Preziosi, Valentina (2011) Modeling and development of controlled topography reactors and their application in the field of industrial biotechnology. [Tesi di dottorato] (Unpublished)

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The mixing of liquids is a common operation in process industries such as chemical and pharmaceutical industries. However the problem of mixing different liquids has not been rigorously characterized yet. Therefore one of the aims of this PhD thesis was focused on mixing in microsystems, like microcapillaries and micromixers. Microfluidic systems, fabricated by utilizing silicone, biomaterials, or stainless steel, have gathered enormous attention in the recent years. Compared to industrial laboratory equipment, these microsystems offer reduced reagent consumption, more safety and lower time for analysis. Their reduced size makes them suitable for mobile field laboratories, while their reduced cost allows them to be disposable after sensitive applications. Microsystems fit perfectly with the Process Intensification (PI) strategy, an engineering expression that refers to making changes that render a manufacturing or processing design substantially improved in terms of energy efficiency, cost-effectiveness or enhancement of other qualities. The design of microfluidic systems often requires unusual geometries and the interplay of multiple physical effects such as pressure gradients and capillarity, which lead to interesting variants of well-studied fluid dynamical problems and some new fluid responses. The rapidly increasing interest in the application and control of emulsions in microfluidics devices for industrial biotechnological purposes motivates this research. In particular emulsification process to form stable samples over time by using different techniques was investigated. Fluid dynamic behavior of a stable oil-in-water emulsion was characterized in microcapillaries and contrast-enhanced optical microscopy was used for direct observation and automated image analysis algorithms have been developed to characterize the velocity and the deformability of drops flowing in capillaries of micrometric dimensions. Fundamental understanding of emulsification process is very important from a biotechnological point of view because it is present in many biological processes. For example the motion of droplets under confined flow has attracted some interest due to the similarities with the shape taken by red blood cells in microcapillaries. Furthermore emulsification process in micro static mixers of different diameter and length was analyzed and theoretical models to predict emulsion particle size distribution were performed. Finally scale-up of these microreactors was performed.

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