Non‐Newtonian Fluids in Action: Revisiting Hydraulic Conductivity and Pore Size Distribution of Porous Media

Core Ideas Experimenting with non‐Newtonian fluids allows for improved media characterization. This unfolds unique signatures of flow–pore interaction. Those signatures can be used in the hydraulic characterization of the medium. Model potential for unsaturated media characterization with only saturated flow experiments. The model allows for obtaining multiple hydraulic conductivities for porous media. Classic porous media flow experiments focus on water as the fluid of choice, thus limiting estimates of saturated hydraulic conductivity to a single averaged value that is rarely informative of the complexity of the pore structure. A theoretical framework is presented for a new method for experimentally estimating a functional pore structure of porous media using a combination of Newtonian and non‐Newtonian fluids. The proposed method builds an analog geometry of parallel capillary tubes (with tortuosity) that has the same functional behavior of real porous media in terms of saturated flow and porosity. The equivalent pore structure is formed by transforming results from N saturated infiltration experiments, comprised of water and N − 1 non‐Newtonian solutions, into a system of equations that yields N representative pore radii ( R i ) (size distribution of tubes) and their corresponding number (derived from percent contribution to water flow, w i ). This feature further allows estimating the soil water retention curve using only saturated experiments. We further show the ability of the proposed theoretical framework to infer additional information about flow in the porous medium as compared to what can be inferred from N (or even more) Newtonian fluids. This example shows the potential of this method and the ability of the proposed framework to extract additional information that an equal or larger number of experiments with only Newtonian fluids cannot extract.