Mixing investigation through a miniaturized channel by means of passive method

Dehgani, Tohid (2018) Mixing investigation through a miniaturized channel by means of passive method. Masters thesis, University of Mohaghegh Ardabili.

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Abstract

Advances in manufacturing in micrometer size, make it possible to produce new devices with a very small size for fluid transferring called microfluidic devices. Micromixers are very small devices that are used to mix at least two different species. Micromixers and mixing process are considered as one of the important parts of microfluidic systems and have many applications in various fields such as chemistry, biochemistry, medicine and pharmacy. In small geometries, the Reynolds number is too low and the flow regime is generally laminar. In laminar flows mixing is mainly based on molecular diffusion, which is a very time consuming, therefore it is necessary to enhance mixing. In this research, the mixing phenomenon in a Y-shaped micromixer with different geometries in different Reynolds numbers is investigated. Utilizing topology optimization, optimal shape of the baffles through the channel generated and effect of Reynolds number and diffusion coefficient on mixing is investigated. Results of three studied microchannels show that in all Reynolds numbers, increasing the diffusion coefficient causes increase in mixing efficiency. It is also observed that, increasing Reynolds number initially reduces the mixing efficiency and then increases it. In low Reynolds numbers, molecular diffusion is the dominant mechanism of mixing therefore increasing the velocity reduce the residence time and consequently diffusion effects. More increasing of Reynolds number cause formation of vortexes just behind of obstacles. These generated vortexes enhance chaotic advection mechanism against diffusion mechanism. Increasing Reynolds number intensify vortex and increases mixing efficiency.

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