Pore‐Scale Modeling of Fluid‐Fluid Interfacial Area in Variably Saturated Porous Media Containing Microscale Surface Roughness

Abstract

A pore-scale model is developed to simulate fluid-fluid interfacial area in variably saturated porous media, with a specific focus on incorporating the effects of solid-surface roughness. The model is designed to quantify total (film and meniscus) fluid-fluid interfacial area (A nw ) over the full range of wetting-phase fluid saturation (S w ) based on the inherent properties of the porous medium. The model employs a triangular pore space bundle-of-cylindrical-capillaries framework, modified with three surface roughness-related parameters. The first parameter (surface roughness factor) represents the overall magnitude of surface roughness, whereas the other two parameters (interface growth factor and critical adsorptive film thickness) reflect the microscale structure of surface roughness. A series of sensitivity analyses were conducted for the controlling variables, and the efficacy of the model was tested using air-water interfacial area data measured for three natural porous media. The model produced good simulations of the measured A nw data over the full range of saturation. The results demonstrate that total interfacial areas for natural media are typically much larger than those for ideal media comprising smooth surfaces due to the substantial contribution of surface roughness to wetting-film interfacial area. The degree to which fluid-fluid interfacial area is influenced by roughness is a function of fluid-retention characteristics and the nature of the rough surfaces. The full impact of roughness may be masked to some degree due to the formation of thick wetting films, which is explicitly quantified by the model. Application of the model provides insight into the importance of the interplay between pore-scale distribution and configuration of wetting fluid and the surface properties of solids. Key Points: • A triangular pore space BCC model is developed to simulate the impact of solid surface roughness on fluid-fluid interfacial area • Model efficacy is tested with air-water interfacial area data measured for three natural porous media • The model presents a means by which to quantify fluid-fluid interfacial area for natural porous media in multiphase fluid systems Correspondence to: M. L. Brusseau,

Predicting the Effect of Relaxation on Interfacial Area Development in Multiphase Flow

“…We do indeed observe these trends in Figure 9, and similar trends can also be seen in the simulation data of Jiang et al. (2020). They also observed an increase in fluid film interfacial area in media with more surface roughness, however the datasets examined in this study were not conducted at sufficiently high image resolution to allow for measurement of interfacial area associated with fluid films.…”

“…The fundamental difference between the glass bead and crushed tuff media is the presence of significant surface roughness in the crushed tuff medium (Jansik et al, 2011). The simulation data in Jiang et al (2020) also shows that when the surface roughness factor was increased the resulting a nw (S w ) curve was flatter at high wetting saturations. Although the magnitude of n is different than for the glass bead data, the overall trends are similar with imbibition above drainage and the value of n being fairly constant over the range of R pts .…”

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“…Water retention in the form of films has been attributed to adsorptive van der Waals forces (Tuller & Or, 2001; Zheng et al., 2015) or capillary force due to surface roughness (Almquist et al., 2018; Kibbey, 2013). The approach of using a roughness factor to account for the effects of roughness on water film was successfully applied in modeling hydraulic properties (Zheng et al., 2015) and estimating fluid–fluid interfacial area in unsaturated “clean” soils (Jiang, Guo, & Brusseau, 2020). When applied to hydrogel‐mediated soils, the current R‐TPSM treats the roughness factor X as an effective and fitting model parameter, which encompasses the possible hydrogel effects on changing water film thickness and area.…”

Multidimensional simulation of PFAS transport and leaching in the vadose zone: impact of surfactant-induced flow and soil heterogeneities

“…The four porous media that will be used for the numerical simulations are referred to as Accusand, Vinton, Hayhook, and high-K sand (i.e., a sand that has a greater hydraulic conductivity than the other three porous media). Detailed measured data and parameters are available for the first three from the literature (Guo et al, 2020;Jiang et al, 2020bJiang et al, , 2020aPeng & Brusseau, 2005). The last high-K sand is a porous medium that is hypothetically constructed to represent the preferential flow pathways.…”