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```					     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

Venturi
(P)
Dynamometer

E       I
Pout
Pump
Motor
T                 Pin

Water Tank
dc motor

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

Figure 1. dc motor (howstuffworks.com)
Centrifugal pump
http://www.cheresources.com/centrifugalpumps1.shtml
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
– Fluid power, P
24
1400                  0.6
22

20                                                       1200
0.5
18

pump efficiency, 
1000
16

fluid power (W)
0.4
14

800
12                                                                             0.3
10                                                       600

8                                      operating point                         0.2
400
6

4                          pump head 1709 rpm                                  0.1
fluid power 1709 rpm     200
2                          pump efficiency 1709 rpm
0                                                         0                    0.0
0.000   0.002   0.004    0.006       0.008    0.010     0.012
3
Flow Rate (m /s)
Pump Affinity Laws
N1 Q1
• NQ          
• N2  Hp
N 2 Q2
• N3  P         2
 N1    H p1

N   
 2     H p2
3
 N1    P

N     1
 2     P2

Pout  Pin V22  V12
Hp                       Z 2  Z1
g         2g

Pout  Pin
Hp 
g
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

Q  C d A2V2
•   V1 = inlet velocity
•   V2 = throat velocity
•   A1 = inlet area
•   A2 = throat area
Throat Velocity
2             2
V1    P1  Z  V2  P2  Z
       1              2
2g     g          2g       g
A2        2        P  P  P2
Z  0    V1  V2     V2 B                1
A1
.    .          
m1  m 2  A v

V2  f (P, B,  )
Discharge Coefficient

B           D2
Cd  0.907  6.53           B
ReD          D1

V1 D1
ReD   
                 A2
V1  V2     V2 B 2
A1
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
–   
Q0
–   No change in elevation
–   No change in pipe diameter
–   Incompressible fluid
–   T = 0
• Consider 1st Law (as a rate eqn.)

  W  m h  h   1 V 2  V 2  g Z  Z 
Q   2 1
           2
2    1       2   1 

Pump Power Derivation
h  u  Pv
W  mh2  h1   mu2  P2v   u1  P v 
                                     1

W  mvP2  P 
 
1

mv  AV  Q


W  Q P  P 
2   1
Efficiencies
output QP2  P 
 pump                   1
input       T
T
 motor 
EI
QP2  P 
 overall           1
EI
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
905 rpm
1099 rpm
1303 rpm
1508 rpm
1709 rpm

3
Flow Rate (m /s)
905 rpm
1099 rpm
1303 rpm
Power Delevered to Fluid (W)

1508 rpm
1709 rpm

3
Flow Rate (m /s)
905 rpm
1099 rpm
1303 rpm
1508 rpm
1709 rpm
pump efficiency

3
Flow Rate (m /s)
Pump Efficiency

905 rpm
1099 rpm
1303 rpm
1508 rpm
1709 rpm

pump power delivered to fluid (W)
Start-up Procedure
1.    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   DC         DC        Inlet      Outlet     Venturi DP   Dyna
speed   voltage    current   Pressure   Pressure   (kPa)        (lbs)
(rpm)   (volts)    (amps)    (in Hg)    (kPa)
Shut-down Procedure

1.   Fully open throttle valve
2.   Turn variac fully counterclockwise
3.   Push pump stop button
4.   Turn pump lever to “off”
5.   Push main stop button
6.   Switch breaker to “off”

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