Polymer Solution-Induced Drag Reduction

One of the more interesting discoveries in polymer solution research has been that extremely dilute solutions of very high molecular weight polymers exhib- 

Polymers useful for drag reduction usually have molecular weights in excess of 1 X 10 g/mol. The polymers used are hnear, and of course they have to be soluble in the flowing fluid. 

While most authors agree that the phenomenon itself is incompletely understood, it seems to have its roots in the dimensions of the polymer chain relative to the size of incipient turbulent bursts. Such polymers in the relaxed state are random coils (see Section 5.3.2), but during flow they become highly extended. The highly extended chains possess significant elastic energy. At the onset of drag reduction, the duration of a turbulent burst is of the order of the terminal relaxation time of the polymer chains in question. 

The basic concept of the energy required to cause flow is expressed by Reynold s number, R the ratio of inertia forces divided by the viscous forces. In terms of flow in a pipe. 

The most spectacular success of polymer drag reducers has been the use of oil-soluble polymers in the trans-Alaska pipeline (122). Flow through the pipeline has been greatly increased by appropriate polymer addition. 

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Mechanically induced reactions for polymers in solution are also of wide import. Cases include the stability of polymers involved in drag reduction and in biological fluids. The shear stability of polymers in solution is also of vital importance in certain commercial hydraulic and lubricating oils. 

Dimitropoulos, C.D., Dubief, Y., Shaqfeh, E.S.G., and Moin, P. (2006) Direct numerical simulations of polymer-induced drag reduction in turbulent boimdary layer flow of inhomogeneous polymer solutions. /. Fluid Mech., 566, 153-166. 

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