Online proceedings - EDA Publishing Association

11-13
May 2011, Aix-en-Provence, France
Interfacial Configurations and Mixing Performances
of Fluids in Staggered Curved-Channel Micromixers
Jyh Jian Chen, Chun Huei Chen, and Shian Ruei Shie
Department of Biomechatronics Engineering, National Pingtung University of Science and Technology
1, Shuefu Road, Neipu, Pingtung 91201, Taiwan
Abstract- A parallel laminar micromixer with staggered
curved channels is designed and fabricated in our study. The
split-and-recombination (SAR) structures of the flow channels
result in the reduction of the diffusion distance of two fluids.
Furthermore, the impinging effects increase the mixing
strength whereas one stream is injected into the other. The
particles trajectories are utilized to numerically examine the
mixing and fluidic behaviors inside the staggered curved
microchannel with tapered structures. The effects of various
Reynolds numbers and channel configurations on mixing
performances are investigated in terms of the experimental
mixing indices and the computational interfacial patterns.
I. INTRODUCTION
Because of the vast application fields of micromixers, such
as DNA hybridization [1], direct methanol fuel cell (DMFC)
[2] and cell sorting [3], the mixing efficiency in these devices
is very important for the overall process performance. With
the progressing of microfabrication technology, micromixers
gradually move from the sub-systems of micro total analysis
systems into the crucial components of MEMS. Mixture of
fluids in a microchannel is strongly restricted to molecular
diffusion due to the low Reynolds number. In order to speed
up the mixing process in microfluidic systems, passive
micromixers with the advantages of low cost, easy
fabrication and no additional power have been applied in the
development to enhance mixing processes.
Parallel laminated mixers with simple two-dimensional
structures are fabricated without difficulty, and mixing in
such laminar flows can be very easily enhanced. Two
representative micromixers were discussed in detail before.
One design splits the main stream into several narrow
streams and rejoins them together. A circular vortex
micromixer with several tangential inlets was presented by
Bohm et al. [4]. The mixing could be performed in a shorter
timescale. The other design is a device with multiple
intersecting channels. Nguyen et al. [5] demonstrated a
micromixer with a square obstacle on the square-wave flow
channel. Results showed that mixing index increased rapidly
with decreasing microchannel width.
When liquid is directed through curved channels, the fluid
at the center experiences a higher centrifugal force than the
surrounding liquid. Therefore, a pair of counter-rotating
vortices is generated and ejects fluid toward the outer wall;
this will enhance the stretching and folding of the flow
element. This mechanism has been employed by many
researchers for heat transfer enhancement [6, 7]. These
vortices (known as Dean Vortices) as a result of differential
centrifugal forces acting on the fluid at the center and at the
surrounding regions also provide enhanced mixing. Howell
et al. [8] fabricated a micromixer with three quarters of a
circular channel. The longitudinal variation of the radial
distribution of the dye is evident. While increasing the aspect
ratio increases the mixing. Yamaguchi et al. [9] expressed
that the interface configuration was affected by secondary
flows induced by centrifugal forces. Simulation results were
validated by images through confocal fluorescence
microscope. Jiang et al. [10] presented a channel comprising
four circular arcs and two straight inlet and outlet sections.
For Dean Numbers, K, larger than 143 (corresponding to
Reynolds numbers, Re, of 313), the interface stretching got
increased and it indicated that chaotic mixing occurred.
Kockmann et al. [11] presented the concentration
distribution in a channel with a 90° bend. The length of the
interface was enlarged by the vortex flow, and the potential
for an exchange of the liquids was increased. Sudarsan and
Ugaz [12] demonstrated a planar split-and-recombine
micromixer. Parallel liquid streams first traveled through a
curved segment that induced simultaneous 90° rotations in
the upper and lower halves of the channel, at which point the
flow was spilt into multiple streams that continued along
curved trajectories such that each individual split stream
experienced a second pair of 90° rotations. It was capable of
generating multiple alternating lamellae of individual fluid
species. Mouza et al. [13] illustrated a micromixer that
comprises a semicircular curved channel and a
split-and-recombine unit consisting of two semicircular
microchannels that form a circle. At relatively low flow
rates, where the secondary Dean flows were weak, the
addition of geometrical features considerably promoted fluid
mixing.
A two-dimensional curved rectangular channels is
designed in our study. The flow system is composed of
several staggered three quarters of ring-shaped channels. The
secondary flow patterns of the curved channels with various
configurations are numerically and experimentally analyzed.
In order to quantify the mixing as a function of the distance
along the curved channel and the interfacial line length,
linear regression is utilized to predict the interfacial line
length at different mixing index.
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