A Gas Kinetic Energy Based Strategy for the Accurate\nRegulation of Taylor Bubble Length in Flow-Focusing Microchannels

Accurate\nregulation of the bubble length determines the microchannel\nreaction performance, but the existing methods focus on the construction\nof complex bubble generation structures with high operating requirements.\nAccordingly, for the flow-focusing microchannel, this study proposes\na convenient method that varies the gas inlet kinetic energy to adjust\nthe bubble length. The results show that the gas inlet kinetic energy\ncan be easily regulated by changing the gas channel width, and the\nbubble size is markedly reduced via expanding the gas channel width,\nwhich for the first time breaks the traditional cognition that the\nbubble size becomes large with the gas inlet width in the T-junction.\nBesides, the reason behind the formation of smaller bubbles in the\nflow-focusing with a wider gas channel is jointly revealed by analyzing\nthe two-phase interface behaviors in flow-focusing and T-junction\nmicrochannels. Especially, a new variable (the liquid equivalent residence\ntime) is proposed to describe the interaction between the two phases,\nand the design criterion for the gas inlet size is proposed to reach\nthe minimal bubble length in flow-focusing microchannels. Finally,\nconsidering the gas inlet kinetic energy effect, a universal bubble\nlength model containing the ratio of Weber numbers for gas and liquid\nand capillary number for liquid is developed, which shows its excellent\nperformance for the flow-focusing microchannels used in this work\nand other studies.