Oil–Particle Separation in a Falling Sphere Configuration: Effect of Oil Film Thickness

High-speed videos of oil-coated solid spheres falling through an aqueous solution were analyzed to determine the amount of oil separated and the velocity of the coated sphere during free fall. The oil-coated sphere configuration is relevant to understanding the recovery of oil from oil sands; hence, bitumen was used as the oil phase. A new form of a capillary number based on a low-Reynolds number solution is introduced to characterize the separation process. The proposed particle-based capillary number takes into account the effect of the oil film thickness and the viscosity ratio. In this study, the separation of oil from an oil-coated sphere is examined as a function of the oil film thickness, while keeping the viscosity ratio constant at 0.08. From the experimental results, it was observed that there is a critical oil film thickness beyond which oil separation from a particle is observed. Higher oil removal efficiencies are obtained at higher oil film thicknesses. The velocity of an oil-coated sphere is higher than the velocity of an oil-free sphere due to the lubrication effect of the oil layer.