Drag reduction effectiveness of dilute and entangled xanthan in turbulent pipe flow

The ability to reduce the frictional drag in turbulent flow in pipes and channels by addition of a small amount of a high molecular weight polymer has application in myriad industries and processes. Here, the drag reduction properties of the polyelectrolyte xanthan are explored in differing solvent environments (salt free versus salt solution) and delivery configurations (homogeneous versus stock solution dilution). Drag reduction effectiveness increases when an entangled xanthan solution is diluted compared to solutions prepared in the dilute regime. Based on dynamic rheological measurements of the elastic modulus, residual entanglements and network structure are hypothesized to account for the observed change in drag reduction effectiveness. Drag reduction effectiveness is unchanged by the presence of salt when the stock solution concentration is sufficiently above the critical concentration c_D. Finally, the drag reduction effectiveness decreases with time when diluted from an entangled stock solution but remains greater than the homogeneous case after more than 24 h.