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II STUOY OF THE EFFECT OF OPERATING PRESSURE
AND ROTATION SPEEDS ON DISTRIBUTION OF
WATER FROM A MEDIUM PRESSURE ROTARY
IRRIGATION SPRINKLER

Thesis for the Degree of M. S.
MICHIGAN STATE UNIVERSITY
NAMIK KEMAL KILIC
1969

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 355W“

3 1293 0062 7 v
3 5547 L Li: " -
[Michigan State '

TH ESIS . .
- UmvchIty

 

ABSTRACT

A STUDY OF THE EFFECT OF OPERATING PRESSURE AND ROTATION
SPEEDS ON DISTRIBUTION OF WATER FROM A MEDIUM
PRESSURE ROTARY IRRIGATION SPRINKLER

by Namik Kemal Kilic

The distribution of water from a rotary irrigation
Sprinkler is a function of the Operating pressure, rotation
speeds, nozzle size, angle of inclination, wind, and spac-
ing. The objective of this study was to investigate the
effect of operating pressure and rotation speeds on the
rate of application, range, and size of water drops from
a rotary irrigation sprinkler.

This study was conducted indoors to eliminate
weather variables. The distribution of water and drop
characteristics were investigated under three operating
pressures (30, 45, and 60 psi), and three rotation speeds
(with oscillating arm, 2.3 and 6 rpm by rotating mechanism).
Other factors were held constant throughout the eXperiment.

Experimental data show that an increase in operat-
ing pressure resulted in: (a) a more even distribution of
water, (b) a general decrease in the diameter of drops,

and (c) a limited increase in the range of sprinkler.

Namik Kemal Ki lic;

An increase of rotation speeds resulted in: (a)
decreasing uniformity of water application, (b) increasing
the size of water drops, and (c) a general decrease in the

range of sprinkler.

g I m
Approvedmgfagfiir M-

Approved £0“ OJ. M

Department éhairman

 

A STUDY OF THE EFFECT OF OPERATING PRESSURE AND ROTATION
SPEEDS ON DISTRIBUTION OF WATER FROM A MEDIUM

PRESSURE ROTARY IRRIGATION SPRINKLER

BY

Namik Kemal Kilic

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Agricultural Engineering

1969

ACKNOWLEDGMENTS

The author wishes to express his sincere thanks
to Professor E. H. Kidder of the Department of Agricultural
Engineering, under whose inspiration and.constant super-
vision this investigation was undertaken.

Grateful acknowledgment is also extended to C. C.

Mueller for his assistance and suggestions.

ii

TABLE OF CONTENTS

ACKNOWLEDGMENTS . . . . . . . . . . . .
LIST OF FIGURES . . . . . . . . . . . .
INTRODUCTION . . . . . . . . . . .~. 0 .
REVIEW OF LITERATURE . . . . . . . . . .

I. Drop formation from a
Sprinkler nozzle . . . . . .

II. Effect of water drops on soil

III. Measurement of drop energy .
DESIGN OF EXPERIMENT . . . . . . . . . .
I. Analysis of the problem ._. .

II. Methodology for measurement .
APPARATUS AND EXPERIMENTAL PROCEDURE . .
DISCUSSION OF RESULT . . . . . . . . . .
I. The rate of water application

II. Range of sprinkler . . . . .

III. Size of drops . . . . . . . .

IV. Limitation of testing method
CONCLUSION . . . . . . . . . . . . . . .
RECOMMENDATION FOR FUTURE WORK . . . . .
REFERENCES . . . . . . . . . . . . . . .

APPENDIX 0 o O O O O O O O O O O O O O 0

iii

Page
ii

iv

15
19
26
26
30
3O
35
38
39
40
42

LIST OF FIGURES
Figure Page

1. Theoretical relationship between intensity
and range of a rotating sprinkler . . . . . 15

2. The relationship between the diameter
of the water drops and its indentation
on a sugared nylon screen . . . . . . . . . 18

3. Pump unit and pressure tank . . . . . . . . 20

4. Slotted barrel shield and sprinkler
rotating mEChanism o o o o o o 0' o o o o o o 20

5. Laboratory where tests were conducted . . . 22

6. The nylon screen placed at 1.5
meter intervals along a radius
emanating from the sprinkler . . . . . . . . 22

7. Sugar-coated nylon screen on hoop shows
the Spots of water dr0p at 9 meter distance
from the sprinkler with oscillating arm . . 23

8. The spots of water drops on nylon screen at
9 meter distance from sprinkler with a
rotating mechanism (6 rpm) at 60 psi . . . . 24

9. Sampling cartons . . . . . . . . . . . . . . 25

10. Application rate versus distance from
sprinkler with 3/32 inch nozzle for the
speed of rotation and pressure tested . . . 27

11. Application rate versus distance from
sprinkler with 3/32 inch nozzle for the
speed of rotation and pressure tested . . . 29

12. The relationship between the rate of
application and range of a rotating
sprinkler with 3/32 inch nozzle for
the rotation and pressure tested . . ... . . 31

13. Dimensionless relationship between operating
pressure and range for the Sprinkler tested. 32

iv

Figure Page

14.

15.

16.

Mean drop diameter versus distance
from sprinkler with 3/32 inch nozzle
for the rotation-and pressure tested . . . . 34

Mean drop diameter versus distance from
sprinkler with rotating mechanism for
rotation and pressure tested .'. . . . . . . 36

Sugar—coated nylon screen on hoop
shows the spots of water drop
overlapping each other . . . . . . . . . . . 37

INTRODUCTION

To have asuccessful.practicelin.high producing
agriculture, it is essential that the sprinkler irrigation
system be planned to fit the requirement of soil, crops,
water supplies and farming Operations found on each indi-
vidual farm. Many factors influence the efficiency and
economy of Sprinkler irrigation. One of the more important
factors is uniformity of water distribution. Numerous
experiments have been conducted to determine the uniformity
of water distribution and various aspects of sprinkler
Operation as affected by.Operating pressure, rotation
speed of the sprinkler, nozzle size, wind and Spacing.
Other important factors are the size, velocity and energy
of water drOps that strike the ground from a Sprinkler.

The compaction of soil by falling water drops is in part
a function of the characteristics of water drops. A care-
ful study, however, indicates that an approximately uniform
application is possible when:

l. the type of pattern produced is correct for the
arrangement of sprinklers

2. the sprinklers are correctly spaced

-3. the sprinklers rotate at a uniform rate

4. the operating pressure is constant
5. there is no appreciable wind
The objective of this study was to investigate the
characteristics of water drops and the uniformity of appli—
cation from an irrigation sprinkler.under different pres-

sures and rotation speeds.

REVIEW OF LITERATURE

I. Drop formation from a
sprinkler nozzle

The formation of water drOps from a Sprinkler noz-
zle is quite complicated and extremely.difficult to analyze.
Baron (1947) studied the atomization of liquid jets and
droplets. He concluded that deformation.of a moving drOp
is forced by vibration of viscous damping. This force
drives the liquid toward the periphery.producing small
water particles of different.sizes. .Further break-up is
a function of the surface tension of.the water and the
resistance of the air. Green (1952) observed that the
surface tension tended to hold the drOps intact in a
Sphere, while air resistance tended to cause oblation by
flattening the leading side of the drops. When the sur-
face tension was overcome, the drop broke up into smaller
drOps.

Levine (1952) determined that the diameter of indi-
vidual drops was fairly small at distances of from 25 to
30 feet from the sprinkler; whereas, the drops were larger
in diameter from 30 to 50 feet out from the sprinkler.

Bilanski and Kidder (1958) concluded that turbu-

lence, distribution of velocities and the.amount of

secondary motion in the jet of water as it emerged from
the sprinkler, caused the formation of droplets. Actual
velocities of a water jet emerging from.an orifice varied
from near zero at the perimeter to a maximum at the center
of the stream. The variation in stream velocity and the
mechanical dispersion caused by the.sprinkler rotation
initiated drop formation. The surface tension tended to
hold the drOps intact in a sphere, while air resistance
tended to cause oblation by flattening the leading side

of the drops. When oblation occurred to such a degree
that the surface tension was overcome, drops broke up into
two or more drops.

Even after drops formed, their characteristics
were dynamic. Green (1952) proposed a mathematical analy-
sis of the distance of travel and the velocity of drOps
from an orifice which resulted in the following relation-

ship:
r = v(m/k)(1-e"k/m’t) - g(m/k)2 (e“k/m’t—1)

- g(m/k)t , (1)
Where r = distance from the orifice
v = initial velocity
m = mass of the drOp
k = constant
t = time

9 = gravitational.accelerationA

In the limiting case, as the value of m/k approached zero,
the value of "r" also approached zero. Consequently, small
drOpS traveled only negligible distances. Actual measure—
ments of drops from an irrigation Sprinkler showed a rapid
increase in the diameter of the drop as the distance from
the sprinkler increased.

Investigators of raindrop simulator [Laws (1941),
Mutchler (1965), and Gunn and Kinzer (1949)] present results
which differ widely from one another. But most of them
agree on the effects of pressure, aperture size and angular
velocity on the values of the median drop diameter. The
size of the nozzle also seems to have a significant effect,
since the nozzle with larger diameter gives better distribu-
tion at any given Operating pressure. It is not yet clearly
known whether the drops separated from the main water jet
approach their terminal velocity within the height of their
fall. The effect of the rotation speed of nozzle on the
energy of the simulated rain is quite pronounced because
the effect is more on the drop velocity than on the drop
size.

Most investigators have considered the following
factors in jet break-up: change in potential energy due
to surface tension, change in kinetic energy due to liquid
motion, turbulence, nozzle dimensions, liquid viscosity and
density, jet velocity, air viscosity, density and drag

force.

II. Effect of water drops
on soil

The deleterious effect of raindrop impact on bare
soil was noted as early as 1877. Neal and Baver (1937)
stated that experimental results Show that the falling
raindrop breaks down soil aggregates, displaces and trans-
ports the soil particles. The continued impact of the
raindrOps compacts and seals the immediate soil surface.

Cook (1936) concluded that water drop velocity was
one of the variables in the water erosion process. Laws
(1941) spent considerable time in studying the distribu-
tion and the intensity of raindrops in relation to the
kinetic energy develOped in a rainstorm. They observed
that infiltration decreased about 70 percent and runoff
increased 1200 percent as the drop size in artificial rain
was stepped from 1mm to 5mm in diameter. Ellison (1945)
showed conclusively that a variation in either drop size
or drop velocity will cause a change in the infiltration
capacity of the soil. This was substantiated by Free's
(1952) finding that soil crusts resulting from water drop
impact had a volume weight of about 30 percent more than
the soil immediately below the crusts. Duley (1939) ob-
served that the rapid reduction in the rates of intake of
water by bare soils as rain falls on the surface was accom-
panied by the formation of a thin compact layer at the sur-
face. This layer was due in part to the beating action of

raindrops and in part to the sorting action as water

flowing over the surface placed fine particles into the
voids around the larger ones. Levine (1952) reported that
infiltration was decreased by the use of large drops from
an irrigation sprinkler. Thus, at present a detailed study
of both drop Spectrum and velocity distribution must remain

the goal of sprinkler designers.

III. Measurement of drop energy

Several methods have been used for determining
drop sizes. Most of them assumed terminal velocities for
purposes of calculating drop energy. Neal and Baver (1937)
developed a method to measure drop energy. Their equipment
consisted of a beam balance connected to a recording pen
and chart. Drops were allowed to fell on a plate at one
end of the beam. The pen at the other end recorded the
deflection.

Many investigators have used photography as a means
of studying the moving water drop. Wortington (1894) used
a high Speed camera to study turbulence created by drop
impacts. Green (1952) worked with a similar technique and
strobe light to measure drop sizes and velocities. Edger—
ton (1937) and Davis (1966) used photographic methods for
recording size of spray drops and drop formation.

Schleusener (1960) used a styrofoam target mounted

on a cantilever beam to measure the energies of drop impacts.

Strain gauges on the beam detected deflection which was

recorded on an oscillograph. However, Brazee's (1963)
"Theoretical aspects of drOplet impact measurements" by
damped oscillating tranducer as a method of measuring
random impact energies Opened questions as to the validity
of such procedures.

Before the impact of a falling drOp of water can
be evaluated, it is necessary to know the size of drops
and velocity of the fall. Most of the experimental study
of the intensity of the drops from varying heights showed
that their acceleration varied approximately inversely as
the square root of time, even if the effects of the wind
and temperature are not considered. Therefore, it would
be more accurate to measure the impact of water drops per

unit area at a given time.

DESIGN OF EXPERIMENT

I. Analysis of the problem

In order to improve the rotary irrigation Sprinkler,
we should know the factors that affect: (1) drop formation
from a nozzle and (2) distribution of water over the ground.
The formation of drops from a nozzle is quite complicated
and extremely difficult to analyze. We assume that the
drOps are spherical in shape and that break-up is homo-
geneous. The effect of the curved pipes in the sprinkler
head and the nozzle shape with its boundary condition are
not taken into consideration. The sprinkler is rotated by
means of a sprinkler rotating mechanism.

The distribution of water from a mechanically
rotated irrigation sprinkler is function of the following

factors:

f(PIDIVIwIergIUarpaerIpwrorr) = 0 (2)

where P Operating pressure
D = diameter of nozzle
V = velocity of water jet from nozzle
w = rate of rotation of sprinkler head

a = angle of inclination

g = acceleration of gravity

10

u ,p = dynamic viscosity and mass density of air
“w’pw = dynamic viscosity and mass density of water
O = surface tension
r = hydraulic radius of the nozzle (as a shape
factor)
The hydraulic radius of the nozzle is included to consider
the effect of nozzle shape on the formation of droplets.
Some work has been done on the velocity and the
range of water drOps from sprinklers. Green (1952) analyzed
it mathematically by assuming friction in the air to be
proportional to the velocity of drOps. By using Laws'
(1941) data, he found the relationship between friction

and size of drops to be in the form:
k = .000251 d (3)

This conclusion was used by Bilanski (1958) to determine
the equation of a Single drop trajectory.

The main considerations in the foregoing discussion
were to find out the effects of pressure and rotation speed
on the distribution of water from an irrigation sprinkler
and to arrive at a compromise value between variable pres—
sure and rotation to get a uniform distribution without
changing the other factors.

A) Range was defined empirically in the form of

n

R = 8? (4)

11

range (radius)

in which R

6 = angle of inclination
P = pressure
n = constant
Theoretically, maximum range may be obtained when 6 = 45°.

Under actual condition maximum range may be obtained when

9 = 23° and may be reached at a limiting pressure beyond
which no further increase in the range is observed. Range
is therefore not a function of angle of inclination and
pressure only. We should take into consideration the other
factors such as the friction exerted by the air on the
smaller drops that are produced at higher pressures. Con-

sequently, the range may be indicated by the equation,
f(RIPIDIVIwIeIgI paIHaIDWIO) = 0

Dimensional analysis of the equation yields,

 

 

 

2
f(%' VDpw’PD' 2:5, EEKEE'w-' elfié)=0 (5)
AW ng g Ig Lw
VDp
where u = Reynolds number
w
V2
-— = Froude number
gD
pwVZD
c = Webers number

0
in the fluid mechanics. The last term 33 may be discarded,
w

Since it has a negligible influence on the phenomenon.

12

If we keep all the variables except rotation, we will

have

R=Df(w\l.-g-.,kl) (6)

where f is an unspecified function. Data may be plotted
(g as abscissa, ngfas ordinate) as a function off the
dimensionlessvariable.

Since the range is prOportional to the pressure,
equation (5) must_take a special form, for variable pres-
sure. By eliminating velocity (V), since it depends on
pressure and diameter of nozzle, some terms of equation
(5) would be transformed into another dimensionless

product,
- “’3 >

By substituting pressure P, in terms of head, and elimi—

nating we get,

V o
R=Df( aowIflzg'kzI (8)

Equation (8) yields the principle: when a rotational

 

sprinkler operates at a constant angle of inclination and
speed of rotation, the range is proportional to the square
root of head and the kinematic viscosity of air. By plot—
ting the data % as abscissa, Vafw %?
the relationship in terms of unity.

as ordinate, we see

 

13

B) The intensity of irrigation sprinkler is

defined as

fQ dt = AI = WRZI (9)
where Q = discharge from nozzle in (t) time
R = range

The discharge is proportional to the square root of pressure
and the range is also proportional to pressure as well as
the rate of rotation. Therefore, there must be a uniform
distribution of water at sufficiently high pressure heads
with a sufficient rotation.

Assuming the evaporation loss and wind effect is
not taken into consideration. The intensity (I) is ex-
pressed as "cm° of water/per unit time." Then the most
important variables that influence the distribution of

water may be written in the form of,
f(I,R,Q,t,w,D,O,r,vw,pw,g) = 0 (10)

It is impossible to form a dimensionless product that con-
tains pw, since pw is the only variable that contains the
dimension of mass. Therefore, pw actually does not enter
the problem. The dimensional analysis of the above equa-

tion yields,

V r
I = R f<9§, WE: 13L, 63> (11)
D

14

for constant 6, the equation becomes,

wh4

where x = Q;
D

Y

ll
2
QIUI

Consequently, if a curve is plotted with ordinate % and

abscissa x or y, the curve will give the performance of
the sprinkler for variations of the rate of rotation or
operating pressure.

We are, in fact, most interested in having a uni-

form distribution. In case of the uniform distribution,
R

by plotting %— as the abscissa, 1% as the ordinate, theo—
x

retically we get a line as in Figure 1.

We can set up a relationship between mean drOp
diameter and intensity by writing the discharge of nozzle

in terms of drop diameter in equation (9), then we get,

“i

t n/6 2
. _ Qt _ i=1
1——--2——

HR ER

n d?
1

 

where d = mean diameter of drops
n = number Of drops (assume countable)

R = range

15

l/Rx
E8

.06-

JU—

002‘ r—

 

 

 

Rx/R

Figure 1. Theoretical relationship between intensity and
range of a rotating sprinkler.
From this equation, we can estimate the number of drOps
falling at certain distance from the sprinkler nozzle.
A second objective of this study was to investigate
those relationships experimentally, and find out through
what combination of pressure and rotation may produce uni—

form distribution.

II. Methodology for measurement

The measurement of rainfall drop size and distribu-
tion has been carried out through the centureis and little
attempt was made to improve on them., Bentley (1904) devel-

oped a simple method of measuring the size of a raindrop.

He used pans of fine uncompacted flour, and let the rain

16

fall for a few seconds into the pans so that each drop
produced a dough pellet. After drying the pellets, he-
measured their diameter. He determined the relationship
between the diameter of pellets and raindrop by calibration.
Laws (1941) utilized Bentley's flour technique and obtained
more measurements.

Wischmeier (1958) develOped another technique to
measure the size of raindr0ps by use of absorbent paper.
This procedure is in common use today. Photographic tech-
niques have been used to determine drop sizes as well as
drop velocities.

Frozen drops, card stain and rupe cell methods have
been used in measurement of droplet size from spray nozzle.
Buchele.and associates (1967) used an automatic particle
counting equipment such as the cathode ray tube raster to
measure Size and distribution Of droplets from Spray nozzle.

Blanchard (1949) used screens to measure the size
of raindrops. When the raindrops passed through a screen,
they left an indication of their size by removing a circu-
lar Spot of soot and carrying it along with them. He
referred to Howell and his co-workers who improved the
screen method by substituting (60 gauge) nylon stockings
for wire screen, and confectioner's sugar for the black

soot.

17

The relationship between the diameter of the rain-
drop and the diameter of its indentation on a sugared nylon
screen is shown in Figure 2.

The use of nylon stockings screen coated with con—

fectioner's sugar appears to Offer a most reliable method

of determining drop sizes.

18

 

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.o .a .etanocmHmR

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*.cmmsom coax: Omemmsm m co

 

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66 95.5245 Poem
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APPARATUS AND EXPERIMENTAL PROCEDURE

This study was conducted in the land development
laboratory located in the basement of the Agricultural
Engineering Building of Michigan State University in East
Lansing, Michigan. Water was obtained from the university
water system and pressurized with a horizontal centrifugal
pump. The pump was driven byra five horse-power electric
motor shown in Figure 3.’

A "Rainbird" model (14 V) irrigation sprinkler was
used throughout the experiment. The sprinkler was mounted
in a barrel with an adjustable width Slot cut in the side.
The slot allowed the stream of water from the sprinkler
to emerge in one direction for sampling purposes. The
test for the measurement of drop Size was carried out with
the same nozzle of 3/32 in.-under pressures of 30, 45 and
60 psi. The rotation of sprinkler was maintained by a
rotating mechanism as shown in Figure 4. This mechanism
consisted of a motor of variable speed and a speed reduc-
tion box, which allowed the sprinkler rotation rate to
vary between 2.3 rpm and several hundred rpm.

The pressure was observed on two gauges having a

scale range from zero to one hundred psi. One gauge was

placed on the pressure tank and the other in the delivery

19

20

 

Figure 3. Pump unit and pressure tank.

 

 

 

Figure A. Slotted barrel shield and
rotating mechanism.

21

line at a distance of one foot from the sprinkler. The
gauges were checked for accuracy with a dead-weight gauge
tester.

Wire window screening was used to minimize the
Splashover of drops from the concrete floor into the cans.
Sampling cans were placed along the screened strip at 1.5
meter intervals as Shown in Figure 5. Each test_for mea-
surement of water distribution was run for two hours. The
water in each can was weighed in grams after each test.
The intensity of water distribution was calculated for
each point on the radius in terms of cm./hr.

The diameter of water drops from the sprinkler
was measured by the screen method. The hoops were designed
in a rectangular shape with a size of 50 x 20 cm. The 60
gauge nylon screen was mounted tightly on the hoops and
coated with confectioner's sugar. It was observed that the
sugar did not stick to the new nylon screen. Therefore,
it was placed in a solution of vaseline in benzene, which
left a thin but sticky layer of vaseline on the nylon
fibers.

Nylon screens coated with confectioner's sugar
were then placed at 1.5 meter intervals and were exposed
to water droplets for one rotation of the sprinkler as
Shown in Figure 6. The relationship between the diameter
of the raindrops and the diameter of the indentations that

they make on the nylon screen was originally plotted by

22

.smaxcfledm OED Eoem wcflpmcmEO msflcme
m wcoam mfim>empcfi AODOE m.H pm
cwomad cemhom cofims one .m Oeswfim

 

.OomHQ EH acme

IQHSUO pwmp EOHOEOHAOmHO Ewes ccsosm
Izomn cfl Hmeemo LOHEEHEQm .Ompospcoo
mews memo» when: ALODEAOQOQ .m Osswfim

 

23

1‘

V-‘yeva-n. v' '

 

 

Figure 7. (a) Sugar-coated nylon
screen on hoop shows the spots of
water drop at 9 meter distance from
the sprinkler with oscillating arm,
a) at 30 psi, b) at “5 psi, 0) at
60 psi operating pressures.

 

2U

 

Figure 8. The spots of water drops
on nylon screen at 9 meter distance
from sprinkler with a rotating
mechanism (6 rpm) at 60 psi.

25

Blanchard (1949). This calibration curve was used in the
determination of the true drop diameters.

As the tests were run, it was impossible to measure
all the indentation diameters on the nylon screen. Sampling

cartons were designed which had 5 holes in them, Figure 9.

 

 

 

 

 

 

 

 

 

 

‘tA\ /»O/ o o I
\\~ // C
/‘,1:r\ 0 2° '"
/©’/ \0\ O o L
I: 50 cm :I
(a) (b)

Figure 9. Sampling cartons: (a) Rectangular holes with
size (5 x 2) cm.: (b) Circular holes with (3)
cm. diameter.

The number of drops in each hole were counted and
their diameters were measured with a caliper in terms of
mm. Their median diameter was calculated in the usual
way after finding their true values from the calibration

curve. This procedure was repeated for each rotation and

pressure setting until all the tests were completed.

DISCUSSION OF RESULT

I. The rate of water application

The rate of water application was determined for
a sprinkler by using catchment cans and the true rate of
water application was Obtained by averaging the total fall-
out of water over a particular target area during a defined
time interval. The numberical values are given in the Appen-
dix, Table I.

The rate of water application from the sprinkler
with an oscillating arm approaches the ideal uniform dis—
tribution as shown in Figure 10(a). The action of the
oscillating drive arm causes the sprinkler to rotate. It
is actuated by the jet issuing from a nozzle. It frequently
diverts the jet from its normal path. This leads to an
excess concentration of water near the sprinkler, which
decreases as the distance from the sprinkler increases.

It reaches an end point at about one-half the trajectory,
when the Operating pressures are 30 and 45 psi, but only
one—fourth of the total trajectory when the Operating
pressure is 60 psi. The rate of water application starts
to increase beyond this minimum point and reaches a maximum
at a distance of approximately three-fourths of the tra-

jectory when the Operating pressures are 30 and 45 psi.

26

27

2t ‘\ OI with oscillating arm

 

 

 

 

 

 

 

 

 

[ 6) 2,3 rpm
3. .3.
S
\
E
U
2*
.|_
m
*—
'¢
a:
.O E 1 L . . L J
z
9
3 c) 60 rpm
.1
a.
0..
<1 .2+
.l.
.0 . . . . ‘ 4
2 4 6 8 IO .
DISTANCE FROM SPRINKLER METERS

Figure 10. Application rate versus distance from sprinkler with
3/32 inch nozzle for the speed of rotation and pressure tested.

28

This point of maximum water application spreads out con-
siderably along the trajectory of the sprinkler at the
operating pressure of 60 psi (Figure ll)°

The pattern of water distribution, when the sprinkler
was rotated by a rotating mechanism-instead of the oscilla—
ting arm, was such that the maximum point was reached at~
a distance of four-fifths of the trajectory, when Operated
at a pressure of 30 psi. This maximum point shifts from
far out to the mid-trajectory distance when the pressure
was increased from 30 to 60 psi.

A higher concentration of water occurred between
the distance of 3 and 9 meters at operating pressures of
30 psi and 45 psi when the rate of rotation was increased
from 2.3 rpm to 6 rpm. However, the effect of increased
rate of rotation to 6 rpm at 60 psi was a pronounced de-
crease in the rate of water application all along the tra-
jectory as shown in Figure 11. This can be explained by
an excess tangential velocity effect on the distribution
of water droplets as the discharge from the sprinkler
nozzle remain constant throughout both the rate of rota-
tions. The tangential velocity effect was such that the
jet of water from the nozzle through the slot of the barrel
at 6 rpm and 60 psi covers more area than the 2.3 rpm and
60 psi. Thus, it was concluded that this was an experi-

mental error rather than a physical phenomenon.

29

,2. d) at 30 psi 6 rp / L
.\\ ///)n
.l - q _______ K4) arm/-

 

 

 

 

s. .3I' .
-= 2 3 rp \_
\ \
S .2 W/\-\
::\:E.______# OSC- ("\m \
l \‘\
b) at 60 psi

c) at 45 psi

APPLICATION RATE

 

 

\\ / .-
,:. ELEM"
' _ ..... . \_/,g§_cinrm
‘ ““““ .e/////
1 1 1 l 1 L 1 L 1 1
2 4 6 8 IO

DISTANCE FROM SPRINKLER (METERS)

Figure 11. Application rate versus distance from sprinkler with
3/32 inch nozzle for the speeds of rotation and pressure tested.

30

In the analysis of the problem we defined the ideal
uniformity of water application as a straight line with %—
as abscissa and g; as ordinate. But this theoretical ap-x
proach does not hold in describing the distribution of
water from the sprinkler in the experiment, except when
the rotation was maintained by the oscillating arm as~

shown in Figure 12(a), (b) and (c)°

II. Range of the sprinkler

The variation of the pressure does not effect the
range of the sprinkler as expected in the analysis of the
problem as shown in Figure 11. High pressure causes a
greater dispersion and break-up of the water jet, resulting
in smaller drops. Since the distance of travel of a water
drop is proportional to its size, the effect of Operating
pressure change is limited.

On the other hand, an increase in the rate of
rotation of the Sprinkler shortens the range as shown in
Figure 13. The effect of rotation on the range was neg-

ligible when the rate of rotation was 6 rpm.

III- Size of drops

The size of drOps was determined by using the data
measured from the nylon screen coated with confectioner's
sugar. Mean diameter of drops was calculated from catch-

ment samples and plotted against the distance from the

'4“ \

)2. \ a) with oscillating arm
(3 \ \
2 IO" '\\\ \\ l
x \\ \
1? 3‘ \\‘

 

 

 

 

 

v \W\
“J I I l
g IE \\ b) 23 rpm
\
IO- \\
t9 3_ \\
H 6- \ \\\60 EgL/\
*5 4» \-\
E? 2_ \\u. \\\‘\\_S§LJ1§L__ _~“~; 2:EE§\\\\\
g \\_3_Q_D§1__./-——‘—‘"" t\
6_ is.“ c) 6.0 rpm
\ \Zxfiini,
4" \\\ \M.\
\\\ . ‘T‘r-~;_____ 1
_ \“30_p_5L___—————————><\\

 

 

Figure l2. The relationship between the rate-of application
and range of a rotational sprinkler with 3/32 inch nozzle for
the rotation and pressure tested.

32

era:

.OOmep LOHECwLQm
OED Ace Owcme USO OASOOOAQ wcHquOQo COOZDOQ QfiEOCOflpOHOE OOOHEOHOEOEHQ .MH Oezmflm

 

 

0? mm On mu
P _ A . lLTIIIa
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ES m . - io_.N
///////amm/mwlt//t/////// .mtw
.oua
.mmd H
/
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£8.30 .om.~
.nnm

 

max

33

sprinkler as shown in Figure 14(a), (b) and (c). Drop
sizes increase as the distance from nozzle increases. The
diameter of drOps ranges from 518 to 5078 microns.

When a sprinkler rotates with the oscillating arm,
an increase in pressure causes smaller drops, and a reduc-
tion in size becomes greater as the distance from the noz—
zle increases. At distances greater than 7 meters from
the nozzle, drop sizes are significantly great at differ-
ent Operating pressures as shown in Figure 14(a). This
result can be explained by pointing out the effect of pres-
sure increase in breaking up the jet of water. The diam—
eter of drops versus the distance from the sprinkler
approximately gives a linear relationship at 45 psi when
the rotation was obtained by oscillating arm.

On the sprinkler with a rotating mechanism, as
operating pressure increases from 30 to 45 psi it produces
a relationship similar to that we had with the oscillating
arm as shown in Figure 14(b). However, the change of
operating pressure from 45 to 60 psi does not effect the
size of drops, within 8 meters of the nozzle, when the
rate of rotation was 6 rpm as shown in Figure 14(c).

Hence it was thought that tangential velocity was another
important factor in breaking-up of the jet of water.

The rate of rotations for a sprinkler with oscil-
lating arm are 1.667, 1.715 and 1.765 rpm at Operating

pressures of 30, 45 and 60 psi respectively. Therefore, the

3A

a) with oscillating arm
3*F .
o
A .
2t 0 .

 

 

 

 

 

 

 

E ‘I T
3. b) 2.3

U)

(I

In

E 2*

2

S.

o l»

O.

8

o I T

Z

<

u:

:5 ///////////£
4. 0) 6,0 rpm '

3" / .3
2L //" [3
//

I # v/ ”l’:i&///////////m«w”#’/rrf.
2 4 6 8
DISTANCE FROM SPRINKLER METERS

Figure 1“. Mean drOp diameter versus distance from Sprinkler
with 3/32 inch nozzle for the rotation and pressure tested.

35

effect of rotation on the sprinkler with the oscillating
arm was negligible. When the rate of sprinkler rotation
was maintained by a rotating mechanism, the effect of
rotation in the diameter of drops was important as Shown
in Figure 15. An increase in the rate of rotation from
2.3 to 6 rpm, produces significantly larger drOpS in the
area farther than 5 meters from the nozzle, when the
Operating pressures are 30 and 45 psi. In the area
within 5 meters of the nozzle, the effect of rotation
was negligible. But when the Operating pressure was 60
psi, an increase in the rate of rotation from 2.3 to 6
rpm causes smaller drops. This result may be explained
by taking into consideration the effect of pressure, as
shown in Figure 14. The effect of pressure on the size

of drops was very clear.

IV. Limitation of Testing Method

The diameter of drOps cannot be measured within
4 meters of the Sprinkler with a 3/32 inch nozzle because
a high number of drOps fall on the same target and overlap
each other on the nylon screen as shown in Figure 16(a)

and (b).

36

— a) at 30 psl

 

 

 

m
a: ./
“J m
*- Ir ,”
U I,
2 I- ,”’ /”’
S. //’
o
LIP? T I V T ' I
a.
g 3 c) at 60 psi .
I 233/
2t W

 

 

//" //
/// ,./
I /// //
HP 1 l A l 1 l l I
2 4 6 8 IO

DISTANCE FROM SPRINKLER METERS

Figure 15. Mean drop diameter versus distance from sprinkler
with rotating mechanism for rotation and pressure tested.

37

 

Figure 16. (a) Sugar—coated nylon
screen on hoop shows the spots of
waterdrop overlapping each other, (a)
at 3 meters from the sprinkler with
the oscillating arm, (b) at 4 meters
from the sprinkler with a rate of
rotation 6 rpm.

 

‘- "Oi-"1
‘Vl.‘~‘r’ . ~ .

‘4'. (.3. . '

‘- (I... '. «.v
_, ”v.01“,

I“ AM ./
_4‘.'

 

CONCLUSION

l. The manufacturer's recommended minimum operating
pressure for this sprinkler is 45 psi. It was found that
higher pressure generally tended to give a more uniform
application rate. The distribution curves Show that the
most uniform application rate resulted when the sprinkler
with oscillating arm operated at 60 psi.

2. The use of nylon screen method for drop size in-
vestigation is feasible. The reliability of these measure-
ments was dependent on the distance from the sprinkler that
the observation was made.

3. An increase of Operating pressure resulted in: (a)
a more even distribution of water, (b) a general decrease
in the diameter drOpS, and (c) a limited increase in the
range of sprinkler.

4. An increase in the rate of rotation resulted in:

(a) decreasing the univormity of water application, (b)
increasing the size of waterdrops, and (c) a general

decrease in the range of sprinkler.

38

RECOMMENDATIONS FOR FUTURE WORK

1. Further studies of irrigation Sprinkler should be
continued to determine what combination of operating pres-
sure and rotation may produce uniform distribution.

2. Future work should be directed to study turbulence,
distribution of velocities, and amount of secondary motion
effect on the dispersion of the water jet as it emerges

from the sprinkler nozzle.

39

REFERENCES

REFERENCES

Baron, T. (1947). Atomization of liquid jets and droplets.
Tech. Rept. NO. 4 on Contr. N6-Ori-7l. Eng. Exp.
Sta., U. of Illinois, 24 pp.

Baver, L. D. (1937). Ewald Wollny, a pioneer in soil and
water conservation research. Soil Science Society
of America Proceedings, 3:330-333.

Bentley, W. A. (1904).' Studies in raindrOp and phenomena.
Monthly Weather Review, 32:450-456.

Bilanski, W. K. and E. H. Kidder (1958). Factors that
effect the distribution of water from a medium
pressure rotary irrigation sprinkler. Transac-
tions A.S.A.E. 1:19-23.

Blanchard, D. C. (1949). The use of sooted screens for
determining raindrop size and distribution.
Occasional Report No. 16, Project Cirrus, General
Electric Research Laboratory, Schenectady, New
York.

Brazee, Ross D. (1963). Theoretical aspects Of droplet
impact measurement. U.S.D.A.~ A.R.S., Wooster,
OhiO, ARS 42-770

Buchele, W. F., L. A. Liljedahl and W. G. Lovely (1967).
Measuring drOplet size mean and variance from
spray nozzle. A.S.A.E. Paper NO. 67-661. 13 pp.

Cock, Howard L. (1936). The nature and controlling vari—
ables of the water erosion process.' Soil Science
Society of America Proceedings 1:487—494.

Davis, John R. (1966). Measuring water distribution from
sprinkler. Transactions A.S.A.E. 9:94-96.

Duley, F. L. and L. L. Kelly (1939). Effect Of soil type,
Slope and surface conditions on intake of water.
University of Nebraska Agricultural Experiment
Station, Lincoln. Res. Bull. 112, 16 pp.

40

41

Edgerton, H. E., F. A. Hauser, and W. B. Tucker (1937).
Studies of drop formation as revealed by high
speed motion camera. Journal of Physical Chem-
istry 41:1017.

Ellison, W. D. (1945). Some effects of raindrops and
surface-flow on soil erosion and infiltration.
Transactions American GeOphysical Union 26:415-
429.

Free, George R. (1952). Soil movement by raindrops.
Agricultural Engineering 33:491—494, 496.

Green, Robert L. (1952). A photographic technique for
measuring the size and velocities of.water drops
from irrigation sprinklers. Agricultural Engi-
neering 33:563-568.

Gunn, Ross and Gilbert D. Kinzer (1949). Journal of
Meterology 6:243-248.

Laws, J. O. (1941). Measurement of fall velocities of
water drOps and raindrops. Transactions American
Geophysical Union 26:709-711.

Levine, Gilbert (1952). Effects of irrigation drOplet
size in infiltration and aggregate breakdown.
Agricultural Engineering 33:559-560.

Mutchler, C. K. and L. F. Hermsmeier (1965). A review of
rainfall simulators. Transactions A.S.A.E. 8:
117-123.

Neal, J. H. and L. D. Baver (1937).. Measuring the impact~
of raindrops. Journal of American Society of
Agron. 29:708-709. ‘

Schleusener, Paul E. and E. H. Kidder (1960). Energy of
falling drops from medium pressure irrigation
sprinkler. Agricultural Engineering 41:100-103.

Wischmeier, W. H. and D. D. Smith (1958). Rainfall energy
and its relation to soil loss equation. Agricul-
tural Engineering 39:458-462.

Worhington, A. M. (1894). The splash ofia drop and allied
phenomena. Annual Report.of Board of Reports of
Smithsonian Institute, pp. 197.

APPENDIX

42

 

 

 

 

Table A-1. Sprinkler distribution data.
rotation sample. application rate in cm/hr
speeds distance_ ' ’
rpm meters at 30 psi at 45 psi at 60 psi
P 1 5 155 170 214
U1 H o o O o
.5. '29 3 0 095 120 164
4., m.'_‘ 0 O O O
.3 ..3 4.5 .067 .107 .169
7' I: 34 4 095 167
gfiflm 6m m6 . .
8‘“ .8 7.5 .840 .103 .143
1‘
5 3:3 9.0 .102 .108 .117
‘S .J“: 10.5 .034 .051 .041
H
E
.9 1.5 .047 .082 .190
G
g 3.0 .034 .066 .187
E 4.0 .044 .093 .245
m E: 5.0 .057 .111 .326
.5 6.0 .086 .121 .296
g m
U N 7.0 .101 .127 .271
8 8.0 °133 .140 .246
fi 9.0 .206 .149 .182
«g 10.0 .056 .048 .045
E
.2 1.5 .079 .105 .111
g 3.0 .073 .124 .146
E 4.5 .102 .175 .204
m g‘ 6.0 .143 .197 .213
.S 7.0 .183 .229 .226
4‘; 0
fl 6 8.0 .220 .219 .213
S 9.0 .207 .140 .124
g 10.0 .006 .006 .007
--—I
3

 

43

Table A-2. Diameter of drOps for 3/32 inch nozzle.

 

 

 

 

rotation sample . .
speeds distance mean drop diameter in mm
rpm meters at 30 psi at 45 psi at 60 psi
'35 3.0 .571 .425* .400*
«a

3,“ 5.0 1.126 .826 .673
08

a... 7.0 1.740 1.607 1.425
3:1;

3H 9.0 3.360 2.296 1.808
2‘ . .
"4 E 3.0 .497 - .302
.ucn g .

gg 2* 5.0 1.148 .846 .704
“'8 "1 7.0 2.155 1.556 1.241
88 ..

-; 9.0 3.490 2.320** 2.358
g 3.0 1.184 .558 .518
Hg

4.3.3 E, 5.0 2.260 1.068 1.063
‘68 “

“g o 7.0 4.226 1.929 1.916
.G (1) KC

33,8 9.0 5.078 3.275 2.108
3

 

*At those points, the diameter of drops could not
be measured.

**This value was measured at 8.5 meters from sprinkler.

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