The local distributions of the syne

The local distributions of the synergy angles βm in the micromixers are demonstrated in Fig. 9. The synergy angles βm are low in the vortices near the gaps and baffles due to the transverse motion. Low βm implies better synergy between the velocity vector and concentration gradient and indicates the enhanced mass transfer. A lack of one gap or baffle can lead to an increase of the synergy angle βm because the relevant vortices disappear and the perturbation effect is weak, which is consistent with the results in Fig. 6. Therefore, the combination of gaps and baffles in the micromixer presented in this work is helpful to reduce synergy angle βm and improve the mixing performance.