Biomedical Engineering Reference
In-Depth Information
less-toxic compounds in micromixers. Detection facilities should be extended to these pre-compounds
to counter this potential misuse.
1.3 ORGANIZATION OF THE Topic
This topic offers a wide spectrum for the study of the mixing processes in microscale, from funda-
mental transport effects to a variety of designs to specific applications in chemistry and life sciences.
After the introduction in Chapter 1, Chapters 2 and 3 discuss the basic terminology and fundamental
physics of transport effects that will be used for designing micromixers. Chapter 2 discusses in detail
the three key mass transport effects often used in micromixers: molecular diffusion, Taylor dispersion,
and chaotic advection. The challenges and advantages of miniaturization in mixing are highlighted in
this chapter with the help of scaling laws. The scaling laws are discussed based on nondimensional
numbers which represent relationships between different transport effects. Chapter 3 discusses the
fundamentals of
the different numerical schemes for modeling the transport phenomena in
micromixers.
Chapter 4 gives an overview on available microtechnologies for making micromixers. Basic
techniques of conventional silicon-based microtechnologies are covered. Since polymers are chemi-
cally and biologically compatible, polymeric micromachining is the focus of this chapter. Technol-
ogies for bonding and sealing are necessary for making a micromixer. This chapter also discusses the
design and fabrication of fluidic interconnects that are needed for interfacing micromixer to larger-
scale devices and equipments.
Different concepts and designs for micromixers are discussed in Chapters 5 to 7. Although all
mixing concepts involve molecular diffusion, Chapter 5 only discusses concepts where molecular
diffusion is the primary mass transfer process. Based on the arrangement of the mixed phases, the four
mixer types discussed in this chapter are parallel mixer, serial mixer, sequential mixer, and injection
mixer.
Chapter 6 is dedicated to micromixers based on chaotic advection. In contrast to the micromixers
discussed in Chapter 5, this class of micromixers relies on bulk mass transport for mixing. The general
concepts for generating chaotic advection are stretching and folding of fluid streams. These stretching
and folding actions can be implemented in a planar design or in a complex three-dimensional channel
structure. A special case of chaotic advection is mixing in microdroplets. Manipulation of the flow
field inside a droplet can lead to the same stretching and folding effects as achieved in a continuous-
flow platform.
Chapter 7 discusses active mixers, where mixing is achieved with energy induced by an external
source. Active mixers are similar to conventional macroscale mixers where fluid motion is driven by an
impeller. However, as discussed in Section 1.1, miniaturization of the impeller concept would not work
because of the dominant viscous force in microscale. This chapter discusses different concepts for
inducing a disturbance into the flow field. The use of electrohydrodynamic, dielectrophoretic, elec-
trokinetic, magnetohydrodynamic, acoustic, and thermal effects in micromixers is discussed here.
Chapter 8 summarizes key diagnostics techniques for characterization of micromixers. Since both
velocity field and concentration field are important for good mixing, diagnostics techniques for these
fields are the focus of this chapter. The quantification of the extent of mixing is important for the
evaluation of performance as well as the design optimization of micromixers.
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