Electrokinetic effects in helical flow of non-linear viscoelastic fluids

Abstract

Helical flows of complex fluids through annular regions have been studied extensively for their large spectrum of applications ranging from extrusion to mud drilling. Such flows include an axial flow in the presence of cylinder rotations, and they become coupled for complex fluids because of their shear thinning nature. Flows in annular confinements also find important applications in porous media and many biological and chemical systems, where electrokinetic effects in the form of surface charge and Electrical Double Layers (EDLs) might also play important roles. However, studies on helical flows of complex fluids in the presence of such effects are rather scarce. As such, here, we investigate helical flows of non-linear viscoelastic fluids in the presence of electrokinetic influences. We show that it is possible to write semi-analytical solutions for the velocity and the stress fields, even when the effects of EDL are present. We demonstrate that electro-osmotic effects compound the influence of the cylinder rotation, which can rapidly accelerate the volume throughput, even for moderate viscoelasticity. Our analysis brings out novel scaling regimes between the axial throughput and viscoelasticity. We further analyze to probe into the streaming potential resulting from a purely pressure driven flow and show that similar to the volume throughput, angular rotation also helps the streaming potential grow rapidly, even when the fluid is weakly viscoelastic.