Characterization of axial flow impellers in pulp fibre suspensions

Two axial flow impellers commonly used in pulp agitation applications were characterized in hardwood and softwood low-consistency pulp fibre suspensions. The impellers operated in the laminar and transition-to-turbulence regimes with the suspension mass concentration significantly affecting both power and axial thrust numbers. Axial force numbers could be collapsed to a single operating curve using the yield stress Reynolds number, but the power number remained a function of suspension properties. CFD was used to model impeller flow using a Bingham approximation to describe the suspension rheology. Model agreement with the experimental measurements was generally good, with the values of NP and Nf determined to within 24 and 16%, respectively. The error can be explained by the uncertainty in the rheological characterization of the pulp suspension, particularly the yield stress.