pumps &pumping system
TRANSCRIPT
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Pumps and Pumping Systems
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Energy Balance for a Typical PumpingSystem
ELECTRICITY
100%
12% LOSS
2% LOSS
24% LOSS
9% LOSS
11% LOSS
MOTOR
COUPLING
PUMPS
VALVES
PIPES
WORK DONE ON WATER
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(Source:ASHRAE HVAC Systems and Equipment Handbook 2004)
Base plate-mounted centrifugal pump installation
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Centrifugal pump
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(Source: Wang, S. K., 2001. Handbook of Air Conditioning and Refrigeration)
A double-suction, horizontal split-case, single-stage centrifugal pump
Pump motor Centrifugal pump body
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CENTRIFUGAL PUMPS
DEFINITION: DEVICE THAT USES AN EXTERNAL POWERSOURCE TO APPLY FORCE TO A FLUID IN ORDER TOMOVE IT FROM ONE PLACE TO ANOTHER
USED TO DECREASE THE MECHANICAL ENERGY OFFLUID.
THE ENERGY DECREASES MAY BE USED TO DECREASETHE VELOCITY. THE PRESSURE OR THE ELEVATION OFTHE FLUID.
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CENTRIFUGAL PUMPS
PUMPS FIND APPLICATION IN VARIOUS TYPES OFINDUSTRIES SUCH AS
-CHEMICAL
-PETROCHEMICAL
-REFINERIES-FERTILISERS
-PAPER
-SUGAR ETC
THE PUBLIC WORKS, THERMAL POWER STATIONS, SEWAGETREATMENT PLANTS AGRICULTURAL SECTOR ALSO FINDMAJOR APPLICATION FOR PUMPS.
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*ADVANTAGES OF CENTRIFUGAL PUMPS
- SIMPLICITY
- LOW FIRST COST
- UNIFORM FLOW ( NON - PULSATING)
- SMALL FLOOR SPACE
- LOW OPERATION & MAINTENANCE EXPENSE
- QUICK OPERATION AND
- ADOPTABILITY TO USE WITH MOTOR OR
TURBINE DRIVE.
CENTRIFUGAL PUMPS
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INDUSTRY /SECTOR ANNUAL SAVING POTENTIAL
(in Rs. Million)* (in MW)
CHEMICAL &
PETROCHEMICAL PLANT 700 29.30
PULP AND PAPER PLANT 675 28.30
STEEL PLANT 400 16.70
FERTILIZER PLANT 300 12.60
THERMAL POWER PLANT 270 11.30
TEXTILE PLANT 100 4.20
CEMENT PLANT 45 1.90
COMMERCIAL BUILDINGS &
HOTELS 60 2.50
PUBLIC WATER WORKS 1500 62.80
OTHERS 200 8.40
TOTAL 4250 178.00
BREAK-UP OF ENERGY SAVINGS POTENTIAL
IN PUMPS
* BASED ON AVERAGE ELECTRICITY PRICE OF Rs 3.00 PER
UNIT AND OPERATING PERIOD OF 8000 HOURS PER YEAR
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HEAD
CAPACITY
CENTRIFUGAL PUMP CHARACTERISTICS
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HEAD
CAPACITY
CENTRIFUGAL PUMP CHARACTERISTICS
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E
FFICIENCY
CAPACITY
CENTRIFUGAL PUMP CHARACTERISTICS
BHP
CAPACITY
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HEAD
CAPACITY
CENTRIFUGAL PUMP CHARACTERISTICS
OPERATING POINT
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ENERGY CONSERVATION IN PUMPS ATDESIGN STAGE
SELECT PUMPS IN THEIR RANGE OF GREATEST EFFICIENCY,WHICH IS USUALLY IN THE RANGE OF 50-70% OF THEIRMAXIMUM CAPACITY.
DO NOT ALLOW AN EXTRA PRESSURE LOSS IN THE PIPINGAS A SAFETY FACTOR
PROVISION FOR AIR VENTING FROM THE SYSTEM IN DESIGN,INSTALLATION AND MAINTENANCE.
DO NOT OVERSIZE THE PUMP.
ENSURE ALL THE JOINTS ARE LEAK PROOF TO AVOID AIR
IMPRESS DURING PUMPING OPERATION. ENSURE THAT (NPSH)A >(NPSH)R
KEEP SECTION LIFT OF 4.5 TO 5M.
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SPECIFIC SPEED
SPECIFIC SPEED IS A CORRELATION OF PUMP CAPACITY,HEAD AND SPEED AT OPTIMUM EFFICIENCY.
DEFINITIONTHE SPECIFIC SPEED OF AN IMPELLER, IS THE REVOLUTIONPER MINUTE AT WHICH A GEOMENTRICALLY SIMILARIMPELLER WOULD RUN, IF IT WERE SUCH A SIZE AS TODISCHARGE 1M3/S, AGAINST 1M HEAD.
THIS IS A NUMBER EXPRESSED AS .
NS = ( N*Q)/H3/4Ns = SPECIFIC SPEED
N = ROTATIVE SPEED IN rpmQ = CAPACITY,m3/s
H = TOTAL HEAD, m
( Head per stage for a multistage pump)
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PUMP SUCTION PRESSURE
* SYSTEM PRESSURE
* STATIC PRESSURE
* LIVE PRESSURE DROP
PUMP DISCHARGE PRESSURE
* SYSTEM PRESSURE* STATIC PRESSURE
* LINE PRESSURE DROP
* PRESSURE DROP ACROSS INSTRUMENTS
* PRESSURE DROP ACROSS EQUIPMENTS DIFFERENTIAL PRESSURE
= DISCHARGE PRESSURE - SUCTION PRESSURE
PUMP PROCESS DESIGN
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HEAD
CAPACITY
CENTRIFUGAL PUMP CHARACTERISTICS
STATIC
HEAD
FRACTIONHEAD
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HEAD
CAPACITY
CENTRIFUGAL PUMP CHARACTERISTICS
STATIC HEAD
EFFICIENCY
SYSTEM CHAR.
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PUMP - OVER DESIGN* MORE USUALLY ENCOUNTERED DUE TO
DESIGNERS OVER PROVISION OF SAFETY
MEASUREMENT
* RESULTS HIGH EQUIPMENTS COST
* THE SYSTEM COULD SUFFER DUE TO THE
FOLLOWING
- THROTTLING MAY OCCUR, LEADING TOWEAR ON VALVES NOT DESIGNED FOR
CONTROL AND INCREASED NOISE LEVELS
- CAVITATION
- OVER LOADED MOTOR
- REDUCED PUMP LIFE ( ESPECIALLY IF THE
FLOW RATES ARE MUCH ABOVE THE
OPTIMUM)
- PUMP INLET CONDITIONS WILL SUFFER
- HIGH ENERGY COST
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PUMP - UNDER DESIGN
* PUMPS OPERATING AWAY FROM THEIR
DESIGNED DUTY POINTS, AT HIGHER HEADSAND DECREASED FLOW , RESULTING IN THE
PLANT BEING UNABLE TO MEET ITS DESIGN
PERFORMANCE
* INCREASE IN NOISE LEVELS
* REDUCED PUMP LIFE
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DESING CONSIDERATIONS
* OVER DESIGN LEADS TO CONSIDERABLE LOSS OFEFFICIENCY & ENERGY IN PUMPS
* MINIMISE OVER DESIGN
* AN IDEAL SAFTY MARGIN FOR A PUMP WILL
BE 10 % EACH ON CAPACITY & HEAD
* THE IDEAL MARGIN FOR MPSH WHOUD BE
0.5 - 1.0 M ON THE NPSH REQUIRED
* THE NORMAL ALLOWABLE MARGINS IN
POWER ARE 5 - 15 % BETWEEN THE MAXIMUMPOWER IN OPERATING A PUMP & THE MOTOR
RATING
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VARIOUS TYPE PUMP EFFICIENCY
* AUXIAL PUMP 80 %
* MIXED FLOW PUMP 70 %
* SINGLE STAGE CENTRIFUGAL PUMP 60 %
* MULTISTAGE CENTRIFUGAL PUMP 40 %
* TURBINE PUMP 50 %
* SUBMERCIBLE PUMP 35 %
* RECIPROCATING PUMP 30 %
* JET PUMP 15 %
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CASE STUDY 1
1.5 Kg/cm27.2m
0.4m
Globe valve
0.15Kg/cm2 0.8Kg/cm2
0.35Kg/cm2
21.2m
7. 5Kg/cm2
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Liquid pumped = hydrocarbon fluid
Flow rate =115m3/hr
Specific gravity at PT =1.20
Viscosity = 0.64
Vapour pressure =1.5Kg/Cm2
Geometric pipe length
Suction =10m
Discharge =100m
Fluid velocity
Suction =1m/s
Discharge =2m/s
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Equilibrium length in m
Pipe fitting suction Discharge
Gate valve 1.6 1.2Strainer 12 9
Elbow 6.1 4.6
Tee 4.8 3NRV 27.5 19.8
Entrance - 8
Exit 12 8Reducer 1.6 1.2
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Find out the following
A) suction & Discharge line sizes
B) Suction & Discharge pressure
C) Motor Hp required
D) (NPSH)a
Pump should be located at the storagearea so that the line pressure drop issmaller. Positive head developed is more.
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RECOMMENDED VELOCITIES FOR SIZING PUMP
SUCTION & DISCHARGE PIPE LINES
DESCRPTION SUCTION DISCHARGE
(m/s) (m/s)
VISCOUS LIQUIDS 0.50 0.80
LIGHT OILS 0.80 1.00
WATER 1.50 1.5 - 2.00
PIPE DIAMETER
PUMPIN
GCOST
CAPITA
LCOST
ECONOMIC PIPE DIAMETER
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Solution:
Suction side:Fluid flow rate = 115m3/hr
Q = Av
Q = /4Ds2*v
115/3600 = /4Ds2*1
Ds = 0.2016m
pf = 4fLv2/2gD
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Geometric length of the suction sideEquivalent length=10mL = (1.6*2)+4.8+(12*1)+(1.6*1)+3(6.1)+12
= 39.9+12=51.9.
L = Geometric length + equivalent pipe length for fitting.L = 10+51.9=61.9 m
NRe = [(D**v)/]= [(0.2016*1*1200)/0.6*10-3 ]
= 403200Since Turbulent flowF = 0.0035+0.264(403200)-0.42
F = 4.67*10-3
F = [(4*4.67*10-3*61.9*12)/2*9.81*0.2016]
= 0.2922m= 0.2922*10-4*1200= 0.0351Kg/Cm2
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Static head = (7.2-0.4)*1200*10-4 = 0.816Kg/Cm2
Suction pressure Kg/Cm2
System pressure 1.5
Static head 0.816
Line pressure drop -0.0351
Suction pressure 2.2809Kg/Cm2
Discharge side:
Q = AdVd
115/3600 = /4Dd2*2
Dd = 0.1426m
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Equivalent length calculation.
Gate value 6*1.2 7.2
Elbow 3*4.6 13.8
Tee 4*3 12.0Entrance 2*8 16.0
Exit 1*8 8
NRV 1*19.8 19.8
76.8 m
L = 100+76.8
= 176.8m
NRe = DVP/
= (0.1426*2*1200)/0.6*10-3
= 570400F = 0.0035+0.264(570400)-0.42
= 4.51*10-3
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pf =[(4*f*L*v2)/2gD]
pf = 4*4.51*10-3*176.8*22/2*9.81*0.1426= .56m
= 4.56*10-4*1200= 0.547Kg/Cm2
Static head = (21.2-0.4)*10-4*1200= 2.496Kg/Cm2
Discharge pressure Kg/Cm2
System pressure 7.5Pressure drop across cv 0.8Pressure drop across orifice 0.15Pressure drop across He 0.35Static head 2.496Line Pressure drop 0.547
Discharge pressure = 11.843Kg/Cm2
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Differential pressure = Discharge pressuresuction pressure= 11.843-2.2809
= 9.5621Kg/Cm2
= 95.621mWC
(NPSH)aSuction pressureVapour pressure
= 2.2809-1.5
= 0.7809 Kg/Cm2
=7.809 mWC
Safety margin = 0.600/7.209 mWC
=7.209/1.2 = 6.0075MLC
Horse power required
HHP = (115/3600)*[(1200*95.621)/75]= 48.87
BHP = HHP/Pump = 48.87/0.6 = 81.45Motor HP = BHP/Motor = 81.45/0.9 = 90
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CASE STUDY 2
CALCULATE NPSH AVAILABLE FOR THE PUMP SHOWN IN FIG.
LIQUID PUMPED CONDENSATE AT 850C AT 50m3/hr.
SPECIFIC GRAVITY AT 850C =0.9VISCOSITY AT 850C =0.32cpVAPOUR AT 850C =0.48kg/cm2
EQUIVALENT PIPE LENGTHFOOT VALVE =12mELBOW =3.2mGATE VALVE =1.4mSTRAINER =0.2mREDUCER =0.9m
0.5m
1m
0.5m
100pipe
4 x 3reducer
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SOLUTION:
Static head =10-4x900x1.5=0.135kg/cm2
System pressure =10.33mwc=1.033kg/cm2
Line pressure droppf =[(4*f*L*v2)/2gD]
L =(12*1)+(3.2*1)+(1.4*1)+(0.2*1)+(0.9*1)=17.7
L = 3+17.7=20.7
/4*D2*v = Q
/4*0.12*v = 50/3600
V= 50/3600*4/*1/0.01
V=1.77m/sec
NRe = [(D**v)/]=[(0.1*900*1.77)/0.32*10-3]=497812.5
F = 0.0035+0.264(497812.5)-0.42
F =4.57*10-3
pf =[(4*4.57*10-3*20.7*1.772)/(2*9.81*0.1)]=0.604m
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Kg/Cm2
System pressure 1.033
Static head -0.135
Line pressure drop(10-4*900*0.604)
-0.054=0.884Kg/Cm2
(NPSH) available
0.884
-0.480 (Vapour pressure)
=0.364 Kg/Cm2
=3.64 mwc
Safety margin =0.60mwc
=3.04mwc
(NPSH)a =3.04mwc
=3.04/0.9
=3.378MLC
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BOILER FEED PUMP WILL HAVE A CAPACITY
OF 1.2 TO 1.25 TIMES THE BOILER CAPACITY
COOLING TOWEER PUMPS IN A POWER PLANT
WILL HAVE A CAPACITY OF 60 TIMES THE
BOILER CAPACITY
PUMP CAPACITY
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PUMP EFFICIENCY = USEFUL OUTPUT POWER, kW
INPUT POWER, kW* 100
HHP
BHP* 100=
INPUT POWER, W =1 .73 VI COS V - SUPPLY VOLTAGE , 440 V
I - CURRENT CONSUMED BY THE PUMP, AMPS
COS - POWER FACTOR, NORMALLY > 0.8
W - POWER CONSUMED IN WATTS
OUTPUT POWER, BHP =
Q - FLOW RATE , m3/s
P - DIFFERENTIAL HEAD, kg/m2Q * P
102
PREDICTION OF PUMP EFFICIENCY
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FLOW RATE MEASURED, Q = 45 m3 /h
HEAD ,P = 30 kg/ cm2
= 30* 104 kg /m2
USEFUL OUTPUT POWER, kW
= (FLOW RATE, m3/ s) * (DIFFERENTIAL HEAD kg /m2) * 1/102
= 45 / 3600 * ( 30* 104) * 1/102
= 36.76 kW
VOLTAGE MEASSURED = 400 V
CURRENT MEASSURED = 85A
POWER FACTOR = 0.85
INPUT POWER, kW = 1 .73 VI COS / 1000
= 1 .73 * 400*85*0.85 / 1000
= 50 kW
36.76
EFFICIENCY = * 100
50
= 73.52 %
PREDICTION OF PUMP EFFICIENCYCASE STUDY 3
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EFFICIENCY OF CENTRIFUGAL PUMPS
Pump = (Output / Input)x100Pump = [Q*H*g*] / [3600 x motor x 1000 x P]
P = Input power in KW = [( 3 *V*I*COS) / 1000]
Q = Flow rate in m3/ h
G = Acceleration due to gravity, 9.807m/s
H = Head in m
= Fluid density, Kg / m3
Pump = Pump efficiency
Motor = Motor efficiencyV = Supply voltage, V
I = Current drawn by the motor, A
Cos = Power factor
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PUMP PERFORMANCE WITH IMPELLER
DIAMETER & OR SPEED CHANGE
Q1,H1,BHP1,D1 & N1 - INITIAL CAPACITY,
HEAD, BRAKE HORSE POWER, DIAMETER
& SPEED
Q2,H2,BHP2,D2 & N2 - NEW CAPACITY,
HEAD, BRAKE HORSE POWER, DIAMETER
& SPEED
DIAMATER CHANGE ONLY
Q2 = Q1( D2 /D1)
H2 = H1(D2/D1)2
BHP2 = BHP1(D2/D1)3
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CENTRIFUGAL PUMPS-CAPACITY
CONTROL
PARALLEL OPERATION
CONTROL VALUE WITH BY PASSREGULATION
SPEED REGULATION
THROTTLING AT CONSTANT SPEED
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ENERGY CONSERVATION OPTIONS IN
PUMPING SYSTEM
IMPELLER TRIMMING DOWN SIZING THE IMPELLER IMPELLER REPAIR AND REPLACEMENT REPLACEMENT WITH SMALLER PUMPS
SPEED VARIATION COMBINED THROTTLING & SPEED CONTROL DECENTRALIZATION OF PUMPING SYSTEM AVOID UNNECESSARY PUMPING
PROVIDE OVERHEAD TANK FOR GRAVITY FLOW
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FOR THE GIVEN PIPE SIZE
Normal Flow Rate = Q1 Normal Pressure Drop = P1 Max. Flow Rate = Q2 Max. Pressure Drop = P
2
What is the relation between P1& P2?
P2 = X2P1
Where X = (Q2/ Q1)
F l
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For example:
Q1 = 65 m3/ h , P1 = 0.45 kg / cm2
Q2 = 80 m3/ h , P2 = ?
P2 = (Q2/ Q1)2
*P1
=(80/65)2 * 0.45= 0.68 kg / cm2
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PUMP PERFORMANCE WITH IMPELLER
DIAMETER & OR SPEED CHANGE
SPEED CHANGE ONLY
Q2 = Q1(N2/N1)
H2 = H1(N2/N2)2
BHP2 = BHP1(N2/N1)3
DIAMETER AND SPEED CHANGE
Q2 = Q1(D2/D1 * N2/N1)
H2 = H1(D2/D1 * N2/N2)2
BHP2 = BHP1(D2/D1 * N2/N1)3
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* THE SUCTION LINE SHOULD NEVER BESMALLER THAN PUMP INLET & SHOULD BE
LARGER IF FEASIBLE
* WHEN TWO OR MORE PUMPS ARE CONNECTED
TO A COMMAN HEADER, A SUCTION LINE
SHOULD BE SELECTED LARGER ENOUGH SO
THAT THE FLUID DOESNOT TRAVEL FASTER
THAN 0.8 m/s THROUGH THE SUCTIONLINE AT
THE COMBINED CAPACITY.
* SLOPE UNIFORMLY TO PUMP FROM FLUID
SUPPLY TO AVOID AIR PACKETS
* BYPASS DESIGN SHOULD TAKE FLUID BACK
TO FLUID SOURCE & NOT INTO SUCTION LINE
* SUCTION LINE SHOULD BE FIRMLY ANCHORED
OR BURIED TO AVOID PUTTING A STRAIN ON
THE PUMP & TO HELP PREVENT SYSTEM
VIBRATIONS FROM ACTING DIRECTLY ON
THE PUMP
DESIGN OF PIPINGS
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DESIGN OF PIPINGS
FACTORS TO BE CONSIDERED IN THE DESIGN OF
SUCTION PIPING :
* PUMP SHOULD BE AS CLOSE TO THE FLUID
SUPPLY AS POSSIBLE
* USE FULL OPENING VALVES & AVOID
CONSTRICTING VALVES
* THE IDEAL PIPE ARRANGEMENT IS SHORT
AND DIRECT, USING NO ELLS. SHOULD ELLS
BE REQUIRED USE 45O LONG, RADIUS INSTEAD
OF 900
ELLS
* IF A REDUCER IS REQUIRED IN SUCTION LINE
BETWEEN MAIN LINE & PUMP, USE AN
ECCENTRIC REDUCER RATHER THAN
CONCENTRIC WITH STRAIGHT PORTION IN
TOP
CAVITATION:
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CAVITATION:
IT IS A PHENOMENON WHICH HAS BEEN KNOWN FOR ITSDESTRUCTIVE POWERS & GENERALLY ARISES BECAUSE OFTHE BOILING OF A LIQUID DUE TO LOW PRESSURE RATHER
THAN HIGH PRESSURE. CAVITATION CAN CREATE SEVERE EROSION ON PUMP
IMPELLERS WHICH IN TURN SETS UP VIBRATION AND NOISE,RUNNING WITH A RESULT AND LOSS IN PUMPINGEFFICIENCY.
VARIOUS FACTORS, EITHER COLLECTIVE OR INDIVIDUALLYCONTRIBUTE TO THIS PHINOMENON IN THE PUMPING FIELD.
ABNORMALLY HIGH SUCTION LIFTS OR IN CORRECT PIPELAYOUTS ARE TWO PROMINENT FAULTS.
GENERALLY SPEAKING, CENTRIFUGAL PUMPS ARE LIMITEDTO SUCTION LIFT OF A APPROXIMATES 4.5M HIGHER VALUECAN BE ACHIEVED UNDER CERTAIN CIRCUMSTANCE .
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THEORETICAL SUCTION LIFT 10.35M FOR WATER AT 40CSUCTION LIFT IS REDUCED BY
ATTITUDE
FRICTIONAL LOSSES IN THE SUCTION BY INCLUDINGVELOCITY HEAD AND ENTERY LOSSES.
THE EFFECT AND VAPOUR PRESSURE OF THE FLUID AT P.T.
REQUIRED NPSH.
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THE EFFICIENCYOF PUMP CAN BE IMPROVED BY THE ADOPTION OF THE FOLLOWING MEASURES
* RIGHT SELECTION OF PUMP FOR A PARTICULAR
APPLICATION
* SELECTION AND INSTALLATION OF CORRECT SIZE PUMPS
* ENERGY EFFICIENT OPERATING PRACTICES
* UNITIZATION OF PUMPS
* INSTALLATION OF VARIABLE SPEED DRIVERS
* SEREGATION OF HIGH-HEAD AND LOW-HEAD USERS
* UTILIZATION OF GRAVITY HEAD
CONCLUSON
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* INSTALLATION OF HIGH EFFICIENCY PUMPS
* RELOCATION OF PROCESS CODENSERS
* ADOPTION OF THE PROPER DESIGN PARAMETERS
FOR PUMPS AND PIPING
* PROPER INSTRUMENTATION AND CONTROL FOR EFFICIENT
OPERATION, MONITORING AND CONTROL
THE ENERGY EFFICIENCY IN PUMPING SYSTEMS IS BEST
ACHIEVED BY ADOPTION OF ENERGY CONSERVATION AND
RATED DESIGN CONSIDERATIONS AT THE IMPLEMENTATION
/ PROJECT STAGE.
CONCLUSON
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VALVES
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Types of Valves
Two basic groups: Stop valves - used to shut off or partially shutoff the flow of fluid ( ex: globe, gate, plug,needle, butterfly)
Check Valves - used to permit flow in onlyone direction (ex: ball-check, swing-check, lift-check)
Special types: Relief valves Pressure-reducing valves Remote-operated valves
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Globe Valve Most common valvein a propulsion plant Body may be straight,
angle, or cross type
Valve inlet and outletopenings aredesigned to suit
varying requirementsof flow
Valve may beoperated in thepartially open position
(throttled) Commonly used in
steam, air, oil andwater lines
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GateValve
Used for a straight line of flow where minimumrestriction is desired
Not suitable for throttling
May be rising stem or nonrising stem
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Ball Valve Most ball valves are
quick acting - only require90o turn to completelyopen or shut valve
Some ball valves mayhave gearing for ease ofuse (also increasesoperating time)
Used in seawater,sanitary, trim and drain,air, hydraulic, and oiltransfer systems
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Butterfly Valve
Lightweight, relatively small, and quick acting
May be used for throttling Used in freshwater, saltwater, lube oil, JP-5,
F-76, and chill water systems
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Check Valve
Allows fluid toflow in a systemin only onedirection
May be swing, lift,or ball type
Check valves
may be built intoglobe valves orball valves
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Relief Valve
Installed in piping systems toprotect them from excessivepressure
The relieving pressure is setby the force exerted on thedisk by the spring
Relief valves may have alever which allows manualopening of the valve for testpurposes
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Valve Operating Devices
Manual Handwheel or lever is directly connected to the stem and
is operated by hand
Hydraulic Hydraulic pressure is applied to one side of a pistonwhich is connected to the stem of the valve
Motor A hydraulic, electric, or air driven motor is used to turn the
stem of the valve
Solenoid Uses an electromagnet to open or close a valve against
spring pressure
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IMPROVING PUMPSPERFORMANCE & REDUCING
ENERGY CONSUMPTION
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Questions
How do pumps perform?
How can I select an efficient pump?
What causes a pump to become inefficient?
How can I determine my pumpsperformance?
How can I improve my pumps performance?
Will improving my pumps performance
reduce my energy bill?
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Basic Concepts
DefinitionEnergy = kilowatt-hours
o One kilowatt is 1.34 horsepower
o Hours = operating time
Energy cost is based on kwhr consumed andunit energy cost ($/kwhr)
Reducing energy costs
Reduce Input Horsepower
Reduce Operating HoursReduce Unit Energy Cost
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Improving Pumping Plant Efficiency
Adjust pump impeller
Repair worn pumpReplace mismatched pump
Convert to an energy-efficientelectric motor
Centrifugal or Booster Pump
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Shaft Frame Impeller Discharge Inlet
StuffingBox
BalanceLine
Volute WearingRings
entrifugal or Booster ump
Deep Well Turbine
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Deep Well Turbine
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SubmersiblePump
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Improving Pumping Plant
Performance
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Impeller Adjustment
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Effect of Impeller Adjustment
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Effect of Impeller AdjustmentCapacity
(gpm)
Total
Head(feet)
Overall
Efficiency(%)
Input
Horsepower
Pump 1 Before 605 148 54 42
After 910 152 71 49
Pump 2 Before 708 181 59 55
After 789 206 63 65
Pump 3 Before 432 302 54 61
After 539 323 65 67
Pump 4 Before 616 488 57 133
After 796 489 68 144
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Same Operating
Time
Same Volume
of Water
Pump 1 +16.7% -22.8%
Pump 2 +18.2% +5.0%
Pump 3 +9.8% -12.3%
Pump 4 +8.3% -16.8%
Effect of Impeller
Adjustment on Energy Use
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Repair Worn Pump
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Effect of Pump Repair
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Effect of Pump Repair
Before Pumping lift = 95 feet
Capacity = 1552 gpm
IHP = 83
Efficiency = 45%
After Pumping lift = 118
feet
Capacity = 2008 gpm
IHP = 89
Efficiency = 67%
Summary of the Effect of Repairing Pumps
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Summary of the Effect of Repairing Pumps
63 pump tests comparing pump performance before-and-after repair
Average percent increase in pump capacity 41% Average percent increase in total head 0.5%
(pumping lift only) Average percent increase in pumping plant
efficiency 33% IHP increased for 58% of the pumping plants.
Average percent increase in input horsepower 17%
Adjusting/Repairing Pumps
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Adjusting/Repairing Pumps
Adjustment/repair will increasepump capacity and total head
Adjustment/repair will increaseinput horsepower
Reduction in operating time isneeded to realize any energysavingsMore acres irrigated per set
Less time per set
Energy costs will increase ifoperating time is not reduced
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Replace Mismatched Pump
A mismatched pump is one that isoperating properly, but is not operatingnear its point of maximum efficiency
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Capacity (gpm)
Efficie
ncy
(%)
00
ImproperlyMatchedPump
Matched Pump
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Mismatched PumpPumping Plant Test Data
Pumping Lift (feet) 113
Discharge Pressure (psi) 50
Total Head (feet) 228
Capacity (gpm) 940
Input Horsepower 112
Overall Efficiency (%) 48
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Test 1
(Normal)
Test 2 Test 3
Capacity (gpm) 940 870 1060Pressure (psi) 50 79 15
Pumping Lift (feet) 113 112 112
Total Head (feet) 228 295 147
IHP 112 112 104Overall Efficiency (%) 48 57 38
Multiple Pump Tests
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Replacing this pump with one operating at anoverall efficiency of 60% would: Reduce the input horsepower by 19% Reduce the annual energy consumptionby 34,000 Kwhr Reduce the annual energy costs by$3,400 (annual operating time of 2000
hours and an energy cost of $0.10/kwhr)
Replacing a Mismatched Pump
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Replacing a Mismatched Pump
Pumping plant efficiency willincrease
Input horsepower demand
will decrease
Energy savings will occurbecause of the reduced
horsepower demand
How do I determine the
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condition of my pump?
Answer: Conduct a pumping plant testand evaluate the results using the
manufacturers pump performance data
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Pumping
Lift
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Pump
Capacity
DischargePressure
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FLOW METER
8 PIPE DIAMETERS DIAMETERS
2 PIPE
FLOW
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Input
Horsepower
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Is a pump worn or mismatched?
Multiple pump tests
Compare pump test datawith manufacturers pumpperformance curves
200TOTAL HEAD (fe et)
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0 100 200 300 400 500 600 700 800 900 1000 1100
PUMP CAPACITY (gpm )
0
50
100
150
200
REPAIRED PUMPPumping Lift = 102 ft
Capacity = 537 gpmInput Horsepower = 28
Overall Efficiency = 50%Kwhr/af = 211
WORN PUMPPumping Lift = 45 ftCapacity = 624 gpm
Input Horsepower = 19
Overall Efficiency = 39%Kwhr/af = 123
LargeDifference
SmallDifference
100TOTAL HEAD (feet)
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2000 2400 2800 3200 3600
PUMP CAPACITY (gpm )
0
20
40
60
80
1983 (64%)1984(54%)
1985 (62%)
100TOTAL HEAD (feet)
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2000 2400 2800 3200 3600
PUMP CAPACITY (gpm )
0
20
40
60
80
1983 (64%)
1984 (66%)
1985 (55%)
Recommended Corrective Action
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Recommended Corrective Action
Eo greater than 60% - no corrective action55% to 60% - consider adjusting impeller
50% to 55% - consider adjusting impeller;
consider repairing or replacing pump ifadjustment has no effect
Less than 50% - consider repairing orreplacing pump
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Energy-efficient Electric Motors
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Horsepower Standard Energy
Efficient10 86.5 91.7
20 86.5 93.0
50 90.2 94.5
75 90.2 95.0
100 91.7 95.8
125 91.7 96.2
Efficiencies of Standardand Energy-efficientElectric Motors
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Variable Frequency Drives
What is a Variable Frequency
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q yDrive?
Electronic device that changes thefrequency of the power to an electricmotor
Reducing the power frequency reduces
the motor rpmReducing the motor rpm, and thus the
pump rpm, decreases the pumphorsepower demando A small reduction in pump rpm results in a
large reduction in the horsepower demand
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When are Variable Freq enc
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When are Variable Frequency
Drives Appropriate?One pump is used to irrigate differently-
sized fields. Pump capacity must be
reduced for the smaller fieldsNumber of laterals changes during the
field irrigation (odd shaped fields)
Fluctuating ground water levels
Fluctuating canal or ditch water levels
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Unthrottled Throttled VFD
Acres 80 50 50Pressure (psi) 80 64 60
Capacity (gpm) 1,100 600 700
Input Horsepower 128 90 55
RPM 1770 1770 1345
Overall Efficiency (%) 40 24 44
Centrifugal pump used to irrigate
Both 80-and 50-acre fields
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Note: Pumping plants should beoperated at the reduced frequency
for at least 1,000 hours per yearto be economical
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Convert To Diesel Engines
Options for Converting From Electric Motors toEngines
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Engines
Direct drive (gear head)
Engine shaft to pump shaftefficiency = 98%
Diesel-generator
Engine shaft to pump shaft
efficiency less than about 80%
Considerations
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Brake Horsepower = Shaft HorsepowerEngines and motors are rated based on
brake horsepower ( 100 HP electric motorprovides the same horsepower as a 100 HPengine
Input horsepower of an engine is greaterthan that of an electric motor for the same
brake horsepower
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Engine HorsepowerMaximum horsepower
Continuous horsepower
About s of the maximum horsepower
Derated for altitude, temperature,accessories, etc.
200
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110
128
144
157167
173
1200 1400 1600 1800 2000 2200
ENGINE RPM
0
50
100
150
BRAKEH
ORSEPOWE
R
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0.390.38
0.37 0.37 0.370.38
1200 1400 1600 1800 2000 2200ENGINE RPM
0.30
0.32
0.34
0.36
0.38
0.40
FUELCONSUM
PTION
(lb/bhp-h
r)
40
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33.2
34.2
35.1 35.134.7
33.9
1200 1400 1600 1800 2000 2200
ENGINE RPM
30
32
34
36
38
EN
GINEEFFIC
IENCY(%)
160
PUMP HP CONTINUOUS ENGINE HP
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1400 1500 1600 1700 1800 1900 2000 2100 2200
RPM
0
20
40
60
80
100
120
140
HORS
EPOWE
R
PUMP HP CONTINUOUS ENGINE HP
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Fuel Use Versus RPM
RPM Pump FlowRate (gpm)
Gallons of Dieselper Hour
Gallons of Waterper Gallon of
Diesel
1500 1228 9 81871600 1731 11 96171700 2161 15 86441800 2486 19 8019
Electric Motors vs Diesel Engines:Which is the Best?
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Which is the Best?
Unit energy cost
Capital costs, maintenance costs, etc
Hours of operation
Horsepower
Cost of pollution control devices for
engines
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ElectricMotor
Diesel Engine
Capital Cost $5,500 $11,500 $16,500 $16,500
Unit Energy Cost $0.14/kwhr $0.95/gal $0.95/gal $1.25/galTotal Cost ($/af) 60.5 37.8 39.9 48.5
Comparison of electric motor and
diesel engine100 HP1,100 gpm2,000 hours per year
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Optimizing PumpSystems for Energy
Efficiency
What Is A Pump System?
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p y
A Pump System comprises of all piping,fittings and valves before and after a pumpas well as the motor and motor driver.
There can be multiple pumps, motors anddrives, and they can be arranged tooperate in parallel or in series.
Pump Systems can have static head(pressure), or be circulating systems(friction only systems)
First, Let's Get A Big PicturePerspective
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133
pOf Energy Flow in Pumping
SystemsElectric utilityfeeder
Transformer
Motor breaker/starter
Motor
Adjustable
speed drive(electrical)
Coupling PumpFluid
system
Ultimategoal
At each interface, there areinefficiencies. The goal should
be to maximize the overall costeffectiveness of the pumping, orhow much flow is delivered perunit of input energy.
Specific Energy Es
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p gy s
= Motor efficiency
= Pump efficiency
m
h
Es =fHS
g
mh
HS
= Fluid density
= Gravitationalconstant
= Static head
= Hydraulic System
factor
fHS
HS
g
=Pel x Time
Pumped Volumeph
ph
Understand The Ultimate Goal
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136
Understand The Ultimate Goal
Electric utilityfeeder
Transformer
Motor breaker/starter
Motor
Adjustable
speed drive(electrical)
Coupling PumpFluid
system
Ultimategoal
Maximize the overall effectiveness.
It Is Essential To Understand The
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137
Ultimate Goal Of The Fluid System To
Optimize It Understand why the system exists
Have clearly defined criteria for what isreally needed
Understand what's negotiable and what'snot
RequirementsFor Designing A System
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For Designing A System
Duration Curve (Flow) System Curve (Pressure vs. Flow)
Pump & Component selection
Annualized Flow Duration Curve
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0
1000
2000
3000
0 2000 4000 6000 8000 10000
Time [hours]
Inflow
[GPM]
Annualized Flow Duration Curve
Understand The Fluid System
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140
Understand The Fluid System
Electric utilityfeeder
Transformer
Motor breaker/starter
Motor
Adjustable
speed drive(electrical)
Coupling Pump Fluidsystem
Ultimategoal
Maximize the overall effectiveness.
System Curves Are Made Up Of TwoFundamental
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141
Components - The Static Head And The
Frictional Head120
80
40
0
Head,ft
500040003000200010000Flow rate, gpm
Static/Fixed
Friction
Total
Hydraulic System f
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Hydraulic System
Factor The Hydraulic System factor is
defined as The ratio of a hydraulic
systems static head to total head.
Head
Flow
Total
head Loss Head
Static Head
SYSTEM CURVE
HSf
HSf
fHSHS
HS +
HF
=
What Are Some Sources OfFriction In Pumping Systems?
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143
Friction In Pumping Systems?
Pipe walls
Valves
Elbows
Tees
Reducers/expanders
Expansion jointsTank inlets/outlets
(In other words, almost everything that the pumpedfluid passes through, as well as the fluid itself)
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Operational Costs Are InfluencedBy The Selection Of Components
And Their Size
al Frictional Cost Per 100 ft Of Pipe
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al Frictional Cost Per 100 ft Of Pipe
Assumptions: 80% combined pump and motor efficiency,electricity cost = 10 /kWh
5000
4000
3000
2000
1000
0
Annualcost($)
500040003000200010000
flow rate (gpm)
12"
14"
16"
Frictional Losses Can Be
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Frictional Losses Can Be
ranslated Into Operating Costs
12-inch line, 100 ft length, 10/kWh, full open valves,
80% combined pump & motor efficiency
Assumptions:
1000
800
600
400
200
0
AnnualC
ost($)
25002000150010005000flow rate (gpm)
Check valveButterfly valveSch. 40 pipe (new)
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Nameplate Data Applies ToOne Particular Operating
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148
One Particular Operating
Point200
150
100
50
0
Head,f
t
500040003000200010000Flow rate, gpm
Rated:3190 gpm, 97 ft
How Do We Know Where We'll Be
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100
90
80
70
60
50
40
30
head(ft)
500040003000200010000
flow rate (gpm)
Operating On The Pump Curve?
Pump and systemcurve intersection(operating point)
System head curve
Pump head curve
Nameplate
Efficiency And Brake Horsepower Are
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Commonly Plotted vs. Pump Flow
100
90
80
70
60
50
40
30
20
10
0head(ft)
,power(bhp),efficiency(%)
500040003000200010000
flow rate (gpm)
System
Pump headbrake hpefficiency
Operating
point
BEP
Using A Larger Pipe Changes The
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g g p gFrictional Part Of The System Curve
100
90
8070
60
50
40
30
head(ft)
500040003000200010000
flow rate (gpm)
System head,12" pipe
System head,
16" pipe
CENTRIFUGAL PUMP PERFORMANCE
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CENTRIFUGAL PUMP PERFORMANCE
WITH VSD REGULATION
FLYGT C 3531
30-60 HZ (295-590 RPM)
Specific Energy in Three DifferentSingle Pump Systems
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Single Pump Systems
Throttling
VSD Regulation
Speed / Flow
No static head 85% static head50% static head
Speed / FlowSpeed / Flow
On-Off Regulation
Now Let's Look At The
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154
Electrical End Of The ShaftElectric utilityfeeder
Transformer
Motor breaker/starter
Motor
Adjustable
speed drive(electrical)
Coupling PumpFluid
system
Maximize the overall effectiveness
Ultimategoal
Motor Efficiency CurvesA D d U Si A d
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Are Dependent Upon Size AndType
100
90
80
70
60
50
Efficiency(%)
1.21.00.80.60.40.20.0
Power (fraction of rated)
Rated horsepower3 57.5 1025 50100 125200fit 7.5 fit 100
Understanding DriveP f
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156
PerformanceElectric utility
feeder
Transformer
Motor breaker/starter
Motor
Adjustable
speed drive(electrical)
Coupling PumpFluid
systemUltimate
goal
Maximize the overall effectiveness
The Efficiency Of Inverters
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y
Is Affected By Operating Speed100
90
80
70
60
efficiency(%
)
1251007550speed (% of rated)
Typical inverter efficienciesas a function of motor speed
Evaluate System Design
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Is the system effectivenessacceptable?
If the system has static head,Compare with frictionlessperformance!
Re-Evaluate System ChoicesRelative To Needs
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Relative To Needs
Number of pumps
Pump sizes
VFD operation?
Pipe diameters
Component selection
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When the System isCommissioned the Theoretical
Calculations Should be
Compared to Actual OperationalData to Ensure that it is
Operating as Intended
Summary
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y
Most avoidable losses are in the pump andfluid system, not in the electrical front end
However, the electrical front end can helpreduce the fluid system losses
Be careful with local optimization
Determine the specific energy and comparewith the ideal
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MEASUREMENTS
Pressure measurement
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Together with temperature and flow,
pressure is the most important parameters inindustrial process control
The unit of pressure is the Pascal (Pa) with1Pa being 1N/m2
At the surface of the earth, the atmosphericpressure is generally about 100KPa. This issometimes referred to as a pressure of 1bar.
1.Manometers
U-tube manometer
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The cistern manometer
The inclined tube manometer
2.Diaphragms
Reluctance diaphragm gauge Capacitance diaphragm gauge
Bourdon tubes
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3
Force-balanceDead-weight tester
Spring
4Electrical pressure gauge
Strain gauge
Piezoelectric
piezoresistance
P
The basic manometer consistsof a U-tube containing a liquid.A
diff b t
Manometers
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P2
P1
1 2P P gh
pressure difference between
the gases above the liquid inthe two limbs produces adifference h in vertical heights
of the liquid in the two limbs.If one of the limbs is open tothe atmosphere then the
pressure difference is thegauge pressure.
Water, alcohol and mercury are commonlyused manometric liquids. U-tubemanometers are simple and cheap and can
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manometers are simple and cheap and can
be used for pressure differences in therange 20 Pa to 140KPa. The accuracy istypically about 1%.
Temperature affect---------liquid expansion
0 0
0
0 0 0
---real temperature
(1 ) exp
1
m V V
V V r r coefficient of cubical ansion of the liquid
V
V
Thus the pressure when measured by a
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U-tube manometer at a temperature ,when the manometer liquid density at
0C is known, is given by:
0
1h gP gh
Cistern manometer
An industrial form of the U-tube manometer is
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An industrial form of the U tube manometer is
cistern manometer. It has one of the limbswith a much greater cross-sectional area thanthe other.A difference in pressure betweenthe two limbs causes a difference in liquid
level with liquid flowing from one limb to theother.
1 2
1 2
2 2
1 2
1 1
( )
( ) ( 1)
P P gH h d g
A h A d
A d AP P d g d g
A A
c d g
Hhd
P1
P2
A2
A1
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This form of manometer thus onlyrequire the level of liquid in one
limb to be measured from a fixedpoint.
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The inclined tube manometerThe inclined tube manometer is a U-tube
manometer with one limb having a largercross-section than the other and the narrowerlimb being inclined at some angle to thehorizontal. It is generally used for themeasurement of small pressure differences
and g ives greater accuracy than thec o n v e n t i o n a l U - t u b e m a n o m e t e r .
dP1
P2
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H d
h
2 21 2 ( 1) ( 1) sin
1 1
A AP P d g gx
A A
x
Since A2 is much greater than A1, theequation approximates to:
1 2 sinP P gx
Initial zero levelwith no pressuredifference
Diaphragms
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With diaphragm pressure gauges, a differencein pressure between two sides of a diaphragmresults in it blowing out to one side or the other.If the fluid for which the pressure is required is
admitted to one side of the diaphragm and theother side is open to the atmosphere, thediaphragm gauge gives the gauge pressure. Iffluids at different pressures are admitted to thetwo sides of the diaphragm, the gauge givesthe pressure difference.
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1.Bourdon tubes
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The bourdon tube may be in the form of aC fl t i l h li l i l I ll f
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C, a flat spiral, a helical spiral. In all forms,
an increase in the pressure in the tubecauses the tube to straighten out to anextent which depends on the pressure.
This displacement may be monitored in avariety of ways, for example, to directlymove a pointer across a scale, to move aslider of a potentiometer, to move the core
of an LVDT.
2 Reluctance diaphragm gaugeThe displacement of thecentral part of the
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p
diaphragm increases thereluctance of the coil on oneside of the diaphragm anddecreases it on the other.
With the two coils connectedin opposite arms of an a.c.bridge, the out of balance
voltage is related to thepressure difference causingthe diaphragm displacement
2
0 0
2
N sL
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AC
d
d
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Capacitance pressure transducers were originally
developed for use in low vacuum research. Thiscapacitance change results from the movement of adiaphragm element. The diaphragm is usually metalor metal-coated quartz and is exposed to the process
pressure on one side and to the reference pressureon the other. Depending on the type of pressure, thecapacitive transducer can be either an absolute,gauge, or differential pressure transducer.
02
d
C d
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The capacitor can also form part of the tuning
circuit of a frequency modulated oscillator and sogive an electrical output related to the pressuredifference across the diaphragm.
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Calibration of thepressure gauges in the
i f 20P t
force balance gauge
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Dead-Weight Tester
Schematic
region of 20Pa to
2000kPa is generallyby means of the Dead-weight tester. Pressure
is produced by windingin a piston. Thepressure is determinedby adding weights to
the platform so that itremains at a constantheight.
MgP
A
Potentiometric Pressure Transducer
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Measurement of lowpressures (vacuum)
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Vacuum tends to be used for pressures lessthan the atmospheric pressure, namely
1.013105 Pa. A unit that is often used forsuch pressure is the torr, this being the
pressure equivalent to that given by a columnof mercury of height 1 mm.
1mmHg=133.322Pa=1 torr
The lower the absolute pressure is, the higherthe degree of vacuum is.
Pressure measurement
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Pressure driven equipment (IC engines, turbines, etc.) Pneumatic or Hydraulic mechanical elements
Biomedical applications (Blood Pressure, BarometricChambers)
Losses in pipes and ducts energy efficiency Atmospheric conditions (weather forecast, altitude)
Indirect measurement of flow rate or velocity
Scuba diving
Many, many more ...
Pressure
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Pressure in a fluid acts equally in all directions
Pressure in a static liquid increases linearly with depth
p=increase indepth (m)
pressureincrease
g h
The pressure at a given depth in a continuous, static body of
liquid is constant.
p1p2
p3 p1 =p2 =p3
Measuring pressure (1)Manometers
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h
p1p2=pa
liquid
density
x y
z
p1 = px
px = py
pz= p2 = pa
(negligible pressure
change in a gas)
(since they are at
the same height)
py - pz =gh
p1 - pa =gh
So a manometer measures gauge pressure.
Measuring Pressure (2)Barometers
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A barometer is used to measure
the pressure of the atmosphere.
The simplest type of barometer
consists of a column of fluid.
p1 = 0vacuum
h
p2 = pa
p2 - p1 =gh
pa =gh
examples
water: h = pa/g =105/(103*9.8) ~10m
mercury: h = pa/g =105/(13.4*103*9.8)
~800mm
PRESSUREMEASUREMENT
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Absolut, Differential
Barometer
Manometer
Absolute pressure
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Presiune
referinta
Pabs = 0
TRPabs
Barometer
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hgP
AhgA0AP
hgabs
hgabs
P=0
Patm
h
h
A
Patm A
0
Well-type manometer
Differentialpressure
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12 PPP
P1P2
Types of pressures
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Static And Dynamic Pressure
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Dynamic pressure = Stagnation pressure (A) - Static pressure (B)
Static And Dynamic Pressure
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Dynamic pressure = Stagnation pressure (A) - Static pressure (B)
Types of pressure transducers:
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Liquid Column manometers Elastic tubes, diaphragms, membranes
(equipped with displacement or strain
sensors) Semiconductor elements (with implanted
stress elements)
Piezoelectic elements (directly convertcrystal lattice stress into voltage)
Liquid Column Manometers
PP
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hgPP
AhgAPAP
12
12
P2
h h
A
P2 A
P1
P1 A
U tube manometer
Liquid Column Manometers
P
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hgPP
AhgAPAP
12
12
P2h h
A
P2 A
P1
P1 A
12 AhgAPAP
InclinedManometer
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r12
r
r
12
h)sin(gPP)sin(hh
h
h)sin(
hgPP
P2h
hr
AP2 A
P1
P1 A
Pressuretransducers
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atm2 PPP
P2Patm
Pressure transducers
Elastic elements Tub
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Changing pressurechange the shape ofthe elastic element
Shape changing isdetected by a resistiveor position transducer
Tip C Spirala Tubrasucit ElicoidalTuburiBourdon
CapsulaDiafragme
P Absoluta
PDiferentialaPlata
Ondulata
evacuat
Diferential sau absolut
Pressure transducers
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Elastic elements Changing pressurechange the shape ofthe elastic element
Shape changing isdetected by aresistive or position
transducer
Pressure Sensor range
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Elastic Type Manometers
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More Elastic types...
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Two dummy gages
mounted elsewhere
Why do we not put 4 active gages?
Dial-type Manometer
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Dial-type Manometer as a mini measurement system
Diaphragm type manometers
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To be able to detect pressure, we need to detect the
diaphragm deflection
Strain gauges used with Diaphragm
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Strain gage based pressure cell
When a strain gage, is used to
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When a strain gage, is used to
measure the deflection of an elasticdiphragme or Bourdon tube it becomesa comonent in apressure transducer
Strain-gage transducers are used fornarrow-span pressure and fordifferential pressure measurements.
Essentially, the strain gage is used tomeasure the displacement of an
elastic diaphragm due to a differencein pressure across the diaphragme If the low pressure side is a sealed
vacuum reference, the transmitter willact as an absolute pressuretransmitter.
Strain gage transducers areavailablefor pressure ranges as low as
1300 MPa
Capacitance based pressurecell
Capacitance pressure
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Capacitance pressure
transducerswere originally developedfor use in low vacuum research. Thiscapacitance change results from themovement of a diaphragm element
(The diaphragm is usually metal ormetal-coated quartz and is exposed tothe process pressure on one side andto the reference pressure on the other.
Depending on the type Differential pressure transducers in avariety of ranges and outputs ofpressure, the capacitive transducercan be either an absolute, gauge, ordifferential pressure transducer.
Capacitance pressure transducershave a wide rangeability, from high
vacuums in the micron range to 70MPa.
The potentiometric pressure
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The potentiometric pressure
sensor provides a simple methodfor obtaining an electronic outputfrom a mechanical pressuregauge.
The device consists of a precisionpotentiometer, whose wiper arm ismechanically linked to a Bourdon
or bellows element. This type of transducer can beused for low differential pressureapplications as well as to detectabsolute and gauge pressures.
The resonant wire pressuretransducer
The resonant-wire pressure transducer
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p was introduced in the late 1970s. a wire is gripped by a static member at one
end, and by the sensing diaphragm at theother. An oscillator circuit causes the wire tooscillate at its resonant frequency.
A change in process pressure changes thewire tension, which in turn changes theresonant frequency of the wire. A digitalcounter circuit detects the shift. Because this
change in frequency can be detected quiteprecisely, This type of transducer can be used for low
differential pressure applications as well asto detect absolute and gauge pressures.
Resonant wire transducers can detectabsolute pressures from 10 mm Hg,differential pressures and gauge pressuresup to 42 MPa. Typical accuracy is 0.1% of
calibrated span, with six-month drift of 0.1%
Piezoelectric sensors
Piezoresistive pressure sensors are sensitive toh i t t d t b t t
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changes in temperature and must be temperature
compensated. Piezoresistive pressure sensors can be used from
about 21 KPa to 100 MPa. Resonant piezoelectric pressure sensors measure
the variation in resonant frequency of quartz crystals under an
applied force. The sensor can consist of a suspended beam that
oscillates while isolated from all other forces. The
beam is maintained in oscillation at its resonantfrequency. Changes in the applied force result inresonant frequency changes. The relationshipbetween the applied pressure P and the oscillationfrequency is:
P = A(1-TO/T) - B(1-TO/T2) where TO is the period of oscillation when the
applied pressure is zero, T is the period ofoscillation when the applied pressure is P, and Aand B are calibration constants for the transducer.
These transducers can be used for absolutepressure measurements with spans from 0-100kPa to 0-6 MPa or for differential pressuremeasurements with spans from 0-40 kPa to 0-275kPa .
Magnetic pressure transducers
These included the use of inductance, reluctance, and eddy currents.
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, , y
Inductance is that property of an electric circuit that expresses the amountof electromotive force (emf) induced by a given rate of change of currentflow in the circuit.
Reluctance is resistance to magnetic flow, the opposition offered bymagnetic substance to magnetic flux.
In these sensors, a change in pressure produces a movement, which in turnchanges the inductance or reluctance of an electric circuit.
Optical pressure transducers
Optical pressure transducers detect theff t f i t ti d t h
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effects of minute motions due to changesin process pressure and generate acorresponding electronic output signal.
A light emitting diode (LED) is used as thelight source, and a vane blocks some ofthe light as it is moved by the diaphragm.As the process pressure moves the vanebetween the source diode and themeasuring diode, the amount of infraredlight received changes.
Optical pressure transducers do notrequire much maintenance.
They have excellent stability and aredesigned for long-durationmeasurements.
They are available with ranges from 35
kPa to 413 MPa and with 0.1% full scaleaccuracy.
Sensor/Cavity System Response(Helmholz Resonator)
4
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0
0.5
1
1.5
2
2.5
3
3.5
Pressure
Pressure signal at the source
Pressure signal at the sensor face
2 / 2C a
fV L a
where Cis the sound velocity,L and a are the
length and area of the connecting tube and V
is the cavity volume.In this second order system air acts as mass,
the pressure acts as a spring and the
connecting tube as a damping element.
Thefundamental natural
frequency of the tube/cavity
system may be expressed as
Bourdon tube over pressureprotection
Most pressure instruments are
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p
provided with overpressureprotection of 50% to 200% ofrange These protectors satisfy themajority of applications. Wherehigher overpressures areexpected and their nature istemporary (pressure spikes ofshort durationseconds or less),snubbers can be installed.
If excessive overpressure isexpected to be of longer duration,one can protect the sensor byinstalling a pressure relief valve.However, this will result in a lossof measurement when the reliefvalve is open.
Mechanical High pressuresensors
In the case of the button repeater ( figA), the diaphragm can detect extruder pressures up to 10,000 psig and canoperate at temperatures up to 4300C because of its selfcooling design It operates on direct force balance
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operate at temperatures up to 4300 C because of its selfcooling design. It operates on direct force balance
between the process pressure (P1) acting on the sensing diaphragm and the pressure of the output air signal (P2)acting on the balancing diaphragm. The pressure of the output air signal follows the process pressure in inverseratio to the areas of the two diaphragms. If the diaphragm area ratio is 200:1, a 1,000-psig increase in processpressure will raise the air output signal by 5 psig.
Another mechanical high pressure sensor uses a helical Bourdon element (Figure B). This device may include asmany as twenty coils and can measure pressures well in excess of 10,000 psig. The standard element material isheavy-duty stainless steel, and the measurement error is around 1% of span. Helical Bourdon tube sensorsprovide high overrange protection and are suitable for fluctuating pressure service, but must be protected fromplugging. An improvement on the design shown in Figure B detects tip motion optically, without requiring anymechanical linkage.
Vacuum mesurement
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Vacuum gauges in use today fall into threemain categories:
mechanical, thermal,
ionization.
Vacuum mesurement
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Semiconductor-type Sensors
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Static Calibration
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2
cyl
mgp
R
Pressure transducers
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Pressure transducers
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Pressure transducers
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Pressure transducers
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Pressure transducers
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Pressure transducers
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Converter a.c. / c.c.Amplifier
Output voltage
Pressureservo-transducer
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ArmInductivemotor
Pivotiaphragm
P1 P2Pressure cell
Reluctance detector
Piezoelectric pressuretransducer
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Differentialamplifier
Charge amplifier
Compensation crystal Y2
Crystal Y1
Diaphragm
P1
Power
Preso-sensitive switch
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Relay
C1 C2
A
Pressure admission
B
Fluid Flow Measurements
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Pitot Tube Venturi Meter
Orifice Meter
Rotameter Others
Coriolis (Vortex shedding)
Turbine
Pitot Tube1 atm
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V1 12
h1
h2
2 21 21 1 2 2
1 2
1 1
2 2s
c c c c
P Pg gv h W v h F
g g g g
Pitot Static Tube
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h
V1
1
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t
i
D
D Ratio of throat diameter to pipe ID
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24
2
1
V
cC Pv g
CV = coefficient of discharge (accounts for friction losses)
Usually CV = 0.98, see Figure 5.9, p 155 for CV as a function of Re.
If a manometer is used to measure P, then
2 4 21V
m fCv gh
Orifice Meter
Vena contracta
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h
V1
P1
Di is the pipe ID and Do is the orifice diameter
Do/Di
Orifice Design Equation
2 4m
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20.61 2i c fD g P
With 0.2
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W
V
If calibrated for one fluid, then
1/ 2
12 1
2
Q Q
Others
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1. Vortex-shedding flow meter flow past a bluntobject causes vortexes2. Turbine meters paddle wheel speed measures
flow rate
3. Thermal gas mass flow meter a slip stream isheated by a constant heat input and temperaturerise is related to the gas mass flow
4. Magnetic flow meters a magnetic field isgenerated across a conducting fluid with the
induced voltage proportional to the flow velocity5. Coriolis mass flow meter fluid enters two U-tubeside channels where coriolis forces cause a twist inthe tubes. Twist angle is proportional to mass flowrate.
Unsteady FlowD1, v1
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1
2
h
z1
z2
Toricellis Equation
D2, v2
2 2v gh
Velocity of surface 1
1
dhv
dt
From the equation of continuity
2
12 1
2
Dv v
D
Flow Measurement, Q
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Tracer method BS5857 Ultrasonic flow measurement
Tank filling method
Installation of an on-line flowmeter
Tracer Method
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The Tracer method is particularly suitable for cooling water flow measurement becauseof their sensitivity and accuracy.
This method is based on injecting a tracer into the cooling water for a few minutes at an
accurately measured constant rate. A series of samples is extracted from the system at a point
where the tracer has become completely mixed with the cooling water. The mass flow rate is
calculated from:
qcw = q1 x C1/C2
where qcw = cooling water mass flow rate, kg/s
q1 = mass flow rate of injected tracer, kg/s
C1 = concentration of injected tracer, kg/kg
C2 = concentration of tracer at downstream position during the plateau periodof constant concentration, kg/kg
The tracer normally used is sodium chloride.
Ultrasonic Flow meter
Operating under Doppler effect principle these meters are non-invasive, meaning
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measurements can be taken without disturbing the system. Scales and rust in the pipes arelikely to impact the accuracy.
Ensure measurements are taken in a sufficiently long length of pipe free from flow
disturbance due to bends, tees and other fittings.
The pipe section where measurement is to be taken should be hammered gently to enable
scales and rusts to fall out.
For better accuracy, a section of the pipe can be replaced with new pipe for flow
measurements.
Tank filing method
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In open flow systems such as water getting pumped to an overhead tank or a sump, the flow
can be measured by noting the difference in tank levels for a specified period during which
the outlet flow from the tank is stopped. The internal tank dimensions should be preferabletaken from the design drawings, in the absence of which direct measurements may be
resorted to.
Installation of an on-lineflowmeter
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If the application to be measured is going to be critical and periodic then the best option
would be to install an on-line flowmeter which can rid of the major problems encountered
with other types.
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additional
PumpsBernoullis Theorem Pressure head: measure of fluids mech. PE
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Velocity head: measure of fluids mech. KE Friction head: measure of energy lost that heats fluid
Z1 + P1/ + V12/2g = Z2 + P2/ + V2
2/2g + [(U2 U1) W Q]
q + wshaft = (h2 h1) + (v22 v12)/2 + g(z2z1)
Z/z: fluid height; P: fluid pressure; : fluid density
V/v: fluid velocity U: internal energy W/w: work
Q/q: heat transferred h: enthalpy g: grav. acceleration
BOTTOM LINE: Total energy within the control volume isconstant under SS conditions.
Flow of Fluids in Pipes
ASSUMPTIONS:
S d fl (fl d i
GOALS: Understand how the fluid pressure and flow speed change frompoint to point along the pipe.
2
2
2
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Steady state flow (flow speed isconstant in time at any givenpoint along pipe).
No internal energy change (notransformation of mechanical
energy to thermal energy, noviscousdrag).
Irrotational flow (no vorticity, nowhirlpools, eddies, etc.)
ANALYSIS:
Conservation of Mass. Work Energy Theorem.
111
Principle of Continuity
v1
Consider the amount (mass m1) of fluid passing into the region betweenpoints 1 and 2 in the pipe during a time t:
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1
2
1111 Atvm
A1 1
length
volume
This is the mass of the fluidthat passed point 1.
Principle of Continuity
1
v1
v2
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12
Conservation of mass (along with steady state flow) says that whateverflowed into the region between 1 and 2 MUSThave flowed out:
222111
222111
21
AvAv
AtvAtv
mm
The productv A is called mass flow rate with units kg/s.
Principle of Continuity
1
v1v2
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12
ASSUMPTION: The fluid density remains constant (liquid).
2211
2211
AvAvAvAv
The productv A is called (volume) flow rate with units m3/s.
For the flow of liquids, pipe cross-sectional area A (and A alone) governs
flow speed. In particular, flow speed increases through a constriction.
Check Question on Principle of Continuity
Water flowing at 0.4 m/s through a pipe of circular cross section 2.0 cm indiameter meets a constriction of diameter 1.0 cm.
a) What is the flow speed within the constricted portion of the pipe in m/s?b) What is the volume flow rate of the water in the pipe?
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The Bernoulli Equation
2
y
y2
v2
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1
y1
111
222
gyAtv
gyAtvPE
Principle of Continuity says:
VAtvAtv 2211
yggygyV
PE
12The change in gravitational PEperunit volume swept out.
v1
The Bernoulli Equation
2
y
y2
v2
1
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1
y1
v1
2111
2222
2
1
2
1
vAtv
vAtvKE
Principle of Continuity says:
VAtvAtv 2211
221222
1
2
1
2
1vvv
V
KE
The change in gravitational KEper unit volume swept out.
The Bernoulli Equation
2
y
y2
v2
p2A2
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1
y1
v1
tvAp
tvApW
222
111
Principle of Continuity says:
VtvAtvA 2211
pppV
W
21The work done on system by adjacent fluidper unit volume swept out.
p1A1
The Bernoulli Equation
V
PE
V
KE
V
W
The Work Energy Theorem relates the net work to the change in totalmechanical energy:
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VVV
021 2 ygvp
22221
211
2
1
2
1gyvpgyvp
Thereby giving us Bernoullis equation in its two common forms:
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BASIC VACUUM
PRACTICE
Why is a Vacuum Needed?
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To move a particle in a (straight) line over a large distance
(Page 5 manual)
Why is a Vacuum Needed?
Atmosphere (High)Vacuum
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Contamination
(usually water)Clean surface
Atmosphere (High)Vacuum
To provide a clean surface
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HOW DO WE CREATE A
VACUUM?
VACUUM PUMPING METHODSVACUUM PUMPS
(METHODS)
Gas Transfer
Vacuum Pump
Entrapment
Vacuum Pump
Positive Displacement Kinetic Adsorption
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Sliding Vane
Rotary Pump
Molecular
Drag Pump
Turbomolecular
Pump
Fluid Entrainment
Pump
Reciprocating
Displacement Pump
Drag
Pump
Positive Displacement
Vacuum Pump
Kinetic
Vacuum Pump
Rotary
Pump
Diaphragm
Pump
Piston
Pump
Liquid Ring
Pump
Rotary
Piston Pump
Rotary
Plunger Pump
Roots
Pump
Multiple Vane
Rotary Pump
Dry
Pump
Adsorption
Pump
Cryopump
Getter
Pump
Getter Ion
Pump
Sputter Ion
Pump
Evaporation
Ion Pump
Bulk Getter
Pump
Cold TrapIon Transfer
Pump
Gaseous
Ring Pump
Turbine
Pump
Axial Flow
Pump
Radial Flow
Pump
Ejector
Pump
Liquid Jet
Pump
Gas Jet
Pump
Vapor Jet
Pump
Diffusion
Pump
Diffusion
Ejector Pump
Self Purifying
Diffusion Pump
Fractionating
Diffusion Pump
Condenser
Sublimation
Pump
BAROMETER
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WATER MERCURY
760
mm
Mercury: 13.58 times
heavier than water:
Column is 13.58 x shorter :
10321 mm/13.58=760 mm
(= 760 Torr)
10.321
mm
29,9
in
(Page 12 manual)
PRESSURE OF 1 STANDARD
ATMOSPHERE:
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ATMOSPHERE:
760 TORR, 1013 mbar
AT SEA LEVEL, 0O C AND 45O LATITUDE
Pressure Equivalents
Atmospheric Pressure (Standard) =
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0
14.7
29.9
760
760
760,000
101,3251.013
1013
gauge pressure (psig)
pounds per square inch (psia)
inches of mercury
millimeter of mercury
torr
millitorr or microns
pascalbar
millibar
THE ATMOSPHERE IS A MIXTURE OF GASES
PARTIAL PRESSURES OF GASES CORRESPOND TO THEIR RELATIVE VOLUMES
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GAS SYMBOL
PERCENT BY
VOLUME
PARTIAL PRESSURE
TORR PASCAL
Nitrogen
Oxygen
ArgonCarbon Dioxide
Neon
Helium
Krypton
HydrogenXenon
Water
N2
O2
ACO2
Ne
He
Kr
H2X
H2O
78
21
0.930.03
0.0018
0.0005
0.0001
0.000050.0000087
Variable
593
158
7.10.25
1.4 x 10-2
4.0 x 10-3
8.7 x 10-4
4.0 x 10
-4
6.6 x 10-5
5 to 50
79,000
21,000
94033
1.8
5.3 x 10-1
1.1 x 10-1
5.1 x 10
-2
8.7 x 10-3
665 to 6650
(Page 13 manual)
VAPOR PRESSURE OF WATER AT
VARIOUS TEMPERATURES
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T (O C)
100
25
0
-40
-78.5-196
P (mbar)
1013
32
6.4
0.13
6.6 x 10 -4
10 -24
(BOILING)
(FREEZING)
(DRY ICE)
(LIQUID NITROGEN)
(Page 14 manual)
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(Page 15 manual)
Vapor Pressure of some Solids
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(Page 15 manual)
PRESSURE RANGES
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RANGE
ROUGH (LOW) VACUUM
HIGH VACUUM
ULTRA HIGH VACUUM
PRESSURE
759 TO 1 x 10 -3 (mbar)
1 x 10 -3 TO 1 x 10 -8 (mbar)
LESS THAN 1 x 10 -8 (mbar)
(Page 17 manual)
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GAS FLOW
CONDUCTANCE
(Page 24 manual)
Viscous and Molecular Flow
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Viscous Flow(momentum transfer
between molecules)
Molecular Flow(molecules move
independently)
FLOW REGIMES
Viscous Flow:
Distance between molecules is small; collisions betweenl l d i t fl th h t t f
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Distance between molecules is small; collisions betweenmolecules dominate; flow through momentum transfer;
generally P greater than 0.1 mbar
Transition Flow:
Region between viscous and molecular flow
Molecular Flow:
Distance between molecules is large; collisions between
molecules and wall dominate; flow through random motion;generally P smaller than 10 mbar-3
(Page 25 manual)
MEAN FREE PATH
MOLECULAR DENSITY AND MEAN FREE PATH
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MOLECULAR DENSITY AND MEAN FREE PATH
1013 mbar (atm) 1 x 10-3 mbar 1 x 10-9 mbar
#
mol/cm3
MFP
3 x 10 19
(30 million trillion)4 x 10 13
(40 trillion)4 x 10 7
(40 million)
2.5 x 10-6 in
6.4 x 10-5
mm
2 inches
5.1 cm
31 miles
50 km
FLOW REGIMES
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Mean Free Path
Characteristic DimensionViscous Flow: is less than 0.01
Mean Free Path
Characteristic Dimension
Molecular Flow: is greater than 1
Mean Free PathCharacteristic Dimension
Transition Flow: is between 0.01 and 1
Conductance in ViscousFlow
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Under viscous flow conditions doubling thepipe diameter increases the conductance
sixteen times.
The conductance is INVERSELY related to
the pipe length
(Page 28 manual)
Conductance in MolecularFlow
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Under molecular flow conditions doubling
the pipe diameter increases the conductance
eight times.
The conductance is INVERSELY related tothe pipe length.
SYSTEM
Series Conductance
RT
= R1
+ R2
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SYSTEM
PUMP
C1
C2
1 = 1 + 1C1 C2CT
1 = C1 + C2C1 x C2CT
CT = C1 x C2
C1 + C2
(Page 29 manual)
GAS LOAD
Outgassing Permeation
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Outgassing
Leaks
Virtual
Real
Backstreaming
Diffusion
GAS LOAD (Q) IS EXPRESSED IN:mbar liters per second
Pumpdown Curve10+1
10-1
Volume
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Pressur
e(mbar)
Time (sec)
10-1110 1 10 3 10 5 10 7 10 9 10 11 10 13 10 15 10 17
10-3
10-5
10-7
10-9
Surface Desorption
Diffusion
Permeation
Roughing Pumps
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2(Page 39 manual)
VACUUM PUMPING METHODSVACUUM PUMPS
(METHODS)
Gas Transfer
Vacuum Pump
Entrapment
Vacuum Pump
Positive Displacement
Vacuum Pump
Kinetic
Vacuum Pump
Adsorption
Pump
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Sliding Vane
Rotary Pump
Molecular
Drag Pump
Turbomolecular
Pump
Fluid Entrainment
Pump
Reciprocating
Displacement Pump
Drag
Pump
Vacuum Pump Vacuum Pump
Rotary
Pump
Diaphragm
Pump
Piston
Pump
Liquid Ring
Pump
Rotary
Piston Pump
Rotary
Plunger Pump
Roots
Pump
Multiple Vane
Rotary Pump
Dry
Pump
Pump
Cryopump
Getter
Pump
Getter Ion
Pump
Sputter Ion
Pump
Evaporation
Ion Pump
Bulk Getter
Pump
Cold TrapIon Transfer
Pump
Gaseous
Ring Pump
Turbine
Pump
Axial Flow
Pump
Radial Flow
Pump
Ejector
Pump
Liquid Jet
Pump
Gas Jet
Pump
Vapor Jet
Pump
Diffusion
Pump
Diffusion
Ejector Pump
Self Purifying
Diffusion Pump
Fractionating
Diffusion Pump
Condenser
Sublimation
Pump
PUMP OPERATING RANGES
Rough VacuumHigh VacuumUltra High
Vacuum
Rotary Vane Mechanical Pump
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10-12 10-10 10-8 10-6 10-4 10-2 1 10+2
P (mbar)
Venturi Pump
y p
Rotary Piston Mechanical Pump
Sorption Pump
Dry Mechanical Pump
Blower/Booster Pump
High Vac. Pumps
Ultra-High Vac. Pumps
VACUUM SYSTEM USE
98
1
23
Chamber
High Vac. PumpR hi P
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1
2
4
6
5
8
7
3
3a
4
56
7
8
9
g pRoughing Pump
Foreline Pump
Hi-Vac. Valve
Roughing ValveForeline Valve
Vent Valve
Roughing Gauge
High Vac. Gauge
7
33a
(Page 44 manual)
Rotary Vane, Oil-SealedMechanical Pump
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(Page 45 manual)
Pump Mechanism
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How the Pump Works
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(Page 46 manual)
OIL BACKSTREAMING
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2
PRESSURE LEVELS: LESS THAN 0.2 mbar
The Molecular Sieve/Zeoli