| dc.description.abstract | In the wide and complex field of multiphase flows, bubbly flows with non-Newtonian liquids are encountered in several important applications, such as in polymer solutions or fermentation broths. Despite the widespread application of non-Newtonian liquids, most of the models and closures used in industry are valid for Newtonian fluids only, if not even restricted to air-water systems. However, it is well known that the non-Newtonian rheology significantly influences the liquid and bubble behaviour. CFD represents a great tool to study such complex systems in more detail and gain useful insights on the dynamics of gas-liquid (and possibly solid) systems with the ultimate aim to help the development or the design of industrial reactors. In this study, a DNS Front Tracking (FT) method is applied to study the rise of bubbles in different power-law fluids. Detailed information is obtained regarding the flow of single or multiple bubbles, especially concerning the viscosity profile around single rising bubbles, their shapes and their rising velocity. To describe the bubble rise velocity in less detailed model, a closure for the drag force is needed. With the use of Front Tracking, an existing drag correlation, which was derived for Newtonian fluids, is adapted and improved to non-Newtonian rheologies. When the effect of the viscosity changes are limited, such as for not extreme exponents (0:5 _ n _ 1:5), the correlation can predict reasonably well the drag coefficient for power-law fluids. | nb_NO |
