Investigation of pressure contours and streamlines indicating local mixing during droplet generation in flow-focusing microchannel via simulations

This study investigates droplet generation in a flow-focusing microchannel using the level-set method. Fluctuating behavior of pressure signals is observed during droplet breakage at the flow-focusing junction and droplet exit from the microchannel outlet. An in-depth analysis of pressure contours through visualization reveals that the same magnitude of pressure develops in both dispersed and continuous phases during the droplet plugging and breakage events. Pressure contour analysis further indicates that high back pressure generated during the droplet breakage results in an intensified circulating flow, an effect that has a wide range of potential applications in enhancing micro-mixing. The spatiotemporal patterns of phase fields, velocity vectors, and streamlines are presented. It is observed that the local magnitude of the local vorticity increases linearly with interfacial tension between the two immiscible phases, thereby enhancing the mixing index (MI). Some other significant insights regarding the pressure signal for droplet plugging, breakage, and exit from channel outlet are analyzed thoroughly, providing a comprehensive understanding of droplet generation.