Elastic Flow Instability and Mixing in Microfluidic Channels: The Elastic Taylor-Couette and Taylor-Dean Instabilities Revisited

Jai A. Pathak Polymers Division National Institute of Standards and Technology, Gaithersburg, MD 20899-8544

Mixing in micro-channels is a challenge as these flows are low Reynolds number flows. In the absence of inertia, dependence on molecular diffusion is required to achieve mixing. In this talk, I will discuss the impact of exciting a purely elastic, i.e. non-inertial, flow instability on mixing in streams of an ideal elastic fluid (which has constant shear viscosity, but whose first normal stress difference exceeds its shear stress, signifying strong elasticity) flowing in a micro-channel. I will quantitatively compare the degree of mixing between analyte streams in two cases: (a) when both streams are ideal Newtonian fluids and (b) when both streams are ideal elastic fluids. Elasticity helps improve the degree of mixing (over the Newtonian case) between the analyte streams. Tracer particle/streak visualization studies of particle trajectories in these fluids flowing in the micro-channel help us elucidate the mechanism of the flow instability and understand the observation of improved mixing in the elastic analyte streams. The mechanism of the instability is strongly analogous to the mechanism of the purely elastic flow instability in elastic versions of the classical Taylor-Couette and Taylor-Dean flows.

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