DROPLET SIZE DISTRIBUTION PARAMETERIZATION FOR FLAT FAN SPRAYS OF AGRICULTURAL TANK MIXTURES

In agricultural spray application of pesticides, the volumetric droplet size distribution (VDSD) critically influences the efficacy of the application as well as the risk of off-target spray deposition. It is critical to have accurate predictions of the VDSD for development of new agrochemicals and spray nozzles. VDSD parameterization and subsequent prediction is complicated in agrochemical sprays by the unique geometries of the nozzles employed, which typically do not have clearly evident hydraulic diameters and vary in size, as well as by the effects of active herbicides and adjuvants on the spray. Herein, scaling based on conservation of energy is utilized to develop a relationship predicting the VDSD for flat fan sprays used in agrochemical application with agrochemical products. To examine the proposed scaling relationship, we made measurements of VDSDs using laser diffraction interferometry for agriculturally relevant tank mixtures, including active pesticides and both emulsion-forming and rheology-modifying drift control adjuvants, sprayed with complex geometry, flat fan nozzles typical of field application. We show that for three distinct nozzle types and three tank mixtures (nine combinations), VDSDs can be normalized by the Sauter mean diameter (D-32), and normalized distributions collapse for given nozzle type-spray tank mix combination. Subsequently, we show for all test combinations that the Sauter mean diameter normalized by the nozzle hydraulic diameter (D-H) scales with the ratio of product of tank mix surface tension and hydraulic diameter divided by the nozzle pressure drop, with a scaling exponent of 1/3.

Automated summary

In agricultural spray application, the size distribution of droplets plays a crucial role in the effectiveness and potential risks. Accurate prediction of droplet size distribution is important for the development of new pesticides and spray nozzles. In this study, a relationship predicting droplet size distribution for flat fan sprays used in agrochemical application was developed based on energy conservation principle. Experimental results showed that the droplet size distribution can be normalized by the Sauter mean diameter for given nozzle type-spray tank mix combination.