Drop Size Distributions for Irrigation Spray Nozzles

DROP size distributions for irrigation spray nozzles, such as may be used in low or reduced pressure sprinkler systems, were measured with a calibrated stain technique. Similar data from other sources, measured with photographic or pellet techniques, were also obtained. The distributions were fitted with the upper limit log normal (ULLN) distribution function. ULLN parameters for each distribution are tabulated. Distribution characteristics such as the volume median drop size may be calculated directly from the ULLN parameters. A simple regression model for predicting ULLN parameters as functions of nozzle style, size and pressure is proposed and fitted to data for flooding and smooth flat plate spray nozzles. The fit of model to data was evaluated by comparing measured and predicted values for 50th (median) and 99th (volume) percentile drop sizes, and by directly comparing measured and predicted distribution functions. The distance between functions was defined analogous to the Euclidean distance between points in space, leading to definition of a pseudo r2 for the (functional) regression model. The fit between data and model for the two nozzle types was quite good. The models were used to explore the influence of nozzle size and pressure on drop size distributions for the two types of nozzles.