Model of droplet dynamics and evaporation for sprinkler irrigation

Information on droplet dynamics and evaporation from sprinklers is important for the design of irrigation systems. To obtain improved predictions, a modified mathematical model of droplet ballistics and evaporation for sprinkler irrigation was developed. Air drag force is an important factor affecting the droplet dynamics and evaporation. Five different schemes for calculating the air drag coefficient of droplet were compared and the optimal one was selected. From sensitivity analyses, it was concluded that droplet evaporation rate was most sensitive to droplet diameter for droplets < 2 mm, and to relative humidity for droplets > 2 mm. The calculation scheme used by Park et al. {Transactions of the ASAE, 25(2), 357–361 (1982) and (3), 795–804, (1983)} was selected since it provided the best prediction of droplet flight distance. The model was verified using experimental results from droplet fall velocities and loss rates. The average relative error between the predicted and measured data of fall velocities and loss rates were 1.2% and 4.3%, respectively. The average relative error of the total evaporation rate between the predicted and measured data was 17.5%.