Performance analysis of a folding flow micromixer

Abstract

The performance of a folding flow micromixer in the Stokes flow regime is investigated computationally and experimentally. Consistency with a previously derived general scaling relation is demonstrated and the geometric parameters in the scaling relation are determined for this mixer. Measured data from a second similar mixer are correctly predicted using the scaling relation, thus showing that the approach allows quantitative prediction of mixing. This paper focuses on the errors associated with such predictions. Basic errors, expressed as variations in the standard deviation of the concentration profile, were estimated to be −10% for the computation and −30% for the experiment at the highest values of Peclet number considered. It is shown that this experimental error was mostly due to depth averaging of the spectroscopic technique used for concentration measurement at the high Peclet numbers. However, extra uncertainty is associated with chip fabrication tolerances and this was investigated further. Measurements at the outlet of nine different mixer chips of notionally identical design revealed variations in mixing of ±26%. This variation was attributed to misalignment of the glass layers determining the geometry of the mixer in the chip. Thus, the combination of measurement error and misalignment means predictions of the concentration standard deviation for the mixer may get non-uniformity wrong by up to 50%. Ensuring a required uniformity, however, simply requires adding a few further elements to the mixer to allow for this uncertainty. Application of the scaling relation to mixer design is highlighted by a discussion of the options available for improving the performance of the experimental mixer.