Factors affecting polymer degradation in turbulent pipe flow

Abstract

A capillary rheometer was used to investigate the effect of various parameters on polymer degradation in turbulent flow. These parameters included polymer concentration, contraction ratio, pipe length, pipe diameter, number of passes, solvent and molecular weight of polymer. A commercial organic drag reducer (ODR), two grades of polyacrylamide (Separan AP 30 and AP 302), and a high-molecular weight polyisobutylene (PIB) were used. The investigation was based on measuring the loss in the drag reduction effectiveness which was manifested by a minimum point on the Fanning friction factor vs Reynolds number plot. In turbulent flow, the polymer degraded more in a poor solvent at low Reynolds numbers; whereas an opposite effect was observed at high Re. The critical Reynolds number Re*, or critical apparent shear/extensional rate ( V/ d)* was found to increase with polymer concentration and molecular weight as represented by the dimensionless concentration c[ν]. There is sufficient evidence to suggest that most fo the degradation takes place at the entrance region due to high extensional straining of polymer molecules. As expected, polymer degradation was found to increase with number of passes. However, the contraction ratio and pipe length did not seem to have much effect. Whilst Re* increased with pipe diameter, the trend was not evident on ( V/ d)*.