Mechanical degradation of polymers in flows through porous media: Effect of flow path length and particle size

In this work, we present an experimental study of flow-induced degradation of hydrolyzed polyacrylamide in aqueous solutions flowing through porous media consisting of beds packed with monodisperse spherical particles. The degradation is analyzed by passing the solution repeatedly through the porous medium at a constant flow velocity, and then characterizing the degraded solution in terms of its resistance coefficient. Repeated passes through the porous medium are equivalent to increasing the path length of the solution. When the polyacrylamide is dissolved in deionized water, it exhibits a gradual extension thickening behavior in terms of increases in flow velocity. In this case, the polymer degrades as it passes through the porous medium, even at relatively low flow rates. When the polyacrylamide is dissolved in a NaC1 solution, it exhibits critical extension thickening in porous media flows, and it only degrades at Reynolds numbers that are higher than the onset of the extension thickening behavior. With repeated passes, the polymer progressively degrades until an asymptotic value of resistance coefficient is reached. The results show that the effect of particle size on degradation rates depends on the basis used for comparison between experiments carried out in beds with different particle sizes. However, the degree of degradation achieved after long path lengths is always higher for the largest particle size employed under equivalent comparison parameters.