title: Experimental and computational fluid dynamics modeling of single-phase and two-phase shear-thinning flow behavior in pipes
Creators: name: Ihmoudah, Abdalsalam A. I.
Publisher: name: Memorial University of Newfoundland
publisherIdentifier: https://ror.org/04haebc03
publisherIdentifierScheme: ROR
Year: 2025

description: The design of transport pipes for Newtonian fluids has well-established and accurate correlations for predicting most of the single- and two-phase flow measurements in both turbulent and laminar flow regions. These correlations are based on many experimental and analytical studies. In contrast, the development of correlations for non-Newtonian fluids for predicting flow pattern maps, slug flow characteristics, and pressure losses has proceeded slowly owing to the complexity and diversity of viscosity behaviour. Many methods are used to analyze non-Newtonian fluids in laminar flow; however, only limited research has been done on developing prediction methods for turbulent flow. In this thesis, we systematically study the effect of rheological parameters on non-Newtonian liquid shear-thinning behaviour (power-law and Herschel-Bulkley models) in laminar, transitional and turbulent flow in both single- and two-phase systems through experiments and using Computational Fluid Dynamics (CFD) simulations. An extensive experimental study was conducted to investigate the effects of rheological models and their estimated parameters on the predictions of laminar, transitional, and turbulent flow based on Newtonian and shear-thinning fluid models. To achieve these goals, two non-Newtonian shear-thinning rheological models were prepared (four power-law fluids and seven Herschel-Bulkley fluids) in the Drilling Technology Laboratory using three materials: carboxymethyl cellulose, bentonite, and xanthan gum. The rheology parameters of the solutions were determined using an API-compliant rotational viscometer and mud balance. The experiments were conducted in a flow loop in a 65-m open-cycle system using test sections with internal diameters of 76.2 mm and 19.1 mm. Pressure transducers were used to provide the pressure data in all the test sections. Flow visualization and video recordings were done using a high-speed camera to capture and compare the behaviour of two-phase Newtonian and non-Newtonian flows. Experimental studies for single phase show that most of the correlations identified in the literature for the laminar flow in the power-law rheology model were the best fit for the pressure loss, transitional velocity, and turbulent flow. For Herschel-Bulkley fluids, pressure losses and transitional regions based on a yielded region were examined, and a new modified model was compared to the experimental results and provided a good estimation. Experiments for two-phase flow utilized Newtonian, power-law, and Herschel-Bulkley fluids to evaluate the transition boundaries of flow pattern maps and slug flow characteristics in 76.2 mm PVC horizontal and vertical pipes. The results obtained show that the translational velocity of the slug increases with increasing concentration, while the flow behaviour index decreases and the consistency index increases for shear-thinning fluid at the same operating conditions. The plug-slug transition boundaries shift up to higher liquid velocities in shear-thinning fluids. As a result, the flow pattern map of Mandhane et al. in horizontal pipes for Newtonian fluid has been slightly adjusted to account for shear-thinning fluid based on the experimental results. For CFD simulations, ANSYS Fluent v.19 was used to simulate single- and two-phase Newtonian and non-Newtonian fluids. The turbulent models associated with wall functions were successfully validated for Newtonian fluid in the single phase. Also, the k-ω and k-ε models give accurate results for power-law fluids with a higher flow behaviour index. For Herschel-Bulkley fluid, the percentile error was observed to increase with an increase in the yield stress. A volume of fluid mothed was selected to evaluate the influence of rheology parameters on shear-thinning fluid in a two-phase model. The study included a flow pattern map, transition boundaries, slug flow characteristics in horizontal and upward vertical flow, and the length, velocity, and shape of Taylor bubbles in a minichannel. The CFD method was reliable for predicting gas/shear thinning in two-phase flow. From this work, a new empirical correlation modified for the calculation of slug frequency in Newtonian and shear-thinning two-phase flow is proposed. The slug frequency and slug shape were found to be affected by changing the rheological properties of the liquid phase in horizontal and vertical pipes. With increasing concentration, a decreased flow behaviour index, and an increasing consistency index of Herschel-Bulkley fluid at the same operating conditions, we found a non-uniform and random distribution of small bubbles due to the effective viscous force of a liquid phase.