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4.6 Mixer Application for µ-TAS 163
4.6 Mixer Application for µ-TAS

Because the Reynolds number in a microchannel in future µ-TAS will be small,
mixingdevices that increase two liquid contact areas are proposed to promote
the diffusion effect. Interweavingof two liquids has been achieved by adopting
various structure geometries in a channel, such as micronozzle arrays and
intersectingchannelswhich induce chaotic flow, as shown in Fig. 4.63 [4.21].
These mixers have been characterized as static devices. On the other hand,
active micromixers with pressure perturbations that are applied transversally
to the main stream, as shown in Fig. 4.64 have been presented [4.22]. They
are called cross-channel mixers [4.23], fabricated by usingMEMS technology,
in which chaotic-like mixingis achieved in an efficient way. The optical mixer
proposed in this book is another type of active mixer to stir a liquid in a
microchannel [4.19].
µ-TAS is also called a Labs-on-a-chip. The chip will have components such
as inlets for loadingthe sample and reagent, microfabricated fluidic channels

pw pw
A z
Df m Df m h
h
x
u c d c u u c d c u
w z
h
a h y
2p/q x
B 0 cycles: 1/2 cycle: 1 cycle:
z
Df m
x
100 mm
Fig. 4.63. Mixing by intersecting microchannels, which induces chaotic behavior of
microflow [4.21]. Courtesy of A. Stroock, Cornel University, USA

Flow direction Periodic perturbation

100 mm
Fig. 4.64. Chaotic mixing by using the mechanical micromixer [4.22]. Courtesy of
Y.K. Lee, University of California, USA