科研之友
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摘要
During an agricultural application, sprays are formed by atomization through a hydraulic nozzle. Fine spray droplets can cause off-target contamination with agrochemicals when they move by air from the application site. Dilute oil-in-water emulsions create coarser sprays than water, when atomized through a flat fan nozzle, and are therefore interesting for drift control purposes. However, different emulsions influence the spray droplet size to a different extent and this effect is not yet well understood. With an aim to develop products with drift reduction properties it is necessary to comprehend the mechanism of interactions between emulsion droplets and the continuous aqueous phase. In this study, we analyze systematically the effects of different physical properties of oils on the spray formation process and investigate how the type of the emulsified oil, the concentration of emulsifier, emulsion droplet size, the spreading properties of the emulsified oil, and its viscosity influence the spray droplet size. Based on the experimental data, we propose a spray formation mechanism of dilute oil-in-water emulsions. We argue that when the liquid sheet leaves the nozzle, some emulsion droplets might merge with the air/water interface of the liquid sheet, spread there and induce a subphase flow, which, reinforced by perturbations in a turbulent flow, will initiate spray atomization. In mixtures of a dilute emulsion and a water soluble surfactant, dynamic surface tension at the interface of the liquid sheet controls the spray formation process. Surfactants located at the interface form a kinetic barrier for the spreading emulsion droplets and thus delay the atomization onset.
- 出版日期2012
