A method for the determination of shear viscosity of power–law fluids in a rectangular duct and concentric annulus

This work deals with a practical approach for the determination of the rheological parameters of the purely viscous power–law fluids in the rectangular channel and concentric annulus. The rectangular channels with a height to width ratio (aspect ratio) of less than 0.1 and concentric annulus of large aspect ratios are used for the determination of the shear viscosity of the non‐Newtonian fluids. For rectangular channels of aspect ratio greater than 0.1, the determination of the shear viscosity for the power–law model requires two geometrical parameters, according to conventional methods. In this work, a practical method is introduced in order to determine rheological parameters of the power–law fluids for rectangular channels and concentric annulus with the aspect ratios between 0 and 1 using one geometric parameter. The validity of the suggested one‐parameter method is firstly compared with the conventionally used two‐parameter model analytically. Then, verification is carried out by experimental method using slit viscometer and a rectangular channel with an aspect ratio of 0.2. Obtained wall shear rate‐wall shear stress values from both geometries are compared, and finally obtained rheological parameters are verified by numerical methods. It has shown that the suggested method is successful for the determination of shear viscosity, and results reveal that rectangular channels with an aspect ratio greater than 0.1 can be used to obtain rheological parameters for power–law fluids.