Dispersion and transport of gas-phase contaminants in dry porous media: effect of heterogeneity and gas velocity

Popovičová, Jarmila; Brusseau, Mark L.

doi:10.1016/s0169-7722(97)00014-4

Cited by 34 publications

(19 citation statements)

References 18 publications

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“…The three/3 parameters sum to unity. When using this model to simulate the data, the Peclet number, which in this case represents the contribution of only mechanical mixing and axial diffusion to dispersion, was fixed at 100 on the basis of results obtained in previous gas-phase transport experiments [Popovi•owi and Brusseau, 1998]. This method allowed us to determine values of the nonequilibrium parameters/3i, fraction of retardation, and Damkohler numbers (•o, kø), ratio of mass transfer and advection timescales, by least squares optimization.…”

Section: Methodsmentioning

confidence: 99%

Contaminant mass transfer during gas‐phase transport in unsaturated porous media

Popovičová¹,

Brusseau²

1998

Water Resources Research

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Abstract. This study was conducted to investigate the relative effects of physical heterogeneity, gas-liquid mass transfer, and rate-limited sorption on the gas-phase transport of contaminants in idealized unsaturated homogeneous and heterogeneous porous media. The transport of methane in the unsaturated homogeneous porous medium was ideal, whereas that of trichloroethene and benzene was nonideal, governed by ratelimited diffusive mass transfer in immobile water and by rate-limited sorption/desorption. Transport of both methane and trichloroethene through the unsaturated heterogeneous porous medium was nonideal. Gas-phase mass transfer between unsaturated advective and nonadvective domains caused nonideal transport of methane. Trichloroethene nonideality was due to a combination of gas-phase mass transfer between advective and nonadvective domains, diffusion within immobile water, and rate-limited sorption/desorption. The transport of trichloroethene through the heterogeneous porous medium was predicted by use of a multiprocess mass transfer model, wherein all parameters were estimated independently. IntroductionSoil venting is generally considered to be an efficient and cost-effective technology for removal of volatile organic compounds from the vadose zone. However, the efficiency of the technique and the duration of remediation depends on many factors, including the presence of physical structures (e.g., fractures, aggregates, macropores) and moisture content. For example, in structured or variably saturated porous media, gas will tend to flow preferentially through the zones of larger intrinsic or relative permeability. In such cases the transport and removal of gas-phase contaminants may be controlled by gas-water mass transfer, mass transfer between macropore and micropore domains, or intraparticle diffusion.Kearl et al. [1991] concluded that gas-phase diffusion between layers of different permeability controlled 'gas-phase transport and removal of contaminants from unsaturated soil columns at gas velocities greater than 120 cm min-x. Gierke et al. [1992] found that mass transfer across the gas-water and the mobile-immobile water interfaces could be considered instantaneous whereas diffusion in immobile water contained within intraaggregate pores caused nonideal gas-phase transport. Conversely, Gimmi et al. [1993] concluded that transport of gas-phase contaminants in unsaturated, aggregated media with no sorption capacity was governed by equilibrium gas-water partitioning. Grathwohl and Reinhard that both rate-limited sorption/desorption and diffusion within immobile water significantly influenced transport. The purpose of this research was to investigate the effect of physical heterogeneity, gas-phase mass transfer between unsaturated macroporous and microporous domains, and gaswater mass transfer on gas-phase transport of contaminants in unsaturated porous media. Idealized systems are used to allow a specific focus on these processes. Mathematical models of varying complexity, including a multiple-pro...

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Section: Methodsmentioning

confidence: 99%

Contaminant mass transfer during gas‐phase transport in unsaturated porous media

Popovičová¹,

Brusseau²

1998

Water Resources Research

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“…[200] Their 3D porous structures with high porosity and network connectivity are known to help ceramics to increase gas sensitivity and selectivity because of a multifunctional combination of hierarchical pores. In brief, macropores perform the role of transport channels for gases or materials, [259,260] mesopores act as molecular sieves and absorb materials transported by macropores, [261,262] and micropores adsorb and fix the gases or other substances inside the material. [261,263] Inspired by the structural advantages of wood templates, our group synthesized hierarchical porous ZnO with lauan and fir woods as biotemplates by using an infiltration/calcination method, and investigated the performance of the gas sensors.…”

Section: Wood-templated Gas Sensorsmentioning

confidence: 99%

Biotemplated Materials for Sustainable Energy and Environment: Current Status and Challenges

2011

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Materials science will play a key role in the further development of emerging solutions for the increasing problems of energy and environment. Materials found in nature have many inspiring structures, such as hierarchical organizations, periodic architectures, or nanostructures, that endow them with amazing functions, such as energy harvesting and conversion, antireflection, structural coloration, superhydrophobicity, and biological self-assembly. Biotemplating is an effective strategy to obtain morphology-controllable materials with structural specificity, complexity, and related unique functions. Herein, we highlight the synthesis and application of biotemplated materials for six key areas of energy and environment technologies, namely, photocatalytic hydrogen evolution, CO(2) reduction, solar cells, lithium-ion batteries, photocatalytic degradation, and gas/vapor sensing. Although the applications differ from each other, a common fundamental challenge is to realize optimum structures for improved performances. We highlight the role of four typical structures derived from biological systems exploited to optimize properties: hierarchical (porous) structures, periodic (porous) structures, hollow structures, and nanostructures. We also provide examples of using biogenic elements (e.g., C, Si, N, I, P, S) for the creation of active materials. Finally, we disscuss the challenges of achieving the desired performance for large-scale commercial applications and provide some useful prototypes from nature for the biomimetic design of new materials or systems. The emphasis is mainly focused on the structural effects and compositional utilization of biotemplated materials.

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“…Mechanical dispersion in the gas phase is not included in the model. Popovicova and Brusseau [1997] report for an experimental study of methane migration, that mechanical dispersion can be neglected, unless advective velocities are large (>288 m d…”

Section: Model Developmentmentioning

confidence: 99%

Coupling between geochemical reactions and multicomponent gas and solute transport in unsaturated media: A reactive transport modeling study

Molins

Mayer

2007

Water Resources Research

107

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[1] The two-way coupling that exists between biogeochemical reactions and vadose zone transport processes, in particular gas phase transport, determines the composition of soil gas. To explore these feedback processes quantitatively, multicomponent gas diffusion and advection are implemented into an existing reactive transport model that includes a full suite of geochemical reactions. Multicomponent gas diffusion is described on the basis of the dusty gas model, which accounts for all relevant gas diffusion mechanisms. The simulation of gas attenuation in partially saturated landfill soil covers, methane production, and oxidation in aquifers contaminated by organic compounds (e.g., an oil spill site) and pyrite oxidation in mine tailings demonstrate that both diffusive and advective gas transport can be affected by geochemical reactions. Methane oxidation in landfill covers reduces the existing upward pressure gradient, thereby decreasing the contribution of advective methane emissions to the atmosphere and enhancing the net flux of atmospheric oxygen into the soil column. At an oil spill site, methane oxidation causes a reversal in the direction of gas advection, which results in advective transport toward the zone of oxidation both from the ground surface and the deeper zone of methane production. Both diffusion and advection contribute to supply atmospheric oxygen into the subsurface, and methane emissions to the atmosphere are averted. During pyrite oxidation in mine tailings, pressure reduction in the reaction zone drives advective gas flow into the sediment column, enhancing the oxidation process. In carbonate-rich mine tailings, calcite dissolution releases carbon dioxide, which partly offsets the pressure reduction caused by O 2 consumption.Citation: Molins, S., and K. U. Mayer (2007), Coupling between geochemical reactions and multicomponent gas and solute transport in unsaturated media: A reactive transport modeling study, Water Resour. Res., 43, W05435,

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Dispersion and transport of gas-phase contaminants in dry porous media: effect of heterogeneity and gas velocity

Cited by 34 publications

References 18 publications

Contaminant mass transfer during gas‐phase transport in unsaturated porous media

Contaminant mass transfer during gas‐phase transport in unsaturated porous media

Biotemplated Materials for Sustainable Energy and Environment: Current Status and Challenges

Coupling between geochemical reactions and multicomponent gas and solute transport in unsaturated media: A reactive transport modeling study

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