An intercomparison of the pore network to the Navier–Stokes modeling approach applied for saturated conductivity estimation from X-ray CT images

AbstractDifferent modeling techniques can be used to estimate the saturated conductivity of a porous medium based on computed tomography (CT) images. In this research, two methods are intercompared: direct modeling using the Navier–Stokes (NS) approach and simplified geometry pore network (PN) modeling. Both modeling approaches rely on pore media geometry which was determined using an X-ray CT scans with voxel size 2 μm. An estimate of the saturated conductivity using both methods was calculated for 20 samples prepared from sand with diverse particle size distributions. PN-estimated saturated conductivity was found to be statistically equivalent to the NS-determined saturated conductivity values. The average value of the ratio of the PN-determined conductivity to the NS-determined conductivity (KsatPN/NS) was equal to 0.927. In addition to the NS and PN modeling approaches, a simple Kozeny-Carman (KC) equation-based estimate was made. The comparison showed that the KC estimate overestimated saturated conductivity by more than double (2.624) the NS estimate. A relationship was observed between the porous media specific surface and the KsatPN/NS ratio. The tortuosity of analyzed samples was estimated, the correlation between the porous media tortuosity and the specific surface of the samples was observed. In case of NS modelling approach the difference between pore media total porosity and total porosity of meshes, which were lower, generated for simulations were observed. The average value of the differences between them was 0.01. The method of NS saturated conductivity error estimation related to pore media porosity underestimation by numerical meshes was proposed. The error was on the average 10% for analyzed samples. The minimum value of the error was 4.6% and maximum 19%.

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Pore morphology of polar firn around closure revealed by X-ray tomography

10.5194/tc-2018-14 ◽

2018 ◽

Author(s):

Alexis Burr ◽

Clément Ballot ◽

Pierre Lhuissier ◽

Patricia Martinerie ◽

Christophe L. Martin ◽

...

Keyword(s):

Sample Size ◽

Morphological Evolution ◽

Total Porosity ◽

Pore Network ◽

Geometrical Parameters ◽

Age Difference ◽

X Ray ◽

Porosity Ratio ◽

Pore Closure ◽

Lock In

Abstract. Understanding the slow densification process of polar firn into ice is essential in order to constrain the age difference between the ice matrix and entrapped gases. The progressive microstructure evolution of the firn column with depth leads to pore closure and gas entrapment. Air transport models in the firn usually include a closed porosity profile based on available data. Pycnometry or melting-refreezing techniques have been used to obtain the ratio of closed to total porosity and air content in closed pores, respectively. X-ray computed tomography is complementary to these methods, as it enables to obtain the full pore network in 3D. This study takes advantage of this non-destructive technique to discuss the morphological evolution of pores on four different Antarctic sites. The computation of refined geometrical parameters for the very cold polar sites Dome C and Lock In (the two Antarctic plateau sites studied here) provides new information that could be used in further studies. The comparison of these two sites shows a more tortuous pore network at Lock In than at Dome C which should result in older gas ages in deep firn. A comprehensive estimation of the different errors related to X-ray tomography and to the sample variability has been performed. The procedure described here may be used as a guideline for further experimental characterization on firn samples. We show that the closed to total porosity ratio, which is classically used for the detection of pore closure, is strongly affected by the sample size, the image reconstruction and by spatial heterogeneities. In this work, we introduce an alternative parameter, the connectivity index, which is practically independent on sample size and image acquisition conditions, and that accurately predicts the close-off depth and density. Its strength also lies in its simple computation, without any assumption on the pore status (open or close). The close-off prediction is obtained for Dome C and Lock In, without any further numerical simulations on images (e.g. by permeability or diffusivity calculations).

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Comparison of the Biological and Chemical Synthesis of Schwertmannite at a Consistent Fe2+ Oxidation Efficiency and the Effect of Extracellular Polymeric Substances of Acidithiobacillus ferrooxidans on Biomineralization

Materials ◽

10.3390/ma11091739 ◽

2018 ◽

Vol 11 (9) ◽

pp. 1739 ◽

Cited By ~ 6

Author(s):

Yongwei Song ◽

Yelin Liu ◽

Heru Wang

Keyword(s):

Specific Surface ◽

Surface Area ◽

Specific Surface Area ◽

Acidithiobacillus Ferrooxidans ◽

Extracellular Polymeric Substances ◽

Shell Shape ◽

X Ray ◽

Removal Capacity ◽

The Difference ◽

Oxidation Efficiency

Schwertmannite is an environmental mineral material that can promote the natural passivation of heavy metal elements, thereby reducing environmental pollution from toxic elements. However, the fundamental reason for the difference between the chemically (H2O2-FeSO4) and biologically (Acidithiobacillus ferrooxidans-FeSO4) synthesized schwertmannite is still unclear. In this study, X-ray diffraction, scanning electron microscopy, the Brunauer–Emmett–Teller method, and X-ray fluorescence spectrometry were used to compare the structure, specific surface area, and elemental composition of schwertmannite synthesized by biological and chemical methods. The removal capacity of As(III) by the two kinds of schwertmannite and the effects of extracellular polymeric substances (EPS) on biogenetic schwertmannite were also investigated. At a consistent Fe2+ oxidation efficiency, the chemical method synthesized more schwertmannite than the biological method over a 60-h period. The biosynthesized schwertmannite had a “chestnut shell” shape, with a larger particle size and specific surface than the chemically synthesized schwertmannite, which was relatively smooth. The saturated adsorption capacities of the biologically and chemically synthesized schwertmannite were 117.0 and 87.0 mg·g−1, respectively. After exfoliation of the EPS from A. ferrooxidans, the biosynthesized schwertmannite displayed a “wool ball” shape, with rough particle surfaces, many microporous structures, and a larger specific surface area. The schwertmannite yield also increased by about 45% compared with that before exfoliation, suggesting that the secretion of EPS by A. ferrooxidans can inhibit the formation of schwertmannite.

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Investigating hydrogel potentialities for improving soil pore network by using X-ray computed microtomography

10.5194/egusphere-egu2020-9985 ◽

2020 ◽

Author(s):

Ilaria Piccoli ◽

Pozza Sara ◽

Carlo Camarotto ◽

Andrea Squartini ◽

Giacomo Guerrini ◽

...

Keyword(s):

Water Saturation ◽

Food Additives ◽

Total Porosity ◽

Pore Network ◽

Future Research ◽

High Water Content ◽

Swelling Properties ◽

X Ray ◽

Computed Microtomography ◽

X Ray Computed

<p>Hydrogels (HGs) are conventionally defined as a natural or synthetic polymeric 3D networks with high hygroscopicity and water-swelling properties. Over the decades, HGs have been widely utilized in various fields of cosmetics, food additives, tissue engineering, drug delivery, and pharmaceuticals. Only recently HGs have been studied also for agronomic purpose. Indeed, their unique physical properties, including their porosity and swellability, make them ideal platforms for water and nutrient delivering. The aim of this study was to investigate the potentialities of two HGs, one formed by polyacrylamide and one by cellulose added with clay and humic acids, for improving soil porosity of three soil types (sandy &#8220;SD&#8221;, silty &#8220;SL&#8221; and clay &#8220;CL&#8221;). Soil pore network was characterized with X-ray computed microtomography (&#181;CT) at 50 &#181;m resolution and subsequent image analysis measuring&#160; total porosity (TP), pore size distribution (PSD), mean diameter (MD), connectivity density and degree of anisotropy. Soil samples were at first saturated and then dried trough freezing and drying cycles with acetone at -80&#176;c.</p><p>Preliminary results showed that at water saturation HG increased TP of four- and two-fold, respectively for SL and CL soil, MD of 40 (SD), 519 (SL) and 164 &#181;m (CL) while no effects were found on other pore architecture indices (e.g., connectivity or anisotropy). The PSD analysis highlighted that HG increased the macroporosity fraction (e.g., pore > 0.8 mm) only in SL (+36%) and CL (+11%) while the other pore classes were not affected. Present study demonstrated that in fine-textured soils at high water content, HG might be a valuable tool to increase not simply the TP but, in particular, the macroporosity fraction which may play a key role in soil functioning and ecosystem services. Future research will investigate the HG performances under dynamic soil moisture conditions on water holding capacity and hydraulic conductivity (Research supported by Fondazione CARIPARO, InnoGel, Progetti Eccellenza 2017).</p>

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Three dimensional simulation of fluid flow in X-ray CT images of porous media

International Journal for Numerical and Analytical Methods in Geomechanics ◽

10.1002/nag.389 ◽

2004 ◽

Vol 28 (13) ◽

pp. 1327-1360 ◽

Cited By ~ 61

Author(s):

A. Al-Omari ◽

E. Masad

Keyword(s):

Porous Media ◽

Fluid Flow ◽

Three Dimensional ◽

Ct Images ◽

X Ray ◽

Dimensional Simulation

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Analysis of Pore Network in Three-dimensional (3D) Grain Bulks Using X-ray CT Images

Transport in Porous Media ◽

10.1007/s11242-007-9172-x ◽

2007 ◽

Vol 73 (3) ◽

pp. 319-332 ◽

Cited By ~ 4

Author(s):

Sureshraja Neethirajan ◽

Digvir S. Jayas

Keyword(s):

Three Dimensional ◽

Pore Network ◽

Ct Images ◽

X Ray ◽

Grain Bulks

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Effect of long-term irrigation and tillage practices on X-ray CT and gas transport derived pore-network characteristics

Soil Research ◽

10.1071/sr18210 ◽

2019 ◽

Vol 57 (6) ◽

pp. 657

Author(s):

Karin Müller ◽

Nicola Dal Ferro ◽

Sheela Katuwal ◽

Craig Tregurtha ◽

Filippo Zanini ◽

...

Keyword(s):

Gas Transport ◽

Greenhouse Gas Emission ◽

Structural Characteristics ◽

Network Connectivity ◽

Total Porosity ◽

Pore Network ◽

Transport Parameters ◽

X Ray ◽

Tillage Practices

The gas transport parameters, diffusivity and air-filled porosity are crucial for soil aeration, microbial activity and greenhouse gas emission, and directly depend on soil structure. In this study, we analysed the effect of long-term tillage and irrigation practices on the surface structure of an arable soil in New Zealand. Our hypothesis was that topsoil structure would change under intensification of arable production, affecting gas exchange. Intact soil cores were collected from plots under intensive tillage (IT) and direct drill (DD), irrigated or rainfed. In total, 32 cores were scanned by X-ray computed tomography (CT) to derive the pore network >30µm. The cores were then used to measure soil-gas diffusivity, air-permeability and air-filled porosity of pores close to the resolution of the X-ray CT scans, namely ≥30µm. The gas measurements allow the calculation of pore-network connectivity and tortuosity parameters, which were compared with the CT-derived structural characteristics. Long-term irrigation had little effect on any of the parameters analysed. Total porosity tended to be lower under IT than DD, whereas the CT-derived porosity was comparable. Both the CT-derived mean pore diameter (MPD) and other morphological parameters, as well as gas measurement-derived parameters, highlighted a less developed structure under IT. The differences in the functional pore-network structure were attributed to SOC depletion and the mechanical disturbance through IT. Significant correlations between CT-derived parameters and functional gas transport parameters such as tortuosity and MPD were found, which suggest that X-ray CT could be useful in the prediction of gas transport.

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Pore morphology of polar firn around closure revealed by X-ray tomography

The Cryosphere ◽

10.5194/tc-12-2481-2018 ◽

2018 ◽

Vol 12 (7) ◽

pp. 2481-2500 ◽

Cited By ~ 8

Author(s):

Alexis Burr ◽

Clément Ballot ◽

Pierre Lhuissier ◽

Patricia Martinerie ◽

Christophe L. Martin ◽

...

Keyword(s):

Sample Size ◽

Morphological Evolution ◽

Total Porosity ◽

Pore Network ◽

Geometrical Parameters ◽

Age Difference ◽

Nondestructive Technique ◽

X Ray ◽

Pore Closure ◽

Lock In

Abstract. Understanding the slow densification process of polar firn into ice is essential in order to constrain the age difference between the ice matrix and entrapped gases. The progressive microstructure evolution of the firn column with depth leads to pore closure and gas entrapment. Air transport models in the firn usually include a closed porosity profile based on available data. Pycnometry or melting–refreezing techniques have been used to obtain the ratio of closed to total porosity and air content in closed pores, respectively. X-ray-computed tomography is complementary to these methods, as it enables one to obtain the full pore network in 3-D. This study takes advantage of this nondestructive technique to discuss the morphological evolution of pores on four different Antarctic sites. The computation of refined geometrical parameters for the very cold polar sites Dome C and Lock In (the two Antarctic plateau sites studied here) provides new information that could be used in further studies. The comparison of these two sites shows a more tortuous pore network at Lock In than at Dome C, which should result in older gas ages in deep firn at Lock In. A comprehensive estimation of the different errors related to X-ray tomography and to the sample variability has been performed. The procedure described here may be used as a guideline for further experimental characterization of firn samples. We show that the closed-to-total porosity ratio, which is classically used for the detection of pore closure, is strongly affected by the sample size, the image reconstruction, and spatial heterogeneities. In this work, we introduce an alternative parameter, the connectivity index, which is practically independent of sample size and image acquisition conditions, and that accurately predicts the close-off depth and density. Its strength also lies in its simple computation, without any assumption of the pore status (open or close). The close-off prediction is obtained for Dome C and Lock In, without any further numerical simulations on images (e.g., by permeability or diffusivity calculations).

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Extraction of physically realistic pore network properties from three-dimensional synchrotron X-ray microtomography images of unconsolidated porous media systems

Journal of Hydrology ◽

10.1016/j.jhydrol.2004.05.005 ◽

2005 ◽

Vol 300 (1-4) ◽

pp. 44-64 ◽

Cited By ~ 187

Author(s):

R.I. Al-Raoush ◽

C.S. Willson

Keyword(s):

Porous Media ◽

Three Dimensional ◽

Pore Network ◽

X Ray ◽

Network Properties ◽

Unconsolidated Porous Media ◽

Media Systems

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Building Pore-Networks via Maximal Inscribed Spheres

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.339.227 ◽

2011 ◽

Vol 339 ◽

pp. 227-233 ◽

Cited By ~ 2

Author(s):

Jun Xi Xie ◽

Qi Zhi Teng ◽

Yu Chen Liu

Keyword(s):

Porous Media ◽

Shape Factor ◽

Darcy’S Law ◽

Pore Network ◽

Ct Images ◽

Darcy's Law ◽

Absolute Permeability ◽

Micro Ct ◽

Pore Networks

Pore-network is a useful tool in the study of porous media. It makes it possible to exam the structure of a porous media and to carry out simulations in a macroscopic way. For instance, with a pore-network, the calculation of permeability can be done by implementing Darcy’s law, a formula in a proportional form. In this paper, the inscribed sphere algorithm is introduced to extract the pore-network from micro-CT images. Also methods for determining shape factor and conductance are introduced. Several samples with different porosity are used for test. Absolute permeability is calculated based on two different ways of evaluating conductance, and the results are compared and analyzed.

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