Design and characterization of a passive recycle micromixer

A new design was devised for a recycle micromixer, i.e., a passive micromixer with side channels for a recycle flow. The geometry, required to perform a recycle flow and effective mixing, was determined by a simulation based on computational fluid dynamics. A recycle flow of the mixed flow of each unit was introduced to the inlet flow, and a circular flow was generated in the body of the mixer. For complete mixing, five units of the micromixer were connected in series. The simulations were performed at Reynolds numbers of 7, 14 and 28 and channel depths of 100, 150 and 200 mum. Mixing efficiency and direction of recycle flow were significantly affected by both Re and channel depth. When channel depth was 150 mum, mixing efficiency of the micromixer increased from 89.3 to 95.6, 98.4 and 98.6% with the increase of Re from 7 to 14, 28 and 42, respectively. The increasing channel depth also increased mixing efficiency. The micromixer was fabricated by a conventional photolithography technique using polydimethylsiloxane. Color dispersion in blue ink was compared with simulated flow patterns. The characterization of mixing in the recycle micromixer was verified by using an aqueous NaOH solution and phenolphthalein solution, composed of the same volume of ethanol and water. For both cases, fully mixed profiles were achieved along five micromixers, connected in a series at a flow rate of 0. 1 ml min(-1) for each flow and a short residence time of 0. 11 s.