Kinetic analysis of a freely rising droplet in water during collision with the horizontal wall

Abstract

An in-depth analysis of the kinetics of the collision between freely rising oil droplets in water in the range of Re = 4.64–463.3 was carried out to understand the physical mechanism and detailed kinetics of the interaction between the oil droplets and wall. The results show that when oil droplets with Re ≥ 27.8 hit the wall vertically at terminal velocities, a “dimple-like” water film is formed near the wall, which significantly affects the pressure distribution within the water film, the oil–water interfacial shear force, and forces on oil droplet. A coupled model describing water film thickness and pressure accurately captures the kinetic behavior of water film drainage near the wall. The film-induced force based on lubrication theory can reasonably predict the motion trajectory of oil droplets near the wall and dominate the motion of oil droplets colliding with the wall. The motion phase diagram with (Re, We) as the control parameter was established to quickly identify the droplet motion rule under different liquid–liquid density ratios.