Development of a new theory for hindered settling suspensions

Above a certain concentration, the fall of any particle in a suspension is observed to be hinder-ed by the presence of other particles in its path. Several theories have been presented which describe the hindered settling nature of suspended particles using monoexponential equations. These equations, however, could explain such phenomenon only within a small range of porosities. Using an extended range of porosities reveals a break in the linear plot of the logarithm of the interface falling rate versus the solid porosity of the medium. In this study, an attempt has been made to describe this non linearity in hindered settling phenomenon. A new theory, based on the classification of a concentrated suspension into a diffusion and a main compartment, has been developed It also determines the mean spherical radii of the settling flocs. Concentrated tricalcium phosphate suspensions are used and interpreted as the model,,for the behavior of such systems. A biexponential relationship is discovered between the sedimentation rate and the solid porosity of the system. The mean values for the floc radius obtained by this new theory is several times larger than that obtained from existing monoexponential equations. II is believed that the higher values obtained reflect the real situation of aggregation occurring in a concentrated suspension.