Fig. 5.

Depth versus time images showing liquid velocities projected on the incident light v_y(y, t). (a) Schematic diagram illustrating the three-dimensional flow field which gives rise to mixing enhancement. (b–d) Liquid slug in bubble-train that flows through a meandering microchannel has not only a transversal recirculation by the secondary flow but also a longitudinal recirculation associated with the toroidal vortices to enhance mixing performance. (e) A bypass flow with the longitudinal recirculation imaged. Each image was taken at a different point of interest shown in Fig. 2(b).