What adjustments must be made to a pipeline hydraulic model to accurately predict flow behavior in a pipeline transporting non-Newtonian fluids?

To accurately predict flow behavior in a pipeline transporting non-Newtonian fluids, several adjustments must be made to a standard pipeline hydraulic model, which is typically designed for Newtonian fluids like water or natural gas. Newtonian fluids have a constant viscosity regardless of the shear rate, while non-Newtonian fluids exhibit a viscosity that changes with shear rate or time. The most important adjustment is to accurately characterize the fluid's rheological properties, specifically its viscosity as a function of shear rate. This requires laboratory testing using a viscometer to determine the fluid's flow curve. Based on the flow curve, an appropriate non-Newtonian fluid model must be selected. Common models include the Power Law model, which describes shear-thinning or shear-thickening behavior, the Bingham Plastic model, which accounts for a yield stress that must be overcome before flow begins, and the Herschel-Bulkley model, which combines both yield stress and shear-dependent viscosity. The selected model is then incorporated into the hydraulic model to calculate the friction factor and pressure drop. The friction factor correlations used for Newtonian fluids, such as the Darcy-Weisbach equation with the Moody diagram, are not applicable to non-Newtonian fluids. Instead, specialized friction factor correlations for non-Newtonian fluids must be used, which take into account the fluid's rheological properties and flow regime (laminar or turbulent). Furthermore, the transition from laminar to turbulent flow in non-Newtonian fluids is different from Newtonian fluids and must be accurately determined using appropriate Reynolds number correlations for the specific fluid model. Finally, the hydraulic model should account for the temperature dependence of the fluid's viscosity, as temperature can significantly affect the flow behavior of non-Newtonian fluids. These adjustments are essential for accurately predicting pressure drop, flow rate, and other hydraulic parameters in pipelines transporting non-Newtonian fluids, which is critical for pipeline design and operation.