Computational fluid dynamics characterization of the hollow-cone atomization: Newtonian and non-Newtonian spray comparison

Disintegration of liquid masses in a free-surface flow is still an open question in the field of small-scale spray applications such as dispensing of detergents or sanitizing products. In this context, the pressure-swirl atomizer is widely investigated. It allows to improve several spray characteristics through the formation and breakup of a conical liquid sheet that results in the well-known hollow-cone atomization. From this perspective, the characterization of a small-scale pressure-swirl spray under laminar flow conditions is the focus of this work. The configuration of the device and the physical properties of the discharged liquid are the key parameters that modify the attributes of such multiscale flow. In this regard, the entire picture of the fragmentation process is structured into multiple stages: internal nozzle flow, outer displacement of the liquid-gas interface, droplet spread into the atmosphere, and droplet-wall interactions on a collection surface. Through the computational fluid dynamics, we analyze the influence of the main fluid/packaging parameters on the hollow-cone spray properties, and on the whole atomization process. Reynolds and Ohnesorge numbers are coupled with the Sauter mean diameter to distinguish different breakup mechanisms and spray performances. The solution of the entire spray system is performed by implementing the volume-of-fluid-to-discrete-phase-model, which allows to capture the liquid-gas interface displacement and track the droplets produced downstream the primary atomization, simultaneously. With this Eulerian-Lagrangian hybrid model, we link key features of the hollow-cone spray process to spray pattern and droplet size distribution for both Newtonian and non-Newtonian fluid properties.