An experimental study and correlation for differential settling of bidisperse suspensions

Sedimentation processes have wide practical applications in mineral processing, metallurgical industries, chemical engineering, environmental technologies, water treatment, and bio-process engineering. The sedimentation process is complex in nature since it involves the physical properties of both the solids and the fluids forming the suspensions as well as the hydrodynamic and physico/chemical phenomena that govern particle-fluid and particle-particle behaviour. The aim of this study is to measure experimentally the lower and upper interface velocities in bidisperse suspensions of solids in liquids using liquids and solids with a wide range in physical properties, and more specifically in solids concentration (glass ballotini and sand) covering concentrated and diluted suspensions. The study covers the experimental investigations on the settling rate of bidisperse suspensions in liquids using particles of equal density and at very low particle Reynolds number (Stoke's law region) and the voidage ranges from ε = 0.62 to 0.95. A correlation is developed for the representation of the experimental data for the particles of two different dimension. The experimental data have been compared with the predictions of the present proposed model as well as the models reported in the literature. An empirical correlation for φ_S1 is also proposed and its dependency on the particle diameter and the concentrations is discussed.