Drag reduction methods

The novel polymer slurry drag reduction method used by Little et al. [2] has been recently researched by Mamonov et al. [25]. Mamonov et al. [25] were able to prepare poly(ethylene oxide) solutions in less than 2 seconds using a special mixer and injected into the flow in a non-fu ly dissolved state. The reported results indicate that more drag reduction occurs when quickly prepared solutions have more time to dissolve. However, no data were reported for drag reduction effects with respect to time,... 

Comparison of averages for different flows and drag reduction methods. 

The MRS closures will attract most interest for use wherever MTE methods fail. For example, in flows with rotation the Coriolis terms enter the Rij equations, but drop out in the equation for Ru — q Therefore, an MRS method probably will be essential for including rotation effects, which are of considerable importance in many practical engineering and geophysical problems. Other effects that have not yet been adequately modeled and for which MRS methods may offer some hope include additive drag reduction, ultrahigh Reynolds numbers, separation, roughness, lateral and transverse curvature, and strong thermal processes that affect the hydrodynamic motions. 

With the recent advance in computational technology, efforts have also been devoted to numerical simulations of drag reduction, such as for viscoelastic polymers via constitutive equations and finite element methods [Dimitropoulos et al., 1998 Fullerton and McComb, 1999 Mitsoulis, 1999 Beris et al., 2000 Yu and Kawaguchi, 2004] and for DR flow with surfactant additives via second-order finite-difference direct numerical simulation (DNS) studies [Yu and Kawaguchi, 2003, 2006]. 

Turbulent drag reduction in homogeneous flows by polymer or surfactant additives is a striking phenomenon with both theoretical and practical implications. On the theoretical side, it remains a challenge to fully understand the drag reduction mechanism and the interaction details between DRAs and the turbulent flow field. New methods, especially computational ones, have been developed to solve this problem, such as direct numerical simulations and stochastic simulations. On the application... 

McMillan, M. L., Hershey, H. C., and Baxter, R. A., Effects of aging, concentration, temperature, method of preparation, and other variables on the drag reduction of aluminum disoaps in toluene, Chem. Eng. Prog. Symp. Sen, 67, 27-44 (1971). 

The discussion so far has related to the drag reduction occurring when a gas is introduced into a shear-thinning fluid initially in streamline flow. A more general method is required for the estimation of the two phase pressure drop for mixtures of gas and non-Newtonian liquids. The well-known Lockhart-Martinelli [1949] method will now be extended to encompass shear-thinning liquids, first by using the modified Lockhart-Martinelli parameter, Xmod (equation 4.8). Figure 4.14 shows a comparison between... 

Concentration, Temperature, Method of Preparation, and Other Variables on the Drag Reduction of Aluminum Disoaps in Toluene", Chem. Eng. Symposium Series, 27-44 ( 1971). 

The paper deals with results of an experimental study on drag reduction by adding polymer solution into a developing flow within a rectangular duct. The length of the duct was 2.5 m. The idea that considerable savings on polymers can be obtained by this method is tested. 

The local values of the drag reduction, mean values of the velocities and turbulence intensities are presented along with the power spectrum density functions. It is shown that extremely high local values of drag reduction can be obtained by this method with very low average concentration of polymer solution. 

Published results show that hydraulic transport of material has been found to be a technically feasible, enviromentally attractive and very economic method of transporting solid particles in different shape and size for short or long distances. The hydrotransport of solids in pipes is a particularly interesting possibility for the industrial applications of drag reduction effect. Despite intensive investigations of drag reduction its practical use for hydrotransport has only been treated in a few technical publications. 

Modern methods of waste-water treatment depend on macromole-cular additives used as coagulants to intensify sedimentation processesy to increase concentration of solid particlesr and to improve separation processes as well. The hydraulic transport of sludge forms a part of the waste-water treatment technology. Sludge is pumped not only between individual treatment processes but also out of the water-treatment plant to the sedimentation fields which are often distant. Even in this case the application of drag reduction is advisable from the point of view of saving electric energy. 

Fig. 3. Various methods of polymer addition for manifestation of the turbulent drag reduction phenomenon (63).

Fig. 10. Effect of injection method on drag-reduction characteristics of 50 ppm of polyacrylamide grafted amylopectin (AP-g-PAM) and 100 ppm of AP-g-PAM B Inlet B Ventury...

Renaux J. (2004) Overview on drag reduction technologies for civil transport aircraft. European Congress on Comp Methods in ApplSci andEngECCOMAS. 

In an effort to extend the effective lifetime of the drag reduction effect, a method similar to that of Little et al. [2] was applied to capsule pipelines. In Little s study, a slurry of partially dissolved poly(ethylene oxide) particles (polymer slurry method) instead of a fiilly dissolved solution (traditional, or dissolved polymer method) was used to reduce the drag. This novel approach has the advantage of having fresh PEO molecules dissolving in-situ to continue drag reduction after the previously dissolved molecules have degraded and lost then-effectiveness. 

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