Passive mixing in a three-dimensional serpentine microchannel

A three-dimensional serpentine microchannel design with a "C-shaped" repeat ing unit is presented in this paper as a means of implementing chaotic adve ction to passively enhance fluid mixing, The device is fabricated in a sili con wafer using a double-sided KOH wet-etching technique to realize a three -dimensional channel geometry. Experiments using phenolphthalein and sodium hydroxide solutions demonstrate the ability of flow in this channel to mix faster and more uniformly than either pure molecular diffusion or flow in a "square-wave" channel for Reynolds numbers from 6 to 70, The mixing capab ility of the channel increases with increasing Reynolds number. At Least 98 % of the maximum intensity of reacted phenolphthalein is observed in the ch annel after five mixing segments for Reynolds numbers greater than 25, At a Reynolds number of 70, the serpentine channel produces 16 times more react ed phenolphthalein than a straight channel and 1.6 times more than the squa re-wave channel. Mixing rates in the serpentine channel at the higher Reyno lds numbers are consistent with the occurrence of chaotic advection. Visual ization of the interface formed in the channel between streams of water and ethyl alcohol indicates that the mixing is due to both diffusion and fluid stirring.