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

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