Non-Newtonian fluid flows in a contraction-expansion microchannel*

Non-Newtonian fluids have been studied widely for various biological and industrial applications. Microfluidics provides a simple and efficient way to understand non-Newtonian fluid flow on small length scales for a wide range of Reynolds and/or Weissenberg number. In this study we show through systematic experiments the behavior of non-Newtonian fluid flow in a planar contraction- expansion microchannel. Five important types of fluids are tested in this geometry to investigate the sole and combined effects of fluid elasticity, shear thinning and inertia. Each characteristic behavior of the fluid plays a role in inducing lip or corner vortices, instability in the flow and bending of streamlines at the channel constriction. Such a fundamental study will possibly help in understanding the flow of non-Newtonian fluids through complex channel geometries of lab-on-a-chip devices.