Breakup dynamics of low-density gas and liquid interface during Taylor bubble formation in a microchannel flow-focusing device

This work aims to investigate the breakup dynamics of the low-density gas and liquid interface during bubble formation in a microchannel flow-focusing device. A high-contrast interface tracking method is developed. After the neck motion analysis in radial and axial directions, the time domain criterion between the liquid squeezing stage and the free pinch-off stage is proved to be two orders of magnitude less than the capillary time and is close to the viscous time of the liquid. Comparing to Nitrogen bubbles, the pinch-off point of Helium bubbles deflects downstream in viscous liquids and upstream in low surface tension liquids. Helium bubbles generate faster in viscous liquids and slower in low surface tension liquids. The power law exponents of thread diameter to the pinch-off remaining time in Helium experiments, which are larger than those in Nitrogen experiments, agree with previous studies in both ranges (1/3-1/2) and tendency. (C) 2020 Elsevier Ltd. All rights reserved.