In this work, the effect of very small impeller clearances off the tank bottom, C, on complete solid off-bottom suspension, Njs, was investigated. Four types of impellers were used six-blade flat-disk turbine, six-blade flat-blade turbine, six-blade flat (45 degreees) pitched-blade turbine, and the high efficiency impeller Chemineer HE-3. The effects of the impeller diameter, D, tank diameter, T, and solids loading, X, were quantified. The presence of two impellers was analyzed using impellers of the same type and size.

Typically, Njs and the power consumption were found to decrease with the impeller clearance. However, for lower C/T values, a slight increase was observed for axial impellers, especially for lower D/T ratios (less than 0.261). The power consumption was lower for the axial-flow impellers as compared with teh radial-flow impellers. For disk and flat-blade turbines, a change in the flow pattern was observed in teh range of 0.13 < CT < 0.19 and 0.19 < C/T < 0.24, respectively. No change in flow pattern was observed up to C/T < 0.25, for the flat (45 degrees) pitched-blade turbines and the Chemineer impellers Correlations to predict the value of Njs as a function of impeller clearance were obtained, for each type of impeller.