Characterisation of the droplet size distribution of a sprinkler using an optical method

Abstract

When evaluating irrigation sprinklers, radius of throw is the first parameter considered for defining spacing and overlapping between adajacent sprinklers. This represents only part of the characteristics of water application quality. An impact sprinkler applies water on a discontinuous mode, varying intensity and droplet size with radius and hydraulic operating conditions. Droplet size distribution determines the sensitivity of sprinkler watering to wind and its impact on soil structure. The following paper presents a measurement sensor and a method for characterising a sprinkler from droplet size distribution measurement. The method lays on the assumption that i) log-normal probability functions can fit droplet distribution at different positions along the radius, ii) distribution parameters can be adjusted on 90% of the radius for all nozzle diameters and operating pressures for one sprinkler type. This method applies for a wide range of hydraulic conditions of the sprinkler in use. It can be used to predict the effects of irrigation on soil surface and the sensitivity of the distribution to wind. Using this characterising method it can be possible to select sprinkler types and functioning parameters compared to soil and climate characteristics. Inversely it is possible from several measurements to characterise a sprinkler droplet distribution model and to determine ranges of functioning pressure or nozzle type selection.