Centrfugal pump.pdf

By: Qusai Waleed Al-Qudah · · · · · · · · · · · · · · 1

The University of Jordan

Faculty of Engineering and Technology

Department of Civil Engineering _________________________________________

Hydraulics Laboratory

0931363


Objectives and Liabilities:

1- to determine the performance characteristics of a centrifugal pump. This is

accomplished by deter mining the capacity and efficiency of a centrifugal pump when

operating under the assigned conditions.

2- To study the performance of pumps in series.

Apparatus:

The centrifugal pump consists basically of three components, an inlet duct, an impeller

and a volute. Two geometrically similar

pumps of different sizes are available. The

flow is measured by flow-meter or by v-

notch. Pressures at various points may be

measured by pressure gauges. Digital

tachometers read the rotate speed in rpm.

The principle of apparatus:

Pumps are generally used to provide certain head at certain flow rate to create a flow

from low pressure to high pressure.

Centrifugal pump are one type of pumps that converts the energy of prime mover

(electric motor) into velocity (kinetic energy) by centrifugal force provided by the

rotation of the vanes, and then the kinetic energy is transformed into pressure energy

of the fluid that flows in the pump.

This conversion process of energy into

pressure is done by two main parts:

1- Impeller: rotating part that converts the

driver energy into kinetic energy.

2- Volute (diffuser): The stationary part

that converts the energy into pressure.


The amount of energy given to fluid is direct proportional to the velocity of the flow at

the edge of the vanes of the impeller; the faster the impeller is or the larger it was (v =

ω * r), the larger kinetic energy is transformed to the fluid. This kinetic energy of the

fluid coming out of an impeller is harnessed by creating a resistance to the flow. The

first resistance is created by the pump volute (casing) that catches the liquid and slows

it down. In the discharge nozzle, the liquid further decelerates and its velocity is

converted to pressure according to Bernoulli’s principle;


Concepts

Centrifugal pump performance curve:

Every pump's performance is represented by the pump performance curve which is a

plot of the developed head against the flow rate, also the curve shows the efficiency of

the pump, the speed of the impeller and its size, these curves are generated according

to tests performed by the manufacturer.

Efficiency of a pump:

The efficiency is an important factor in selecting a pump for a certain system, this

quantity represents the ratio between energy input (from motor) to energy output (to

the flow) of the pump;

Pumps in Series and pumps in parallel:

Sometimes the required head for a system can't match any single pump performance

curve or the suitable pump is not in stock, for those purposes two or more pumps can

be connect in series to increase the head coming out of pumps;

o Pumps are connected in series by attaching on of the pumps discharge to the

other ones suction, ( When larger flow rate is required and no single pump is

available for use, then two or more pumps can be connected in parallel ).

o Pumps are connected in parallel when their discharge is connected to a common

pipe.

Produce of this experiment:

1- Start by making sure that the value between both pumps, and the outlet and inlet valve

for each pump are fully open.

2- Turn on the power for each pump and set the impellers speed to 3000rpm using the

control knob.

3- For each pump, separately, measure the flow rate and pressure head before and after

the pump.

4- Partially close the outlet flow valve to reduce the flow rate and the record the now

flow rate along with the pressures before and after the pump.

5- Repeat step NO.4 for different flow rate, until the flow is minimal.

6- After taking the several readings for each pump separately, connect both pumps in

series and repeat step NO.4.


Theoretical of this experiment:

When the pump start, the fluid enters the suction nozzle and then into enter of the

impeller, ( suction eye ). As the impeller rotates, it spins the fluid sitting in the cavities

between the vanes outward and provides centrifugal acceleration. As the fluid leaves

the eye of the impeller, low pressure is developed, causing continuous flow into the

pump inlet.

Same in the axial flow pump, the head developed by a pump is determined by

measuring the pressures on the suction and discharge sides of the pump.

The velocities are computed by measuring the discharge and dividing it by the

respective pipe cross areas therefore, the net head delivered by the pump to the fluid

is:

(

) (

)

Where:

H: head developed by the pump in m.

P1,2: pressure head at the suction side and delivery side of the pump in Pa.

V1,2: velocity at the suction side and delivery side of the pump in

.

Z1,2: elevation at the suction side and delivery side of the pump in m.

ρ: the density of water =

g: gravity acceleration =

( )

Usually the intake pipe is larger than the discharge pipe, however in the current

apparatus the discharge and suction pipe are the same size, therefore the velocity

heads cancel out.

Also the assumption is made that both suction side and delivery side are on the same

elevation, resulting in neglecting the elevation head, the net total can be repressed:

Where:

H: head developed by the pump in m.

: Pressure head.



( )

we will cross the equation with 10^5 ti convert from bar to Pa.


The total power output, in watts, of the pump is equal to the production of the pump

total pressure and the volumetric flow rate:

Where:

Q: flow rate in m^3/sec



( )

V: velocity at the suction side and delivery side of the pump in

.

The power input, in watts, from the dynamometer s given by:

(

)

Where:

τ: torque in N.m

ω: angular velocity.

F: force ( measured load on motor ) in N

r: torque arm=0.178m.

N:impeller speed in rpm.

The total power output of the pump is equal to the production of the pump total

pressure and the volumetric flow rate:

ἠ


The statement of connection:

1- Parallel:


2- In series:


Calculation about this experiment: For a parallel pumps

For pump NO.1, At N = 2500rpm

Q

P1

P2

F

N

H

m

Pout

watt

Pin

watt ἠ%

0.0048 30000 40000 30 1.019367992 48 1397.3 3.435196

0.004 35000 120000 26.5 8.664627931 340 1234.282 27.54639

0.0025 30000 160000 25.5 13.25178389 325 1187.705 27.3637

0.002 20000 180000 20.5 16.30988787 320 954.8217 33.51411

0.001 20000 190000 17.5 17.32925586 170 815.0917 20.85655

0 30000 195000 13 16.81957187 0 605.4967 0

0

2

4

6

8

10

12

14

16

18

20

0 0.001 0.002 0.003 0.004 0.005 0.006

H

Q

H m

Poly. (H m)

By: Qusai Waleed Al-Qudah · · · · · · · · · · · · · 10

For pump NO.2 at N=2500rpm

Q

P1

P2

F

N

H

m

Pout

watt

Pin

watt ἠ%

2.3 -2000 0 6.5 0.203874 4.6 302.7483 1.519414

2 -1000 30000 6 3.160041 62 279.46 22.18564

1.5 -1000 60000 5.5 6.218145 91.5 256.1717 35.71824

1 -2000 95000 4.5 9.88787 97 209.595 46.27973

0.5 -1000 80000 4 8.256881 40.5 186.3067 21.73835

0 -1500 80000 2.5 8.307849 0 116.4417 0

-5

0

5

10

15

20

25

30

35

40

0 0.001 0.002 0.003 0.004 0.005 0.006

H

Q

ἠ%

Poly. (ἠ%)


0

2

4

6

8

10

12

0 0.5 1 1.5 2 2.5

H

Q

H m

Poly. (H m)

-10

0

10

20

30

40

50

0 0.5 1 1.5 2 2.5

ױ

Q

ἠ%

Poly. (ἠ%)


The difference between to pumps is

Simple calculation for a parallel pumps:

(

)

ἠ

-10

0

10

20

30

40

50

0 2 4 6 8 10

ױ

Q

Pump NO.1

Pump NO.2

Poly. (Pump NO.1)

Poly. (Pump NO.2)


Pump in series:

Q

P1

P2

H

m

Pout

watt

0.0028 20000 30000 1.019368 28

0.0024 20000 130000 11.21305 264

0.002 20000 180000 16.30989 320

0.0014 19000 220000 20.4893 281.4

0.001 20000 240000 22.4261 220

0 22000 260000 24.26096 0

0

5

10

15

20

25

30

0 0.5 1 1.5 2 2.5 3

H

Q

h

Poly. (h)


Conclosion: 1- Generally in pumps increasing the flow rate will decrease the provided head as shown

in the plots of pump 1 and pump 2, a point of equilibrium between the both criterions

needed for the systems shall be found.

2- Some experimental errors regarding the first point were found in pump 2 performance

curve and in the experimental curve for pumps in series.

3- The experimental curve of the pumps in series showed smaller maximum head (Q = 0)

than the theoretical one calculated from plots of pump 1 and pump 2, so when

selecting the pumps in series to be used for a system I think we should test them

experimentally rather than calculating them theoretically so that we get the exact

amount of head, selecting the pumps in series using theoretical analysis would result a

failure in achieving the required head in an actual system.

4- The efficiency of the pumps was not calculated due to lack of givens (input power).

-50

0

50

100

150

200

250

300

350

0 0.0005 0.001 0.0015 0.002 0.0025 0.003

Axi

s Ti

tle

Axis Title

Pout watt

Poly. (Pout watt)

Documents

Centrfugal pump.pdf