The challenge of theoretical and numerical studies of annular fluid flow with varying eccentricity is mainly due to the required coordinate systems. Computational fluid dynamics (CFD) modeling provides the state-of-the-art approach of investigating fluid flow in such complex geometries. In this study, results from a series of numerical simulations for the fully developed laminar flow of non-Newtonian power law fluids in concentric and eccentric annular geometries are used to investigate the effect of eccentricity, flow behavior index, and diameter ratio (ratio of the outer diameter of the inner tubing to the inner diameter of the outer tubing) on axial friction pressure losses.

The friction pressure gradients predicted by the CFD simulations were verified by comparing with the published studies and flow data from a field scale experimental set-up. At a constant flow rate, it is confirmed that frictional pressure losses are decreased with increasing eccentricity. A good agreement was obtained with the Haciislamoglu et al. correlation, and the results of this study, especially at low values of eccentricity. At very high eccentricities, data from the CFD model yields lower friction pressure compared to Haciislamoglu et al. correlation. Haciislamoglu et al. type expression is obtained, incorporating the improved data of this study.

Next, this paper presents the results of an experimental study carried out to investigate friction pressure behavior of drag reducing polymer solutions, flowing turbulently through an eccentric annulus. The experimental set-up includes 30 ft of 3½-in. x 2 3/8-in., 200 ft of 3½-in. x 1¾-in., 69 ft of 5½-in. x 4-in., and 79 ft of 5-in. x 3½-in. fully eccentric annuli. Data analysis enabled the development of a new correlation using fluids apparent viscosity at 511 sec-1, generalized Reynolds number, and diameter ratio, all of which can be easily determined in the field, as independent variables. These new correlations for laminar and turbulent flow of drag reducing polymer solutions present an improvement to existing correlations, and also permit undemanding hydraulic program calculations for varying annular configurations.

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