Sandwich mixer–reactor: influence of the diffusion coefficient and flow rate ratios

Abstract

A sandwich mixer consists of mixing two solutions in a channel, one central laminar flow being sandwiched between two outer flow solutions. The present numerical study considers the convectiondiffusion of two reacting species A and B, provided respectively by the two incoming solutions. The simulations show how the diffusion coefficient, flow rate and species concentration ratios influence, via the transversal diffusion length and reaction kinetics, the reaction extent at the end of the sandwich mixer. First, this extent can be enhanced up to 60% if the species with the lowest diffusion coefficient is located in the outer solutions where the flow velocity is small compared to that of the central part (higher residence time). Secondly, decreasing the outer flow rates (to confine the reaction close to the walls) and increasing the local concentration to keep the same flux ratio improve the extent by 300%.Comparison with a bi-lamination passive mixer, with an ideal mixer and an electro-osmotic driven flow mixer is presented. These conclusions are also demonstrated for consecutive reactions, showing an amplification of the effects described above. The results are also presented versus the residence time in the mixer-reactor to show the time window for which the gain is appreciable.

Multidirectional vortices mixing in three-stream micromixers with two inlets

“…The flows of the two designs consist of three streams after the second passage. Most of the previous works, on the mixing of two fluids with one core stream being sandwiched between two outer streams, considered mixing in flows with parabolic velocity profiles (Abonnenc et al 2009;Knight et al 1998;Wu and Nguyen 2005). In this work, we examine the mixing behaviors of the complicated three-stream flow with multidirectional vortices in the CSC channel for a wide range of the Reynolds number (0.03 B Re B 81).…”

“…Comparison of micromixers based on chaotic advection in three-dimensional (3D) structures and those designs based on planar structures shows that the 3D structures are better at mixing, but their fabrication requires either multi-step lithography or aligned assembly of multiple layers (Chen and Meiners 2004;Liu et al 2000;Stroock et al 2002). In planar micromixers, effective mixing can be obtained by lamination (Abonnenc et al 2009;Hessel et al 2003;Wu and Nguyen 2005), hydrodynamic focusing (Knight et al 1998), flow impinging (Bothe et al 2006), Dean vortices (Jiang et al 2004;Yi and Bau 2003), separation vortices (Bhagat et al 2007;Chung et al 2008;Wang et al 2002) or a combination of the above strategies (Lee et al 2010;Sudarsan and Ugaz 2006;Tsai and Wu 2011).…”

Numerical study of the effect on mixing of the position of fluid stream interfaces in a rectangular microchannel

“…So, exploring a way to increase mixing performance for the range of Reynolds numbers where low mixing is depicted is an interesting and important issue. Abonnenc et al (2009) studied mixing of two fluid flows in a microchannel, with one central laminar flow being sandwiched between two outer flows. The effects of the diffusion coefficient, flow rates and species concentration ratios were analyzed.…”

Density-induced asymmetric pair of Dean vortices and its effects on mass transfer in a curved microchannel with two-layer laminar stream

“…This phenomenon is widely observed in many microfluidic devices [1][2][3][4][5][6][7][8][9][10]. For some applications that require intensive mixing or reaction of the two streams [8][9][10], the low mixing rate becomes a performance limiting factor.…”