This paper shows the microfabrication process of a split and recombination (SAR) micromixer and the effect of the cross-sectional rotation of fluidic interfaces, which is based on three dimensional microchannels composed of two poly-dimethysiloxane (PDMS) layers. When fluids pass through the nth SAR mixing unit, the number of interfaces increases to 2~(n+1)-1 through SAR mixing. The cross-sectional rotation of interfaces induced by the different time of expanding at slanted walls enhances mixing efficiency. The effect of the rotation is compared by three types of the SAR micromixer characterized by the existence and the direction of the rotation. The first type, No-R type, has flat walls which do not induce the rotation. The second type, Co-R type, has slanted walls which induce counter-clockwise rotations. The third type, Count-R type, has slanted walls and the counter-clockwise rotation alternates with the clockwise rotation. Water and blue dye is used in the mixing experiment as mixing fluids. Each inlet's flow rate range is between 1μl/min (Re0.1179) and 100μl/min (Re11.79). In No-R type, there is a clear contrast in interfaces which means that there is no rotation effect in SAR mixing process. In Co-R and Count-R, the contrast is unclear because of the rotation. Mixing in the SAR micromixer is almost complete after the 7th unit, whose length is 4200μm. The performance of the micromixer is estimated by numerical analysis using CFD ACE+. The flow rate and the diffusion coefficient are set 5μl/min (Re0.5893) and 10~(-10)m~2/s, respectively for each inlet. The cross-sectional view of simulational SAR mixing agrees with experimental observations. The simulation estimates that the degree of mixing is more than 90% after the 6th unit of the No-R and CoR type SAR micromixer.
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