Micromixers based on chaotic advection - Micromixers Fundamentals Design and Fabrication - page 230

FIGURE 6.37
Theoretical and experimental results of the position and the velocity of a plug as functions of time at a switching
frequency of f h ¼ 0.05 Hz (capillary with inner radius R i ¼ 0.475 mm and outer radius R i ¼ 0.69 mm, kinematic
viscosity n ¼ 10 cSt, heat flux q 00 ¼ 2 10 4 W/m 2 , and plug length L plug ¼ 1 mm).
6.4.2 Mixing in microdroplets
6.4.2.1 Droplet-based mixing in a straight channel
Chaotic advection in the microdroplets cannot be achieved in a straight microchannel. As shown in
Figs. 6.30 (h) and 6.32 , the flow pattern inside a droplet or a plug is steady and symmetrical. Although,
during the formation process at a T-junction, the single vortex may improve transversal transport
between the mixing liquids, the two symmetrical vortices in a straight channel keep them separately in
each half of the droplet. In this case, the initial distribution at the instance of the breakup is crucial for
good mixing during the passage of the liquid plug through the straight microchannel. If the velocity of
the single vortex during the formation process is high enough, the mixing liquids can rotate at least
a full 360 . When this plug is broken up from the injection port, the mixing fluids are equally