Rheological properties of Aspergillus niger pellet suspensions

Summary Shear diagrams for Aspergillus niger pellet suspensions were obtained using a helical ribbon impeller system. Experimental results concerning the effects of pellet size and surface nature on the rheological behaviour are given. In addition, the influence of the quantity of biomass was studied; it can be quantified by the model proposed by R. Wittler et al. (1983).Symbols b Fitting parameter eq. 5 (-) - C Fitting parameter eq. 5 (Pa s)^0.5 - c Maximum tangential velocity (-) - d_R Diameter of the ribbon impeller (mm) - Em Fitting parameter eq. 5 (-) - Ex Pellet volume fraction (or P.V.F.) (-) - H Height of the ribbon impeller (mm) - K Consistency index (Pa) (s)ⁿ - M Torque (arbitrary unit) - N Rotational speed (l) (s)^-1 - n Flow behaviour index (-) - _s Apparent viscosity of pellet suspension (Pa s) - p Width of the ribbon (mm) - s Pitch of the ribbon impeller (mm) - t Vessel diameter for the impeller-vessel system (mm) - Shear rate (s)^-1 - Shear stress (Pa)