Direct experimental observation of shear-viscosity-distribution dependent dispersion in non-Newtonian fluid flow in porous media

Non-Newtonian fluid flow in porous media results in spatially varying viscosity, driven by flow-pore-geometry interactions, potentially leading to non-monotonic dispersion. In this work, using high-resolution micro-particle image velocimetry (PIV), we present a direct experimental observation of shear-viscosity-distribution dependent transport with non-Newtonian fluid flows in porous media. We experimentally investigate dispersion in porous media in a microfluidic chip featuring a physical rock geometry, comparing a shear-thinning, non-Newtonian fluid with its Newtonian analogue at various Pe´clet numbers. We demonstrate that, in the absence of advective fluxes driven by elastic instabilities, non-Newtonian fluid flows at either extreme of the shear-dependent viscosity (₀, ∞) converge to the Newtonian analogue. In contrast, flows between these extremes, the non-Newtonian velocity fields are broadly distributed along the streamline curvature, leading to a larger enhancement in dispersion.