Speaker
Description
Understanding the collision and mixing of droplets is of importance in many applications such as fuel combustion, spray painting or icing phenomena on flight systems. The parameters determining the coalescence of two droplets also determine the dynamics and mixing during the droplet coalescence, as well as the threshold criteria for drop rebound or coalescence regimes. The coalescence is influenced by interfacial tensions, the ambient gas atmosphere, evaporation rate, the flow and stability of the thin gas layer between both droplets, Marangoni effects and the dynamics of the approaching droplets. Further drop mixing is determined by the internal flow, induced by the drop coalescence. Computational Fluid Dynamics (CFD) simulations of such processes are extremely complicated since very different length scales are involved in the problem.
The objective of this experimental study is the characterization of the coalescence and mixing of two different liquid drops under the terrestrial and microgravity conditions during parabolic flight campaign. The coalescence of two liquid convex surfaces of relatively large radii of curvature is studied in this work. The deformation of the surfaces, caused by the dynamics of the gas or vapor flow in the gap and by the Marangoni stresses, is observed using a high-speed video system. Additionally, a high-speed micro-PIV system is employed to characterize the internal flow during the drop coalescence and the influence of fluid properties, ambient conditions and collision properties. Longer lasting observations of the drop coalescence are planned under microgravity conditions on the International Space Station (ISS).
This study is performed in the framework of the Lufo IV “DropCoal” project.
| Keywords | drop coalescence, microgravity, drop mixing, marangoni flow |
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