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Binary drop coalescence in liquids.

机译：液体中的二元液滴合并。

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Experiments on binary drop collisions within an index-matched liquid were conducted for Weber numbers (We) of 1-50 and collision angles of 15-80° below the horizontal. Drop pairs of water/glycerin mixture were injected into silicone oil and, due to gravitational effects, traveled on downward trajectories before colliding. A dual-field high-speed PIV measurement system was employed to quantify drop trajectories and overall collision conditions while simultaneously examining detailed velocity fields near the collision interface.;In the We range examined, for equal size drops, both rebounding and coalescing behavior occurred. The drops coalesced for We > 10 and rebounded for We 10, and this boundary was found to be insensitive to collision angle. Coalescence was found to result from a combination of vortical flow within drops and strong drop deformation characteristic of higher We. Flow through the centers of opposing ring vortices, strengthened by drop deformation, enhanced drainage of the thin film in the impact region, leading to film rupture and coalescence. The collision angle affected the eventual location of film rupture, with the rupture location moving higher in the thin film region as the collision angle increased. The film rupture location correlated closely with the location of maximum downward velocity in the thin film. The time between collision and rupture increases with We until We = 30. For We > 30, the time decreases as We increases.;Unequal size drop collisions with drop size ratios (Ds/D L) of 0.7 and 0.5 were also examined. Coalescence occurs above We* = 11 similar to equal size drops. As drop size ratio decreases, the intervening film deforms more. If the velocity ratio uL/u s 1, the deformed interface becomes flat before coalescence. The rupture location varies due to the asymmetry of the drops. As collision offset increases (B > 0), the film rupture time is shortened and mixing of the fluid from both drops is enhanced after coalescence.;The presence of tracer particles in the intervening film does not affect the minimum Weber number for coalescence, but the film ruptures earlier compared with cases lacking tracer particles.
机译：在折射率匹配的液体中进行二元液滴碰撞实验，测试的韦伯数（We）为1-50，碰撞角度为水平以下15-80°。将滴水/甘油混合物滴入硅油中，由于重力作用，在碰撞之前沿向下的轨迹行进。使用双场高速PIV测量系统来量化跌落轨迹和总体碰撞条件，同时检查碰撞界面附近的详细速度场。在We范围内，对于相等大小的液滴，会发生回弹和聚结行为。当We> 10时，水滴聚结，当We <10时，水滴反弹，发现该边界对碰撞角不敏感。发现聚结是由液滴内的涡流和较高We的强液滴变形特性共同导致的。流经相对的环形涡旋中心，由于液滴变形而增强，影响区域的薄膜排水能力增强，导致薄膜破裂和聚结。碰撞角影响膜破裂的最终位置，随着碰撞角增加，破裂位置在薄膜区域中移动得更高。膜破裂位置与薄膜中最大向下速度的位置紧密相关。直到We = 30为止，碰撞和破裂之间的时间随We的增加而增加。当We> 30时，时间随着We的增加而减小。;还检查了液滴尺寸比（Ds / D L）为0.7和0.5的非均匀液滴碰撞。合并发生在We * = 11以上，类似于大小相等的液滴。随着液滴尺寸比的减小，中间膜变形更大。如果速度比uL / u s <1，则变形的界面在聚结之前变平。破裂位置由于液滴的不对称性而变化。随着碰撞偏移量的增加（B> 0），聚结后膜的破裂时间缩短，两个液滴的流体混合得到增强。;中间膜中示踪剂颗粒的存在不会影响聚结的最小韦伯数，但与缺少示踪颗粒的情况相比，该膜更早破裂。

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