Pump Lab

Centrifugal Pump Date Performed: October 15, 2007 Date Submitted: October 29, 2007 By: Davinder Dhaliwal, Vineet Kapoor & Jagroop Randhawa

Summary The centrifugal pump is composed of many different parts and many different values were taken and put together at the end to find the characteristics of the pump at different rpm’s. We found out that our overall efficiency for the pump averaged around 20%. And the calculated flow of water compared to the one we read on the flow meter was within 4% error margin. Our calculate pressure change from suction to discharge to that of the one we read on the meter was within 13% error margin. So overall our readings were very close to the ones we read.

Introduction A centrifugal pump converts kinetic energy into static pressure using a rotating impeller. The rotating impellers increase the velocity of the fluid and therefore increasing the kinetic energy of the fluid. Once the shaped casing guides the fluid to the outlet, all of the kinetic energy is converted to potential energy, which increases the pressure at the pump outlet.

Experiment Procedure Refer to CHEN 302 – Centrifugal Pump Lab Manual for detailed procedure

Report 1)

TABLE OF RAW DATA

Table 1: 1500 rpm Trials 1 2 3 4 5

Weight of torque (grams) 350.0 300.0 300.0 250.0 200.0

Flow rate (GPM) 21 19 15 9 0

Differential Pressure (lbs/in2) 4.5 4.7 4.7 4.9 5.1

Suction (inHg)

Discharge ( lbs/in2)

Voltage (Watts)

0 0 0 0 0

5.0 5.5 5.8 6.2 6.5

250 250 220 200 175

Differential Pressure (lbs/in2) 7.5 8.0 8.5 8.9 9.5

Suction (inHg)

Discharge (lbs/in2)

Voltage (watts)

0.5 1.1 0 0 0

8.2 10 11 12 13

600 570 550 510 390

Differential Pressure (lbs/in2) 11.9 12.1 12.6 13.8 14.3

Suction (inHg)

Discharge (lbs/in2)

Voltage (Watts)

3 2 1.5 0 0

13.5 14.2 16.1 19.5 21.0

1090 1000 940 860 660

Table 2: 2000 rpm Trials 1 2 3 4 5

Weight of torque (grams) 650.0 600.0 555.0 500.0 350.0

Flow rate (GPM) 38 34 28 19 0

Table 3: 2500 rpm Trials 1 2 3 4 5

Weight of torque (grams) 1050 950 850 750 550

Flow rate (GPM) 52 45 38 23 0

Comments: At 1500 rpm the discharge and suction pressure doesn’t equal to the differential pressure reading but as the rpm was increased to 2000 rpm the sum of suction and discharge pressure was very close to differential pressure reading. Table 4: Accuracy flow meter Flow meter (gpm) 49 40.5 29 20 10

Tank Depth (inches) 3.5 6.6 7.5 8.7 9.5

lbs of H2O (From Graph) 72 112 128 144 154

Time (sec) 11 20 36 54 110

Comments: Reading from the flow meter and calculated flow by timing were very close to each other. You can see the comparison in Table 12. 2)

PUMP PERFORMANCE CURVE

3)

CALCULATIONS

1. Pump Performance a) Calculate head in meters from the observed differential pressure. Table 5: Head Calculations 1500rpm

2000rpm

2500rpm

Differential Pressure (lbs/in2)

head (m)

Differential Pressure (lbs/in2)

head (m)

Differential Pressure (lbs/in2)

head (m)

4.50

3.16

7.50

5.27

11.90

8.37

4.70

3.30

8.00

5.62

12.10

8.51

4.70

3.30

8.50

5.98

12.60

8.86

4.90

3.44

8.90

6.26

13.80

9.70

5.10

3.59

9.50

6.68

14.30

10.05

Flow Rate (m3/s) 0.00328068

b) Convert observed flow in gpm to m3/s Table 6: Flow Rate in m3/s 1500rpm Flow Rate (gpm) 21

Flow Rate (m3/s) 0.00132489

2000rpm Flow Rate (gpm) 38

Flow Rate (m3/s) 0.00239742

2500rpm Flow Rate (gpm) 52

19

0.00119871

34

0.00214506

45

0.00283905

15

0.00094635

28

0.00176652

38

0.00239742

9

0.00056781

19

0.00119871

23

0.00145107

0

0

0

0

0

0

c) Calculate hydraulic power (delivered to fluid by the pump) Table 7: Calculating Hydraulic Power 1500rpm

2000rpm

Flow

Flow

2500rpm

3

Head (m)

Hydraulic Power (kW)

Flow 3 (m /s)

Head (m)

Hydraulic Power (kW)

0.0411

0.0024

5.2726

0.1240

0.0033

8.3658

0.2692

3.3042

0.0389

0.0021

5.6241

0.1183

0.0028

8.5065

0.2369

0.0009

3.3042

0.0307

0.0018

5.9756

0.1036

0.0024

8.8580

0.2083

0.0006

3.4448

0.0192

0.0012

6.2568

0.0736

0.0015

9.7016

0.1381

0.0000

3.5854

0.0000

0.0000

6.6786

0.0000

0.0000

10.053

0.0000

3

Head (m)

Hydraulic Power (kW)

0.0013

3.1636

0.0012

(m

/s)

(m

/s)

d) Calculate Shaft Power Table 8: Calculating Shaft Power 1500rpm

2000rpm

2500rpm

Mass of Weights (kg)

Shaft Power (W)

Mass of Weights (kg)

Shaft Power (W)

Mass of Weights (kg)

Shaft Power (W)

0.350

164.389

0.650

407.058

1.050

821.943

0.300

140.905

0.600

375.746

0.950

743.663

0.300

140.905

0.555

347.565

0.850

665.383

0.250

117.420

0.500

313.121

0.750

587.102

0.200

93.936

0.350

219.185

0.550

430.542

e) Efficiency Calculations Table 9: Calculating Hydraulic Efficiency 1500rpm

2000rpm

2500rpm

Hydraulic Power (W)

Shaft Power (W)

Hydraulic Efficiency (%)

Hydraulic Power (W)

Shaft Power (W)

Hydraulic Efficiency (%)

Hydraulic Power (W)

Shaft Power (W)

Hydraulic Efficiency (%)

41.117

164.389

25.012

124.004

407.058

30.464

269.242

821.943

32.757

38.855

140.905

27.575

118.348

375.746

31.497

236.914

743.663

31.858

30.675

140.905

21.770

103.555

347.565

29.794

208.328

665.383

31.309

19.188

117.420

16.341

73.576

313.121

23.498

138.102

587.102

23.523

0.000

93.936

0.000

0.000

219.185

0.000

0.000

430.542

0.000

WaltMeter reading (W)

Motor Efficiency (%)

Table 10: Calculating Motor Efficiency 1500rpm Shaft Power (W)

WaltMeter reading (W)

Motor Efficiency (%)

2000rpm Shaft Power (W)

WaltMeter reading (W)

Motor Efficiency (%)

2500rpm Shaft Power (W)

164.39

250

65.76

140.90

250

56.36

407.06

600

67.84

821.94

1090

75.41

375.75

570

65.92

743.66

1000

74.37

140.90

220

64.05

347.56

550

63.19

665.38

940

70.79

117.42

200

58.71

313.12

510

61.40

587.10

860

68.27

93.94

175

53.68

219.18

390

56.20

430.54

660

65.23

WaltMeter reading (W)

Overall Efficiency (%)

Table 11: Calculating Overall Efficiency 1500rpm Hydraulic Power (W)

Overall Efficiency (%)

2000rpm Hydraulic Power (W)

WaltMeter reading (W)

Overall Efficiency (%)

2500rpm Hydraulic Power (W)

WaltMeter reading (W)

41.117

250

16.447

124.004

600

20.667

269.242

1090

24.701

38.855

250

15.542

118.348

570

20.763

236.914

1000

23.691

30.675

220

13.943

103.555

550

18.828

208.328

940

22.163

19.188

200

9.594

73.576

510

14.427

138.102

860

16.058

0.000

175

0.000

0.000

390

0.000

0.000

660

0.000

EFFICIENCY NUMBERS ON PUMP PERFORMANCE CURVES

i. HYDRAULIC EFFICIENCY TREND

II. MOTOR EFFICIENCY TREND

III

OVERALL EFFICIENCY TREND

COMMENT: From the above curves it can be noticed that both hydraulic efficiency and overall efficiency are going up as the capacity of the pumps are increasing. However, the motor efficiency is keeping steady as the flow rate increases. 4)

ACCURACY OF FLOW METER

TABLE 12: CALCULATION OF FLOW OF WATER Flow of Water (lb/s)

Calculated Flow of Water (gpm)

Actual Flow of Water (gpm)

6.55 5.6

47.08 40.28

3.56 2.67 1.4

25.58 19.18 10.07

49 40.5 29 20 10

Comment: Calculated flow of water was very close to the actual measured flow of water.

6) Calculate differential pressure from suction and discharge pressure gauges. Table 13: Calculated Differential Pressure at 1500rpm Differential Pressure (lbs/in2)

Suction (inHg)

Discharge ( lbs/in2)

Calculated ( lbs/in2)

4.5 4.7 4.7 4.9 5.1

0 0 0 0 0

5 5.5 5.8 6.2 6.5

5 5.5 5.8 6.2 6.5

Table 14: Calculated Differential Pressure at 2000rpm Differential Pressure (lbs/in2) 7.5 8 8.5 8.9 9.5

Suction (inHg)

Discharge ( lbs/in2)

Calculated ( lbs/in2)

0.5 1.1 0 0 0

8.2 10 11 12 13

8.45 9.46 11 12 9.5

Table 15: Calculated Differential Pressure at 1500rpm Differential Pressure (lbs/in2) 11.9

Suction (inHg)

Discharge ( lbs/in2)

Calculated ( lbs/in2)

3

13.5

12.03

12.1

2

14.2

13.22

12.6

1.5

16.1

15.4

13.8

0

19.5

19.5

14.3

0

21

21

Comment: As differential pressure is increased, error is reduced.

7) PRIMING THE PUMP A pump starting out full or air might not have enough pressure to pump put the air, therefore it will never achieve the flow of liquid. To prime the pump, an operator should fill the pump up with the liquid to remove all the air. Usually there is a check valve fitted in the suction line so that the liquid will not drain out if the pump is stopped. The reason to do pump prim is that if there were vapours present in the pump while the motor is on, the impeller of the pump becomes gas-bound and the pump will be powerless. 8) CAVITATION At high flow rate and high rpm we noticed a white strip. The pump sounded different and we could hear growling sounds and vibration. As the suction valve was closed the liquid inside the pump started vaporizing due to pressure drop to vapor pressure limit. Some bubbles could also be seen in the pump. 9) The calculated NPSHA for the pump was 7.59m.

Conclusion •

When operating the pump, we need to first prime the pump therefore the data won’t have a high % error in calculations

•

When cavitation occurs within the pump, to correct it you must change operating conditions such as increasing suction pressure and maintaining pipe lines.

•

The pump has a better efficiency when running at higher rpm’s

•

The measured flow rate and the calculated flow rate were not the same due to equipment.

•

The differential pressure measured and the differential pressure calculated was not equal due to lack of pressure sensitivity in pressure gauges.

Recommendations 

Using gauges which sense lower pressure and this will provide more accurate readings.



Torque arm sometimes got stuck while weights were placed on it, a digital weighing machine will provide more accurate results.

References •

Centrifugal Pump Lab Module Chen 302

•

Applied Fluid Mechanics Text Book pg.407