sprinkler Volume Mean Droplet Diameter as a Function of Pressure

Abstract

ABSTRACT Afinite difference numerical model was developed to determine the volume mean droplet diameter at any distance from a sprinkler as a function of nozzle size and pressure. An empirically derived drag coefficient, which incorporates nozzle diameter and pressure, was incorporated in the model. Droplet size data from a medium size impact sprinkler fitted with nozzles of diameters 4.0 mm (5/32 in.) and 3.2 mm (1/8 in.) were utilized to establish the drag coefficient. The model was verified with the same sprinkler using two other nozzle sizes - 3.6 mm (9/64 in.) and 4.4 mm (11/64 in.). A total of 140 indoor tests were conducted. Pressures between 69 kPa (10 psi) and 414 kPa (60 psi) at 28 kPa (4 psi) increments were evaluated using 4.0 mm (5/32 in.) and 3.2 mm (1/8 in.) circular and 3.5 mm (9/64 in.) square nozzles. Nozzle pressure had a major influence on droplet size: higher pressure promoted smaller droplets over the entire application profile. The volume mean droplet diameter of total water applied as a function of nozzle size and pressure were determined.