Experimental research on the dynamics of a train of droplets impacting, from droplets to liquid film, continuity and inheritance

The propagation of the droplet inside the air treatment can be simplified as the droplet impact the wall, liquid film, or collide with each other. We build a visual experimental platform for a train of droplets using the micro-vertical injection pump and the high-speed imaging system in order to examine the variations in the impact behavior of the falling droplets. The variables are the impacting velocity and the contact angle. The dynamic process of the first impact (the droplet impact on the plate surface) and, second impact (the droplet impact on the static one resting on the surface) and the final impact (the droplet impacts on the liquid film converged by the previous droplets) are captured and analyzed respectively. The results indicate that the impact velocity and the contact angle are the driving factors of the impact behavior promoting the formation of the tip sub-droplet and the sub-droplet of adhesion respectively. When the droplet impacts the liquid film, there is no generation of the sub-droplet, whose behavior is not dependent on the contact angle but rather the initial velocity. The splashing and protrusion height are converging as the velocity increases. While the velocity retards the splashing process. • The whole process of the vertical droplet flow impacting is analyzed visually. • The sub-droplet of tip and adhesion were generated in first and second impact. • A new point of view on the continuous issues has been proposed, the timeline. • The splashing process of the film is retarded due to the impact velocity.