A practical guide to the staggered herringbone mixer

Abstract

An analytical model of mixing in the staggered herringbone mixer (SHM) was derived to estimate mixing parameters and provide practical expressions to guide mixer design and operation for a wide range of possible solutes and flow conditions. Mixing in microfluidic systems has historically been characterized by the mixing of a specific solute system or by the redistribution of flow streams; this approach does not give any insight into the ideal operational parameters of the mixer with an arbitrary real system. For Stokes-flow mixers, mixing can be computed from a relationship between solute diffusivity, flow rate, and mixer length. Confocal microscopy and computational fluid dynamics (CFD) modeling were used to directly determine the extent of mixing for several solutes in the staggered herringbone mixer over a range of Reynolds numbers (Re) and Péclet numbers (Pe); the results were used to develop and evaluate an analytical model of its behavior. Mixing was found to be a function of only Pe and downstream position in the mixer. Required mixer length was proportional to log(Pe); this analytical model matched well with the confocal data and CFD model for Pe<5 x 10(4), at which point the experiments reached the limit of resolution. For particular solutes, required length and mixing time depend upon Re and diffusivity. This analytical model is applicable to other solute systems, and possibly to other embodiments of the mixer, to enable optimal design, operation, and estimation of performance.

A novel passive micromixer: lamination in a planar channel system

“…The stucture still works as a mixer, but the degree of mixing becomes more unpredictable. For the staggered herringbone mixers, which also relies on grooves on the channel bed to rotate the flow field, it has been reported that at high Reynolds numbers (>10) vortices form in the grooves which significantly reduces the rotation (Williams et al 2008). Similar effects are also seen for three dimensional mixers working by the split and recombine principle, for example, good lamination is only observed with the caterpillar mixers for low Reynolds numbers (<30, (Schonfeld et al 2004)).…”

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

“…Kee and Gavriilidis [21] numerically evaluated mixing performance of the SHM at Re = 0.001 − 10, in which 3-D velocity field was obtained via COMSOL simulations, and particle tracking methods were used to quantify the mixing performance to avoid numerical diffusion problems. Recently, Williams and colleagues [22] used confocal microscopy and COMSOL modeling to develop and evaluate analytical models of mixing in the SHM. They concluded that mixing was only a function of Péclet number and downstream position in the mixer.…”

“…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.…”

Multi-injection microstructured reactor for intensification of fast exothermic reactions: proof of concept

“…The herringbone mixing structure [32][33][34] was chosen as static mixer as it was found to be efficient at low Reynolds numbers. In the experiments described in the present study, the Reynolds number were estimated to be in the range of Re≈20.…”