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KAGAKU KOGAKU RONBUNSHU, Vol.35, No.3, 265-273, 2009
Analysis of Fluid Mixing in an Agitated Vessel Based on a Streakline
The flow system in an agitated vessel is extremely complex because it is time-dependent, three-dimensional and spatially unsymmetric. Therefore, many questions on the mechanism of fluid mixing remain unsolved. In two-dimensional laminar mixing caused by chaotic flow, stable and unstable manifolds play important roles in the analysis of the fluid mixing. These invariant manifolds make the invariant structure controlling the mechanism of fluid mixing and act as the template of the mixing pattern. However, we do not know whether a similar invariant structure also exists in three-dimensional flow systems. In this study, we analyzed the mechanism of laminar fluid mixing in a three-dimensional agitated vessel with a two-blade paddle impeller, focusing on the particular streakline that grows from the tip of a blade and acts like an unstable manifold. On the basis of a visualizing experiment and numerical simulation with a simple flow model, we showed that this streakline is closely concerned with the formation of mixing pattern, and its strong stretching and folding near the side wall of the agitated vessel give rise to laminar global fluid mixing.