X-ray Microtomography Determination of Air−Water Interfacial Area−Water Saturation Relationships in Sandy Porous Media

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Abstract
In this work, total smooth air–water interfacial areas were measured for a series of nine natural and model sandy porous media as a function of water saturation using synchrotron X-ray microtomography. Interfacial areas decreased linearly with water saturation, while the estimated maximum interfacial area compared favorably to the media geometric surface areas. Importantly, relative interfacial area (i.e., normalized by geometric surface area) versus water saturation plots for all media collapsed into a single linear cluster (r2 = 0.93), suggesting that geometric surface area is an important, and perhaps sufficient, descriptor of sandy media that governs total smooth interfacial area−water saturation relationships. Measured relationships were used to develop an empirical model for estimating interfacial area−water saturation relationships for sandy porous media. Model-based interfacial area estimates for independent media were generally slightly higher than interfacial areas measured using aqueous-phase interfacial tracer methods, which may indicate that microtomography captures regions of the air–water interface that are not accessible to aqueous-phase interfacial tracers. The empirical model presented here requires only average particle diameter and porosity as input parameters and can be used to readily estimate air–water interfacial area−water saturation relationships for sandy porous media.

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