Thin films and interfacial dynamics for environmental applications

Abstract

In this thesis I explore a range of fluid dynamics problems related to thin films and interfacial dynamics, with motivation from environmental applications. Specifically, the research topics I studied include the dynamics of a gravity current spreading under coupled leakage mechanisms, and the motion of elongated bubbles confined in small geometries, which can be applied in controllable bubble surface coating and particulate separation, for example.

Motivated by previous studies of confined bubbles in a pure fluid, I have investigated the particle-interface interaction by introducing particulate impurities in the continuous phase, where systematic bubble surface coating is observed. The different coating stages are studied, and the analytic solutions for the film thicknesses show excellent agreement with experimental measurements. The effects of different particle sizes are then investigated, demonstrating applications in particle separation due to the distinct particle-interface interactions by size.

With the bubble motion at steady state widely investigated in the literature, I conducted an investigation of the transient bubble dynamics. Combining theory, experiments and simulations, different regions of the bubble shape profile are categorized and described by similarity solutions. Moreover, to allow continuous particle separation, the bubble dynamics in a vertical capillary are further examined, where the motion is governed by the combination of buoyancy and external flows. Both the hysteresis in the bubble profile and symmetry-breaking film profiles are found, providing insights in fine-tuning the bubble film profile.

With the understandings of fluid flows in confinement of small geometries and inspired by the CO$_2$ sequestration projects, I carried out an investigation on dynamics of a gravity current in a porous medium. The spreading dynamics are investigated, with the realistic consideration of coupled leakage mechanisms from a permeable substrate and a fixed edge. Applications of this research can be applied to two-phase flows in geological systems, in predicting a more accurate current profile, and estimating the timescale of a sequestration life cycle.