EXPERIMENTAL INVESTIGATION OF A SUBMILLIMETER SPHERE IMPACT ON DROPLET SURFACE

Impact of spheres on liquid surfaces is a universal phenomenon in nature and industrial processes. However, the relevant researches mainly focused on the impact of millimeter or larger spheres on the horizontal liquid surface. Further studies on the dynamic characteristics of submillimeter sphere impact process and the influence of curved interface on impact behavior is necessary. Herein, we presented the observation on the impact of submillimeter spheres on the curved surface of droplet by using high-speed microphotography technology. Owing to the existence of curved liquid surface, the impact phenomenon is different from those after impact horizontal liquid surface. The azimuthal angle of TPCL (three phase contact line) pinned point is positive linear correlation with the impact angle during wetting process, while the non-axisymmetric cavity is first formed on the higher side of TPCL pinned point and the curvature radius is larger. The evolution of the dominant forces and the energy conversion mechanism during the impact process were revealed. The influence of impact velocity and angle α on impact behavior were analyzed, and the impact pattern diagram was provided. The results show that the form drag dominates the motion of the sphere at the slamming stage, while the kinetic energy loss of the sphere is positive correlation with spheres velocity. The surface tension dominates the process at the cavity development stage, and the kinetic energy of the sphere is transformed into the surface energy that maintains the cavity. The cavity length of oscillation mode increases with the increase of Weber number We, and the cavity development velocity is basically consistent. According to the dimensional analysis and experimental results, the relationship between critical Weber number We_cr and α is We_cr^1/2 = α/40 by fitting.