Improved serpentine laminating micromixer: Numerical investigation and experimental verification

It is a difficult task to achieve an efficient mixing inside a microchannel since the flow is characterized by low Reynolds number (Re). Recently, the serpentine laminating micromixer (SLM) was reported to achieve an efficient chaotic mixing by introducing 'F'-shape mixing units successively in two layers such that two chaotic mixing mechanisms, namely splitting/recombination and chaotic advection, enhance the mixing performance in combination. The present study describes an improved serpentine laminating micromixer (ISLM) with a novel redesign of the 'F'-shape mixing unit. Reduced cross-sectional area at the recombination region of ISLM locally enhances advection effect which helps better vertical lamination, resulting in improved mixing performance. Flow characteristics and mixing performances of SLM and ISLM are investigated numerically and verified experimentally. Numerical analysis system is developed based on a finite element method and a colored particle tracking method, while mixing entropy is adopted as a quantitative mixing measure. Numerical analysis result confirms enhanced vertical lamination performance and consequently improved mixing performance of ISLM. For experimental verification, SLM and ISLM were fabricated by polydimethylsiloxane (PDMS) casting against SU-8 patterned masters. Mixing performance is observed by normalized red color intensity change of phenolphthalein along the downchannel. Flow characteristics of SLM and ISLM are investigated by tracing the red interface of two streams via optical micrograph. The normalized mixing intensity behavior confirms improved mixing performance of ISLM, which is consistent with numerical analysis result.