Numerical modeling of kinetic interphase mass transfer during air sparging using a dual‐media approach

Abstract

Abstract. A dual-media multiphase flow approach is proposed for modeling the local interphase mass transfer that occurs during in situ air sparging. The method is applied to two-or three-phase flow in porous media to simulate the small gas channels that form during air sparging, allowing resolution of the local diffusive mass transfer of contaminants between the flowing gas phase and nearby stagnant liquid-filled zones. This approach provides a good match with laboratory column experiments in which dissolved trichloroethylene (TCE) is removed by air sparging, and it is shown that the simulation results are very sensitive to the nature of the local mass transfer regime. The numerical model is then applied to hypothetical field air-sparging cases involving either a dissolved plume of TCE or a TCE nonaqueous phase liquid source. In these simulations the local mass transfer appears to play a much smaller role than in the laboratory-scale tests, and significant deviations from local equilibrium simulations only occur when the mass transfer rates are reduced below the calibrated laboratory-scale values.

Modeling Kinetic Interphase Mass Transfer for Two-Phase Flow in Porous Media Including Fluid–Fluid Interfacial Area

“…The assumption that the composition of a phase is at or close to the equilibrium might be good if the time scale of mass transfer is large compared to the time scale of flow. However, if large flow velocities occur as, e.g., during air sparging, the local equilibrium assumption gives completely wrong results, see Falta (2000Falta ( , 2003 and VanAntwerp et al (2008).…”

“…Therefore, current models need to find a way to estimate or get rid of interfacial area. Three different approaches are commonly used: (1) lumping interfacial area into an effective rate coefficient K κ α→β [1/s] and then empirical estimation of the effective coefficient from a modified Sherwood number (usually done for DNAPL pool dissolution, see e.g., Miller et al 1990;Powers et al 1992Powers et al , 1994Imhoff et al 1994, andZhang andSchwartz 2000), (2) assumption of local equilibrium (e.g., Coats 1980;Young 1984;Allen 1985;Baehr and Corapcioglu 1984;Abriola and Pinder 1985a,b;Parker et al 1987), or (3) a dual domain approach (Falta 2000(Falta , 2003VanAntwerp et al 2008).…”

Mass and Heat Transfer During Two-Phase Flow in Porous Media - Theory and Modeling

“…However, if large flow velocities occur as e.g. during air sparging, the local equilibrium assumption gives completely wrong results, see Falta (2000;2003) and van Antwerp et al (2008). We will investigate and quantify this issue later in Sec.…”

Improved Predictions of Carbon Tetrachloride Contaminant Flow and Transport: Implementation of Kinetic Volatilization and Multicomponent NAPL Behavior

“…Often, the diffusional resistance on one side of the interface is considered dominant so that mass transfer rates can be described with a single overall mass transfer coefficient. Mathematically, the interphase mass transfer can then be described with a first-order rate expression rather than explicitly modeling all the elements of the mass transfer process (e.g., Lingineni and Khir, 1992;Armstrong et al 1994;Lee et al 2000;Falta 2000;Anwar et al 2003;Harper et al 2003;Abriola et al 2004;Wilkins et al 1995;van der Ham and Brouwers 1998;Yoon et al 2002;Bohy et al 2006;Mohtar 2006, 2007).…”