A note to further explain the mechanism of turbulent flow drag reduction by polymer from chemistry view

In our previous work regarding the mechanism of drag reduction and degradation by flexible linear polymers, we proposed a correlation based on the Fourier series to predict the drag reduction and its degradation, where a phase angle was involved, but the physical meaning for the correlation especially of the employed phase angle was not clear, which is however important for reasonable explanation of the drag reduction mechanism over flexible linear polymers. This letter aims to clarify this issue. We use several steps of deduction from the viscoelastic theory, and conclude that the Fourier series employed to predict the drag reduction and its degradation is due to viscoelastic property of drag-reducing polymer solution, and the phase angle represents the hysteresis of polymer in turbulent flow. Besides, our new view of drag reduction by flexible polymers can also explain why a maximum drag reduction in rotational flow appears before degradation happens.

Physical and Chemical Characterization of Drag Reducing Polymer Based on Polyvinylpyrrolidone (PVP) in Human Blood Flow

A new attempt to use Polyvinylpyrrolidone (PVP) as a bio-drag reducing polymer agent for human blood flow has been studied. PVP was added at 0, 500, 750 and 1000 part per million (ppm) and mixed with human blood at room temperature for 2 minutes. Then, a cone on plate rheometer was used to investigate the effectiveness of PVP agent on blood rheological properties. The results showed significant effecting of PVP on blood fluidity characteristics, where the viscosity decreased as the PVP content increased or as a shear rate increased. For a certain shear rate, the shear stress decreased as PVP content increased. These changes will lead to increased mixing efficiency within the capillaries, increased oxygen transportation, increased tissue perfusion, modified red blood cells (RBCs) distribution, reduced pressure drop gradients, enhanced turbulent flow tendency, enhanced viscoelasticity nature of the blood and its strengthened non-Newtonian pattern. Also, the results showed that the viscosity-shear stress relationships become more linear at higher PVP concentrations. PVP addition caused no shifting in UV-absorbing positions and only moderate intensity changing. Atomic force microscopy (AFM) parameters provide other indicators about the role of PVP as a drag reduction agent for blood flow, where all of the amplitude, hybrid and special parameters decreased significantly.

Impact of Polymer Degradation On Past Studies of the Mean Velocity Profile in Turbulent Boundary Layers

The current study reexamines past studies of how drag-reducing polymer solutions modify the log-region of a developing turbulent boundary layer. The classical view was that the polymers modify the intercept constant without impacting the von Kármán coefficient, which results in the log-region being unaltered though shifted outward from the wall. However, recent work has shown this to be not accurate, especially at high drag reduction (>40%). While the deviations to the von Kármán coefficient were conjectured to be related to polymeric properties, this had not been explored. This work examines the scatter in both log-region parameters and estimates the local polymeric properties. This shows that the scatter of the von Kármán coefficient between studies is related to the inner variable based Weissenberg number. In addition, recent polymer ocean results are included that support the implicit assumption in past studies that the maximum wall concentration should be used to define the local polymeric properties.

Investigation of Surfactant-Polymer Interactions Using Rheology and Surface Tension Measurements

The interactions between surfactants and a drag-reducing polymer were investigated at a low polymer concentration of 500 ppm, using measurements of the rheology and surface activity of surfactant-polymer solutions. A well-known drag-reducing polymer (anionic sodium carboxymethyl cellulose) and five different surfactants (two anionic, two non-ionic, and one zwitterionic) were selected for the interaction studies. The surfactant-polymer solutions were shear thinning in nature, and they followed the power law model. The interaction between the surfactant and polymer had a strong effect on the consistency index of the solution and a marginal effect on the flow behavior index. The surface tension versus surfactant concentration plots were interpreted in terms of the interactions between surfactant and polymer. The critical aggregation concentration (CAC) of the surfactant was estimated based on the surface tension and rheological data. The CAC values of the same charge surfactants as that of the polymer were found to be significantly higher than other combinations of surfactant and polymer, such as non-ionic surfactant/anionic polymer, and zwitterionic surfactant/anionic polymer.

Drag-reducing polymers improve hepatic vaso-occlusion in SCD mice

Key Points Nanomolar concentrations of drag-reducing polymer (DRP) reduce vaso-occlusion in the liver of sickle cell disease (SCD) mice. The potential for DRP as a rheology-based treatment/therapy for SCD warrants further study.