The streamline distributions at the

The streamline distributions at the middle of the height of two micromixers A and B are demonstrated in Fig. 12. At Re = 1, there is no vortex in both of the micromixers. But the difference between the streamlines in the two micromixers is obvious. In micromixer A, the unsymmetrical bending of the streamline appears due to the stagger location of the gaps. Since the location of the gap G1 is not at the center of the y axis, the fluids collide on B1 from the inclined side. However, the two fluids flow symmetrically in micromixer B. At Re = 10, single vortices are generated behind the gaps G1 and G2, respectively, in micromixer A. The recirculated region appears behind baffle B2 owing to the inclined collision. In contrast, two pairs of expansion vortices can be generated behind G1 and G2, respectively, in micromixer B. When Re increases to 40, owing to the high flow rate, a part of fluid jets on baffle B2, while the other part of the fluid flows around baffle B1 and then collides on baffle B3 in micromixer A. The separation effect of baffles B2 and B3 is enhanced and the vortices are generated behind them. For micromixer B,symmetrical separation vortices and expansion vortices are observed behind the gaps and baffles.