Droplet distribution characteristics of impact sprinklers with circular and noncircular nozzles: Effect of nozzle aspect ratios and equivalent diameters

Abstract

An experiment was carried out to investigate the droplet distribution characteristics of an impact sprinkler by using circular and noncircular nozzles. The noncircular nozzles used were selected by employing the principle of an equal flow rate under the same pressure. Using a two-dimensional video distrometer (2DVD) technique, the diameter, velocity, and kinetic energy of the droplets were measured. Due to its specific geometric structure, the sprinkler with elliptic and rhombic nozzles showed better water distribution than those having a circular nozzle at low working pressure. The mass mean droplet diameters of the sprays produced by the sprinklers with the noncircular nozzles were significantly larger than those produced by the circular nozzle in the near and middle ranges of the wetted radius. Coarse droplets were observed from rhombic nozzles at distal points but the droplet velocities were similar to those close to the sprinkler. A logarithmic model was developed to describe the relationship between diameter and velocity, and this model fitted with a correlation coefficient (R2) of 0.99. The kinetic energy intensity increased gradually with the distance from the sprinkler and rapidly decreased at the end of the sprinkler wetted radius. Under working pressures of 150 and 200 kPa, the uniformity coefficients of kinetic energy intensity were simulated for a rectangular combination spacing of the sprinkler with elliptic and rhombic nozzles using MATLAB. The optimum combination spacing was found to be 1.0 times the wetted radius, and the uniformity coefficients for kinetic energy intensity were 57.0, 57.1, 60.5, and 65.4%. The results provide valuable data for studying the external spraying characteristics of sprinklers and for optimising nozzle structures and irrigation systems.