Chapter 3. Laminar Mixing: A Dynamical Systems Approach

Summary

The only efficient route to good mixing in laminar flows is by chaos. The dynamics of chaotic mixing processes is examined in this chapter using two examples: a simple 2D model, the sine flow, and a practical industrial mixer, the Kenics static mixer. Chaotic motion creates complex and intricate mixing structures, but after sufficient time a universal and predictable length scale distribution emerges in all these flows. The basic mechanism that controls mixing in the simple 2D model and the 3D device is identical and common to all laminar chaotic flows. The continuous repetition of two simple actions, stretching and folding, creates robust and complex mixing structures that have self-similar statistical properties. A collection of scaling relationships can be developed from the self-similarity concepts for predicting and optimizing mixing performance in these flows. Moreover, since stretching controls the location and density of the intermaterial area between mixture components, it has a direct impact on the evolution of reactions. The location of the reactive zones is practically identical to the mixing structure determined only by the chaotic stretching process.