Micromixers efficiency characterization

P. Guichardon, L. Falk, Characterization of micromixing efficiency by the iodide-iodate reaction system. Part I. Experimental procedure, Chem. Er. Sci., 2000, 55, 4233. 

This measure can be used to characterize micromixing efficiency at all spatial locations. / p cannot be obtained directly in complex flows, but it is predictable from the stretching field. 

The material and process parameters, which govern the micro-mixing efficiency can only be determined by the selectivity of extremely fast chemical reactions, whose progress (conversion and yield) can be simply and rapidly monitored. Consequently the application of chemical reactions as probes of molecular resolution [94] represents the most sensitive investigating method for characterizing micromixing. There are a number of comprehensive reviews of this technique [13, 40, 94, 565]. 

Instead, the Kolmogorov micro-scales (1.328) to (1.330) characterize the dissipation scales of turbulence and might indicate the effectiveness of micromixing in the flow provided that the turbulent energy dissipation rate and the kinematic viscosity of the fluid is known. If the Kolmogorov micro length scale is much larger than the molecular scales, the molecules are not efficiently mixed by turbulent diffusion. 

The present chapter aims to be complementary to the studies and reviews already published to present theoretical basis elements for the understanding of mixing principles in laminar flows, mainly developed in micromixers. Among different characterization techniques of mixing efficiency, this chapter more specifically focuses on the chemical test method, called the Villermaux-Dushman reaction, that we have developed over many years and which is named in memory of Professor Jacques Villermaux. It will be shown how to obtain the mixing time and how to relate it to operating parameters such as the Reynolds number of the flow and the specific power dissipation per unit mass of fluid. A non-exhaustive comparison of several micromixers will be presented. 

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. 

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