DIRECT DETERMINATION OF APPARENT SLIP FOR A DUCTED FLOW OF POLYACRYLAMIDE SOLUTIONS

Velocity profiles were measured up to a minimum distance of 0. 15 mu m from the wall for tube flow of aqueous solutions of anionic Polyacrylamides (Praestol from the Stockhausen Corporation, at a concentration c//o equals 0. 25 percentage by weight). The profiles measured could be reclculated on the basis of the flow curve. Extrapolation of the profile to the wall resulted in finite velocity values (slip-velocity nu //s). This slip phenomenon could not be calculated in advance on the basis of the flow curve alone. The results indicate that the Polyacrylamide solution does not glide directly along the wall but, instead, by mediation of a low viscous Newtonian fluid lining the wall.