19 January 2006 Mixing in microchannels based on hydrodynamic focusing and time-interleaved segmentation: modeling and experiment
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This paper reports a new mixing concept in microscale using hydrodynamic focusing and sequential segmentation. Both focusing and segmentation were used in the present study to reduce mixing path, to shorten mixing time, and to enhance mixing quality. Transversal mixing path is reduced by hydrodynamic focusing, while sequential segmentation shortens the axial mixing path. Assuming the same viscosity in the different streams, the focused width can be adjusted by the flow rate ratio. The axial mixing path can be controlled by the switching frequency of the inlet valves and the mean velocity of the flow. Both flow rate ratio and pulse width modulation of the switching signal can adjust the desired mixing ratio. This paper first presents a time-dependent two-dimensional analytical model for the mixing concept. This model considers an arbitrary mixing ratio between solute and solvent as well as the axial Taylor-Aris dispersion. A polymeric micromixer was designed and fabricated by CO2 laser micromachining and hot lamination. Sequential segmentation was realized by two piezoelectric valves. The sheath streams for hydrodynamic focusing are introduced through other two inlets. We also designed a measurement system that can synchronize of the mixer's switching signal with the camera's trigger signal. The system allows our relatively slow and low-resolution CCD camera to freeze and to capture a large transient concentration field. The concentration profile along the mixing channel agrees qualitatively well with the analytical model.
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Nam-Trung Nguyen, Nam-Trung Nguyen, Xiaoyang Huang, Xiaoyang Huang, } "Mixing in microchannels based on hydrodynamic focusing and time-interleaved segmentation: modeling and experiment", Proc. SPIE 6036, BioMEMS and Nanotechnology II, 60360L (19 January 2006); doi: 10.1117/12.639034; https://doi.org/10.1117/12.639034

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