Experimental setup:

Figure-1: Experimental setup for study of pump characteristics

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Observed Data:

Room temperature= 31.5 0C

Water temperature= 30 0C

Length of water reservoir= 83 cm

Width of water reservoir= 32 cm

2 pipes internal diameter, d= 2 inch

Distance between motor shaft and torque arm d= 9 inch= 0.2286 m

Gravitational accelerations, g = 9.81 ms-2

At 30 ºC, Density of water = 995.647 kg/m3 [Elementary Principle of Chemical Process]

At 31.5 ºC, Density of CCl4 = 1559.68 kg/m3 [Calculating from Perry’s Chemical Engineering

Handbook]

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Table -1: Observed data for pump characteristics curves

Motor

speed

(rpm)

Height of

water level

h (m)

Time of

water

collection

t (sec)

Suction

Head

(in CCl4)

Discharge

pressure

head

(m H20)

Suction

pressure

head

(inch)

Mass of

the load

M (g)

2000

150 10.4 16.7 1.5 0.66447797 720

120 10.3 15.1 1.9 0.60081541 700

70 10.4 10.2 4 0.40584882 575

2200

163 10.2 19.5 1.9 0.77588745 800

145 10.4 16.5 2.5 0.65652015 800

95 10.3 10.7 4.8 0.42574337 725

2400

170 10.5 19.8 2 0.78782418 850

145 10.4 17.5 3 0.69630925 850

95 10.4 11.6 6 0.46155356 800

Calculated data:

Area of the tank =83×32 cm2 = 0.2656m2

Cross sectional area of each of the 2 4 inch diameter pipes = 8.103×10-3 m2

Distance between motor shaft and torque arm=9 inch =9×2.54

100 m=0.2286m

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Table-2: Calculated data for volume of the tank, volumetric flow rate, suction

head and developed head.

Motor speed

(rpm)

Angular

velocity of

motor

(sec-1)

Volume of

the tank

occupied by

water

(m3)

Volumetric

flow rate,

Q

(m3/s)

Suction head

With respect

to Water

(m)

Developed

head

∆H

(m)

2000 209.44

0.037409 0.003597 0.66447797 0.835522

0.029927 0.002906 0.60081541 1.299185

0.017458 0.001679 0.40584882 3.594151

2200 230.384

0.040651 0.003985 0.77588745 1.124113

0.036162 0.003477 0.65652015 1.84348

0.023692 0.0023 0.42574337 4.374257

2400 251.328

0.042397 0.004038 0.78782418 1.212176

0.036162 0.003477 0.69630925 2.303691

0.023692 0.002278 0.46155356 5.538446

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Table-3: Calculated data for finding output and input power and thus efficiency

Angular

velocity

(sec-1)

Downward

force, F

(N)

Moment of

torque

(N.m)

Power input

(w)

Power

output

(w)

Efficiency

(%)

209.44

7.0632 1.614648 338.1718 29.35437 8.680312

6.867 1.569796 328.7781 36.87576 11.216

5.64075 1.289475 270.0677 58.94153 21.82472

230.384

7.848 1.794053 413.3211 43.75349 10.58583

7.848 1.794053 413.3211 62.60623 15.14712

7.11225 1.62586 374.5722 98.26674 26.23439

251.328

8.3385 1.906181 479.0767 47.80864 9.979329

8.3385 1.906181 479.0767 78.2354 16.33045

7.848 1.794053 450.8957 123.2299 27.33002

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Sample calculation:

Area of the tank, A= 83×32×cm2=83x32x10-4 m2 = 0.2656 m3

Cross-sectional area of 4 inch pipe dia. = x (2x2.54/100)π 2 =8.103x10-3m3

Distance between motor shaft and torque arm=9 inch =9×2.54

100 m=0.2286m

For 4th observation:

Height of water,

h = 163 mm

= 0.163 m

Volume of tank occupied by water,

V= A x h

= (area of tank- 2 × area of cross-section of 4 inch diameter pipe) × h

= (0.2656 -2× 8.103×10-3) × 0.163 m3

=0.040651 m3

Time of taking water, t = 10.2 seconds

Flow rate of water,

Q = V/t

= 0.040651/10.2 m3/s

= 0.003985 m3/s

Discharge pressure head = 1.9 m

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Suction pressure head = 19.5 in (of CCl4)

= 19.5×2.54/100 m (of CCl4)

= (19.5×0.0254) × 1559.68/995.647 m (of water)

= 0.77588745 m (of water)

Developed head,

∆H = Discharge head - Suction head

= (1.9 – 0.77588745) m

= 1.124113 m

Downward force at the end of torque arm,

F = M × g

= ((800×9.81)/1000) N

= 7.848 N

Moment of the torque,

τ = F×d

= (7.848 × 0.2286m)

= 1.794053 N.m

Angular velocity,

ω = 2πf

= 2 ×π ×2200/60

= 230.384 sec-1

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Power input,

Pi = τ x ω

= 1.794053 × 230.384

= 413.321106 W

Power output,

Po = ∆H×Q×ρ×g

= 1.124113 ×0.003985×995.647×9.81

= 43.75349 W

Efficiency = ((power output)/(power input)) ×100 %

= ( 43.75349 )/413.321106 ×100%

= 10.58583 %

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Results:

Motor speed

(rpm)

Developed

head

∆H

(m)

Volumetric

flow rate,

Q

(m3/s)

Power input,

Pi

(w)

Power

output, Po

(w)

Efficiency

(%)

209.44 0.835522 0.003597 338.1718 29.35437 8.680312

1.299185 0.002906 328.7781 36.87576 11.216

3.594151 0.001679 270.0677 58.94153 21.82472

230.384

1.124113 0.003985 413.3211 43.75349 10.58583

1.84348 0.003477 413.3211 62.60623 15.14712

4.374257 0.0023 374.5722 98.26674 26.23439

251.328 1.212176 0.004038 479.0767 47.80864 9.979329

2.303691 0.003477 479.0767 78.2354 16.33045

5.538446 0.002278 450.8957 123.2299 27.33002

Discussions:

10

The objective of this experiment was to study the characteristic curves of a centrifugal pump.

We applied three different speeds, 2000 rpm, 2200 rpm and 2400 rpm. For each speed we noted

readings for 3 different power inputs. Using the observed data we plotted graphs of head vs.

flow rate, fluid power vs. flow rate and efficiency vs. flow rate. The different graphs are

discussed below.

1. Head vs. fluid flow:

With increasing fluid flow the pressure head decreases. The curves were supposed to be linear

the same relationship is revealed for all three speeds but the structure of the graph fluctuated

slightly from the general convention due to some instrumental error.

2. Fluid power vs. flow rate:

Generally the fluid power increases as the flow rate increases from zero. At one point it reaches a

peak and then it decreases with increasing fluid flow. But our graph seems a little bit different.

This may be due to some machineries problem like the voltage power supply controller was not

accurate in reading

3. Efficiency vs. flow rate:

Efficiency varies with fluid power in the same way as fluid power. We found that the efficiency

was very small. . And the main reason of this low efficiency is different types of energy losses

such as

1. fluid friction in the passages & channels of the pump

2. shock losses due to the sudden change in direction of the liquid leaving the impeller and

joining the streams of liquid traveling circumferentially around the casing.

3. leakage loss

4. reciprocating loss

5. mechanical loss

6. hydraulic loss etc

There may also have been experimental errors while taking readings. For example,

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The time counting may have not been very accurate.

The discharge pressure was also fluctuating making it difficult to take an accurate

reading.

the pump that we used in the laboratory have some problem and controlling the constant

speed with the help of a tachometer was really a tough job.

In addition, some error could be introduced in the weight readings due to the parallax

error of our eyes.

References:

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1. Fluid Mechanics with Engineering Applications. (SI Metric Edition) by Robert L.

Daugherty, Joseph B. Franzini and E. John Finnemore

2. www.fluidscience.com/centrifugalpump/curves

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