Biomedical Engineering Reference
In-Depth Information
Experimental
Model (Re = 0.2)
a
Re = 0.2
Concentration
1.00
0.75
Inlet, l = 0
Cycle 2, l = 2.4 mm Cycle 4, l = 4.8 mm
0.50
“Serpentine”
0.25
0.00
Cycle 6, l = 7.2 mm Cycle 8, l = 9.6 mm Cycle 10, l = 12 mm
b
Re = 0.01
1
2
Concentration
1.00
0.75
1
4
3
“Model A”
Inlet, l = 0
l = 0.64 mm
l = 1.27 mm
l = 1.91 mm
0.50
0.25
0.00
l = 2.55 mm
l = 3.18 mm
l = 3.82 mm
l = 4.45 mm
2
3
4
c
d
Re = 0.01
Serpentine mixer
Model B, Re = 0.2
Model A, Re = 0.2
Model A, Re = 60
1
2
0.5
0.4
0.3
0.2
0.1
0.0
3
σ'
“Model B”
0
2
4
6
8
10
12
l (mm)
2
3
FIGURE 3.96
Microluidic.homogenizer.with.complex.3-D.architecture..(From.H..M..Xia,.S..Y..M..
Wan,.C..Shu,.and.Y..T..Chew,.“Chaotic.micromixers.using.two-layer.crossing.channels.to.exhibit.fast.
mixing.at.low.Reynolds.numbers.”.
Lab Chip
.5,.748-755,.2005..Reproduced.with.permission.from.
The.Royal.Society.of.Chemistry.
again that a nonobvious and gratifying feature of these mixers is that they perform better as the
Re…increases!
We note that one drawback of these 3-D serpentine mixer designs is that they consume large
amounts of chip real estate. However, using lamination technologies, it is possible to “fold” back
a serpentine channel over itself in a multilayer device, as shown in the example of
Figure 3.92a
.
An interesting feature about serpentine mixers is that a small change in their architecture
can drastically change their performance. In 2004, a team led by Jun Keun Chang from Seoul
National University in Korea presented a serpentine composed of overlapping “sigmoids”—a
small diference, one might think, from overlapping square “C”'s—(see
Figure 3.97
). Yet the
improvement with respect to C-segment-type serpentines was signiicant, especially at high Re.
he mechanism of operation of this mixer is best understood by looking at where the luid is
forced to go through (see cross-sectional planes in
Figure 3.97d
), and realizing that there must
occur a rotational motion (which enhances mixing).
In 2005, Chong Ahn's laboratory in Pohang University of Science and Technology in Pohang
(South Korea) introduced a mixer with overlapping “F” turns (
Figure 3.98
). Although it looks
very similar to a serpentine mixer, it is based on a rather diferent principle. he novelty of the
design is that the “F” essentially behaves like a fork that splits the low in the horizontal dimen-
sion and recombines (stacks) it in the vertical dimension, yielding a layered low at the out-
let that signiicantly shortens the difusive path between the inlet solutions. he characteristic
