Characterization of Laminar Transient Flow Regimes and Mixing in T-shaped Micromixers

Abstract

Convective micromixers create vortices in curved channel elements allowing characteristic mixing times below 1 millisecond for gaseous and liquid media. This contribution gives an overview about the flow regimes of symmetrical 1:1 mixing in T-shaped micromixers with rectangular cross-sections for Reynolds numbers (Re) from 0.01 to 1000 in the mixing channel. First, symmetrical vortices are formed for Re > 10 in the so-called Dean flow. At Re > 140, fluid from one side swaps to the opposite side and creates a double vortex, which enhances mixing. For Re > 240, the flow becomes unsteady, and a kind of wake flow establishes. From 240 < Re < 500, the wake flow is periodic with a Strouhal number of about 0.23. The mixing quality also shows a periodic behavior and reaches its maximum at this point. With further increasing the Re number, the flow becomes chaotic, and the two components are often flowing parallel in the mixing channel, which decreases the mixing quality. Besides detailed CFD simulations, the periodic flow is observed in experimental studies with stroboscopic imaging. The decreasing mixing quality is also reflected in a lower selectivity of parallel chemical test reactions for Re > 500. With the knowledge of the flow regimes in microchannels, design criteria can be formulated for efficient mixing devices.