Experiments and Direct Numerical Simulations of binary collisions of miscible liquid droplets with different viscosities

Abstract: Binary droplet collisions are of importance in a variety of practical applications comprising dispersed two-phase flows. The background of our research is the prediction of properties of particulate products formed in spray processes. To gain a more thorough understanding of the elementary sub-processes inside a spray, experiments and direct numerical simulations of binary droplet collisions are used. The aim of these investigations is to develop semi-analytical descriptions for the outcome of droplet collisions. Such collision models can then be employed as closure terms for scale-reduced simulations. In the present work we focus on the collision of droplets of different liquids. These kinds of collisions take place in every spray drying process when droplets with different solids contents collide in recirculation zones. A new experimental method has been developed allowing for high spatial and time resolved recordings via Laser-induced fluorescence. The results obtained with the proposed method will be compared with DNS simulations. The viscosities of the droplets are different whereas the interfacial tension and density are equal. The liquids are miscible and no surface tension is acting between the two liquids. Our intention is to discover elementary phenomena caused by the viscosity ratio of the droplets.