| 1. |
- Poulsen, Tjalfe, et al.
(author)
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Apparent porous media gas dispersion in response to rapid pressure fluctuations
- 2011
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In: Soil science. - 0038-075X .- 1538-9243. ; 176:12, s. 635-641
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Journal article (peer-reviewed)abstract
- The impact of rapid pressure fluctuations (frequency >0.02 min−1) on gas transport in two filter sands with different gas permeability (kg) was investigated. Pressure fluctuation–induced gas transport characterized as a dispersion process governed by a pressure fluctuation–induced dispersion coefficient (Dp) was measured using a column containing the sand, connected to a membrane pump for generating pressure fluctuations. Measurements ofDp in both sands were carried out for different combinations of pressure-fluctuation amplitude (A) and frequency (f). To assess if Dp is affected by the presence of a background steady gas flux in addition to the gas movement induced by the pressure fluctuations, Dpmeasurements were carried out for different constant pore gas velocities (u). Measurements of Dp corresponding to a total of 102 combinations of u, A, f, and kg were carried out. The results showed that the value of Dp increases with increasing A, f, and kg but is independent of u. Relations between Dp and A, f, and kg were generally strong.
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| 2. |
- Sharma, Prabhakar, 1976-, et al.
(author)
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Gas Dispersion and Immobile Gas Content in Granular Porous Media: : Effect of Particle Size Nonuniformity
- 2010
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In: Soil science. - 0038-075X .- 1538-9243. ; 175:9, s. 426-431
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Journal article (peer-reviewed)abstract
- Gas dispersion is an important process often controlling gastransport in porous media. At present, however, relatively little is knownabout the relationship between gas dispersion and porous media physicalproperties. In this study, gas dispersion and mobile gas content in porousmedia were measured as a function of medium average particle diameter,particle size range, and pore gas velocity. A set of natural granular mediaconsisting of sand and gravel with uniform particle size distributionscovering average particle diameters from 0.5 to 14 mm was used. Cleansand and gravel were used to obtain media with specific particle sizedistributions via mechanical sieving. Gas dispersion and mobile gas contentwere measured by column tracer experiments using atmospheric airand nitrogen as tracer gases. Gas dispersion coefficients, gas dispersivities,and mobile gas contents were determined by fitting the advectiondispersionequation to the measured gas breakthrough curves. The resultsshowed that gas dispersivity decreased with increasing mean particle diameterand increased with increasing particle size range (width of particlesize distribution). Thus, the largest dispersivities were observed for mediawith a small mean particle diameter and a wide particle size distribution.A model concept for predicting gas dispersivity from mean particle diameterand particle size range was proposed. The mobile gas contentincreased with increasing pore gas velocity but was independent of eitherparticle size range or mean particle diameter.
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| 3. |
- Sharma, Prabhakar, 1976-, et al.
(author)
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Gas dispersion and immobile gas volume in solid and porous particle biofilter materials at low air flow velocities
- 2010
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In: Journal of the air & waste management association. - : Informa UK Limited. - 1047-3289 .- 1096-2247 .- 2162-2906. ; 60:7, s. 830-837
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Journal article (peer-reviewed)abstract
- Gas-phase dispersion in granular biofilter materials with awide range of particle sizes was investigated using atmosphericair and nitrogen as tracer gases. Two types ofmaterials were used: (1) light extended clay aggregates(LECA), consisting of highly porous particles, and (2)gravel, consisting of solid particles. LECA is a commercialmaterial that is used for insulation, as a soil conditioner,and as a carrier material in biofilters for air cleaning. Thesetwo materials were selected to have approximately thesame particle shape. Column gas transport experimentswere conducted for both materials using different meanparticle diameters, different particle size ranges, and differentgas flow velocities. Measured breakthrough curveswere modeled using the advection-dispersion equationmodified for mass transfer between mobile and immobilegas phases. The results showed that gas dispersivity increasedwith increasing mean particle diameter for LECAbut was independent of mean particle diameter for gravel.Gas dispersivity also increased with increasing particlesize range for both media. Dispersivities in LECA weregenerally higher than for gravel. The mobile gas contentin both materials increased with increasing gas flow velocitybut it did not show any strong dependency onmean particle diameter or particle size range. The relativefraction of mobile gas compared with total porosity washighest for gravel and lowest for LECA likely because of itshigh internal porosity.
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| 4. |
- Sharma, Prabhakar, 1976-, et al.
(author)
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Gas phase dispersion in compost as a function of differentwater contents and air flow rates
- 2009
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In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 107:3-4, s. 101-107
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Journal article (peer-reviewed)abstract
- Gas phase dispersion in a natural porous medium (yard waste compost) was investigated as afunction of gas flow velocity and compost volumetric water content using oxygen and nitrogenas tracer gases. The compost was chosen because it has a very wide water content range andbecause it represents a wide range of porousmedia, including soils and biofilter media. Columnbreakthrough curves for oxygen and nitrogen were measured at relatively low pore gasvelocities, corresponding to those observed in for instance soil vapor extraction systems orbiofilters for air cleaning at biogas plants or composting facilities. Total gas mechanicaldispersion–molecular diffusion coefficients were fitted from the breakthrough curves using aone-dimensional numerical solution to the advection–dispersion equation and used todetermine gas dispersivities at different volumetric gas contents. The results showed that gasmechanical dispersion dominated over molecular diffusion with mechanical dispersion for allwater contents and pore gas velocities investigated. Importance of mechanical dispersionincreased with increasing pore gas velocity and compost water content. The results furthershowed that gas dispersivity was relatively constant at high values of compost gas-filledporosity but increased with decreasing gas-filled porosity at lower values of gas-filled porosity.Results finally showed that measurement uncertainty in gas dispersivity is generally highest atlow values of pore gas velocity.
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| 5. |
- Sharma, Prabhakar, 1976-, et al.
(author)
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Gaseous Oxygen Uptake in Porous Media at Different Moisture Contents and Airflow Velocities
- 2009
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In: Journal of the Air & Waste Management Association. - : Informa UK Limited. - 1047-3289 .- 1096-2247 .- 2162-2906. ; 59:6, s. 676-682
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Journal article (peer-reviewed)abstract
- The presence and distribution of water in the pore space isa critical factor for flow and transport of gases throughunsaturated porous media. The water content also affectsthe biological activity necessary for treatment of pollutedgas streams in biofilters. In this research, microbial activityand quantity of inactive volume in a porous mediumas a function of moisture content and gas flow rate wereinvestigated. Yard waste compost was used as a test medium,and oxygen uptake rate measurements were used toquantify microbial activity and effective active compostvolume using batch and column flow-through systems.Compost water contents were varied from air-dry to fieldcapacity and gas flows ranged from 0.2 to 2 L min1. Theresults showed that overall microbial activity and therelative fraction of active compost medium volume increasedwith airflow velocity for all levels of water contentup to a certain flow rate above which the oxygen uptakerate assumed a constant value independent of gas flow.The actual value of the maximum oxygen uptake rate wascontrolled by the water content. The oxygen uptake ratealso increased with increasing water content and reacheda maximum between 42 and 48% volumetric water content,above which it decreased, again likely because offormation of inactive zones in the compost medium.Overall, maximum possible oxygen uptake rate as a functionof gas flow rate across all water contents and gas flowscould be approximated by a linear expression. The relativefraction of active volume also increased with gas flowrate and reached approximately 80% for the highest gasflows used.
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