Drag reduction degradation

Chain degradation in turbulent flow has been frequently reported in conjunction with drag reduction and in simple shear flow at high Reynolds numbers [187], Using poly(decyl methacrylate) under conditions of turbulent flow in a capillary tube, Muller and Klein observed that the hydrodynamic volume, [r ] M, is the determining factor for the degradation rate in various solvents and at various polymer concentrations [188], The initial MWD of the polymers used in their experiments are, however, too broad (Mw/Iiln = 5 ) to allow for a precise... 

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. 

According to his interpretation, both the degradation characteristics and the extent of drag reduction are determined by the relationship between compact and flexible chain segments. As a consequence of this, it is not the absolute volume of the (gel) coil which is the decisive value, but the behavior of the polymer chain. 

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. 

In turbulent flow, the macromolecules are also believed to experience burst-induced elongation. However, it has to date not been possible to formulate structure-property relationships which allow an ad hoc prediction of the onset of mechanical degradation and its influence on drag reduction. 

The experimental techniques were dealt with briefly in Sect. 5, where it must be noted that, for both the quantitative and qualitative description of the drag-reduction phenomenon, precisely defined measuring equipment must be used in order to be able to establish whether degradation arises as a result of the nature of the flow of the apparatus as such (corners, edges, burrs, surface, roughness). 

Brostow W (1983) Drag reduction and mechanical degradation in polymer solutions in flow Polymer 24 631... 

Patterson RW, Abernathy FH (1970) Turbulent flow drag reduction and degradation with dilute polymer solutions Fluid Mech 43 689... 

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... 

Pollert, J. Sellin, R.J. Mechanical degradation of drag reducing polymer and surfactant additives a review. In Drag Reduction in Fluid Flows Techniques for Friction Control Sellin, R., Moses, R., Eds. Ellis Horwood West Sussex, U.K., 1989 179-188. 

Patterson, G.K. Shen, A.-M. Chen, I.-M. Rates of shear degradation of drag reducing polymer. In Drag Reduction, 3rd International Conference on Drag Reduction, University of Bristol, Bristol, Jul 2-5, 1984 Sellin, R.H.J., Moses, R.T., Eds. E.4-1-E.4-6. 

Hunston, D. Effects of molecular weight distribution in drag reduction and shear degradation. J. Polym. Sci. Polym. Chem. Ed. 1976, 14, 713-727. 

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.)... 

Decades of research in polymer drag reduction have shown that the effects of variables such as polymer molecular structure, flexibility, molecular weight, concentration, and solvency are important. They are described below along with polymer mechanical degradation. 

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