Transcript Pump Lab Notes Given in Class

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
Paddle meter
Valve
Venturi
(P)
Dynamometer
E
I
Pout
Pump
Motor
T
Water Tank
Pin
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
– Pump head, Hp
– Fluid power, P
24
1400
0.6
22
20
1200
0.5
Head (m)
14
800
12
10
600
operating point
8
400
6
pump head 1709 rpm
200
fluid power 1709 rpm
pump efficiency 1709 rpm
system load - head
4
2
0
0.000
fluid power (W)
1000
16
0.002
0.004
0.006
0.008
3
Flow Rate (m /s)
0.010
0
0.012
pump efficiency, 
18
0.4
0.3
0.2
0.1
0.0
Pump Affinity Laws
• NQ
• N2  Hp
• N3  P
N1 Q1

N 2 Q2
2
H p1
 N1 

 
H p2
 N2 
3
 N1 
P1

 
P2
 N2 
Determination of Pump Head
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
V2
P2

 Z1 

 Z2
2g
Z  0
g
g
2g
A2
V1  V2
 V2 B 2
A1
.
.
P  P1  P2

m 1  m 2  A v
V2  f (P, B,  )
Discharge Coefficient
B
Cd  0.907  6.53
ReD
ReD
V1 D1


D2
B
D1
A2
2
V1  V2
 V2 B
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.)


1 2


2



Q  W  mh2  h1   V2  V1  g Z 2  Z1 
2


Pump Power Derivation
h  u  Pv
 h2  h1   m
 u2  P2v  u1  P1v
W  m
 vP2  P1 
W  m

m v  AV  Q

W  QP2  P1 
Efficiencies
output QP2  P1 
 pump 

input
T
T
 motor 
EI
QP2  P1 
 overall 
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
Pump Head (m)
905 rpm
1099 rpm
1303 rpm
1508 rpm
1709 rpm
3
Flow Rate (m /s)
Power Delevered to Fluid (W)
905 rpm
1099 rpm
1303 rpm
1508 rpm
1709 rpm
3
Flow Rate (m /s)
pump efficiency
905 rpm
1099 rpm
1303 rpm
1508 rpm
1709 rpm
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.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Fill pvc tube with water (3/4 full)
Bleed pump
Switch breaker to “on”
Push main start button
Make sure variac is turned counterclockwise
Make sure throttle valve is fully open
Turn lever to “pump”
Push “reset” button
Push “start” button
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.
2.
3.
4.
5.
6.
Fully open throttle valve
Turn variac fully counterclockwise
Push pump stop button
Turn pump lever to “off”
Push main stop button
Switch breaker to “off”