Curtin University of Technology

Department of Mechanical Engineering

FLUID MECHANICS 433

LABORATORY REPORT 1

Pump Characteristic Curves

Prepared by : Nang The Truong

Student ID No. : 14392665

Date performed : 27th July 2012

Date submitted : 10th August 2012

Table of Contents

I. Introduction..........................................................................................................1

II. Objectives............................................................................................................1

III. Nomenclature.......................................................................................................1

IV. Theory..................................................................................................................2

1. Pump Curves.....................................................................................................2

2. Similarity............................................................................................................2

V. Apparatus.............................................................................................................3

VI. Procedures...........................................................................................................3

VII. Results..............................................................................................................5

1. Single pump......................................................................................................5

2. Parallel pumps.................................................................................................10

VIII. Discussions.....................................................................................................11

IX. Conclusions.......................................................................................................13

Appendix A – Pump curves calculations at pump operating speed 1200 rpm and zero

flow rate.....................................................................................................................14

Appendix B – Similarity laws.....................................................................................15

List of tables Table 1 : Records for single pump experiment............................................................5

Table 2 : Efficiencies of a single pump at various pump speeds and input powers... .6

Table 3 : Efficiencies of a single pump at speeds of 1400 and 1800 rpm...................7

Table 4 : Records for parallel pump experiment.......................................................10

Table 5 : Experimental Power input of pump #1 and pump #2..................................10

Table 6 : Experimental Power output of pump #1 and pump #2...............................10

Table 7 : Theoretical pump #1 and #2 flow rates and increased pressures..............11

List of FiguresFigure 1 : Laboratory apparatus..................................................................................3

Figure 2 : Pump curves at various pump operating speeds and flow rates.................8

Figure 3 : Efficiencies at various pump operating speeds and flow rates....................9

I. Introduction

It is very common in engineering processes where fluid such air, water or oil are

required to be delivered from one location to another. This can be typically

achieved by pressure difference between the points. However, in a more complex

system where fluid flows through various directions, pipes, junctions,etc. energy

losses occurs due to friction along the pipe, valves, entrance and exists. In such

cases, work needs to be added into the system to overcome these losses. For this

purpose, pumps are introduced to do the job. Due to economic and design

purposes, selecting the right pump is as significant as its role and also the

purpose of this lab. Eventually, process of constructing a pump curve, application

similarity laws and effects of pumps arranged in parrallel will be discussed.

II. Objectives

Construct and analyse pump characteristic curves for a rotary dynamic pump

operating at various speeds of 1200, 1600 and 2000 rpm.

Applying similarity law to determine the pump characteristic curves for operation

at various speeds of 1400 and 1800 rpm.

III. Nomenclature

µ efficiency

Pin Input power to the motor [W]

Pout Hydraulic power output of the pump [W]

Δp Pressure increased [Pa]

Q Flow rate [m/s] or [l/s]

m Mass of counterweight [kg]

T Applied Torque [Nm]

ω Angular velocity [rad/s]

g Gravity acceleration [m/s2]

N Rotational speed [rpm]

H Head [mm Hg]

1

IV. Theory

1. Pump Curves

Efficiency of the pump at each operating point can be determined by the

equation:

η=PoutP¿

(1

)

The hydraulic power output of the pump Pout and input power to the motor Pin can

be obtained as below :

Pout=∆ p .Q (2)

P¿=T .ω=rN 2π60mg (3)

,where r = 0.235 is the length of lever arm .

2. Similarity

To determine flow rate, head and efficiency for pump operating at other speeds,

three similarity laws can be applied :

For flow rate:

Q1Q2

=ω1ω2

(4)

For head (pressure increase):

∆ P1∆ P2

=ω12

ω22

(5)

For efficiency

η1 = η2 (6)

2

V. Apparatus

Figure 1 : Laboratory apparatus

VI. Procedures

Single Pump

1. Valves were set so that only pump #2 was operating. Valve at pipe discharge

to tank was fully close.

2. Motor started to drive pump #2 at operating speed of 1200 rpm.

3. Head losses Hs and Hd were recorded from manometer. Weights were added

to the lever arm until the motor is balanced. Balance mass was also recorded.

4. The discharge valve was now fully open. The flow rate could be read and

recorded from the rotameter.

5. The flow rate was increased to 4 intermediate values so that head loss and

balance mass were recorded in accordant with each set.

6. Steps 1 to 5 were repeated for pump speeds of 1600 and 2000 rpm.

3

Pumps in parallel

1. Valves were set so that pump #2 was operating at speed of 1600 rpm, and

isolated from pump #1.

2. Valve on the suction of pump #1 was open. Pump #1 started to operate at the

same speed as pump#2. Valve isolating pump #1 and pump $2 was open.

3. Discharge valve at the tank was fully open. Flow rate through pump #2 was

recorded using the rotameter. The total flow rate could be read from the

mercury manometer. Head loss Hs and Hd were recorded from the

manometer. The masses required to balance each motor were also noted

down.

4. Step 1 to 3 were repeated for 4 additional flow rates.

4

VII. Results

1. Single pump

Table 1 : Records for single pump experiment

Pump speed,

N [rpm]

Flowrate,

Q [l/s]

Hs

[mmHg

]

Hd

[mm

Hg]

Pressure increase,

ΔP [Pa]

Balance

mass, m [g]

1200

0 930 1183 33754 330

0.8 936 1177 32153 350

1.2 941 1171 30686 375

2.5 976 1138 21613 440

2.65 982 1132 20012 440

1600

0 848 1265 55634 450

1 852 1259 54300 580

1.8 868 1243 50031 600

2.7 896 1216 42693 650

4 957 1155 26416 700

2000

0 730 1376 86187 600

1 743 1368 83385 700

1.9 766 1345 77248 865

3.6 827 1285 61105 975

5.2 942 1171 30552 1040

5

Table 2 : Efficiencies of a single pump at various pump speeds and input powers

Pump speed,

N [rpm]

Hydraulic power

output ,

Pout [W]

Input Power,

Pin [W]Efficiency = Pout/Pin

1200

0 96 0

26 101 25

37 109 34

54 127 42

53 127 42

1600

0 130 0

54 168 32

90 174 52

115 188 61

106 203 52

2000

0 174 0

83 203 41

147 251 59

220 282 78

159 301 53

6

Table 3 : Efficiencies of a single pump at speeds of 1400 and 1800 rpm

Pump speed, N

[rpm]Flowrate, Q [l/s]

Pressure

increase,

ΔP [Pa]

Efficiency = Pout/Pin

1400

0.00 45943 0

0.93 43764 25

1.40 41767 34

2.92 29418 42

3.09 27239 42

1800

0.00 75947 0

1.20 72345 25

1.80 69043 34

3.75 48630 42

3.98 45028 42

7

0 1 2 3 4 5 60

10000

20000

30000

40000

50000

60000

70000

80000

90000

100000

1200rpm1600rpm2000rpm

Flowrate , Q [l/s]

Pres

sure

incr

ease

, P

[Pa]

Figure 2 : Pump curves at various pump operating speeds and flow rates

8

0 1 2 3 4 5 60

10

20

30

40

50

60

70

80

90

1200rpm1600rpm2000rpm

Flowrate, Q [l/s]

Efficie

ncy

Figure 3 : Efficiencies at various pump operating speeds and flow rates

9

2. Parallel pumps

Nominating speed of pump #1 and pump #2: 1600 rpm

Table 4 : Records for parallel pump experiment

Total

Flow

rate,

Q [l/s]

Pump #1

Flowrate,

Q [l/s]

Pump #2

Flowrate,

Q [l/s]

Hs

[mmH

g]

Hd

[mmH

g]

Pump #1

Mass,

m [g]

Pump #2

Mass,

m [g]

ΔP,

[Pa]

0 0 0 814 1400 500 400 78182

3 2.8 0.2 836 1279 650 430 59103

4 3.2 0.8 845 1265 750 500 56035

6 3.6 2.4 885 1230 790 630 46029

7.5 3.9 3.6 943 1173 850 680 30686

Table 5 : Experimental Power input of pump #1 and pump #2

Power input P#1, [W] Power input P#2, [W]

193 155

251 166

290 193

305 243

328 263

Table 6 : Experimental Power output of pump #1 and pump #2

Power output P#1, [W] Power output P#2, [W]

0 0

165 12

179 45

166 110

120 110

10

Assuming total flow rate is evenly distributed between the pumps . Theoretical flow

rates for each pump are therefore half total flow rates. In addition, both pumps are

assumed to operate on the pump curve shown in figure 1. Applying flow rates from

table 7 in conjunction with figure 1 for operating speed at 1600 rpm, the pressure

increase ∆P, [Pa] can be obtained and tabulated as below

Table 7 : Theoretical pump #1 and #2 flow rates and increased pressures

Total Flowrate, Q

[l/s]

Pump #1 & #2 Flowrate, Q

[l/s]

Delta P,

[Pa]

Power

output

0 0 56000 0

3 1.5 52000 78

4 2 48300 97

6 3 38500 116

7.5 3.75 29500 111

VIII. Discussions

Figure 1 shows that, for a single pump at all operating speeds, the pressure

increase drops down non-linearly as the flow rate increases. At a particular flow

rate, the pressure increase at higher operating speed will also be larger than that

at lower operating speed. In fact, if not considering losses due to pipe roughness,

losses within the pump and valves, elbow, entrance and exist of pipe system, etc.

the theoretical curve can be shown as linear. These losses will cause the

difference between the two curves. The effects of these losses on pump

performance are clearer via operating efficiency as shown in figure 2. Rotary

dynamic pump performance is relatively low which is less than 80%, specifically

at low flow rate and operating speed. The efficiency reaches its maximum point at

some particular value of the flow rate and then falls with a continued increase in

the flow rate. These points are typically considered as normal or design flow rate

or capacity for the pump. The points on various curves corresponding to the

maximum efficiency are called as the best efficiency points (BEP). Apparently, in

selecting a pump for a particular application, it is desirable to have the pump

operate near its maximum efficiency. 11

Operation of the pump at zero discharge should also be considered. From table

1, the head developed at zero discharge is called the shutoff head. It represents

the rise in pressure head across the pump with the discharge valve closed. Since

there is no flow with the valve closed, the related efficiency is zero as shown in

table 2. The input power to the pump is simply dissipated as heat. Although

centrifugal pumps can be operated for short periods of time with the discharge

valve closed, damage will occur due to overheating and large mechanical stress

with any extended operation with the valve closed.

Due to time and cost, pump characteristics are not always determined

experimentally. Performance of the same pump operating at different speeds can

be predicted by using similarity laws. Shown in table 3 are characteristics of the

pump at operating speed at 1400 and 1800 rpm. The behaviour and performance

are as per discussions above. However, assumptions should be considered

carefully when applying these laws. The similarity law shown as equations (4),

(5), and (6) are based on the condition that, as the impeller diameter is changed,

all other important geometric variables are properly scaled to maintain geometric

similarity. This is not normally the case in practice due to difficulties associated

with manufacturing the pumps. The effects of viscosity and surface roughness

have also been neglected. It has been found that the effect of these on efficiency

as pump size decreases due to smaller clearances and blade size. Lastly, it

should also be aware that the similarity laws will not be very accurate if tests on a

model pump with water are used to predict the performance of a prototype pump

with a highly viscous fluid, such as oil, because at much smaller Reynolds

number associated with the oil flow, the fluid physics involved is different from the

higher Reynolds number flow associated with water.

In practice,it is common to see a combination of pumps arranged in series or

parallel to provide addition head or flow. Theoretically, the pump flow rate is

assumed to be evenly distributed when the pumps are arranged in parallel.

However, at relatively low flow rate as at less than 4 [l/s], this is not the case.

Pump #1 does a majority of work comparing with pump #2. Nonetheless, the total

flow rate had been increased as opposed to that from the operation of a single

pump at the same head. For a single pump system at operating speed of 1600

12

rpm and ∆P of 30 KPa, the total flow rate was about 3.6 l/s, whereas it was 7.5 l/s

for a parallel pump system.

IX. Conclusions

Pump curves had been constructed for a single pump operating at three different

speeds of 1200, 1600 and 2000 rpm. Similarity laws were introduced to

determine theoretical pump characteristics at other speeds of 1400 and 1600

rpm. Finally, effect of pumps arranged in parrallel were also analysised.

13

Appendix A – Pump curves calculations at pump operating speed

1200 rpm and zero flow rate

Given Hg = 13600 [kg/m3]

For Hs = 930 [mmHg], Hd = 1183 [mmHg], pressure increase is obtained as:

∆ P=❑Hgg∆ H

∆ P=13600×9.81× 1183−9301000

∆ P=33754 [Pa ]

From equation (2), output power of the pump is determined as :

Pout=33754×0

Pout=0[ ls ]From equation (3), input power to the motor is calculated as :

P¿=0.235×1200×( 2π60 )×0.33×9.81P¿=96 [W ]

Pump efficiency can be obtained using equation (1) :

η= 096

=0

14

Appendix B – Similarity laws

Given pump operating speed of 1400 rpm.

From equation (4), flow rate is calculated as :

Q1=Q2×(ω1ω2 )=0×( 14001200 )Q1=0

From equation (5), the pressure increase is :

∆ P1=∆ P2×ω12

ω22=33754×( 1400212002 )

∆ P1=45943 [Pa ]

15