We experimentally study the displacement of viscous liquid by gas in a square capillary tube. The liquid is partially wetting in a way that no spontaneous imbibition along the interior corners would occur even in the absence of forced displacement. The gas–liquid interface exhibits a variety of morphologies with an increasing displacement rate. At a low displacement rate, a constantly moving meniscus can be observed, without any liquid deposition on the tube wall. An increase in the displacement rate gives rise to the deposition of two ultra-thin liquid filaments at each corner, which immediately break into tiny droplets. An additional thicker filament is entrained at each corner as the displacement rate further increases, connecting the thinner ones and the meniscus. When the displacement rate is high, liquid films are entrained on the tube wall and eventually collapse, entrapping an amount of gas in the form of Taylor bubbles. Quantitative measurements show that both the thicker filaments and the liquid films retract at constant speeds. Empirical relations predicting the film thickness and the bubble length are proposed and agree with the experimental results.

中文翻译：

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方毛细管中动态润湿转变气泡形成实验

我们通过实验研究了方形毛细管中气体对粘性液体的置换。液体部分润湿，即使在没有强制位移的情况下，也不会发生沿内角的自吸。随着置换率的增加，气液界面呈现出多种形态。在低位移速率下，可以观察到不断移动的弯液面，管壁上没有任何液体沉积。位移速率的增加导致在每个角处沉积两条超细液体细丝，这些细丝立即分解成微小的液滴。随着位移率的进一步增加，每个角处都会夹带一根额外的较粗的细丝，将较细的细丝和弯月面连接起来。当位移率高时，液膜被夹带在管壁上并最终坍塌，以泰勒气泡的形式捕获大量气体。定量测量表明，较粗的长丝和液膜均以恒定速度收缩。提出了预测薄膜厚度和气泡长度的经验关系，并与实验结果一致。