The effect of a temperature-dependent viscosity on cooling droplet-droplet collisions

A detailed understanding of the collision dynamics of liquid droplets is relevant to natural phenomena and industrial applications. These droplets could experience temperature changes altering their physical properties, which affect the droplet collisions. As viscosity is one of the relevant physical properties, this study focuses on the effect of temperature on viscosity, with an Arrhenius temperature dependence, of collisions of two equal-sized droplets using the Volume of Fluid Method. The results show that the higher temperature of the droplets leads to an effectively lower viscosity, leading to increased interface oscillations. This leads to the onset of separation at lower Weber numbers as expected. The local cooling droplets will create a local viscosity profiles, which results in the formation of a ridge upon combination of droplets. In addition, the collision outcomes sometimes cannot be explained solely on basis of an effective viscosity, undermining the usefulness of existing collision regime maps.