Drag Reduction Performance of Mechanically Degraded Dilute Polyethylene Oxide Solutions

TL;DR

This study investigates how mechanical degradation of polyethylene oxide solutions affects their ability to reduce drag in turbulent pipe flow, revealing that degraded samples with the same mean molecular weight can perform better due to changes in molecular weight distribution.

Contribution

It demonstrates that molecular weight distribution, especially the presence of longer chains, influences drag reduction performance beyond mean molecular weight alone.

Findings

Degraded PEO solutions can outperform non-degraded ones at the same mean molecular weight.

Deviations in drag reduction performance scale with molecular weight differences.

Longer polymer chains in degraded solutions enhance flow control at certain conditions.

Abstract

Mechanical degradation of dilute solutions of polyethylene oxide (PEO) via chain scission was investigated within a turbulent pipe flow. Comparisons of the drag reduction performance with and without degradation were made by matching the onset of drag reduction conditions, which has been shown for PEO to be related to the mean molecular weight. The bulk flow behavior of both the degraded and non-degraded samples were generally consistent with trends observed in the literature, but a subset of conditions showed significant deviation in the slope increment (drag reduction performance) between the degraded and non-degraded samples. When they deviated, the degraded samples were consistently more efficient than the non-degraded samples even though they had the same mean molecular weight. The deviations were shown to scale with the normalized difference between the initial and final molecular weights. The current data and analysis as well as the literature suggests that the deviations in the polymer performance (slope increment) are related to changes in the molecular weight distribution. More specifically, the improved performance of the degraded samples relative to the non-degraded ones at the mean molecular weight of the degraded sample indicates an excess of longer polymer chains since the higher chain fractions in a degraded solution more effectively control the flow properties when within a certain degree of degradation and Reynolds number.