Introduction - Micromixers Fundamentals Design and Fabrication - page 1

CHAPTER

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Introduction

CHAPTER OUTLINE

1.1 Micromixers and Mixing in Microscale...............................................................................................

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1.2 Micromixers as Microreactors ...........................................................................................................

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1.3 Organization of the Topic....................................................................................................................

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References .............................................................................................................................................. 8

1.1 MICROMIXERS AND MIXING IN MICROSCALE
This topic discusses the design, fabrication, and characterization of micromixers, which are defined as
miniaturized mixing devices for at least two different phases, which could be liquids, solids, or gases.
The structures of a micromixer are fabricated partially or in whole, using microtechnology or
precision engineering. The characteristic channel size of micromixers is in the sub-millimeter range.
Common channel widths are on the order of 100-500

m, while channel length could be a few
millimeters or more. The channel height is on the order of the channel width or is smaller. The overall
volume defined by a micromixer is from microliters to milliliters. Compared to molecular size scale,
the length scale and volume scale of micromixers are very large. This fact leads to two key char-
acteristics of micromixers. First, designing the micromixers relies on manipulating the flow using
channel geometry or external disturbances. Second, while micromixers bring advantages and new
features into chemical engineering, molecular-level processes such as reaction kinetics remain almost
unchanged.
Mixing is a transport process for species, temperature, and phases to reduce inhomogeneity.
Mixing leads to secondary effects such as reaction and change in properties. In conventional
macroscale mixing techniques, there are three established terminologies for mixing: macromixing,
mesomixing, and micromixing [1] . Macromixing refers to mixing governed by the largest scale of
fluid motion. For instance, the scale of macromixing corresponds to the diameter of the mixing
tank. Micromixing is mixing at the smallest scale of fluid motion and molecular motion. In
conventional macroscale mixing, the smallest scale of fluid motion is the size of turbulent eddies,
also called the Kolmogorov scale. Mesomixing is in the scale between macromixing and micro-
scale. Although micromixers may have dimensions on the order of micrometers, transport process
in micromixers may still be classified as mesomixing. Since structures in micromixers may have
a size approaching the Kolmogorov scale, this topic avoids the use of micromixing for describing
mixing processes.
There are many different ways to provide mixing in macroscale such as molecular diffusion, eddy
diffusion, advection, and Taylor dispersion. Eddy diffusion is the transport of large groups of species

m