Degradation of flow drag reduction with polymer additives — A new molecular view

Drag reduction and degradation by sodium alginate in turbulent flow

The utilization of drag-reducing polymers has long been hindered by their irritancy, corrosiveness, and toxicity across various domains. In this investigation, we explored sodium alginate, a natural drag reducer, for its efficacy in reducing drag and its resilience to shear in millimeter-scale pipelines. Initially, an experimental setup was devised to assess the drag reduction capabilities of sodium alginate at varying concentrations and flow rates using Response Surface Methodology (RSM). The relationship between drag reduction (DR), concentration (C), and flow rate (Q) was established by analyzing the experimental data. Subsequently, variance analysis was employed to validate the data accuracy, with a comparison between predicted and experimental DR values revealing an error margin within ± 20%. Analysis of cyclic shear testing of sodium alginate solution in tubes demonstrated its effectiveness as a shear flow drag reducer. Furthermore, results from laser particle size analysis indicated minimal molecular breakage of sodium alginate during cyclic shear.

On the fluid drag reduction in scallop surface

In the field of biomimetics, the tiny riblet structures inspired by shark skin have been extensively studied for their drag reduction properties in turbulent flows. Here, we show that the ridged surface texture of another swimming creature in the ocean, i.e., the scallops, also has some friction drag reduction effect. In this study, we investigated the potential drag reduction effects of scallop shell textures using computational fluid dynamics simulations. Specifically, we constructed a conceptual model featuring an undulating surface pattern on a conical shell geometry that mimics scallop. Simulations modeled turbulent fluid flows over the model inserted at different orientations relative to the flow direction. The results demonstrate appreciable friction drag reduction generated by the ribbed hierarchical structures encasing the scallop, while partial pressure drag reduction exhibits dependence on alignment of scallop to the predominant flow direction. Theoretical mechanisms based on classic drag reduction theory in turbulence was established to explain the drag reduction phenomena. Given the analogous working environments of scallops and seafaring vessels, these findings may shed light on the biomimetic design of surface textures to enhance maritime engineering applications. Besides, this work elucidates an additional evolutionary example of fluid drag reduction, expanding the biological repertoire of swimming species.

Investigation of drag reduction by slurry-like drag-reducing agent in microtube flow using response surface methodology (RSM)

In this study, we investigated the drag reduction property of a premixed slurry drag reducer in a millimeter-scale pipe. The aim of this study is to establish the correlation between Darcy friction factor and drag reducer concentration (C) and volume flow (Q). First, the experimental plan was designed by using the response surface method (RSM), and then the experimental data were processed to establish the quadratic correlation between the response variable and the description variable. After that, ANOVA analysis of variance was used to verify the accuracy of the experimental data and the correlation. Finally, the prediction model is extended to a larger concentration and volume flow range, and it is found that the accuracy between the predicted value of friction coefficient and the experimental value is ± 30%, thus verifying that the correlation is suitable for the small-scale fully turbulent region. Compared with traditional experimental design and correlation methods, the implementation of Response Surface Methodology (RSM) in this study not only reduces the experimental time but also yields a more robust correlation for predicting the friction coefficient.

Tandem Synthesis of Ultra-High Molecular Weight Drag Reducing Poly-α-Olefins for Low-Temperature Pipeline Transportation

Ultra-high molecular weight poly-α-olefins are widely used as drag reducing agents (DRAs) for pipeline transportation of oil and refined petroleum products. The synthesis of polyolefin DRAs is based on low-temperature Ziegler-Natta (ZN) polymerization of higher α-olefins. 1-Hexene based DRAs, the most effective at room temperature, typically lose DR activity at low temperatures. The use of 1-hexene copolymers with C8-C12 linear α-olefins appears to offer a solution to the problem of low-temperature drag reducing. The present work aims to develop two-stage synthesis of polyolefin DRAs that is based on selective oligomerization of ethylene in the presence of efficient chromium/aminodiphosphine catalysts (Cr-PNP), followed by polymerization of the olefin mixtures, formed at oligomerization stage, using efficient titanium-magnesium ZN catalyst. We have shown that oligomerization of ethylene in α-olefin reaction media proceeds faster than in saturated hydrocarbons, providing the formation of 1-hexene, 1-octene, and branched C10 and C12 olefins; the composition and the ratio of the reaction products depended on the nature of PNP ligand. Oligomerizates were used in ZN polymerization 'as is', without additional treatment. Due to branched character of C10+ hydrocarbons, formed during oligomerization of ethylene, resulting polyolefins demonstrate higher low-temperature DR efficiency at low polymer concentrations (~1 ppm) in comparison with benchmark polymers prepared from the mixtures of linear α-olefins and from pure 1-hexene. We assume that faster solubility and more efficient solvation of the polyolefins, prepared using 'tandem' ethylene-based process, represent an advantage of these type polymers over conventional poly(1-hexene) and linear α-olefin-based polymers when used as 'winter' DRAs.

Prediction and New Insight for the Drag Reduction of Turbulent Flow with Polymers and Its Degradation Mechanism

A physicochemical understanding of the mechanism of turbulent flow drag reduction with polymer and its degradation is of great interest from both science and industry perspectives. Although the correlation based on the Fourier series has been proposed to predict the drag reduction and its degradation, its physical meaning was not clear until now. This letter aims to clarify this issue. We develop a comprehensive model to predict the drag reduction and degradation of polymers in turbulent flow from a chemical thermodynamics and kinetics viewpoint. We demonstrate that the Fourier series employed to predict the drag reduction and its degradation is due to the viscoelastic property of drag-reducing polymer solution, and the phase angle in the model, in physical nature, represents the hysteresis of the polymer in turbulent flow. Besides, our new insight of drag reduction with flexible polymers can also explain why a maximum drag reduction in rotational flow appears before degradation happens.