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

Numerical investigation of the near head-on collision dynamics of non-newtonian droplets:a comparative study using the volume of fluid and the local front reconstruction method

Droplet-droplet interactions of highly viscous liquid suspensions have a major impact on industrial processes such as spray drying, fuel combustion, or waste treatment. The efficiency of these processes depends heavily on the morphology of the droplets after the collision (i.e., surface area and volume). Although often encountered, the physical mechanisms governing merging and break-up of non-Newtonian droplets are largely unknown. It is therefore of paramount importance to gain a better understanding of the complex physics dominating the collision of non-Newtonian droplets. In this research, we investigate numerically the collision of droplets using the local front reconstruction method (LFRM) and the volume of fluid (VOF) method. The coalescence and stretching separation regime are studied using a xanthan solution, whose shear-thinning rheology is described with the Carreau−Yasuda model. The capabilities of the two methods to capture the complex topological changes are assessed by a one-to-one comparison of the numerical results with experiments for near head-on collisions at various We numbers