Long-term degradation of high molar mass poly(ethylene oxide) in a turbulent pilot-scale pipe flow

Abstract

The long-term drag reduction capability of poly(ethylene oxide) with a nominal molar weight of Mw=4×106 g/mol dissolved in water was investigated in a pilot-scale pipe flow device (inner diameter of test section 26 mm) at a Reynolds number of 105. A total loss of the initially high (75%) drag reduction capability was observed over a flow distance of several ∼10 km while the molar weight of the polymer was still Mw∼5×105 g/mol. Mechanical degradation in the turbulent flow as well as ageing of the polymer dissolved in water caused this loss in drag reduction capability. A simple ansatz of two independent, statistical polymer chain scission mechanisms was used to describe the polymer degradation empirically using a modified Brostow model. This empirical description was applied successfully and suggested that the polymer exhibited at least 15 cleavage points for mechanical degradation.