Scale-down of mixing equipment : microfluidics

Most efficient micro-mixers proposed in the last decade are based on pressure-driven flows that include the bakers transformation as known from the working principle of static mixers frequently applied in different polymer processing operations. The mechanism to achieve effective mixing in laminar flows is that of chaotic advection, which is repetitive stretching andfolding. The low Reynolds and high Péclet numbers that are typicallyfor micro-mixers, require application of this mechanism to obtain sufficient mixing. Essential is to generate a spatial-periodic alternating transversal flow. Different designs to achieve this are reviewed and optimized with as typical examples the staggered herringbone mixer and the barrier-embedded mixer, and a serpentine channel that only functions at Reynolds numbers larger than fifty. Two different approaches of active mechanisms to enhance mixing in micro channels are discussed: the first based on magnetic particles, the second on artificial cilia. Finally, the chapter concludes with some interesting phenomena concerning dispersive mixing on small scales showing an excellent correspondence between experiments and novel boundary integral simulations.