Theoretical and experimental studies of mixing enhancement in micromixers.

摘要

In combination with low processing flow rate, the small physical dimensions of microscale mixers or reactors imply laminar flow, which precludes convective turbulent mixing normally relied upon for effective mixing in conventional-size processing equipment. The objective of this work is to investigate mixing enhancement in microchannel mixers, through a theoretical as well as an experimental study of currently utilized and proposed micromixing configurations. The design of our proposed micromixers for mixing enhancement is based essentially on the mechanisms of fluid multilamination and elongational flow. In these mixing configurations, mixing is enhanced by placing static or passive mixing structures on the mixer channel floor. This geometric constraint leads to the desired reduction in the fluid diffusion path while at the same time increasing significantly the fluid contact areas via creation of folding as well as local and global re-orientation of fluid interfaces.;In order to establish the experimental platform for the mixing studies, preliminary numerical study is conducted first using computational fluid dynamics (CFD) approach. Using the CFD tools, one of the proposed mixing configurations herein referred to as multilaminated/elongational flow micromixer-4 (MEFM-4) is selected based on the set criteria of minimum pressure drop and high mixing performance. The novel multichannel MEFM-4 and a standard T junction micromixer (TjM), fabricated via silicon micro-electromechanical systems (MEMS) technology, are then characterized experimentally for their mixing performance using residence-time distribution (RTD) measure in conjunction with UV-vis absorption spectroscopy detection technique. The RTD measure chosen represents an innovative technique for the characterization of mixing in micromixers/reactors. Using the RTD and its coefficient of variation as measures for evaluating mixing, the proposed MEFM-4 exhibits better mixing performance than the standard TjM. The results from the numerical simulations and experiments are in very good agreement thus establishing the validity of the mathematical model and the associated solution algorithm implemented in the CFD simulations. The CFD code in conjunction with the numerically obtained RTD can then be used as a predictive tool in the design, evaluation, and optimization of micromixers. The present work describes the efficient design, fabrication and characterization of an effective microchannel mixer for microchemical systems' applications.