Decrease In Power-law Index Research Articles

Power Law Fluids in a Circular Curved Tube. Part II. Axial Laminar Dispersion

Abstract The application of Taylor's dispersion theory to non-Newtonian laminar dispersion in a circular curved pipe wrapped in a coil is discussed. An analytical expression for the dispersion coefficient in laminar flow under two conditions, viz. Dean's constraint and relaxing Dean's constraint, is discussed along with system parameters. The present expression of dispersion coefficient under two different conditions reduces to the reported results in the literature for Newtonian fluids. The effect of power law index in combination with other process parameters on dispersion coefficient is studied. It is found that the dispersion coefficient decreases with decrease in power law index, and that it decreases with increase in Reynolds number and Schmidt number at a fixed curvature ratio.

Study on the lubrication approximation for power law fluids

To appreciate the effectiveness of lubrication approximation for the non-Newtonian fluid, power law fluid flowing between nonparallel plates was investigated under condition with no inertia. First the flow problem was successfully reduced to a single ordinary differential equation, and then the above governing equation was solved numerically. Effectiveness of lubrication approximation with various power law indices below 1 and various diverged angles was investigated in terms of normalized flow velocity and ratio of the approximate to exact flow rate. As the power law index decreases and diverged angle increases, the error of lubrication approximation becomes increasingly larger. It was shown that the proper selection of the constitutive law should be considered first to make the lubrication approximation work.