TEMPERATURE EFFECTS ON ATOMIZATION BY FLAT-FAN NOZZLES: IMPLICATIONS FOR DRIFT MANAGEMENT AND EVIDENCE FOR SURFACTANT CONCENTRATION GRADIENTS

Abstract

The effect of temperature on the atomization of a range of agricultural spray liquids is described, from approx. 3 °C to 40 °C, for water, a nonionic surfactant, two polymeric adjuvants, two blank formulations of an insecticide [emulsifiable concentrate (EC) and wettable powder (WP)], and two organo-silicone surfactants. In general, the potential for drift (% volume < 150 μm) was increased to varying degrees with increasing carrier liquid temperature, but not for all the spray liquids tested, with the wettable powder a notable exception.No general relationship could be found linking temperature with change in spray cloud characteristics (e.g., arithmetic mean, number median diameter, percent spray volume < 150 μm, etc.). The surface tension (surface age 170 ms) and viscosity (zero shear rate) of the test materials were also measured at representative temperatures, but no simple or unifying linear relationship between these physicochemical properties and spray cloud characteristics could be discerned. The investigation was widened to study the most disparate spray liquid, an organo-silicone adjuvant, comparing atomization at points across the short axis of the spray cloud with water, at 5 °C and 35 °C. From the data, we would hypothesize that surfactant concentration gradients are formed within the spray sheet prior to ligament/drop formation. Therefore, the effects of surfactants on the atomization of a liquid through a flat-fan hydraulic nozzle cannot be considered as a single process driven by a single value for surfactant concentration. The supporting evidence for a more complex description is discussed.The research reported reinforces previous work suggesting that the relationship between physicochemical properties of liquids and the atomization characteristics of those spray liquids is far from simple and cannot be predicted from simple measurements of surface tension or viscosity based on our current experimentation. The data also showed that the particulate (WP) formulation was the most stable when atomized (i.e., least prone to change), and that the effect on atomization of the often multiple components of agricultural spray formulations still represents significant opportunities for improved understanding.