Influence of Mechanical Degradation on Polymer Drag Reduction*

Addition of dilute (~ 10 ppm) polymer solutions can reduce the skin friction by up to 75% in both internal and external flows. The higher the molecular weight, lower is the required concentration for maximum drag reduction, but more susceptible is the polymer to chain scission in shear flows and passage constriction. Therefore, it is also important to see if skin friction reduction is sensitive to the mechanical degradation of the polymer. Thus, the current study makes a two-fold comparison; it compares the Fanning friction factor from pipe flows and then the slope increment analysis using the resulting Prandtl-Karman plots of the degraded and non-degraded polymer samples. This was performed using polyethylene oxide (PEO) solutions of 2 and 4 million grams/mol. The 4 million grams/mol sample was degraded to 2 million grams/mol by passing the sample through a contraction. The degraded molecular weight was confirmed based on the onset of drag reduction, which is inversely related to the molecular weight for PEO. This presentation will report the findings from these experiments.