Download - Pipe System Design
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Fall 2009 CE154 1
Pipe System DesignCE154 - Hydraulic Design
Lecture 7
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Pump System
Fall 2009 CE154 2
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Fall 2009 CE154 3
Pump Terminology
Pump head (dynamic head) H
Pump discharge Q
Pump speed n Pump power P
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Centrifugal Pump
Fall 2009 CE154 4
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Rotary Pump
Fall 2009 CE154 5
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Reciprocating Pump
Fall 2009 CE154 6
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Fall 2009 CE154 7
Pump Terminology
Power P
Motor
efficiency m
PumpEfficiency p
Q, H
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Fall 2009 CE154 8
Pump Terminology
Pump Output (Water) Power (Q in gpm, H inft, s is specific gravity and dimensionless, andP in horsepower)
Pump Input (Brake) Power
3960QHsPw
p
QHsbhp3960
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Fall 2009 CE154 9
Pump Terminology
Electric Motor Power
Typically motor efficiency is approximately
98%
mp
QHsmhp
3960
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Fall 2009 CE154 10
Pump Terminology
Single or Double suction pump Single or multiple stage pump
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Fall 2009 CE154 11
Pump Specific Speed
Q is gpm per suction, n is rpm, H is ft per stage
Pump Type Ns (US unit)
Radial Pump 500-4200
Mixed flow Pump 4200-9000Axial flow Pump 9000-15000
HQN
ns 75.0
5.0
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Fall 2009 CE154 12
Pump Performance
Variable-Speed pumps may bedesirable when different operatingmodes require different pump head orflow
Homologous lawsQ1/Q2 = n1/n2
H1/H2 = (n1/n2)2P1/P2 = (n1/n2)3
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Pump Performance Curves
Fall 2009 CE154 13
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Fall 2009 CE154 14
Pump Terminology Static Lift elevation difference
between pump centerline and thesuction water surface. If the pump ishigher, static lift is positive. If pump is
lower, static lift is negative. Static Discharge elevation differencebetween the pump centerline and theend discharge point. If pump is higher,static discharge is negative.
Total Static Head sum of static liftand static discharge.
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Fall 2009 CE154 15
Pump Terminology
Shutoff Head head at 0 flow
Operating point the point where thepump curve and the system curveintersect. A system curveis a curvedescribing the head-flow relationshipof the pipeline system.
QbaH 2
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Fall 2009 CE154 16
System Curve
friction losses
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Fall 2009 CE154 17
Operating Point
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Fall 2009 CE154 18
Pump Terminology
Net positive suction head (NPSH)- to ensure that water does not vaporize atthe pump impeller tip
- NPSH available = available suction head +atmospheric pressure vapor pressure suction head loss = determined by localcondition
- NPSH required = characteristic of andprovided by pump curve
hhhhNPSH svpsatmA
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Fall 2009 CE154 19
Example (p. 10.3 Mays HDH)
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Fall 2009 CE154 20
Atmospheric Pressure
At mean sea level,1 atomospheric pressure = 14.69 psia
= 1.03 kg/cm2
= 760 mm HgEl.(ft) 0 1000 2000 4000 6000 8000
Patm(psia) 14.69 14.17 13.66 12.69 11.8 10.9
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Fall 2009 CE154 21
Vapor pressure
Vapor pressure of water at atmosphericpressure
T
(F)
32 40 50 60 68 80 90
Pv(psia)
0.089 0.112 0.178 0.256 0.339 0.507 0.698
T(F) 100 120 140 160 180 200 212
Pv(psia)
0.949 1.69 2.89 4.74 7.51 11.53 14.70
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Fall 2009 CE154 22
Pipe System Design
Determine system curve- identify all loss-incurring elementsincluding friction, transitions, fittings,
valves and other special equipment inthe system (use Darcy-Weisbachequation to compute friction loss)
- identify suction and dischargeconditions
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Fall 2009 CE154 23
Design Scenario Ex. 8-1
Need to deliver water from SantaTeresa Water Treatment Plant atelevation 300 ft to Cisco Power Plant atelevation 330 ft. The maximum flow
demand is 200 cfs. Design pipe size andregulating devices for operation. Basic design approach
- consider steady-state, governing case- design pipe size and control equipment- check transientcondition to verifypipe pressure class
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Fall 2009 CE154 24
Example 8-1
1. Prepare a list of available design data:- Design discharge 200 cfs- Suction water elevation El. 300 ft
North Am. Vertical Datum (NAVD88 )- Discharge water elevation El. 330 ftNAVD88
2. Prepare a list of data requirements:- Topographic maps to route pipeline- Right of way maps- Utility and road crossing maps
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Fall 2009 CE154 25
Example 8-1
- Select a pump station site to setpreliminary pump elevation:
-- assume 2 Pumps set at El. 290 ft
-- station design includes 40 ft ofpipeline, 4 isolation valves and 2 pumpdischarge valves
- No other information on discharge siteis needed (for hydraulic design), otherthan the maximum tank level at 330 ft.
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Fall 2009 CE154 26
Example 8-1
3. Assume that we have selected a routethat results in a pipeline 8.0 miles long,and the fittings include- 80 bends of 90,- 25 bends of 45,- 10 butterfly valves for isolation
4. Determine pipe diameter- rule of thumb maintain operatingvelocity at 6-8 ft/sec (h V2,consider economic analysis later)
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Fall 2009 CE154 27
Example 8-1 Pipe Sizing
Design maximum discharge Q = 200 cfsassume V = 8 ft/secA = 200/8 = 25 ft2
D = 5.64 ft = 67.7 inchesSay D = 72 inch why?A = 28.27 ft2V = 7.1 ft/sec
Next, determine pipe material. For thissize, steel and reinforced concretepipes are available. Say RCP.
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Fall 2009 CE154 28
Example 8-1
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Fall 2009 CE154 29
Example 8-1 Friction loss
From roughness chart, for 72 concretepipes, in the mid roughness range, i.e., notnew but not seriously corroded,
e/D = 0.0005 f=0.017 From equation for turbulent rough flows,
f= 0.017 O.K.
D
e
f
log214.11
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Fall 2009 CE154 30
Example 8-1 Friction loss
When the pipe is significantly corroded,the chart shows that
e/D = 0.0017 and f=0.023
When new pipe, the chart showse/D = 0.000165 and f=0.0135
Use the mid roughness values fordesign, and use the new pipe and roughpipe values to check the system designto ensure operability.
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Fall 2009 CE154 31
Example 8-1 Friction loss
Compute friction loss:h = f L/D V2/2g
= 0.017 x 8 x 5280 / 6 x V2/2g
= 119.7 V2/2g= 119.7 x (7.1)2/2/32.2= 93.7 ft
Compute minor losses:Size the butterfly valves:
Use Val Matic valve data
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Fall 2009 CE154 32
Example 8-1 Valve data
Val Matic butterfly valve data
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Fall 2009 CE154 33
Example 8-1 Valve sizing
Q=Cv(P)1/2
Q = 200 cfs x 448.8 gpm/cfs = 89760 gpm
Considerations:- use the smallest size of valve that can
pass the design flow with acceptable headlosses
Valve size (in) Fully-open Q (gpm) P (psi)
72 266500 142 87100 1
54 144000 1
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Fall 2009 CE154 34
Example 8-1 Valve loss
For this example, lets try 72 valves. At 266500 gpm, the valve incurs 1 psiof loss.In terms of
Q = 266500 gpm = 593.8 cfsA = 28.27 ft2, V = 21.0 fps,
h = 1 psi = 2.31 ft, kv = 0.337 At 200 cfs, V=7.1 fps, h = 0.26 ft pervalve
gkh V2
2
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Fall 2009 CE154 35
Example 8-1(Val Matic BFV)
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Fall 2009 CE154 36
Example 8-1 Minor loss
Compute 90 bend losses:Assume r/D=2, from Slide 34 of lastlecture, kb90 = 0.19
There are 80 bends at 90.
Compute 45 bend losses (25 of them):Assume r/D=2, k
b45
= 0.1 (Crane TP410).There are 25 bends at 45
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Fall 2009 CE154 37
minor loss Reference
This web link provides a few pages fromthe Crane Co. technical paper 410(selling for $35 at Crane Co.) for
calculating minor losseshttp://www.lightmypump.com/help16.html
http://www.lightmypump.com/help16.htmlhttp://www.lightmypump.com/help16.htmlhttp://www.lightmypump.com/help16.htmlhttp://www.lightmypump.com/help16.html -
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Fall 2009 CE154 38
Example 8-1 System head loss
Compute total head loss:
Since we have suction piping as well, computeloss in the suction pipe
g
g
gD
Lf
ggD
Lf
Vh
Vh
Vknknknh
Vknknkn
Vh
l
l
bbbbvvl
bbbbvvl
28.140
2)1.02519.080337.0107.119(
2)(
2)(
2
2
2
2
45459090
2
45459090
2
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Fall 2009 CE154 39
Example 8-1 Pipe sizing
Assume the pumpstation has 2 pumps.To have the samevelocity in the pipes,the pump dischargeand suction pipediameter is 54.
Additionally, 1 pipebifurcation and 1combining tocontribute to minor
losses
549.50
2
1
72
1
1
2
1
2
1
D
DA
A
D
D
E l 8 1 P S i
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Fall 2009 CE154 40
Example 8-1 Pump StationLoss
Losses at pump station:
f = 0.0175 from Slide 32, Lecture 8
hf = (0.0175 x 40 / 4.5)V542
/2g= 0.16V542/2g
Bifurcation loss: kbi = 0.3 V542/2g
Combining loss: kcm = 0.5 V542
/2g Valve loss: kv = (0.337 x 2 +3.0) V542/2g
Total loss = 4.63 V542/2g
E l 8 1 S t
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Fall 2009 CE154 41
Example 8-1 SystemSchematics
El. 300 ftEl. 290 ft
El. 330 ft
Hp
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Fall 2009 CE154 42
Example 8-1 System Curve
Total static headHst = 330-300 = 30 ft
Losses
pump station loss + pipeline loss= 4.63 V542/2g + 140.8 V722/2g= 4.63 Q542/(2gA542) + 140.8 Q722/(2gA722)= 4.63 Q
72
2/(8gA54
2) + 140.8Q72
2/51483.8)= 4.63Q2/65159.2 + 140.8Q2/51483.8= (0.000071 + 0.002734)Q2= 0.002805Q2
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Fall 2009 CE154 43
Example 8-1 System Curve
System CurveH = 30 + 0.002805 Q2
H
(ft)
30. 31.8 37.0 45.8 58.1 73.8 93.1 115.9 142.2 172.0
Q(cfs
)
0 25 50 75 100 125 150 175 200 225
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Fall 2009 CE154 44
Example 8-1 System Curve
The Q in system curve is the total flow
Since we have 2 pumps, each pump putsout half of the total Q
In this case, need to construct the 2-parallel-operating pump curve bydoubling the flows
Plot the system curve over the pumpcurve to determine the pump operationpoint
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Fall 2009 CE154 45
Example 8-1 Pump Selection
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Fall 2009 CE154 46
8-1 Pump Operating Point
Select 17.57 impeller
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Fall 2009 CE154 47
Ex. 8-1 Pump operating point
For new and old pipe conditions, revisesystem curves and determine if the pumpcan operate at these limits. In new pipes,pump may run-out (fall off the far end of
the pump curve), or not meeting the higherNPSH requirement. In really old pipes, pump may not be able
to deliver the required flow rate.
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Fall 2009 CE154 48
Ex. 8-1 New Pipe Operation
In this case, new pipe f=0.0135 insteadof 0.017. Friction loss coefficientbecomes 116.2 instead of 140.8. System
curves becomesH = 30 + 0.002326Q2
E l 8 1 N i
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Fall 2009 CE154 49
Example 8-1 New pipecondition
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Fall 2009 CE154 50
Ex. 8-1 Pump Suction Design Verify NPSHA meets NPSHR
Assume average temperature of 68F,
hatm = 14.53 psia, interpolated from Table on
Slide 18 hv = 0.339 psia
hs = 300-290 = 10 ft
hs = 4.63 V542/2g = 4.63 (6.29)2/64.4 = 2.84 ft NPSHA = (14.53-0.339)x2.31 + 10 2.84 = 39.9 ft
NPSHR = 7 ft from pump curve OK
hhhhNPSH svpsatmA
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Fall 2009 CE154 51
Example 8-1 System HGL
El. 300 ftEl. 290 ft
El. 330 ft
Hp
Normal operation HGL
PipePressure
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Fall 2009 CE154 52
Example 8-1 Steel Pipe design
Internal pressure p
Cutting the steel pipe in half, integratethe pressure over the top inside surface,the resulting force is supported by the
wall thickness at the two ends.
p
t
pipe diameter D
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Fall 2009 CE154 53
Example 8-1 Pipe design
Total force on the top side
Stress on the wall
pDprprdpr 2cossin 00
t
pDs2
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Fall 2009 CE154 54
Steel Pipe Specifications
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Fall 2009 CE154 55
Steel Pipe Specifications
Concrete cylinder pipe
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Fall 2009 CE154 56
Concrete cylinder pipe(Ameron)
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Fall 2009 CE154 57
Example 8-1 Pipe design
Separate the pipeline into differentsections of similar design pressure leveland select pipe classes to match thepressure requirements.
This pressure is the normal designpressure.
Consider transient conditions to ensuresafe operation, e.g., pump start, pumpshutdown, valve closure, & loss of power
Concepts of hydraulic
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Fall 2009 CE154 58
Concepts of hydraulictransients
Bulk modulus of elasticity
Change in density is accompanied by change
in pressure. This change is transmittedthrough the system at the speed of theelastic wave (sonic wave)
d
dpE
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Fall 2009 CE154 59
Wave speed
E = elastic modulus of pipe wall
K = bulk modulus of watere = pipe wall thicknessD = pipe diameter = water density
a = wave speed
E
K
e
D
K
a
1
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Fall 2009 CE154 60
Transient pressure
Joukowsky equation
V = instantaneous change in velocity
a = wave speed in pipeg = gravitational accelerationH = rise in head
g
VaH
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Fall 2009 CE154 61
Transient considerations
Consider normal (pump start, valveclosure, etc.) and abnormal (powerfailure, valve malfunction, etc.)
operations to determine pressurefluctuations
Vacuum pressure and subsequent vapor
pocket collapse Remedial actions
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Fall 2009 CE154 62
Example 8-1 Discussion
Pump suction design requirement ofsuction tank, suction pipe velocity,function of isolation valves
Pipe system design proportions ofhead loss elements, cost consideration,right of way consideration
Pump selection multiple pumps vs.single pump, power consumption
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Fall 2009 CE154 63
Homework #8
Design a pipeline system to deliver a maximumof 60 cfs of cooling water from AndersonReservoir with minimum water El. 300 ft to a
Calpine power plant 15 miles away at El. 250ft. The minimum water pressure at the endof the line should be 10 ft above atmospheric.Ground elevation at the reservoir is El. 220
ft. Draw the pipeline profile with normaloperation HGL. Try the attached pump curveto see if it is appropriate to use. If not, websearch for a pump curve or design your own.
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Homework #8