Experiment: Performance Characteristics of a Centrifugal Pump
Introduction and Theory
Centrifugal pumps are the most commonly used pumps in the industry. In order to properly
design a pipe system, or select the appropriate pump for an existing system, engineers use
performance charts provided by pump manufacturers. An example of such a chart for a
small size centrifugal pump is shown in Figure 1 below (it is not for the pump tested here).
Figure 1 An example of manufacturer’s pump chart.
In Figure 1, the horizontal axis is the volumetric flow rate through the pump and the
horizontal axis is the increase of the total head across the pump. The total head at any
V2
location is defined as H = +
+ z , where P is pressure, is specific weight of the fluid,
2g
P
V is the (average) velocity and z is elevation (measured from an arbitrary level). Therefore,
the change of total head from the inlet to the outlet of the pump is:
H =
Pout − Pin
+
2
Vout
− Vin2
+ ( zout − zin )
2g
In this experiment (and for most applications) the changes in velocity and elevation are
negligible, and the change of total head can be expressed simply as H =
Pout − Pin
.
Other Useful Equations
W pump =V P
= 2N / 60
Wshaft =T
= W pump / Wshaft 100%
1. Pumping power:
2. Angular velocity:
3. Shaft power:
4. Pump efficiency
Where
N = rotational speed (RPM)
V = volumetric flow rate
T = shaft torque
Experimental Goal
To determine the following characteristics of the investigated centrifugal pump:
H (V ) , Wshaft (V ) and (V ) , each at two (or more) rotational speeds. Uncertainties on all
reported quantities must be calculated and reported (error bars).
Test Stand Description
The centrifugal pump system used in the experiment is presented in Figure 2.
Flow Meter
Needle Valve
Pout
Tachometer
Pin
Variable
Speed D.C.
Motor
Torque
Meter
Pump
Sump Tank
Figure 2 Centrifugal Pump System
Water is pumped from the sump tank, through the tested centrifugal pump, needle valve,
flow meter and back to the tank. The inlet and outlet pressures of the pump are monitored
by pressure gauges Pin and Pout, respectively.
The pump is driven by a DC motor controlled with a SCR (semiconductor-controlled rectifier)
controller. The coupling between the motor and the pump is instrumented with a torque
meter and a tachometer generator which measure torque and rotational speed, respectively.
The torque meter and drive couplings are covered for safety reasons.
Technical Details of the Equipment
1. Centrifugal Pump: The pump is a typical fractional horsepower water pump capable of
delivering flow rate of 26 gallons per minute (gpm).
2. Electric Motor: The motor is a Permanent Magnet DC motor rated at ½ HP and 1725 full
load RPM. The motor RPM may be varied continuously from 0 to full-load RPM.
3. Torque Meter: The pump torque is measured by means of the torque meter, which is
mounted in-line between the pump and motor. Torque is read on a calibrated scale, using
stroboscopic light while the instrument is rotating. Torque may be read to an accuracy of ½%
of the full scale (FS). The torque range is 0-25 lb-in.
4. Tachometer: The Tachometer Generator is mounted to one side of the motor and
connected by a belt/pulley arrangement. The Tachometer Indicator is mounted on the vertical
panel. The range of the device is 0-2000 rpm with 2% of accuracy (FS).
5. Flow meter: The Flow meter is a direct reading glass rotameter with a SS 316 float. The
maximum flow rate is 30 gpm with a 2% accuracy (FS). See the manufacturer’s instructions
for the location of the float reading edge.
6. Pressure gages: The inlet pressure gage has the range of -20 to 40 inH20 and the accuracy
of 1 inH20. The outlet pressure gage has the range of 0-10 psig and accuracy of 0.2 psi.
The uncertainty associated with every direct measurement in this experiment must be estimated
and recorded as a part of measured results.
Starting the Test Stand
Warning: Do not operate the pump with the needle valve fully closed.
1.
2.
3.
4.
Ensure that master speed dial is set to 0 and FWD/BRAKE/REV switch to BRAKE
position.
Close the needle valve about half way, turn ON/OF switch of the motor to ON, set the
FWD/BRAKE/REV switch to FWD
Turn master speed dial to desired speed setting.
Adjust the needle valve until the desired flow rate is reached and take measurements
Presentation of Results
H , the shaft
power Wshaft and the pump efficiency , all as functions of the volumetric flow rate V . Graph the
Based on the direct measurements recorded, calculate and graph the head increase
results for all speeds together (two curves per graph). Based on the estimated uncertainties of all direct
and
measurements calculate the uncertainties of V , H , W
shaft
(see lecture notes or [1]). Include
error bars when graphing results.
Discuss all the observed trends. Then compare qualitatively the experimental curves with the typical
pump characteristics of Figure 1. Discuss possible sources of experimental error.
References
(1) J.P. Holman, Experimental Methods for Engineers, 7th Edition, McGraw Hill, New York, 2001
(2) Centrifugal Pump System Model 9010 Instructions by Technovate, Pompano Beach, FL
Abbreviated Individual Reports
The lab reports for Experiments 6 through 8 will follow an abbreviated format.
The following items are now required (see sample report on next pages):
• Title Page with Abstract
• Experimental Results – follow the instructions from each lab handout
and present all the results in tables and/or graphs. Include the most
important equations, as needed
• Sample calculations, including units
• References, as needed
Writing an Abstract
Abstract is a stand-alone autonomous paragraph which describes all the work
done in a nutshell. It should not refer to tables or graphs in the report. Abstract
should not exceed 250 words and should discuss the following:
• Intro statement of the problem investigated, including the objective
• How was the objective pursued
• Summary of most important results and conclusions
• Relevance of the conclusions to engineering
See the sample below.
1
(Sample Abbreviated Report)
Abbreviated Report, ME 304, Session# 3, Exp. #8
Performed by Team A on 1/6/2020
Submitted by: Mark Smith on 1/13/2020
Venturi and Orifice Flow Meters
Abstract
In principal, any calibrated obstruction could be used as a flow meter by measuring the
pressure drop across the obstruction. This laboratory investigates two types of obstruction
flow meters that are commonly used in industry: Venturi flow meter and orifice flow meter.
The main objective of the lab was to determine calibration curves for the two flow meters.
Using an instrumented pipe system, water was pumped through a reference flow meter
(rotameter type) and through the two investigated obstruction flow meters (all in series) and
both the flow rate Q and the pressure drop P across each of the two flow meters were
recorded at various flow rates Q. The determined calibration curves Q(P) were shown to
follow closely (within 5%) the form Q = a P , where a is a constant. The orifice flow meter
showed about 100% higher flow rates than the Venturi flow meter at the same pressure drop.
This laboratory demonstrated how measurement of pressure drop across an obstruction flow
meter can be used to determine the flow rate in a duct. This can be a very convenient and
cost-effective method of flow measurement, especially for large ducts.
2
Experimental Results
The measured results are presented for each flow rate in Table 1 and all values converted to
SI units are presented in Table 2. In the tables ΔPV and ΔPO are the pressure drops across
the Venturi and the orifice flow meters, respectively.
Table 1 Averaged Measured Values
ΔPV
(mbar)
1.0
7.4
18.1
22.9
31.0
39.2
48.3
57.9
Q
(GPM)
2
4
6
7
8
9
10
12
Table 2 Averaged Measured Values in SI units
ΔPO
(mbar)
0.4
2.6
6.2
6.6
10.3
12.7
17.3
21.5
Q
(m3/s)
ΔPV
(Pa)
ΔPO
(Pa)
0.000126
100
40
0.000252
740
260
0.000379
1810
620
0.000442
2290
660
0.000505
3100
1030
0.000568
3920
1270
0.000631
4830
1730
0.000757
5790
2150
The data of Table 2 was used to create Figure 1, which graphs two calibration curves: one
for the Venturi flow meter Q(PV) and the other for the orifice flow meter Q(PO).
0.0008
0.0007
0.0005
3
Q (m /s)
0.0006
0.0004
Venturi
0.0003
Orifice
0.0002
0.0001
0
0
1000
2000
3000
4000
5000
6000
P V , P O (Pa)
Figure 1 Calibration curves for the tested Venturi and orifice flow meters.
The two solid lines in Figure 1 represent least square fits of the form Q = a P .
Sample Calculations
3
4
gpm
V_dot [m^3/s]
gpm
Trial
1
50
+/in^3/min
9
10
13
12
17
19
15
16
22
24,5
15
20
2
60
3
70
2079
2310
3003
2772
3927
4389
3465
3696
5082
5659,5
3465
4620
0
Average
γh
P1
Psi
inches
P1
Head
139,536
139,536
139,536
139,536
139,536
139,536
139,536
139,536
139,536
139,536
139,536
139,536
-1,8
-2
-3
-2,5
-4
-5
-3
-3
-7
-9
-3
-5,5
Psi
P2
Psi
+/psi
-0,065
-0,07222
-0,10833
-0,09028
-0,14444
-0,18056
-0,10833
-0,10833
-0,25278
-0,325
-0,10833
-0,19861
0
0,036
0,036
0,036
0,036
0,036
0,036
0,036
0,036
0,036
0,036
0,036
0,036
1,00
0,90
0,20
0,50
0,50
0,30
1,20
1,10
1,00
0,50
2,20
1,50
Change in head at various volumetric flow rates
80,00
70,00
60,00
ΔH [in]
50,00
40,00
30,00
20,00
10,00
0,00
0
1000
2000
3000
4000
5000
6000
V_dot [in^3/min]
Low RPM
Mid RPM
High RPM
Linear (Mid RPM)
Linear (High RPM)
Inches
P2
Head
27,69
24,92
5,54
13,85
13,85
8,31
33,23
30,46
27,69
13,85
60,92
41,54
Mid RPM
High RPM
Linear (Mid RPM)
Linear (High RPM)
12,0
10,0
8,0
Efficiency [%]
Low RPM
6,0
4,0
2,0
0,0
-2,0
-4,0
Data
+/psi
0,2
0,2
0,2
0,2
0,2
0,2
0,2
0,2
0,2
0,2
0,2
0,2
P2-P1/SW
Delta_H
+/Head
in
29,49
26,92
8,54
16,35
17,85
13,31
36,23
33,46
34,69
22,85
63,92
47,04
6,54
6,54
6,54
6,54
6,54
6,54
6,54
6,54
6,54
6,54
6,54
6,54
Delta_p
+/Psi
psi
1,07
0,97
0,31
0,59
0,64
0,48
1,31
1,21
1,25
0,83
2,31
1,70
N [rpm]
rpm
2*pi*N/60
omega [-]
rad/s
T
in*lb
0,24
0,24
0,24
0,24
0,24
0,24
0,24
0,24
0,24
0,24
0,24
0,24
3080
3080
3102
3085
3085
3088
3088
3090
3090
3090
3092
3091
4
4
4
4
4,5
4,5
4,5
4,5
5
5
5
5
323
323
325
323
323
323
323
324
324
324
324
324
Shaft power at various volumetric flow rates
0,3000
0,2500
W_sh [hp]
0,2000
0,1500
0,1000
0,0500
0,0000
0
5
10
15
V_dot [GPM]
Low RPM
High RPM
Expon. (Mid RPM)
Mid RPM
Expon. (Low RPM)
Expon. (High RPM)
20
25
30
High RPM
Expon. (Mid RPM)
Expon. (Low RPM)
Expon. (High RPM)
Pump efficiency at various volumetric flow rates
12,0
10,0
Efficiency [%]
8,0
6,0
4,0
2,0
0,0
0
5
10
15
-2,0
-4,0
V_dot [GPM]
Low RPM
Mid RPM
High RPM
Poly. (Low RPM)
20
25
30
V_dot*Delta_P
W_p
W_p
lb*in/min
hp
2214
0,00559
2246
0,00567
926
0,00234
1636
0,00413
2531
0,00639
2109
0,00533
4533
0,01145
4466
0,01128
6367
0,01608
4669
0,01179
7998
0,02020
7848
0,01982
unc +- lbin/min unc +- hp
639
0,00161
681
0,00172
752
0,00190
737
0,00186
1017
0,00257
1103
0,00279
1001
0,00253
1041
0,00263
1375
0,00347
1451
0,00367
1140
0,00288
1328
0,00335
T*omega
W_sh
hp
0,1955
0,1955
0,1969
0,1958
0,2203
0,2205
0,2205
0,2206
0,2451
0,2451
0,2453
0,2452
unc +- hp
2,18E-08
2,18E-08
2,19E-08
2,19E-08
2,27E-08
2,27E-08
2,27E-08
2,27E-08
2,35E-08
2,35E-08
2,35E-08
2,35E-08
W_p/W_sh
Efficiency
%
2,9
2,9
1,2
2,1
2,9
2,4
5,2
5,1
6,6
4,8
8,2
8,1
unc eff %
0,8
0,9
1,0
1,0
1,2
1,3
1,1
1,2
1,4
1,5
1,2
1,4
γ
N Unc.
lb/ft^3
2%
62,4 rpm
lb/in^3
40
0,036111 rad/s
4,18879
power
1 HP
Flow meter Unc (in^3/min)
Density
62,4
ft-lb/s
550
Torque Unc. (in-lb)
0,125
Flow meter Unc (gpm)
0,6
Flow meter Unc (in^3/min)
139,536
Gravity
32,2
in-lb/min
396000
Experimental Results: Low RPM (891)
V_dot [gpm]
9,0
10,0
13,0
12,0
± ΔH [in]
0,60
29,5
0,60
26,9
0,60
8,5
0,60
16,3
± W_p [hp]
6,5 0,00559
6,5 0,00567
6,5 0,00234
6,5 0,00413
±
W_sh [hp]
0,00161
0,1955
0,00172
0,1955
0,00190
0,1969
0,00186
0,1958
±
η [%]
2,18E-08 2,9
2,18E-08 2,9
2,19E-08 1,2
2,19E-08 2,1
±
0,8
0,9
1,0
1,0
±
η [%]
2,27E-08 2,9
2,27E-08 2,4
2,27E-08 5,2
2,27E-08 5,1
±
1,2
1,3
1,1
1,2
Experimental Results: Mid RPM (1153)
V_dot [gpm]
17,0
19,0
15,0
16,0
± ΔH [in]
0,6
17,8
0,6
13,3
0,6
36,2
0,6
33,5
± W_p [hp]
6,5 0,00639
6,5 0,00533
6,5 0,01145
6,5 0,01128
±
W_sh [hp]
0,00257
0,2203
0,00279
0,2205
0,00253
0,2205
0,00263
0,2206
Experimental Results: High RPM (1444)
V_dot [gpm]
22,0
24,5
15,0
20,0
± ΔH [in]
± W_p [hp]
0,6
34,7 6,54 0,01608
0,6
22,8 6,54 0,01179
0,6
63,9 6,54 0,02020
0,6
47,0 6,54 0,01982
±
W_sh [hp]
0,00347
0,2451
0,00367
0,2451
0,00288
0,2453
0,00335
0,2452
±
2,35E-08
2,35E-08
2,35E-08
2,35E-08
η [%] ±
6,56 1,42
4,81 1,5
8,23 1,17
8,08 1,37
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