Inertial microfluidics is an active field of research that deals with crossflow positioning of the suspended entities in microflows. Until now, the majority of the studies have focused on the behavior of rigid particles in order to provide guidelines for microfluidic applications such as sorting and filtering. Deformable entities such as bubbles and droplets are considered in fewer studies despite their importance in multiphase microflows. In this paper, we show that the trajectory of bubbles flowing in rectangular and square microchannels can be controlled by tuning the balance of forces acting on them. A T-junction geometry is employed to introduce bubbles into a microchannel and analyze their lateral equilibrium position in a range of Reynolds (1 < Re < 40) and capillary numbers (0.1 < Ca < 1). We find that the Reynolds number (Re), the capillary number (Ca), the diameter of the bubble (), and the aspect ratio of the channel are the influential parameters in this phenomenon. For instance, at high Re, the flow pushes the bubble towards the wall while large Ca or moves the bubble towards the center. Moreover, in the shallow channels, having aspect ratios higher than one, the bubble moves towards the narrower sidewalls. One important outcome of this study is that the equilibrium position of bubbles in rectangular channels is different from that of solid particles. The experimental observations are in good agreement with the performed numerical simulations and provide insights into the dynamics of bubbles in laminar flows which can be utilized in the design of flow based multiphase flow reactors.

中文翻译：

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矩形微流体通道中气泡的惯性操纵†

惯性微流体是一个活跃的研究领域，涉及微流中悬浮实体的错流定位。到目前为止，大多数研究都集中在刚性颗粒的行为上，以便为微流体应用（例如分选和过滤）提供指导。尽管它们在多相微流中很重要，但在较少的研究中考虑了诸如气泡和液滴之类的可变形实体。在本文中，我们表明可以通过调整作用在矩形和方形微通道上的力的平衡来控制在矩形和方形微通道中流动的气泡的轨迹。采用T形结几何形状将气泡引入微通道，并分析它们在雷诺（1 <Re <40）和毛细管数（0.1 <Ca <1）范围内的横向平衡位置。我们发现雷诺数（Re）），而通道的长宽比则是这种现象的影响参数。例如，在高Re时，流动将气泡推向壁，而较大的Ca或将气泡推向中心。而且，在纵横比大于1的浅通道中，气泡向着较窄的侧壁移动。这项研究的重要成果之一是矩形通道中气泡的平衡位置与固体颗粒的平衡位置不同。实验观察结果与所进行的数值模拟非常吻合，并提供了对层流中气泡动力学的见解，可用于设计基于流的多相流反应器。