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fluids travel along a curved channel. This effect induces a
secondary flow. Figure 6 shows concentration distributions
and vector planes of various cross sections a-e. The
simulation results and confocal images are illustrated at an
inlet velocity of 0.5 m/s. Re is equal to 50, and K equal to
22.36. The red- and blue-colored liquids are utilized in the
computation. The fluid with red color stands for species A,
and the fluid with blue color for species B. Fluid flows
around a curved channel and the fluid near the center
experiences a larger centrifugal force than that near the
surrounding. The velocity along the central axis is the largest
and is the most strongly affected by the centrifugal forces.
Two counter-rotating vortices coinciding with its plane of
curvature, above and below the symmetry plane of the
channel, are created. As a result, fluid is transported in the
outward direction and is transported back by recirculation
along the channel walls. Thus, the vertical interface that
crosses the central axis is distorted. As the fluid proceeds to
the curved channel, main stream is separated as two streams.
Fluids in the angled channels show blue fluids surrounded by
red fluids and the lamellae of two species. It accompanies by
a corresponding increase in interfacial area, shown in Figs.
6(a) and (c). In vector planes, the length of the arrow means
the magnitude of the velocity vector. Compared with the
vector planes between two branch channels, a large amount
of fluid tends to flow along the original curved channel (Fig.
6(b)) and the rest of the fluid moves into the angled channel
(Fig. 6(a)). The uneven split of two fluids inside the
staggered channels can be observed. Then two streams
merge and it produces a strong impact around the
interconnection (Fig. 6(e)). And then the fluid is divided into
two sub-streams again. The vertical interface observed in the
inlet is heavily and permanently distorted by the Dean
Vortex, SAR microstructures and the impinged effect. The
mixing performance is increased. Confocal images are used
to qualitatively compare with the computational results. The
fluorescence images are classified into two distinct regions, a
red region from rhodamine and a black region from DI water.
The results of numerical results are compatible with the
visual experiment.
11-13
May 2011, Aix-en-Provence, France
(c)
(d)
(e)
Fig. 6. The mixing characteristics at nine cross-sectional areas along the
downchannel.
A particle trajectory is the path of a particle moving in a
fluid. Being able to visualize this trajectory can be very
helpful in understanding flow patterns and flow distribution.
A streak line is defined as a line formed by the particles
which pass through a given location in the flow field. At the
steady state, the streak lines coincide with the particle
trajectories. In this study, the streak lines are determined by
integrating the vector equations for motion and obtained
from CFD-ACE+ TM software. Top view of streak lines
through the mixing channels is depicted in Fig. 7(a). The
streak lines stretch from the inlet, then split into two streams,
and merge into one main stream. It shows most of the fluid
keeps flowing in the original channel and the rest of the fluid
flows into the angled channel. After passing the second split
portion, a similar trend can be observed. This uneven split of
the streams increases the contact surface of the mixing fluids.
Fig. 7(b) demonstrates the magnified images of the streak
lines near the two split portions of the curved channel marked
by two blue ovals in Fig. 7(a). Two streams merge and
produce an impact around the interconnection. Due to the
split-and-recombine and the impinging effects, the mixing
performance can be improved.
(a)
(a)
(b)
(b)
Fig. 7. (a) Top views of streak lines through the mixing channels. (b) Top views
of streak lines through the mixing channels at the interconnection.
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