Pressure losses in the laminar flow of shear-thinning power-law fluids across a sudden axisymmetric expansion

A numerical investigation was carried out to study the laminar non-Newtonian flow through an axisymmetric sudden expansion having a diameter ratio of 1 to 2.6. The fluids were inelastic and shear thinning with a viscosity obeying the power law model. The recirculation length and strength and, most importantly, the local loss coefficient C-1 were quantified as a function of the inlet pipe Reynolds number and shear-thinning intensity. When using the generalised Reynolds number introduced by Metzner and Reed [AIChEJ 1 (1955) 434] (Re-gen), at low Reynolds numbers C-1 increased by more than 100% when n varied from 1.0 to 0.2, whereas C-1 decreased by more than 50% at high Reynolds numbers. However, this feature was shown to be related to the definition of the Reynolds number. A correlation between C-1, Re-gen and n is presented at the end. (C) 2003 Elsevier Inc. All rights reserved.