Mixing simulations of species in a zigzag microchannel have
been performed by a finite element method. Most of the calculations
have been achieved at constant Peclet number (diffusion
coefficient scaling) for different Reynolds numbers. Below a critical
Reynolds number of 80, the flow profile remains parabolic and
the mixing, only ensured by molecular diffusion, is strongly
dependent on the effective length and width of the channel.
Indeed, a large number of angles, inducing a larger effective width,
worsens the mixing efficiency. For higher Reynolds numbers,
results emphasize the effects of laminar recirculations along the
channel. These recirculations induce a transversal component of
the velocity, which improves the mixing process. The mixing
efficiency obtained is then greatly enhanced, as compared to an
equivalent straight channel. In addition, the decrease of D toward
physical values illustrates an encouraging enhancement of this
mixing gain. To extend these conclusions, lower values of D would
be interesting to investigate with higher numerical capacity.
Further numerical studies could also envisage (i) the effect of
narrowing the zigzag angle value and (ii) the impact of recirculations
on chemical reactions’ efficiency. From an experimental
standpoint, it would be interesting to study the conditions that
reduce the critical Reynolds number associated to the recirculation
phenomenon, such as (i) channels with larger width and larger
depth-to-width ratio or (ii) fluids with heavy particles or different
densities using the inertial effect.