Wall effects during settling in cylinders

Abstract

The phenomena of syneresis and shear densification were analysed through the sedimentation of alumina suspensions. Experiments compared cylinder settling tests with a rod inserted in a cylinder against free settling without a rod for the cases of polymer flocculated and salt coagulated suspensions. Additionally, dye intrusion was used to visualise the final bed structure to identify the influence of cylinder walls and the potential presence of aggregate arching structures.It was found that, for various cylinder diameters, polymer flocculated alumina suspensions settled more quickly when a rod was placed in the centre of the settling cylinder. This is attributed to shear induced densification..