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TRANSCRIPT
Lecture 6: Irrigation networks hydraulics
Prepared by
Husam Al-Najar
The Islamic University of Gaza- Civil Engineering DepartmentIrrigation and Drainage- ECIV 5327
Irrigation network
Irrigation network
Energy Losses(Head losses)
Major Losses Minor losses
The roughness of the pipe
The properties of the fluid
The mean velocity, V
The pipe diameter, D
The pipe length, L
Head (Energy) LossesWhen a fluid is flowing through a pipe, the fluid experiences some resistance due to which some of energy (head) of fluid is lost.
A. Major losses
1. Darcy-Weisbach formula2. The Hazen -Williams Formula3. The Manning Formula4. The Chezy Formula
Useful Formulas to find the Major losses
The Hazen -Williams formulaIt has been used extensively for designing of water- supply systems
V C R SHW h= 0 85 0 63 0 54. . .
85.1
87.47.10
=
HWf C
QD
Lh
85.1
62.7
=
HWf C
VDLh
V = mean velocity (m/s)Rh = hydraulic radiusS = head loss per unit length of pipe = CHW = Hazen-williams Coefficient
hLf
Hazen-Williams Coefficient, CHW, for different types of pipe
Example 1: A 100 m long pipe with D = 20 cm. It is made of riveted steel and carries a discharge of 30 l/s. Determine the head loss in the pipe using Hazen-Williams formula.
Solution:
V C R SHW h= 0 85 0 63 0 54. . .
54.063.0 )100/()05.0)(110(85.0 hfV=
RH = D/4 = 0.2/4 = 0.05 m
CHW = 110 from previous table
V = Q/A = 2
3
)2.0)(4/14.3()10(30 −x
=
hf = 0.68 m
The Manning Formula
V n R Sh=1 2 3 1 2/ /
3/16
223.10
DQLnh f =
2233.135.6 Vn
DLh f =
B. Minor lossesIt is due to the change of the velocity of the flowing fluid in the magnitude or in direction [turbulence within bulk flow as it moves through and fitting]
The minor losses occurs at :
• Valves • Tees• Bends• Reducers• And other appurtenances
It has the common form
g
VKL 2
2
The loss coefficient for elbows, bends, and tees
Compound Pipe flow The system is called compound pipe flow: When two or more pipes with
different diameters are connected together head to tail (in series) or connected to two common nodes (in parallel)
A. Flow Through Pipes in Series• pipes of different lengths and different diameters connected end
to end (in series) to form a pipeline
• Discharge:The discharge through each pipe is the same
332211 VAVAVAQ ===
332211 VAVAVAQ ===
B. Flow Through Parallel Pipes:
If a main pipe divides into two or more branches and again join together downstream to form a single pipe, then the branched pipes are said to be connected in parallel (compound pipes).
• Points A and B are called nodes.
Q1, L1, D1, f1
Q2, L2, D2, f2
Q3, L3, D3, f3
• Discharge:
• Head loss: the head loss for each branch is the same
∑=
=++=3
1321
iiQQQQQ
Q1, L1, D1, f1
Q2, L2, D2, f2
Q3, L3, D3, f3
321 fffL hhhh ===
gV
DL
fg
VDLf
gV
DLf
222
23
3
33
22
2
22
21
1
11 ==
Example 2.Three pipes connected in series have to be replaced by one pipe of the same total length. The diameters are 200mm, 250mm, and 300mm, and the lengths are 250 m, 500 m, and 250 m, respectively. Determine the slope of the new pipe that can transport flow of 40 l/s. All pipes are galvanized iron.
Sol: mCQ
DLh
hwf 5.2
12004.0
2.02507.107.10
85.1
87.4
85.1
87.41 =
=
=
mh f 7.1120
04.025.05007.10
85.1
87.42 =
=
mh f 35.0120
04.03.0
2507.1085.1
87.43 =
=
mh totalf 55.435.7.15.2 =++=∴ −
120
04.010007.10.554 7.1085.1
87.4
85.1
87.4
=⇒
=
DCQ
DLh
hwf
mD 235.0=∴ sm
AQv /922.0
235.04
04.02
=×
==∴π
54.063.0
54.063.0
4235.012085.0922.0 85.0 SSRCv hhw ×
××=⇒=
%45.00045.0 ==∴ S
Pump Classification
DynamicPositive displacement
Centrifugal SpecialReciprocating Rotary
Radial
Mix
Axial
Ejector
Electrom
echanical
Gas lift
Vane
Screw
Gear
Diaphragm
Plunger
Piston
Definition: Water pumps are devices designed to convert mechanical energy to hydraulic energy. They are used to move water from lower points to higher points with a required discharge and pressure head.
Pumping Systems
All forms of water pumps may be classified into two basic categories:
1. Turbo-hydraulic (Dynamic) pumps : Which includes three main types:
A. Centrifugal pumps ( Radial - flow pumps ).
B. Propeller pumps ( Axial - flow pumps ).
C. Jet pumps ( Mixed - flow pumps ).
Different types of impellers
Semi open ClosedOpen
Installation of centrifugal pump either submersible (wet) or dry
Dry execution situation (vertical and horizontal)
Wet execution (vertical and submersible)
Installation of centrifugal pump either submersible (wet) or dry
A. Screw pumps
Guide rim
Lining
el. motor
Touch point
Alternative drive with gear box and belt drive.
Gear box
Sec. A-A
In the screw pump a revolving shaft fitted with blades rotates in an inclined trough and pushes the water up the trough.
2. Positive Displacement pumps
B. Reciprocating pumps
Pumps System Curve
System Characteristic Curve• It is a graphic representation of the system head and is developed by plotting the
total head, Ht , over a range of flow rates starting from zero to the maximum expected value of Q.
• This curve is usually referred to as a system characteristic curve or simply system curve.
• For a given pipeline system (including a pump or a group of pumps), a unique system head-capacity (H-Q) curve can be plotted.
• The total head, Ht , that the pump delivers includes the elevation head and the head losses incurred in the system. The friction loss and other minor losses in the pipeline depend on the velocity of the water in the pipe, and hence the total head loss can be related to the discharge rate.
H H h h h hV
gt stat f d md f s msd= + + ∑ + + +∑2
2hfs : is the friction losses in the suction pipe. hfd : is the friction losses in the discharge (delivery) pipe.hms : is the minor losses in the suction pipe.hmd: is the minor losses in the discharge (delivery) pipe.
Pump Characteristic Curves
• Pump manufacturers provide information on the performance of their pumps in the form of curves, commonly called pump characteristic curves (or simply pump curves).
• In pump curves the following information may be given:• the discharge on the x-axis,• the head on the left y-axis,• the pump power input on the right y-axis,• the pump efficiency as a percentage,• the speed of the pump (rpm = revolutions/min).• the NPSH of the pump.
• The pump characteristic curves are very important to help select the required pump for the specified conditions.
• If the system curve is plotted on the pump curves we may produce. • The point of intersection is called the operating point. • This matching point indicates the actual working conditions, and therefore the proper
pump that satisfy all required performance characteristic is selected.
Pump Characteristic Curves
system curve
0
20
40
60
80
100
120
0 0.2 0.4 0.6 0.8Discharge (m3/s)
Hea
d (m
)
system operating point
Static head
Head vs. dischargecurve for pump
What happens as the static head changes (a tank fills)?
ph
Pumps in Pipe Systems
Multiple-Pump Operation• To install a pumping station that can be effectively operated over a
large range of fluctuations in both discharge and pressure head, it may be advantageous to install several identical pumps at the station.
Pumps in Parallel Pumps in Series
Qtotal =Q1+Q2+Q3 HTotal =H1+H2+H3
Long arm short arm
Low water level
Water pocket
Well
pivotWooden rod Load
Irrigation wells
Historical Background
GearsRotating wheel with water pockets
Channel
Low water level
Motor
Pump Shaft
Turbine Pump
Well
Submersible Pump and motor
Line shaft turbine pump Submersible pump
Irrigation well pumps
Submersible Well pumps components
Electric motor13Pump/motor coupling12Suction adapter11Suction inlet10Pump shaft9Lock collets8Intermediate bowl bearing7Up thrust collar6Impeller5Intermediate bowl4Discharge bearing3Discharge bowl2
Discharge pipe1
Line Shaft turbine pump
Two stage turbine pumpSingle- stage turbine pump
Table 1. Characteristics of Turbine Pumps
Pipe diameter (mm)
Capacity m3/h
fromfrom toto
Head per stage (m)Speed rpm
Model
Figure 1. Classification of pumps based on specific speed
Example 3
It is required to abstract 227 m3/ h water from well at 50 m depth for irrigation. Select the best and the most efficient irrigation pump for this purpose
1. The required flow = 227/ 0.2271 = 1000 Gpm = 0.0631 m3/s
2. For deep wells it is preferred to use turbine pumps
3. Turbine pumps are easy to maintain)
4. Specific speed based on one stage at 1440 rpm (Table 1)
5. Use figure 1. the efficiency = 78%, while the highest efficiency 83% could be reached at specific speed 2000. So we have to try 2 or 3 stages. On each stage the head should be divided by 2 and 3, respectively.
, 64.51 N 4/3sph
QN= 993
500631.01440 64.51 N 4/3s ==
2 stages:
3 stages:
6. Refer to figure 1. three stages will reach to the best efficiency, therefore the best pump for this purpose is Model 12S (Table 1) with head around 10 m for each stage and provide the required flow. So we need 5 stages pump of this model to cover the required head.
The specific speed at 5 stages =
7. At figure 1. (Q = 1000 Gpm, Ns= 3322, The efficiency equals 81% the best we can reach.
From Table 1. The best pump is Turbine pump, 12S model with pipe diameter 300 mm, 5 stages at speed 1440 rpm
1671 25
0631.01440 64.51 N 4/3s ==
2264 67.16
0631.01440 64.51 N 4/3s ==
3322 10
0631.01440 64.51 N 4/3s ==