Impact of a Jet

Date of Experiment: Report due date: Report submission date: Checked by:

Item/marks Format/10 Abstract and Introduction/10 Figures and Diagrams/15 Materials and Method/10 Results Discussions/45 References/10 Total

Impact of a Jet

Student Name: Mohd Kamarul Yusri Bin Yusof

Group Members: Nikki Hills, Baapu Seeraj, Lau Siang Yang, Chin Di Yuan

School of Engineering

Taylor’s University

Malaysia

7th November 2011

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Table of Content

Abstract 3

1.0 Introduction 3

2.0 Experiment Design 4

2.1 Materials 5

2.2Methods 5

2.3 Procedure 6

3.0 Result and Discussions 7-10

3.1 Table results from experiment 7-8

3.2 Graph of force on vane (N) against rate of delivery of momentum ṁuo (kgm/s2) 8

3.3 Discussions 9-12

4.0 Conclusions/ Recommendations 13

References 14

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Abstract

The impact of a jet experiment is used to investigate the force created by the impact of a jet

on vanes of different shapes. In the experiment, 3 different vanes consisting of a Flat Plate,

Conical Cup, and Hemispherical Cup are tested to 4 different flow rates. The distance

between the center of the jockey weight and the pivot are measured by using the principal

of moment of a force. The product of the clockwise force and the perpendicular distance

will equal the product of the anti clockwise force and its perpendicular distance. In a

whole, the hemispherical cup vane will have the largest force created by impact of the jet.

1.0 Introduction

Throughout the years, engineers have found many ways to use the force that can be

imparted by a jet of fluid on a surface diverting the flow. For example, firemen can make

use of the kinetic energy stored in a water jet to deliver water above the level in the nozzle

to extinguish fires in high-rise building. This enormous amount of kinetic energy produce

by water jets is also used in the industry for cutting metals and debarring. There’s a lot of

technological importance of the water jet that can be cited through its application. This

experiment aims at assessing the different forces exerted by the same water jet on a

different type of vanes. The experiment uses the principal of moment of force to help

measure the force of impact of the water jet by using the product of the clockwise force

and the perpendicular distance will equal the product of the anti clockwise force and its

perpendicular distance and thus the force can be determined. Besides that, the experiment

will help the students compared the results obtained from the experiment with the

theoretical calculations.

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2.0 Experiment Design

Aim: To measure the force generated by impact of the jet on vanes of different shapes and

to compare the results taken from the experiments with the theoretical calculations.

Figure 1. Jet Impact Apparatus

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2.1 Materials

A Jet Impact Apparatus is used for this experiment. In addition, a Volumetric Hydraulic

Bench is also used to investigate the forced generated by the jet of water on 3 different

shapes of vanes that is the Flat Plate, the Conical Cup and the Hemispherical Cup. Lastly, a

stopwatch and a thermometer is used to measure the time and temperature of water

respectively.

2.2 Methods

Measuring the distance of the jockey weight from its zero position (y) and the time taken

(t) for the water to fill up the tank up to 35l, 25l and 15l depending on the rate of water

flow are the method used in this experiment. The data obtained from the experiment is then

tabulated in the “table of results of experiment”. Next, a graph of force of vanes against

rate of delivery of momentum is then plot from the data given in the “table of results of

experiment”. The experimental graph and the theoretical calculations graph are then

compared. A conclusion can then be made through all the data given.

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2.3 Procedure

A flat plate vane is used by screwing it with the Retaining Screw that is located on the

top part of the Jet Impact Apparatus. The weigh beam is then balanced by adjusting the

position of the jockey weight until the tally reaches its balanced position. The jockey

weight is considered to be at its zero position. Water is then supplied through the bench

supply valve followed by switching on the water pump. The rate of water flow is then

increased to the maximum and the force of the water jet will shift the lever, which will

then be maintained, back to its balanced position by adjusting the jockey weight on the

weight beam. The new position of the jockey weight from the pivot to center of the jockey

weight is measured and recorded. Next, the outlet of the weighing tank is clogged and the

stopwatch is started almost simultaneously. The time taken for the water to fill up the

weighing tank at 35l, 25l, 15l, and 5l subject to the rate of water flow is recorded. The time

taken for the water to fill up the tank is taken again and the average of both recorded data

is obtained to reduce the error in the experiment. Next, 3 different position of the jockey

weight from the pivot to its center are then obtained and recorded by lowering the flow rate

of the water. The experiment is then repeated with the conical cup and the hemispherical

cup.

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3.0 Results and Discussions

3.1 Table of results of experiment

Table 1. The results of Jet Impact on Flat Plate Vane

Volume

(l)

Quantity

(kg)

t

(s)

y

(m)

m

(kg/s)

u

(m/s)

u!

(m/s)

muo

(N)

F

(N)

15 14.98 67 0.17 0.224 2.856 2.733 0.612 6.671

25 24.85 80 0.19 0.311 3.965 3.877 1.205 7.456

25 24.85 65 0.21 0.382 4.871 4.799 1.833 8.241

35 34.86 80 0.23 0.436 5.559 5.497 2.397 9.025

Table 2. The results of Jet Impact on Conical Plate Vane

Volume

(l)

Quantity

(kg)

t

(s)

y

(m)

m

(kg/s)

u

(m/s)

u!

(m/s)

muo

(N)

F

(N)

15 14.98 73 0.18 0.205 2.613 2.733 0.561 7.063

25 24.85 84 0.21 0.296 3.774 3.877 1.148 8.241

25 24.85 70 0.24 0.355 4.526 4.800 1.704 9.418

35 34.86 83 0.27 0.422 5.381 5.497 2.319 10.59

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Table 3. The results of Jet Impact on Hemispherical Vane

Volume

(l)

Quantity

(kg)

t

(s)

y

(m)

m

(kg/s)

u

(m/s)

u!

(m/s)

muo

(N)

F

(N)

15 14.98 82 0.18 0.183 2.333 2.181 0.399 7.063

25 24.85 85 0.22 0.292 3.723 3.629 1.059 8.633

25 24.85 66 0.26 0.377 4.806 4.734 1.785 10.21

35 34.86 81 0.30 0.431 5.495 5.432 2.341 11.77

3.2 Graph of force on vane (N) against the rate of delivery of

momentum muo (kgm/!2)

Figure 2. Graph of force vane (N) against the rate of delivery of momentum muo

(kgm/!2)

0  2  4  6  8  10  12  14  

0   0.5   1   1.5   2   2.5  

Force  on  vane  (N)    

Rate  of  Delivery  of  momentum  (kgm/s2)    

Graph  of  force  on  vane  (N)  against  the  rate  of  delivery  of  momentum  (kgm/s2)  

Flat  plate  

Conical  cup  

Hemispherical  cup  

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3.3 Discussions

Figure 3. Graph of force vane (N) against the rate of delivery of momentum muo

(kgm/!2) based on ideal results

The actual slope of the graph can be obtained by using the formula y!!y!X2!X!

Therefore,

For flat plate vane,

0.785/0.593: 1.323

For conical plate vane,

1.178/0.587: 2.006

For hemispherical cup vane,

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1.57/0.66: 2.38

To measure the deviation from real flow from ideal flow,

Actual value/ Ideal value

For flat plate vane,

1.323/1 x100% = 132%

For conical plate vane,

2.006/1.5 x 100% = 134%

For hemispherical vane,

2.38/2.00 x 100% = 119%

1. By adding a small plastics ball into the volume-measuring device the water level at the

indicator can be accurately obtained. Next, the tally and the weigh beam should be lowered

at eye level so that parallax error can be prevented when balancing the jet impact force.

The central part of the jockey weight should be clearly marked so that it is easier to obtain

an accurate distance between the position of center of jockey weight and pivot. Another

thing is allowing the water to fill up just before starting the stopwatch then compare it with

the volume filled up before starting the stopwatch can reduce the error caused by the

reaction time of the stopwatch. Finally, the accurateness of the experiment can be

improved by repeating the step a couple of times.

2. Moment: Force x Perpendicular Distance

Force: Mass x Acceleration

Therefore,

Moment: 0.6 x 9.81 x 0.17: 1.0

a) (0.6 + 0.001) x 9.81 x 0.17: 1.002

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1.002-1.000: 0.002

The difference is negligible because there is small difference.

b) 0.6 x 9.81 x (0.17 + 0.001): 1.006

1.006-1.000: 0.006

The difference is negligible because there is small difference.

3. A real jet has a velocity distribution maximum at the center and zero distribution at the

edge because of the viscosity of the fluid. No slip condition is occurred because of the

viscosity of the fluid. This is because the no slip condition will cause the fluid to have no

velocity relative to the boundary therefore will cause the real jet to have the zero

distribution at the edge. The opening nozzle of the jet is bigger than the walls of the nozzle

because of no slip condition only occurs at the surface around the walls of the nozzle. The

center of the jet has a maximum velocity; the average velocity of the jet will remain

unchanged, uo.

4. The speed of the jet nozzle is u=!/996.5 x 78.5 x 10-6

u=0.224/996.5 x 78.5 x 10-6 = 2.86 m/s

uo = (2.86)2- 0.687=2.73 m/s

When jet has 10% greater area,

78.5 x 110% = 86.4

u=2.54m/s

When jet is 10% slower at vane,

2.73 x 90% = 2.457

u= 2.54m/s

Therefore when the area of the jet is increase by 10% the jet will be 10% slower at the

vane. This can be concluded by the exit speed of the jet is both the same in both

calculations.

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5. When the cone and the hemisphere are faced on the opposite way, the ideal force would

be lower. This is because when both the cone and hemisphere are faced oppositely, there

would be a tip at the center of the vane thus there wills stagnation point at the center of the

vane streamline, which will cause the force to be lower. Momentum theory cannot predict

the actual result due to the theory does not take into account the no slip condition, the

water viscosity, friction between the air particles and lastly the energy that is loss due to

heating. It is only taken account of ideal flow when the momentum of the fluid is

conserved.

6. The water jet will go through the air before hitting the vane. The water molecules will

collide with the air particles causing friction between both molecules and particles. The air

friction will convert the potential energy of the water jet into heat because of friction.

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4.0 Conclusion/ Recommendations

In conclusion, the hemispherical cup vane generates the highest force of the impact of

the jet compared to conical cup vane and the flat plate vane as seen from Figure 2. The

graph on Figure 2 deduced that the force on vane (N) for hemispherical cup vane is the

highest when the rate of delivery of the momentum muo (kgm/s2) is max. The

complications faced during the experiment are the difficulty in obtaining the reading of the

volume on the weighing tank because of the Volumetric Hydraulic Bench is not well

maintained thus the volume-measuring device is foggy. In order to improve this

experiment, a small plastics ball should be put inside the volume-measuring device so that

the indication of water level is much more clear. Next, there is a time delay between the

clogging of the weighing tank and before the stopwatch is start. This can be solved by

filling up the whole weighing tank first and get the volume reading and start the stopwatch

right before the flushing of the water thus producing a much more accurate reading.

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References

1. Frederick Institute Of Technology, undated, Impact of a Jet, 8th November 2011,

http://staff.fit.ac.cy/eng.fm/classes/amee202/Fluids%20Lab%20Impact%20of%20a%20Jet.

pdf .

2. Volunteer State Community College, 14th June 2008, Density of Water (g/mL) vs.

Temperature(oC),8thNovember2011,

http://www2.volstate.edu/CHEM/Density_of_Water.htm.

3. Taylor’s School of Engineering, 2011/2012, Lab Handbook (Impact of Jet), 8th

November 2011.

4. Eric W.Weisstein, 1996-2007, No Slip Condition, 8th November 2011,

http://scienceworld.wolfram.com/physics/NoSlipCondition.html

5. Tom Benson, 11th July 2008, Mass Flow Rate, 8th November 2011,

http://www.grc.nasa.gov/WWW/k-12/airplane/mflow.html

6. R.C. Hibbeler, 2010,Engineering Statics Twelfth Edition, Moment (Chapter 4-Force

Resultant System), 8th November 2011.