Geometrical optimization of helical flow in grooved micromixers

Abstract

Owing to the enhancement of surface effects at the micro-scale, patterned grooves on a micro-channel floor remain a powerful method to induce helical flows within a pressure driven system. Although there have been a number of numerical studies on geometrical effects concerning fluid mixing within the staggered herringbone mixer, all have focused mainly on the groove angle and depth, two factors that contribute greatly to the magnitude of helical flow. Here we present a new geometrical factor that significantly affects the generation of helical flow over patterned grooves. By varying the ratio of the length of the grooves to the neighboring ridges, helical flow can be optimized for a given groove depth and channel aspect ratio, with up to 50% increases in transverse flow possible. A thorough numerical study of over 700 cases details the magnitude of helical flow over unsymmetrical patterned grooves in a slanted groove micro-mixer, where the optimized parameters for the slanted groove mixer can be translated to the staggered herringbone mixer. The optimized groove geometries are shown to have a large dependence on the channel aspect ratio, the groove depth ratio, and the ridge length.

Evaluation of Floor-grooved Micromixers using Concentration-channel Length Profiles

“…To characterize the mixing performance of the micromixers in order to better understand and design more efficient micromixers for different applications, a number of techniques, both experimentally [14][15][16][17][18] and theoretically [12,[19][20][21][22][23][24][25][26][27][28], have been employed. Particularly, CFD has been widely used to study the mixing behavior of micromixers in details.…”

Fundamentals of Microfluidics Devices

“…89,90 The herringbone mixer has been thoroughly investigated by other groups and provides adequate mixing within reasonable times with very little footprints in terms of size. 42,91,92 Other improvements have also been made to this design with the inclusion of embedded barriers parallel to the flow direction generating hyperbolic instead of elliptical or helical streams. 93 A drawback for such designs is the need for complex 3D fabrication involving multiple steps.…”

“…The top and bottom plates are separated by a spacer, and silicone oil is used between the plates to prevent droplet evaporation. 92 Both plate surfaces are coated with a hydrophobic layer to enable smooth actuation of aqueous droplets. Recent innovations in digital microfluidic device infrastructure include coplanar designs (where both electrodes are located at the bottom surface) and the use of substrates that are mechanically flexible facilitating integration of different physicochemical environments on a common platform.…”

One-step electroplating 3D template with gradient height to enhance micromixing in microfluidic chips

“…By contrast, passive micromixers take advantage of special channel designs, which disturb the fluid flow condition in microchannels. Different channel structures, such as twisted or serpentine microchannels (Jen et al 2003;Kang et al 2009;Kim et al 2005), obstructions (Ali Asgar et al 2007;Lin et al 2007), staggered herringbone or grooved channel (Lynn and Dandy 2007;Stroock et al 2002), and cascaded microchannels (SadAbadi et al 2013), have been designed to increase mixing efficiency depending on the Reynolds number. Compared with active micromixers, passive micromixers are inexpensive and easy to fabricate.…”