Turbulent drag reduction by polymeric additives, discovered by Toms in 1948 and therefore often referred to as Toms’ Phenomenon, is an energy-saving technique widely employed in crude oil and petroleum product pipelines, in wellbore development, and in shale fracturing operations. Fluid mechanically, Toms’ Phenomenon is bounded between (1) the Prandtl-Karman law PK for turbulent flow of Newtonian fluids: 1/√f=4.0log(Re√f)-0.4 and (2) an additive-independent asymptote of Maximum Drag Reduction MDR: 1/√f=19.0log(Re√f)-32.4, where f denotes Fanning friction factor and Re the Reynolds number. The bounds PK and MDR envelop a third “polymeric regime” between them, wherein the flow depends upon polymeric parameters. The present paper will consider three chemical aspects of the polymeric regime, namely: (i) polymer conformation, (ii) polymer contour length, and (iii) polymer chain degradation. Polymer conformation appears to determine the friction factor trajectory exhibited, either Type A, characteristic of initially randomly-coiling macromolecules, such as polyethyleneoxide PEO in water, or Type B, characteristic of extended macromolecules, such as partially hydrolysed polyacrylamide PAMH in deionized water, as well as a host of other polyelectrolytes in solvents of low ionic strength (and also many relatively rigid additives, including fibres, of paper, nylon and asbestos, clays and crystal sols). Polymer contour length appears to control additive performance, as measured by an intrinsic slip that physically represents the extent of drag reduction per unit concentration of polymer. Polymer chain degradation always accompanies drag reduction, as macromolecules extended to their contour lengths suffer midpoint scission in the turbulent flow field, eventually diminishing drag reduction. The kinetics of polymer degradation and the associated “falloff” in drag reduction efficacy have thus far eluded precise delineation.

Chemical considerations in turbulent drag reduction by polymeric additives

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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