Characteristics of laminar viscous shear-thinning fluid flows in eccentricannular channels

Laminar fully developed flows of time-independent viscous shear-thinning fl uids in straight eccentric annuli are considered. The fluid rheology is mod eled by the power-law constitutive equation, which is representative of man y industrial process liquids. The annulus models flow channels in process h eat exchangers, extruders, and drilling wells, among others. The flow cross -section geometry is mapped into a unit circle by means of a coordinate tra nsformation, and the governing momentum equation is solved by finite-differ ence techniques using second-order accurate discretization. Numerical solut ions for a wide variation of annuli radius ratio (0.2 less than or equal to r* less than or equal to 0.8), inner core eccentricity (0 less than or equ al to epsilon* less than or equal to 0.8), and shear index (1 greater than or equal to n greater than or equal to 0.2), are presented. Both fluid rheo logy and annuli eccentricity are seen to have a strong influence on the flo w behavior. The eccentricity causes the flow to stagnate in the narrow gap with higher peak velocities in wide gap, and large azimuthal variations in the velocity field. The fluid pseudoplasticity gives rise to even greater f low maldistribution around the annulus, with non-uniform velocity fields, w all shear-stress distribution, and friction factor characteristics. (C) 199 9 Elsevier Science B.V. All rights reserved.