Bubble breakup in a microfluidic T-junction

We conduct a computational fluid dynamics simulation to investigate the behaviors of bubble breakup in a microfluidic T-junction using volume-of-fluid method to represent the interface. The evolution of bubble morphology and the distributions of velocity and pressure in flow field are analyzed, and the effect of width ratio between main channel and branch on the bubble morphology are evaluated. The results indicate that, the tunnel breakup, obstructed breakup, combined breakup and non-breakup are observed during the bubble flows through the T-junctions under different condition. The whole bubble breakup process undergoes the extension, squeeze and pinch-off stages, while the non-breakup process experiences extension and pushing stages. We find that, in the squeeze stage, a local vortex flow forms at the front edge of the bubble for the tunnel breakup while the velocity inside the bubble is of a parabolic distribution for the obstructed breakup. Irrespective of non-breakup regimes, there is a sudden pressure drop occurring at the gas-liquid interface of the bubble in the squeeze stage, and the pressure drop at the front interface is far larger than that at the depression region. The transition of the bubble breakup regime through the T-junction occurs with an increase in width ratio of main channel to the branch, which sequentially experiences the non-breakup regime, tunnel breakup regime and obstructed breakup regime. The flow regime diagrams are plotted with a power-law correlation to distinguish the bubble/droplet breakup and non-breakup regimes, which also characterize the difference between bubble and droplet breakup through a T-junction.