Experimental study of impacting a spherical hydrophobic particle on an air – water interface

Film flotation is a process for separating hydrophobic mineral materials from hydrophilic at the gas-liquid free surface. In this study, for simulation of this process, the impact of spherical hydrophobic particles on an air–water interface was experimented. The aim of this study is to obtain a critical impact velocity in which the hydrophobic particle remains on the liquid surface so that it penetrates completely at higher velocities than the critical velocity. A mathematical model based on energy balance approach was developed to predict the critical impact velocity. The Teflon particles of diameter 3-5mm were used. Distilled water with density of 1000.71 kg/m3 was used as the fluid. The particle impact velocity, cavity profile and velocity of three-phase contact line were obtained for the first time for a number of different particles by using a high speed video camera with the rate of 4500 fps. In the model, the critical impact velocity was obtained by employing the cavity profile and fitted advancing contact angle at critical conditions. It was showed that the mathematical model was in good agreement with experimental observations, including showing a decrease in critical impact velocity with increasing particle diameter.