Solid particle distribution of moderately concentrated suspensions in a pilot plant stirred vessel

Detailed particle distribution of a solid–liquid suspension in the just suspended state was measured by means of a conductivity probe. A total of eight experimental settings were investigated, involving two particle diameters (0.14 and 0.35 mm), two average particle concentrations (5 and 10 vol.%) and two impeller off-bottom clearances (H2/d = 1 and 0.5). A pilot plant stirred vessel of 1m in diameter stirred with flat six pitchedblade turbine was used. A particle-filled layer of suspension was observed in all these experiments, and was particularly pronounced at the solid concentration of 10 vol.% and impeller off-bottom clearance H2/d = 0.5. The local solid concentration profiles within this layer were investigated. The axial and radial concentration gradients and their standard deviations were determined. The results indicate the presence of a concentration gradient in the radial direction within the particle layer, and of significant concentration fluctuations at the interface between the particle layer and the clear liquid layer in the upper part of the stirred vessel.