Static micro-mixing analysis by using sequential quadratic programming and a confocal microscope

Abstract

Molecular diffusion transport in a straight micro-channel has very little influence on mixing due to the extremely small length and velocity scales. As an alternative to a complex geometry, we propose a static-type micro-mixer with a concise configuration. This simpler geometry, but with careful design, achieves a less pressure drop but still allows a reasonably good mixing effect, which might be suitable for practical mass-production-type devices. In our research, the influence of the obstacles in a Y-channel type mixer on mixing was numerically and experimentally investigated by using precise nonlinear analysis. The layout and the size of the obstacles in a Y-channel micromixer were optimized to obtain the maximum possible mixing ratio by using sequential quadratic programming (SQP), a nonlinear approximate optimization technique. In the experimental setup, a Polydimethylsiloxane (PDMS) micro Y-channel was fabricated in which two DI water and ethanol working fluids passed by. A laser induced fluorescence (LIF) confocal microscope was adopted in order to determine the mixing ratio by using the fluorescence intensity of the flow using He/Ne laser scanner. This procedure could be easily extended as a guideline to the optimization of other types of static micro-mixers.