Micro-PIV of viscoelastic fluid flow in media

The present experimental investigation combines the bulk flow properties of polymer solutions and measurable rheological parameters as they flow through a distinctive micro-porous structure, with micro-PIV (micro- particle image velocimetry) to measure the velocity distribution and velocity fluctuations within individual pores of a novel porous glass structure. To investigate the effects of fluid elasticity at pore scale, aqueous solutions of a polyacrylamide (PAA) & polyethylene oxide (PEO) in the concentration range of 50-200 ppm, which were characterized in both shear and extensional flows using shear and capillary break-up extensional rheometers (CaBER) respectively, were used as working fluids. The velocity field measurement includes the velocity magnitude and fluctuation intensity in several different pores within the porous material across a Weissenberg number Wi range of approximately 0.01 to 1 for each of the test fluids. The global averaged fluctuation intensity increases with Wi but the critical value, which indicates the onset of significant unsteadiness (i.e. well above noise floor/Newtonian baseline) within the flow at pore scale gives an approximately constant value of Wi approximate to 0.4, approximate to 0.4, which is almost 40 times higher than the value that is observed in the pressure-drop measurements for the data to rise above the Newtonian base line. We therefore postulate that the enhanced pressure-drop behaviour of the bulk flow may not be due to local velocity fluctuations within the pores but due to mean flow effects, at least over a significant portion of the data (up to Wi approximate to 0.4). approximate to 0.4).