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DETERMINATION OF EVAPORATION AND DRIFT LOSSES FROM SPRINKLER IRRIGATION SYSTEMS UNDER VARIOUS OPERATING AND CLIMATIC CONDITIONS
Abstract
Quantitative determinations of evaporation and drift losses from sprinkler sprays were made under the different operating and climatic conditions at the University of Nebraska Field Laboratory at Mead, Nebraska. Droplet size distribution in drift was also evaluated under various wind conditions. The average evaporation losses determined by an electrical conductivity method, ranged from 1.5 to 16.8 percent of the total volume discharged by sprinklers. The results of the multiple regression analysis of the data indicated that average wind velocity and vapor pressure deficit were the most significant factors affecting the evaporation from the sprays. An exponential relationship between the evaporation loss and wind velocity was found. The relationship between the vapor pressure deficit and evaporation loss was also exponential. For the pressure levels used in this study, the operating pressure factor did not have a significant effect on evaporation from the sprays. A comparison of the evaporation losses estimated by various theoretical and experimental equations for a given set of operating and climatic conditions showed that experimentally obtained prediction equations estimate greater evaporation losses than the theoretical equations. Drift losses defined as the quantity of spray droplets passing through a plane perpendicular to the direction of wind a short distance downwind outside the sprinkler application pattern, ranged from 2.0 percent at a wind velocity of 2.68 m/s to 15.1 percent at a wind velocity of 6.71 m/s at an operating pressure of 310 kPa (45 psi) when the losses were measured at 21 m from the lateral. When the losses were determined at 26 m, the drift losses varied from 1.5 percent to 10.4 percent of the total volume discharged by the sprinklers. Drift losses increased in proportion to approximately the second power of the average wind velocity. Wind velocity is the predominant factor controlling the amount of drift from a given sprinkler system operated at a specified pressure. Drift losses decreased drastically with increasing distance from the lateral. Combined spray losses ranged from 1.8 to 29.0 percent of the total volume discharged by the sprinklers, when the losses due to wind drift at 21 m were considered in the estimation of the combined losses. When the drift losses at 26 m were considered, the combined losses varied from 1.7 to 22.9 percent. On the average, 47 percent of the total losses were due to drift for wind velocities greater than 4.0 m/s, and for wind velocities less than 4.0 m/s, the drift losses consisted of 25 percent of the total losses. In addition to spray loss determinations, an analysis of the droplet size distribution in the drift was made by applying the modified log-probability function called 'Upper Limit Equation' to the observed droplet size data. The results showed that distribution of droplets in the drift can be represented by the upper limit equation. Volume mean diameters, d(,50), and 95-percent sizes, d(,95), increased with increasing wind velocity.
Subject Area
Agricultural engineering
Recommended Citation
YAZAR, ATTILA, "DETERMINATION OF EVAPORATION AND DRIFT LOSSES FROM SPRINKLER IRRIGATION SYSTEMS UNDER VARIOUS OPERATING AND CLIMATIC CONDITIONS" (1980). ETD collection for University of Nebraska-Lincoln. AAI8111685.
https://digitalcommons.unl.edu/dissertations/AAI8111685