Biomedical Engineering Reference
In-Depth Information
Figure 6.33
The mixing zone is enlarged by a succession of stretching and folding.
Modeling the internal convection in the plug may be performed by considering
the problem in the moving coordinates system. In this system, the plug has fixed
boundaries (to the first order) and the solid walls are moving with a velocity -
V
.
Specifying this value of the velocity on the solid walls, and symmetry conditions on
the side surfaces with no contact of any wall, the numerical solution is straightfor-
ward. We show in Figure 6.35 the result obtained with the COMSOL numerical
software [9].
6.2.12.6 Mixing in Digital Microfluidics
The preceding examples concerned mixing in microflows. With the development of
digital microfluidics (see Chapter 4), the mixing of fluids and substances in micro-
drops is now a growing subject of study. The understanding of the mixing phenom-
ena in microdrops is only at a qualitative stage. In order to illustrate this problem
and to familiarize the reader with internal microdrop motion, we show in Figures
6.36 and 6.37 the principle of mixing two fluids in a microdrop by moving the drop
along a designated path [15].
It appears that mixing in digital microfluidics shows very special patterns. Right
now it is a new topic of investigation.
Figure 6.34
Mixing in a plug flow due to the friction at the walls.
