1. Welcome

2. HYDRAULICS OF MICROIRRIGATION
Dr K Yell Reddy, FIE
Principal Scientist & Project Manager
AP Water Management Project

4. Tube Section Section (internal) A = 3.14 x r2
Example: pipe PVC with diameter (external) 24 mm ; thickness 2mm
A: the internal radius will be (24- (2x2mm) / 2) =10 mm the section will be 10 x 10 x 3.14= 314 mm2 or 3.14 cm2

5. Water Flow in Pipes V = L / t (m/sec) Q = A x V (m3/h or cm3/sec)
Velocity = Length / time
V = L / t (m/sec)
Flow rate = Section x Velocity
Q = A x V (m3/h or cm3/sec)
Example :in a pipe of 8” the flow rate is 100 m3/h flow velocity ??
Internal section 8” (20 cm de diameter) is 10 x 10 x 3.14=314 cm2
The flow rate 100m3/h or liter/3600 sec =27777 cm3/sec
the velocity V=Q/A will be / 314 = cm/sec or 0.9 m/sec

6. Water Flow in Pipes Q = A x V (m3/h or cm3/sec)
Flow rate = section x Velocity
Q = A x V (m3/h or cm3/sec)
The flow rate will change ?? The velocity will change ??
Q = A1 x V1= A2 x V2= A3 x V (m3/h or cm3/sec) the flow rate is constant

7. Pressure
the pressure is the force applied by a liquid on a surface
P = F / A
kg (or lb)
bar (or psi)
cm2 (or sq.inch)

8. P = F / A Pressure head (on bottom of 10 meters water)
the pressure is defined in kg per cm2
here the volume will be of 10m on 1 cm2 , or 1000cm x 1cm
or 1000 cm3 =1liter =1kg
the pressure will be of 1kg/cm2= 1 At
10m
1 At= 1kg/cm2
1psi= 1 lb/inch2
1At=14.22 psi
P = F / A

9. Pressure and hydrostaticB
no friction
37 m
Pressure 10 At. A
20 m
Sea level

10. Pressure and hydrostatic
Pressure = 10 At – ((37-20) / 10) = 8.3 At B
no friction
37 m
Pressure 10 At. A
20 m
Sea level

11. Pressure due to gravity
pipe of 5000 m slope 1.2% A B
100 C
1200m D
1300 m
Pressure at: A B C D E E
2400 m
1.2%

12. Pressure due to gravity
Pipe of 5000 m slope 1.2% A
100 B
1200m C
1300 m
1.2m D
14.4m
2400 m E
15.6m
Pressure at:
28.8m
1.2%
A: 0 atm B: atm C: =1.56 atm D: =3.12 atm E: “’+2.88= 6 atm
(5000 x1.2%=60m=6 atm.)

13. HEAD LOSS ΔH = the total energy drop of a pipe section
k = constant for a given pipe size and type of flow
Q = discharge rate
ΔL = pipe section length
m = an exponent

14. Hazen-Williams equation Among all the equations, the Hazen-Williams formula is commonly and most frequently used (Keller and karmeli, 1975; Jeppson, 1982). The Hazen-Williams formula for smooth pipe (C=150) can be shown as
where,
ΔH = energy drop by friction for a given pipe length (ΔL), m
Q = discharge rate, l s-1
∆L = length of pipe, m
D = inside diameter of the pipe, cm
The above equation modified into the following form is used in computation of frictional head loss

15. where, Hf = frictional head loss, m
L = length of pipe, m
Q = flow rate, l h-1
D = internal diameter of pipe, mm
C = a constant having different values for different pipe materials and sizes (Hazen-Williams constant)
For PVC pipes the following values of C are generally used
C = ( D < 17 mm )
C = ( 17  D < 21 mm )
C = ( D  21 mm ).

16. Darcy-Weisbach equation
where,
D = internal diameter of pipe, m
V = velocity of flow, m s-1
g = acceleration due to gravity, m s-2
f = Darcy’s frictional factor
Hf and L are equal to ΔH and ΔL as defined earlier
Considering discharge in place of velocity and taking
g = 9.81 m s-2 in the above, we get,

17. The Blasius formula Re = Reynolds number
where, Q = flow rate in pipe, l h-1
k = a constant equal to 3600
η = kinematic viscosity of water, m2 s-1
D = internal diameter of pipe, mm

18. For laminar flow
(Re 4000)
For turbulent flow, the Blasius equation is
(4,000  Re 1,00,00)
For fully turbulent flow
(Re  1,00,000)

19. Temperature effect
ηT = kinematic viscosity of water at temperature, T oC
T = temperature of water in oC
η20 = kinematic viscosity of water at 20 oC (1.003 x m2 s-1)

20. von Bernuth (1990) listed out the following advantages by insertion of the Blasius friction factor into the Darcy-Weisbach eqution
It is theoretically sound and dimensionally homogeneous. Both the Blasius and D-W equations have theoretical base.
It is very accurate for plastic pipe when Reynolds numbers are less than 100,000. The Reynolds number limit is non-restrictive for irrigation-system design using smaller than 80 mm.
It is conveniently written in readily available terms: flow rate, length, and diameter.
It can be easily corrected for viscosity changes directly.

21. Types of Emitters Flow regime (Reynolds number) 1. Laminar flow
2. Partially turbulent flow
3. Fully turbulent flow
Lateral connection
1. In-line
2. On-line
Q vs H
Pressure Compensating
Non-Pressure Compensating

22. Emitting Pipes
Dripper

24. Integral Emitter

25. Emitter flow
Q = emitter flow rate, l h-1
k = constant of proportionality
H = pressure head at emission point, m
x = emitter flow exponent
‘x’ is typically between between 0.0 to 1.0 For laminar flow condition x=1.0, fully turbulent flow x=0.5, and for perfect pressure compensating x=0.0

26. Uniformity Concept
For typical field layouts the actual emitter discharge rates vary considerably and depend upon
i)      Emitter characteristics
ii)      Variability in manufacturing and aging of emitters
iii)   Frictional head losses throughout the pipe distribution
network
iv)     Elevation differences throughout the field
v)      Number of clogged emitters in the system
vi)   Number and degree of partially clogged emitters in the
system and
vii) Variation in the water temperature throughout the system.

27. Emitter flow variation
Pressure variations(%) for different emitter flow variations and x-values
x-value
Emitter flow variation 5%
10%
15%
20%
25%
0.1 40 65 80 89 94
0.2 23 41 56 67 76
0.3 16 30 42 52 62
0.4 12 33 43 51
0.5 10 19 28 36 44
0.6 8 24 31 38
0.7 7 14 21 27 34
0.8 6 18
0.9
5.5 11 17 22
1.0 5 15 20 25

28. .
Comparison of pressure heads along the lateral obtained with DW and HW equations

29. Christiansen Uniformity Coefficient (CUC)
where, CUC = Christiansen uniformity coefficient
n = number of emitters along the lateral
qi = discharge of emitter i
qave= average emitter discharge

30. Emission uniformity (EU)
where, EU=design emission uniformity in percent
n = number of emitters per plant
Cv = manufacturer’s coefficient of variation
Qmin = minimum emitter discharge rate, l h-1
Qave = average emitter discharge rate, l h-1
General Criteria
> 90% : Excellent
80-90% : Good
70-80% : fair
< 70% : poor

31. Pipeline Selection Constant diameter pipes
Velocity limit criterion (1.5 m/s)
Critical flow method

33. Fig. Moisture availability to crops in different irrigation methods5 10 20 15
Days
Drip method
Sprinkler method
Surface method
Wilting point (15 atm)
Field capacity (1/3 atm)
Moisture content
Fig. Moisture availability to crops in different irrigation methods

34. Layout of Drip Irrigation System
LEGEND
1 Water source Flow control valve
2 Pumpset Submain
3 Fertilizer applicator Lateral pipe
4 Filter Emitter/dripper
5 Watermeter Endcap
6 Mainline 1 2 3 4 5 6 7 10 11 8 9

35. Drip Irrigation Layout
GW recharge
pit

36. Thank U