Assessing XMT‐Measurement Variability of Air‐Water Interfacial Areas in Natural Porous Media

By employing kinetic interface sensitive (KIS) tracers, we investigate three different types of glass‐bead materials and three natural porous media systems to quantitatively characterize the influence of the porous‐medium grain‐, pore‐size and texture on the specific capillary‐associated interfacial area (FIFA) between an organic liquid and water. By interpreting the breakthrough curves (BTCs) of the reaction product of the KIS tracer hydrolysis, we obtain a relation for the specific IFA and wetting phase saturation. The immiscible displacement process coupled with the reactive tracer transport across the fluid–fluid interface is simulated with a Darcy‐scale numerical model. Linear relations between the specific capillary‐associated FIFA and the inverse mean grain diameter can be established for measurements with glass beads and natural soils. We find that the grain size has minimal effect on the capillary‐associated FIFA for unconsolidated porous media formed by glass beads. Conversely, for unconsolidated porous media formed by natural soils, the capillary‐associated FIFA linearly increases with the inverse mean grain diameter, and it is much larger than that from glass beads. This indicates that the surface roughness and the irregular shape of the grains can cause the capillary‐associated FIFA to increase. The results are also compared with the data collected from literature, measured with high resolution microtomography and partitioning tracer methods. Our study considerably expands the applicability range of the KIS tracers and enhances the confidence in the robustness of the method.

Section: Comparison Of Measured Interfacial Area With Literature Datasupporting

confidence: 91%

Section: Comparison Of Measured Interfacial Area With Literature Datamentioning

confidence: 99%

Estimation of Capillary‐Associated NAPL‐Water Interfacial Areas for Unconsolidated Porous Media by Kinetic Interface Sensitive (KIS) Tracer Method

Tatomir,

Gao,

Abdullah

et al. 2023

“…(2020b). The capillary pressure water saturation curve ( P c –S w ) and the specific air–water interfacial area curve (A aw –S w ) measured by various methods were reported in the literature (Araujo & Brusseau, 2020; Araujo et al., 2015; Brusseau et al., 2007). Note that A aw denotes the specific air–water interfacial area in the pore network, which is different from a aw (i.e., the air–water interfacial area in a pore body) in Section 2.…”

Section: Pore‐network Modeling Of Pfas Transport In a Water‐unsaturat...mentioning

confidence: 99%

“…At near water‐saturated conditions, the bulk capillary air–water interfaces are greater than the thin‐water‐film air–water interfaces. As the water saturation decreases, the bulk capillary air–water interfaces first increase and then decrease (Araujo & Brusseau, 2020; Dalla et al., 2002; Kibbey & Chen, 2012; Porter et al., 2009; Reeves & Celia, 1996). Conversely, the thin‐water‐film air–water interfaces increase monotonically as the water saturation decreases and quickly become the dominant air–water interfaces (Brusseau et al., 2007; Costanza‐Robinson & Brusseau, 2002; Kibbey & Chen, 2012).…”

Section: Introductionmentioning

confidence: 99%

Pore‐Scale Modeling of PFAS Transport in Water‐Unsaturated Porous Media: Air–Water Interfacial Adsorption and Mass‐Transfer Processes in Thin Water Films

Chen

Guo

2023

Air–water interfacial adsorption complicates PFAS transport in vadose zones. Air–water interfaces can arise from pendular rings between soil grains and thin water films on grain surfaces, the latter of which account for over 90% of the total air–water interfaces for most field‐relevant conditions. However, whether all thin‐water‐film air–water interfaces are accessible by PFAS and how mass‐transfer limitations in thin water films control PFAS transport in soils remain unknown. We develop a pore‐scale model that represents both PFAS adsorption at bulk capillary and thin‐water‐film air–water interfaces and the mass‐transfer processes between bulk capillary water and thin water films (including advection, aqueous diffusion, and surface diffusion along air–water interfaces). We apply the pore‐scale model to a series of numerical experiments—constrained by experimentally‐determined hydraulic parameters and air–water interfacial area data sets—to examine the impact of thin‐water‐film mass‐transfer limitations in a sand medium. Our analyses suggest: (1) The mass‐transfer limitations between bulk capillary water and thin water films inside a pore are negligible due to surface diffusion. (2) However, strong mass‐transfer limitations arise in thin water films of pore clusters where pendular rings disconnect. The mass‐transfer limitations lead to early arrival and long tailing behaviors even if surface diffusion is present. (3) Despite the mass‐transfer limitations, all air–water interfaces in the thin water films were accessed by PFAS under the simulated conditions. These findings highlight the importance of incorporating the thin‐water‐film mass‐transfer limitations and surface diffusion for modeling PFAS transport in vadose zones.This article is protected by copyright. All rights reserved.

“…Many researchers have used x‐ray microtomography (µCT) to visualize the movement and distribution of multi‐phase fluids within porous media in three dimensions (e.g., Blunt et al., 2013; Wildenschild & Sheppard, 2013). Traditionally, this methodology has required experiments to be limited to observations under quasi‐equilibrium flow conditions due to the time required to acquire a µCT image (e.g., Araujo & Brusseau, 2020; Costanza‐Robinson et al., 2008; Porter et al., 2010). With the recent advent of fast µCT, it is now possible to conduct non‐equilibrium multi‐phase flow experiments (e.g., Berg et al., 2013; Leu et al., 2014; Meisenheimer, McClure, et al., 2020; Schlüter et al., 2016; Singh et al., 2017).…”

Section: Introductionmentioning

confidence: 99%

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

Meisenheimer

Wildenschild

2021

Fluid-fluid interfacial area is an important parameter of relevance to multiphase flow in porous media due to its implicit inclusion in mass transfer rate expressions (e.g., Johns & Gladden, 1999), thereby controlling the reaction efficiency of the undergoing process, but it also influences the fluid flow processes within the system (e.g., Culligan et al., 2004). There is a need to better understand this relationship between interfacial area generation and fluid flow processes so that more robust theories and models can be developed to optimize the performance of many multiphase processes such as in situ groundwater remediation and geologic carbon capture and storage. There is growing interest in studying what effect equilibrium in a multi-phase flow system, and the resulting relaxation of fluid interfaces during this time, has on macroscopic invariants (i.e., wetting saturation, average capillary pressure, specific interfacial area, and Euler characteristic) (e.g., Gray et al., 2015; Meisenheimer, McClure, et al., 2020; Schlüter et al., 2017). As will be demonstrated later, interfacial relaxation leads to distinct differences in interfacial area development between flow experiments conducted under non-equilibrium (where flow is never stopped between points of reversal) and quasi-equilibrium conditions (where flow is stopped at a number of intermediate points, and fluids are allowed to relax toward equilibrium). Many researchers have used x-ray microtomography (µCT) to visualize the movement and distribution of multi-phase fluids within porous media in three dimensions (e.g., Blunt et al., 2013; Wildenschild & Sheppard, 2013). Traditionally, this methodology has required experiments to be limited to observations under quasi-equilibrium flow conditions due to the time required to acquire a µCT image (e.g.