Flow of dilute polyacrylamide solutions through a sudden planar contraction

• Published in: Journal of non-Newtonian fluid mechanics Vol. 28; no. 3; pp. 267 - 285
• Main Authors: Wunderlich, A.M., Brunn, P.O., Durst, F.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1988
• ISSN: 0377-0257; 1873-2631
• DOI: 10.1016/0377-0257(88)87001-0

The flow of partially hydrolyzed polyacrylamide solutions through a 10:1.2 sudden planar contraction was investigated by means of laser-Doppler anemometry. The resultant velocity profiles are compared with those for Newtonian water flow. It is shown that velocity profiles of dilute high molecular weight HPAM solutions of concentrations of 25 ppm and 50 ppm exhibit a velocity maximum upstream of the sudden planar contraction. They first appear near the wall and move towards the channel axis as the flow approaches the contraction. Furthermore, it is found that the centreline velocity profiles of the polymer solution show an earlier response to the downstream flow restriction than water. This is associated with enhanced recirculation regions in front of the sudden channel contraction. Streamlines calculated from the experimentally obtained velocity data reveal all the characteristics of a diverging flow field upstream of the contraction. The experiments reveal that, for the volume flow rate investigated, the flow of dilute polymers remains two-dimensional in the centre throughout the major part of the channel. The addition of small amounts of the divalent salt CaCl 2 reduces the polymer effects to pure Newtonian flow behaviour.