Influence of the Reynolds number on chaotic mixing in a spatially periodic micromixer and its characterization using dynamical system techniques

A micromixer is a key component of various microfluidic systems, such as microreactors and μ-total analysis systems. One important strategy for passive mixer design is to generate chaotic advection using channel geometry, which usually has spatially periodic structures. In this paper, the influence of the Reynolds number on chaotic mixing in such mixers is studied with three mixer models. Characterization of the mixer with dynamical system techniques is also studied. The influence of fluid inertial effects on the occurrence of chaotic advection is first discussed. It is found that at low Re(Re < 1), the flow could become reversible in the mixer, which raises the difficulty to generate chaotic advection. In this case, specific fluid manipulations, such as stretching and folding processes, are necessary. This study also proposes a characterization method using Lyapunov exponent (λ) and Poincare mapping information, which allows us to analyze the mixing performance of the mixer with one single mixer unit. Results show that it objectively reflects the dynamical properties of the mixers, such as being globally chaotic, partially chaotic or stable. So it can be used as an analytical tool to differentiate, evaluate and optimize various chaotic micromixers.

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