Department of Chemical Engineering, Stanford University , Stanford, California 94305, United States.
Langmuir. 2016 Nov 22;32(46):12031-12038. doi: 10.1021/acs.langmuir.6b03258. Epub 2016 Nov 10.
An experimental and theoretical investigation is conducted to understand the role of compressibility on the quasi-static expansion and contraction of a bubble that is pinned at the opening of a small capillary. The results show that there are two regimes of expansion and contraction depending on the values of two dimensionless parameters which correspond to a dimensionless volume and maximum capillary pressure. In one regime, not all bubble sizes are accessible during expansion and contraction, and the bubbles exhibit a hysteretic behavior when cycling through expansion and contraction. We call this the bubble shape hysteresis. The magnitude of the bubble shape hysteresis is computed for a realistic range of the nondimensional parameters. In the other regime, the bubble size can be varied continuously, but compressibility can still make it difficult to smoothly control the size of the bubble. The theoretical analysis shows that compressibility affects the evolution of the bubbles, even when the bubble is smaller than a hemispherical cap. The analysis also provides the infusion and withdrawal rates that a syringe pump must supply to expand and contract the bubble at a desired rate, accounting for compressibility. The validity of the assumptions used in the model is verified by comparison against experimental data.
对一种在小毛细管开口处被固定的气泡进行准静态膨胀和收缩的压缩性影响展开实验和理论研究。结果表明,取决于两个无量纲参数的数值,存在两种膨胀和收缩的状态,这两个参数分别对应于无量纲体积和最大毛细管压力。在一个状态下,在膨胀和收缩过程中并不是所有的气泡尺寸都可达到,并且气泡在循环通过膨胀和收缩时表现出滞后行为。我们将这种现象称为气泡形状滞后。针对无量纲参数的实际范围,计算了气泡形状滞后的幅度。在另一个状态下,气泡尺寸可以连续变化,但压缩性仍然可能难以平滑地控制气泡的尺寸。理论分析表明,即使气泡小于半球形帽,压缩性也会影响气泡的演变。该分析还提供了注射器泵必须提供的注入和提取速率,以在考虑压缩性的情况下按期望的速率扩展和收缩气泡。通过与实验数据进行比较,验证了模型中使用的假设的有效性。