Multiphase flow of non-Newtonian fluids in pipes

Flocculated suspensions of fine particles generally exhibit shear-thinning non-Newtonian flow characteristics and their rheological behaviour can usually be adequately represented either by the Ostwaldt-de Waele power-law model or by the Bingham plastic model. Occasionally, it may be necessary to resort to the three-parameter Herschel-Bulkley model. The properties of such suspensions make them highly suitable for the transport of coarse particles under conditions of laminar flow as their enhanced density and low apparent viscosity in the core region give rise to an effective support mechanism. At the same time, the apparent viscosity in the high shear-rate region at the walls will be sufficiently low to give acceptable pressure gradients in the pipeline. The injection of air into a shear-thinning fluid in laminar flow can result in substantial reductions in pressure gradient and it is therefore probable that the pressure gradient for a suspension containing coarse particles will be similarly reduced.