Non-colloidal sedimentation compared with Kynch theory

Instantaneous concentration profiles of the batch sedimentation of non-colloidal hard spheres were measured for various initial suspension concentrations from 0.04 to 0.55 using the magnetic resonance imaging (MRI) technique. Measured profiles commonly had two distinct interfaces, the upper one between the clarified fluid and the settling suspension, and the lower one between the settling suspension and the sediment. The upper interface was found to keep spreading due to polydispersity, especially for suspensions with low initial concentration. It was observed that the lower interface pattern is highly dependent on the initial concentration. If the pattern is considered to be spread due to the broadening effects of hydrodynamic diffusion and polydispersity, its overall behavior seems to be consistent with Kynch' s prediction. For all initial concentrations the sediment was incompressible with packing concentration 0.60 +/- 0.01. Three transition concentrations separating four regions of different profile patterns were determined by fitting the experimental results to the Richardson-Zaki formula. The validity of the first (0.16) and third (0.46) transition concentrations was cross-checked by various criteria based on the analysis of the experimental results, The second transition concentration (0.33) determined from the flux curve analysis could not be confirmed experimentally.