Transitional flow of non-Newtonian fluids in open channels of different cross-sectional shapes

This work investigated the prediction of transitional flow of non-Newtonian fluids in open channels. A number of empirical methods are available in the literature, which purport to predict the frictional losses associated with the transitional flow in open channels of different shapes, but with no conclusive guidelines. Therefore, a large experimental database for non-Newtonian flow in flumes of rectangular, triangular, semi-circular and trapezoidal cross-sections at slopes varying from 1 degrees to 5 degrees was used to achieve this objective. Aqueous suspensions of bentonite and kaolin clay and solutions of carboxymethyl cellulose (CMC) of various concentrations were used to span a wide range of rheological characteristics. The steady shear stress-shear rate behaviour of each test fluid was measured using in-line tube viscometry. In this work, predictive models of transitional flow in triangular, semi-circular and trapezoidal channels, as well as a combined model applicable to all four channels of shapes were established. The method used to establish these models is based on the Haldenwang [19, 22] model. Based on a detailed comparison of the extensive experimental data with model velocities was conducted for power law, Bingham plastic and yield shear-thinning fluids, it was found that the combined model adequately predicted transition for all shapes tested in this work with an acceptable level of reliability.