Biomedical Engineering Reference
In-Depth Information
Figure 6.27
Sketch of compaction of a long channel on a biochip to realize micromixing.
and passive. Active micromixers use actuated devices, such as piezoelectric actuated
membranes [13], whereas passive micromixers use only the energy of the flow and
special morphological design promoting mixing of the compounds [2, 13].
6.2.12.2 Parallel Flows
In the preceding section, we established a relation for the concentration diffusion
between parallel flows. Let us analyze this relation. Figures 6.29 and 6.30 show
the concentration distribution in a half channel. The difficulty of mixing the flows
is obvious: for typical dimensions, velocity, and liquids, the mixing length is very
important and often not acceptable for compact microsystems.
It is interesting to estimate the length
L
at which a relative concentration of
c
/(
c
0
/2) = 90% at the wall is reached. Using the inverse
erf
function and (6.80), and
y
=
R
, we find
R U
erfinv
(0.1) 0.0889
=
=
4
DL
Figure 6.28
Example of a micromixer based on a long mixing length. The micromixer incorporated
in the global design of a proteomic reactor. (Courtesy of N. Sarrut, CEA/LETI.)
