Calculation of the Evolution of Surface Area and Free Volume During the Infiltration of Fiber Felts

Pfrang, Andreas; Schladitz, Katja; Wiegmann, Andreas; Schimmel, Thomas

doi:10.1002/cvde.200706590

Cited by 7 publications

(7 citation statements)

References 29 publications

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“…Fluid flow within the processed CT scan image is simulated using the FlowDict module of the multidisciplinary commercial GeoDict ® program package (Math2Market, Kaiserslautern, Germany), which has been developed to predict (microstructure-based) physical material properties (Pfrang et al, 2007). In the past, GeoDict was successfully applied to several studies with geoscientific background concerning fluid flow or particle tracking in fractured as well as porous media (Khan et al, 2012;Leu et al, 2014;Pudlo et al, 2014;Rücker et al, 2015;Schwarz and Enzmann, 2013).…”

Section: Simulationmentioning

confidence: 99%

Simulating stress-dependent fluid flow in a fractured core sample using real-time X-ray CT data

et al. 2016

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Abstract. Various geoscientific applications require a fast prediction of fracture permeability for an optimal workflow. Hence, the objective of the current study is to introduce and validate a practical method to characterize and approximate single flow in fractures under different stress conditions by using a core-flooding apparatus, in situ X-ray computed tomography (CT) scans and a finite-volume method solving the Navier-Stokes-Brinkman equations. The permeability of the fractured sandstone sample was measured stepwise during a loading-unloading cycle (0.7 to 22.1 MPa and back) to validate the numerical results. Simultaneously, the pressurized core sample was imaged with a medical X-ray CT scanner with a voxel dimension of 0.5 × 0.5 × 1.0 mm 3 . Fracture geometries were obtained by CT images based on a modification of the simplified missing attenuation (MSMA) approach. Simulation results revealed both qualitative plausibility and a quantitative approximation of the experimentally derived permeabilities. The qualitative results indicate flow channeling along several preferential flow paths with less pronounced tortuosity. Significant changes in permeability can be assigned to temporal and permanent changes within the fracture due to applied stresses. The deviations of the quantitative results appear to be mainly caused by both local underestimation of hydraulic properties due to compositional matrix heterogeneities and the low CT resolution affecting the accurate capturing of sub-grid-scale features. Both affect the proper reproduction of the actual connectivity and therefore also the depiction of the expected permeability hysteresis. Furthermore, the threshold value CT mat (1862.6 HU) depicting the matrix material represents the most sensitive input parameter of the simulations. Small variations of CT mat can cause enormous changes in simulated permeability by up to a factor of 2.6 ± 0.1 and, thus, have to be defined with caution. Nevertheless, comparison with further CT-based flow simulations indicates that the proposed method represents a valuable method to approximate actual permeabilities, particularly for smooth fractures (< 35 µm). However, further systematic investigations concerning the applicability of the method are essential for future studies. Thus, some recommendations are compiled by also including suggestions of comparable studies.

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Section: Simulationmentioning

confidence: 99%

Simulating stress-dependent fluid flow in a fractured core sample using real-time X-ray CT data

et al. 2016

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“…Similarly, the inverted image data structure gives a solid particle grain size distribution (GSD) of L10, L50, and L90 in the whole ROI volume (see Table 1). Estimation of the specific surface area, however, is not based on simply adding up the voxel surfaces but on a Poisson line process, i.e, the count of surface crossings along rays in all directions (Pfrang et al 2007). This algorithm is convergent and consistent for isotropic media (i.e., no preferred surface orientation), but is slightly biased in case of highly anisotropic media like pure clay.…”

Section: Resultsmentioning

confidence: 99%

“…To perform this job, we applied the GeoDict software package on the 16-bit segmented 3D image, which allows us to directly map the pore structure and provide us for a more detailed analysis of the microstructure. The GeoDict software package computes, in general, predictions of physical material properties on basis of real (i.e., tomographic) microstructures (Pfrang et al 2007; http:// www.geodict.com/). The bin size chosen corresponds to the effective image resolution (0.74 μm) which means all voxels along all three x, y, z-directions of the chosen ROI (2.5 × 10 8 in total) are brought into account for the calculation.…”

Section: Resultsmentioning

confidence: 99%

“…Moreover, pore-scale modeling provides a way for the better understanding and effective parameterization of macroscopic fluid flow for a success with simulation tools. Using μCT geometrical datasets, an increasing number of investigations of (multi-phase) fluid flow at the (yet non-matrix) pore scale level have been published in the last few years (Wildenschild et al 2005;Culligan et al 2006;Fourie et al 2007;Pfrang et al 2007;Porter and Wildenschild 2010;Silin et al 2011). Meanwhile, spatial resolution in synchrotron-based tomography has improved to submicron voxel resolution (nano-CT).…”

Section: Introductionmentioning

confidence: 97%

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3D simulation of the permeability tensor in a soil aggregate on basis of nanotomographic imaging and LBE solver

et al. 2011

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Purpose: The purpose of this hydropedological work is to investigate the feasibility of a method to calculate permeability of soil peds on the matrix pore scale resolution. This paper focuses on imaging of the intra-aggregate microstructure and, based on the three-dimensional (3D) images, quantification of the pore network connectivity and permeability tensor. Finally, lattice Boltzmann equation (LBE) simulations of Navier-Stokes flow in the thus derived pore network allow to compute the heterogeneous 3D flow velocity field. Materials and methods: Nanotomographic X-ray absorption mode imaging of a single soil ped has been performed at the TOMCAT beamline of the Swiss Light Source synchrotron facility with 0.74 µm spatial resolution. Segmentation of the 3D Nano-CT images into solid phase and pore space allowed to study the statistical properties of the connected pore network. The thus derived pore network data were used as direct input for the software package GeoDict integrated with a LBE algorithm to perform saturated water flow modeling. Results and discussion: The soil ped features quantified from the tomographic images were pore and grain size distributions (PSD, GSD), porosity, percolation tensor in x, y, z-direction and percolation pathways (macropores). The PSD frequency has a peak in the range 3-8 µm (mesopores) contributing 50% of the total. In general, the matrix pore structure and, hence, saturated flow field velocity of our sample is highly anisotropic. LBE-simulated pore scale fluid flow is used to ultimately determine gross parameters (coefficients) of Darcy's law such as the saturated hydraulic conductivity, Ks. The thus simulated Ks=105±24 cm day(-1) of a single soil ped (mean of three ROIs and directions) is one order of magnitude higher than the value of Ks=12±2 cm day(-1) predicted by a classical pedotranfer function approach. This Ks underestimation by PTF is typical for macropore flow. Conclusions: Integration of 3D image evaluation with the LBE approach as an essential step toward understanding the highly heterogeneous intra-aggregate microstructure is now possible on the submicron scale. Modeling the resulting anisotropic fluid advection field is, however, just a first step for 3D models of biogeochemical reactions at soil interfaces on this pore scale

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“…[23] The chemistry of carbon formation during the infiltration process is complex due to the evolutive heat and mass exchanges, and the complex chemical compositions of products resulting from precursor pyrolysis. The ultimate microstructure of deposited pyrocarbon is determined by carbon formation mechanisms, which include gas-phase reactions by the formation of relevant intermediates of carbon formation (nucleation mechanism) as well as surface reactions of these intermediates (growth mechanism).…”

Section: Deposition Mechanism Of Vapor Infiltrating Cnfs/cfs Hybrid Mmentioning

confidence: 99%

Fabrication and Characteristics of Carbon Nanofiber‐Reinforced Carbon/Carbon Composites by Fast Catalytic Infiltration Processes

Zhang

Luo

et al. 2009

Chemical Vapor Deposition

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The simultaneous in-situ growth of carbon nanofibers (CNFs) and densification of a CNFs/CF hybrid multiscale felt are accomplished in a single step by thermal gradient chemical vapor infiltration using Fe as the catalyst and vaporized kerosene under atmospheric pressure. A three-dimensional CNF network which could bridge dissimilar components of composites is formed on carbon fibers (CFs). The length of CNFs can reach several micrometers and the diameters are about 80 nm. Smooth and rough surface densified CNFs can be produced after further higher temperature infiltration. CNFs, anchoring to CFs by the adherence of the catalyst nanoparticles, enhance the bonding between CFs and pyrocarbon as well as promoting the formation of a rough laminar pyrocarbon matrix. The deposition mechanisms and physical model are also discussed. This fast catalytic infiltration process can be applied to other ceramic materials and has significant enlargement potential.

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Calculation of the Evolution of Surface Area and Free Volume During the Infiltration of Fiber Felts

Cited by 7 publications

References 29 publications

Simulating stress-dependent fluid flow in a fractured core sample using real-time X-ray CT data

Simulating stress-dependent fluid flow in a fractured core sample using real-time X-ray CT data

3D simulation of the permeability tensor in a soil aggregate on basis of nanotomographic imaging and LBE solver

Fabrication and Characteristics of Carbon Nanofiber‐Reinforced Carbon/Carbon Composites by Fast Catalytic Infiltration Processes

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