Thermal Atomization during Droplet Impingement on Superhydrophobic Substrates*

Water droplets impinging superheated substrates may be characterized by dynamic vapor bubbles rising to the surface and causing a spray of tiny droplets to erupt from the droplet. This spray, known as thermal atomization, is the focus of an experimental study of water droplets impinging superheated, superhydrophobic surfaces. In this study, atomization of impinging droplets is quantified for superhydrophobic substrates of varying microstructure shape and dimensions over a range of superheat temperatures, Weber numbers, and inclination angle. Each silicon microstructured substrate was placed on an aluminum heating block, and impingement events were captured with a high speed camera. The level of thermal atomization was quantified by estimating the volume of liquid spray present for each event using a new image processing technique. Leidenfrost temperature is estimated for each scenario. Additionally, the effect of varying parameters on maximum droplet diameter and atomization drop velocities is explored. We find thermal atomization is most significantly altered by microstructure spacing and design as well as Weber number.