Experimental study and visualization of impacting spherical hydrophobic particles on an air - Liquid interface: Newtonian and Boger liquid analysis

The impact of solid particles on gas-liquid interfaces has recently attracted considerable attention due to its numerous applications. In this study, the particle impacts on Newtonian and Non-Newtonian liquid surfaces were investigated. A viscoelastic fluid with constant viscosity was selected as a Non -Newtonian fluid to assess the elastic effect. The critical impact velocity, which is the maximum velocity that the particle would remain on the liquid surfaces, was evaluated. Also, the impact of 3-5 mm spherical hydrophobic particles on the surface of pure water and Boger fluid was experimentally studied. The particle impact onto the fluid interface was captured utilizing a high-speed camera with a rate of 4500 fps. A mathematical model was presented based on the energy balance for predicting the critical velocity. The sequential images of the hydrophobic sphere falling process were analyzed, and the floatation and penetration regimes were observed. The maximum penetration depth, rebound depth, rebound height, and the pinch-off depth were determined for different particle sizes. It was found that, at critical velocities, the particle penetration was associated with oscillatory motions. It was also shown that the increase in particle size would decrease the critical velocity. In addition, the particle velocity and the velocity of the three-phase contact line were analyzed at critical conditions. The mathematical model predictions were compared with the experiments, and good agreement was found. (c) 2020 Elsevier Ltd. All rights reserved.