Mixing performance of a chaotic micro-mixer

Abstract

Micro-mixing of liquids is a difficult problem since the mixing performance is governed by the slow diffusive mass transfer. In the present work a novel chaotic micro-mixer, which combines several features, viz. curved channels for induction of secondary flows, split-and-recombine structures and flow separation due to forward- and backward-facing steps, is investigated. Image processing technique is used to monitor the extent of mixing. In the study by Jiang et al. [Jiang, F., Drese, K.S., Hardt, S., Kuepper, M. and Schönfeld, F., 2004, Helical flows and chaotic mixing in curved micro channels. AIChE J, 50: 2297–2305], it is shown that simple planar meandering channels induce chaotic convection by means of alternating Dean flows for sufficiently high flow rates. The mixing performance, however, is drastically decreased for lower Dean numbers (i.e., K < 150). The novel mixer design overcomes this drawback by combining different mixing methods. Especially at relatively low Dean numbers the mixing performance is found to be superior in comparison to the planar meandering mixer. Moreover, the dependence of the mixing performance on the viscosity and viscosity differences is investigated. Finally, a simple correlation for the prediction of the mixing time is proposed.