Influence of Viscosity Function Simplification on Non·newtonian Velocity and Shear-rate Profiles in Rectangular Ducts

The velocity, shear-rate, variable viscosity, and variable power-law index profiles are calculated for non-Newtonian fluids using the finite difference method. The calculations are carried out for an actual viscosity function obtained by a cilrve fit through measured data and for the corresponding power law model, the simplest and most often used form for non­ Newtonian viscosity function approximation. The obtained results are compared between themselves and with reference results of Newtonian flow. The objective was to determine the influence of an experimental non-Newtonian viscosity function and its simplification on the above profiles. Interestingly, but not surprisingly. the influence of viscosity function simplification is very weak on the velocity profile, somewhat stronger on the shear-rate profile, while the corresponding differences of viscosity and local power-law index profiles are remarkable. Some other characteristic results along with appropriate analysis· are presented.