43 KJEMI 6 2025 Hauna Fathmadinda Hosen Date: 2nd of December PhD thesis: Bubble Hydrodynamics and Interfacial Mass Transfer in Complex Liquids, Effects of Salt Presence and Fluid Rheology Trial lecture: Floatation a bubble- based technology for separation of suspended solid particles from liquids Assessment Committee • First opponent: Professor Robert Zenit, Brown University, USA • Second opponent: Chief Scientist John Christian Morud, SINTEF Industry, Norway. • Chair of the committee: Professor Jana P. Jakobsen, Department of Chemical Engineering, NTNU Supervisors • Main supervisor: Professor Jannike Solsvik, Department of Chemical Engineering, NTNU • Co-supervisor: Professor Hugo Jakobsen, Department of Chemical Engineering, NTNU Summary of thesis Bubble dynamics and interfacial mass transfer serve as key determinants for efficient industrial processes involving gas–liquid bubbly flows. Understanding these mechanisms becomes particularly challenging in complex fluids, such as those exhibiting shear-dependent rheology or non-uniform interfacial properties. This thesis investigates the individual effects of salts and fluid rheology on single bubbles, using photographic techniques and computational approaches. The study identifies initial bubble size and dissolution time as important parameters, under which interface immobilization emerges progressively in Newtonian liquids but is suppressed in non-Newtonian ones. The extent of these effects is quantified through the time-dependent mass transfer coefficient to determine the optimal conditions for mass transfer. Furthermore, semi-empirical correlations are developed for both Newtonian and non-Newtonian fluids, where the average local viscosity near the bubble interface is proposed to improve the prediction of bubble dynamics and dissolution processes. This work provides new insight into the mechanisms behind the synthesis of anisotropic (non-spherical) gold nanoparticles. It examines how combinations of surface-active molecules affect particle growth and explores the use of tannic acid, a natural compound, as a reducing agent. The study also investigates how these nanoparticles interact with fiber optic sensor probes to evaluate their sensitivity for biosensing applications. The findings show that growth conditions, such as pH and the choice of reducing agent, significantly influence particle shape and size. Tannic acid allows slower and more controlled growth, producing diverse morphologies with tunable properties. These insights contribute to a better understanding of how to design nanoparticles with specific characteristics for targeted applications. Why is this relevant? Gold nanoparticles are already used in diagnostics and medical research. Improving control over their synthesis can lead to more efficient and sustainable production methods and enhance the performance of biosensors. In the future, this knowledge could support the development of advanced point-of-care tools for early disease detection.
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