Experiment 9: Centrifugal Pump - الصفحات الشخصية | الجامعة ...site.iugaza.edu.ps/bbashbash/files/pump.pdf · · 2013-04-23Hydraulics Lab - ECIV 3122 Experiment

Hydraulics Lab - ECIV 3122 Experiment (9): Centrifugal Pump

Experiment 9: Centrifugal Pump

Introduction:

Pumps fall into two main categories: positive displacement pumps and

rotodynamic pumps.

In a positive displacement pump, a fixed volume of fluid is forced from one

chamber into another. One of the oldest and most familiar designs is the reciprocating

engine, utilising a piston moving inside a cylinder. Steam pumps, the 'nodding

donkey', stirrup pumps and hydraulic rams are all of this type. Animal hearts are also

positive displacement pumps, which use volume reduction of one chamber to force

flow into another chamber.

The FM50 pump is, by contrast, a rotodynamic machine. Rotodynamic (or simply

dynamic) pumps impart momentum to a fluid, which then causes the fluid to move

into the delivery chamber or outlet. Turbines and centrifugal pumps all fall into this

category.

Pumps

Turbo-hydraulic (Kinetic) pumps Positive Displacement Pumps

Centrifugal Propeller Jet Screw Reciprocating

Pump (Radial) (Axial) (Mixed)

Description:

The apparatus consists of a tank and pipework which delivers water to and from a

small centrifugal pump. The unit is fitted with electronic sensors which measure the

process variables. Signals from these sensors are sent to a computer via an interface

device, and the unit is supplied with data

logging software as standard.

Pump speed and outlet pressure may

be varied to allow the collection of

performance data over a range of

parameters. The inlet (suction) head

pressure may be adjusted to investigate

the onset of cavitation. An alternative

impeller is also supplied so that the effect

of impeller design may be studied.

For more Details refer to Instruction

Manual FM50.

Figure 1: Centrifugal Pump Demonstration Unit


Exercise B

Objective

To create head, power and efficiency characteristic curves for a centrifugal

pump.

Theory

One way of illustrating pump characteristics is to construct contour lines of

constant power or efficiency on a graph of pump head plotted against pump

discharge. These allow engineers to see the maximum efficiency of a pump

over a range of operating parameters, which can assist in the selection of an

appropriate pump to suit particular conditions. An example is given in Figure

2.

Figure 2

Equipment Set Up

If the equipment is not yet ready for use, proceed as follows:

Ensure the drain valve is fully closed.

If necessary, fill the reservoir to within 20cm of the top rim.

Ensure the inlet valve and gate valve are both fully open.

Ensure the equipment is connected to the IFD7 and the IFD7 is connected to a

suitable PC. The red and green indicator lights on the IFD7 should both be

illuminated.

Ensure the IFD7 is connected to an appropriate mains supply, and switch on

the supply.

Run the FM50-304 software. Check that 'IFD: OK' is displayed in the bottom

right corner of the screen and that there are values displayed in all the sensor

display boxes on the mimic diagram.


Procedure

Switch on the IFD7.

Switch on the FM50 pump within the software using the Pump On button.

In the software, rename the current (blank) results table to '50%' (this will be

the only table if results from Exercise A are not available).

On the mimic diagram of the software, set the pump speed to 50%.

The interface will increase the pump speed until it reaches the required setting.

Allow water to circulate until all air has been f1ushed from the system.

Partially closing and opening the inlet and gate valves a few times will help in

priming the system and eliminating any bubbles caught within the valve

mechanism. Leave the inlet valve fully open.

Close the gate valve to give a flow rate Q of 0. (Note that the pump may not

run well with the gate valve closed or nearly closed, as the back pressure

produced is outside normal operating parameters. The pump should begin to

run more smoothly as the experiment progresses).

Select the icon to record the sensor readings and pump settings on the

results table of the software.

Open the gate valve to allow a low flow rate. Allow sufficient time for the

sensor readings to stabilise then select the icon to record the next set of

data.

Open the gate valve in small increments, allowing the sensor readings to

stabilise then recording the sensor and pump data each time.

Create a new results sheet by selecting the icon (you may also wish to

save the results at this time to avoid losing the data in the event of problems).

Close the gate valve.

Set the pump to 60%.

Select the icon to record the sensor readings and pump settings on the new

results table.

Repeat as before, opening the gate valve in small increments and allowing the

sensor readings to stabilise then recording the sensor and pump data each time.


Repeat the procedure at 70%, 80%, 90% and 100%. Create a new results sheet

for each setting (and save the results if desired- the same file may be

overwritten each time as more data is added). For convenience, rename each

sheet of results in the software with the pump setting.

Ensure the results are saved after taking the final set of results.

Switch the pump off. If not proceeding directly to another exercise then switch off the IFD7 and close the FM50 software.


Results

On the same graph plot Total Head Ht against Flow Rate Q for each setting. Graphs may be produced using the software graph facility, in which case the resulting graph with multiple plots must be printed. Alternatively the results may be imported into a more sophisticated spreadsheet program that allows the following procedure to be performed.

Select a value for efficiency, for example 40%. On each line plotted, mark the points at which an efficiency of 40% is achieved (the data is unlikely to include recorded points at which the efficiency is exactly 40%, so estimate the points based on the values obtained). Where the pump performance at a particular setting does not ever correspond to the efficiency chosen, note whether the efficiency would lie above the line or to the right of the pump performance curve. Join the marked points to form a smooth curve.

Repeat for other efficiency values. for example 35%.45% and 5090. to give a

family of efficiency curves.

Create and/or print a second head-flow rate graph for all pump frequencies.

Using the same procedure as for drawing contour lines of constant efficiency,

produce curves for constant mechanical power.

Conclusion

Examine and describe the shapes of the efficiency and power curves obtained.

Are the shapes consistent? How do they relate to the head-flow rate

characteristic? How do the efficiency and power curves relate to each other?

Compare the results to the example pump curves presented in the theory

section. How does the pump in the example compare to the pump on the FM50

in terms of capacity, power, and efficiency?


Calculations

Table 1: Example of data taken from the Software (Setting 50%)

Sample Number

Notes

Pump Setting

S [%]

Pump Speed

n [rpm]

Water Temperature

T [°C]

Inlet Pressure

Pin [kPa]

Outlet Pressure

Pout [kPa]

Motor Torque

t [Nm]

Flow Rate

Q [l/s]

Density of

water

[kg/m³]

1

50 750 26.7 2.6 18.5 0.62 0.04 997

2

50 750 27.2 2.7 18.3 0.64 0.12 996

3

50 750 26.7 2.3 17.7 0.64 0.21 997

4

50 750 26.9 2.2 17.0 0.66 0.29 997

5

50 750 27.1 1.6 15.4 0.65 0.40 997

6

50 750 27.4 1.3 14.0 0.67 0.49 996

7

50 750 26.7 0.9 13.1 0.66 0.54 997

8

50 750 27.0 0.3 11.0 0.67 0.60 997

9

50 750 26.6 0.2 10.1 0.69 0.64 997

10

50 750 26.7 -0.4 9.5 0.68 0.66 997

11

50 750 26.8 -0.6 8.6 0.68 0.69 997

12

50 750 27.1 -0.9 8.1 0.68 0.72 996

13

50 750 26.7 -1.1 7.1 0.67 0.74 997

14

50 750 27.1 -1.0 7.2 0.70 0.76 996

15

50 750 26.7 -1.1 6.5 0.68 0.76 997

16

50 750 27.5 -1.0 6.2 0.69 0.76 996

17

50 750 27.1 -1.2 6.2 0.72 0.77 996

18

50 750 26.7 -1.2 6.2 0.70 0.77 997

19

50 750 27.4 -1.2 6.4 0.68 0.76 996

Table 1 (Cont.): Example 50% setting (n = 750 rpm)

Inlet Velocity

Vin [m/s]

Outlet Velocity

Vout [m/s]

Static Head

Hs [m]

Velocity Head

Hv [m]

Elevation Head

He [m]

Total Head

Ht [m]

Hydraulic Power

Ph [W]

Mechanical Power

Pm [W]

Pump Efficiency

E [%]

Predicted Flow Rate [l/s]

0.090 0.162 1.627 0.001 0.075 1.70 0.7 48.4 1.3 0.03

0.275 0.495 1.596 0.009 0.075 1.68 2.0 50.5 3.9 0.08

0.491 0.885 1.570 0.028 0.075 1.67 3.5 50.3 6.9 0.14

0.675 1.218 1.516 0.052 0.075 1.64 4.7 52.1 9.0 0.20

0.919 1.657 1.413 0.097 0.075 1.58 6.2 50.8 12.2 0.27

1.135 2.046 1.302 0.148 0.075 1.52 7.3 52.7 13.9 0.33

1.256 2.266 1.250 0.181 0.075 1.51 8.0 51.8 15.5 0.36

1.378 2.485 1.097 0.218 0.075 1.39 8.1 52.6 15.5 0.40

1.468 2.647 1.020 0.247 0.075 1.34 8.4 54.4 15.4 0.42

1.531 2.761 1.012 0.269 0.075 1.36 8.8 53.2 16.6 0.44

1.594 2.875 0.935 0.292 0.075 1.30 8.8 53.3 16.5 0.46

1.653 2.980 0.919 0.313 0.075 1.31 9.2 53.4 17.2 0.48

1.716 3.094 0.837 0.338 0.075 1.25 9.1 52.8 17.2 0.50

1.747 3.151 0.839 0.350 0.075 1.26 9.4 54.9 17.1 0.51

1.747 3.151 0.777 0.350 0.075 1.20 8.9 53.1 16.8 0.51

1.747 3.151 0.733 0.350 0.075 1.16 8.6 54.2 15.9 0.51

1.774 3.199 0.757 0.361 0.075 1.19 9.0 56.2 16.0 0.51

1.774 3.199 0.754 0.361 0.075 1.19 9.0 55.1 16.2 0.51

1.747 3.151 0.775 0.350 0.075 1.20 8.9 53.8 16.5 0.51


Table 1 (Cont.): 50% setting (n = 750 rpm)

Predicted Total Head [m]

Vapour Pressure

Pv [kPa]

Net +ve Suction Head

Available [m]

Pipe Length

L [m]

Pipe Diameter

d [m]

Coefficient k

[-]

Coefficient C

[-]

System Head Loss [m]

Walkthrough Questions

Score [%]

0.757 36.64 6.73 0.916 0.032 4.9 140 0.06 0.746 37.33 6.68 0.916

4.9

0.21

0.743 36.64 6.72 0.916

4.9

0.40 0.730 36.89 6.71 0.916

4.9

0.58

0.704 37.14 6.67 0.916

4.9

0.86 0.678 37.58 6.64 0.916

4.9

1.13

0.669 36.70 6.72 0.916

4.9

1.29 0.618 37.08 6.66 0.916

4.9

1.46

0.597 36.57 6.73 0.916

4.9

1.60 0.603 36.64 6.69 0.916

4.9

1.69

0.578 36.82 6.68 0.916

4.9

1.79 0.581 37.20 6.63 0.916

4.9

1.88

0.555 36.64 6.69 0.916

4.9

1.98 0.562 37.20 6.65 0.916

4.9

2.04

0.534 36.70 6.69 0.916

4.9

2.04 0.515 37.65 6.60 0.916

4.9

2.04

0.530 37.20 6.64 0.916

4.9

2.08 0.529 36.64 6.70 0.916

4.9

2.08

0.533 37.58 6.59 0.916

4.9

2.04

Figure 3: Pump Curves for different velocities

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60

Tota

l He

ad H

t [m

]

Flow Rate Q [l/s]

Pump Curves for different velocities (rpm)

750

900

1050

1200

1350

1500


Exercise C

Objective

To investigate the use of the affinity laws in predicting the head-flow

characteristic for a pump.

Theory

When selecting a pump for a system, it is seldom practical to test the

performance of every size of pump in a manufacturer's range at all speeds at

which it may be designed to run. It is therefore useful to have a mathematical

solution that allows assumptions can be made about operating characteristics

of a pump running at one speed, impeller size, etc. from experimental results

taken at another.

The multiple curves obtained from plotting measured pump characteristics on

dimensional axes can be reduced to a single curve if appropriate dimensionless

groups are used. Provided the effects of t1uid viscosity on pump performance

are small, and that cavitation is not occurring, the characteristic of a given type

and shape of pump may be represented by:

∫

[ ]

where n is the pump speed (rpm or Hz), and D is the impeller diameter (m)

For a single curve of the type suggested by this equation to represent more

than one operating condition of the particular type of pump, the criterion of

dynamic similarity must be fulfilled. That is, all fluid velocities at

corresponding points within the machine are in the same direction and

proportional to impeller speed. When this is the case, as for a particular pump

operated at different speeds, a simple graph of data is formed, as depicted in

Figure 4:

Figure 4: Dimensionless head-discharge characteristic of a particular centrifugal pump

operated at different speeds


The dimensionless equation given previously is the basis from which the

affinity laws are derived. The affinity laws allow the performance of

geometrically similar pumps of different sizes or speeds to be predicted

accurately enough for practical purposes.

The methods used for deriving the affinity laws will not be presented here, but

the laws are as follows:

Power Coefficient ̅

Flow Coefficient

Head Coefficient

These Laws are most often used to calculate changes in now rate, head and

power of a pump when the size, rotational speed or fluid density is changed.

The following formulae are derived from the above considerations, and allow

calculation of total head H, and power Pm at one speed n. to be deduced from

those measured at another speed n2:

More generally, the relationship between two geometrically similar machines

with characteristic diameters D1 and D2 operating at rotational speeds n1 and

n2 is shown in Figure 5. For any two points at which values of (gH / n2D

2) and

(Q / nD3) are the same, it follows that:

(

)

(

)

and

(

)

These are termed corresponding points.

The power coefficient

and the resulting efficiency E can be compared in

a similar manner.

Figure 5: Relationship of performance characteristics for geometrically similar machines

operating at different speeds


Equipment Set Up

If the results from Exercise B are available then no further data is required.

Ensure you understand the Theory section then proceed directly to the results.

This experiment may be undertaken directly following another experiment, in

which case the equipment will already be prepared and need only be switched

back out of standby mode again.

If the equipment is not yet ready for use, proceed as follows:

Ensure the drain valve is fully closed.

If necessary, fill the reservoir to within 20cm of the top rim. Ensure the inlet

valve and the gate valve are both fully open.

Ensure the equipment is connected to the IFD7 and the IFD7 is connected to a

suitable PC. The red and green indicator lights on the IFD7 should both be

illuminated.

Ensure the IFD7 is connected to an appropriate mains supply, and switch on

the supply.

Run the FM50-304 software. Check that 'IFD: OK' is displayed in the bottom

right corner of the screen and that there are values displayed in all the sensor

display boxes on the mimic diagram

Procedure

The results from Exercise B may be used to perform the calculations and to

create the graphs for this exercise. Where these results are available, no further

data is required. Proceed directly to the Results section. If results are not

available, proceed as follows:

Switch on the IFD7.

Switch on the FM50 pump within the software.

In the software, set the pump to 50%.

Allow water to circulate until all air has been flushed from the system. Close

the gate valve to give a flow rate Q of 0.

Select the icon to record the sensor readings and pump settings on the

results table of the software.

Open the gate valve to give a very low flow rate. Allow sufficient time for the

sensor readings to stabilise then select the icon to record the next set of

data.

Open the gate valve in small increments, allowing the sensor readings to

stabilise then recording the sensor and pump data each time.

Create a new results sheet by selecting the icon (you may also wish to

save the results at this time to avoid losing the data in the event of problems).

Set the pump to 70%.



Select the icon to record the sensor readings and pump settings on the new

results table.

Open the gate valve to give a very low flow rate. Allow sufficient time for the

sensor readings to stubilise, then select the icon to record the next set of

data.

Repeat, opening the gate valve in small increments and allowing the sensor

readings to stabilise, then recording the sensor and pump data each time.

Ensure the results are saved using 'Save' or 'Save As .. .' from the software File

menu after taking the final set of results.

Switch off the FM50 within the software using the Power On/Standby button.

Switch off the IFD7.

Results The results taken at 70% will be used with the affinity laws to give predicted

results at 50%. This will then be compared to the actual results at 50%.

The software uses the affinity laws

and

to calculate the predicted values of Ht2 at predicted flow rates Q2 and 50%

setting from the measured values of Htl and Q1 and the values n1 = 70 and n2 =

50.

Plot a graph of Predicted Head against Predicted Flow Rate.

Plot the measured Total Head at 50% against measured Flow Rate at 50% (if

the data is exported into a dedicated spread sheet package or similar then it

may be possible to plot both graphs on the same axes).

Conclusion

Compare the predicted results at 50% with the measured results. How accurate

were the values obtained using the affinity laws? Discuss the advantages and

disadvantages of this technique for pump system design


Calculations

Table 2: Data for 50% Setting and 70% setting from software

Practical

70% = 1050 rpm 50% = 750 rpm

Sample Number

Flow Rate

Q [l/s]

Total Head

Ht [m]

Flow Rate

Q [l/s]

Total Head

Ht [m]

1 0.08 3.41 0.04 1.70

2 0.15 3.38 0.12 1.68

3 0.27 3.26 0.21 1.67

4 0.43 3.26 0.29 1.64

5 0.56 3.11 0.40 1.58

6 0.66 2.99 0.49 1.52

7 0.76 2.88 0.54 1.51

8 0.82 2.79 0.60 1.39

9 0.89 2.68 0.64 1.34

10 0.93 2.63 0.66 1.36

11 1.00 2.58 0.69 1.30

12 1.01 2.52 0.72 1.31

13 1.04 2.42 0.74 1.25

14 1.04 2.33 0.76 1.26

15 1.06 2.44 0.76 1.20

16 1.05 2.34 0.76 1.16

17 1.06 2.34 0.77 1.19

18 1.08 2.38 0.77 1.19

19 1.08 2.35 0.76 1.20

20 1.06 2.34

Figure 6

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

0.00 0.50 1.00 1.50

Tota

l He

ad H

t [m

]

Flow Rate Q [l/s]

Practical

70% = 1050 rpm

50% = 750 rpm


Using Similarity Laws to calculate Q and Ht for 50%

and

Table 3: Data for 70% setting from software and 50% Setting from Similarity Laws

Similarity Laws

70% = 1050 rpm Calculated 50% = 750 rpm

Sample Number

Flow Rate

Q [l/s]

Total Head

Ht [m]

Flow Rate

Q [l/s]

Total Head

Ht [m]

1 0.08 3.41 0.06 1.74

2 0.15 3.38 0.10 1.72

3 0.27 3.26 0.19 1.66

4 0.43 3.26 0.30 1.66

5 0.56 3.11 0.40 1.59

6 0.66 2.99 0.47 1.53

7 0.76 2.88 0.54 1.47

8 0.82 2.79 0.59 1.42

9 0.89 2.68 0.64 1.37

10 0.93 2.63 0.66 1.34

11 1.00 2.58 0.71 1.32

12 1.01 2.52 0.72 1.29

13 1.04 2.42 0.74 1.23

14 1.04 2.33 0.74 1.19

15 1.06 2.44 0.76 1.24

16 1.05 2.34 0.75 1.19

17 1.06 2.34 0.76 1.19

18 1.08 2.38 0.77 1.22

19 1.08 2.35 0.77 1.20

20 1.06 2.34 0.76 1.19

Figure 7

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

0.00 0.50 1.00 1.50

Tota

l He

ad H

t [m

]

Flow Rate Q [l/s]

Affinity Laws

70% = 1050rpm

Calculated50% = 750rpm


Exercise D

Objective

To investigate the effect of changing inlet head on pump performance.

Method

By varying the pressure at the inlet to the pump using a manual valve to

control the available flow.

Theory

In both the design and operation of a rotodynamic machine, careful attention

has to be paid to the fluid conditions on the suction side. In particular, it is

important to check the minimum pressure that can arise at any point to ensure

that cavitation does not take place.

Cavitation

If the pressure at any point is less than the vapour pressure of the liquid at the

temperature at that point, vaporisation will occur. This is most likely to arise in

the suction side where the lowest pressures are experienced. The vaporised

liquid appears as bubbles within the liquid, and these subsequently collapse

with such force that mechanical damage may be sustained. This condition,

known as cavitation, is accompanied by a marked increase in noise and

vibration in addition to the loss of head.

بالحذريج. suction pipeرؤية جكىى الفماعات عي طزيك إغالق الصوام الوىجىد في يوكي

FM 51هالدظة: الفماعات جكىى اوضخ في الجهاس االخز


Exercise E

Objective

To obtain a Head - Flow curve for the piping system through which the fluid is

to be pumped. To determine the operating point of the pump.

Theory

System analysis for a pumping installation is used to select the most suitable

pumping units and to define their operating points. System analysis involves

calculating a head - flow curve for the pumping system (valves, pipes, fittings

etc.) and using this curve in conjunction with the performance curves of the

available pumps to select the most appropriate pump(s) for use within the

system.

The system curve is a graphic representation of the flow rate in the system with

respect to system head. It represents the relationship between flow rate and

hydraulic losses in a system. Such losses are due to the system design (e.g.

bends and fittings, surface roughness) and operating conditions (e.g.

temperature).

Assuming that

Flow velocity is proportional to volume now rate

Losses in the system are proportional to the square of the now velocity

it follows that system head loss must be proportional to the square of the

volume flow rate, and the system head - now graph will therefore be parabolic

in shape.

بالي الشزح هىجىد في الكحالىج الخاص بالجهاس

Calculations

Table 4

System Curve

Sample Number

Pump Setting

S [%]

Pump Speed

n [rpm]

Flow Rate

Q [l/s]

Total Head

Ht [m]

1 100 1500 1.49 4.28

2 90 1350 1.36 3.78

3 80 1200 1.22 3.03

4 70 1050 1.08 2.33

5 60 900 0.92 1.71

6 50 750 0.77 1.16

7 40 600 0.61 0.74

8 30 450 0.46 0.38

9 20 300 0.30 0.15

10 10 150 0.13 -0.01

11 0 0 0.00 -0.05


Table 5

Pump Curve

Sample Number

Pump Setting

S [%]

Pump Speed

n [rpm]

Flow Rate

Q [l/s]

Total Head

Ht [m]

1 70 1050 1.08 2.28

2 70 1050 1.02 2.38

3 70 1050 1.00 2.55

4 70 1050 0.97 2.60

5 70 1050 0.92 2.69

6 70 1050 0.85 2.74

7 70 1050 0.80 2.86

8 70 1050 0.69 2.89

9 70 1050 0.61 3.10

10 70 1050 0.49 3.16

11 70 1050 0.35 3.28

12 70 1050 0.24 3.34

13 70 1050 0.13 3.39

14 70 1050 0.09 3.41

Figure 8

جن اخذها عٌذ system curve، ألى لزاءات pump curveهالدظة: ًمطة الحشغيل في الزسوة كاًث اخز ًمطة في

flowأعلى ( outlet valve fully opened

-1.00

0.00

1.00

2.00

3.00

4.00

5.00

0.00 0.50 1.00 1.50 2.00Tota

l He

ad H

t [m

]

Flow Rate Q [l/s]

Operating Point

Pump Curve

System Curve

Operating Point

Documents

Experiment 9: Centrifugal Pump - الصفحات الشخصية | الجامعة ...site.iugaza.edu.ps/bbashbash/files/pump.pdf · · 2013-04-23Hydraulics Lab - ECIV 3122 Experiment