Boger fluid flow through hyperbolic contraction microchannels

Abstract

Boger fluids are characterized by their constant viscosity and elasticity and are very useful to study pure elastic flow behavior. In this paper we assess the potential of a microfluidic hyperbolic contraction as a device to measure the relaxation time of low viscosity polymer solutions, which are difficult to characterize in a conventional capillary break-up extensional rheometer. For this purpose we initially characterize the shear and extensional rheology of aqueous solutions of polyacrylamide (PAA) at different concentrations (400, 250, 125 and 50 ppm) with 1% (w/w) of NaCl, which result in low viscosity Boger fluids. Subsequently, flow visualizations of their flow through a microfluidic hyperbolic contraction were carried out in order to quantify the relation between their degree of elasticity and the vortex growth upstream of the microchannel.