Micromixer flow focusing

Figure 4.43 Flow focusing interdigital micromixer made of glass (by courtesy of IMM).

As mentioned earlier, most microscale flow visualization techniques have focused on determination of flow velocity in liquids (or velocimetry). Fluorescence-based techniques, e.g., LIF and PF, have been extensively used for this application. However, in this section, we will look at another microfluidic application for which the development of microscale flow visualization techniques have been critical-micromixing. 

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. 

However, this is difficult to get fast mixing in a conventional batch reactor and also in a large flow reactor, raising the need for a flow microreactor. You may remember that the generation and the reaction of oxiranyllithium species described in Chap. 2 would fail if the residence time cannot be controlled in the order of seconds. This is why a flow microreactor equipped with a micromixer is needed for this reaction. This chapter focuses on extremely fast mixing in a micromixer, which is needed to set a short residence time. 

In Chap. 3, we learned that the flow microreactor system, consisting of micromixers and flow microreactors, enables reactions with residence times in the order of seconds or less. This chapter describes the principle of residence time control for reactions that involve short-lived intermediates. In particular, we focus on the reactions involving aryllithium species containing alkoxycarbonyl groups as intermediates. 

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