Experimental and Computational Investigation of Chaotic Advection Mixing in Laminar Rectangular Stirred Tanks

Abstract

The phenomenon of chaotic advection mixing in laminar stirred tanks, particularly when handling high-viscosity fluids, represents a common and challenging issue in various industrial chemical processes. The effectiveness of the mixing process is often constrained by the stretching, folding, and squeezing of fluid particles. Previous research efforts have predominantly concentrated on optimizing impeller design and operational parameters to induce stretching and folding of fluid particles. However, the mechanism of triggering chaos through the squeezing of fluid particles remains comparatively less explored. The study endeavors to address the intricate problem of laminar mixing by proposing the utilization of unbaffled rectangular stirred tanks. Through a combined approach of experimental and computational investigations, we illustrate that the implementation of rectangular stirred tanks yields significant improvements in chaotic mixing within laminar flow regimes. These tanks have the capacity to not only enhance chaotic mixing but also distort or completely eliminate the fluid segregation regions. Remarkably, as the L/W ratio of the tanks is increased from 1 to 2.5, the observed asymptotic area coverage from a frontal perspective escalates from approximately 55% to about 85%. Concurrently, the dimensionless mixing time experiences a substantial reduction, decreasing from 1950 to 350. Of particular note is the observation of macroscopic homogeneous mixing in tanks with L/W ratios of 2 and 2.5 at Re=24.33, with dimensionless mixing times of 550 and 350, respectively. The research underscores the potential of rectangular stirred tanks as a cost-effective and straightforward approach to significantly enhance the chaotic mixing performance in laminar flow. Furthermore, it also hints at the broader applicability of the approach in various industrial mixing contexts.

Keywords: Laminar rectangular stirred tank, Computational fluid dynamics, Segregation region, Chaotic advection mixing, Squeezing effect