The expansion of bubbles in viscous fluids in microchannels is normally overlooked. The bubble dynamics in liquids with varying viscosities (1.15 ∼ 101.47 mPa·s) and contact angles (29.3 ∼ 137.6°) in a microchannel were investigated under various inlet pressure drops (8 ∼ 202 kPa). The findings indicate that bubble formation occurs within a squeezing-shearing regime over a wide Capillary number range of 0.0023–0.43. Interestingly, the wettability affects the bubble length rather than the bubble shape, and the poor wettability can hinders the decrease of length in higher viscosity fluids. Bubble expansion causes decreasing curvature radii of bubble caps, and non-linear rapid increases in its length and velocity along the microchannel. The bubble’s pressure–volume relation at the inlet and outlet confirms the validation of Boyle’s law in slug flow. A linear decline in pressure along the microchannel was deduced from this law. Further analysis suggests that besides the friction of the liquid slug, the pressure drop is influenced by the interface effect, film flow, and liquid circulation. Finally, a model for total pressure drop was developed, which effectively predicted the length and velocity of bubbles in the expansion process. This study offers valuable insights for a deeper understanding of bubble expansion behaviors in microchannels.

中文翻译：

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微通道膨胀效应下气液段塞流的流体动力学


微通道中粘性流体中气泡的膨胀通常被忽略。研究了不同入口压降 （8 ∼ 202 kPa） 下微通道中不同粘度 （1.15 ∼ 101.47 mPa·s） 和接触角 （29.3 ∼ 137.6°） 的液体中的气泡动力学。研究结果表明，气泡形成发生在 0.0023-0.43 的较宽毛细管数范围内的挤压-剪切状态下。有趣的是，润湿性影响气泡长度而不是气泡形状，而较差的润湿性会阻碍高粘度流体长度的减少。气泡膨胀导致气泡帽的曲率半径减小，并且其长度和速度沿微通道呈非线性快速增加。气泡在入口和出口处的压力-体积关系证实了波义耳定律在段塞流中的验证。从该定律推导出沿微通道的压力线性下降。进一步分析表明，除了液力块的摩擦外，压降还受到界面效应、薄膜流动和液体循环的影响。最后，建立了总压降模型，有效预测了膨胀过程中气泡的长度和速度。这项研究为更深入地了解微通道中的气泡膨胀行为提供了有价值的见解。