Experimental approaches to a better understanding of mixing performance of microfluidic devices

Two experimental methods are presented that were used to describe the mixing performance of five micromixers differing in mixing principle and internal geometry. The well-known "Villermaux/Dushman method" was adapted to continuous processes and subsequently modified in such a way that the sensitivity of the method can now be adjusted to different flow rates. In addition, a new physical method was developed to investigate mixing performance that is based on the phase transfer of a solvatochromatic dye between two immiscible fluids. The combination of both methods allows considering very different aspects of mixing performance in both single and multiphase systems. Micromixers can thus be compared qualitatively and quantitatively. In this context the completeness of mixing as well as the influence of pressure drop, hold-up and retention time on the mixing efficiency is discussed. (C) 2004 Elsevier B.V. All rights reserved.