Drag reduction applications

Dynamic topologies. Polymer aggregates seem most promising for drag reduction applications because both the shear stability, and the performance are improved through supramolecular associations. However, many fundamental questions remain unanswered. How does the strength of the secondary bonds... 

Although the above correlation is based upon data for polymer solutions which are considered concentrated for most drag reduction applications, it has been shown to be consistent with observed dependence of drag reduction upon both concentration and degradation in more dilute solutions, as well as observed dependence upon pipe diameter [1,10]. For example. Fig. 4 shows predicted friction factor characteristics for both fresh... 

The paper sets out details of specific drag reduction applications and are divided from flow point of view into internal and external flow. These include hydrotransport, transport of sludges in pipelines and sedimentation, heating circuits, irrigation, hydro-power stations, sewers, marine and hydrofoils and jet-cutting. Wherever possible field test or industrial utilization results are included and discussed. 

The effect of polymer additives on turbulent flow is at the origin of the important phenomenon of drag reduction and has found other industrial applications such as oil recovery and antimisting action. Drag reduction in dilute polymer solutions... 

A. Gyr and H.-W. Bewersdorff, Drag Reduction of Turbulent Flows by Additives, Vol. 32 of Fluid Mechanics and its Applications, Kluwer Academic Publishers, Dordrecht, 1995. 

Drag reduction decreases with flow time — which is in most application undesirable — and is obviously caused by a degradation of the polymer chain. Degradation of polymeric additives in turbulent flow cannot be easily understood on the basis of present knowledge, i.e., predictions towards the onset of chain scission cannot yet be made. These difficulties can be attributed, on the one hand, to the complex fluid structure and, on the other hand, to the fact that both shear and tensile stresses act simultaneously in turbulent flows. 

The fields of application listed below (Tab. 1) are only a few examples to indicate the potential for employing the drag reduction effect. 

The proposed mechanisms of models to explain the drag reduction phenomenon are based on either a molecular approach or fluid dynamical continuum considerations, but these models are mainly empirical or semi-empirical in nature. Models constructed from the equations of motion (or energy) and from the constitutive equations of the dilute polymer solutions are generally not suitable for use in engineering applications due to the difficulty of placing numerical values on all the parameters. In the absence of a more generally accurate model, semi-empirical ones remain the most useful for applications. 

The presence of small amounts of certain polymers can produce spectacular reduction in the frictional losses of fluids in turbulent flow through conduits. Drag reduction has an immense field of applications, both currently and potentially. The list of exploitable situations as described in Sect. 2 could be extended, but a big snag exists drag reduction decreases with flow time. This is believed to be due to mechanical degradation of added polymer (Brostow 1983). In Fig. 32 and Fig. 33 the influence of Mw on drag reduction is displayed. 

However, as was shown at the Iutam Symposium in Essen in 1984 and the subsequent 3rd International Conference on Drag Reduction in Bristol in 1984, a wide variety of large-scale technical applications are offered. Of these many possibilities, let it suffice to mention here the application of polymers in sewage systems (e.g., Dembek) and the hydro-transportation of coal in pipelines (e.g., Golda). 

Actual Examples of Thermal Engineering Applications of Microscopic Effects Drag Reduction of Liquid Flow by Ultra-small Concave and Convex Surfaces... 

The phenomenon of drag reduction (DR) in flow by dissolution of small amounts of certain polymers has an immense field of applications (46), including petroleum pipelines and firefighting. However, DR is complicated by mechanical degradation... 

Harwigsson, I. Surfactant Aggregation and Its Application to Drag Reduction. Ph.D. dissertation, Lund University, Sweden. 1995. 

DRAG REDUCTION IN TURBULENT FLOW. Dilute solutions of polymers in water or other solvents sometimes give the peculiar effect of a reduction in drag in turbulent flow. The phenomenon was first noted by Toms and has prompted many theoretical studies and some practical applications. As shown in Fig. 5.11, the friction factor can be significantly below the normal value for turbulent flow with only a few parts per million of polymer in water, and at 50 to 100 ppm, the drag reduction may be as much as 70 percent. Similar effects have been shown for some polymers in organic solvents. 

The major applications of drag reduction have been to increase the flow of water in a line of fixed size. Only a few parts per million of polyethylene oxide, a cheap nontoxic polymer, can double the capacity of a fire hose or a line carrying cooling water. In a long pipeline or with repeated use, degradation of the polymer under the high shear reduces its effectiveness. 

The mechanical stability of polymers was related to the polymer s conformation in some of the earlier drag-reduction studies. Above a critical stress, degradation was faster the more contracted and entangled the polymer s conformation (5-7). In petroleum applications the mechanical instability of synthetic relative to carbohydrate polymers was well-recognized. The relative stability problems (possibly related to DUEVs (8)) encountered in the use of high molecular weight hydrolyzed poly(acrylamide) (HPAM) led to the development of an inverse-emulsion polymerization technique (9). (Current research directions using this technique are discussed in Chapter 9.)... 

In addition to their water solubility and blandness, the main functions and effects of polyfethylene oxide) resins which lead to these diverse applications are lubrication, flocculation, thickening, adhesion, hydrodynamic drag reduction, and formation of association complexes. 

Corresponding-states studies of the viscosity-concentration behavior of dilute and semidilute polymer solutions with Robert Simha led one of the authors (JLZ) to their applications in turbulent flows, a phenomenon that is generally called drag reduction. About six decades ago, Mysels [Mysels, 1949 Agoston et al., 1954] and Toms [1949] discovered that small amounts of aluminum soaps and high polymers added to a fluid in turbulent flow could significantly reduce pressure losses. 

Over the past 60 years, a great deal of applied and theoretical research has been carried out on both polymer and surfactant DRAs because of their potential useful applications and the influence of the additives on both turbulent structure and rheology. Important results include the identification of maximum drag reduction asymptotes (MDRAs) both Virk s MDRA for polymer solutions [Virk et al., 1970 see Eq. (2.5)] and Zakin et al. s MDRA for surfactant solutions [Zakin et al., 1996 see Eq. (2.6)], relating solution nanostructures and rheological properties to macroscopic DR phenomena hypotheses on the influence of DRAs on turbulent structures, mechanisms for turbulent drag reduction, developing heat transfer enhancement techniques, and so on. 

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