Drag reduction experiments with very large pipes

Various substances have been tested in the laboratory for their suitability as flow enhancers in aqueous solutions. The following maximum drag reductions (%) were obtained with pipes of 14 mm diameter and a Reynolds number of 10⁵: Na-carboxy methylcellulose (32), hydroxyethyl cellulose (42), cetyltrimethylammonium chloride/-naphthol (74; Re=10⁴), polyethylene oxide (76), K-polyphosphate/Na-pyrophosphate (77), polyacrylamide (80). The tested, partially hydrolysed polyacrylamide which was produced by a special process was found to be not only extremely effective and highly resistant to shear degradation but also unaffected by the salt content, the temperature and the water spoilage. Experiments were therefore made with this material on an industrial scale, that is to say with pipes up to 750 mm in diameter and 3200m in length. Whilst in the laboratory (pipes up to 14 mm in diameter) drag reductions were measured according to the Virk asymptote, the results obtained with large pipe diameters were lower. At diameters ranging from 300 to 750 mm a maximum drag reduction of 65% (at a concentration of 30 ppm PAAM and a constant wall shear stress of 50 Pa) has been obtained independently of the diameter.Symbols c concentration - d diameter - FE (as index) flow enhancer - k roughness - l length - n degree of polymerization - p pressure drop - r radius - Re Reynolds number - T temperature - v velocity - w (as index) water - drag reduction - friction factor - kinematic viscosity - density - wall shear stress Dedicated to Prof. Dr. R. Bonart on the occasion of his 60th birthday