Turbulent and Transition Pipe Flow of Dilute Aqueous Polymer Solutions

Abstract

The addition of minute quantities of high molecular weight polymers to water can produce a large reduction in the turbulent pipe flow friction. A laser-Doppler instrument for measuring local velocity is used to study transition and turbulent pipe flow of a 50-WPPM aqueous solution of Polyox WSR 301 (polyethylene oxide) at the center of a 14-mm diam pipe. The addition of the polymer to water does not significantly alter the level of the longitudinal turbulence intensity at the center line over the range of Reynolds numbers studied. A surprising result of polymer addition occurs below a Reynolds number of 2,500 in the region of the hump. The increased relative band widths of the frequency spectra in this region imply an uncertainty in the fluid velocity. This result, together with the observed concurrent decrease in the ratio of center line to bulk velocity relative to pure water, shows that the flow is no longer of the steady Poiseuille type after the addition of Polyox WSR 301. The absence of spikes from the frequency spectra further implies that the flow is not intermittent in the sense that laminar and turbulent slugs are alternately passing the point of measurement. At these Reynolds numbers,more » the flow is probably laminar but unsteady. (18 refs.)« less