Peclet micromixers

A numerical study of the free-radical polymerization of styrene (Scheme 6.15) compared the behavior of an interdigital micromixer with a T-junction and a straight tube [37, 48], The diffusion coefficient of the reactive species was varied to simulate the viscosity increase during a polymerization. The performance of the polymerization turned out to be largely dependent on the radial Peclet number. This dimensionless number is defined as the ratio of the characteristic time of diffusion in the direction perpendicular to the main flow to the characteristic time of convection in the flow direction (i.e., the mean residence time) and, therefore, is directly proportional to the characteristic length of the reactor. 

Fig. 6.32 Comparison of the polydispersity index (DPI) obtained in a multilamination micromixer (open symbols) and in a tube reactor (filled symbols) as a function of the radial Peclet number. (Courtesy of the Royal Society of Chemistry [48].)...

Micromixers are also commonly characterized accordingly to three nondimen-sional fluid parameters Re (as discussed above), Peclet number Pe, and Strouhal number St. Peclet number is defined as ... 

In micromixers, two operating parameters are of importance the Reynolds number Re and the Peclet number Pe. The Reynolds number, given by... 

It has been shown in this chapter how to characterize mixing efficiency in micromixers and particularly how to relate mixing time to relevant operating parameters such as the Peclet number and the specific power dissipation. In spite of a low mixing energetic efficiency, micromixers can mix in a few milliseconds, much faster than conventional mixers. 

The characteristic dimensionless numbers such as Reynolds number (Re) and Peclet number (Pe) are very suitable for discussing the operating conditions for micromixers. From the definitions in Equations (7.1) and (7.2), the relation... 

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