MIGRATION OF MACROMOLECULES UNDER FLOW - THE PHYSICAL ORIGIN AND ENGINEERING IMPLICATIONS

During flow, an initially homogeneous polymer solution may develop pos ition-dependent concentration gradients due to migration of the polyme r molecules with respect to the bulk flow. We review the experimental evidence, especially the anomalous experimental observations of intere st to engineers, concerned with enhancement (which is sometimes rather dramatic) in heat, mass and momentum transfer during the flow of such ''slipping fluids''. Further, we critically review and discuss the me rits of various heuristic and more fundamental fluid mechanical or the rmodynamic models, which attempt to explain this phenomenon. We show t hat many theoretical predictions are often in conflict with each other even qualitatively, and the reported studies providing direct experim ental evidence are few. Directions for future work in the area have be en highlighted.