Centrifugal Pump Full

MEM554 – Thermalfluids Lab Centrifugal Pump

TABLE OF CONTENTS

Page

Table of Contents ……………………………………………………………………………. 0

Title ……………………………………………………………………………………………….. 1

1. Objective ……….…………………………………………………………………………….. 1

2. Introduction ……………….………………………………………………………………. 1-2

3. Theoretical Background ………………………………………………………………. 3-5

4. Apparatus ……………………………………………………………………………………. 6-7

5. Experimental Procedure ……………………………………………………………… 8

6. Data and Results …………………………………………………………………………. 9-11

7. Sample Calculation ……………………………………………………………………… 12-13

8. Analysis Results …………………………………………………………………………… 14-15

9. Discussion …………………………………………………………………………………… 16-22

10. Conclusion ………………………………………………………………………………… 23-26

11. Appendix ………………………………………………………………………………….. 27

12. References ………………………………………………………………………………. 28

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TITLE : CENTRIFUGAL PUMP

1. OBJECTIVE

The objectives of this experiment are toobtain the performance characteristics of a centrifugal

pump at three different impeller speeds.

The performance characteristics of pump are:

Pressure (head) jump

Power requirement

Flow rate influence

Pump speed influence

2. INTRODUCTION

A pump is a device used to move gases, liquids, or slurries. A pump moves liquids or

gases from lower pressure to higher pressure, and overcomes this difference in pressure by

adding energy to the system (such as a water system). A gas pump is generally called a

compressor.The earliest pump was described by Archimedes in the 3rd century BC and is

known as the Archimedes screw pump. Pumps work by using mechanical forces to push the

material, either by physically lifting, or by the force of compression.

Pumps fall into three categories: positive displacement, kinetic (centrifugal), and jet. Their

names describe the method for moving water.

i. A positive displacement pump causes a fluid to move by trapping a fixed volume of

water and then forcing (displacement) that trapped volume into the receiving pipe.

Positive displacement pumps can be further classified as either rotary-type (for

example the rotary vane pump) or reciprocating-type (for example the diaphragm

pump).

ii. A centrifugal pump causes a fluid to move by transferring the kinetic (rotational)

energy from a motor (through an impeller) into water pressure (potential energy).

iii. A eductor-jet pump is special type of pump without moving parts that uses the kinetic

energy of a fluid to increase the pressure of a second fluid.

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A centrifugal pump is one of the simplest pieces of equipment. Its purpose is to convert

energy of an electric motor or engine into velocity or kinetic energy and then into pressure of

a fluid that is being pumped. The energy changes occur into two main parts of the pump, the

impeller and the volute. The impeller is the rotating part that converts driver energy into the

kinetic energy. The volute is the stationary part that converts the kinetic energy into pressure.

Liquid enters the pump suction and then the eye of the impeller. When the impeller rotates, it

spins the liquid sitting in the cavities between the vanes outward and imparts centrifugal

acceleration. As the liquid leaves the eye of the impeller a low pressure area is created at the

eye allowing more liquid to enter the pump inlet.

Centrifugal Pumps are classified into three general categories:

i. Radial Flow - a centrifugal pump in which the pressure is developed wholly by

centrifugal force.

ii. Mixed Flow - a centrifugal pump in which the pressure is developed partly by

centrifugal force and partly by the lift of the vanes of the impeller on the liquid.

iii. Axial Flow - a centrifugal pump in which the pressure is developed by the

propelling or lifting action of the vanes of the impeller on the liquid.

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3. THEORY:

One of the most common radial-flow turbo machines is the centrifugal pump. The

type of pump has two main components: an impelleer attached to a rotating shaft and a

stationary casing (or housing) enclosing the impeller. Schematic diagram of basic elements of

centrifugal pump is as shown below.

Figure 3.1: Basic Elements of a Centrifugal Pump

Energy is added to the fluid by the rotating blades, and both pressure and absolute velocity

are increased as the fluid dlows from the eye to the periphery of into the blades. The kinetic

energy is converted into further increase in pressure as the fluid flows from the impeller into

the casing enclosing the impeller.

Due to the general complexity of flow through a centrifugal pump, the actual

performance of the pump cannot be predicted on a completely theoretical basis. Actual pump

performance is determined experimentally through tests on the pump and the results are

presented as pump performance curves. Performance characteristics for a givenpump

geometry and operating speed are usually given in the form of plots of head rise, efficiency

and power versus flow rate (commonly referred as capacity). This information is most helpful

to the engineer responsible for incorporating pumps into a given pipe flow system.

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Discharge

Blade

Hub plate

Impeller

Casing, housing or volute

Inflow

Eye


Consider the experimental arrangement for determining the head rise (or pressure rise) gained

by a fluid flowing through a pump, as shown schematically below.

Figure 3.2: Experimental Arrangement for Pump Performance Characteristics

The pump head rise can be expressed using the energy equation as

h2 = ( p2−p1)/ ρg + ( z2−z1 ) + (V 22−V 1

2 ) / 2g (1)

Typically the differences in elevations and velocities (between inlet and outlet) are so small

so that

hp = ( p2−p1) / pg (2)

The power, Pf gained by the fluid is given by the equation

Pf = ρgQ hp (3)

The pump overall efficiency, η , is the ratio of power actually gained by the fluid to the shaft

power supplied W shaft as given by the equation

η = Pf / W shaft (4)

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Z2 – Z1

P1

P2


Where, W shaft the shaft power, is the product of the Torque applied to the shaft and the angular

velocity, ω.

W shaft = Tshaftω (5)

Where

ω = 2 πN60

Typical performance curve for the axial centrifugal pump of a given size operating at

constant speed is shown below:

Figure 3.3: Typical Performance Characteristics of an Axial Centrifugal Pump

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4. APPARATUS

The experimental set-up consists of:

I. Water-flow bench and centrifugal pump

II. Instrumentation for data acquisition consists of;

Instrument panel:

a) Speed Control to change pump speed. Pump speed can varied over

range of 0-3000 rpm.

b) Pump suction and delivery pressure.

c) Torque measurement.

Flow measurement using “V” notch weir

a) Flow rate in the system can be measured relating to the height of the

water seen in the glass to graph T1 (Appendix) and the reading off the

flow rate in liter per minute.

Speed measurement

a) Pump motor speed measurements are made using digital tachometer.

Figure 4.1 : Centrifugal Pump Apparatus

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Motor

Torque reading

Inlet pressure reading

Valves

Discharge pressure reading


Figure 4.2 : Water – flow bench

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5. PROCEDURE

Preliminaries

1. Students will be adequately supervised

2. Pump discharge and suction valves is turn to fully open and motor speed control is

turn to zero.

3. The electrical supply and motor drive switch is switch on. Motor control knob is

adjusted slowly to around half way position. Ensure that there are no leaks in the

system. All gauges etcis checked. The motor speed is reduced back to zero. The

apparatus is ready for testing.

Actual Experiment

1. Suction valve is opened and discharge valve is closed. Speed control is adjusted to

50% and maximum pump speed N1 is selected.

2. Discharge valve is fully open and allow water to circulate. The volume of flow is

indicated and suitable increments in flow are decided to give adequate sample points

(about 15 points between zero and maximum flow).

3. The discharge valve is closed (corresponding to no flow). Read all measurements

when the measured readings are ready.

4. Discharge valve is open slightly, to give the first increment in volume flow. Take the

measurements when readings are steady

5. Step 4 is repeated. The valve is fully open correspon to the final measurements.

6. The entire experiment is repeated at pump speed correspond to speed control position

of 75% and 100%.

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7. SAMPLE CALCULATION

Sample calculation:

Constants:

ρ = 1000 kg/m3

g = 9.81 m/s2

1 hp = 746 W

For N = 1439 rpm,

ω=2 πN60

ω=2 π (1439)

60

ω = 150.69 rad/s

For torque = 0.9 Nm

Shaft power,

Ẇshaft = Tshaft ω

= (0.9 Nm) (150.69 rad/s)

= 135.62 W

BHP = Ẇshaft ÷ 746 x 100

= 135.62 W ÷ 746

= 18.2 %

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For volume flow rate, Q = 46 L/min

Q = 46 L/min ÷ (1000 m3) (60s)

= 0.8 x 10-3 m3/s

Water head , h=( P2−P1)

ρg

= (55158.06 – 490.32) N/m2 ÷ (1000 kg/m3) (9.81 m/s2)

= 5.57 m

Output power=ρgQh

= (1000 kgm-3) (9.81 ms-2) (0.8 x 10-3 m3/s)( 5.57 m)

= 43.71 W

Efficiency ,η=Output powerẆ shaft

x 100

= (43.71 W) ÷ (135.62 W) x 100

= 32.2 %

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9. DISCUSSION

Nursyafawani Kasram Binti Mohd Hisham2014802024

From the experiment, characteristics of a centrifugal pump ran at different speeds (N1 = 1439

rpm, N2 = 2178 rpm and N3 = 2945 rpm) are observed and drawn in graphs. These

characteristics curves are essential in defining the properties of a pump, since only size and

shape cannot be sufficient to select a pump for certain purpose. Standard test were done

according to the procedures defined by the lab manual and characteristics curves are drawn as

shown in Figure 1, Figure 2 and Figure 3.

From the pump performance curves, it can be predicted that the maximum volume

flow rate through a pump occurs when its net head is zero, H = 0. This flow rate is called the

pump’s free delivery. The free delivery condition is achieved when there is no flow

restriction at the pump inlet or outlet or when there is no load on the pump. At this operating

point, Q is large, but H is zero and the pump’s efficiency is zero because the pump is doing

no useful work. At the other extreme, the shutoff head is the net head that occurs when the

volume flow rate is zero, Q = 0, and is achieved when the outlet port of the pump is blocked

off. Under this condition, H is large but Q is zero. The pump’s efficiency is again zero

because the pump is doing no useful work. Between these two extremes, from shutoff to free

delivery, the pump’s net head may increase from its shutoff value somewhat as the flow rate

increases, but H must eventually decrease to zero as the volume flow rate increases to its free

delivery value. The pump’s efficiency will reaches its maximum value somewhere between

the shutoff condition and the free delivery condition; this operating point of maximum

efficiency is appropriately called the best efficiency point (BEP).

For output power and volume flow rate obtained from the experiment, it can be seen

from Table 1 to Table 3 that the increased number of value in volume flow rate due to water

height is increasing in the matter of time. While for output power, there are inclined and

declined values can be seen from the tables. By comparing all these three speeds, it can be

said that the higher speed used in the experiment, the bigger number of output power will be

produced.

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The efficiency of the pump for each test increases to a certain point and then decreases as

shown in Figure 1 to Figure 3. This is because of the increasing frictional losses in the long

blade passages of these narrow impellers. Since impeller blade have finite thickness, an

impellers with too many blades leads to passage losses due to excessive flow and large skin

friction drag. Also, the efficiencies depend upon the design of the machine, shape of the blade

and, hence, the capacity handled. The value of the effectiveness of the experiment data is

increasing due to the increasing value of the speed. The higher value of efficiency will give

the better performance of the operated machine. To get the better efficiency, the rate of power

output and input must be bigger.

It can be concluded from the experiment that the pump with speed of N = 1439 rpm

has the best performance since its line of efficiency intersect both lines of head and BHP at

one point which is called the best efficiency point. It occurs at 0.19 m 3/s with the efficiency

of 28.5%. While, the other line of efficiency for N = 2178 rpm and also for N = 2945 rpm

only intersect with the line of head which it cannot produce the best efficiency point.

The error that may occur during the experiment is parallax error when taking the data

reading of water height and pressure value for inlet pressure. While adjusting the discharge

water pressure, the machine causes other apparatus, such as the discharge pipe to vibrate

extremely hard. This may be due to the material of pipe which it cannot absorb the vibration,

and a steel pipe is recommended in this situation.

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NUR HAEZAH BINTI OTHMAN2014444256

The main objective of this experiment is to obtain performance characteristics for a

variable speed centrifugal pump operating at 3 different impeller speeds. The performance

characteristics of pump are pressure (head) jump, power requirement, flow rate influence and

pump speed influence. Pump speed was adjusted to 3 variables that were 1439 rpm, 2178 rpm

and 2945 rpm. The performance characteristics of the pump that we want to find are pressure

head, power requirement, flow rate influence and pump speed influence.

For each test, as the water height increases, the torque (T) also increases. as the torque

increased, the brake horsepower also increased. For test 1, the graph showed that the water

head (h) decreased with increasing of volume flow rate while the output power increased at

the beginning and ending. For the graph efficiency (η) versus flow rate (Q), we get the

efficiency curve increasing until 34.7% and the drop until 20.6%. The max point at

approximately at value of 88 l/min where the maximum efficiency is 34.7% at water head

4.27 m and output power of 62.83 W.

For test 2, the graph efficiency (η) versus flow rate (Q) that we have plotted it follow

the same nature as the previous speed but the maximum efficiency is 45.0% at the flow rate

of 123 l/min. While in test 3, the graph efficiency (η) versus flow rate (Q) that we have

plotted it follow the same nature as the previous speed but the maximum efficiency is 50.9%

at the flow rate of 173 l/min. Error might occur during the experiment. The level of water

might not exactly at zero when the readings are taken. Other error that occurred during the

experiment is water in the tank always waving and not stable. So, it is hard for us to get the

accurate readings of the water height.

In order to overcome this problems, we must consider during the experiment that is:

1. The apparatus must be checked carefully to make sure it is in a good condition before

carrying the experiment because it may effects the results of the experiment.

2. The reading at the pump suction and delivery pressure gauges must be read with more

carefully to avoid any error.

3. The reading should be taken several times and the average value should be taken to

know the average reading that more accurate.

4. The eyes must sharp and perpendicular to the calibration scale of the water level.

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After the result was drawn into graph, we could see that efficiency increase first and

decrease later as flow rate increasing, break horse power was directly proportional to flow

rate and pump head was inversely proportional to flow rate. Efficiencies depend upon the size

of the machine and, hence, the capacity handled. The larger the machine, the higher is the

efficiency. However, the higher value of efficiency will gives the best performance of

operated machine. The rate of power output and input must be bigger in order to get the better

efficiency.

Based on this experiment, it can be concluded pump which its speed of N = 1439 rpm

has the best performance because it has resulted the intersection of its line of efficiency with

the line of head and break horse power(bhp). The intersection line at this one point is known

as the best efficiency point of the pump. It intersects at the flow rate of 0.19 m 3/s where the

efficiency of 28.5%. Meanwhile, both of the pump where its speed are N= 2178 rpm and N =

2945 rpm cannot produce the best efficiency point since the line of efficiency just only

intersects with the line of head.

The efficiency of the system can be increased by several ways. The examples are by

increasing clearances as impellers reduce in size, by using smoother surface finish of the

pump and tube, power supplied to drive the pump and by increasing the power supplied to

drive the pump.

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Muhammad Afiq Bin Kamil2013463544

This “Fluid Machinery-Centrifugal Pump” experiment is about to study about the

performance characteristics of the centrifugal pump with different impeller speeds. There are

4 performance characteristics of the centrifugal pump which are pressure (head) jump, power

requirement, flow rate influence and pump speed influence.

Based on the result obtained, the graphs of pump performance were plotted by

varying the 3 different impeller speeds. From graph 1 with impeller speed 50% (1439rpm),

the water head decrease when volume flow rate increase. Theoretically, if the total head at the

zero flow rate is the maximum head and also called the shut-off head, the total head decreases

as the flow increase. The trend of the graph BHP against volume flow rate showed the

increment. Theoretically, the trend of BHP should be decrease. There is some error during

conducting this experiment that influences the different between experimental result and the

theoretical. The relation between torque and BHP is donated by the equation (BHP=T x ω).

For the graph efficiency against volume flow rate, the efficiency increase as the flow rate

increase. After the efficiency reached the peak, the efficiency is slightly decreased as the flow

rate increase. The best efficiency point recorded is 34.7% which is correspond with BHP at

24.2 hp and head at 432.2 m.

From the graph 2 (speed at 2178 rpm) for the water head against volume flow rate, the

trend showed that the decrement of the water head as the volume flow rate decreased. The

graph of BHP was not satisfied according to the theory. Based on the graph of BHP against

flow rate, the BHP increased as the flow rate increased. The best efficiency point recorded is

44.8% which is correspond with BHP at 70.3 hp and head at 1144.8 m. By comparing the

efficiency between impeller speed 1439 rpm and 2178 rpm, the efficiency of impeller speed

2178 rpm is greater than the impeller speed 1439 rpm.

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From the graph 3 with impeller speed 2945 rpm, the head decreased as the volume

flow rate increased. The BHP also increased when the volume flow rate increased. The trend

of graph of pump efficiency against volume flow rate showed the increment and decrement.

The best efficiency point recorded is 51% which is correspond with BHP at 165.4 hp and

head at 2208m. By comparing the pump efficiency of the 3 different speeds, the impeller

speed with 2945 rpm showed the highest pump efficiency compared to others. We can say

that the efficiency increased as the impeller speeds increase.

There some errors influenced the result obtained from the experiment. Firstly, the

parallax error occurred when the observer taking the reading. Secondly, is the equipment

problem also influenced the result obtained.

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Mohamad Faiz Bin Mhd Noor2013413702

Centrifugal pumps are a sub-class of dynamic axisymmetric work-absorbing turbomachinery. Centrifugal pumps are used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. The rotational energy typically comes from an engine or electric motor.

From the experiment, characteristics of a centrifugal pump ran at different speeds (N1 = 1439 rpm, N2 = 2178 rpm and N3 = 2945 rpm) are observed and drawn in graphs. The graphs of pump performance were plotted by varying the 3 different impeller speeds. From graph 1 with impeller speed 50% (1439rpm), the water head decrease when volume flow rate increase. Theoretically, if the total head at the zero flow rate is the maximum head and also called the shut-off head, the total head decreases as the flow increase.

From the calculation of the result, we can see that as we increase the volume flow rate of the pump, the pressure of the pump will slightly decrease. Then, the efficiency and water head will increase. But, for the water head, it shows the decrease value. Each speed of the pump gives the different value of the result. Beside that we can know the efficiency of the pump sudden drop as the increasing of the volume flow rate. From the pump performance curves, it can be predicted that the maximum volume flow rate through a pump occurs when its net head is zero, H = 0. This flow rate is called the pump’s free delivery. The free delivery condition is achieved when there is no flow restriction at the pump inlet or outlet or when there is no load on the pump

From the Figure 1 which is the graph of Pump Performance Curves for N = 1439 rpm, it can be said that at this speed the pump has its best performance. This is because its line of efficiency intersect with both lines of head and BHP at one point. This point is called the best efficiency point. We make a straight line across this point to get the value and we found that its occur at 0.19 m3/s with the calculated efficiency is 28.5%. The other line of efficiency for N=2178 rpm and N=2945 rpm onlu intersect with line head so it cannot produce the best efficiency point

When we want to increase the efficiency of the system we must choose the backward-inclined blades centrifugal pump instead of radial blades or forward inclined blades centrifugal pump.

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There were some error occur while do the experiment and this affect the calculation result of the experiment. The error happen such as below:

- Parallax error o This error occur when the observer take the reading of the value for the

equipment in the experiment. o The wrong sight will little bit affect the reading of the experiment data.

- Equipment problemo The error of the equipment also affect the result of calculation and this will

make the error for the data later.

Some precaution must be take an action, there are:

- Make sure the observer eye is in the right way in order to take the reading of the data to avoid any error occur.

- Ensure that all the equipment in the good condition before start the experiment.- Make sure all the safety aspects have followed while do the experiment.

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10. CONCLUSION

Nursyafawani Kasram Binti Mohd Hisham2014802024

From the experiment, the characteristics of this pump which is the efficiency, brake

horsepower and the head can be defined by using three different speeds of pump. Based on

the graph obtained from the data result, it can be seen that the entire graph are incline at first

and then slowly it started to decline.

However, it is to be noted that some of the value of readings obtained may be

inaccurate due to certain errors that occurred during the experiment such as parallax error and

the error due to the apparatus itself. Yet it still leads and produced the expected results

accordingly and as required. Thus, the objective of this experiment is achieved in order to

define any centrifugal pump characteristics.

Last but not least, it can be concluded that the best performance of this centrifugal

pump to operate is at speed N1 = 1439 rpm since it produced the best efficiency point at 0.19

m3/s with the efficiency of 28.5%. While, when the pump was operated at the other two

speeds, it does not produce the best efficiency point.

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Nur Haezah Binti Othman2014444256

As a conclusion, the brake horse power, (bhp) and efficiency, η are rising with the

increasing of flow rate. Meanwhile, the head, H approximately constant at low discharge and

then drop as flow rate increases for a given speed and impeller size. The highest efficiency of

the pump is the best condition for the pump to operate. Thus, performance curves of the type

are very important to the engineer as possible for the selection of pumps for a particular flow

system. In order to select a pump for a particular application, it is necessary to utilize both the

system curve, as determined by the system equation, and the pump performance curve.

Besides, the horsepower required to drive the pump rises monotonically with the flow rate.

Lastly, we can said that the experiment is achieved its objective to obtain and analyze

the performance characteristic of a centrifugal pump operating at a given impeller speed since

it produced the best efficiency point at 0.19m3/s with the efficiency of 28.5% by centrifugal

pump speed of N= 1439 rpm

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Muhammad Afiq Bin Kamil2013463544

As the conclusion, the objective of “Fluid Machinery-Centrifugal Pump” experiment

which to investigate performance characteristics for the centrifugal pump by the 3 different

speeds was achieved. At the end of the experiment, we can find the best operating range of

the pump by observing the interception of the graph. The BHP of the pump for the all

impeller speeds should be decrease as the flow rate increase. The trend of efficiency curve is

influence by the friction loss by the pipe. It is important to choose the pump with higher

efficiency in order to operate the pump with the best condition. Thus, the performance curve

is important to the engineer to choose the pump with best efficiency. The pump with highest

efficiency will use less energy to operate the pump for a specific performance point. There

are several ways to overcome the errors of the experiment. Firstly, the position of the eyes

must be perpendicular to scale in order to avoid parallax error. Secondly, make sure that the

equipment used is well operated.

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Mohamad Faiz Bin Mhd Noor2013413702

As a conclusion, we can say that the objective of this experiment which to obtain

performance characteristics for a centrifugal pump of variable speed operating at 3 different

impeller speeds based on the pump characteristics included pressure (head) jump, power

requirement, flow rate influence and pump fluid influence had achieved. We also study that

all these characteristics will affect its efficiency. However, it is to be noted that, some of the

value of readings obtained may be inaccurate due to certain errors that occurred during the

experiment as the parallax error and equipment problem. The highest efficiency of the pump

is the best condition for the pump to operate.

This centrifugal pump will operate at its best performance is at speed N=1439 rpm. At

this speed it produced the best efficiency which is 28.5% at point 0.19 m3/s. While, when the

pump operate at other two different speed , it does not produce best efficiency point.

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11.0 APPENDIX

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12.0 REFERENCES

1. FLUID MECHANICS Fundamentals and Application, Yunus A. Cengel & John

M.Cimbala, McGraw Hill.

2. INTRODUCTION TO FLUID MECHANICS, Robert W. Fox, Alan McDonald, Second

Edition, John Wiley & Sons.

3. “Working of Centrifugal Pump”. http://www.learnengineering.org/2014/01/centrifugal-

hydraulic-pumps.html. (Retrieved on 23 October 2015)

4. “Centrifugal Pump Principles”. http://www.thomasnet.com/articles/pumps-valves-

accessories/centrifugal-principles. (Retrieved on 23 October 2015)

5. “Understanding pump performance curve”. http://www.progressivedairy.com/index.php?

option=com_content&id=10280:understanding-pump-performance-

curves&Itemid=121. (Retrieved on 23 October 2015)

6. ” System Curve and Pump Performance Curve”.

http://www.engineeringtoolbox.com/pump-system-curves-d_635.html. (Retrieved on 24

October 2015)

7. “System curve and pump performance curve”.

http://www.engineeringtoolbox.com/pump-system-curves-d_635.html. (retrieved on 24

October 2015)

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http://www.engineeringtoolbox.com/pump-system-curves-d_635.html

http://www.thomasnet.com/articles/pumps-valves-accessories/centrifugal-principles

http://www.thomasnet.com/articles/pumps-valves-accessories/centrifugal-principles

http://www.learnengineering.org/2014/01/centrifugal-hydraulic-pumps.html

http://www.learnengineering.org/2014/01/centrifugal-hydraulic-pumps.html

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