acceptable. The
differences might be due to errors when taking the measurement and
might be due to systematic errors while handling experiment
apparatus.
B. Comparing the force exerted on the hemispherical vane with
the one on the flat plate, which one is greater? Why?Comparison of
force on both plates
Force exerted on both hemispherical plates and the flat plate
was totally different. Force exerted on hemispherical plate greater
than flat plate because it lies on the behaviour of water jet when
it strikes the flat surface. It forms a radial sheet which impinges
on the inner wall of the surrounding cylinder, and then divides,
some of the water flowing down the cylinder wall and the rest
flowing upwards. Although visibility is impaired by the spray which
is generated, it does seem that some water falls on to the top side
of the vane. This would have the effect of producing a small
momentum force in the downwards direction, so reducing the net
upwards force on the vane.1) Comparing the percentage of relative
error for the two plates as function of jet velocity. Comment on
the analysis. Can one deduce sources of error due to the shape of
the plates? Explain your reason. State other possible sources of
error.
Comparison of the percentage of relative error for the two
plates
Based on our data, the percentage of relative error for both
plates different, that is 7.70% for flat plate and 12.35% for
hemispherical plate. The percentage of error ranged from around
0.52% to around 31%. If we have less percentage relative error, so
it means jet velocity is more constant. Some of the percentages of
error are large due to several errors made during the experiment.
The shape of the plate can be as sources of error, because the
equation using the angle where the impact of the velocity from
water to the surface of the plate, so if the plate is not in
perfect shape , in case got incomplete sphere , the angle will be
different which will get a different force. Then possible source of
error could be is spring coil. The shape of coil must be in a
standard position which is straight. If not, the velocity that
applied by the water is not accurate. i. Briefly discuss factors
contributing to errors or inaccuracy in experimental data and
propose recommendation to improve the results.
While conducting the experiment several errors may have been
made which affected accuracy of our data. Firstly, parallax error
occurred when we were taking the reading of 5 L water in the water
tank and when we were synchronizing the height of weight with
standard height. Secondly, the control valve may not be open to
maximum. Thirdly, the time reading for increasing of 5 L water may
not be accurate. The contact angle between water and the plates
also may not be the same as stated in experimental procedure. The
spring that was used to balance the weights may not be able to be
compressed to its full potential
There are some precautionary steps that we must follow in order
to obtain data with high degree of accuracy.First of all,make sure
that all the apparatus is in good condition and do some repetition
in the experiment so that the reading will accurate and
precise.Secondly, always remember to open the control valve to its
maximum so steady flow rate of water can be achieved. Next, tally
the standard height carefully so that the weight height and the
standard height is equal. Parallax error can be avoided via placing
our eye position perpendicular to the meniscus of
water.Furthermore,the surfaces of plates also should be examined
before carrying the experiment to eliminate possibilities of defect
surfaces.The control valve should be handled carefully and slowly
to avoid disturbance in the water flow rate. The person who taking
the time reading should remained focus and alert while taking the
time do that better data can be obtained. 8.0 CONCLUSIONS
From our experiment, we found that the force produced by the jet
is directly proportional to the square of the velocity of water for
both flat plate and the hemisphere, F ( 2V The force produced by
the hemisphere plate is greater than the flat plate that is
approximately two-fold. This happen due to the structure of
hemisphere plate that curve, resulting fountain out of the water
jet nozzles experienced rate of change of momentum is higher
compared to flat plate structures. Surface area nozzle jet large
flow rates will slow the water. This will reduce water flow
velocity and lower the rate of change of momentum flow. With this,
the power produced will also be less. From question 5, the
relationship with the power nozzle diameter can be described as
follows:
Fth ( 9.0REFERENCES
Fluid Mechanics (Fundamental and Application) Second Edition in
SI Units
by Yunus A. Cengel and John M. Cimbala
Fundamental of Fluid Mechanics by Bruce R. Munson, Donald F.
Young, Theodore H. Okiishi10.0APPENDICES
Data table for graph of Log Fmea vs Log V
Flat plate
Log V Log Fmea
1.2560.77
1.20.691
1.1260.594
1.0650.469
1.0410.293
0.907-0.008
Hemispherical plate
Log V Log Fmea
1.2050.946
1.1830.895
1.1420.837
1.1150.77
1.0910.691
1.0450.594
1.0090.469
0.9170.293
0.782-0.008
Water jet
Water jet
Nozzle d
Nozzle d
Diagram 2 Hemispherical Surface
Diagram 1- Flat Surface
Water Volume Scale
Water Tank Valve
Pump Switch
Control Valve
Jet Impact Plate
Standard Indicator
Weight Mass
Plate Apparatus
Spring Coils
JET IMPACT
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