Performance analysis of a folding flow micromixer |
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Authors: | Z Chen M R Bown B O’Sullivan J M MacInnes R W K Allen M Mulder M Blom R van’t Oever |
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Affiliation: | (1) University of Sheffield, Sheffield, UK;(2) Micronit Microfluidics, Enschede, The Netherlands |
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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 Péclet 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 Péclet 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. |
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