A study on a droplet impact on a fiber during coalescence-separation: Phenomena and models

•A model was established to calculate the minimum threshold velocity of capture.•Another model was improved to calculate the maximum threshold velocity of capture.•A new phenomenon of a droplet adhere on the fiber surface was observed.•Two threshold velocities limit a range map in which droplets can be captured. Droplets impact on fibers occurred in liquid phase plays a vital role in the coalescence-separation applications, however, the mechanism and details are still unclear. Here we investigated the impact process through energy conversion and impact dynamics and two models are established to determine the threshold velocities of capture. The adhering phenomenon is observed when the impact velocity is smaller than the minimum threshold velocity Vc1. The droplet may be captured by fibers when the impact velocity is larger than Vc1 and smaller than the maximum threshold velocity Vc2. These two velocities limit a range in which the droplet may be captured by fibers are significant to facilitate the optimization of coalescence separation. This study opens up opportunities for understanding the details of coalescence separation as well as improving efficiency of industrial applications.