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Micromixers are one of the common pieces of equipment in microfluidic devices and have been widely used for a variety of applications. They are generally divided into active and passive categories. Active micromixers use external energy sources for mixing. Pressure-based micromixers are a common type of active micromixer that use a variety of strategies to create disturbances in the flow and improve mixing. Of all the strategies used for this type of micromixer, oscillating bubble injection has rarely been investigated. In this study, we investigate the flow characteristics and mass transfer process in a two-dimensional micromixer based on oscillating bubble injection. Different parameters affect the mixing performance in this micromixer. In this study, the effects of Reynolds number, bubble oscillation frequency, bubble oscillation amplitude, and side channel geometry on three variables of mixing index, pressure drop, and air inlet pressure have been investigated. The results show that with increasing Reynolds number at constant bubble oscillation frequency and amplitude, the mixing index decreases. Also, with increasing bubble oscillation frequency at constant Reynolds number and constant oscillation amplitude, the mixing index will increase. Increasing the bubble oscillation amplitude at constant Reynolds number and constant oscillation frequency will increase the mixing index. In a simple side channel with a constant diameter, the bubble becomes unstable, so this geometry is undesirable. Changing the side channel geometry by introducing an expansion in the side channel will solve this problem. Nevertheless, increasing the side channel expansion width will reduce the mixing index. The best mixing index was 78.19% in 4.5 seconds, and it shows that the proposed micromixer of this research has good performance in a relatively short time.

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