The coalescence characteristics of two vibrated droplets at a certain distance on a microstructured surface with gradient wettability are investigated using a high-speed camera in this work. The results show that the volume ratio of the two droplets has a significant effect on the vibration modes. With the change in the volume ratio, the droplet exhibits different vibration modes, such as the pumping mode (PM), the rocking mode (RM) or the pumping–rocking mixed mode (PRM). In addition, the coalescence time of the two droplets varies with the volume ratio. When the volume ratio is close to 1, the two vibrated droplets are in synchronous PM and the coalescence time is the shortest. When the volume ratio is far from 1, the two droplets may show the RM, the asynchronous PM or the PRM. At this point, the coalescence time is increased, particularly for small volume ratios. Finally, the movement characteristics of three-phase contact lines are discussed, and a theoretical model is proposed to analyze the coalescence process. This work provides a new method to remove droplets rapidly, which is essential to enhance the heat-transfer performance of dropwise condensation.

中文翻译：

---

润湿性梯度表面振动液滴的聚结特性

在这项工作中，使用高速相机研究了具有梯度润湿性的微结构表面上一定距离处的两个振动液滴的聚结特性。结果表明，两种液滴的体积比对振动模式有显着影响。随着体积比的变化，液滴表现出不同的振动模式，例如泵送模式（PM）、摇摆模式（RM）或泵送-摇摆混合模式（PRM）。此外，两个液滴的聚结时间随体积比的变化而变化。当体积比接近1时，两个振动液滴处于同步PM状态，并且聚结时间最短。当体积比远离1时，两个液滴可能表现出RM、异步PM或PRM。此时，聚结时间增加，特别是对于小体积比。最后，讨论了三相接触线的运动特性，并提出了分析合并过程的理论模型。这项工作提供了一种快速去除液滴的新方法，这对于增强滴状冷凝的传热性能至关重要。