ME 388 – Applied Instrumentation Laboratory

Centrifugal Pump Lab

References

• Streeter and Wylie, Fluid Mechanics (Ch.10)

• Holman, Experimental Methods for Engineers, (Ch.6)

• Munson (Ch.9)

• Any Fluid Mechanics book

Lab Objectives

• Understand operation of a dc motor

• Analyze fluid flow using– Centrifugal pump– Venturi flow meter

• Evaluate pump performance as a function of impeller (shaft) speed– Develop pump performance curves– Assess efficiencies

Lab Set-up

Motor

E I

T

Pump

Water Tank

Venturi

P( )

ValvePaddle meter

Dynamometer

Pin

Pout

dc motor

Figure 1. dc motor (howstuffworks.com)

•Armature or rotor •Commutator •Brushes •Axle •Field magnet •DC power supply

http://www.cheresources.com/centrifugalpumps1.shtml Centrifugal pump

http://www.pumpworld.com/contents.htm

Cavitation

Centrifugal pump operation

• Rotating impeller delivers energy to fluid

• Governing equations or Affinity Laws relate pump speed to:– Flow rate, Q

– Pump head, Hp

– Fluid power, P

Pump Affinity Laws

• N Q

• N2 Hp

• N3 P

2

13

2

1

2

12

2

1

2

1

2

1

P

P

N

N

H

H

N

N

Q

Q

N

N

p

p

Determination of Pump Head

12

21

22

2ZZ

g

VV

g

PPH inout

p

g

PPH inout

p

Determination of Flow Rate

• Use Venturi meter to determine Q

• Fluid is incompressible (const. )Q = Vfluid Area

Venturi Meter

• As V , kinetic energy T = 0 Height = 0 Pv or P

Calculate Q from Venturi data

22VACQ d

• V1 = inlet velocity

• V2 = throat velocity

• A1 = inlet area

• A2 = throat area

Throat Velocity

22

22

11

21

22Z

g

P

g

VZ

g

P

g

V

0Z 22

1

221 BV

A

AVV 21 PPP

),,(2 BPfV

vAmm 21

..

Discharge Coefficient

eDd R

BC 53.6907.0

1

2

D

DB

11DV

ReD 2

21

221 BV

A

AVV

Solve for Q

• Use MS EXCEL (or Matlab)

• Calculate throat velocity

• Calculate discharge coefficient using Reynold’s number and throat velocity

• Calculate throat area

• Solve for Q

Power and Pump Efficiency• Assumptions

– – No change in elevation– No change in pipe diameter– Incompressible fluid T = 0

• Consider 1st Law (as a rate eqn.)

0Q

12

21

2212 2

1ZZgVVhhmWQ

Pump Power Derivation

Pvuh vPuvPumhhmW 112212

12 PPvmW

QVAvm

12 PPQW

Efficiencies

EI

PPQEI

T

T

PPQ

input

output

overall

motor

pump

12

12

Summary of Lab Requirements

• Plots relating Hp, P, and pump to Q

• Plot relating P to pump

• Regression analyses

• Uncertainty of overall (requires unc. of Q)

• Compare Hp, P, Q for two N’s

– For fully open valve position– WRT affinity laws

Flow Rate (m3/s)

Pu

mp

He

ad

(m

) 905 rpm 1099 rpm 1303 rpm 1508 rpm

1709 rpm

905 rpm 1099 rpm 1303 rpm 1508 rpm

Flow Rate (m3/s)

Po

we

r D

ele

vere

d to

Flu

id (

W)

1709 rpm

pum

p ef

ficie

ncy

Flow Rate (m3/s)

905 rpm 1099 rpm 1303 rpm 1508 rpm

1709 rpm

Pum

p E

ffic

ienc

y

pump power delivered to fluid (W)

905 rpm 1099 rpm 1303 rpm 1508 rpm 1709 rpm

Start-up Procedure1. Fill pvc tube with water (3/4 full)

2. Bleed pump

3. Switch breaker to “on”

4. Push main start button

5. Make sure variac is turned counterclockwise

6. Make sure throttle valve is fully open

7. Turn lever to “pump”

8. Push “reset” button

9. Push “start” button

10. Adjust variac to desired rpm using tach.

Pump lab raw data

Shaft speed (rpm)

DC voltage (volts)

DC current (amps)

Inlet Pressure (in Hg)

Outlet Pressure (kPa)

Venturi DP (kPa)

Dyna (lbs)

Shut-down Procedure

1. Fully open throttle valve2. Turn variac fully counterclockwise3. Push pump stop button4. Turn pump lever to “off”5. Push main stop button6. Switch breaker to “off”