Gas-filled Pore Research Articles

Pore development in viscoelastic foods during drying.

In this paper, we present a numerical model that can describe the pore formation/cavitation in viscoelastic food materials during drying. The food material has been idealized as a spherical object, with a core/shell structure and a central gas-filled cavity. The shell represents a skin as present in fruits/vegetables, having a higher elastic modulus than the tissue, which we approximate as a hydrogel. The gas-filled pore is in equilibrium with the core hydrogel material, and it represents pores in food tissues as present in intercellular junctions. The presence of a rigid skin is a known prerequisite for cavitation (inflation of the pore) during drying. For modeling, we follow the framework of Suo and coworkers, describing the inhomogeneous large deformation of soft materials like hydrogels - where stresses couple back to moisture transport. In this paper, we have extended such models with energy transport and viscoelasticity, as foods are viscoelastic materials, which are commonly heated during their drying. To approach the realistic properties of food materials we have made viscoelastic relaxation times a function of Tg/T, the ratio of (moisture dependent) glass transition temperature and actual product temperature. We clearly show that pore inflation only occurs if the skin gets into a glassy state, as has been observed during the (spray) drying of droplets of soft materials like foods.

Effectiveness and characteristics of atmospheric CO2 removal in croplands via enhanced weathering of industrial Ca-rich silicate byproducts

Enhanced weathering of industrial Ca-rich silicate byproducts in croplands is potentially profitable for large-scale atmospheric CO2 removal; during the weathering process, CO2 dissolves to form HCO3− and CO32− in alkaline soil pore water, which eventually flows into the ocean. However, the effectiveness of such systems is still in doubt, owing to the unrealistic models used for prediction and the insufficient consideration of the dynamic influences of soils on fluid chemistry. We determined the effectiveness of such systems for atmospheric CO2 removal, along with their characteristics, through a set of batch- and flow-through-type laboratory experiments, using andosol and decomposed granite soil as agricultural and non-agricultural soils, respectively, and Portland cement, steelmaking slag, and coal fly ash as industrial byproducts. The results of the batch-type experiments demonstrated that agricultural soils were suitable for CO2 removal, owing to their moderately high pH and Ca concentrations in pore water that prevented intensive calcium carbonate precipitation. The flow-through experiments demonstrated that a higher Ca-content byproduct can have a large atmospheric CO2 removal capacity. However, the magnitude of CO2 removal and its time-dependent behavior were difficult to predict because they were not in conjunction with the changes in the average pH value. This indicated that the diffusive transport of CO2 from the atmosphere-soil interface to deeper soils was more complex than expected. Maximizing CO2 removal requires a better understanding of the diffusive transport of CO2 through gas-filled pore spaces, created by unsteady-state air–water two-phase flow, due to intermittent rainfall.

Spatiotemporal variation in upper crustal seismic anisotropy and VP/VS ratio in Groningen gas field, Netherlands: insights from shear wave splitting

SUMMARY We investigated pore fluid characteristics of reservoir at the Groningen gas field, Netherlands using seismic anisotropy from shear wave splitting. We obtained 663 high-quality splitting parameters, such as delay time (δt) and fast-axis direction (φ), from local induced earthquakes that occurred during 2014–2020. We then conducted δt tomography and spatial averaging of φ to probe the spatiotemporal changes in the parameters. Our results demonstrate that crustal anisotropy in Groningen is closely related to changes in fluid flow and compaction of the reservoir. Low anisotropy strength (normalized delay time, δtn) was detected near shut-in wells where considerable reservoir compaction has occurred, whereas high anisotropy strength occurred near operating wells with less compaction. The temporal variation in δtn further shows that the long-term trend is distinctly different between the shut-in and production wells: while δtn near the shut-in wells remained nearly constant at <6 ms km–1 during the entire period, δtn near the operating wells notably showed high values exceeding 10 ms km–1 in 2015 and a decreasing trend until 2017. In addition to this long-term variation, short-term δtn variation was observed, which can be related to fluid flow perturbations owing to seasonal gas production fluctuations. The φ values along the NNW–SSE, WNW–ESE and E–W directions could be related to not only the in situ maximum horizontal stress direction but also the gas flow direction near the extraction wells. The observed negative relationship between the spatial distribution of P-to-S velocity ratio and the anisotropy strength can potentially indicate that gas-filled pore spaces are dominant in the reservoir.

DIFFUSION EVOLUTION OF A PORE IN BOUNDED PARTICLE IN A HYDROGEN ATMOSPHERE

The problem of the diffusion evolution of a pore filled with molecular hydrogen in a spherical granule in a hydrogen medium is solved. The initial position of the pore is displaced relative to the center of the granule. A nonlinear system of equations is obtained, which describes the behavior of the size of the gas-filled pore, the amount of gas in it and its position relative to the center of the bounded particle with time. Numerical calculations have shown the existence of two stages of evolution. The first (fast) stage is associated with the equalization of pressure in the pore with the external. The second is the slow diffusion “healing” of the pore, when the amount of gas adjusts to its size and the gas pressure is approximately equal to the external.

Capillary Bundle Model for the Estimation of Air-water Interfacial Area and the Gas-filled Pore Size Distribution in Unsaturated Soil

Capillary Bundle Model for the Estimation of Air-water Interfacial Area and the Gas-filled Pore Size Distribution in Unsaturated Soil

Gas-filled pore in bounded particle

The diffusive evolution has been studied of gas-filled pore has in a bounded particle in gas media. The nonlinear equation set, describing the behaviour of gas-filled pore on bounded particle is obtained. Asymptotic modes are considered for evolution of small and large pores. Analytical solutions are obtained in asymptotic modes. The comparison is conducted of these solutions with results of numerical solution of complete equation set. The characteristic regularities of gas-filled pore behavior are found at arbitrary pore position relative to matrix particle center.

Efficiency of single-well geothermal systems with multi-lateral drills

Drilling costs, induced seismicity, scaling and corrosion, emissions, and assessment of the inherent uncertainty associated with the reservoir properties for long-term sustainable provision of thermal energy are the major challenges of deep geothermal systems. In particular, the cost of drilling typically comprises 50–70 % of the total capital investment of a geothermal power plant. As drilling costs are definitive for the accomplishment of deep geothermal systems, the concept to use one single drill hole for extraction and injection is arisen to reduce the overall drilling costs. The aim of this study is to overcome some simplifications made in the previous published studies to investigate such single-well systems in more detail and further resolve the governing physical processes. Focus of the study is on reservoirs with a low natural permeability (around 10−14 m2). Firstly, an analytical solution is applied for justifying the numerical approach to produce consistent results for the presented simplest single-well design. Secondly, the efficiency of different single-well concepts is investigated via sensitivity analysis of variations in reservoir and operational parameters. Lastly, the previous study results are compared with the current approach for the gas-filled porous medium application. The results for the single-well system either with multi-laterals or without laterals demonstrate that the variation of permeability in different directions and the porosity play a crucial role on the overall performance. Single-well systems with multi-laterals are efficient, if the permeability is isotropic and in a range between 1 × 10−14 and 1 × 10-12 m2. The results of gas-filled pore space applications show that the capillary entry pressure has a significant impact on the wetting phase saturation. Simultaneous injection and extraction affect the saturation and heat exchange localized around the wells which decreases the thermal output power.

Toward a mechanistic understanding of "peat collapse" and its potential contribution to coastal wetland loss.

Coastal wetlands are susceptible to loss in both health and extent via stressors associated with global climate change and anthropogenic disturbance. Peat collapse may represent an additional phenomenon contributing to coastal wetland loss in organic‐rich soils through rapid vertical elevation decline. However, the term “peat collapse” has been inconsistently used in the literature, leading to ambiguities regarding the mechanisms, timing, and spatial extent of its contribution to coastal wetland loss. For example, it is unclear whether peat collapse is distinct from general subsidence, or what biogeochemical changes or sequence of events may constitute peat collapse. A critical analysis of peer‐reviewed literature related to peat collapse was supplemented with fundamental principles of soil physics and biogeochemistry to develop a conceptual framework for coastal wetland peat collapse. We propose that coastal wetland peat collapse is a specific type of shallow subsidence unique to highly organic soils in which a loss of soil strength and structural integrity contributes to a decline in elevation, over the course of a few months to a few years, below the lower limit for emergent plant growth and natural recovery. We further posit that coastal wetland peat collapse is driven by severe stress or death of the vegetation, which compromises the supportive structure roots provide to low‐density organic soils and shifts the carbon balance of the ecosystem toward a net source, as mineralization is no longer offset by sequestration. Under these conditions, four mechanisms may contribute to peat collapse: (1) compression of gas‐filled pore spaces within the soil during dry‐down conditions; (2) deconsolidation of excessively waterlogged peat, followed by transport; (3) compaction of aerenchyma tissue in wetland plant roots, and possibly collapse of root channels; and (4) acceleration of soil mineralization due to the addition of labile carbon (dying roots), oxygen (decreased flooding), nutrients (eutrophication), or sulfate (saltwater intrusion). Scientists and land managers should focus efforts on monitoring vegetation health across the coastal landscape as an indicator for peat collapse vulnerability and move toward codifying the term “peat collapse” in the scientific literature. Once clarified, the contribution of peat collapse to coastal wetland loss can be evaluated.

Variability in methane emissions from West Siberia's shallow boreal lakes on a regional scale and its environmental controls

Abstract. Small lakes represent an important source of atmospheric CH4 from northern wetlands. However, spatiotemporal variations in flux magnitudes and the lack of knowledge about their main environmental controls contribute large uncertainty into the global CH4 budget. In this study, we measured methane fluxes from small lakes using chambers and bubble traps. Field investigations were carried out in July–August 2014 within the West Siberian middle and southern taiga zones. The average and median of measured methane chamber fluxes were 0.32 and 0.30 mgCH4 m−2 h−1 for middle taiga lakes and 8.6 and 4.1 mgCH4 m−2 h−1 for southern taiga lakes, respectively. Pronounced flux variability was found during measurements on individual lakes, between individual lakes and between zones. To analyze these differences and the influences of environmental controls, we developed a new dynamic process-based model. It shows good performance with emission rates from the southern taiga lakes and poor performance for individual lakes in the middle taiga region. The model shows that, in addition to well-known controls such as temperature, pH and lake depth, there are significant variations in the maximal methane production potential between these climatic zones. In addition, the model shows that variations in gas-filled pore space in lake sediments are capable of controlling the total methane emissions from individual lakes. The CH4 emissions exhibited distinct zonal differences not only in absolute values but also in their probability density functions: the middle taiga lake fluxes were best described by a lognormal distribution while the southern taiga lakes followed a power-law distribution. The latter suggests applicability of self-organized criticality theory for methane emissions from the southern taiga zone, which could help to explain the strong variability within individual lakes.

Behavior models of gas-filled pores in amorphous and crystalline bodies

A mathematical model of the behavior of an isolated gas-filled pore in amorphous and crystalline bodies is presented. The balance of surface tension forces, the external pressure, and gas pressure in the pore, which affect the pore, is laid at the basis of the variation in the pore size and gas pressure in it. A qualitative analysis of distinctions in the behavior of the pore in amorphous and crystalline bodies is performed, and a set of differential equations that describe the pore behavior in both cases is analyzed. The proposed model of behavior of the gas-filled pore in an infinite space can serve as the basis for the analysis of more complex cases.

Greens tensor of a weakly anisotropic cubic crystal: Efficiency of point defect absorption by spherical pore

Using the Lifshitz-Rozentsveig method, an improved expression for the Green tensor in the case of a weakly anisotropic cubic crystal has been derived. It contains a number of additional terms disregard previously. An expression for the energy of elastic interaction of a point defect with a gas-filled pore, which differs from its analogue (commonly used referring to Eshelby) by an additional factor in the radial part, has been derived. In the case of weak interaction (in comparison with thermal energy), a correction to the efficiency of point defect absorption by a gas-filled pore is obtained, which appears quadratic in the anisotropy parameter and negative. As a result, the pore exhibits preference for absorption of vacancies in comparison with absorption of interstitials.

Quantifying Factors Limiting Aerobic Degradation During Aerobic Bioreactor Landfilling

A bioreactor landfill cell at Yolo County, California was operated aerobically for six months to quantify the extent of aerobic degradation and mechanisms limiting aerobic activity during air injection and liquid addition. The portion of the solid waste degraded anaerobically was estimated and tracked through time. From an analysis of in situ aerobic respiration and gas tracer data, it was found that a large fraction of the gas-filled pore space was in immobile zones where it was difficult to maintain aerobic conditions, even at relatively moderate landfill cell-average moisture contents of 33-36%. Even with the intentional injection of air, anaerobic activity was never less than 13%, and sometimes exceeded 65%. Analyses of gas tracer and respiration data were used to quantify rates of respiration and rates of mass transfer to immobile gas zones. The similarity of these rates indicated that waste degradation was influenced significantly by rates of oxygen transfer to immobile gas zones, which comprised 32-92% of the gas-filled pore space. Gas tracer tests might be useful for estimating the size of the mobile/immobile gas zones, rates of mass transfer between these regions, and the difficulty of degrading waste aerobically in particular waste bodies.

Gas permeability and tortuosity for packed layers of processed municipal solid wastes and incinerator residue.

To make a proper evaluation of gas component movement inside a landfill site, it is important to investigate the different parameters related to gas flow. In this work gas-filled porosity, intrinsic permeability, tortuosity and equivalent pore radius were determined for various packed wastes, such as incineration ash, shredded bulky waste and shredded incombustible waste. These parameters were measured/inferred for samples packed in a column and exposed to a controlled gas flow. The effect of waste conditions, especially the moisture content, on these parameters was also investigated. The intrinsic permeability of such packed wastes was generally in the order of 10(-10) to 10(-9) m2, except for some ash that was one to two orders lower. The tortuosity of waste layer was greater than that of a particulate material and ranged between 2 and 10. The equivalent pore radius was generally in the order of 10(-4) m, which means that gas diffusion is still ordinary in such packed waste layer. The obtained results will be utilized when simulating gas flow inside a landfill site for biogas extraction or site aeration.

Generation of Highly Ozonized Water Using a Microporous Hollow Fiber Module

The generation of an environmentally friendly and highly ozonized water has been investigated. This was achieved by contacting highly concentrated ozone gas and water through a microporous hollow fibers module. According to the experimental results, it was observed that the ozone mass transfer in this system was controlled by the liquid phase. The maximum gradient approach was then used to model the ozone transfer within the module in both wetted and non-wetted modes. The corresponding validity was checked through the agreement between our experimental results and the calculated results under the gas-filled pore assumption. Furthermore, this model was used for a parameter study, and revealed that the connection of modules in series was more effective than that in parallel for the production of highly ozonized water.

Carbon-dioxide exchange in lichens: determination of transport and carboxylation characteristics

Measurements were made of net rates of CO2 assimilation in lichens at various ambient concentrations of CO2 in air and in helox (79% He, 21% O2). Because of the faster rate of CO2 diffusion in the pores of lichen thalli when filled with helox than when filled with air, a given net rate of assimilation was achieved at a lower ambient concentration of CO2 in helox. The differences were used to estimate resistances to diffusion through the gas-filled pore systems in lichens. The technique was first tested with five lichen species, and then applied in a detailed study with Ramalina maciformis, in which gas-phase resistances were determined in samples at four different states of hydration and with two irradiances. By assuming, on the basis of previous evidence, that the phycobiont in R. maciformis is fully turgid and photosynthetically competent at the smallest hydration imposed (equilibration with vapour at 97% relative humidity), and that, with this state of hydration, diffusion of CO2 to the phycobiont takes place through continuously gas-filled pores, it was possible also to determine both the dependence of net rate of assimilation in the phycobiont on local concentration of CO2 in the algal layer, and, with the wetter samples, the extents to which diffusion of CO2 to the phycobiont was impeded by water films. In equilibrium with air of 97% relative humidity, the thallus water content being 0.5 g per g dry weight, the resistance to CO2 diffusion through the thallus was about twice as large as the resistance to CO2 uptake within the phycobiont. Total resistance to diffusion increased rapidly with increase in hydration. At a water content of 2 g per g it was about 50 times as great as the resistance to uptake within the phycobiont and more than two-thirds of it was attributable to impedance of transfer by water. The influences of water content on rate of assimilation at various irradiances are discussed. The analysis shows that the local CO2 compensation concentration of the phycobiont in R. maciformis is close to zero, indicating that photorespiratory release of CO2 does not take place in the alga, Trebouxia sp., under the conditions of these experiments.

Influence of matric potential and soil compaction on growth of the take-all fungus through soil

Growth responses of the take-all fungus, Gaeumannomyces graminis var. tritici , to matric potentials between zero and −0.01 MPa were investigated. Growth was influenced by soil compaction. The range of matric potentials over which the fungus grew well was restricted with increasing bulk density. In soil near saturation, when total gas-filled pore space (GFP) was less than 0.08 cm 3 air cm −3 soil, no growth occurred at any level of compaction, probably because oxygen became limiting. Above GFP 0.27 cm 3 air cm −3 soil, differences in growth due to compaction could not be distinguished. It is argued that, when total GFP was in the range 0.08–0.27 cm 3 air cm −3 soil, the size distribution and number of GFPs are primarily responsible for the differences in growth observed at different levels of compaction. These observations have implications for predicting the impact of changing tillage practice on disease severity.

Theoretical investigation of the response of gas-filled micropores and cavitation nuclei to ultrasound

Theory is discussed for the transverse oscillation of a small circular interface set into a rigid baffle between gas and liquid. The angular resonance frequency is given by (15πT/4ρa3)1/2, in which a is the radius of the interface, T is the interfacial surface tension, and ρ is the density of the liquid. Damping parameters are obtained for the radiation, viscous, and boundary-layer mechanisms of dissipation. This model system is extended for discussion of the pulsation of gas trapped in a pit or cavity in a solid, which may simulate one type of cavitation nucleus, and straight-through cylindrical holes or pores in a solid sheet, which is applicable to the hydrophobic membranes with gas-trapping micropores used in studies of biological effects produced by ultrasound. Fixed and free conditions at the three-phase line at the periphery of an interface are considered. Finally, the partially gas-filled cavity is treated, and also the partially gas-filled pore with two interfaces which have different mass, stiffness, and damping parameters. The results of these theoretical considerations are expected to be of value for quantitatively evaluating that specific form of stable cavitation which involves the direct activation of pre-existing, stable bodies of gas into ultrasonic pulsation, as experimentally observed, for example, by D. Miller, J. Acoust. Soc. Am. 71, 471–476 (1982).

Determining Gas-Filled Pore Volume in a Water-Drive Gas-Storage Reservoir

Introduction The increased importance of underground natural gas storage as a means of solving marketing problems has dictated that engineering attention be directed to the study of storage-field behavior. As a result, considerable effort has been expended by various researchers in attempts to determine methods by which the behavior of depleted producing gas fields subject to water flux and utilized for storage could be described and predicted. One of the most extensive recent efforts in this area has resulted in the monograph, "Movement of Underground Water in Contact with Natural Gas".This paper, using as background much of the material presented in the monograph, explores the determination of gas-filled pore volume. This includes the initial, or discovery gas-filled pore volume, as well as the pore volume at any time during the field's history. Comparison of the initial and the gas-filled pore volume at some later date indicates growth of the gas bubble. The term gas bubble will be used to denote the gas-filled pore volume. The need for additional storage capacity frequently leads to storage of gas at pressures exceeding the reservoir discovery pressure. Under these conditions the gas bubble grows in size. Because there is always some safe limit of gas bubble size, knowledge of its size at any time is desirable. The ability to reliably predict gas-bubble growth from a postulated gas-in-place schedule is of considerable value when evaluating possible storage programs. An efficient and effective method for determining values of the factors governing water movement and field behavior is required. In this paper a material balance as the equation of a straight line has been utilized to evaluate these factors, which include initial gas-bubble size. This general procedure is not new, and discussions of several approaches using the linearity of the material balance to determine the factors governing the behavior of waterdrive oil and gas reservoirs are found in the literature. However, the use of the form of linear material balance equation presented here, to the authors' knowledge, has not been previously reported and will be shown to be a comprehensive and instructive procedure for determining the necessary factors. This method provides for the determination of two of the four factors simultaneously, and implicitly for values of the other two. Selection of optimized values for the factors utilizes as a criterion the minimum deviation between calculated and observed field pressures. Once the factors influencing reservoir behavior have been determined, they may be used with a gas injection-withdrawal schedule to calculate reservoir pressure and gas-filled pore volume behavior resulting from past or future storage operations. Discussion Material Balance Applied to Storage ReservoirsA common procedure used in an attempt to describe and predict the behavior of a petroleum reservoir is the material balance, which in its most general form relates the amount of material remaining in the reservoir to the amount originally present, less the amount produced from the reservoir. JPT P. 383ˆ