Abstract The present work studies the dynamics of large and small bubbles in sudden expansions and contractions in vertical pipes. The experimental apparatus was designed to permit changes in flow patterns through singularities provoked by an expansion followed by a contraction. The data were obtained through particle image velocimetry and the shadow sizer technique. Size and velocity distributions for small and long bubbles are presented for six vertical pipe positions and compared with existing theories for the motion of small and large confined bubbles. Results for the mean velocity profiles, local shear rate and turbulent kinetic energy of the continuous phase are also presented. Predictions on the permissible largest diameter of bubbles as a function of space coordinates and flow conditions based on phenomenological theories are compared with the experimental data. Results indicate that bubble breakup and coalescence are essentially ruled by the dynamic pressure forces of the turbulent motions, but shear induced breakup is also observed for the small and large bubbles. The formation of a gas pocket in the contraction is identified as an important promoter of bubble breakup.

中文翻译：

---

垂直管道突然膨胀和收缩中大小气泡的破裂和聚结

摘要 目前的工作研究了垂直管道突然膨胀和收缩时大小气泡的动力学。实验装置被设计成允许通过由膨胀和收缩引起的奇点改变流动模式。这些数据是通过粒子图像测速和阴影尺寸技术获得的。给出了六个垂直管道位置的小气泡和长气泡的尺寸和速度分布，并与现有的小气泡和大受限气泡运动的理论进行了比较。还提供了连续相的平均速度分布、局部剪切速率和湍流动能的结果。将基于现象学理论对作为空间坐标和流动条件的函数的气泡最大允许直径的预测与实验数据进行比较。结果表明，气泡破裂和聚结基本上受湍流运动的动态压力控制，但也观察到小气泡和大气泡的剪切诱导破裂。收缩中气袋的形成被认为是气泡破裂的重要促进因素。