Three-dimensional simulations of two-phase plug flow in a microfluidic channel

A fundamental understanding of two-phase flow behavior in microfluidics is crucial for various technological applications across different disciplines, including energy, chemical, and material engineering, as well as biomedical, environmental, and pharmaceutical sciences. In this work, we elucidate the flow fields of low Capillary number [Ca similar to O(10(-3))] segmented Taylor flows of immiscible CO2 emulsions/bubbles transported by water in a low aspect ratio microchannel. We conducted high-resolution two- and three-dimensional (2D and 3D) numerical simulations using an improved volume-of-fluid two-phase flow solver and validated their accuracy against experimental data. Our results show that 3D simulations are necessary to accurately capture the dynamics of liquid and supercritical CO2 emulsions produced at relatively higher Ca. The 3D simulation results also reveal diverse patterns of spanwise vortices, which are overlooked in 2D simulations. Calculating the Q-criterion in 3D revealed that vortices with relatively higher vorticity magnitudes are adjacent to the sidewalls, with the strongest ones emerging across the microchannel in the third dimension. More specifically, gaseous CO2 bubbles display relatively intense vortex patterns near the interfacial region of the bubble body and the cap due to the influence of the surrounding thin liquid film and slug flow. At higher Ca, liquid and supercritical CO2 emulsions exhibit similar flow dynamics, however, with prominent vortex patterns occurring in the upstream cap region. These findings pinpoint specific areas within the emulsions/bubbles that require attention to enhance stabilization or exchanging mechanisms for low-Ca Taylor flow of emulsions/bubbles.