Drift of Droplets from Air-Induction Nozzles

Abstract. For more than 20 years, air-induction or air-inclusion (AI) nozzles have had increased use for pesticide application due to their drift reduction capabilities. The pressure drop created by the pre-orifice and the venturi chamber results in a slower-moving liquid sheet exiting the main orifice, which in turn results in larger droplet sizes, which are less prone to drift. However, two additional factors somewhat mitigate the advantage of larger droplets from AI nozzles: the lower initial spray jet momentum from AI nozzles (compared to standard nozzles of the same flow rating at the same pressure) means that droplets from AI nozzles are more affected by lateral crosswind, and the lower effective liquid density of droplets from AI nozzles due to the presence of air inclusions means that AI droplets are more affected by aerodynamic drag than pure liquid droplets of comparable sizes from standard nozzles. In this work, theoretical and numerical models are developed to quantify these effects and develop tools for accurate drift prediction from sprayers using AI nozzles. The reduction in spray density due to the presence of air inclusions is in the range of 12% to 36%. This reduction in density affects the aerodynamic drift of the spray droplets, with the result that a droplet with 30% air inclusions would have the drift characteristics of a normal droplet with 20% smaller diameter. HighlightsSprays from air induction (AI) nozzles typically contain 12% to 36% air inclusions by volume.A droplet with 30% air inclusions would have the same drift characteristics as a water droplet of 20% smaller diameter.An analytical model is developed to predict the drift distances of small droplets. Keywords: Air induction, Droplet size, Nozzles, Pesticides, Sprayers.