Droplet fragmentation using a mesh

Abstract

Atomization and spray generation naturally occur around us in a wide variety of situations ranging from drop impacts to bubble bursting. However, controlling this process is key in many applications such as internal combustion engines, gas turbines, and agricultural spraying. Here we show how a drop can be fragmented into thousands of smaller droplets by impacting it onto a mesh. We demonstrate the unexpected possibility to transfer liquid outside the projected impact area of the drop and the existence of a well-defined cone envelope for the resulting spray. Self-similarity of the flow studied at the primary repeating unit - the hole - allows us to predict the global nature of the atomization process: mass transfer and spray geometry. We explain how these elementary units capture the momentum of the flow atop them and how side wall interactions can lead to saturation effects. At the grid level, this translates into surface fraction and hole aspect ratio being governing parameters of the system that can be tuned to control and optimize spray characteristics. As a result of the fragmentation, the momentum exerted on the target is reduced - a major advantage in crop protection and pathogen dispersion prevention under rain. In addition, pesticide drift in agricultural sprays can be controlled by using initially large drops that are subsequently atomized and conically sprayed by a mesh atop the crop. Beyond droplet-substrate interaction, this inexpensive spraying method enhances surface exchange phenomena such as evaporation and has major implications in many applications such as cooling towers or multieffect desalination.