Determination of the characteristic and diffusion times of polyacrylamide solutions using falling balls and needles

Abstract

The present study determined the apparent viscosity and the characteristic time of aqueous polyacrylamide Separan AP-273 solutions by using a falling ball viscometer. Two laser beams and a digital timer system were used to accurately measure the terminal velocity of a falling ball or needle in the falling ball viscometer. The diffusion time of the polyacrylamide solution was determined by measuring the terminal velocities of falling balls. A consistent diffusion time was observed for balls, whereas in the case of needles, the diffusion time depended on the ratio of the needles' length to their diameters. The diffusion time decreased as the ratio increased for a given Separan solution. The characteristic time and the diffusion time of the polyacrylamide solution decreased as degradation continued. The effect of degradation on the heat transfer was more significant than that on the friction factor. A computer-aided image-processing technique was employed to visualize the flow phenomena around balls. For a time interval of 3 min, recirculating eddies were formed both upstream and downstream of the falling ball, whereas for a time interval of 10 min the eddies disappeared.