Comparing methodologies for the characterization of water drops emitted by an irrigation sprinkler

Abstract

A variety of techniques have been proposed for sprinkler drop characterization. Two of them, the disdrometer method (D) and the low-speed photographic method (P), have recently been applied in the literature. A statistical method for the improvement of disdrometer measurements (DM) has been proposed to improve D measurements. The aims of this study were: (1) to compare the disdrometer and photographic methods under indoor conditions, (2) to produce a drop characterization data set, (3) to assess the effect of the statistical treatment of disdrometer data, and (4) to gain insight into the relationship between drop variables. The drops resulting from an impact sprinkler operating at 200, 300, and 400 kPa were characterized at distances of 3, 6, 9, and 12 m from the sprinkler. In each method, diameters responded to operating pressure and distance from the sprinkler according to the expected trends. The difference in volumetric diameter estimation between methods P and D amounted to -4% of the average P volumetric diameter. The application of DM to this data set increased the difference in volumetric diameter with method P to 15%. Drop velocity and angle could be measured with method P and showed clear relationships with drop diameter. Finally, regression equations are presented relating the most relevant experimental variables. The disdrometer resulted in fast measurements of drop diameter, while the photographic method provided additional variables but required intense work in the laboratory and particularly in the office.