NUMERICAL FLOW SIMULATION OF VISCOPLASTIC FLUIDS IN ANNULI

This paper describes numerical solutions for the laminar flow of non-N ewtonian fluids in vertical annuli using the Herschel-Bulkley model to describe the rheological behaviour of such materials. Numerical solut ions have been obtained when there is both axial and tangential flows in either a concentric or eccentric annulus. The tangential flow arise s from the rotation of the inner cylinder of the annulus and the axial flow from a constant axial pressure gradient. The flow is analysed by solving the momentum and continuity equation numerically using the fi nite element method. The dimensionless velocity, deformation and stres s profiles with other quantities such as the apparent viscosity and pr essure distribution have been calculated for various eccentricities, r adius ratios, fluid properties and flow parameters; the results give i nsights into the flow behaviour in the annuli. It is shown that the in clusion of rotational effects, for a fixed pressure gradient, is likel y to increase the axial volumetric flowrate over non-rotating situatio ns in concentric geometries. New results reveal that, in eccentric ann uli, the situation is reversed and the flowrate gradually decreases as the rotation rate is increased.