Off-campus UNL users: To download campus access dissertations, please use the following link to log into our proxy server with your NU ID and password. When you are done browsing please remember to return to this page and log out.
Non-UNL users: Please talk to your librarian about requesting this dissertation through interlibrary loan.
SPRINKLER WATER DROPLET EVAPORATION SIMULATED ABOVE A PLANT CANOPY
Abstract
Theoretical equations describing droplet trajectory and evaporation were combined with a mathematical relationship for droplet size distribution, as a function of nozzle size and pressure, to predict water droplet evaporation from a conventional impact sprinkler and spray nozzle. Predicted losses agreed favorably with measured losses. Under constant atmospheric conditions, predicted droplet evaporation losses increased proportionally with nozzle height. Losses increased nearly ten times when droplet sizes were reduced from 1.0 to 0.3 mm, at a nozzle height of 4.5 m. Droplet sizes smaller than 1.0 mm reached equilibrium temperature within 2.0 seconds after leaving the nozzle, for an initial water temperature of 15 degrees C, and dry and wet bulb temperatures of 38.0 and 25.8 degrees C, respectively. However, the average temperature (based on volume) for all droplets after 2.0 seconds was more than 2 degrees below the wet bulb temperature. Predicted droplet evaporation increased less than 0.1 percent, when wind was varied from 0 to 15 m/s. Average flight time increased less than 7 percent under these wind conditions. The equations in this study did not consider droplet break up due to wind. If droplets break up, the model would under-predict true loss. The droplet evaporation model was combined with a crop energy balance model to validate sprinkler evaporation loss as a function of climatic and irrigation system characteristics. An increase in net water loss of 15 percent (assuming no runoff) was observed for a given day with irrigation, compared to the same day without irrigation. However, the effective loss (the increase in loss due to irrigation above what would have occurred had no water been applied, divided by the irrigated depth) was only 3.1 percent. Also, by assuming irrigation water was at the wet bulb temperature of the ambient air, an error equivalent to 24 percent of the net incoming radiation could be made in the energy balance of the plant-environment system.
Subject Area
Agricultural engineering
Recommended Citation
THOMPSON, ALLEN L, "SPRINKLER WATER DROPLET EVAPORATION SIMULATED ABOVE A PLANT CANOPY" (1986). ETD collection for University of Nebraska-Lincoln. AAI8614481.
https://digitalcommons.unl.edu/dissertations/AAI8614481