Micromixers based on chaotic advection - Micromixers Fundamentals Design and Fabrication - page 218

FIGURE 6.26
Barrier embedded mixer.
Bertsch et al. reported a miniaturized version of the conventional Kenics static mixer with helical
flow-twisting elements [37] . Two designs were tested for this concept. The first design was formed by
four mixing elements, which was made of 24 rectangular bars placed at 45 . The four mixing elements
were arranged at an angle of 45 in the channel. The second design consists of right-handed and left-
handed helical elements containing six small-helix structures. Because of this complex geometry, the
micromixer was fabricated by stereo-micro-lithography. The complex structure was built up layer by
layer. Kim et al. [38] improved the Kenics design with embedded barriers. The rationale of the barriers
is the same as in the case of the BEM discussed above. Hyperbolic points exist with the introduction of
the barriers. The complex structure of the micromixer was realized by stereo-micro-lithography. Each
unit of the design reported by Kim et al. [38] rotates the mixing streams by 180 , while the design of
Bertsch et al. [37] allows a 90 rotation after each mixing unit.
6.4 CHAOTIC ADVECTION IN MULTIPHASE FLOW
6.4.1 Multiphase systems in microscale
Most micromixers discussed in this topic are based on single-phase miscible liquids. Multiphase
systems consist of two or more partially immiscible or immiscible fluids. Multiphase immiscible
systems provide interesting microscale effects, which enhance mixing and minimize undesired effects
of single-phase flows such as Taylor dispersion and absorption of species to the channel wall. Intro-
ducing a multiphase system in a microchannel results in different flow forms. Each of the forms may
find its own applications in mixing in microscale. The forms of a multiphase system depend on the flow
conditions, which dictate the balance between the several body forces and surface forces. A multiphase
system in microchannels may have the forms of floating droplets, long plugs, or thin wetting films.
Flow systems with droplets and plugs formed in an immiscible carrier fluid are called segmented flows