Rapid fluid mixing phenomenon in microchannels offers significant advantages in lab-on-chip testing, drug preparations, micro-assay, and micro-combustor applications. Development of new materials for microchannels and advances in micro fabrication techniques continue to aid fluid mixing research that is vital to microfludic applications. Due to the need for low cost and biocompatibility, polymers began to play important role in design of micromixers. Recently, a number of methods and devices are designed to enhance mixing at the microscale [1–3]. A novel idea of introducing bubbles into two mixing streams with three mixing chambers downstream is tested by means of experiments [3]. The interaction among the bubbles in the mixing chamber results in the stretching and folding of the laminar flow interface leading to a rapid chaotic mixing in short period of time. However, the physics of recirculation zones, bubble formation, and bubble fragmentation must be fully understood in order to design efficient micromixers using this technique. The objective of the present work is to numerically study the formation of recirculation zones, bubble formation, and bubble break-up in microchannels. Numerical calculations were performed with finite volume CFD code ANSYS Fluent. Results obtained with structured grids with about 47,000 grid points. Different gas velocities, liquids velocities and inlet angles were used to investigate the flowfield. Results show that the liquid velocity has a major effect on the circulations inside the channel which impact the formation of the gas bubble. Also, at low liquid velocities, the length of the gas slug is affected by the gas velocity.

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