Turbulent flow drag reduction and degradation with dilute polymer solutions

Abstract

Experimental studies of drag reduction and polymer degradation in turbulent pipe flow with dilute water solutions of unfractionated polyethylene oxide are described. Drag reduction results indicate that the magnitude of the reduction cannot be correlated on the basis of weight average molecular weight, rather the phenomenon depends strongly on the concentration of the highest molecular weight species present in the molecular weight distribution. Polymer degradation in turbulent flow is found to be severe for high molecular weight polymers causing appreciable changes in drag reduction and molecular weight with the duration of flow. Data indicates that drag reduction exists in the limit of infinite dilution suggesting that the phenomenon is due to the interaction of individual polymer molecules with the surrounding solvent and that the extent of reduction is relatively independent of pipe diameter when a comparison is carried out at equal solvent wall shear stresses. Consideration of the high viscosity obtained with solutions in an irrotational laminar flow field suggests this is due to polymer molecule deformation and that this phenomenon is central to the mechanism of turbulent flow drag reduction.

Water‐soluble polymers. LXXXII. Shear degradation effects on drag reduction behavior of dilute polymer solutions

“…17,[22][23][24][25][26][27][28][29] The rate of shear degradation is greatest for high molecular weight polymers at low concentration. [27][28][29] Shear degradation typically results in a rapid decrease in molecular weight that approaches a limiting polymer molecular weight (M tϱ ) after long degradation times.…”

A Short Review on Drag-Reduced Turbulent Flow of Inhomogeneous Polymer Solutions

“…Until now, some researches [60,[64][65][66][67][68][69] have indicated that polymer molecular weight, molecular weight distribution, temperature, solvent solubility, polymer concentration, turbulent intensity, preparation and storage methods, entrance or end effects, and flow geometry may influence polymer degradation in turbulent flows. Nevertheless, it is noteworthy that due to various experimental conditions some conflicting results still exist when explaining degradation with the above factors.…”

A review on drag reduction with special reference to micellar systems

“…[I 17,124,125] an electrolyte Polyethylene oxide Hydrocarbons, [126,127] e. g. benzene trichloroethylene Polyethylene oxide Blood transfusion [128] fluids Polyacrylamide Water [103,108,109,119, [126] A study of the drag reducing ability of the above polymers has led to the conclusion that any macromolecular substance with a linear structure and high molecular weight, i. e. above 500,000, is a good drag reducer. The advantage of polymers is that they are effective at very low concentrations; but, as they are very prone to mechanical degradation in dilute solutions [157][158][159][160][161] they have limited practical applicability.…”

“…But Paterson [157] found pipe drag reduction with poly(ethylene oxide) solutions as dilute as 0.03 ppm, and, at the molecular separation distances and volume fractions involved, it is quite unlikely that molecular entanglement could play any part in drag reduction. Nevertheless, Ellis et al [254] showed that polymer solutions stored for several weeks showed lower drag reduction than freshly mixed ones, the implication being that there has been a molecular disentanglement during storage.…”