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Berlin Brandenburg

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  • 1
    Language: English
    In: Journal of Colloid And Interface Science, Dec 1, 2015, Vol.459, p.230(11)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jcis.2015.07.074 Byline: Helmut Geistlinger, Iman Ataei-Dadavi Abstract: Display Omitted Article History: Received 18 May 2015; Revised 23 July 2015; Accepted 31 July 2015
    Keywords: Monomolecular Films – Analysis
    ISSN: 0021-9797
    Source: Cengage Learning, Inc.
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  • 2
    Language: English
    In: Journal of Colloid And Interface Science, 01 December 2015, Vol.459, pp.230-240
    Description: We demonstrated that a change in the surface chemistry, i.e., a change from heterogeneous to homogeneous wettability, can dramatically influence capillary trapping, i.e., from significant trapping (∼5%) to no trapping. Furthermore, the displacement process (water displaces air) in glass-beads monolayer with heterogeneous wettability shows (i) a heterogeneous morphology and a stochastic advancement of the interface in the highly ordered structure, (ii) capillary trapping of a broad variety of gas clusters, notably large ganglia-like and network-like gas clusters, and (iii) a variation in the contact angle between 30° and 100°. In the second part of this paper, we compared the experimental results of capillary trapping for the monolayer that possesses a heterogeneous wettability with predictions from the invasion percolation theory and found excellent agreement, e.g., that the experimental cluster size distribution can be described by a universal power-law with an averaged exponent = 2.06; that is a deviation of 5% from the theoretical value. This agreement indicates that capillary trapping within the 2D-monolayer is governed by the 3D critical exponent; therefore, the monolayer shows a trapping behavior similar to a 3D-porous media. We proposed an analytical approach to calculate the mass transfer rate constant using functional relationships predicted by percolation theory and compare this result with results derived from empirical relationships, which are often used for modelling the dissolution process of trapped non-wetting phases.
    Keywords: Glass Beads Monolayer ; Heterogeneous Wettability ; Capillary Trapping ; Pore-Scale Model ; Invasion Percolation Theory ; Universal Scaling Law ; Dissolution Trapping ; Mass Transfer Rate ; Engineering ; Chemistry
    ISSN: 0021-9797
    E-ISSN: 1095-7103
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  • 3
    Language: English
    In: Advances in Water Resources, 2015, Vol.79, p.35(16)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.advwatres.2015.02.010 Byline: Helmut Geistlinger, Sadjad Mohammadian Abstract: * We studied capillary trapping in strongly water wet systems by [mu]-CT. * Percolation theory explains our key experimental results for Ca 〈10.sup.-6. * Universal power law of the renormalized cluster-size distribution. * Flow rate independence of the trapping efficiency. * Impact of buoyancy on the maximal cluster size. Article History: Received 6 August 2014; Revised 13 February 2015; Accepted 16 February 2015
    ISSN: 0309-1708
    Source: Cengage Learning, Inc.
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  • 4
    Language: English
    In: Transport in Porous Media, 2016, Vol.112(1), pp.207-227
    Description: According to experimental observations, capillary trapping is strongly dependent on the roughness of the pore–solid interface. We performed imbibition experiments in the range of capillary numbers ( Ca ) from $$10^{-6}$$ 10 - 6 to $$5\times 10^{-5}$$ 5 × 10 - 5 using 2D-micromodels, which exhibit a rough surface. The microstructure comprises a double-porosity structure with pronounced macropores. The dynamics of precursor thin-film flow and its importance for capillary trapping are studied. The experimental data for thin-film flow advancement show a square-root time dependence. Based on the experimental data, we conducted inverse modeling to investigate the influence of surface roughness on the dynamic contact angle of precursor thin-film flow. Our experimental results show that trapped gas saturation decreases logarithmically with an increasing capillary number. Cluster analysis shows that the morphology and number of trapped clusters change with capillary number. We demonstrate that capillary trapping shows significant differences for vertical flow and horizontal flow. We found that our experimental results agree with theoretical results of percolation theory for $$Ca =10^{-6}$$ C a = 10 - 6 : (i) a universal power-like cluster size distribution, (ii) the linear surface–volume relationship of trapped clusters, and (iii) the existence of the cutoff correlation length for the maximal cluster height. The good agreement is a strong argument that the experimental cluster size distribution is caused by a percolation-like trapping process (ordinary percolation). For the first time, it is demonstrated experimentally that the transition zone model proposed by Wilkinson (Phys Rev A 30:520–531, 1984) can be applied to 2D-micromodels, if bicontinuity is generalized such that it holds for the thin-film water phase and the bulk gas phase.
    Keywords: 2D-micromodel with rough surface ; Precursor thin-film flow ; Snap-off trapping ; Universal power law ; Ordinary bond percolation
    ISSN: 0169-3913
    E-ISSN: 1573-1634
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  • 5
    Language: English
    In: Vadose Zone Journal, 01 October 2018, Vol.17(1)
    Description: Evaporation—a key process for water exchange between soil and atmosphere—is controlled by convective and diffusive surface fluxes that determine the functional time dependence of the evaporation rate (). Recent studies demonstrated that only a pore-scale surface flux model can capture the correct () curve. These studies also showed that a realistic estimate of the hydraulically connected region (HCR) of the pore-size distribution (PSD) is crucial for coupling surface flux to internal water flux. Since previous studies were often based on natural sands and glass beads, the main focus of our study was to test these conclusions for real soils. Therefore, we investigated the evaporation process within undisturbed soil columns of a sandy soil and loamy sand and measured the hydraulic functions via HYPROP experiments (a system to measure hydraulic properties using the evaporation method). Based on the isolated pore evaporation (IPE) model using a discretized form of the PSD, we developed a continuous IPE model and applied it to our experiments. Because the PSD plays a central role in the IPE model, we determined the PSD of the loamy sand soil via X-ray microtomography (μCT) for pores 〉19 μm. The consistency of the experimental data, i.e., (i) the retention curve for deriving the HCR of the pore size distribution, (ii) the unsaturated hydraulic conductivity for calculating the characteristic lengths of the evaporation process, and (iii) the high accuracy of the mass loss data strongly support the HYPROP method for this kind of complex evaporation experiment. The continuous IPE model describes the characteristic Stage 1 behavior well (functional form of the evaporation rate and length of Stage 1) for both soil types if a realistic HCR estimate is used that (i) is derived from a characteristic length analysis estimating the lower boundary of the HCR and (ii) the upper range of the HCR is based on the true PSD derived from μCT data.
    Keywords: Agriculture
    ISSN: 1539-1663
    E-ISSN: 1539-1663
    Source: Directory of Open Access Journals (DOAJ)
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  • 6
    Language: English
    In: Advances in Water Resources, May 2015, Vol.79, pp.35-50
    Description: To understand capillary trapping mechanism, we conduct a real Monte-Carlo experiment by using packed glass beads with nearly the same pore size distribution, but different stochastic realizations. We study gas phase trapping during imbibition for capillary numbers from 2 × 10 to 10 using X-ray micro tomography and compare the experimental results with predictions from percolation theory. We found excellent agreement. Percolation theory explains (i) that the capillary desaturation curves are not dependent on flow rate, (ii) the linear dependence of the total gas surface on gas saturation that is a direct consequence of the linear relationship between cluster surface area and cluster volume, which is a prediction from percolation theory for large finite clusters, (iii) the power-like cluster size distribution with an exponent = 2.15 that only deviates by 2% from the theoretical one ( = 2.19), and (iv) that the maximal -extension of trapped large gas cluster is described by the cut-off correlation length ( – bond number).
    Keywords: Capillary Trapping ; Thin-Film Flow ; Trapped Gas Cluster ; X-Ray Micro Computer Tomography ; Monte-Carlo Experiment ; Percolation Theory ; Engineering
    ISSN: 0309-1708
    E-ISSN: 1872-9657
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  • 7
    In: Water Resources Research, May 2014, Vol.50(5), pp.4514-4529
    Description: A major difficulty in modeling multiphase flow in porous media is the emergence of trapped phases. Our experiments demonstrate that gas can be trapped in either single‐pores, multipores, or in large connected networks. These large connected clusters can comprise up to eight grain volumes and can contain up to 50% of the whole trapped gas volume. About 85% of the gas volume is trapped by gas clusters. This variety of possible trapped gas clusters of different shape and volume will lead to a better process understanding of bubble‐mediated mass transfer. Since multipore gas bubbles are in contact with the solid surface through ultrathin adsorbed water films the interfacial area between trapped gas clusters and intergranular capillary water is only about 80% of the total gas surface. We could derive a significant (R = 0.98) linear relationship between the gas‐water‐interface and gas saturation. We found no systematic dependency of the front velocity of the invading water phase in the velocity range from 0.1 to 0.6 cm/min corresponding to capillary numbers from 2 × 10 to 10. Our experimental results indicate that the capillary trapping mechanism is controlled by the local pore structure and local connectivity and not by thermodynamics, i.e., by the minimum of the , at least in the considered velocity range. Consistent with this physical picture is our finding that the trapping frequency (= bubble‐size distribution) reflects the pore size distribution for the whole range of pore radii, i.e., the capillary trapping process is determined by statistics and not by thermodynamics. No systematic dependency of trapping efficiency on capillary number Majority of trapped gas bubbles (85%) are multipore trapped Trapping of gas clusters is determined by statistics and not by thermodynamics
    Keywords: Gas Clusters ; Capillary Trapping ; Interfacial Area
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 8
    Language: English
    In: Vadose Zone Journal, 2015, Vol.14(5), p.0
    Description: We used X-ray computed microtomography to study gas trapping in a fluctuating water table. Our results show that capillary forces control trapping and phase distribution in dynamic capillary fringes. In porous media, the nonwetting phase is trapped on water saturation due to capillary forces acting in a heterogeneous porous structure. Within the capillary fringe, the gas phase is trapped and released along with the fluctuation of the water table, creating a highly active zone for biological transformations and mass transport. We conducted column experiments to observe and quantify the magnitude and structure of the trapped gas phase at the pore scale using computed microtomography. Different grain size distributions of glass beads were used to study the effect of the pore structure on trapping at various capillary numbers. Viscous forces were found to have negligible impact on phase trapping compared with capillary and buoyancy forces. Residual gas saturations ranged from 0.5 to 10%, while residual saturation increased with decreasing grain size. The gas phase was trapped by snap-off in single pores but also in pore clusters, while this single-pore trapping was dominant for grains larger than 1 mm in diameter. Gas surface area was found to increase linearly with increasing gas volume and with decreasing grain size.
    Keywords: Grain Size ; Water Table ; Mass Transport ; Buoyancy ; Pores ; Porous Media ; Particle Size ; Water Table ; Saturation ; Vadose Water ; Fluctuations ; Trapping ; Buoyancy ; Methods and Instruments ; General;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 9
    Language: English
    In: Sensors & Actuators: B. Chemical, 1994, Vol.18(1), pp.125-131
    Keywords: Engineering
    ISSN: 0925-4005
    E-ISSN: 1873-3077
    Source: ScienceDirect Journals (Elsevier)
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  • 10
    Language: English
    In: Sensors & Actuators: B. Chemical, 1993, Vol.14(1), pp.685-686
    Keywords: Engineering
    ISSN: 0925-4005
    E-ISSN: 1873-3077
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