Abstract: The impact behavior between discrete phase and concave-wall was complex and changeable in cylindrical section equipment and pipeline, which directly affected the mass transfer efficiency of inter-phase. In this work, the dynamic characteristic of CCl4 single droplet with iodine containing under water impacting the concave-wall was systematically studied by experiment and image post-processing. The results showed that the settlement velocity of CCl4 droplet under water was relatively stable and only was related to the droplet initial diameter. The process of droplet impacting the concave-wall was divided to five stages, falling stage, spreading stage, relaxing stage, rolling stage, and wetting stage, respectively. The droplets stretched along the circumferential direction of concave-wall and contracted along the normal direction of concave-wall. The effect of the impact angle between droplet and concave-wall θ on the droplet stretching property was greater than the droplet initial diameter and concave-wall curvature radius. The droplet vertically impacted at the lowest point of the concave-wall, then bounced rapidly and contracted strongly when θ=90°. The spreading time was shorter and the deformation rate was the smallest, there was no rolling stage. At the range of θ=100°~150°, the droplet deformation rate increased with the increase of impact angle, the sliding deformation rate was less than the rolling deformation rate. The travel distance, times and duration of droplet oscillation at the concave-wall lowest point increased. At the same time, the oscillation amplitude of droplet velocity increased in the gravity direction. The droplets were mainly sliding and spreading at the range of θ=110°~130°. The phenomenon of droplet rolling along the concave-wall was more likely to occur at θ>130°. The droplet was close to the pure rolling state when θ=154.2°, the droplet diffusing and relaxing stages were very short, the droplet earlier got into the wetting state. The impact angle was increased for the droplet rolling along the concave-wall, effectively reducing the wall adhesion and droplet breakage.

Key words: liquid-liquid, droplet, concave-wall, eccentric distance, impact angle, dynamic characteristic

摘要： 采用实验观测与图像处理相结合，对CCl4液滴在水下撞击凹壁面后的动态特性进行了系统研究。结果表明，液滴撞击凹壁面的过程经历了下降、扩散、松弛、滚动和润湿五个阶段。液滴与凹壁面间的撞击角θ对液滴拉伸特性的影响大于液滴初始直径和壁面曲率半径。当θ=90°时液滴垂直撞击壁面最低点，液滴迅速弹跳并强烈回缩，铺展时间短且变形率最小。在θ=100°~150°时，随着撞击角增加液滴变形幅度增大，相邻时刻滑动变形率小于滚动变形率。110°<θ<130°时液滴以滑动和铺展为主。θ>130°时液滴沿壁面滚动现象更容易发生。θ=154.2°时液滴接近纯滚动状态。增大撞击角，液滴沿凹壁面滚动下滑有效降低壁面黏附和液滴破碎。

关键词: 液液两相, 液滴, 凹壁面, 偏心距, 撞击角, 动态特性