Experiment No. 3
EFFECT OF HEIGHT OF RISER ON WATER DISTRIBUTION
Object:-To investigate the effect of height of riser on the radial distribution of water from a Rotary Sprinkler.
Apparatus:-Sprinkler Test Rig (Catch Assembly, Display Unit, Pump Set and Storage Tank) and Stop Watch.
Theory:-When the water jet leaves a sprinkler, it initially travels outward and upward. As it slows down and breaks up, the drops lose their lateral velocity and fall almost vertically to the ground. If the riser pipe is too short however, water drops will reach the ground too soon and may still have a considerable lateral velocity. This has an effect of reducing the throw of the sprinkler and upsetting the water distribution pattern.
When compared to good sprinkler system uniformity, a poor system will use more water to irrigate a given area. Improving the application uniformity of a sprinkler system can reduce the water supply necessary to irrigate a given area. This savings in water will lower pumping and operating costs.
The increase in CU from 70 to 90% would reduce the water requirement by 38.3% with such a savings 62% more land can be irrigated.
CU (%) | Water applied over entire area to get at-least 1” on 90% of the area | Water saved with CU > 70% | Greater area irrigated with CU > 70% |
90 | 1.19” | 38.3% | 62.0% |
80 | 1.47” | 23.8% | 31.3% |
70 | 1.93” | 00.0% | 00.0% |
Where,CU = Coefficient of Uniformity
= Mean value of readings (Sum of all the readings i.e. )
n = Number of readings
Experimental
Setup:-The rig is set up for normal use with the display tubes primed. Catch cans are positioned 1.0 m apart from each other. The riser height is adjusted until the base of sprinkler is 0.6 m above the level of catch can. Pressure is adjusted at 2.5 lb/in2. Ensure that jet dispersal screw has been removed. Run the test for 10-15 minutes or until a reasonable height of water is acquired in the display tubes. Note the height of water in display tubes, which shows the depth of water in each catchcan. Similarly repeat the experiment for various riser heights with nozzle size and pressure unchanged.
Observations:-
Pressure = _______ bar;Nozzle size = ______ mm
Catch Can No. | Riser Height (cm) | |||||
d1 = | d2 = | d3 = | ||||
(mm) | (mm) | (mm) | (mm) | (mm) | (mm) | |
1 | ||||||
2 | ||||||
3 | ||||||
4 | ||||||
5 | ||||||
6 | ||||||
7 | ||||||
8 | ||||||
9 | ||||||
10 | ||||||
∑ | ||||||
mm | mm | mm | ||||
CU | % | % | % | |||
Graph:-Depth of water is plotted against distance from the sprinkler for various heights of riser, as shown in the attached Figure.
[Attach the graph]
Result:-Based on the value of Coefficient of Uniformity i.e. _______%, it is evident that the sprinkler at riser height of _________ cm, with the nozzle size of ______ mm at a pressure of ______ kg/cm2, gives the best radial distribution of water within the wetting circle of the rotary sprinkler. Hence it is suitable for the field conditions.
Conclusion:-