Electrohydrodynamically driven chaotic advection in a translating drop

Interfacial transport between a dispersed and a continuous phase plays an important role in many current and future manufacturing processes. The classic liquid-liquid extraction process considering the internal circulation generated by the interfacial stresses for a translating drop, where the resistance to mass transfer lies, is still a diffusion limited process in many applications. The reason being that even though the Peclet numbers are high there is no convective mechanism to transport mass since the streamlines are closed, limiting the transport to slower diffusion processes. It has been shown theoretically that applying time dependent forcing or producing a three-dimensional flow may significantly increase transport rates by mixing of passive scalars inside the drop through chaotic advection. This thesis considers two possibilities for driving chaotic advection inside of a translating drop. The first method is by applying time dependent electric fields to a translating drop resulting in an axisymmetric chaotic flow. The second method is by applying steady electric fields resulting in 3D chaotic streamlines generated by tilting the electric field relative to the drop translational motion by an angle α. The numerical analysis includes approximations of the degree of mixing by Poincaré mapping and quantitative estimates of the rate of mixing by calculating the largest Lyapunov exponent. Experiments are performed using a castor oil/silicone oil system for the continuous and dispersed phases respectively. Drop sizes are approximately 5mm in diameter under nearly isopycnic conditions. For the axisymmetric experiments the complex chaotic structures are visualized and examined by illuminating non-dissolving passive crystals injected in the translating drops and the results are compared with numerical particle simulations. For the 3D experiments a single Lagrangian trajectory is recreated by visualizing small neutrally buoyant glass particles inside the dispersed phase using a stereoscopic particle tracking technique. In both cases the experimental results compare well the numerical predictions.