Dynamics of binary droplet collisions

Abstract

Binary droplet collisions, relevant for various natural phenomena and technological processes, embodies a rich fluid-dynamical platform covering a wide range of physical scales. This review begins with the collision between two identical droplets to reveal the underlying physics of the transition between droplet coalescence, bouncing, and separation. The interplay between the macroscopic droplet motion, the internal flow, and the microscopic interfacial gas film dynamics involving rarefied flow and van der Waals molecular force reflect the essential multi-scale and multi-physics characteristics of the collision dynamics. The review then discusses the collision between unequal-sized droplets, non-Newtonian fluids, dissimilar fluids, and the analogical jet-jet collisions. Fundamental understanding on the basic binary droplet collisions phenomena and its inference on practical processes is emphasized.