Sedimentation model and analysis for differential settling of two - particle - size suspensions in the Stokes region

A model is developed for predicting the settling velocity in suspensions of particles of two different sizes based on experimental data for the settling rate of two-size suspensions in various liquids using particles of equal density. In these experiments, the retarding effect of the smaller particles on the settling velocities of the larger ones is taken into account. The model considers Steinour's fundamental equation and assumes a fixed arrangement of particles and constant velocity in a single-size suspension under creeping flow conditions and the flow spaces changing in shape and size with the volumetric concentration of solids. Based on the foregoing, a simplified model equation is proposed for the settling of particles in a suspension as a function of their free fall velocity and of the solids concentration. Different experimental conditions are used to show the effect of solids concentration, liquid density, and viscosity on the settling behaviour of the glass beads with low particle Reynolds numbers and bed porosity ranging from 0.62 to 0.95. The present study involves the lower and upper interface velocities of two-size suspensions of solids in liquids (concentrated and dilute suspensions) covering a wide range in the properties of the liquids and solids, and more specifically in solids concentration (Glass beads and Sand).