PIPE-FLOW OF AQUEOUS POLYACRYLAMIDE SOLUTIONS STUDIED BY MEANS OF NUCLEAR-MAGNETIC-RESONANCE IMAGING

Flow behaviour of aqueous polyacrylamide solutions in a straight circular pipe of 26.2 mm in diameter was investigated by using phase flow encoded nuclear magnetic resonance imaging (NMRI). Premixed polyacrylamide solutions of four different concentrations, i.e. 1 000, 500, 300, and 200 wt. ppm were studied. The mean axial velocity profiles of the dilute polyacrylamide solutions were measured at various mean bulk flow rates up to 800 mm s(-1). Laminar flows to unsteady turbulent flows through a transition flow regime were observed. For turbulent flows, the mean velocity profiles and the streamwise turbulence intensities were obtained by using a time-averaged NMRI method. The theological behavior of the polyacrylamide solutions, that is the shear stress dependence on the shear rate, was also characterized by using the velocity profile data from NMRI together with pressure drop measurements. The results were compared with independently measured theological data from a cone-and-plate viscometer.