Thesis (Ph.D.)--Brown University, 2005. / Vita. Thesis advisor: Humphrey Maris. Includes bibliographical references (leaves 141-145). Also available online.

Evaporation, wetting and multiphase flows of drops and bubbles are everyday life phenomena with potential impact in many industrial, biological, medical or engineering applications. The understanding and controlling of the physical and chemical mechanisms governing these phenomena have become of paramount importance. This thesis encompasses three topics: evaporation of sessile droplets of polymer solutions, the role of thermocapillarity on self-rewetting fluid dynamics and migration of bubbles in liquid flows. Firstly, the evaporative behaviour of sessile droplets of aqueous polymer solutions and the effect of different molecular weights on the drying process has been studied. Drop shape analysis allowed monitoring the evolution of all stages during drying and indicating the transitions between stages. The mechanisms taking place during the crucial stages of pinning and depinning were illustrated, revealing the effects of adhesion and contact line friction forces on the final morphology of the dried polymeric deposits. Additionally, the effect of varying substrates from hydrophilic to hydrophobic was examined demonstrating the importance of interfacial interaction phenomena. The initial spreading dynamics of binary alcohol mixtures (and pure liquids) deposited on different substrates in partially wetting situations, under non-isothermal conditions was systematically investigated. Moreover, the temporal and spatial thermal dynamics within pure droplets and alcohol mixtures using IR thermography revealed the existence of characteristic thermal patterns due to thermal and/or solutal instabilities. The contribution of the Marangoni effect as an important heat transport mechanism within the evaporating droplets was investigated. The motion of buoyancy-driven bubbles in a vertical microchannel and the significant role of thermocapillarity was reported in this series of experiments. The behaviour of the bubbles in self-rewetting fluid flows departed considerably from that of pure liquids flows. Furthermore, heat transfer coefficient calculations in the single and two phase flows demonstrated that the presence of Marangoni (surface tension) stresses resulted in the enhancement of the heat transfer distribution in the self-rewetting fluid flows compared with the pure ones.

<p> Using a single bubble suspended in a liquid flow regime, the effects of velocity, bubble size, and surfactant levels on the gas transfer process across the bubble interface were investigated. Mass transfer data reported in the literature for non-circulating carbon dioxide bubbles was verified. A mathematical model predicting the mass transfer process for the single bubble system used in this study was formulated and this model provided a reasonable fit for experimental data obtained for the dissolution of a carbon dioxide bubble into an aqueous solution of a second sparingly soluble gas. The fate of a hypothetical air bubble in an aerator was briefly considered.</p> / Thesis / Master of Engineering (MEngr)