Cell colonization in degradable 3D porous matrices
Lawrence, Benjamin J
2008-01-01
Cell colonization is an important in a wide variety of biological processes and applications including vascularization, wound healing, tissue engineering, stem cell differentiation and biosensors. During colonization porous 3D structures are used to support and guide the ingrowth of cells into the matrix. In this review, we summarize our understanding of various factors affecting cell colonization in three-dimensional environment. The structural, biological and degradation properties of the matrix all play key roles during colonization. Further, specific scaffold properties such as porosity, pore size, fiber thickness, topography and scaffold stiffness as well as important cell material interactions such as cell adhesion and mechanotransduction also influence colonization. PMID:19262124
Highly porous 3D nanofiber scaffold using an electrospinning technique.
Kim, Geunhyung; Kim, WanDoo
2007-04-01
A successful 3D tissue-engineering scaffold must have a highly porous structure and good mechanical stability. High porosity and optimally designed pore size provide structural space for cell accommodation and migration and enable the exchange of nutrients between the scaffold and environment. Poly(epsilon-carprolactone) fibers were electrospun using an auxiliary electrode and chemical blowing agent (BA), and characterized according to porosity, pore size, and their mechanical properties. We also investigated the effect of the BA on the electrospinning processability. The growth characteristic of human dermal fibroblasts cells cultured in the webs showed the good adhesion with the blown web relative to a normal electrospun mat. The blown nanofiber web had good tensile properties and high porosity compared to a typical electrospun nanofiber scaffold. PMID:16924612
Vorticity and upscaled dispersion in 3D heterogeneous porous media
NASA Astrophysics Data System (ADS)
Di Dato, Mariaines; Chiogna, Gabriele; de Barros, Felipe; Bellin, Alberto; Fiori, Aldo
2015-04-01
Modeling flow in porous media is relevant for many environmental, energy and industrial applications. From an environmental perspective, the relevance of porous media flow becomes evident in subsurface hydrology. In general, flow in natural porous media is creeping, yet the large variability in the hydraulic conductivity values encountered in natural aquifers leads to highly heterogeneous flow fields. This natural variability in the conductivity field will affect both dilution rates of chemical species and reactive mixing. A physical consequence of this heterogeneity is also the presence of a various localized kinematical features such as straining, shearing and vorticity in aquifers, which will influence the shape of solute clouds and its fate and transport. This work aims in fundamentally characterizing the vorticity field in spatially heterogeneous flow fields as a function of their statistical properties in order to analyze the impact on transport processes. In our study, three-dimensional porous formations are constructed with an ensemble of N independent, non-overlapping spheroidal inclusions submerged into an homogeneous matrix, of conductivity K0. The inclusions are randomly located in a domain of volume W and are fully characterized by the geometry of spheroid (oblate or prolate), their conductivity K (random and drawn from a given probability density function fκ), the centroid location ¯x, the axes ratio e, the orientation of the rotational axis (α1,α2) and the volume w. Under the assumption of diluted medium, the flow problem is solved analitically by means of only two parameters: the conductivity contrast κ = K/K0 and the volume fraction n = Nw/W . Through the variation of these parameters of the problem, it is possible to approximate the structure of natural heterogeneous porous media. Using a random distribution of the orientation of the inclusions, we create media defined by the same global anisotropy f = Iz/Ix but different micro
NASA Astrophysics Data System (ADS)
Sotoda, Naoya; Tanaka, Kenji; Shirafuji, Tatsuru
2015-09-01
Plasma in contact with HAuCl4 aqueous solution can promote the synthesis of gold nanoparticles. To scale up this process, we have developed 3D integrated micro-solution plasma (3D IMSP). It can generate a large number of argon microplasmas in contact with the aqueous solution flowing in a porous dielectric material. The porous dielectric material in our prototype 3D IMSP reactor, however, consists of non-regularly arranged random-sized pores. These pore parameters may be the parameters for controlling the size and dispersion of synthesized gold nanoparticles. We have hence fabricated a 3D IMSP reactor with an artificial porous dielectric material that has regularly arranged same-sized pores by using a 3D printer. We have applied the reactor to the gold- nanoparticle synthesis. We have confirmed the synthesis of gold nanoparticles through the observation of a plasmon resonance absorption peak at 550 nm in the HAuCl4 aqueous solution treated with 3D IMSP. The size and distribution of the synthesized gold nanoparticles are under investigation. We expect that these characteristics of the gold nanoparticles can be manipulated by changing pore size and their distribution in the porous dielectric material.
Computing Radiative Transfer in a 3D Medium
NASA Technical Reports Server (NTRS)
Von Allmen, Paul; Lee, Seungwon
2012-01-01
A package of software computes the time-dependent propagation of a narrow laser beam in an arbitrary three- dimensional (3D) medium with absorption and scattering, using the transient-discrete-ordinates method and a direct integration method. Unlike prior software that utilizes a Monte Carlo method, this software enables simulation at very small signal-to-noise ratios. The ability to simulate propagation of a narrow laser beam in a 3D medium is an improvement over other discrete-ordinate software. Unlike other direct-integration software, this software is not limited to simulation of propagation of thermal radiation with broad angular spread in three dimensions or of a laser pulse with narrow angular spread in two dimensions. Uses for this software include (1) computing scattering of a pulsed laser beam on a material having given elastic scattering and absorption profiles, and (2) evaluating concepts for laser-based instruments for sensing oceanic turbulence and related measurements of oceanic mixed-layer depths. With suitable augmentation, this software could be used to compute radiative transfer in ultrasound imaging in biological tissues, radiative transfer in the upper Earth crust for oil exploration, and propagation of laser pulses in telecommunication applications.
3D Bioprinting Using a Templated Porous Bioink.
Armstrong, James P K; Burke, Madeline; Carter, Benjamin M; Davis, Sean A; Perriman, Adam W
2016-07-01
3D tissue printing with adult stem cells is reported. A novel cell-containing multicomponent bioink is used in a two-step 3D printing process to engineer bone and cartilage architectures. PMID:27125336
Solute transport through a deforming porous medium
NASA Astrophysics Data System (ADS)
Peters, Glen P.; Smith, David W.
2002-06-01
Solute transport through a porous medium is typically modelled assuming the porous medium is rigid. However, many applications exist where the porous medium is deforming, including, municipal landfill liners, mine tailings dams, and land subsidence. In this paper, mass balance laws are used to derive the flow and transport equations for a deforming porous medium. The equations are derived in both spatial and material co-ordinate systems. Solute transport through an engineered landfill liner is used as an illustrative example to show the differences between the theory for a rigid porous medium, and small and large deformation analysis of a deforming porous medium. It is found that the large deformation model produces shorter solute breakthrough times, followed by the small deformation model, and then the rigid porous medium model. It is also found that it is important to include spatial and temporal void ratio variations in the large deformation analysis. It is shown that a non-linear large deformation model may greatly reduce the solute breakthrough time, compared to a standard transport analysis typically employed by environmental engineers.
3D finite element analysis of porous Ti-based alloy prostheses.
Mircheski, Ile; Gradišar, Marko
2016-11-01
In this paper, novel designs of porous acetabular cups are created and tested with 3D finite element analysis (FEA). The aim is to develop a porous acetabular cup with low effective radial stiffness of the structure, which will be near to the architectural and mechanical behavior of the natural bone. For the realization of this research, a 3D-scanner technology was used for obtaining a 3D-CAD model of the pelvis bone, a 3D-CAD software for creating a porous acetabular cup, and a 3D-FEA software for virtual testing of a novel design of the porous acetabular cup. The results obtained from this research reveal that a porous acetabular cup from Ti-based alloys with 60 ± 5% porosity has the mechanical behavior and effective radial stiffness (Young's modulus in radial direction) that meet and exceed the required properties of the natural bone. The virtual testing with 3D-FEA of a novel design with porous structure during the very early stage of the design and the development of orthopedic implants, enables obtaining a new or improved biomedical implant for a relatively short time and reduced price. PMID:27015664
Elastic properties of model 3-D porous ceramics and foams
NASA Astrophysics Data System (ADS)
Roberts, Anthony; Garboczi, Edward
2000-03-01
The novel properties of many new porous materials are related to their interesting internal microstructure. Apart from simple cases, there exist no theoretical means of predicting the bulk properties of these materials. This limits our ability to guide microstructure optimization for a particular purpose. We use a large scale finite element method to demonstrate the complex relationship between microstructure and the effective properties of realistic three-dimensional model porous ceramics and foams. We find that pore-shape and interconnectivity strongly influence the properties of sintered ceramics. For porous foams we have studied the role of coordination number, random disorder, and strut shape on the Young's modulus and Poisson's ratio. We find that that Voronoi tesselations, commonly used to model solid foams, show unphysical behavior, in particular they are incompressible (rubber-like) at low densities. Deletion of just 10% of the bonds in the model reduces the bulk modulus by 75%, more in line with experimental evidence. The FEM results are generally in good agreement with experimental data for ceramics and foams, and can be used as both a predictive and interpretative tool by experimentalists.
Chemical Dealloying Derived 3D Porous Current Collector for Li Metal Anodes.
Yun, Qinbai; He, Yan-Bing; Lv, Wei; Zhao, Yan; Li, Baohua; Kang, Feiyu; Yang, Quan-Hong
2016-08-01
A 3D porous Cu current collector is fabricated through chemical dealloying from a commerial Cu-Zn alloy tape. The interlinked porous framework naturally integrated can accommodate Li deposition, suppressing dendrite growth and alleviating the huge volume change during cycling. The Li metal anode combined with such a porous Cu collector demonstrates excellent performance and commerial potentials in Li-based secondary batteries. PMID:27219349
3D Hierarchical Porous Mo2 C for Efficient Hydrogen Evolution.
Ang, Huixiang; Wang, Huanwen; Li, Bing; Zong, Yun; Wang, Xuefeng; Yan, Qingyu
2016-06-01
Porous electrocatalyst for hydrogen production. 3D hierarchical porous molybdenum carbide provides a low operating potential (97 mV at 10 mA cm(-2) ). These beneficial textures of large specific surface area (302 m(2) g(-1) ) and hierarchical porous architecture containing dominant pore size distribution peak at 11 Å in width can provide large surface active sites and facilitate proton mass transport. PMID:27076208
Method to prepare nanoparticles on porous mediums
Vieth, Gabriel M [Knoxville, TN; Dudney, Nancy J [Oak Ridge, TN; Dai, Sheng [Knoxville, TN
2010-08-10
A method to prepare porous medium decorated with nanoparticles involves contacting a suspension of nanoparticles in an ionic liquid with a porous medium such that the particles diffuse into the pores of the medium followed by heating the resulting composition to a temperature equal to or greater than the thermal decomposition temperature of the ionic liquid resulting in the removal of the liquid portion of the suspension. The nanoparticles can be a metal, an alloy, or a metal compound. The resulting compositions can be used as catalysts, sensors, or separators.
Permeability modification in 3D porous media due to polymer retention
NASA Astrophysics Data System (ADS)
Parsa, Shima; Sizaret, Hubert; Weitz, David
2015-11-01
We combine confocal microscopy and bulk transport measurements to quantify the changes in the permeability of a model porous media after flow of a polymer solution. The 3D micromodel is made of closely packed glass beads with diameter of 150 micrometers. By matching the index of refraction of the fluid with beads we are able to measure the fluid velocities at pore level deep in the medium using particle image velocimetry. Our measurement shows that the medium permeability decreases 60% after flow of multiple pore volumes of polymer solution and then flushing with water. At constant flow rate we estimate that the pore velocity increases almost 23% due to this reduction in permeability. Our microscopic measurements of the velocities in pores shows that the average velocity increases considerably more than estimated bulk value. Also the distribution of velocities has a slower decay indicating somewhat higher probability of large velocities in the medium after retention of polymer. These changes in velocities are not uniform and depends on the pore size.
Transport of iron oxide nanoparticles in saturated porous media: a large-scale 3D study
NASA Astrophysics Data System (ADS)
Velimirovic, Milica; Schmid, Doris; Micić, Vesna; Miyajima, Kumiko; Klaas, Norbert; Braun, Jürgen; Bosch, Julian; Meckenstock, Rainer; von der Kammer, Frank; Hofmann, Thilo
2016-04-01
Iron oxide nanoparticles (FeOxNp) have a high potential as electron acceptor for in situ microbial oxidation of a wide range of recalcitrant groundwater contaminants (Bosch et al., 2010). Tosco et al. (2012) reported on high colloidal stability of FeOxNp dispersed in water, their low deposition behavior, and consequently improved transport in column experiments compared to extensively studied zerovalent iron nanoparticles. However, determination of FeOxNp transport behavior at the field-relevant conditions has not been done before. The present work is aimed to evaluate different complementary methods for detection, quantification and transport characterization of FeOxNp in a large-scale three-dimensional (3D) model aquifer. Prior to that, batch-scale experiments were performed in order to elucidate the potential of the selected methods for direct and indirect characterization and detection of FeOxNp. Direct methods included measurements of particle size distribution, particle concentration, Fetot content and turbidity of the FeOxNp suspension. Indirect methods included measurements of particle zeta potential, as well as TOC content and pH of the FeOxNp suspension. The results of the batch experiments indicated that the most suitable approach for detecting and quantifying FeOxNp was measuring Fetot content and suspension turbidity, as well as particle size determined using dynamic light scattering principle. These complementary methods were further applied in a large-scale 3D study containing medium and coarse sand in order to 1) assess the transport of FeOxNp in saturated porous medium during injection (VFeOx = 6 m3, cparticle = 20 g/L, Qinj = 0.7 m3/h), and 2) illustrate their spatial distribution after injection. The outcomes of the large-scale 3D study confirmed that FeOxNp transport can be successfully investigated applying complementary methods. Monitoring data including Fetot content, turbidity and particle size showed the transport of particles towards the
NASA Astrophysics Data System (ADS)
Kang, Hyun-Wook; Seol, Young-Joon; Cho, Dong-Woo
2009-01-01
Scaffold fabrication using solid freeform fabrication (SFF) technology is a hot topic in tissue engineering. Here, we present a new indirect SFF technology based on microstereolithography (MSTL), which has the highest resolution of all SFF methods, to construct a three-dimensional (3D) porous scaffold by combining SFF with molding technology. To realize this indirect method, we investigated and modified a water-soluble photopolymer. We used MSTL technology to fabricate a high-resolution 3D porous mold composed of the modified polymer. The mold can be removed using an appropriate solvent. We tested two materials, polycaprolactone and calcium sulfate hemihydrate, using the molding process, and developed a lost-mold shape forming process by dissolving the mold. This procedure demonstrated that the proposed method can yield scaffold pore sizes as small as 60-70 µm. In addition, cytotoxicity test results indicated that the proposed process is feasible for producing 3D porous scaffolds.
Thermoforming techniques for manufacturing porous scaffolds for application in 3D cell cultivation.
Borowiec, Justyna; Hampl, Jörg; Gebinoga, Michael; Elsarnagawy, Tarek; Elnakady, Yasser A; Fouad, Hassan; Almajhadi, Fahd; Fernekorn, Uta; Weise, Frank; Singh, Sukhdeep; Elsarnagawy, Dief; Schober, Andreas
2015-04-01
Within the scientific community, there is an increasing demand to apply advanced cell cultivation substrates with increased physiological functionalities for studying spatially defined cellular interactions. Porous polymeric scaffolds are utilized for mimicking an organ-like structure or engineering complex tissues and have become a key element for three-dimensional (3D) cell cultivation in the meantime. As a consequence, efficient 3D scaffold fabrication methods play an important role in modern biotechnology. Here, we present a novel thermoforming procedure for manufacturing porous 3D scaffolds from permeable materials. We address the issue of precise thermoforming of porous polymer foils by using multilayer polymer thermoforming technology. This technology offers a new method for structuring porous polymer foils that are otherwise available for non-porous polymers only. We successfully manufactured 3D scaffolds from solvent casted and phase separated polylactic acid (PLA) foils and investigated their biocompatibility and basic cellular performance. The HepG2 cell culture in PLA scaffold has shown enhanced albumin secretion rate in comparison to a previously reported polycarbonate based scaffold with similar geometry. PMID:25686978
NASA Astrophysics Data System (ADS)
Rieger, Elisabeth; Dupret-Bories, Agnès; Salou, Laetitia; Metz-Boutigue, Marie-Helene; Layrolle, Pierre; Debry, Christian; Lavalle, Philippe; Engin Vrana, Nihal
2015-05-01
Porous titanium implants are widely employed in the orthopaedics field to ensure good bone fixation. Recently, the use of porous titanium implants has also been investigated in artificial larynx development in a clinical setting. Such uses necessitate a better understanding of the interaction of soft tissues with porous titanium structures. Moreover, surface treatments of titanium have been generally evaluated in planar structures, while the porous titanium implants have complex 3 dimensional (3D) architectures. In this study, the determining factors for soft tissue integration of 3D porous titanium implants were investigated as a function of surface treatments via quantification of the interaction of serum proteins and cells with single titanium microbeads (300-500 μm in diameter). Samples were either acid etched or nanostructured by anodization. When the samples are used in 3D configuration (porous titanium discs of 2 mm thickness) in vivo (in subcutis of rats for 2 weeks), a better integration was observed for both anodized and acid etched samples compared to the non-treated implants. If the implants were also pre-treated with rat serum before implantation, the integration was further facilitated. In order to understand the underlying reasons for this effect, human fibroblast cell culture tests under several conditions (directly on beads, beads in suspension, beads encapsulated in gelatin hydrogels) were conducted to mimic the different interactions of cells with Ti implants in vivo. Physical characterization showed that surface treatments increased hydrophilicity, protein adsorption and roughness. Surface treatments also resulted in improved adsorption of serum albumin which in turn facilitated the adsorption of other proteins such as apolipoprotein as quantified by protein sequencing. The cellular response to the beads showed considerable difference with respect to the cell culture configuration. When the titanium microbeads were entrapped in cell
3-D model of ICME in the interplanetary medium
NASA Astrophysics Data System (ADS)
Borgazzi, A.; Lara, A.; Niembro, T.
2011-12-01
We developed a method that describes with simply geometry the coordinates of intersection between the leading edge of an ICME and the position of an arbitrary satellite. When a fast CME is ejected from the Sun to the interplanetary space in most of the cases drives a shock. As the CME moves in the corona and later in the interplanetary space more material is stacking in the front and edges of the ejecta. In a first approximation, it is possible to assume the shape of these structures, the CME and the stacked material as a cone of revolution, (the ice-cream model [Schwenn et al., (2005)]). The interface may change due to the interaction of the structure and the non-shocked material in front of the ICME but the original shape of a cone of revolution is preserved. We assume, in a three dimensional geometry, an ice-cream cone shape for the ICME and apply an analytical model for its transport in the interplanetary medium. The goal of the present method is to give the time and the intersection coordinates between the leading edge of the ICME and any satellite that may be in the path of the ICME. With this information we can modelate the travel of the ICME in the interplanetary space using STEREO data.
Condiment-Derived 3D Architecture Porous Carbon for Electrochemical Supercapacitors.
Qian, Wenjing; Zhu, Jingyue; Zhang, Ye; Wu, Xiao; Yan, Feng
2015-10-01
The one-step synthesis of porous carbon nanoflakes possessing a 3D texture is achieved by cooking (carbonization) a mixture containing two condiments, sodium glutamate (SG) and sodium chloride, which are commonly used in kitchens. The prepared 3D porous carbons are composed of interconnected carbon nanoflakes and possess instinct heteroatom doping such as nitrogen and oxygen, which furnishes the electrochemical activity. The combination of micropores and mesopores with 3D configurations facilitates persistent and fast ion transport and shorten diffusion pathways for high-performance supercapacitor applications. Sodium glutamate carbonized at 800 °C exhibits high charge storage capacity with a specific capacitance of 320 F g(-1) in 6 m KOH at a current density of 1 A g(-1) and good stability over 10,000 cycles. PMID:26150228
A 3-D constitutive model for pressure-dependent phase transformation of porous shape memory alloys.
Ashrafi, M J; Arghavani, J; Naghdabadi, R; Sohrabpour, S
2015-02-01
Porous shape memory alloys (SMAs) exhibit the interesting characteristics of porous metals together with shape memory effect and pseudo-elasticity of SMAs that make them appropriate for biomedical applications. In this paper, a 3-D phenomenological constitutive model for the pseudo-elastic behavior and shape memory effect of porous SMAs is developed within the framework of irreversible thermodynamics. Comparing to micromechanical and computational models, the proposed model is computationally cost effective and predicts the behavior of porous SMAs under proportional and non-proportional multiaxial loadings. Considering the pressure dependency of phase transformation in porous SMAs, proper internal variables, free energy and limit functions are introduced. With the aim of numerical implementation, time discretization and solution algorithm for the proposed model are also presented. Due to lack of enough experimental data on multiaxial loadings of porous SMAs, we employ a computational simulation method (CSM) together with available experimental data to validate the proposed constitutive model. The method is based on a 3-D finite element model of a representative volume element (RVE) with random pores pattern. Good agreement between the numerical predictions of the model and CSM results is observed for elastic and phase transformation behaviors in various thermomechanical loadings. PMID:25528691
Scaling of bubble growth in a porous medium
Satik, C.; Li, X.; Yortsos, Y.C.
1994-09-01
Processes involving liquid-to-gas phase change in porous media are routinely encountered. Growth of a gas phase by solute diffusion in the liquid is typical of the `solution gas-drive` process for the recovery of oil. The growth of a single gas cluster in a porous medium driven by a constant supersaturation is examined. Patterns and rates of growth are derived. It is shown that the growth pattern is not compact and changes from pure percolation to pure Diffusion-Limited-Aggregation (DLA) as the size of the cluster increases. The scaling of the cluster sizes that delineate these patterns, with supersaturation and diffusivity is presented for the case of quasi-static diffusion. In 3-D, the diffusive growth law is found to be R{sub g} {approximately} t{sup 2/3}, which is different than the classical R{sub g} {approximately} t{sup 1/2}.
Debbaut, Charlotte; Vierendeels, Jan; Siggers, Jennifer H; Repetto, Rodolfo; Monbaliu, Diethard; Segers, Patrick
2014-01-01
The hepatic blood circulation is complex, particularly at the microcirculatory level. Previously, 2D liver lobule models using porous media and a 3D model using real sinusoidal geometries have been developed. We extended these models to investigate the role of vascular septa (VS) and anisotropic permeability. The lobule was modelled as a hexagonal prism (with or without VS) and the tissue was treated as a porous medium (isotropic or anisotropic permeability). Models were solved using computational fluid dynamics. VS inclusion resulted in more spatially homogeneous perfusion. Anisotropic permeability resulted in a larger axial velocity component than isotropic permeability. A parameter study revealed that results are most sensitive to the lobule size and radial pressure drop. Our model provides insight into hepatic microhaemodynamics, and suggests that inclusion of VS in the model leads to perfusion patterns that are likely to reflect physiological reality. The model has potential for applications to unphysiological and pathological conditions. PMID:23237543
Proton exchange membrane micro fuel cells on 3D porous silicon gas diffusion layers
NASA Astrophysics Data System (ADS)
Kouassi, S.; Gautier, G.; Thery, J.; Desplobain, S.; Borella, M.; Ventura, L.; Laurent, J.-Y.
2012-10-01
Since the 90's, porous silicon has been studied and implemented in many devices, especially in MEMS technology. In this article, we present a new approach to build miniaturized proton exchange membrane micro-fuel cells using porous silicon as a hydrogen diffusion layer. In particular, we propose an innovative process to build micro fuel cells from a “corrugated iron like” 3D structured porous silicon substrates. This structure is able to increase up to 40% the cell area keeping a constant footprint on the silicon wafer. We propose here a process route to perform electrochemically 3D porous gas diffusion layers and to deposit fuel cell active layers on such substrates. The prototype peak power performance was measured to be 90 mW cm-2 in a “breathing configuration” at room temperature. These performances are less than expected if we compare with a reference 2D micro fuel cell. Actually, the active layer deposition processes are not fully optimized but this prototype demonstrates the feasibility of these 3D devices.
Mechanical properties and shape memory effect of 3D-printed PLA-based porous scaffolds.
Senatov, F S; Niaza, K V; Zadorozhnyy, M Yu; Maksimkin, A V; Kaloshkin, S D; Estrin, Y Z
2016-04-01
In the present work polylactide (PLA)/15wt% hydroxyapatite (HA) porous scaffolds with pre-modeled structure were obtained by 3D-printing by fused filament fabrication. Composite filament was obtained by extrusion. Mechanical properties, structural characteristics and shape memory effect (SME) were studied. Direct heating was used for activation of SME. The average pore size and porosity of the scaffolds were 700μm and 30vol%, respectively. Dispersed particles of HA acted as nucleation centers during the ordering of PLA molecular chains and formed an additional rigid fixed phase that reduced molecular mobility, which led to a shift of the onset of recovery stress growth from 53 to 57°C. A more rapid development of stresses was observed for PLA/HA composites with the maximum recovery stress of 3.0MPa at 70°C. Ceramic particles inhibited the growth of cracks during compression-heating-compression cycles when porous PLA/HA 3D-scaffolds recovered their initial shape. Shape recovery at the last cycle was about 96%. SME during heating may have resulted in "self-healing" of scaffold by narrowing the cracks. PLA/HA 3D-scaffolds were found to withstand up to three compression-heating-compression cycles without delamination. It was shown that PLA/15%HA porous scaffolds obtained by 3D-printing with shape recovery of 98% may be used as self-fitting implant for small bone defect replacement owing to SME. PMID:26710259
A 3D porous Ni-Cu alloy film for high-performance hydrazine electrooxidation
NASA Astrophysics Data System (ADS)
Sun, Ming; Lu, Zhiyi; Luo, Liang; Chang, Zheng; Sun, Xiaoming
2016-01-01
Structural design and catalyst screening are two most important factors for achieving exceptional electrocatalytic performance. Herein we demonstrate that constructing a three-dimensional (3D) porous Ni-Cu alloy film is greatly beneficial for improving the hydrazine oxidation reaction (HzOR) performance. A facile electrodeposition process is employed to synthesize a Ni-Cu alloy film with a 3D hierarchical porous structure. As an integrated electrode for HzOR, the Ni-Cu alloy film exhibits superior catalytic activity and stability to the Ni or Cu counterparts. The synthesis parameters are also systematically tuned for optimizing the HzOR performance. The excellent HzOR performance of the Ni-Cu alloy film is attributed to its high intrinsic activity, large electrochemical specific surface area, and 3D porous architecture which offers a ``superaerophobic'' surface to effectively remove the gas product in a small volume. It is believed that the Ni-Cu alloy film electrode has potential application in direct hydrazine fuel cells as well as other catalytic fields.Structural design and catalyst screening are two most important factors for achieving exceptional electrocatalytic performance. Herein we demonstrate that constructing a three-dimensional (3D) porous Ni-Cu alloy film is greatly beneficial for improving the hydrazine oxidation reaction (HzOR) performance. A facile electrodeposition process is employed to synthesize a Ni-Cu alloy film with a 3D hierarchical porous structure. As an integrated electrode for HzOR, the Ni-Cu alloy film exhibits superior catalytic activity and stability to the Ni or Cu counterparts. The synthesis parameters are also systematically tuned for optimizing the HzOR performance. The excellent HzOR performance of the Ni-Cu alloy film is attributed to its high intrinsic activity, large electrochemical specific surface area, and 3D porous architecture which offers a ``superaerophobic'' surface to effectively remove the gas product in a small
Bottom-up topography assembly into 3D porous scaffold to mediate cell activities.
Cheng, Delin; Hou, Jie; Hao, Lijing; Cao, Xiaodong; Gao, Huichang; Fu, Xiaoling; Wang, Yingjun
2016-08-01
Native cells live in a three-dimensional (3D) extracellular matrix (ECM) capable of regulating cell activities through various physical and chemical factors. Designed topographies have been well proven to trigger significant difference in cell behaviours. However, present topographies are almost all constructed on two-dimensional (2D) substrates like discs and films, which are far from features like 3D and porosity required in application like bone repair. Here we bottom-up assembled poly(lactic-co-glycolic acid)/calcium carbonate (PLGA/CC) microspheres with superficial porous topography intactly into a 3D porous scaffold. Because the scaffold was obtained through a mild technique, the bioactivity of released BMP-2 was well retained. Mouse bone marrow mesenchymal stem cells (mMSCs) were cultured on produced scaffolds having different 3D topographies. It turned out that osteogenic differentiation of mMSCs did respond to the 3D topographies, while proliferation didn't. Gene expression of αv and β1 integrins revealed that adhesion was supposed to be the underlying mechanism for osteogenic response. The study provides insight into enhancing function of practical scaffolds by elaborate topography design. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1056-1063, 2016. PMID:26013977
3D Porous Sponge-Inspired Electrode for Stretchable Lithium-Ion Batteries.
Liu, Wei; Chen, Zheng; Zhou, Guangmin; Sun, Yongming; Lee, Hye Ryoung; Liu, Chong; Yao, Hongbin; Bao, Zhenan; Cui, Yi
2016-05-01
A stretchable Li4 Ti5 O12 anode and a LiFePO4 cathode with 80% stretchability are prepared using a 3D interconnected porous polydimethylsiloxane sponge based on sugar cubes. 82% and 91% capacity retention for anode and cathode are achieved after 500 stretch-release cycles. Slight capacity decay of 6% in the battery using the electrode in stretched state is observed. PMID:26992146
Synthesis of various 3D porous gold-based alloy nanostructures with branched shapes.
Swiatkowska-Warkocka, Zaneta; Pyatenko, Alexander; Koshizaki, Naoto; Kawaguchi, Kenji
2016-12-01
This paper presents a facile and flexible synthesis platform for various 3D porous gold-iron nanostructures based on selective laser heating of colloidal nanoparticles and selective acid treatment. The presented approach allows to create porous gold-based nanostructures with different morphologies. In addition, for the first time, our studies indicate that various nanoarchitectures (brain-like, flower-like, cage-like, or raspberry-like structures) can be obtained by varying the experimental conditions such as size of Au and Fe3O4 nanoparticles, solvent, laser fluence, and irradiation time. We believe that these porous structures will find immediate applications in catalysis and separations, where high surface area and magnetic properties are often simultaneously required. PMID:27565959
Ducci, Daniela; Sellerino, Mariangela
2013-03-01
The aim of this paper is to apply a methodology in order to reconstruct a lithostratigraphic 3D model of an aquifer so as to define some parameters involved in the evaluation of the aquifer vulnerability to contamination of porous aquifers. The DRASTIC, SINTACS and AVI methods have been applied to an alluvial coastal aquifer of southern Italy. The stratigraphic reconstruction has been obtained by interpolating stratigraphic data from more than one borehole per 2 km. The lithostratigraphic reconstruction of a 3D model has been applied and used for three-dimensional or two-dimensional representations. In the first two methods, the layers of the vadose zone and the aquifer media have been evaluated not only by the interpolation of the single boreholes and piezometers, but also by the 3D model, assigning the scores of the parameters of each layer of the 3D model. The comparison between the maps constructed from the weighted values in each borehole and the maps deriving from the attribution of the values of each layer of the 3D model, highlights that the second representation avoids or minimizes the "bullseye" effect linked to the presence of boreholes with higher or lower values. The study has demonstrated that it is possible to integrate a 3D lithostratigraphic model of an aquifer in the assessment of the parameters involved in the evaluation of the aquifer vulnerability to contamination by Point Count System methods. PMID:23391897
Pore-scale intermittent velocity structure underpinning anomalous transport through 3-D porous media
NASA Astrophysics Data System (ADS)
Kang, Peter K.; Anna, Pietro; Nunes, Joao P.; Bijeljic, Branko; Blunt, Martin J.; Juanes, Ruben
2014-09-01
We study the nature of non-Fickian particle transport in 3-D porous media by simulating fluid flow in the intricate pore space of real rock. We solve the full Navier-Stokes equations at the same resolution as the 3-D micro-CT (computed tomography) image of the rock sample and simulate particle transport along the streamlines of the velocity field. We find that transport at the pore scale is markedly anomalous: longitudinal spreading is superdiffusive, while transverse spreading is subdiffusive. We demonstrate that this anomalous behavior originates from the intermittent structure of the velocity field at the pore scale, which in turn emanates from the interplay between velocity heterogeneity and velocity correlation. Finally, we propose a continuous time random walk model that honors this intermittent structure at the pore scale and captures the anomalous 3-D transport behavior at the macroscale.
Electrochemical fabrication of 2D and 3D nickel nanowires using porous anodic alumina templates
NASA Astrophysics Data System (ADS)
Mebed, A. M.; Abd-Elnaiem, Alaa M.; Al-Hosiny, Najm M.
2016-06-01
Mechanically stable nickel (Ni) nanowires array and nanowires network were synthesized by pulse electrochemical deposition using 2D and 3D porous anodic alumina (PAA) templates. The structures and morphologies of as-prepared films were characterized by X-ray diffraction and scanning electron microscopy, respectively. The grown Ni nanowire using 3D PAA revealed more strength and larger surface area than has grown Ni use 2D PAA template. The prepared nanowires have a face-centered cubic crystal structure with average grain size 15 nm, and the preferred orientation of the nucleation of the nanowires is (111). The diameter of the nanowires is about 50-70 nm with length 3 µm. The resulting 3D Ni nanowire lattice, which provides enhanced mechanical stability and an increased surface area, benefits energy storage and many other applications which utilize the large surface area.
Comparison of unstable water infiltration in porous media in 2D and 3D experiments
NASA Astrophysics Data System (ADS)
Schütz, C.; Neuweiler, I.; Lehmann, P.; Papafotiou, A.; Vontobel, P.; Hartmann, S.
2010-05-01
Water infiltration into unsaturated soil is an important process for groundwater recharge and thus for water balance of natural hydrosystems. The characteristics of infiltration patterns depend on porous media properties and initial moisture content. Infiltration fronts into soil can be unstable in layered media with fine over dry coarse material. To predict arrival times of infiltration fronts and average water content in upscaled models, it is necessary to understand occurrence of instabilities. The unstable flow behavior is not captured by standard models and finger characteristics have mostly been investigated experimentally. Most experiments in the past were carried out in 2D setups and it is not clear how the results of such studies relate to real 3D systems. The aim of this study is to compare development and finger characteristics of unstable infiltration in 2D and 3D setups. We carried out laboratory experiments on fast infiltration in 2D and 3D setups and measured water content in porous media with neutron transmission technology at the NEUTRA beam line at the Paul Scherrer Institute, Switzerland. The 2D experiments were carried out in a glass sandbox (260 mm high, 75 mm wide and 11 mm deep). For the 3D experiments aluminum cylindrical column (150 mm in height and 100 mm in diameter) were used. Both columns were filled homogeneously with coarse quartz sand (grain size 0.7 - 1.2 mm) below fine sand layer (0.1 - 0.3 mm) of 20 - 30 mm thickness. Two dimensional projection images of water content with spatial resolution of 125 microns were deduced from neutron images every 2 second. For the 3D setup water content distribution was reconstructed in 3D to monitor water content inside the fingers over time. Water content and finger-width (15 - 23 mm) were similar for 2D and 3D setups. In both cases water content was maximum when the front passes and was decreasing afterwards (indicating "overshoot" behavior). Also the water content difference between values after
Fan, Li-Zhen; Chen, Tian-Tian; Song, Wei-Li; Li, Xiaogang; Zhang, Shichao
2015-01-01
Supercapacitors fabricated by 3D porous carbon frameworks, such as graphene- and carbon nanotube (CNT)-based aerogels, have been highly attractive due to their various advantages. However, their high cost along with insufficient yield has inhibited their large-scale applications. Here we have demonstrated a facile and easily scalable approach for large-scale preparing novel 3D nitrogen-containing porous carbon frameworks using ultralow-cost commercial cotton. Electrochemical performance suggests that the optimal nitrogen-containing cotton-derived carbon frameworks with a high nitrogen content (12.1 mol%) along with low surface area 285 m(2) g(-1) present high specific capacities of the 308 and 200 F g(-1) in KOH electrolyte at current densities of 0.1 and 10 A g(-1), respectively, with very limited capacitance loss upon 10,000 cycles in both aqueous and gel electrolytes. Moreover, the electrode exhibits the highest capacitance up to 220 F g(-1) at 0.1 A g(-1) and excellent flexibility (with negligible capacitance loss under different bending angles) in the polyvinyl alcohol/KOH gel electrolyte. The observed excellent performance competes well with that found in the electrodes of similar 3D frameworks formed by graphene or CNTs. Therefore, the ultralow-cost and simply strategy here demonstrates great potential for scalable producing high-performance carbon-based supercapacitors in the industry. PMID:26472144
Ababou, R.
1996-12-31
Subsurface flow processes are inherently three-dimensional and heterogeneous over many scales. Taking this into account, for instance assuming random heterogeneity in 3-D space, puts heavy constraints on numerical models. An efficient numerical code has been developed for solving the porous media flow equations, appropriately generalized to account for 3-D, random-like heterogeneity. The code is based on implicit finite differences (or finite volumes), and uses specialized versions of pre-conditioned iterative solvers that take advantage of sparseness. With Diagonally Scaled Conjugate Gradients, in particular, large systems on the order of several million equations, with randomly variable coefficients, have been solved efficiently on Cray-2 and Cray-Y/MP8 machines, in serial mode as well as parallel mode (autotasking). The present work addresses, first, the numerical aspects and computational issues associated with detailed 3-D flow simulations, and secondly, presents a specific application related to the conductivity homogenization problem (identifying a macroscale conduction law, and an equivalent or effective conductivity). Analytical expressions of effective conductivities are compared with empirical values obtained from several large scale simulations conducted for single realizations of random porous media.
Fan, Li-Zhen; Chen, Tian-Tian; Song, Wei-Li; Li, Xiaogang; Zhang, Shichao
2015-01-01
Supercapacitors fabricated by 3D porous carbon frameworks, such as graphene- and carbon nanotube (CNT)-based aerogels, have been highly attractive due to their various advantages. However, their high cost along with insufficient yield has inhibited their large-scale applications. Here we have demonstrated a facile and easily scalable approach for large-scale preparing novel 3D nitrogen-containing porous carbon frameworks using ultralow-cost commercial cotton. Electrochemical performance suggests that the optimal nitrogen-containing cotton-derived carbon frameworks with a high nitrogen content (12.1 mol%) along with low surface area 285 m2 g−1 present high specific capacities of the 308 and 200 F g−1 in KOH electrolyte at current densities of 0.1 and 10 A g−1, respectively, with very limited capacitance loss upon 10,000 cycles in both aqueous and gel electrolytes. Moreover, the electrode exhibits the highest capacitance up to 220 F g−1 at 0.1 A g−1 and excellent flexibility (with negligible capacitance loss under different bending angles) in the polyvinyl alcohol/KOH gel electrolyte. The observed excellent performance competes well with that found in the electrodes of similar 3D frameworks formed by graphene or CNTs. Therefore, the ultralow-cost and simply strategy here demonstrates great potential for scalable producing high-performance carbon-based supercapacitors in the industry. PMID:26472144
NASA Astrophysics Data System (ADS)
Fan, Li-Zhen; Chen, Tian-Tian; Song, Wei-Li; Li, Xiaogang; Zhang, Shichao
2015-10-01
Supercapacitors fabricated by 3D porous carbon frameworks, such as graphene- and carbon nanotube (CNT)-based aerogels, have been highly attractive due to their various advantages. However, their high cost along with insufficient yield has inhibited their large-scale applications. Here we have demonstrated a facile and easily scalable approach for large-scale preparing novel 3D nitrogen-containing porous carbon frameworks using ultralow-cost commercial cotton. Electrochemical performance suggests that the optimal nitrogen-containing cotton-derived carbon frameworks with a high nitrogen content (12.1 mol%) along with low surface area 285 m2 g-1 present high specific capacities of the 308 and 200 F g-1 in KOH electrolyte at current densities of 0.1 and 10 A g-1, respectively, with very limited capacitance loss upon 10,000 cycles in both aqueous and gel electrolytes. Moreover, the electrode exhibits the highest capacitance up to 220 F g-1 at 0.1 A g-1 and excellent flexibility (with negligible capacitance loss under different bending angles) in the polyvinyl alcohol/KOH gel electrolyte. The observed excellent performance competes well with that found in the electrodes of similar 3D frameworks formed by graphene or CNTs. Therefore, the ultralow-cost and simply strategy here demonstrates great potential for scalable producing high-performance carbon-based supercapacitors in the industry.
From micro-scale 3D simulations to macro-scale model of periodic porous media
NASA Astrophysics Data System (ADS)
Crevacore, Eleonora; Tosco, Tiziana; Marchisio, Daniele; Sethi, Rajandrea; Messina, Francesca
2015-04-01
In environmental engineering, the transport of colloidal suspensions in porous media is studied to understand the fate of potentially harmful nano-particles and to design new remediation technologies. In this perspective, averaging techniques applied to micro-scale numerical simulations are a powerful tool to extrapolate accurate macro-scale models. Choosing two simplified packing configurations of soil grains and starting from a single elementary cell (module), it is possible to take advantage of the periodicity of the structures to reduce the computation costs of full 3D simulations. Steady-state flow simulations for incompressible fluid in laminar regime are implemented. Transport simulations are based on the pore-scale advection-diffusion equation, that can be enriched introducing also the Stokes velocity (to consider the gravity effect) and the interception mechanism. Simulations are carried on a domain composed of several elementary modules, that serve as control volumes in a finite volume method for the macro-scale method. The periodicity of the medium involves the periodicity of the flow field and this will be of great importance during the up-scaling procedure, allowing relevant simplifications. Micro-scale numerical data are treated in order to compute the mean concentration (volume and area averages) and fluxes on each module. The simulation results are used to compare the micro-scale averaged equation to the integral form of the macroscopic one, making a distinction between those terms that could be computed exactly and those for which a closure in needed. Of particular interest it is the investigation of the origin of macro-scale terms such as the dispersion and tortuosity, trying to describe them with micro-scale known quantities. Traditionally, to study the colloidal transport many simplifications are introduced, such those concerning ultra-simplified geometry that usually account for a single collector. Gradual removal of such hypothesis leads to a
A miniature microbial fuel cell with conducting nanofibers-based 3D porous biofilm
NASA Astrophysics Data System (ADS)
Jiang, Huawei; Halverson, Larry J.; Dong, Liang
2015-12-01
Miniature microbial fuel cell (MFC) technology has received growing interest due to its potential applications in high-throughput screening of bacteria and mutants to elucidate mechanisms of electricity generation. This paper reports a novel miniature MFC with an improved output power density and short startup time, utilizing electrospun conducting poly(3,4-ethylenedioxythiophene) (PEDOT) nanofibers as a 3D porous anode within a 12 μl anolyte chamber. This device results in 423 μW cm-3 power density based on the volume of the anolyte chamber, using Shewanella oneidensis MR-1 as a model biocatalyst without any optimization of bacterial culture. The device also excels in a startup time of only 1hr. The high conductivity of the electrospun nanofibers makes them suitable for efficient electron transfer. The mean pore size of the conducting nanofibers is several micrometers, which is favorable for bacterial penetration and colonization of surfaces of the nanofibers. We demonstrate that S. oneidensis can fully colonize the interior region of this nanofibers-based porous anode. This work represents a new attempt to explore the use of electrospun PEDOT nanofibers as a 3D anode material for MFCs. The presented miniature MFC potentially will provide a high-sensitivity, high-throughput tool to screen suitable bacterial species and mutant strains for use in large-size MFCs.
Cox, Sophie C; Thornby, John A; Gibbons, Gregory J; Williams, Mark A; Mallick, Kajal K
2015-02-01
A systematic characterisation of bone tissue scaffolds fabricated via 3D printing from hydroxyapatite (HA) and poly(vinyl)alcohol (PVOH) composite powders is presented. Flowability of HA:PVOH precursor materials was observed to affect mechanical stability, microstructure and porosity of 3D printed scaffolds. Anisotropic behaviour of constructs and part failure at the boundaries of interlayer bonds was highlighted by compressive strength testing. A trade-off between the ability to facilitate removal of PVOH thermal degradation products during sintering and the compressive strength of green parts was revealed. The ultimate compressive strength of 55% porous green scaffolds printed along the Y-axis and dried in a vacuum oven for 6h was 0.88 ± 0.02 MPa. Critically, the pores of 3D printed constructs could be user designed, ensuring bulk interconnectivity, and the imperfect packing of powder particles created an inherent surface roughness and non-designed porosity within the scaffold. These features are considered promising since they are known to facilitate osteoconduction and osteointegration in-vivo. Characterisation techniques utilised in this study include two funnel flow tests, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), compressive strength testing and computed tomography (CT). PMID:25492194
Huang, Jian-Wen; Lv, Xiang-Guo; Li, Zhe; Song, Lu-Jie; Feng, Chao; Xie, Min-Kai; Li, Chao; Li, Hong-Bin; Wang, Ji-Hong; Zhu, Wei-Dong; Chen, Shi-Yan; Wang, Hua-Ping; Xu, Yue-Min
2015-09-01
The goal of this study was to evaluate the effects of urethral reconstruction with a three-dimensional (3D) porous bacterial cellulose (BC) scaffold seeded with lingual keratinocytes in a rabbit model. A novel 3D porous BC scaffold was prepared by gelatin sponge interfering in the BC fermentation process. Rabbit lingual keratinocytes were isolated, expanded, and seeded onto 3D porous BC. BC alone (group 1, N = 10), 3D porous BC alone (group 2, N = 10), and 3D porous BC seeded with lingual keratinocytes (group 3, N = 10) were used to repair rabbit ventral urethral defects (2.0 × 0.8 cm). Scanning electron microscopy revealed that BC consisted of a compact laminate while 3D porous BC was composed of a porous sheet buttressed by a dense outer layer. The average pore diameter and porosity of the 3D porous BC were 4.23 ± 1.14 μm and 67.00 ± 6.80%, respectively. At 3 months postoperatively, macroscopic examinations and retrograde urethrograms of urethras revealed that all urethras maintained wide calibers in group 3. Strictures were found in all rabbits in groups 1 and 2. Histologically, at 1 month postoperatively, intact epithelium occurred in group 3, and discontinued epithelium was found in groups 1 and 2. However, groups 2 and 3 exhibited similar epithelial regeneration, which was superior to that of group 1 at 3 months (p < 0.05). Comparisons of smooth muscle content and endothelia density among the three groups revealed a significant increase at each time point (p < 0.05). Our results demonstrated that 3D porous BC seeded with lingual keratinocytes enhanced urethral tissue regeneration. 3D porous BC could potentially be used as an optimized scaffold for urethral reconstruction. PMID:26358641
Hard and soft probe medium interactions in a 3D hydro+micro approach at RHIC
NASA Astrophysics Data System (ADS)
Bass, S. A.; Renk, T.; Ruppert, J.; Nonaka, C.
2007-08-01
We utilize a 3D hybrid hydro+micro model for a comprehensive and consistent description of soft and hard particle production in ultra-relativistic heavy-ion collisions at RHIC. In the soft sector we focus on the dynamics of (multi-) strange baryons, where a clear strangeness dependence of their collision rates and freeze-out is observed. In the hard sector we study the radiative energy loss of hard partons in a soft medium in the multiple soft scattering approximation. While the nuclear suppression factor RAA does not reflect the high quality of the medium description (except in a reduced systematic uncertainty in extracting the quenching power of the medium), the hydrodynamical model also allows us to study different centralities and in particular the angular variation of RAA with respect to the reaction plane, allowing for a controlled variation of the in-medium path length.
Dynamics of osmosis in a porous medium
Cardoso, Silvana S. S.; Cartwright, Julyan H. E.
2014-01-01
We derive from kinetic theory, fluid mechanics and thermodynamics the minimal continuum-level equations governing the flow of a binary, non-electrolytic mixture in an isotropic porous medium with osmotic effects. For dilute mixtures, these equations are linear and in this limit provide a theoretical basis for the widely used semi-empirical relations of Kedem & Katchalsky (Kedem & Katchalsky 1958 Biochim. Biophys. Acta 27, 229–246 (doi:10.1016/0006-3002(58)90330-5), which have hitherto been validated experimentally but not theoretically. The above linearity between the fluxes and the driving forces breaks down for concentrated or non-ideal mixtures, for which our equations go beyond the Kedem–Katchalsky formulation. We show that the heretofore empirical solute permeability coefficient reflects the momentum transfer between the solute molecules that are rejected at a pore entrance and the solvent molecules entering the pore space; it can be related to the inefficiency of a Maxwellian demi-demon. PMID:26064566
Dynamics of osmosis in a porous medium.
Cardoso, Silvana S S; Cartwright, Julyan H E
2014-11-01
We derive from kinetic theory, fluid mechanics and thermodynamics the minimal continuum-level equations governing the flow of a binary, non-electrolytic mixture in an isotropic porous medium with osmotic effects. For dilute mixtures, these equations are linear and in this limit provide a theoretical basis for the widely used semi-empirical relations of Kedem & Katchalsky (Kedem & Katchalsky 1958 Biochim. Biophys. Acta 27, 229-246 (doi:10.1016/0006-3002(58)90330-5), which have hitherto been validated experimentally but not theoretically. The above linearity between the fluxes and the driving forces breaks down for concentrated or non-ideal mixtures, for which our equations go beyond the Kedem-Katchalsky formulation. We show that the heretofore empirical solute permeability coefficient reflects the momentum transfer between the solute molecules that are rejected at a pore entrance and the solvent molecules entering the pore space; it can be related to the inefficiency of a Maxwellian demi-demon. PMID:26064566
Multi-contrast 3D X-ray imaging of porous and composite materials
Sarapata, Adrian; Herzen, Julia; Ruiz-Yaniz, Maite; Zanette, Irene; Rack, Alexander; Pfeiffer, Franz
2015-04-13
Grating-based X-ray computed tomography allows for simultaneous and nondestructive determination of the full X-ray complex index of refraction and the scattering coefficient distribution inside an object in three dimensions. Its multi-contrast capabilities combined with a high resolution of a few micrometers make it a suitable tool for assessing multiple phases inside porous and composite materials such as concrete. Here, we present quantitative results of a proof-of-principle experiment performed on a concrete sample. Thanks to the complementarity of the contrast channels, more concrete phases could be distinguished than in conventional attenuation-based imaging. The phase-contrast reconstruction shows high contrast between the hardened cement paste and the aggregates and thus allows easy 3D segmentation. Thanks to the dark-field image, micro-cracks inside the coarse aggregates are visible. We believe that these results are extremely interesting in the field of porous and composite materials studies because of unique information provided by grating interferometry in a non-destructive way.
Amperometric biosensor based on 3D ordered freestanding porous Pt nanowire array electrode.
Wang, Yunli; Zhu, Yingchun; Chen, Jingjing; Zeng, Yi
2012-09-28
A three-dimensionally (3D) ordered freestanding porous platinum (Pt) nanowire array electrode (PPNWAE) with pores of several nanometers in size and a Pt nanowire array electrode (PNWAE) without pores were facilely fabricated by metal electrodeposition and direct integration with a Pt disk electrode. The unusual PPNWAE with high active area showed excellent sensitivity (0.36 mA cm(-2) mM(-1)) and a wide detection range (4.5 μM-27.1 mM) to hydrogen peroxide (H(2)O(2)). A glucose oxidase (GOD)-based biosensor (PPNWAE/GOD) with a considerably wide detection range (4.5 μM-189.5 mM) to glucose was demonstrated. Furthermore, a lower detection limit, higher sensitivity and smaller value of Michaelis-Menten constant k(m) were recorded for PPNWAE-based biosensors compared with PNWAE-based biosensors. Particularly, the response current to glucose of PPNWAE/GOD was ca. 100% higher than that of PNWAE/GOD and the response current to H(2)O(2) of PPNWAE was ca. 50% higher than that of PNWAE, owing to the granular and rougher porous nanowire surface enabling greater bioactivity for GOD. The selectivity of PPNWAE/GOD glucose biosensor was also estimated. PMID:22898987
Maji, Kanchan; Dasgupta, Sudip; Pramanik, Krishna; Bissoyi, Akalabya
2016-01-01
The aim of the present study was to prepare and characterize bioglass-natural biopolymer based composite scaffold and evaluate its bone regeneration ability. Bioactive glass nanoparticles (58S) in the size range of 20–30 nm were synthesized using sol-gel method. Porous scaffolds with varying bioglass composition from 10 to 30 wt% in chitosan, gelatin matrix were fabricated using the method of freeze drying of its slurry at 40 wt% solids loading. Samples were cross-linked with glutaraldehyde to obtain interconnected porous 3D microstructure with improved mechanical strength. The prepared scaffolds exhibited >80% porosity with a mean pore size range between 100 and 300 microns. Scaffold containing 30 wt% bioglass (GCB 30) showed a maximum compressive strength of 2.2 ± 0.1 MPa. Swelling and degradation studies showed that the scaffold had excellent properties of hydrophilicity and biodegradability. GCB 30 scaffold was shown to be noncytotoxic and supported mesenchymal stem cell attachment, proliferation, and differentiation as indicated by MTT assay and RUNX-2 expression. Higher cellular activity was observed in GCB 30 scaffold as compared to GCB 0 scaffold suggesting the fact that 58S bioglass nanoparticles addition into the scaffold promoted better cell adhesion, proliferation, and differentiation. Thus, the study showed that the developed composite scaffolds are potential candidates for regenerating damaged bone tissue. PMID:26884764
Evaluation of 3D nano-macro porous bioactive glass scaffold for hard tissue engineering.
Wang, S; Falk, M M; Rashad, A; Saad, M M; Marques, A C; Almeida, R M; Marei, M K; Jain, H
2011-05-01
Recently, nano-macro dual-porous, three-dimensional (3D) glass structures were developed for use as bioscaffolds for hard tissue regeneration, but there have been concerns regarding the interconnectivity and homogeneity of nanopores in the scaffolds, as well as the cytotoxicity of the environment deep inside due to limited fluid access. Therefore, mercury porosimetry, nitrogen absorption, and TEM have been used to characterize nanopore network of the scaffolds. In parallel, viability of MG 63 human osteosarcoma cells seeded on scaffold surface was investigated by fluorescence, confocal and electron microscopy methods. The results show that cells attach, migrate and penetrate inside the glass scaffold with high proliferation and viability rate. Additionally, scaffolds were implanted under the skin of a male New Zealand rabbit for in vivo animal test. Initial observations show the formation of new tissue with blood vessels and collagen fibers deep inside the implanted scaffolds with no obvious inflammatory reaction. Thus, the new nano-macro dual-porous glass structure could be a promising bioscaffold for use in regenerative medicine and tissue engineering for bone regeneration. PMID:21445655
Primary human osteoblast culture on 3D porous collagen-hydroxyapatite scaffolds.
Jones, Gemma L; Walton, Robin; Czernuszka, Jan; Griffiths, Sarah L; El Haj, Alicia J; Cartmell, Sarah H
2010-09-15
There is a need in tissue-engineering for 3D scaffolds that mimic the natural extracellular matrix of bone to enhance cell adhesion, proliferation, and differentiation. The scaffold is also required to be degradable. A highly porous scaffold has been developed to incorporate two of the extracellular components found in bone-collagen and hydroxyapatite (HA). The scaffold's collagen component is an afibrillar monomeric type I atelocollagen extracted from foetal calf's skin. This provided a novel environment for the inclusion of HA powder. Five hundred thousand primary human osteoblasts were seeded onto 4 mm cubed scaffolds that varied in ratio of HA to collagen. Weight ratios of 1:99, 25:75, 50:50, and 75:25 hydroxyapatite:collagen (HA:Collagen) were analysed. The scaffolds plus cells were cultured for 21 days. DNA assays and live/dead viability staining demonstrated that all of the scaffolds supported cell proliferation and viability. An alkaline phosphatase assay showed similar osteoblast phenotype maintenance on all of the 3D scaffolds analysed at 21 days. MicroCT analysis demonstrated an increase in total sample volume (correlating to increase in unmineralised matrix production). An even distribution of HA throughout the collagen matrix was observed using this technique. Also at 3 weeks, reductions in the percentage of the mineralised phase of the constructs were seen. These results indicate that each of the ratios of HA/collagen scaffolds have great potential for bone tissue engineering. PMID:20694991
Non-parametric 3D map of the intergalactic medium using the Lyman-alpha forest
NASA Astrophysics Data System (ADS)
Cisewski, Jessi; Croft, Rupert A. C.; Freeman, Peter E.; Genovese, Christopher R.; Khandai, Nishikanta; Ozbek, Melih; Wasserman, Larry
2014-05-01
Visualizing the high-redshift Universe is difficult due to the dearth of available data; however, the Lyman-alpha forest provides a means to map the intergalactic medium at redshifts not accessible to large galaxy surveys. Large-scale structure surveys, such as the Baryon Oscillation Spectroscopic Survey (BOSS), have collected quasar (QSO) spectra that enable the reconstruction of H I density fluctuations. The data fall on a collection of lines defined by the lines of sight (LOS) of the QSO, and a major issue with producing a 3D reconstruction is determining how to model the regions between the LOS. We present a method that produces a 3D map of this relatively uncharted portion of the Universe by employing local polynomial smoothing, a non-parametric methodology. The performance of the method is analysed on simulated data that mimics the varying number of LOS expected in real data, and then is applied to a sample region selected from BOSS. Evaluation of the reconstruction is assessed by considering various features of the predicted 3D maps including visual comparison of slices, probability density functions (PDFs), counts of local minima and maxima, and standardized correlation functions. This 3D reconstruction allows for an initial investigation of the topology of this portion of the Universe using persistent homology.
The numerical simulation for a 3D two-phase anisotropic medium based on BISQ model
NASA Astrophysics Data System (ADS)
Wang, Zhejiang; He, Qiaodeng; Wang, Deli
2008-03-01
Biot-flow and squirt-flow are the two most important fluid flow mechanisms in porous media containing fluids. Based on the BISQ (Biot-Squirt) model where the two mechanisms are treated simultaneously, the elastic wave-field simulation in the porous medium is limited to two-dimensions and two-components (2D2C) or two-dimensions and three-components (2D3C). There is no previous report on wave simulation in three-dimensions and three-components. Only through three dimensional numerical simulations can we have an overall understanding of wave field coupling relations and the spatial distribution characteristics between the solid and fluid phases in the dual-phase anisotropic medium. In this paper, based on the BISQ equation, we present elastic wave propagation in a three dimensional dual-phase anisotropic medium simulated by the staggered-grid high-order finite-difference method. We analyze the resulting wave fields and show that the results are an improvement.
NASA Astrophysics Data System (ADS)
Bao, Weizhai; Mondal, Anjon Kumar; Xu, Jing; Wang, Chengyin; Su, Dawei; Wang, Guoxiu
2016-09-01
We report a rational design and synthesis of 3D hybrid-porous carbon with a hierarchical pore architecture for high performance supercapacitors. It contains micropores (<2 nm diameter) and mesopores (2-4 nm), derived from carbonization of unique porous metal organic frameworks (MOFs). Owning to the synergistic effect of micropores and mesopores, the hybrid-porous carbon has exceptionally high ion-accessible surface area and low ion diffusion resistance, which is desired for supercapacitor applications. When applied as electrode materials in supercapacitors, 3D hybrid-porous carbon demonstrates a specific capacitance of 332 F g-1 at a constant charge/discharge current of 500 mA g-1. The supercapacitors can endure more than 10,000 cycles without degradation of capacitance.
Lee, Kwang Hoon; Lee, Young-Woo; Lee, Seung Woo; Ha, Jeong Sook; Lee, Sang-Soo; Son, Jeong Gon
2015-01-01
A simple ice-templated self-assembly process is used to prepare a three-dimensional (3D) and vertically porous nanocomposite of layered vanadium phosphates (VOPO4) and graphene nanosheets with high surface area and high electrical conductivity. The resulting 3D VOPO4–graphene nanocomposite has a much higher capacitance of 527.9 F g−1 at a current density of 0.5 A g−1, compared with ~247 F g−1 of simple 3D VOPO4, with solid cycling stability. The enhanced pseudocapacitive behavior mainly originates from vertically porous structures from directionally grown ice crystals and simultaneously inducing radial segregation and forming inter-stacked structures of VOPO4–graphene nanosheets. This VOPO4–graphene nanocomposite electrode exhibits high surface area, vertically porous structure to the separator, structural stability from interstacked structure and high electrical conductivity, which would provide the short diffusion paths of electrolyte ions and fast transportation of charges within the conductive frameworks. In addition, an asymmetric supercapacitor (ASC) is fabricated by using vertically porous VOPO4–graphene as the positive electrode and vertically porous 3D graphene as the negative electrode; it exhibits a wide cell voltage of 1.6 V and a largely enhanced energy density of 108 Wh kg−1. PMID:26333591
3D distribution of interstellar medium in the Galaxy: Preparation for analysis of Gaia observations
NASA Astrophysics Data System (ADS)
Puspitarini, Lucky; Lallement, Rosine
2015-09-01
Accurate and detailed three-dimensional (3D) maps of Galactic interstellar medium (ISM) are still lacking. One way to obtain such 3D descriptions is to record a large set of individual absorption or reddening measurements toward target stars located at various known distances and directions. The inversion of these measurements using a tomographic method can produce spatial distribution of the ISM. Until recently absorption data were very limited and distances to the target stars are still uncertain, but the situation will greatly improve thanks to current and future massive stellar surveys from ground, and to Gaia mission. To prepare absorption data for inversion from a huge number of stellar spectra, automated tools are needed. We have developed various spectral analysis tools adapted to different type of spectra, early- or late- type star. We also have used diffuse interstellar bands (DIBs) to trace IS structures and kinematics. Although we do not know yet their carriers, they can be a promising tool to trace distant interstellar clouds or Galactic arms. We present some examples of the interstellar fitting and show the potentiality of DIBs in tracing the ISM. We will also briefly show and comment the latest 3D map of the local ISM which reveal nearby cloud complexes and cavities.
3D distribution of interstellar medium in the Galaxy: Preparation for analysis of Gaia observations
Puspitarini, Lucky; Lallement, Rosine
2015-09-30
Accurate and detailed three-dimensional (3D) maps of Galactic interstellar medium (ISM) are still lacking. One way to obtain such 3D descriptions is to record a large set of individual absorption or reddening measurements toward target stars located at various known distances and directions. The inversion of these measurements using a tomographic method can produce spatial distribution of the ISM. Until recently absorption data were very limited and distances to the target stars are still uncertain, but the situation will greatly improve thanks to current and future massive stellar surveys from ground, and to Gaia mission. To prepare absorption data for inversion from a huge number of stellar spectra, automated tools are needed. We have developed various spectral analysis tools adapted to different type of spectra, early- or late- type star. We also have used diffuse interstellar bands (DIBs) to trace IS structures and kinematics. Although we do not know yet their carriers, they can be a promising tool to trace distant interstellar clouds or Galactic arms. We present some examples of the interstellar fitting and show the potentiality of DIBs in tracing the ISM. We will also briefly show and comment the latest 3D map of the local ISM which reveal nearby cloud complexes and cavities.
3D Printing Bioceramic Porous Scaffolds with Good Mechanical Property and Cell Affinity
Chang, Chih-Hao; Lin, Chih-Yang; Liu, Fwu-Hsing; Chen, Mark Hung-Chih; Lin, Chun-Pin; Ho, Hong-Nerng; Liao, Yunn-Shiuan
2015-01-01
Artificial bone grafting is widely used in current orthopedic surgery for bone defect problems. Unfortunately, surgeons remain unsatisfied with the current commercially available products. One of the major complaints is that these products cannot provide sufficient mechanical strength to support the human skeletal structure. In this study, we aimed to develop a bone scaffold with better mechanical property and good cell affinity by 3D printing (3DP) techniques. A self-developed 3D printer with laser-aided gelling (LAG) process was used to fabricate bioceramic scaffolds with inter-porous structures. To improve the mechanical property of the bioceramic parts after heating, CaCO3 was added to the silica ceramic slurry. CaCO3 was blended into a homogenous SiO2-sol dispersion at weight ratios varying from 0/100 to 5/95 to 9/91 (w/w). Bi-component CaCO3/SiO2-sol was prepared as a biocomposite for the 3DP scaffold. The well-mixed biocomposite was used to fabricate the bioceramic green part using the LAG method. The varied scaffolds were sintered at different temperatures ranging from 900 to 1500°C, and the mechanical property was subsequently analyzed. The scaffolds showed good property with the composite ratio of 5:95 CaCO3:SiO2 at a sintering temperature of 1300°C. The compressive strength was 47 MPa, and the porosity was 34%. The topography of the sintered 3DP bioceramic scaffold was examined by SEM, EDS and XRD. The silica bioceramic presented no cytotoxicity and good MG-63 osteoblast-like cell affinity, demonstrating good biocompatibility. Therefore, the new silica biocomposite is viable for fabricating 3DP bone bioceramics with improved mechanical property and good cell affinity. PMID:26618362
3D Printing Bioceramic Porous Scaffolds with Good Mechanical Property and Cell Affinity.
Chang, Chih-Hao; Lin, Chih-Yang; Liu, Fwu-Hsing; Chen, Mark Hung-Chih; Lin, Chun-Pin; Ho, Hong-Nerng; Liao, Yunn-Shiuan
2015-01-01
Artificial bone grafting is widely used in current orthopedic surgery for bone defect problems. Unfortunately, surgeons remain unsatisfied with the current commercially available products. One of the major complaints is that these products cannot provide sufficient mechanical strength to support the human skeletal structure. In this study, we aimed to develop a bone scaffold with better mechanical property and good cell affinity by 3D printing (3DP) techniques. A self-developed 3D printer with laser-aided gelling (LAG) process was used to fabricate bioceramic scaffolds with inter-porous structures. To improve the mechanical property of the bioceramic parts after heating, CaCO3 was added to the silica ceramic slurry. CaCO3 was blended into a homogenous SiO2-sol dispersion at weight ratios varying from 0/100 to 5/95 to 9/91 (w/w). Bi-component CaCO3/SiO2-sol was prepared as a biocomposite for the 3DP scaffold. The well-mixed biocomposite was used to fabricate the bioceramic green part using the LAG method. The varied scaffolds were sintered at different temperatures ranging from 900 to 1500°C, and the mechanical property was subsequently analyzed. The scaffolds showed good property with the composite ratio of 5:95 CaCO3:SiO2 at a sintering temperature of 1300°C. The compressive strength was 47 MPa, and the porosity was 34%. The topography of the sintered 3DP bioceramic scaffold was examined by SEM, EDS and XRD. The silica bioceramic presented no cytotoxicity and good MG-63 osteoblast-like cell affinity, demonstrating good biocompatibility. Therefore, the new silica biocomposite is viable for fabricating 3DP bone bioceramics with improved mechanical property and good cell affinity. PMID:26618362
Magnetic field penetration into a 3D ordered Josephson medium and applicability of the bean model
NASA Astrophysics Data System (ADS)
Zelikman, M. A.
2014-11-01
The results of calculation of penetration of an external magnetic field into a 3D ordered Josephson medium, based on analysis of modification of the configuration in the direction of the decrease in its Gibbs potential, are reported. When the external field slightly exceeds the stability threshold, the Meissner configuration is transformed into a periodic sequence of linear vortices, which are parallel to the boundary of the medium and are located at a certain distance from it. There exists a critical value I C separating two possible regimes of penetration of the external magnetic field into the medium. For I > I C, for any value of the external field, a finite-length boundary current configuration appears, which completely compensates the external field in the bulk of the sample. At the sample boundary, the field decreases with increasing depth almost linearly. The values of the slope of the magnetic field dependence are rational fractions, which remain constant in finite intervals of I. When the value of I exceeds the upper boundary of such an interval, the slope increases and assumes the value of another rational fraction. If, however, I < I C, such a situation takes place only up to a certain value of external field H max. For higher values, the field penetrates into the medium to an infinite depth. These results lead to the conclusion that the Bean assumptions are violated and that Bean's model is inapplicable for analyzing the processes considered here.
Osteogenic effect of controlled released rhBMP-2 in 3D printed porous hydroxyapatite scaffold.
Wang, Hai; Wu, Gui; Zhang, Jing; Zhou, Kui; Yin, Bo; Su, Xinlin; Qiu, Guixing; Yang, Guang; Zhang, Xianglin; Zhou, Gang; Wu, Zhihong
2016-05-01
Recently, 3D printing as effective technology has been highlighted in the biomedical field. Previously, a porous hydroxyapatite (HA) scaffold with the biocompatibility and osteoconductivity has been developed by this method. However, its osteoinductivity is limited. The main purpose of this study was to improve it by the introduction of recombinant human bone morphogenetic protein-2 (rhBMP-2). This scaffold was developed by coating rhBMP-2-delivery microspheres with collagen. These synthesized scaffolds were characterized by Scanning Electron Microscopy (SEM), a delivery test in vitro, cell culture, and the experiments in vivo by a Micro-computed tomography (μCT) scan and histological evaluation of VanGieson staining. SEM results indicated the surface of scaffolds were more fit for the adhesion of hMSCs to coat collagen/rhBMP-2 microspheres. Biphasic release of rhBMP-2 could continue for more than 21 days, and keep its osteoinductivity to induce osteogenic differentiation of hMSCs in vitro. In addition, the experiments in vivo showed that the scaffold had a good bone regeneration capacity. These findings demonstrate that the HA/Collagen/Chitosan Microspheres system can simultaneously achieve localized long-term controlled release of rhBMP-2 and bone regeneration, which provides a promising route for improving the treatment of bone defects. PMID:26896655
Cation Exchange in Dynamic 3D Porous Magnets: Improvement of the Physical Properties.
Grancha, Thais; Acosta, Alvaro; Cano, Joan; Ferrando-Soria, Jesús; Seoane, Beatriz; Gascon, Jorge; Pasán, Jorge; Armentano, Donatella; Pardo, Emilio
2015-11-16
We report two novel three-dimensional porous coordination polymers (PCPs) of formulas Li4{Mn4[Cu2(Me3mpba)2]3}·68H2O (2) and K4{Mn4[Cu2(Me3mpba)2]3}·69H2O (3) obtained-via alkali cation exchange in a single-crystal to single-crystal process-from the earlier reported anionic manganese(II)-copper(II) PCP of formula Na4{Mn4[Cu2(Me3mpba)2]3}·60H2O (1) [Me3mpba(4-) = N,N'-2,4,6-trimethyl-1,3-phenylenebis(oxamate)]. This postsynthetic process succeeds where the direct synthesis in solution from the corresponding building blocks fails and affords significantly more robust PCPs with enhanced magnetic properties [long-range 3D magnetic ordering temperatures for the dehydrated phases (1'-3') of 2.0 (1'), 12.0 (2'), and 20.0 K (3')]. Changes in the adsorptive properties upon postsynthetic exchange suggest that the nature, electrostatic properties, mobility, and location of the cations within the framework are crucial for the enhanced structural stability. Overall, these results further confirm the potential of postsynthetic methods (including cation exchange) to obtain PCPs with novel or enhanced physical properties while maintaining unaltered their open-framework structures. PMID:26492551
NASA Astrophysics Data System (ADS)
De Lucia, Marco; Kühn, Michael
2015-04-01
The 3D imaging of porous media through micro tomography allows the characterization of porous space and mineral abundances with unprecedented resolution. Such images can be used to perform computational determination of permeability and to obtain a realistic measure of the mineral surfaces exposed to fluid flow and thus to chemical interactions. However, the volume of the plugs that can be analysed with such detail is in the order of 1 cm3, so that their representativity at a larger scale, i.e. as needed for reactive transport modelling at Darcy scale, is questionable at best. In fact, the fine scale heterogeneity (from plug to plug at few cm distance within the same core) would originate substantially different readings of the investigated properties. Therefore, a comprehensive approach including the spatial variability and heterogeneity at the micro- and plug scale needs to be adopted to gain full advantage from the high resolution images in view of the upscaling to Darcy scale. In the framework of the collaborative project H2STORE, micro-CT imaging of different core samples from potential H2-storage sites has been performed by partners at TU Clausthal and Jena University before and after treatment with H2/CO2 mixtures in pressurized autoclaves. We present here the workflow which has been implemented to extract the relevant features from the available data concerning the heterogeneity of the medium at the microscopic and plug scale and to correlate the observed chemical reactions and changes in the porous structure with the geometrical features of the medium. First, a multivariate indicator-based geostatistical model for the microscopic structure of the plugs has been built and fitted to the available images. This involved the implementation of exploratory analysis algorithms such as experimental indicator variograms and cross-variograms. The implemented methods are able to efficiently deal with images in the order of 10003 voxels making use of parallelization
Simultaneous elastic parameter inversion in 2-D/3-D TTI medium combined later arrival times
NASA Astrophysics Data System (ADS)
Bai, Chao-ying; Wang, Tao; Yang, Shang-bei; Li, Xing-wang; Huang, Guo-jiao
2016-04-01
Traditional traveltime inversion for anisotropic medium is, in general, based on a "weak" assumption in the anisotropic property, which simplifies both the forward part (ray tracing is performed once only) and the inversion part (a linear inversion solver is possible). But for some real applications, a general (both "weak" and "strong") anisotropic medium should be considered. In such cases, one has to develop a ray tracing algorithm to handle with the general (including "strong") anisotropic medium and also to design a non-linear inversion solver for later tomography. Meanwhile, it is constructive to investigate how much the tomographic resolution can be improved by introducing the later arrivals. For this motivation, we incorporated our newly developed ray tracing algorithm (multistage irregular shortest-path method) for general anisotropic media with a non-linear inversion solver (a damped minimum norm, constrained least squares problem with a conjugate gradient approach) to formulate a non-linear inversion solver for anisotropic medium. This anisotropic traveltime inversion procedure is able to combine the later (reflected) arrival times. Both 2-D/3-D synthetic inversion experiments and comparison tests show that (1) the proposed anisotropic traveltime inversion scheme is able to recover the high contrast anomalies and (2) it is possible to improve the tomographic resolution by introducing the later (reflected) arrivals, but not as expected in the isotropic medium, because the different velocity (qP, qSV and qSH) sensitivities (or derivatives) respective to the different elastic parameters are not the same but are also dependent on the inclination angle.
Intermittent Lagrangian velocities and accelerations in three-dimensional porous medium flow.
Holzner, M; Morales, V L; Willmann, M; Dentz, M
2015-07-01
Intermittency of Lagrangian velocity and acceleration is a key to understanding transport in complex systems ranging from fluid turbulence to flow in porous media. High-resolution optical particle tracking in a three-dimensional (3D) porous medium provides detailed 3D information on Lagrangian velocities and accelerations. We find sharp transitions close to pore throats, and low flow variability in the pore bodies, which gives rise to stretched exponential Lagrangian velocity and acceleration distributions characterized by a sharp peak at low velocity, superlinear evolution of particle dispersion, and double-peak behavior in the propagators. The velocity distribution is quantified in terms of pore geometry and flow connectivity, which forms the basis for a continuous-time random-walk model that sheds light on the observed Lagrangian flow and transport behaviors. PMID:26274277
Intermittent Lagrangian velocities and accelerations in three-dimensional porous medium flow
NASA Astrophysics Data System (ADS)
Holzner, M.; Morales, V. L.; Willmann, M.; Dentz, M.
2015-07-01
Intermittency of Lagrangian velocity and acceleration is a key to understanding transport in complex systems ranging from fluid turbulence to flow in porous media. High-resolution optical particle tracking in a three-dimensional (3D) porous medium provides detailed 3D information on Lagrangian velocities and accelerations. We find sharp transitions close to pore throats, and low flow variability in the pore bodies, which gives rise to stretched exponential Lagrangian velocity and acceleration distributions characterized by a sharp peak at low velocity, superlinear evolution of particle dispersion, and double-peak behavior in the propagators. The velocity distribution is quantified in terms of pore geometry and flow connectivity, which forms the basis for a continuous-time random-walk model that sheds light on the observed Lagrangian flow and transport behaviors.
Anisotropy of a synthetic layered porous medium
Furre, A.K.; Holt, R.M.
1995-12-31
Artificial, periodically laminated porous sandstones are manufactured in order to study acoustic behavior compared to permeability of porous rocks. Cores are made by mixing sand and epoxy. The laminated media are built up by two alternating types of layers, one highly permeable layer with low velocity, the other with lower permeability but higher velocity (the permeability of each layer is, however, of the order of 1-50 Darcy). Permeability and acoustic measurements are performed at different incidence angles to the layers. The wave velocities in dry samples show anisotropy largely confirming the Backus theory. Fluid saturation increases the velocities and introduces an attenuation anisotropy which may be linked to fluid flow anisotropy. The spectral contents of the waves traces do not depend on the angle of incidence, in contrast to the case when anisotropy is induced by fractures.
NASA Astrophysics Data System (ADS)
Mural, Prasanna Kumar S.; Jain, Shubham; Kumar, Sachin; Madras, Giridhar; Bose, Suryasarathi
2016-04-01
3D porous membranes were developed by etching one of the phases (here PEO, polyethylene oxide) from melt-mixed PE/PEO binary blends. Herein, we have systematically discussed the development of these membranes using X-ray micro-computed tomography. The 3D tomograms of the extruded strands and hot-pressed samples revealed a clear picture as to how the morphology develops and coarsens over a function of time during post-processing operations like compression molding. The coarsening of PE/PEO blends was traced using X-ray micro-computed tomography and scanning electron microscopy (SEM) of annealed blends at different times. It is now understood from X-ray micro-computed tomography that by the addition of a compatibilizer (here lightly maleated PE), a stable morphology can be visualized in 3D. In order to anchor biocidal graphene oxide sheets onto these 3D porous membranes, the PE membranes were chemically modified with acid/ethylene diamine treatment to anchor the GO sheets which were further confirmed by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and surface Raman mapping. The transport properties through the membrane clearly reveal unimpeded permeation of water which suggests that anchoring GO on to the membranes does not clog the pores. Antibacterial studies through the direct contact of bacteria with GO anchored PE membranes resulted in 99% of bacterial inactivation. The possible bacterial inactivation through physical disruption of the bacterial cell wall and/or reactive oxygen species (ROS) is discussed herein. Thus this study opens new avenues in designing polyolefin based antibacterial 3D porous membranes for water purification.3D porous membranes were developed by etching one of the phases (here PEO, polyethylene oxide) from melt-mixed PE/PEO binary blends. Herein, we have systematically discussed the development of these membranes using X-ray micro-computed tomography. The 3D tomograms of the extruded strands and
Rolland du Roscoat, S; Martins, J M F; Séchet, P; Vince, E; Latil, P; Geindreau, C
2014-06-01
The development of reliable models to accurately predict biofilm growth in porous media relies on a good knowledge of the temporal evolution of biofilms structure within the porous network. Since little is known on the true 3D structure of biofilms developed in porous media, this work aimed at developing a new experimental protocol to visualize the 3D microstructure of bacterial biofilms in porous media. The main originality of the proposed procedure lies on the combination of the more recent advances in synchrotron microtomography (Paganin mode) and of a new contrast agent (1-chloronaphtalene) that has never been applied to biofilm visualization. It is shown that the proposed methodology takes advantage of the contrasting properties of 1-chloronaphtalene to prevent some limitations observed with more classical contrast agents. A quantitative analysis of the microstructural properties (volume fractions and specific surface area) of bacterial biofilms developed in columns of clay beads is also proposed on the basis of the obtained 3D images. PMID:24293082
Vigorous convection in a layered, heterogeneous porous medium
NASA Astrophysics Data System (ADS)
Hewitt, D.; Neufeld, J. A.; Lister, J. R.
2014-12-01
Convective flow in a porous medium plays an important role in numerous geophysical and industrial processes, and has recently been investigated in the context of geological CO2 sequestration. Previous studies of vigorous porous convection at high Rayleigh number Ra have focused on homogeneous porous media, whereas natural porous media are often highly heterogeneous. In particular, many geological porous formations are interspersed with thin, roughly horizontal, low-permeability layers. In order to gain understanding of the interaction of low-permeability layering with convective flow, and to develop simple parameterized models of the underlying physical processes, we have performed a numerical study of high-Ra convection in a two-dimensional porous medium that contains a thin, horizontal, low-permeability interior layer. The medium is heated at the lower boundary and cooled at the upper, which sets up statistically steady convective flow throughout the domain. This archetypal system is readily applicable to compositional convection, owing to an assumption of thermal equilibrium between solid and liquid phase in the medium. We show that, in the limit that both the dimensionless thickness h and permeability Π of the low-permeability layer are small, the flow is described solely by the impedance of the layer Ω= h/Π and by Ra. As Ω → 0 (i.e. h → 0), the system reduces to a homogeneous medium. We observe two notable features as Ω is increased: the dominant horizontal lengthscale of the flow increases; and, surprisingly, the heat flux through the cell, as measured by the Nusselt number Nu, can increase. For larger values of Ω, Nu always decreases. We explore the dependence of the flow on Ra, and develop simple theoretical models to describe some of the observed features of the relationship Nu(Ω). The theoretical models have implications for the simulation of convective dissolution of CO2 at reservoir scales, as heterogeneities can be much smaller than the grid
3D Characterization of the Magnetic Signature of a Medium Sized Impact Crater at Odessa, TX
NASA Astrophysics Data System (ADS)
Robinson, A.; Soule, D.; Everett, M.; Rodman, T.; Mangue Ndong, M.; Pereira, A.; Platt, P.; Trahan, A.
2008-12-01
Meteorite impacts are a common occurrence throughout Earth's geologic history. Many of the surface expressions of large ancient impacts have been subsequently erased by weathering and erosion processes. The study of preserved meteorite impacts is necessary to better understand this natural hazard which has been increasingly linked to rapid climate change and mass extinctions. The 60 ka Odessa meteorite crater located in Ector Co. Texas, is unique because it is not only well-preserved, but also has been the subject of extensive geologic examination. Geologic mapping and numeric models indicate that the crater was caused by a relatively small oblique impactor. The crater rim is remarkably well exposed. Much of the ejecta blanket is present, although deeply eroded. There has been considerable site disturbance due to drilling, shaft excavation, trenching, construction of a museum, trails, and the oil/gas activity in surrounding fields. Two previous geophysical investigations have shown that our data clearly corresponds to large-scale thrust deformation. With this in mind we have performed 3D high resolution magnetic gradiometer surveys that will allow us to quantify and characterize the magnetic signature of small to medium impacts. We will tie this data set to a 3D photorealistic outcrop image provided by laser scanning with coarser-scale, below-ground geophysical information. Our geophysical imagery provides a useful constraint on numerical simulations of the impact and its immediate regional-scale environmental effects. This information can be used to identify impact sites whose surface expression has been erased by natural erosional processes, allowing for improved frequency estimates and improved geo-hazard assessment.
A geometric pore-scale model for predicting the permeability of 3D flow through fibrous porous media
NASA Astrophysics Data System (ADS)
Woudberg, Sonia
2012-05-01
A geometric pore-scale model, based on rectangular geometry, is used to quantify the fluid-solid interaction in fibrous porous media in order to predict the permeability. The analytical modeling procedure is based on sound physical principles. Permeability predictions are presented for flow parallel and perpendicular to the axes of unidirectional fibres. In the latter case maximum possible staggering is introduced. A weighted average is performed to obtain the permeability prediction for 3D flow through fibrous porous media. Effects such as pore blockage at very low porosities and developing flow are incorporated into the predictive equations for the permeability to provide a model that is applicable over the entire porosity range. The resulting 3D model leads to satisfactory agreement with other three-dimensional models and data from the literature.
NASA Astrophysics Data System (ADS)
Jung, Gyeong-Bok; Kim, Ji-Hye; Burm, Jin Sik; Park, Hun-Kuk
2013-05-01
We propose a simple, low-cost, large-area, and functional surface enhanced Raman scattering (SERS) substrate for biomedical applications. The SERS substrate with chitosan-silver nanoparticles (chitosan-Ag NPs) hybrid 3D porous structure was fabricated simply by a one-step method. The chitosan was used as a template for the Ag NPs deposition. SERS enhancement by the chitosan-Ag NPs substrate was experimentally verified using rhodamine B as an analyte. Thiolated single stranded DNA was also measured for atopic dermatitis genetic markers (chemokines CCL17) at a low concentration of 5 pM. We successfully designed a novel SERS substrate with silver nanoparticle hybridized 3D porous chitosan that has the potential to become a highly sensitive and selective tool for biomedical applications.
Ren, Long; Hui, K N; Hui, K S; Liu, Yundan; Qi, Xiang; Zhong, Jianxin; Du, Yi; Yang, Jianping
2015-01-01
New and novel 3D hierarchical porous graphene aerogels (HPGA) with uniform and tunable meso-pores (e.g., 21 and 53 nm) on graphene nanosheets (GNS) were prepared by a hydrothermal self-assembly process and an in-situ carbothermal reaction. The size and distribution of the meso-pores on the individual GNS were uniform and could be tuned by controlling the sizes of the Co3O4 NPs used in the hydrothermal reaction. This unique architecture of HPGA prevents the stacking of GNS and promises more electrochemically active sites that enhance the electrochemical storage level significantly. HPGA, as a lithium-ion battery anode, exhibited superior electrochemical performance, including a high reversible specific capacity of 1100 mAh/g at a current density of 0.1 A/g, outstanding cycling stability and excellent rate performance. Even at a large current density of 20 A/g, the reversible capacity was retained at 300 mAh/g, which is larger than that of most porous carbon-based anodes reported, suggesting it to be a promising candidate for energy storage. The proposed 3D HPGA is expected to provide an important platform that can promote the development of 3D topological porous systems in a range of energy storage and generation fields. PMID:26382852
Ren, Long; Hui, K. N.; Hui, K. S.; Liu, Yundan; Qi, Xiang; Zhong, Jianxin; Du, Yi; Yang, Jianping
2015-01-01
New and novel 3D hierarchical porous graphene aerogels (HPGA) with uniform and tunable meso-pores (e.g., 21 and 53 nm) on graphene nanosheets (GNS) were prepared by a hydrothermal self-assembly process and an in-situ carbothermal reaction. The size and distribution of the meso-pores on the individual GNS were uniform and could be tuned by controlling the sizes of the Co3O4 NPs used in the hydrothermal reaction. This unique architecture of HPGA prevents the stacking of GNS and promises more electrochemically active sites that enhance the electrochemical storage level significantly. HPGA, as a lithium-ion battery anode, exhibited superior electrochemical performance, including a high reversible specific capacity of 1100 mAh/g at a current density of 0.1 A/g, outstanding cycling stability and excellent rate performance. Even at a large current density of 20 A/g, the reversible capacity was retained at 300 mAh/g, which is larger than that of most porous carbon-based anodes reported, suggesting it to be a promising candidate for energy storage. The proposed 3D HPGA is expected to provide an important platform that can promote the development of 3D topological porous systems in a range of energy storage and generation fields. PMID:26382852
NASA Astrophysics Data System (ADS)
Ren, Long; Hui, K. N.; Hui, K. S.; Liu, Yundan; Qi, Xiang; Zhong, Jianxin; Du, Yi; Yang, Jianping
2015-09-01
New and novel 3D hierarchical porous graphene aerogels (HPGA) with uniform and tunable meso-pores (e.g., 21 and 53 nm) on graphene nanosheets (GNS) were prepared by a hydrothermal self-assembly process and an in-situ carbothermal reaction. The size and distribution of the meso-pores on the individual GNS were uniform and could be tuned by controlling the sizes of the Co3O4 NPs used in the hydrothermal reaction. This unique architecture of HPGA prevents the stacking of GNS and promises more electrochemically active sites that enhance the electrochemical storage level significantly. HPGA, as a lithium-ion battery anode, exhibited superior electrochemical performance, including a high reversible specific capacity of 1100 mAh/g at a current density of 0.1 A/g, outstanding cycling stability and excellent rate performance. Even at a large current density of 20 A/g, the reversible capacity was retained at 300 mAh/g, which is larger than that of most porous carbon-based anodes reported, suggesting it to be a promising candidate for energy storage. The proposed 3D HPGA is expected to provide an important platform that can promote the development of 3D topological porous systems in a range of energy storage and generation fields.
Mural, Prasanna Kumar S; Jain, Shubham; Kumar, Sachin; Madras, Giridhar; Bose, Suryasarathi
2016-04-14
3D porous membranes were developed by etching one of the phases (here PEO, polyethylene oxide) from melt-mixed PE/PEO binary blends. Herein, we have systematically discussed the development of these membranes using X-ray micro-computed tomography. The 3D tomograms of the extruded strands and hot-pressed samples revealed a clear picture as to how the morphology develops and coarsens over a function of time during post-processing operations like compression molding. The coarsening of PE/PEO blends was traced using X-ray micro-computed tomography and scanning electron microscopy (SEM) of annealed blends at different times. It is now understood from X-ray micro-computed tomography that by the addition of a compatibilizer (here lightly maleated PE), a stable morphology can be visualized in 3D. In order to anchor biocidal graphene oxide sheets onto these 3D porous membranes, the PE membranes were chemically modified with acid/ethylene diamine treatment to anchor the GO sheets which were further confirmed by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and surface Raman mapping. The transport properties through the membrane clearly reveal unimpeded permeation of water which suggests that anchoring GO on to the membranes does not clog the pores. Antibacterial studies through the direct contact of bacteria with GO anchored PE membranes resulted in 99% of bacterial inactivation. The possible bacterial inactivation through physical disruption of the bacterial cell wall and/or reactive oxygen species (ROS) is discussed herein. Thus this study opens new avenues in designing polyolefin based antibacterial 3D porous membranes for water purification. PMID:27020773
NASA Astrophysics Data System (ADS)
Yuan, Zhinan; Zhao, Naiqin; Shi, Chunsheng; Liu, Enzuo; He, Chunnian; He, Fang
2016-05-01
A SiO2/porous carbon nanocomposite was synthesized by a facile combined heat and acid treatments method. The nanocomposite featured a 3D porous carbon structure with amorphous SiO2 nanoparticles embedded in the wall of the pores. The microstructure improved the electrical conductivity, shortened the diffusion distance of lithium ions, and alleviated the volume expansion of SiO2 during Li intercalation. Accordingly, the SiO2/porous carbon nanocomposite displayed excellent cyclic performance with a high reversible capacity of 434 mAh g-1 after 50 cycles at 0.1 A g-1 and rate capability delivering a capacity of 187.4 mAh g-1 even at 5 A g-1.
Characterization of Porous Medium Properties Using 2D NMR
NASA Astrophysics Data System (ADS)
Sun, Boqin; Dunn, Keh-Jim
2003-03-01
We have successfully applied the concept of 2D NMR to the characterization of properties of fluid-saturated porous medium. Using a two-windowed modified CPMG pulse sequence, we were able to explore the magnetic internal filed gradient distribution within the pore space of a fluid-saturated porous medium due to magnetic susceptibility contrast between the solid matrix and pore fluid. Similar scheme is used to identify and quantify different types of pore fluids, such as oil, water, and gas, based on the contrast in their diffusion coefficients. The magic angle spinning technique (MAS) can also be applied in the 2D NMR framework for delineating the chemical shift spectra of the pore fluids in a porous medium at different T1 or T2 relaxation times. The results can be displayed in a two-dimensional plot, with one axis being the T1 or T2 relaxation times, the other axis being the internal field gradient, diffusion coefficient, or chemical shift, and the third axis being the proton population. Our preliminary laboratory work indicates that the 2D NMR approach can be a powerful tool for the characterization of properties of fluid-saturated porous medium, such as fluid typing, oil viscosity determination, surface wettability, etc.
Instability of fluid flow over saturated porous medium
NASA Astrophysics Data System (ADS)
Lyubimova, Tatyana; Kolchanova, Ekaterina; Lyubimov, Dmitry
2013-04-01
We investigate the stability of a fluid flow over a saturated porous medium. The problem is of importance due to the applications to washing out of contaminants from the bottom layer of vegetation, whose properties are similar to the properties of porous medium. In the case of porous medium with the relatively high permeability and porosity the flow involves a part of the fluid saturating the porous medium, with the tangential fluid velocity drop occurring because of the resistance of the solid matrix. The drop leads to the instability analogous to Kelvin-Helmholtz one accompanied by the formation of travelling waves. In the present paper we consider a two-layer system consisting of a pure fluid layer and a porous layer saturated by the fluid located underneath. The system is bounded by a rigid surface at the bottom and a non-deformable free surface at the top. It is under the gravity and inclined at a slight angle to the horizontal axis. The boundary conditions at the interface between the fluid and porous layers are the continuity of fluid velocities and the balance of normal and tangential stresses taking into account the resistance of the solid matrix with respect to the fluid flow near the interface [1-2]. The problem is solved in the framework of the Brinkman model applying the classical shooting algorithm with orthogonalization. The stability boundaries of the stationary fluid flow over the saturated porous medium with respect to the small oscillatory perturbations are obtained for the various values of the Darcy number and the ratio of the porous layer thickness to the full thickness of the system d. It was shown that at the d > 0.5 with increasing the porous layer thickness (or with decreasing of the fluid layer thickness) the stability threshold rises. This is because of the fact that the instability is primarily caused by perturbations located in the fluid layer. At the d < 0.5 the reduction of the porous layer thickness leads to the stability threshold
Instant gelation synthesis of 3D porous MoS2@C nanocomposites for lithium ion batteries
NASA Astrophysics Data System (ADS)
Fei, Ling; Xu, Yun; Wu, Xiaofei; Chen, Gen; Li, Yuling; Li, Binsong; Deng, Shuguang; Smirnov, Sergei; Fan, Hongyou; Luo, Hongmei
2014-03-01
Three-dimensional (3D) nanoporous architectures, possessing high surface area, massive pores, and excellent structural stability, are highly desirable for many applications including catalysts and electrode materials in lithium ion batteries. However, the preparation of such materials remains a major challenge. Here, we introduce a novel method, instant gelation, for the synthesis of such materials. The as-prepared porous 3D MoS2@C nanocomposites, with layered MoS2 clusters or strips ingrained in porous and conductive 3D carbon matrix, indeed showed excellent electrochemical performance when applied as anode materials for lithium ion batteries. Its interconnected carbon network ensures good conductivity and fast electron transport; the micro-, and mesoporous nature effectively shortens the lithium ion diffusion path and provides room necessary for volume expansion. The large specific surface area is beneficial for a better contact between electrode materials and electrolyte.Three-dimensional (3D) nanoporous architectures, possessing high surface area, massive pores, and excellent structural stability, are highly desirable for many applications including catalysts and electrode materials in lithium ion batteries. However, the preparation of such materials remains a major challenge. Here, we introduce a novel method, instant gelation, for the synthesis of such materials. The as-prepared porous 3D MoS2@C nanocomposites, with layered MoS2 clusters or strips ingrained in porous and conductive 3D carbon matrix, indeed showed excellent electrochemical performance when applied as anode materials for lithium ion batteries. Its interconnected carbon network ensures good conductivity and fast electron transport; the micro-, and mesoporous nature effectively shortens the lithium ion diffusion path and provides room necessary for volume expansion. The large specific surface area is beneficial for a better contact between electrode materials and electrolyte. Electronic
NASA Astrophysics Data System (ADS)
Peters, C. A.; Crandell, L. E.; Um, W.; Jones, K. W.; Lindquist, W. B.
2011-12-01
Geochemical reactions in the subsurface can alter the porosity and permeability of a porous medium through mineral precipitation and dissolution. While effects on porosity are relatively well understood, changes in permeability are more difficult to estimate. In this work, pore-network modeling is used to estimate the permeability of a porous medium using pore and throat size distributions. These distributions can be determined from 2D Scanning Electron Microscopy (SEM) images of thin sections or from 3D X-ray Computed Tomography (CT) images of small cores. Each method has unique advantages as well as unique sources of error. 3D CT imaging has the advantage of reconstructing a 3D pore network without the inherent geometry-based biases of 2D images but is limited by resolutions around 1 μm. 2D SEM imaging has the advantage of higher resolution, and the ability to examine sub-grain scale variations in porosity and mineralogy, but is limited by the small size of the sample of pores that are quantified. A pore network model was created to estimate flow permeability in a sand-packed experimental column investigating reaction of sediments with caustic radioactive tank wastes in the context of the Hanford, WA site. Before, periodically during, and after reaction, 3D images of the porous medium in the column were produced using the X2B beam line facility at the National Synchrotron Light Source (NSLS) at Brookhaven National Lab. These images were interpreted using 3DMA-Rock to characterize the pore and throat size distributions. After completion of the experiment, the column was sectioned and imaged using 2D SEM in backscattered electron mode. The 2D images were interpreted using erosion-dilation to estimate the pore and throat size distributions. A bias correction was determined by comparison with the 3D image data. A special image processing method was developed to infer the pore space before reaction by digitally removing the precipitate. The different sets of pore
Asphaltene multilayer growth in porous medium probed by SANS
NASA Astrophysics Data System (ADS)
Gummel, J.; Corvis, Y.; Jestin, J.; M'hamdi, J.; Barré, L.
2009-02-01
Presence of suspended particles such as asphaltene in crude oils could significantly affect the production by means of deposition in porous media especially near the well bore. We investigate this phenomenon using the ability of Small Angle Neutron Scattering technique to probe directly the asphaltene adsorption process in a porous medium at the nanometer length scale under flow conditions. A device based on a quartz tube filled with SiC particles constitute the porous medium in which an asphaltene solution in a mixture of good (toluene)/bad (heptane) solvent is injected under controlled flow. The contrast matching technique enables to match the porous medium scattering contributions and to measure the signal of the deposit. Such a device can be used for curves surface measurements on a setup originally designed for bulk studies and permit thus the direct comparison with measurements on flat surfaces (neutron reflectivity) and indirect adsorption measurements (adsorption isotherm). We show here that asphaltene in good solvent leads to a monolayer whereas addition of bad solvent results in a multilayer growth which is consistent with the deposition behaviour described in the literature.
Moment tensors of a dislocation in a porous medium
NASA Astrophysics Data System (ADS)
Wang, Zhi; Hu, Hengshan
2016-06-01
A dislocation can be represented by a moment tensor for calculating seismic waves. However, the moment tensor expression was derived in an elastic medium and cannot completely describe a dislocation in a porous medium. In this paper, effective moment tensors of a dislocation in a porous medium are derived. It is found that the dislocation is equivalent to two independent moment tensors, i.e., the bulk moment tensor acting on the bulk of the porous medium and the isotropic fluid moment tensor acting on the pore fluid. Both of them are caused by the solid dislocation as well as the fluid-solid relative motion corresponding to fluid injection towards the surrounding rocks (or fluid outflow) through the fault plane. For a shear dislocation, the fluid moment tensor is zero, and the dislocation is equivalent to a double couple acting on the bulk; for an opening dislocation or fluid injection, the two moment tensors are needed to describe the source. The fluid moment tensor only affects the radiated compressional waves. By calculating the ratio of the radiation fields generated by unit fluid moment tensor and bulk moment tensor, it is found that the fast compressional wave radiated by the bulk moment tensor is much stronger than that radiated by the fluid moment tensor, while the slow compressional wave radiated by the fluid moment tensor is several times stronger than that radiated by the bulk moment tensor.
NASA Astrophysics Data System (ADS)
Bartlewska-Urban, Monika; Zombroń, Marek; Strzelecki, Tomasz
2016-03-01
The following study presents numerical calculations for establishing the impact of temperature changes on the process of distortion of bi-phase medium represented using Biot consolidation equations with Kelvin-Voigt rheological skeleton presented, on the example of thermo-consolidation of a pavement of expressway S17. We analyzed the behavior of the expressway under the action of its own weight, dynamic load caused by traffic and temperature gradient. This paper presents the application of the Biot consolidation model with the Kelvin-Voigt skeleton rheological characteristics and the influence of temperature on the deformation process is taken into account. A three-dimensional model of the medium was created describing the thermal consolidation of a porous medium. The 3D geometrical model of the area under investigation was based on data obtained from the land surveying and soil investigation of a 200 m long section of the expressway and its shoulders.
Oxygen- and Nitrogen-Enriched 3D Porous Carbon for Supercapacitors of High Volumetric Capacity.
Li, Jia; Liu, Kang; Gao, Xiang; Yao, Bin; Huo, Kaifu; Cheng, Yongliang; Cheng, Xiaofeng; Chen, Dongchang; Wang, Bo; Sun, Wanmei; Ding, Dong; Liu, Meilin; Huang, Liang
2015-11-11
Efficient utilization and broader commercialization of alternative energies (e.g., solar, wind, and geothermal) hinges on the performance and cost of energy storage and conversion systems. For now and in the foreseeable future, the combination of rechargeable batteries and electrochemical capacitors remains the most promising option for many energy storage applications. Porous carbonaceous materials have been widely used as an electrode for batteries and supercapacitors. To date, however, the highest specific capacitance of an electrochemical double layer capacitor is only ∼200 F/g, although a wide variety of synthetic approaches have been explored in creating optimized porous structures. Here, we report our findings in the synthesis of porous carbon through a simple, one-step process: direct carbonization of kelp in an NH3 atmosphere at 700 °C. The resulting oxygen- and nitrogen-enriched carbon has a three-dimensional structure with specific surface area greater than 1000 m(2)/g. When evaluated as an electrode for electrochemical double layer capacitors, the porous carbon structure demonstrated excellent volumetric capacitance (>360 F/cm(3)) with excellent cycling stability. This simple approach to low-cost carbonaceous materials with unique architecture and functionality could be a promising alternative to fabrication of porous carbon structures for many practical applications, including batteries and fuel cells. PMID:26477268
Oscillatory motion of a viscous fluid in a porous medium
Siraev, R. R.
2015-08-15
An oscillatory flow of an incompressible fluid in a saturated porous medium in the presence of a solid inclusion has been theoretically studied. Unsteady filtration has been described by the Brinkman–Forchheimer equation, where inertial effects and terms with acceleration characteristic of high filtration rates and the presence of pulsations are taken into account. The convective part of the acceleration is responsible for nonlinear effects near macroinhomogeneities. These effects can play a noticeable role in unsteady flows in the porous medium, as is shown for the problem of a solid ball streamed by an oscillatory flow having a given velocity at infinity. The results indicate that a secondary averaged flow appears in the case of high frequencies and cannot be described by Darcy’s or Forchheimer’s filtration laws.
Liu, Yong; Ma, Jiaqi; Lu, Ting; Pan, Likun
2016-01-01
Carbon nanofibers reinforced 3D porous carbon polyhedra network (e-CNF-PCP) was prepared through electrospinning and subsequent thermal treatment. The morphology, structure and electrochemical performance of the e-CNF-PCP were characterized using scanning electron microscopy, Raman spectra, nitrogen adsorption-desorption, cyclic voltammetry and electrochemical impedance spectroscopy, and their electrosorption performance in NaCl solution was studied. The results show that the e-CNF-PCP exhibits a high electrosorption capacity of 16.98 mg g−1 at 1.2 V in 500 mg l−1 NaCl solution, which shows great improvement compared with those of electrospun carbon nanofibers and porous carbon polyhedra. The e-CNF-PCP should be a very promising candidate as electrode material for CDI applications. PMID:27608826
Liu, Yong; Ma, Jiaqi; Lu, Ting; Pan, Likun
2016-01-01
Carbon nanofibers reinforced 3D porous carbon polyhedra network (e-CNF-PCP) was prepared through electrospinning and subsequent thermal treatment. The morphology, structure and electrochemical performance of the e-CNF-PCP were characterized using scanning electron microscopy, Raman spectra, nitrogen adsorption-desorption, cyclic voltammetry and electrochemical impedance spectroscopy, and their electrosorption performance in NaCl solution was studied. The results show that the e-CNF-PCP exhibits a high electrosorption capacity of 16.98 mg g(-1) at 1.2 V in 500 mg l(-1) NaCl solution, which shows great improvement compared with those of electrospun carbon nanofibers and porous carbon polyhedra. The e-CNF-PCP should be a very promising candidate as electrode material for CDI applications. PMID:27608826
Laboratory investigations of steam flow in a porous medium.
Herkelrath, W.N.; Moench, A.F.; O'Neal, II, C. F.
1983-01-01
Experiments were carried out in the laboratory to test a theory of transient flow of pure steam in a uniform porous medium. It was found in experiments run at 100o, 125o, and 146oC that the time required for steam pressure transients to propagate through an unconsolidated material containing sand, silt, and clay was 10-25 times longer than predicted by conventional superheated steam flow theory. -from Authors
Drying of porous materials in a medium with variable potentials
Liu, J.Y. )
1991-08-01
This paper presents an application of the Luikov system of heat and mass transfer equations in dimensionless form to predict the temperature and moisture distributions in a slab of capillary-porous material during drying. The heat and mass potentials of the external medium in the boundary conditions are assumed to vary linearly with time. The method of solution is illustrated by considering the drying of a slab of lumber. Numerical results based on the estimated thermophysical properties of spruce are presented.
Petrochenko, Peter E; Torgersen, Jan; Gruber, Peter; Hicks, Lucas A; Zheng, Jiwen; Kumar, Girish; Narayan, Roger J; Goering, Peter L; Liska, Robert; Stampfl, Jürgen; Ovsianikov, Aleksandr
2015-04-01
A reproducible method is needed to fabricate 3D scaffold constructs that results in periodic and uniform structures with precise control at sub-micrometer and micrometer length scales. In this study, fabrication of scaffolds by two-photon polymerization (2PP) of a biodegradable urethane and acrylate-based photoelastomer is demonstrated. This material supports 2PP processing with sub-micrometer spatial resolution. The high photoreactivity of the biophotoelastomer permits 2PP processing at a scanning speed of 1000 mm s(-1), facilitating rapid fabrication of relatively large structures (>5 mm(3)). These structures are custom printed for in vitro assay screening in 96-well plates and are sufficiently flexible to enable facile handling and transplantation. These results indicate that stable scaffolds with porosities of greater than 60% can be produced using 2PP. Human bone marrow stromal cells grown on 3D scaffolds exhibit increased growth and proliferation compared to smooth 2D scaffold controls. 3D scaffolds adsorb larger amounts of protein than smooth 2D scaffolds due to their larger surface area; the scaffolds also allow cells to attach in multiple planes and to completely infiltrate the porous scaffolds. The flexible photoelastomer material is biocompatible in vitro and is associated with facile handling, making it a viable candidate for further study of complex 3D-printed scaffolds. PMID:25522214
Gauvin, Robert; Chen, Ying-Chieh; Lee, Jin Woo; Soman, Pranav; Zorlutuna, Pinar; Nichol, Jason W.; Bae, Hojae; Chen, Shaochen; Khademhosseini, Ali
2013-01-01
The success of tissue engineering will rely on the ability to generate complex, cell seeded three-dimensional (3D) structures. Therefore, methods that can be used to precisely engineer the architecture and topography of scaffolding materials will represent a critical aspect of functional tissue engineering. Previous approaches for 3D scaffold fabrication based on top-down and process driven methods are often not adequate to produce complex structures due to the lack of control on scaffold architecture, porosity, and cellular interactions. The proposed projection stereolithography (PSL) platform can be used to design intricate 3D tissue scaffolds that can be engineered to mimic the microarchitecture of tissues, based on computer aided design (CAD). The PSL system was developed, programmed and optimized to fabricate 3D scaffolds using gelatin methacrylate (GelMA). Variation of the structure and prepolymer concentration enabled tailoring the mechanical properties of the scaffolds. A dynamic cell seeding method was utilized to improve the coverage of the scaffold throughout its thickness. The results demonstrated that the interconnectivity of pores allowed for uniform human umbilical vein endothelial cells (HUVECs) distribution and proliferation in the scaffolds, leading to high cell density and confluency at the end of the culture period. Moreover, immunohistochemistry results showed that cells seeded on the scaffold maintained their endothelial phenotype, demonstrating the biological functionality of the microfabricated GelMA scaffolds. PMID:22365811
Gauvin, Robert; Chen, Ying-Chieh; Lee, Jin Woo; Soman, Pranav; Zorlutuna, Pinar; Nichol, Jason W; Bae, Hojae; Chen, Shaochen; Khademhosseini, Ali
2012-05-01
The success of tissue engineering will rely on the ability to generate complex, cell seeded three-dimensional (3D) structures. Therefore, methods that can be used to precisely engineer the architecture and topography of scaffolding materials will represent a critical aspect of functional tissue engineering. Previous approaches for 3D scaffold fabrication based on top-down and process driven methods are often not adequate to produce complex structures due to the lack of control on scaffold architecture, porosity, and cellular interactions. The proposed projection stereolithography (PSL) platform can be used to design intricate 3D tissue scaffolds that can be engineered to mimic the microarchitecture of tissues, based on computer aided design (CAD). The PSL system was developed, programmed and optimized to fabricate 3D scaffolds using gelatin methacrylate (GelMA). Variation of the structure and prepolymer concentration enabled tailoring the mechanical properties of the scaffolds. A dynamic cell seeding method was utilized to improve the coverage of the scaffold throughout its thickness. The results demonstrated that the interconnectivity of pores allowed for uniform human umbilical vein endothelial cells (HUVECs) distribution and proliferation in the scaffolds, leading to high cell density and confluency at the end of the culture period. Moreover, immunohistochemistry results showed that cells seeded on the scaffold maintained their endothelial phenotype, demonstrating the biological functionality of the microfabricated GelMA scaffolds. PMID:22365811
Ma, Fangwei; Ma, Di; Wu, Guang; Geng, Weidan; Shao, Jinqiu; Song, Shijiao; Wan, Jiafeng; Qiu, Jieshan
2016-05-10
A smart and sustainable strategy based on charge-induced self-assembly and nanocrystal-assisted catalytic graphitization is explored for the efficient construction of 3D nanostructure hierarchical porous graphitic carbons from the pectin biopolymer. The electrostatic interaction between the negatively charged pectin chains and magnesium ions plays a crucial role in the formation of 3D architectures. The 3D HPGCs possess a three-dimensional carbon framework with a hierarchical porous structure, flake-like graphitic carbon walls and high surface area (1320 m(2) g(-1)). The 3D HPGCs show an outstanding specific capacitance of 274 F g(-1) and excellent rate capability with a high capacitance retention of 85% at a high current density of 50 A g(-1) for supercapacitor electrodes. This strategy provided a novel approach to effectively construct 3D porous carbon nanostructures from biopolymers. PMID:27115341
Real-time 3D imaging of Haines jumps in porous media flow
Berg, Steffen; Ott, Holger; Klapp, Stephan A.; Schwing, Alex; Neiteler, Rob; Brussee, Niels; Makurat, Axel; Leu, Leon; Enzmann, Frieder; Schwarz, Jens-Oliver; Kersten, Michael; Irvine, Sarah; Stampanoni, Marco
2013-01-01
Newly developed high-speed, synchrotron-based X-ray computed microtomography enabled us to directly image pore-scale displacement events in porous rock in real time. Common approaches to modeling macroscopic fluid behavior are phenomenological, have many shortcomings, and lack consistent links to elementary pore-scale displacement processes, such as Haines jumps and snap-off. Unlike the common singular pore jump paradigm based on observations of restricted artificial capillaries, we found that Haines jumps typically cascade through 10–20 geometrically defined pores per event, accounting for 64% of the energy dissipation. Real-time imaging provided a more detailed fundamental understanding of the elementary processes in porous media, such as hysteresis, snap-off, and nonwetting phase entrapment, and it opens the way for a rigorous process for upscaling based on thermodynamic models. PMID:23431151
3D Porous Crystalline Polyimide Covalent Organic Frameworks for Drug Delivery.
Fang, Qianrong; Wang, Junhua; Gu, Shuang; Kaspar, Robert B; Zhuang, Zhongbin; Zheng, Jie; Guo, Hongxia; Qiu, Shilun; Yan, Yushan
2015-07-01
Three-dimensional porous crystalline polyimide covalent organic frameworks (termed PI-COFs) have been synthesized. These PI-COFs feature non- or interpenetrated structures that can be obtained by choosing tetrahedral building units of different sizes. Both PI-COFs show high thermal stability (>450 °C) and surface area (up to 2403 m(2) g(-1)). They also show high loading and good release control for drug delivery applications. PMID:26099722
Optimization and Use of 3D sintered porous material in medical field for mixing fibrin glue.
NASA Astrophysics Data System (ADS)
Delmotte, Y.; Laroumanie, H.; Brossard, G.
2012-04-01
In medical field, Mixing of two or more chemical components (liquids and/or gases) is extremely important as improper mixing can affect the physico-chemical properties of the final product. At Baxter Healthcare Corporation, we are using a sintered porous material (PM) as a micro-mixer in medical device for mixing Fibrinogen and Thrombin in order to obtain a homogeneous polymerized Fibrin glue clot used in surgery. First trials were carried out with an interconnected PM from Porvair® (made of PE - porosity: 40% - permeability: 18Darcy). The injection rate is very low, usually about 10mL/min (Re number about 50) which keeps fluids in a laminar flow. Such a low flow rate does not favour mixing of fluids having gradient of viscosity if a mixer is not used. Promising results that were obtained lead the team to understand this ability to mix fluids which will be presented in the poster. Topology of porous media (PM) which associates a solid phase with interconnected (or not) porous structure is known and used in many commodity products. Researches on PM usually focus on flows inside this structure. By opposition to transport and filtration capacity, as well as mechanic and thermic properties, mixing is rarely associated with PM. However over the past few years, we shown that some type of PM have a real capacity to mix certain fluids. Poster will also describe the problematic of mixing complex biological fluids as fibrinogen and Thrombin. They indeed present a large viscosity difference (ratio about 120) limiting the diffusion and the interaction between the two solutions. As those products are expensive, we used Water (1cPo) and Glycerol 87% (120cPo) which are matching the viscosities of Thrombin and Fibrinogen. A parametric investigation of the "porous micro-mixer" as well as a scale up investigation was carried out to examine the influence of both diffusion and advection to successful mix fluids of different viscosity. Experiments were implemented with Planar Laser
Zhang, Yong; Chen, Kun; Baron, Matthew; Teylan, Merilee A.; Kim, Yong; Song, Zhihuan; Greengard, Paul
2010-01-01
Acquisition and quantitative analysis of high resolution images of dendritic spines are challenging tasks but are necessary for the study of animal models of neurological and psychiatric diseases. Currently available methods for automated dendritic spine detection are for the most part customized for 2D image slices, not volumetric 3D images. In this work, a fully automated method is proposed to detect and segment dendritic spines from 3D confocal microscopy images of medium-sized spiny neurons (MSNs). MSNs constitute a major neuronal population in striatum, and abnormalities in their function are associated with several neurological and psychiatric diseases. Such automated detection is critical for the development of new 3D neuronal assays which can be used for the screening of drugs and the studies of their therapeutic effects. The proposed method utilizes a generalized gradient vector flow (GGVF) with a new smoothing constraint and then detects feature points near the central regions of dendrites and spines. Then, the central regions are refined and separated based on eigen-analysis and multiple shape measurements. Finally, the spines are segmented in 3D space using the fast marching algorithm, taking the detected central regions of spines as initial points. The proposed method is compared with three popular existing methods for centerline extraction and also with manual results for dendritic spine detection in 3D space. The experimental results and comparisons show that the proposed method is able to automatically and accurately detect, segment, and quantitate dendritic spines in 3D images of MSNs. PMID:20100579
PHT3D-UZF: A reactive transport model for variably-saturated porous media
Wu, Ming Zhi; Post, Vincent E. A.; Salmon, S. Ursula; Morway, Eric; Prommer, H.
2016-01-01
A modified version of the MODFLOW/MT3DMS-based reactive transport model PHT3D was developed to extend current reactive transport capabilities to the variably-saturated component of the subsurface system and incorporate diffusive reactive transport of gaseous species. Referred to as PHT3D-UZF, this code incorporates flux terms calculated by MODFLOW's unsaturated-zone flow (UZF1) package. A volume-averaged approach similar to the method used in UZF-MT3DMS was adopted. The PHREEQC-based computation of chemical processes within PHT3D-UZF in combination with the analytical solution method of UZF1 allows for comprehensive reactive transport investigations (i.e., biogeochemical transformations) that jointly involve saturated and unsaturated zone processes. Intended for regional-scale applications, UZF1 simulates downward-only flux within the unsaturated zone. The model was tested by comparing simulation results with those of existing numerical models. The comparison was performed for several benchmark problems that cover a range of important hydrological and reactive transport processes. A 2D simulation scenario was defined to illustrate the geochemical evolution following dewatering in a sandy acid sulfate soil environment. Other potential applications include the simulation of biogeochemical processes in variably-saturated systems that track the transport and fate of agricultural pollutants, nutrients, natural and xenobiotic organic compounds and micropollutants such as pharmaceuticals, as well as the evolution of isotope patterns.
PHT3D-UZF: A Reactive Transport Model for Variably-Saturated Porous Media.
Wu, Ming Zhi; Post, Vincent E A; Salmon, S Ursula; Morway, Eric D; Prommer, Henning
2016-01-01
A modified version of the MODFLOW/MT3DMS-based reactive transport model PHT3D was developed to extend current reactive transport capabilities to the variably-saturated component of the subsurface system and incorporate diffusive reactive transport of gaseous species. Referred to as PHT3D-UZF, this code incorporates flux terms calculated by MODFLOW's unsaturated-zone flow (UZF1) package. A volume-averaged approach similar to the method used in UZF-MT3DMS was adopted. The PHREEQC-based computation of chemical processes within PHT3D-UZF in combination with the analytical solution method of UZF1 allows for comprehensive reactive transport investigations (i.e., biogeochemical transformations) that jointly involve saturated and unsaturated zone processes. Intended for regional-scale applications, UZF1 simulates downward-only flux within the unsaturated zone. The model was tested by comparing simulation results with those of existing numerical models. The comparison was performed for several benchmark problems that cover a range of important hydrological and reactive transport processes. A 2D simulation scenario was defined to illustrate the geochemical evolution following dewatering in a sandy acid sulfate soil environment. Other potential applications include the simulation of biogeochemical processes in variably-saturated systems that track the transport and fate of agricultural pollutants, nutrients, natural and xenobiotic organic compounds and micropollutants such as pharmaceuticals, as well as the evolution of isotope patterns. PMID:25628017
3D-printed silicate porous bioceramics using a non-sacrificial preceramic polymer binder.
Zocca, A; Elsayed, H; Bernardo, E; Gomes, C M; Lopez-Heredia, M A; Knabe, C; Colombo, P; Günster, J
2015-06-01
Silicate bioceramics possess an excellent bioactivity; however, shaping them into complex geometries is still challenging. Therefore, this paper aims to present a new strategy for the shaping of a bioglass-ceramic with controlled geometry and properties starting from a glass powder combined with a preceramic polymer, i.e. a silicon resin, and reactive fillers. The powder-based three-dimensional (3D)-printing of wollastonite (CaSiO3)-based silicate bioceramic parts was demonstrated in this work. The resin plays a dual role, as it not only acts as a non-sacrificial binder for the filler powders in the printing process but it also reacts with the fillers to generate the desired bioceramic phases. The mechanical and physical properties, i.e. ball-on-three-balls test, density, porosity and morphology, were evaluated in 3D-printed discs. These samples possessed a total porosity around 64 vol% and a biaxial flexural strength around 6 MPa. The raw materials used in this work also enabled the 3D-printing of scaffolds possessing a designed multi-scale porosity, suitable bioceramic phase assemblage and a compressive strength of 1 MPa (for cylindrical scaffolds with total porosity ~80 vol%). Solubility in TRIS/HCl and in vitro assays, i.e. viability, cytotoxicity and apoptosis assays, were also performed. In vitro tests indicated good cell viability and no cytotoxicity effect on the cells. PMID:26000907
SAGE 2D and 3D Simulations of the Explosive Venting of Supercritical Fluids Through Porous Media
NASA Astrophysics Data System (ADS)
Weaver, R.; Gisler, G.; Svensen, H.; Mazzini, A.
2008-12-01
Magmatic intrusive events in large igneous provinces heat sedimentary country rock leading to the eventual release of volatiles. This has been proposed as a contributor to climate change and other environmental impacts. By means of numerical simulations, we examine ways in which these volatiles can be released explosively from depth. Gases and fluids cooked out of country rock by metamorphic heating may be confined for a time by impermeable clays or other barriers, developing high pressures and supercritical fluids. If confinement is suddenly breached (by an earthquake for example) in such a way that the fluid has access to porous sediments, a violent eruption of a non-magmatic mixture of fluid and sediment may result. Surface manifestations of these events could be hydrothermal vent complexes, kimberlite pipes, pockmarks, or mud volcanoes. These are widespread on Earth, especially in large igneous provinces, as in the Karoo Basin of South Africa, the North Sea off the Norwegian margin, and the Siberian Traps. We have performed 2D and 3D simulations with the Sage hydrocode (from Los Alamos and Science Applications International) of supercritical venting in a variety of geometries and configurations. The simulations show several different patterns of propagation and fracturing in porous or otherwise weakened overburden, dependent on depth, source conditions (fluid availability, temperature, and pressure), and manner of confinement breach. Results will be given for a variety of 2D and 3D simulations of these events exploring the release of volatiles into the atmosphere.
NASA Astrophysics Data System (ADS)
Riasi, S.; Huang, G.; Montemagno, C.; Yeghiazarian, L.
2013-12-01
Micro-scale modeling of multiphase flow in porous media is critical to characterize porous materials. Several modeling techniques have been implemented to date, but none can be used as a general strategy for all porous media applications due to challenges presented by non-smooth high-curvature solid surfaces, and by a wide range of pore sizes and porosities. Finite approaches like the finite volume method require a high quality, problem-dependent mesh, while particle-based approaches like the lattice Boltzmann require too many particles to achieve a stable meaningful solution. Both come at a large computational cost. Other methods such as pore network modeling (PNM) have been developed to accelerate the solution process by simplifying the solution domain, but so far a unique and straightforward methodology to implement PNM is lacking. We have developed a general, stable and fast methodology to model multi-phase fluid flow in porous materials, irrespective of their porosity and solid phase topology. We have applied this methodology to highly porous fibrous materials in which void spaces are not distinctly separated, and where simplifying the geometry into a network of pore bodies and throats, as in PNM, does not result in a topology-consistent network. To this end, we have reduced the complexity of the 3-D void space geometry by working with its medial surface. We have used a non-iterative fast medial surface finder algorithm to determine a voxel-wide medial surface of the void space, and then solved the quasi-static drainage and imbibition on the resulting domain. The medial surface accurately represents the topology of the porous structure including corners, irregular cross sections, etc. This methodology is capable of capturing corner menisci and the snap-off mechanism numerically. It also allows for calculation of pore size distribution, permeability and capillary pressure-saturation-specific interfacial area surface of the porous structure. To show the
3D electromagnetic modelling of a TTI medium and TTI effects in inversion
NASA Astrophysics Data System (ADS)
Jaysaval, Piyoosh; Shantsev, Daniil; de la Kethulle de Ryhove, Sébastien
2016-04-01
We present a numerical algorithm for 3D electromagnetic (EM) forward modelling in conducting media with general electric anisotropy. The algorithm is based on the finite-difference discretization of frequency-domain Maxwell's equations on a Lebedev grid, in which all components of the electric field are collocated but half a spatial step staggered with respect to the magnetic field components, which also are collocated. This leads to a system of linear equations that is solved using a stabilized biconjugate gradient method with a multigrid preconditioner. We validate the accuracy of the numerical results for layered and 3D tilted transverse isotropic (TTI) earth models representing typical scenarios used in the marine controlled-source EM method. It is then demonstrated that not taking into account the full anisotropy of the conductivity tensor can lead to misleading inversion results. For simulation data corresponding to a 3D model with a TTI anticlinal structure, a standard vertical transverse isotropic inversion is not able to image a resistor, while for a 3D model with a TTI synclinal structure the inversion produces a false resistive anomaly. If inversion uses the proposed forward solver that can handle TTI anisotropy, it produces resistivity images consistent with the true models.
Bharatham, B Hemabarathy; Abu Bakar, Md Zuki; Perimal, Enoch Kumar; Yusof, Loqman Mohamed; Hamid, Muhajir
2014-01-01
A novel porous three-dimensional bone scaffold was developed using a natural polymer (alginate/Alg) in combination with a naturally obtained biomineral (nano cockle shell powder/nCP) through lyophilization techniques. The scaffold was developed in varying composition mixture of Alg-nCP and characterized using various evaluation techniques as well as preliminary in vitro studies on MG63 human osteoblast cells. Morphological observations using SEM revealed variations in structures with the use of different Alg-nCP composition ratios. All the developed scaffolds showed a porous structure with pore sizes ideal for facilitating new bone growth; however, not all combination mixtures showed subsequent favorable characteristics to be used for biological applications. Scaffolds produced using the combination mixture of 40% Alg and 60% nCP produced significantly promising results in terms of mechanical strength, degradation rate, and increased cell proliferation rates making it potentially the optimum composition mixture of Alg-nCP with future application prospects. PMID:25110655
Bharatham, B. Hemabarathy; Abu Bakar, Md. Zuki; Perimal, Enoch Kumar; Yusof, Loqman Mohamed; Hamid, Muhajir
2014-01-01
A novel porous three-dimensional bone scaffold was developed using a natural polymer (alginate/Alg) in combination with a naturally obtained biomineral (nano cockle shell powder/nCP) through lyophilization techniques. The scaffold was developed in varying composition mixture of Alg-nCP and characterized using various evaluation techniques as well as preliminary in vitro studies on MG63 human osteoblast cells. Morphological observations using SEM revealed variations in structures with the use of different Alg-nCP composition ratios. All the developed scaffolds showed a porous structure with pore sizes ideal for facilitating new bone growth; however, not all combination mixtures showed subsequent favorable characteristics to be used for biological applications. Scaffolds produced using the combination mixture of 40% Alg and 60% nCP produced significantly promising results in terms of mechanical strength, degradation rate, and increased cell proliferation rates making it potentially the optimum composition mixture of Alg-nCP with future application prospects. PMID:25110655
Large-scale fabrication, 3D tomography, and lithium-ion battery application of porous silicon.
Ge, Mingyuan; Lu, Yunhao; Ercius, Peter; Rong, Jiepeng; Fang, Xin; Mecklenburg, Matthew; Zhou, Chongwu
2014-01-01
Recently, silicon-based lithium-ion battery anodes have shown encouraging results, as they can offer high capacities and long cyclic lifetimes. The applications of this technology are largely impeded by the complicated and expensive approaches in producing Si with desired nanostructures. We report a cost-efficient method to produce nanoporous Si particles from metallurgical Si through ball-milling and inexpensive stain-etching. The porosity of porous Si is derived from particle's three-dimensional reconstructions by scanning transmission electron microscopy (STEM) tomography, which shows the particles' highly porous structure when etched under proper conditions. Nanoporous Si anodes with a reversible capacity of 2900 mAh/g was attained at a charging rate of 400 mA/g, and a stable capacity above 1100 mAh/g was retained for extended 600 cycles tested at 2000 mA/g. The synthetic route is low-cost and scalable for mass production, promising Si as a potential anode material for the next-generation lithium-ion batteries with enhanced capacity and energy density. PMID:24279924
Stability of a stationary moving droplet in porous medium
NASA Astrophysics Data System (ADS)
Lyubimov, Dmitriy; Shklyaev, Sergey; Lyubimova, Tatyana; Zikanov, Oleg
2008-11-01
We consider sedimentation of a drop in a porous medium saturated by another fluid. Brinkman model is applied, whereas the interface of drop is assumed sharp and the capillary forces are neglected. The velocity of stationary sedimentation for the spherical drop is obtained. The resulting expression matches both the Hadamard-Rybczynski formula and the result for the conventional Darcy model in corresponding asymptotic limits. Stability of the stationary motion is studied. It is shown, that the drop is always unstable to perturbations that lead to formation of a cusp in the vicinity of the rear stagnation point. This behavior is similar to that for a drop in the absence of the porous matrix. Thus, the Brinkman model eliminates the unphysical features inherent to the Darcy model.
Mehr, Nima Ghavidel; Li, Xian; Chen, Gaoping; Favis, Basil D; Hoemann, Caroline D
2015-07-01
Poly(epsilon-caprolactone) (PCL) is a hydrophobic bioplastic under development for bone tissue engineering applications. Limited information is available on the role of internal geometry and cell-surface attachment on osseous integration potential. We tested the hypothesis that human bone marrow mesenchymal stem cells (MSCs) deposit more mineral inside porous 3D PCL scaffolds with fully interconnected 84 or 141 µm pores, when the surfaces are coated with chitosan via Layer-by-Layer (LbL)-deposited polyelectrolytes. Freshly trypsinized MSCs were seeded on PCL 3D cylinders using a novel static cold seeding method in 2% serum to optimally populate all depths of the scaffold discs, followed by 10 days of culture in proliferation medium and 21 additional days in osteogenic medium. MSCs were observed by SEM and histology to spread faster and to proliferate more on chitosan-coated pore surfaces. Most pores, with or without chitosan, became filled by collagen networks sparsely populated with fibroblast-like cells. After 21 days of culture in osteogenic medium, sporadic matrix mineralization was detected histologically and by micro-CT in highly cellular surface layers that enveloped all scaffolds and in cell aggregates in 141 µm pores near the edges. LbL-chitosan promoted punctate mineral deposition on the surfaces of 84 µm pores (p < 0.05 vs. PCL-only) but not the 141 µm pores. This study revealed that LbL-chitosan coatings are sufficient to promote MSC attachment to PCL but only enhance mineral formation in 84 µm pores, suggesting a potential inhibitory role for MSC-derived fibroblasts in osteoblast terminal differentiation. PMID:25504184
Prodanović, M; Lindquist, W B; Seright, R S
2006-06-01
Using oil-wet polyethylene core models, we present the development of robust throat finding techniques for the extraction, from X-ray microtomographic images, of a pore network description of porous media having porosity up to 50%. Measurements of volume, surface area, shape factor, and principal diameters are extracted for pores and area, shape factor and principal diameters for throats. We also present results on the partitioning of wetting and non-wetting phases in the pore space at fixed volume increments of the injected fluid during a complete cycle of drainage and imbibition. We compare these results with fixed fractional flow injection, where wetting and non-wetting phase are simultaneously injected at fixed volume ratio. Finally we demonstrate the ability to differentiate three fluid phases (oil, water, air) in the pore space. PMID:16364351
Zhang, Daojun; Zhang, Jingchao; Zhang, Renchun; Shi, Huaizhong; Guo, Yuanyuan; Guo, Xiuli; Li, Sujuan; Yuan, Baiqing
2015-11-01
Novel electroactive materials with high surface area and stability have great potential for electrochemical sensor. Herein, we demonstrate the exploitation of a porous Cu-based metal-organic framework (Cu-MOF) with large pore size as nonenzymatic sensors for the electrochemical determination of hydrogen peroxide (H2O2) and glucose. The Cu-MOF shows high stability even in NaOH solution. The as-prepared Cu-MOF modified carbon paste electrode (CPE) presents a well-behaved redox event from electroactive metal centers in the MOF at the physiological pH which can be utilized to catalyze the electroreduction of H2O2. It also exhibited excellent electrocatalytic activity towards the oxidation of glucose in alkaline solution. The results showed that the nonenzymatic sensors based on the Cu-MOF display excellent analytical performances, which make it a promising candidate in electrochemical sensor. PMID:26452944
Singaravelu, Sivakumar; Ramanathan, Giriprasath; Raja, M D; Nagiah, Naveen; Padmapriya, P; Kaveri, Krishnasamy; Sivagnanam, Uma Tiruchirapalli
2016-05-01
The medicated wound dressing material with highly interconnected pores, mimicking the function of the extracellular matrix was fabricated for the promotion of cell growth. In this study, keratin (K), fibrin (F) and gelatin (G) composite scaffold (KFG-SPG) was fabricated by freeze drying technique and the mupirocin (D) drug was successfully incorporated with KFG-SPG (KFG-SPG-D) intended for tissue engineering applications. The fabrication of scaffold was performed without the use of any strong chemical solvents, and the solid sponge scaffold was obtained with well interconnected pores. The porous morphology of the scaffold was confirmed by SEM analysis and exhibited competent mechanical properties. KFG-SPG and KFG-SPG-D possess high level of biocompatibility, cell proliferation and cell adhesion of NIH 3T3 fibroblast and human keratinocytes (HaCaT) cell lines thereby indicating the scaffolds potential as a suitable medicated dressing for wound healing. PMID:26875534
Numerical methods for a general class of porous medium equations
Rose, M. E.
1980-03-01
The partial differential equation par. deltau/par. deltat + par. delta(f(u))/par. deltax = par. delta(g(u)par. deltau/par. deltax)/par. deltax, where g(u) is a non-negative diffusion coefficient that may vanish for one or more values of u, was used to model fluid flow through a porous medium. Error estimates for a numerical procedure to approximate the solution are derived. A revised version of this report will appear in Computers and Mathematics with Applications.
Heat and Mass Transfer in a Freezing Unsaturated Porous Medium
NASA Astrophysics Data System (ADS)
Jame, Yih-Wu; Norum, Donald I.
1980-08-01
A numerical simulation of a laboratory experiment involving coupled heat and mass transfer in a horizontal porous medium column with one end subjected to a temperature below 0°C has been carried out. The model is essentially that of Harlan (1973) and is solved numerically by the finite difference method using the Crank-Nicholson scheme. The solution yields temperature, liquid water content, and ice content profiles along the column as a function of time. Comparison of the experimental results and the simulation analysis results shows that Harlan's model, with some modification in the hydraulic conductivity of the frozen medium, can be used successfully to simulate numerically the coupled heat and mass transfer processes when ice lensing does not occur.
Ragothaman, Murali; Palanisamy, Thanikaivelan; Kalirajan, Cheirmadurai
2014-12-19
Here we report the preparation of collagen-poly(dialdehyde) guar gum based hybrid functionalized scaffolds covalently immobilized with platelet derived growth factor - BB for tissue engineering applications. Poly(dialdehyde) guar gum was synthesized from selective oxidation of guar gum using sodium periodate. The synthesized poly(dialdehyde) guar gum not only promotes crosslinking of collagen but also immobilizes the platelet derived growth factor through imine bonds. The covalent crosslinking formed in collagen improves thermal, swelling and biodegradation properties of the hybrid scaffolds. The prepared hybrid scaffolds show 3D interconnected honeycomb porous structure when viewed under a microscope. The release of immobilized platelet derived growth factor was seen up to 13th day of incubation thereby proving its sustained delivery. The developed hybrid scaffold leads to a quantum increase in NIH 3T3 fibroblast cell density and proliferation thereby demonstrating its potential for tissue engineering applications. PMID:25263907
Pak, Tannaz; Butler, Ian B.; Geiger, Sebastian; van Dijke, Marinus I. J.; Sorbie, Ken S.
2015-01-01
Using X-ray computed microtomography, we have visualized and quantified the in situ structure of a trapped nonwetting phase (oil) in a highly heterogeneous carbonate rock after injecting a wetting phase (brine) at low and high capillary numbers. We imaged the process of capillary desaturation in 3D and demonstrated its impacts on the trapped nonwetting phase cluster size distribution. We have identified a previously unidentified pore-scale event during capillary desaturation. This pore-scale event, described as droplet fragmentation of the nonwetting phase, occurs in larger pores. It increases volumetric production of the nonwetting phase after capillary trapping and enlarges the fluid−fluid interface, which can enhance mass transfer between the phases. Droplet fragmentation therefore has implications for a range of multiphase flow processes in natural and engineered porous media with complex heterogeneous pore spaces. PMID:25646491
Luo, Zuyuan; Yang, Yue; Deng, Yi; Sun, Yuhua; Yang, Hongtao; Wei, Shicheng
2016-07-01
Good bioactivity and osteogenesis of three-dimensional porous alginate scaffolds (PAS) are critical for bone tissue engineering. In this work, alginate and bone-forming peptide-1 (BFP-1), derived from bone morphogenetic protein-7 (BMP-7), have been combined together (without carbodiimide chemistry treatment) to develop peptide-incorporated PAS (p-PAS) for promoting bone repairing ability. The mechanical properties and SEM images show no difference between pure PAS and p-PAS. The release kinetics of the labeled peptide with 6-carboxy tetramethyl rhodamine from the PAS matrix suggests that the peptide is released in a relatively sustained manner. In the cell experiment, p-PAS show higher cell adhesion, spreading, proliferation and alkaline phosphatase (ALP) activity than the pristine PAS group, indicating that the BFP-1 released from p-PAS could significantly promote the aggregation and differentiation of osteoblasts, especially at 10μg/mL of trapped peptide concentration (p-PAS-10). Furthermore, p-PAS-10 was implanted into Beagle calvarial defects and bone regeneration was analyzed after 4 weeks. New bone formation was assessed by calcein and Masson's trichrome staining. The data reveal that p-PAS group exhibits significantly enhanced oseto-regenerative capability in vivo. The peptide-modified PAS with promoted bioactivity and osteogenic differentiation in vitro as well as bone formation ability in vivo could be promising tissue engineering materials for repairing and regeneration of bone defects. PMID:27022863
Characterization of Silk Fibroin/Chitosan 3D Porous Scaffold and In Vitro Cytology
Zeng, Shuguang; Liu, Lei; Shi, Yong; Qiu, Junqi; Fang, Wei; Rong, Mingdeng; Guo, Zehong; Gao, Wenfeng
2015-01-01
Bone tissue engineering is a powerful tool to treat bone defects caused by trauma, infection, tumors and other factors. Both silk fibroin (SF) and chitosan (CS) are non-toxic and have good biocompatibility, but are poor biological scaffolds when used alone. In this study, the microscopic structure and related properties of SF/CS composite scaffolds with different component ratios were examined. The scaffold material most suitable for osteoblast growth was determined, and these results offer an experimental basis for the future reconstruction of bone defects. First, via freeze-drying and chemical crosslinking methods, SF/CS composites with different component ratios were prepared and their structure was characterized. Changes in the internal structure of the SF and CS mixture were observed, confirming that the mutual modification between the two components was complete and stable. The internal structure of the composite material was porous and three-dimensional with a porosity above 90%. We next studied the pore size, swelling ratio, water absorption ratio, degradation and in vitro cell proliferation. For the 40% SF-60% CS group, the pore size of the scaffold was suitable for the growth of osteoblasts, and the rate of degradation was steady. This favors the early adhesion, growth and proliferation of MG-63 cells. In addition to good biocompatibility and satisfactory cell affinity, this material promotes the secretion of extracellular matrix materials by osteoblasts. Thus, 40% SF-60% CS is a good material for bone tissue engineering. PMID:26083846
Axisymmetric viscous gravity currents flowing over a deep porous medium
NASA Astrophysics Data System (ADS)
Spannuth, Melissa; Neufeld, Jerome; Wettlaufer, John S.; Grae Worster, M.
2006-11-01
When a viscous fluid flows over a porous substrate, it not only spreads but also seeps into the underlying medium. Such flows have relevance to the design of shingle beds for use as safety features around storage facilities of dense fluids and to flow through fissures in porous rocks. Whereas previous investigations have been confined to two-dimensional flows of fixed volume, we have investigated currents fed by a constant fluid flux flowing axisymmetrically over a deep porous bed. Our experimental system consisted of glycerin spreading over monodisperse glass spheres of known permeability and the data were analyzed using scaling analyses. We have also solved a mathematical model using the well-known equations for a viscous gravity current spreading due to the slope of its free surface augmented by a simple draining law. Its predictions agree well with our experimental results and quantify, in particular, the maximum distance to which the current spreads as a function of the material and input properties.
Han, Lei; Yang, Da-Peng; Liu, Aihua
2015-01-15
A novel three-dimensional (3D) hierarchical porous cobalt oxide (Co3O4) architecture was first synthesized through a simple, cost-effective and environmentally friendly leaf-templated strategy. The Co3O4 nanoparticles (30-100 nm) with irregular shapes were interconnected with each other to form a 3D multilayer porous network structure, which provided high specific surface area and numerous electrocatalytic active sites. Subsequently, Co3O4 was successfully utilized as direct electrochemical sensing interface for non-enzymatic detection of H2O2 and glucose. By using chronoamperometry, the current response of the sensor at +0.31 V was linear with H2O2 concentration within 0.4-200 μM with a low limit of detection (LOD) of 0.24 μM (S/N=3) and a high sensitivity of 389.7 μA mM(-1) cm(-2). Two linear ranges of 1-300 μM (with LOD of 0.1 μM and sensitivity of 471.5 μA mM(-1) cm(-2)) and 4-12.5 mM were found at +0.59 V for glucose. In addition, the as-prepared sensor showed excellent stability and anti-interference performance for possible interferents such as ascorbic acid, uric acid, dopamine, acetaminophen and especially 0.15 M chloride ions. Similarly, other various metal oxide nanostructures may be also prepared using this similar strategy for possible applications in catalysis, electrochemical sensors, and fuel cells. PMID:25078713
Oil displacement through a porous medium with a temperature gradient
NASA Astrophysics Data System (ADS)
Oliveira, Cláudio L. N.; Andrade, José S., Jr.; Herrmann, Hans J.
2011-06-01
We investigate the effect of a temperature gradient on oil recovery in a two-dimensional pore-network model. The oil viscosity depends on temperature as μo∝eB/T, where B is a physicochemical parameter, depending on the type of oil, and T is the temperature. A temperature gradient is applied across the medium in the flow direction. Initially, the porous medium is saturated with oil, and then another fluid is injected. We have considered two cases representing different injection strategies. In the first case, the invading fluid viscosity is constant (finite viscosity ratio), while in the second one, the invading fluid is inviscid (infinite viscosity ratio). Our results show that for the case of finite viscosity ratio, recovery increases with ΔT independent of strength or sign of the gradient. For an infinite viscosity ratio, a positive temperature gradient is necessary to enhance recovery. Moreover, we show that for ΔT>0, the percentage of oil recovery generally decreases (increases) with B for a finite (infinite) viscosity ratio. Finally, we also extend our results for infinite viscosity ratio to a three-dimensional porous media geometry.
NASA Astrophysics Data System (ADS)
Brueck, C. L.; Meisenheimer, D.; Wildenschild, D.
2015-12-01
Understanding the mechanisms controlling colloid transport and deposition in the vadose zone is an important step in protecting our water resources. Not only may these particles themselves be undesirable contaminants, but they can also aid in the transport of smaller, molecular-scale contaminants by chemical attachment. In this research, we examined the influence that air-water interfaces (AWI) and air-water-solid contact lines (AWS) have on colloid deposition and mobilization in three-dimensional systems. We used x-ray microtomography to visualize the transport of hydrophobic colloids as they move through a partially saturated glass bead pack. Drainage and imbibition experiments were conducted using syringe pumps to control the flow of a colloid suspension through the porous media at 0.6 mL/hr. The high ionic strength fluid was adjusted to a pH of 9.5 and a concentration of 1.0 mol/L KI. During the drainage and imbibition, the flow was periodically halted and allowed to equilibrate before collecting the microtomography scans. Dopants were used to enhance the contrast between the four phases (water, air, beads, and colloids), including potassium iodide dissolved in the fluid, and an outer layer of silver coating the colloids. We hypothesized that AWIs and AWSs will scour and mobilize a significant percentage of colloids, and therefore reduce the concentration of colloids along the vertical profile of the column. The concentration of potassium iodide, and thus the ionic strength, necessary for adequate image segmentation was also explored in separate experiments so that the influence of ionic strength on colloid deposition and mobilization can be studied.
Zhang, Wenli; Lin, Haibo; Lin, Zheqi; Yin, Jian; Lu, Haiyan; Liu, Dechen; Zhao, Mingzhu
2015-06-22
Lignin-derived hierarchical porous carbon (LHPC) was prepared through a facile template-free method. Solidification of the lignin-KOH solution resulted in KOH crystalizing within lignin. The crystalized KOH particles in solid lignin acted both as template and activating agent in the heat-treatment process. The obtained LHPC, exhibiting a 3D network, consisted of macroporous cores, mesoporous channels, and micropores. The LHPC comprised 12.27 at % oxygen-containing groups, which resulted in pseudocapacitance. The LHPC displayed a capacitance of 165.0 F g(-1) in 1 M H2 SO4 at 0.05 A g(-1) , and the capacitance was still 123.5 F g(-1) even at 10 A g(-1) . The LHPC also displayed excellent cycling stability with capacitance retention of 97.3 % after 5000 galvanostatic charge-discharge cycles. On account of the facile preparation of LHPC, this paper offers a facile alternative method for the preparation of hierarchical porous carbon for electrochemical energy storage devices. PMID:26033894
Hou, Jianhua; Cao, Chuanbao; Ma, Xilan; Idrees, Faryal; Xu, Bin; Hao, Xin; Lin, Wei
2014-01-01
Controlled micro/mesopores interconnected structures of three-dimensional (3D) carbon with high specific surface areas (SSA) are successfully prepared by carbonization and activation of biomass (raw rice brans) through KOH. The highest SSA of 2475 m2 g−1 with optimized pore volume of 1.21 cm3 g−1 (40% for mesopores) is achieved for KOH/RBC = 4 mass ratio, than others. The as-prepared 3D porous carbon-based electrode materials for supercapacitors exhibit high specific capacitance specifically at large current densities of 10 A g−1 and 100 A g−1 i.e., 265 F g−1 and 182 F g−1 in 6 M KOH electrolyte, respectively. Moreover, a high power density ca. 1223 W kg−1 (550 W L−1) and energy density 70 W h kg−1 (32 W h L−1) are achieved on the base of active material loading (~10 mg cm2) in the ionic liquid. The findings can open a new avenue to use abundant agricultural by-products as ideal materials with promising applications in high-performance energy-storage devices. PMID:25434348
Flow-induced compaction of a deformable porous medium
NASA Astrophysics Data System (ADS)
Hewitt, Duncan R.; Nijjer, Japinder S.; Worster, M. Grae; Neufeld, Jerome A.
2016-02-01
Fluid flowing through a deformable porous medium imparts viscous drag on the solid matrix, causing it to deform. This effect is investigated theoretically and experimentally in a one-dimensional configuration. The experiments consist of the downwards flow of water through a saturated pack of small, soft, hydrogel spheres, driven by a pressure head that can be increased or decreased. As the pressure head is increased, the effective permeability of the medium decreases and, in contrast to flow through a rigid medium, the flux of water is found to increase towards a finite upper bound such that it becomes insensitive to changes in the pressure head. Measurements of the internal deformation, extracted by particle tracking, show that the medium compacts differentially, with the porosity being lower at the base than at the upper free surface. A general theoretical model is derived, and the predictions of the model give good agreement with experimental measurements from a series of experiments in which the applied pressure head is sequentially increased. However, contrary to theory, all the experimental results display a distinct and repeatable hysteresis: the flux through the material for a particular applied pressure drop is appreciably lower when the pressure has been decreased to that value compared to when it has been increased to the same value.
Flow-induced compaction of a deformable porous medium.
Hewitt, Duncan R; Nijjer, Japinder S; Worster, M Grae; Neufeld, Jerome A
2016-02-01
Fluid flowing through a deformable porous medium imparts viscous drag on the solid matrix, causing it to deform. This effect is investigated theoretically and experimentally in a one-dimensional configuration. The experiments consist of the downwards flow of water through a saturated pack of small, soft, hydrogel spheres, driven by a pressure head that can be increased or decreased. As the pressure head is increased, the effective permeability of the medium decreases and, in contrast to flow through a rigid medium, the flux of water is found to increase towards a finite upper bound such that it becomes insensitive to changes in the pressure head. Measurements of the internal deformation, extracted by particle tracking, show that the medium compacts differentially, with the porosity being lower at the base than at the upper free surface. A general theoretical model is derived, and the predictions of the model give good agreement with experimental measurements from a series of experiments in which the applied pressure head is sequentially increased. However, contrary to theory, all the experimental results display a distinct and repeatable hysteresis: the flux through the material for a particular applied pressure drop is appreciably lower when the pressure has been decreased to that value compared to when it has been increased to the same value. PMID:26986422
NASA Astrophysics Data System (ADS)
Yang, Pengliang; Brossier, Romain; Métivier, Ludovic; Virieux, Jean
2016-07-01
In this paper we study 3D multiparameter full waveform inversion (FWI) in viscoelastic media based on the generalized Maxwell/Zener body (GMB/GZB) including arbitrary number of attenuation mechanisms. We present a frequency-domain energy analysis to establish the stability condition of a full anisotropic viscoelastic system, according to zero-valued boundary condition and the elastic-viscoelastic correspondence principle: the real-valued stiffness matrix becomes a complex-valued one in Fourier domain when seismic attenuation is taken into account. We develop a least-squares optimization approach to linearly relate the quality factor with the anelastic coefficients by estimating a set of constants which are independent of the spatial coordinates, which supplies an explicit incorporation of the parameter Q in the general viscoelastic wave equation. By introducing the Lagrangian multipliers into the matrix expression of the wave equation with implicit time integration, we build a systematic formulation of multiparameter full waveform inversion for full anisotropic viscoelastic wave equation, while the equivalent form of the state and adjoint equation with explicit time integration is available to be resolved efficiently. In particular, this formulation lays the foundation for the inversion of the parameter Q in the time domain with full anisotropic viscoelastic properties. In the 3D isotropic viscoelastic settings, the anelastic coefficients and the quality factors using bulk and shear moduli parameterization can be related to the counterparts using P- and S- velocity. Gradients with respect to any other parameter of interest can be found by chain rule. Pioneering numerical validations as well as the real applications of this most generic framework will be carried out to disclose the potential of viscoelastic FWI when adequate high performance computing resources and the field data are available.
NASA Technical Reports Server (NTRS)
Leventis, Nicholas
2005-01-01
In analogy to supramolecular assemblies, which are pursued because of properties above and beyond those of the individual molecules, self-standing monolithic three-dimensional assemblies of nanoparticles also have unique properties attributed to their structure. For example, ultra low-density 3-D assemblies of silica nanoparticles, known as silica aerogels, are characterized by large internal void space, high surface area and very low thermal conductivity. Aerogels, however, are also extremely fragile materials, limiting their application to a few specialized environments, e.g., in nuclear reactors as Cerenkov radiation detectors, in space (refer to NASA's Stardust Program) and aboard certain planetary vehicles (thermal insulators on Mars Rovers in 1997 and 2004). The fragility problem is traced to well-defined weak points in the aerogel skeletal framework, the interparticle necks. Using the surface functionality of the nanoparticle building blocks as a focal point, we have directed attachment of a conformal polymer coating over the entire framework, rendering all necks wider. Thus, although the bulk density may increase only by 3x, the mesoporosity (pores in the range 2-50 nm) remains unchanged, while the strength of the material increases by up to 300... Having addressed the fragility problem, aerogels are now robust materials, and a variety of applications, ranging from thermal/acoustic insulators to catalyst supports, to platform for sensors, and dielectrics are all within reach. Our approach employs molecular science to manipulate nanoscopic matter for achieving useful macroscopic properties, and in our view it resides at the core of what defines nanotechnology. In that spirit, this technology is expandable in three directions. Thus, we have already crosslinked successfully amine-modified silica, and we anticipate that more rich chemistry will be realized by been creative with the nanoparticle surface modifiers. On the other hand, although we do not expect
Takaki, Yasuhiro; Urano, Yohei; Nishio, Hiroyuki
2012-11-19
The discontinuity of motion parallax offered by multi-view displays was assessed by subjective evaluation. A super multi-view head-up display, which provides dense viewing points and has short-, medium-, and long-distance display ranges, was used. The results showed that discontinuity perception depended on the ratio of an image shift between adjacent parallax images to a pixel pitch of three-dimensional (3D) images and the crosstalk between viewing points. When the ratio was less than 0.2 and the crosstalk was small, the discontinuity was not perceived. When the ratio was greater than 1 and the crosstalk was small, the discontinuity was perceived, and the resolution of the 3D images decreased twice. When the crosstalk was large, the discontinuity was not perceived even when the ratio was 1 or 2. However, the resolution decreased two or more times. PMID:23187574
NASA Astrophysics Data System (ADS)
Huang, Qun-xing; Yan, Fei Wang Jian-hua; Chi, Yong
2013-04-01
A new approach to inverse radiation analysis is presented for non-intrusive 3-D flame temperature reconstruction using flame emission images from four CCD camera detectors installed on the furnace wall. The scattering from participating medium in the flame was considered by combining the discrete radiative transfer method with the discrete ordinate method. A modified minimum residual algorithm was employed to calculate the least squares solution of the ill-conditioned inverse problem. A numerical test problem simulating real temperature measurements in an industrial furnace was used to assess the performance of the proposed method. These assessments indicate that this method is capable of reconstructing 3-D temperature distributions fast and accurately, even with noisy flame emission data. Such a capability has potential in real-time temperature measurement for combustion optimization and pollution emission control.
The porous medium permeability and effective diffusion coefficient direct correlation
NASA Astrophysics Data System (ADS)
Markicevic, Bojan
2012-11-01
Dimensionless analysis of a momentum and mass transport in the homogeneous porous medium reveals that the permeability and effective to the molecular diffusion coefficient ratio can be expressed as a function of medium pore and throat sizes and two additional geometrical scales. These two scales, each one pertinent to the momentum and mass transport, respectively, are referred to as permeability and diffusivity characteristic scales. Based on these findings, it can be shown that the medium permeability and effective diffusivity can be correlated, and, at the same time, that one microscopic scale needs to be known in this correlation. The same is implied from the Katz-Thompson formula - which correlates the permeability, effective diffusivity, and breakthrough capillary pressure length scale. We recast the correlation developed into the Katz-Thompson formula form, showing how corresponding members are related. It turns out that the coefficient from the Katz-Thompson formula is equal to the ratio of the permeability to diffusivity characteristic length scales, and it is indeed constant for the homogeneous media. As porous media are heterogeneous materials, the analysis is extended onto such materials using heterogeneous capillary networks. The networks with the uniform, normal and log-normal pore size distribution functions are generated, where the networks are sufficiently large to obtain small variations in permeability and effective diffusivity for pore size distribution set. For such stochastically homogeneous media, the effective pore size averages are used in calculating the permeability and effective diffusivity showing the true nature of the coefficient in the Katz-Thompson formula.
Fabrication of 3D porous SF/β-TCP hybrid scaffolds for bone tissue reconstruction.
Park, Hyun Jung; Min, Kyung Dan; Lee, Min Chae; Kim, Soo Hyeon; Lee, Ok Joo; Ju, Hyung Woo; Moon, Bo Mi; Lee, Jung Min; Park, Ye Ri; Kim, Dong Wook; Jeong, Ju Yeon; Park, Chan Hum
2016-07-01
Bio-ceramic is a biomaterial actively studied in the field of bone tissue engineering. But, only certain ceramic materials can resolve the corrosion problem and possess the biological affinity of conventional metal biomaterials. Therefore, the recent development of composites of hybrid composites and polymers has been widely studied. In this study, we aimed to select the best scaffold of silk fibroin and β-TCP hybrid for bone tissue engineering. We fabricated three groups of scaffold such as SF (silk fibroin scaffold), GS (silk fibroin/small granule size of β-TCP scaffold) and GM (silk fibroin/medium granule size of β-TCP scaffold), and we compared the characteristics of each group. During characterization of the scaffold, we used scanning electron microscopy (SEM) and a Fourier transform infrared spectroscopy (FTIR) for structural analysis. We compared the physiological properties of the scaffold regarding the swelling ratio, water uptake and porosity. To evaluate the mechanical properties, we examined the compressive strength of the scaffold. During in vitro testing, we evaluated cell attachment and cell proliferation (CCK-8). Finally, we confirmed in vivo new bone regeneration from the implanted scaffolds using histological staining and micro-CT. From these evaluations, the fabricated scaffold demonstrated high porosity with good inter-pore connectivity, showed good biocompatibility and high compressive strength and modulus. In particular, the present study indicates that the GM scaffold using β-TCP accelerates new bone regeneration of implanted scaffolds. Accordingly, our scaffold is expected to act a useful application in the field of bone tissue engineering. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1779-1787, 2016. PMID:26999521
Axisymmetric flows from fluid injection into a confined porous medium
NASA Astrophysics Data System (ADS)
Guo, Bo; Zheng, Zhong; Celia, Michael A.; Stone, Howard A.
2016-02-01
We study the axisymmetric flows generated from fluid injection into a horizontal confined porous medium that is originally saturated with another fluid of different density and viscosity. Neglecting the effects of surface tension and fluid mixing, we use the lubrication approximation to obtain a nonlinear advection-diffusion equation that describes the time evolution of the sharp fluid-fluid interface. The flow behaviors are controlled by two dimensionless groups: M, the viscosity ratio of displaced fluid relative to injected fluid, and Γ, which measures the relative importance of buoyancy and fluid injection. For this axisymmetric geometry, the similarity solution involving R2/T (where R is the dimensionless radial coordinate and T is the dimensionless time) is an exact solution to the nonlinear governing equation for all times. Four analytical expressions are identified as asymptotic approximations (two of which are new solutions): (i) injection-driven flow with the injected fluid being more viscous than the displaced fluid (Γ ≪ 1 and M < 1) where we identify a self-similar solution that indicates a parabolic interface shape; (ii) injection-driven flow with injected and displaced fluids of equal viscosity (Γ ≪ 1 and M = 1), where we find a self-similar solution that predicts a distinct parabolic interface shape; (iii) injection-driven flow with a less viscous injected fluid (Γ ≪ 1 and M > 1) for which there is a rarefaction wave solution, assuming that the Saffman-Taylor instability does not occur at the reservoir scale; and (iv) buoyancy-driven flow (Γ ≫ 1) for which there is a well-known self-similar solution corresponding to gravity currents in an unconfined porous medium [S. Lyle et al. "Axisymmetric gravity currents in a porous medium," J. Fluid Mech. 543, 293-302 (2005)]. The various axisymmetric flows are summarized in a Γ-M regime diagram with five distinct dynamic behaviors including the four asymptotic regimes and an intermediate regime
Parametric study of barometric pumping of a fractured porous medium
NASA Astrophysics Data System (ADS)
Adler, Pierre; Mourzenko, Valeri; Thovert, Jean Francois; Pili, Eric; Guillon, Sophie
2015-04-01
Fluctuations in the ambient atmospheric pressure result in motion of air in porous fractured media. This mechanism, known as barometric pumping, efficiently transports gaseous species through the vadose zone to the atmosphere. This is of interest in fields, such as transport of trace gases from soil to atmosphere, remediation of contaminated sites, radon in buildings, leakage from carbon sequestration sites and detection of nuclear explosions. The fractures are modeled as polygonal plane surfaces with a given transmissivity embedded in a permeable matrix. The slightly compressible fluid obeys Darcy's law in these two media with exchanges between them. The solute obeys convection-diffusion equations in both media again with exchanges. The numerical methodology is briefly described. The fractures and the porous medium are meshed by triangles and tetrahedra, respectively. The equations are discretized by the finite volume method and a Flux Limiting Scheme diminishes numerical dispersion. This model is applied to the Roselend Natural Laboratory. At a 55 m depth, a sealed cavity allows for gas release experiments across fractured porous rocks in the unsaturated zone. The standard case consist of hexagonal fractures with a radius of 5m, of aperture 0.5 mm and of density larger than 2.4 10-3 m-3; the pressure fluctuations are sinusoidal, of amplitude 0.01 bar and period 1 week; the solute concentration is equal to 1 at the bottom. Systematic results will be presented. First, the precision of the calculations is assessed. Second, the pressure and solute concentration fields are displayed and discussed. Within the time limit, the influence of the major parameters (fracture density, aperture, porosity, diffusion coefficient, pressure fluctuations including real recordings, …) is illustrated and discussed relatively to the standard case. Emphasis is put on some paradoxical results which are obtained. These results are discussed in terms of the amplification of solute
Two-phase flow in a chemically active porous medium
Darmon, Alexandre Dauchot, Olivier; Benzaquen, Michael; Salez, Thomas
2014-12-28
We study the problem of the transformation of a given reactant species into an immiscible product species, as they flow through a chemically active porous medium. We derive the equation governing the evolution of the volume fraction of the species, in a one-dimensional macroscopic description, identify the relevant dimensionless numbers, and provide simple models for capillary pressure and relative permeabilities, which are quantities of crucial importance when tackling multiphase flows in porous media. We set the domain of validity of our models and discuss the importance of viscous coupling terms in the extended Darcy’s law. We investigate numerically the steady regime and demonstrate that the spatial transformation rate of the species along the reactor is non-monotonous, as testified by the existence of an inflection point in the volume fraction profiles. We obtain the scaling of the location of this inflection point with the dimensionless lengths of the problem. Eventually, we provide key elements for optimization of the reactor.
Porous-medium convection: new problems from CO2 sequestration
NASA Astrophysics Data System (ADS)
Lister, John
2013-11-01
Large scale injection and storage of supercritical carbon dioxide (CO2) into deep saline aquifers is proposed to offset anthropogenic emissions and mitigate climate change. Many aspects of the resultant porous flows provoke fundamental fluid-mechanical problems. The rise and spread of the buoyant CO2 plume beneath an overlying impermeable stratum is a classic gravity current, but with the undesirable extra possibility of upward leakage through fractures. Fortunately, long-term trapping mechanisms exist. One such, dissolution of CO2 into the underlying brine, produces a denser solution which thus convects reassuringly downwards. Consideration of the convective flux prompts re-examination of high-Ra convection in a porous medium, which is found to have a strikingly different asymptotic form from that in a pure fluid. The high-Ra regime of Rayleigh-Darcy convection has an ordered interior with a linear mean temperature gradient and a superposed vertical columnar heat-exchanger flow whose wavelength is consistent with the Ra - 5 / 14 scaling predicted by an asymptotic stability analysis. Quantification of the convective dissolution flux allows evolution towards saturation in confined aquifers, or the erosion of a gravity current in open aquifers, to be calculated.
Thermal Dispersion Within a Porous Medium Near a Solid Wall
NASA Technical Reports Server (NTRS)
Simon, T.; McFadden, G.; Ibrahim, M.
2006-01-01
The regenerator is a key component to Stirling cycle machine efficiency. Typical regenerators are of sintered fine wires or layers of fine-wire screens. Such porous materials are contained within solid-waH casings. Thermal energy exchange between the regenerator and the casing is important to cycle performance for the matrix and casing would not have the same axial temperature profile in an actual machine. Exchange from one to the other may allow shunting of thermal energy, reducing cycle efficiency. In this paper, temperature profiles within the near-wall region of the matrix are measured and thermal energy transport, termed thermal dispersion, is inferred. The data show how the wall affects thermal transport. Transport normal to the mean flow direction is by conduction within the solid and fluid and by advective transport within the matrix. In the near-wall region, both may be interrupted from their normal in-core pattern. Solid conduction paths are broken and scales of advective transport are damped. An equation is presented which describes this change for a wire screen mesh. The near-wall layer typically acts as an insulating layer. This should be considered in design or analysis. Effective thermal conductivity within the core is uniform. In-core transverse thermal effective conductivity values are compared to direct and indirect measurements reported elsewhere and to 3D numerical simulation results, computed previously and reported elsewhere. The 3-D CFD model is composed of six cylinders in cross flow, staggered in arrangement to match the dimensions and porosity of the matrix used in the experiments. The commercial code FLUENT is used to obtain the flow and thermal fields. The thermal dispersion and effective thermal conductivities for the matrix are computed from the results.
Tear film dynamics: modeling the glycocalyx as a porous medium
NASA Astrophysics Data System (ADS)
Siddique, Javed; Mastroberardinob, , Antonio; Braun, Richard; Anderson, Daniel
2015-11-01
The human tear film is a complex fluid structure composed of multiple layers: an aqueous layer that comprises most of the film and an outermost thinner lipid layer coat a forest of large transmembrane mucins at the epithelial surface. The glycocalyx helps provide stability to the ocular surface by assisting the tear film to wet it. It is also permeable to water, but less so to ions. We formulate a thin film model based on lubrication theory in order to understand the dynamics between the aqueous layer and the glycocalyx, which we treat as a rigid porous medium. We present numerical solutions for the evolution of the tear film and discuss the roles played by the key parameters of the system. This work was supported by the Simons Foundation Grant No. 281839.
Properties of equilibrium carbon dioxide hydrate in porous medium
NASA Astrophysics Data System (ADS)
Voronov, V. P.; Gorodetskii, E. E.; Podnek, V. E.; Grigoriev, B. A.
2016-09-01
Specific heat capacity, dissociation heat and hydration number of carbon dioxide hydrate in porous medium are determined by adiabatic calorimetry method. The measurements were carried out in the temperature range 250-290 K and in pressure range 1-5 MPa. The measured specific heat of the hydrate is approximately 2.7 J/(g K), which is significantly larger than the specific heat of methane hydrate. In particular, at heating, larger value of the specific heat of carbon dioxide hydrate is a result of gas emission from the hydrate. The hydration number at the hydrate-gas coexistence changes from 6.2 to 6.9. The dissociation heat of carbon dioxide hydrate varies from the 55 kJ/mol near the upper quadruple point to the 57 kJ/mol near the lower quadruple point.
Wen Lili; Wang Dong'e; Wang Chenggang; Wang Feng; Li Dongfeng Deng Kejian
2009-03-15
A new metal-organic framework, [Zn{sub 5}(trencba){sub 2}(OH){sub 2}Cl{sub 2}.4H{sub 2}O] (1) [H{sub 3}trencba=N,N,N',N',N'',N''-tris[(4-carboxylate-2-yl)methyl]-tris (2-aminoethyl)amine], constructed from a flexible tripodal ligand based on C{sub 3} symmetric tris(2-aminoethyl)amine, has been synthesized hydrothermally and characterized by elemental analysis, IR, TG, XRD and single-crystal X-ray diffraction analysis. Compound 1 contains an unprecedented linear penta-nuclear zinc cluster fragment. Each ligand links four penta-nuclear fragments, and every fragment links eight ligands to generate a three-dimensional non-interpenetrated porous framework. The uncoordinated water molecules were observed trapped in the void pores. Compound 1 represents the first example of (6,8)-connected 3D bi-nodal framework based on a single kind of organic ligand. The photoluminescence measurements showed that complex 1 exhibits relatively stronger blue emissions at room temperature than that of the ligand. - Graphical abstract: The MOF [Zn{sub 5}(trencba){sub 2}(OH){sub 2}Cl{sub 2}.4H{sub 2}O] (H{sub 3}trencba=N,N,N',N',N',N'-tris[(4-carboxylate-2-yl)methyl]-tris (2-aminoethyl)amine) reveals a (6,8)-connected bi-nodal three-dimensional porous framework with unprecedented penta-nuclear fragment, which appears to be a good candidate of hybrid inorganic-organic photoactive materials.
NASA Astrophysics Data System (ADS)
Mirabolghasemi, Maryam; Prodanović, Maša; DiCarlo, David; Ji, Hongyu
2015-10-01
Understanding the mechanisms of filtration through porous media is relevant in many engineering applications ranging from waste water treatment and aquifer contamination in environmental engineering to estimating the permeability reduction in near wellbore region during drilling or water re-injection in petroleum engineering. In this paper we present a pore-scale approach that models straining through the pore structures extracted from X-ray tomographic images of rock and grain pack samples from the first principles, enabling the examination of current macroscopic models. While continuum models are widely used for fast prediction of the retention profiles and permeability of the host porous medium, they require a number of phenomenological parameters which are derived from matching experimental results. One of these parameters is the rate of entrapment, which is the sink term in the advection-diffusion equation. Here we find the constitutive relationship for the rate of entrapment as a product of the filtration coefficient, velocity, and concentration and validate it by comparing with core flood experiments. Results show that the pore-scale simulation gives close approximations of filtration coefficient when pore bridging and straining are the main particle capture mechanisms.
Fredrich, J.T.
1999-02-10
We present advances in the application of laser scanning confocal microscopy (LSCM) to image, reconstruct, and characterize statistically the microgeometry of porous geologic and engineering materials. We discuss technical and practical aspects of this imaging technique, including both its advantages and limitations. Confocal imaging can be used to optically section a material, with sub-micron resolution possible in the lateral and axial planes. The resultant volumetric image data, consisting of fluorescence intensities for typically {approximately}50 million voxels in XYZ space, can be used to reconstruct the three-dimensional structure of the two-phase medium. We present several examples of this application, including studying pore geometry in sandstone, characterizing brittle failure processes in low-porosity rock deformed under triaxial loading conditions in the laboratory, and analyzing the microstructure of porous ceramic insulations. We then describe approaches to extract statistical microgeometric descriptions from volumetric image data, and present results derived from confocal volumetric data sets. Finally, we develop the use of confocal image data to automatically generate a three-dimensional mesh for numerical pore-scale flow simulations.
High-contrast 3D microscopic imaging of deep layers in a biological medium
NASA Astrophysics Data System (ADS)
Faridian, Ahmad; Pedrini, Giancarlo; Osten, Wolfgang
2014-03-01
Multilayer imaging of biological specimens is a demanding field of research, but scattering is one of the major obstacles in imaging the internal layers of a specimen. Although in many studies the biological object is assumed to be a weak scatterer, this condition is hardly satisfied for sub-millimeter sized organisms. The scattering medium is inhomogeneously distributed inside the specimen. Therefore, the scattering which occurs in the upper layers of a given internal layer of interest is different from the lower layers. That results in a different amount of collectable information for a specific point in the layer from each view. An opposed view dark-field digital holographic microscope (DHM) has been implemented in this work to collect the information concurrently from both views and increase the image quality. Implementing a DHM system gives the possibility to perform digital refocusing process and obtain multilayer images from each side without depth scanning of the object. The results have been presented and discussed here for a Drosophila embryo.
Large-scale 3D mapping of the intergalactic medium using the Lyman α forest
NASA Astrophysics Data System (ADS)
Ozbek, Melih; Croft, Rupert A. C.; Khandai, Nishikanta
2016-03-01
Maps of the large-scale structure of the Universe at redshifts 2-4 can be made with the Lyman α forest which are complementary to low-redshift galaxy surveys. We apply the Wiener interpolation method of Caucci et al. to construct three-dimensional maps from sets of Lyman α forest spectra taken from cosmological hydrodynamic simulations. We mimic some current and future quasar redshift surveys [Baryon Oscillation Spectroscopic Survey (BOSS), extended BOSS (eBOSS) and Mid-Scale Dark Energy Spectroscopic Instrument (MS-DESI)] by choosing similar sightline densities. We use these appropriate subsets of the Lyman α absorption sightlines to reconstruct the full three-dimensional Lyman α flux field and perform comparisons between the true and the reconstructed fields. We study global statistical properties of the intergalactic medium (IGM) maps with autocorrelation and cross-correlation analysis, slice plots, local peaks and point-by-point scatter. We find that both the density field and the statistical properties of the IGM are recovered well enough that the resulting IGM maps can be meaningfully considered to represent large-scale maps of the Universe in agreement with Caucci et al., on larger scales and for sparser sightlines than had been tested previously. Quantitatively, for sightline parameters comparable to current and near future surveys the correlation coefficient between true and reconstructed fields is r > 0.9 on scales >30 h-1 Mpc. The properties of the maps are relatively insensitive to the precise form of the covariance matrix used. The final BOSS quasar Lyman α forest sample will allow maps to be made with a resolution of ˜30 h-1 Mpc over a volume of ˜15 h-3 Gpc3 between redshifts 1.9 and 2.3.
Xin X.; Zhu Y.; Zhou, X.; Wang, F.; Yao, X.; Xu, X.; Liu, Z.
2012-04-28
A 3D porous architecture of Si/graphene nanocomposite has been rationally designed and constructed through a series of controlled chemical processes. In contrast to random mixture of Si nanoparticles and graphene nanosheets, the porous nanoarchitectured composite has superior electrochemical stability because the Si nanoparticles are firmly riveted on the graphene nanosheets through a thin SiO{sub x} layer. The 3D graphene network enhances electrical conductivity, and improves rate performance, demonstrating a superior rate capability over the 2D nanostructure. This 3D porous architecture can deliver a reversible capacity of {approx}900 mA h g{sup -1} with very little fading when the charge rates change from 100 mA g{sup -1} to 1 A g{sup -1}. Furthermore, the 3D nanoarchitechture of Si/graphene can be cycled at extremely high Li{sup +} extraction rates, such as 5 A g{sup -1} and 10 A g{sup -1}, for over than 100 times. Both the highly conductive graphene network and porous architecture are considered to contribute to the remarkable rate capability and cycling stability, thereby pointing to a new synthesis route to improving the electrochemical performances of the Si-based anode materials for advanced Li-ion batteries.
Yan, D; Cheng, S; Zhuo, R F; Chen, J T; Feng, J J; Feng, H T; Li, H J; Wu, Z G; Wang, J; Yan, P X
2009-03-11
Hydrohausmannite nanoparticles (approximately 10 nm) were prepared by the hydrothermal method at 100 degrees C for 72 h. Subsequent annealing was done in air at 400 degrees C and 800 degrees C for 10 h, Mn(3)O(4) nanoparticles (approximately 25 nm) and 3D Mn(2)O(3) porous networks were obtained, respectively. The products were characterized by XRD, TEM, SAED and FESEM. Time-dependent experiments were carried out to exhibit the formation process of the Mn(2)O(3) networks. Their microwave absorption properties were investigated by mixing the product and paraffin wax with 50 vol%. The Mn(3)O(4) nanoparticles possess excellent microwave absorbing properties with the minimum reflection loss of -27.1 dB at 3.1 GHz. In contrast, the Mn(2)O(3) networks show the weakest absorption of all samples. The absorption becomes weaker with the annealing time increasing at 800 degrees C. The attenuation of microwave can be attributed to dielectric loss and their absorption mechanism was discussed in detail. PMID:19417534
Huang, Jianfei; Zhu, Yihua; Yang, Xiaoling; Chen, Wei; Zhou, Ying; Li, Chunzhong
2015-01-14
Convenient determination of glucose in a sensitive, reliable and cost-effective way has aroused sustained research passion, bringing along assiduous investigation of high-performance electroactive nanomaterials to build enzymeless sensors. In addition to the intrinsic electrocatalytic capability of the sensing materials, electrode architecture at the microscale is also crucial for fully enhancing the performance. In this work, free-standing porous CuO nanowire (NW) was taken as a model sensing material to illustrate this point, where an in situ formed 3D CuO nanowire array (NWA) and CuO nanowires pile (NWP) immobilized with polymer binder by conventional drop-casting technique were both studied for enzymeless glucose sensing. The NWA electrode exhibited greatly promoted electrochemistry characterized by decreased overpotential for electro-oxidation of glucose and over 5-fold higher sensitivity compared to the NWP counterpart, benefiting from the binder-free nanoarray structure. Besides, its sensing performance was also satisfying in terms of rapidness, selectivity and durability. Further, the CuO NWA was utilized to fabricate a flexible sensor which showed excellent performance stability against mechanical bending. Thanks to its favorable electrode architecture, the CuO NWA is believed to offer opportunities for building high-efficiency flexible electrochemical devices. PMID:25415769
Lai, Chuan; Guo, Xiaogang; Xiong, Zhongshu; Liu, Changlu; Zhu, Hui; Wu, Mei; Zhang, Daixiong
2016-02-01
The present study reports the removal of Ca (II), Cr (III), Mg (II) ions from aqueous solution using 3D-porous nickel films (3DNFs) as a novel adsorbent material prepared by hydrogen bubble dynamic template (HBDT) method at room temperature. The structure morphology and the phase constitution of 3DNFs were characterized by FESEM, EDS and XRD. Adsorption process of Ca (II), Cr (III), Mg (II) ions was fast as the equilibrium was established within 30min, and the maximum adsorption at equilibrium was 44.1mg/g, 46.4mg/g and 32.7mg/g, respectively. The adsorption kinetics well fitted using a pseudo second-order kinetic model. The adsorption isotherm data of all the three metals fit well the Langmuir and Freundlich adsorption isotherm model. It was found out that kinetics of adsorption varies with initial concentration of metal ions. Thermodynamic parameters (i.e., the standard Gibbs free energies (ΔG), enthalpy change (ΔH), standard entropy change (ΔS)) were also evaluated. Thermodynamic analysis indicated that a high temperature is favored for the adsorption of metal ions by 3DNFs. These results suggest that 3DNFs have good potential application in effective adsorption of metal ions with satisfactory results. PMID:26520822
A fractal approach to low velocity non-Darcy flow in a low permeability porous medium
NASA Astrophysics Data System (ADS)
Cai, Jian-Chao
2014-04-01
In this paper, the mechanism for fluid flow at low velocity in a porous medium is analyzed based on plastic flow of oil in a reservoir and the fractal approach. The analytical expressions for flow rate and velocity of non-Newtonian fluid flow in the low permeability porous medium are derived, and the threshold pressure gradient (TPG) is also obtained. It is notable that the TPG (J) and permeability (K) of the porous medium analytically exhibit the scaling behavior J ~ K-DT/(1=DT), where DT is the fractal dimension for tortuous capillaries. The fractal characteristics of tortuosity for capillaries should be considered in analysis of non-Darcy flow in a low permeability porous medium. The model predictions of TPG show good agreement with those obtained by the available expression and experimental data. The proposed model may be conducible to a better understanding of the mechanism for nonlinear flow in the low permeability porous medium.
Pacht, J.A.; Brooks, L.; Messa, F.
1995-12-31
Carbonate debris flow are very important plays in Leonard strata along the northwestern margin of the Midland Basin. Delineation of these strata, however, is difficult and detailed stratigraphic analysis of both 2D and 3D seismic data is important in reducing risk. Porous debris flows are best developed during lowstand time. When sea-level falls to a point at or below the shelf margin, sand to boulder-sized clasts created by reef-front erosion are funneled through slope gullies onto the base of the slope. Large debris flows exhibit well-defined mounds which downlap onto the sequence boundary. Many of these flows, however, are too thin to exhibit discrete reflections. 3D seismic data are used to define subtle changes in amplitude and frequency which suggest presence of porous strata. Along the northwest shelf, porous debris flows exhibit lower amplitude (dim spots) and lower frequency than surrounding strata. They are commonly developed immediately downdip of major slump scars.
NASA Astrophysics Data System (ADS)
Rohan, Eduard; Naili, Salah; Nguyen, Vu-Hieu
2016-08-01
We study wave propagation in an elastic porous medium saturated with a compressible Newtonian fluid. The porous network is interconnected whereby the pores are characterized by two very different characteristic sizes. At the mesoscopic scale, the medium is described using the Biot model, characterized by a high contrast in the hydraulic permeability and anisotropic elasticity, whereas the contrast in the Biot coupling coefficient is only moderate. Fluid motion is governed by the Darcy flow model extended by inertia terms and by the mass conservation equation. The homogenization method based on the asymptotic analysis is used to obtain a macroscopic model. To respect the high contrast in the material properties, they are scaled by the small parameter, which is involved in the asymptotic analysis and characterized by the size of the heterogeneities. Using the estimates of wavelengths in the double-porosity networks, it is shown that the macroscopic descriptions depend on the contrast in the static permeability associated with pores and micropores and on the frequency. Moreover, the microflow in the double porosity is responsible for fading memory effects via the macroscopic poroviscoelastic constitutive law. xml:lang="fr"
Identification of the permeability field of a porous medium from the injection of a passive tracer
Zhan, Lang; Yortsos, Yannis C.
2000-07-01
We propose a method for the direct inversion of the permeability field of a porous medium from the analysis of the displacement of a passive tracer. By monitoring the displacement front at successive time intervals (for example, using a tomographic method), the permeability can be directly obtained from the solution of a nonlinear boundary-value problem. Well posedness requires knowledge of the pressure profile or the permeability at no-flow boundaries. The method is tested using synthetic data in two dimensions (2D) (and some 3D) geometries for a variety of heterogeneous fields and found to work well when the permeability contrast is not too large. However, it is sensitive to sharp variations in permeability. In the latter case, a modified approach based on the successive injection in both directions and the use of an optimization technique leads to improved estimates. The sensitivity to measurement errors is analyzed. An important feature of the direct method is that it also applies to anisotropic porous media. When the principal axes of anisotropy are known, a suitable procedure is proposed and demonstrated using synthetic data. (c) 2000 The American Physical Society.
Holford, D.J.
1994-01-01
This document is a user`s manual for the Rn3D finite element code. Rn3D was developed to simulate gas flow and radon transport in variably saturated, nonisothermal porous media. The Rn3D model is applicable to a wide range of problems involving radon transport in soil because it can simulate either steady-state or transient flow and transport in one-, two- or three-dimensions (including radially symmetric two-dimensional problems). The porous materials may be heterogeneous and anisotropic. This manual describes all pertinent mathematics related to the governing, boundary, and constitutive equations of the model, as well as the development of the finite element equations used in the code. Instructions are given for constructing Rn3D input files and executing the code, as well as a description of all output files generated by the code. Five verification problems are given that test various aspects of code operation, complete with example input files, FORTRAN programs for the respective analytical solutions, and plots of model results. An example simulation is presented to illustrate the type of problem Rn3D is designed to solve. Finally, instructions are given on how to convert Rn3D to simulate systems other than radon, air, and water.
NASA Astrophysics Data System (ADS)
Huang, Jianfei; Zhu, Yihua; Yang, Xiaoling; Chen, Wei; Zhou, Ying; Li, Chunzhong
2014-12-01
Convenient determination of glucose in a sensitive, reliable and cost-effective way has aroused sustained research passion, bringing along assiduous investigation of high-performance electroactive nanomaterials to build enzymeless sensors. In addition to the intrinsic electrocatalytic capability of the sensing materials, electrode architecture at the microscale is also crucial for fully enhancing the performance. In this work, free-standing porous CuO nanowire (NW) was taken as a model sensing material to illustrate this point, where an in situ formed 3D CuO nanowire array (NWA) and CuO nanowires pile (NWP) immobilized with polymer binder by conventional drop-casting technique were both studied for enzymeless glucose sensing. The NWA electrode exhibited greatly promoted electrochemistry characterized by decreased overpotential for electro-oxidation of glucose and over 5-fold higher sensitivity compared to the NWP counterpart, benefiting from the binder-free nanoarray structure. Besides, its sensing performance was also satisfying in terms of rapidness, selectivity and durability. Further, the CuO NWA was utilized to fabricate a flexible sensor which showed excellent performance stability against mechanical bending. Thanks to its favorable electrode architecture, the CuO NWA is believed to offer opportunities for building high-efficiency flexible electrochemical devices.Convenient determination of glucose in a sensitive, reliable and cost-effective way has aroused sustained research passion, bringing along assiduous investigation of high-performance electroactive nanomaterials to build enzymeless sensors. In addition to the intrinsic electrocatalytic capability of the sensing materials, electrode architecture at the microscale is also crucial for fully enhancing the performance. In this work, free-standing porous CuO nanowire (NW) was taken as a model sensing material to illustrate this point, where an in situ formed 3D CuO nanowire array (NWA) and CuO nanowires
Luquet, David; Marchiano, Régis; Coulouvrat, François
2015-10-28
Many situations involve the propagation of acoustical shock waves through flows. Natural sources such as lightning, volcano explosions, or meteoroid atmospheric entries, emit loud, low frequency, and impulsive sound that is influenced by atmospheric wind and turbulence. The sonic boom produced by a supersonic aircraft and explosion noises are examples of intense anthropogenic sources in the atmosphere. The Buzz-Saw-Noise produced by turbo-engine fan blades rotating at supersonic speed also propagates in a fast flow within the engine nacelle. Simulating these situations is challenging, given the 3D nature of the problem, the long range propagation distances relative to the central wavelength, the strongly nonlinear behavior of shocks associated to a wide-band spectrum, and finally the key role of the flow motion. With this in view, the so-called FLHOWARD (acronym for FLow and Heterogeneous One-Way Approximation for Resolution of Diffraction) method is presented with three-dimensional applications. A scalar nonlinear wave equation is established in the framework of atmospheric applications, assuming weak heterogeneities and a slow wind. It takes into account diffraction, absorption and relaxation properties of the atmosphere, quadratic nonlinearities including weak shock waves, heterogeneities of the medium in sound speed and density, and presence of a flow (assuming a mean stratified wind and 3D turbulent ? flow fluctuations of smaller amplitude). This equation is solved in the framework of the one-way method. A split-step technique allows the splitting of the non-linear wave equation into simpler equations, each corresponding to a physical effect. Each sub-equation is solved using an analytical method if possible, and finite-differences otherwise. Nonlinear effects are solved in the time domain, and others in the frequency domain. Homogeneous diffraction is handled by means of the angular spectrum method. Ground is assumed perfectly flat and rigid. Due to the 3D
NASA Astrophysics Data System (ADS)
Luquet, David; Marchiano, Régis; Coulouvrat, François
2015-10-01
Many situations involve the propagation of acoustical shock waves through flows. Natural sources such as lightning, volcano explosions, or meteoroid atmospheric entries, emit loud, low frequency, and impulsive sound that is influenced by atmospheric wind and turbulence. The sonic boom produced by a supersonic aircraft and explosion noises are examples of intense anthropogenic sources in the atmosphere. The Buzz-Saw-Noise produced by turbo-engine fan blades rotating at supersonic speed also propagates in a fast flow within the engine nacelle. Simulating these situations is challenging, given the 3D nature of the problem, the long range propagation distances relative to the central wavelength, the strongly nonlinear behavior of shocks associated to a wide-band spectrum, and finally the key role of the flow motion. With this in view, the so-called FLHOWARD (acronym for FLow and Heterogeneous One-Way Approximation for Resolution of Diffraction) method is presented with three-dimensional applications. A scalar nonlinear wave equation is established in the framework of atmospheric applications, assuming weak heterogeneities and a slow wind. It takes into account diffraction, absorption and relaxation properties of the atmosphere, quadratic nonlinearities including weak shock waves, heterogeneities of the medium in sound speed and density, and presence of a flow (assuming a mean stratified wind and 3D turbulent ? flow fluctuations of smaller amplitude). This equation is solved in the framework of the one-way method. A split-step technique allows the splitting of the non-linear wave equation into simpler equations, each corresponding to a physical effect. Each sub-equation is solved using an analytical method if possible, and finite-differences otherwise. Nonlinear effects are solved in the time domain, and others in the frequency domain. Homogeneous diffraction is handled by means of the angular spectrum method. Ground is assumed perfectly flat and rigid. Due to the 3D
Flow regimes for fluid injection into a confined porous medium
Zheng, Zhong; Guo, Bo; Christov, Ivan C.; Celia, Michael A.; Stone, Howard A.
2015-02-24
We report theoretical and numerical studies of the flow behaviour when a fluid is injected into a confined porous medium saturated with another fluid of different density and viscosity. For a two-dimensional configuration with point source injection, a nonlinear convection–diffusion equation is derived to describe the time evolution of the fluid–fluid interface. In the early time period, the fluid motion is mainly driven by the buoyancy force and the governing equation is reduced to a nonlinear diffusion equation with a well-known self-similar solution. In the late time period, the fluid flow is mainly driven by the injection, and the governing equation is approximated by a nonlinear hyperbolic equation that determines the global spreading rate; a shock solution is obtained when the injected fluid is more viscous than the displaced fluid, whereas a rarefaction wave solution is found when the injected fluid is less viscous. In the late time period, we also obtain analytical solutions including the diffusive term associated with the buoyancy effects (for an injected fluid with a viscosity higher than or equal to that of the displaced fluid), which provide the structure of the moving front. Numerical simulations of the convection–diffusion equation are performed; the various analytical solutions are verified as appropriate asymptotic limits, and the transition processes between the individual limits are demonstrated.
Flow regimes for fluid injection into a confined porous medium
Zheng, Zhong; Guo, Bo; Christov, Ivan C.; Celia, Michael A.; Stone, Howard A.
2015-02-24
We report theoretical and numerical studies of the flow behaviour when a fluid is injected into a confined porous medium saturated with another fluid of different density and viscosity. For a two-dimensional configuration with point source injection, a nonlinear convection–diffusion equation is derived to describe the time evolution of the fluid–fluid interface. In the early time period, the fluid motion is mainly driven by the buoyancy force and the governing equation is reduced to a nonlinear diffusion equation with a well-known self-similar solution. In the late time period, the fluid flow is mainly driven by the injection, and the governingmore » equation is approximated by a nonlinear hyperbolic equation that determines the global spreading rate; a shock solution is obtained when the injected fluid is more viscous than the displaced fluid, whereas a rarefaction wave solution is found when the injected fluid is less viscous. In the late time period, we also obtain analytical solutions including the diffusive term associated with the buoyancy effects (for an injected fluid with a viscosity higher than or equal to that of the displaced fluid), which provide the structure of the moving front. Numerical simulations of the convection–diffusion equation are performed; the various analytical solutions are verified as appropriate asymptotic limits, and the transition processes between the individual limits are demonstrated.« less
Inclusion-based effective medium models for the field-scale permeability of 3D fractured rock masses
NASA Astrophysics Data System (ADS)
Ebigbo, Anozie; Lang, Philipp S.; Paluszny, Adriana; Zimmerman, Robert W.
2016-04-01
Fractures that are more permeable than their host rock can act as preferential, or at least additional, pathways for fluid to flow through the rock. The additional transmissivity contributed by these fractures will be of great relevance in several areas of earth science and engineering, such as radioactive waste disposal in crystalline rock, exploitation of fractured hydrocarbon and geothermal reservoirs, or hydraulic fracturing. In describing or predicting flow through fractured rock, the effective permeability of the rock mass, comprising both the rock matrix and a network of fractures, is a crucial parameter, and will depend on several geometric properties of the fractures/networks, such as lateral extent, aperture, orientation, and fracture density. This study investigates the ability of classical inclusion-based effective medium models (following the work of Sævik et al., Transp. Porous Media, 2013) to predict this permeability. In these models, the fractures are represented as thin, spheroidal inclusions, the interiors of which are treated as porous media having a high (but finite) permeability. The predictions of various effective medium models, such as the symmetric and asymmetric self-consistent schemes, the differential scheme, and Maxwell's method, are tested against the results of explicit numerical simulations of mono- and polydisperse isotropic fracture networks embedded in a permeable rock matrix. Comparisons are also made with the Hashin-Shrikman bounds, Snow's model, and Mourzenko's heuristic model (Mourzenko et al., Phys. Rev. E, 2011). This problem is characterised mathematically by two small parameters, the aspect ratio of the spheroidal fractures, α, and the ratio between matrix and fracture permeability, κ. Two different regimes can be identified, corresponding to α/κ < 1 and α/κ > 1. The lower the value of α/κ, the more significant is flow through the matrix. Due to differing flow patterns, the dependence of effective permeability on
NASA Astrophysics Data System (ADS)
Guerrero, Miguel; Pané, Salvador; Nelson, Bradley J.; Baró, Maria Dolors; Roldán, Mònica; Sort, Jordi; Pellicer, Eva
2013-11-01
Three-dimensional (3D) hierarchically porous composite Cu-BiOCl films have been prepared by a facile one-step galvanostatic electrodeposition process from acidic electrolytic solutions containing Cu(ii) and Bi(iii) chloride salts and Triton X-100. The films show spherical, micron-sized pores that spread over the whole film thickness. In turn, the pore walls are made of randomly packed BiOCl nanoplates that are assembled leaving micro-nanopore voids beneath. It is believed that Cu grows within the interstitial spaces between the hydrogen bubbles produced from the reduction of H+ ions. Then, the BiOCl sheets accommodate in the porous network defined by the Cu building blocks. The presence of Cu tends to enhance the mechanical stability of the composite material. The resulting porous Cu-BiOCl films exhibit homogeneous and stable-in-time photoluminescent response arising from the BiOCl component that spreads over the entire 3D porous structure, as demonstrated by confocal scanning laser microscopy. A broad-band emission covering the entire visible range, in the wavelength interval 450-750 nm, is obtained. The present work paves the way for the facile and controlled preparation of a new generation of photoluminescent membranes.Three-dimensional (3D) hierarchically porous composite Cu-BiOCl films have been prepared by a facile one-step galvanostatic electrodeposition process from acidic electrolytic solutions containing Cu(ii) and Bi(iii) chloride salts and Triton X-100. The films show spherical, micron-sized pores that spread over the whole film thickness. In turn, the pore walls are made of randomly packed BiOCl nanoplates that are assembled leaving micro-nanopore voids beneath. It is believed that Cu grows within the interstitial spaces between the hydrogen bubbles produced from the reduction of H+ ions. Then, the BiOCl sheets accommodate in the porous network defined by the Cu building blocks. The presence of Cu tends to enhance the mechanical stability of the
Ebrahimi-Barough, Somayeh; Hoveizi, Elham; Norouzi Javidan, Abbas; Ai, Jafar
2015-08-01
Neural tissue engineering is an important area of research in the field of tissue-engineering especially for neurodegenerative disease such as spinal cord injury. The differentiation capacity of human endometrial stem cells (hEnSCs) into neuronal cells has yet to be elucidated. Here, the major aim of the present study was to investigate the differentiation ability of hEnSCs cultured on polylactic acid/chitosan (PLA/CS) nanofibrous scaffold into neuroglial cells in response to conditioned medium of BE(2)-C human neuroblastoma cells and growth factors. Here we investigated the use PLA/CS scaffold as a three dimensional (3D) system that increased neuro-glial cells differentiation. Human EnSCs after three passages were differentiated in neuro-glial like cells under neuroblastoma conditioned medium with FGF2/PDGF-AA on PLA/CS scaffold. By day 18, differentiated cells were analyzed for expression of neuroglial markers by qRT-PCR and immunofluorescence. The results revealed that hEnSCs attach, grow and differentiation on the nanofibrous PLA/CS scaffold. Additionally, our study showed the expression of neural and glial lineage markers such as Nestin, NF-L, MAP2, PDGFRa, CNP, Olig2, MBP, and GFAP in the level of mRNA and MAP2, Tuj-1, and NF-L in the protein level after 18 days. Our results demonstrate that hEnSCs cultured on PLA/CS nanofibrous scaffold have the potential to differentiate in neuronal and glial cells in presence of neuroblastoma conditioned medium on PLA/CS scaffold. The result of this study may have impact in tissue engineering and cells-base therapy of neurodegenerative diseases and have a great potential for wide application. PMID:25611196
NASA Astrophysics Data System (ADS)
Fan, Qi; Lei, Lixu; Sun, Yueming
2014-06-01
A facile and efficient synthesis was developed to fabricate a 3D-porous LiNbO3 nanocomposite by microwave-induced auto-combustion. Such a material shows a high reversible capacity, excellent rate performance and stable cycle performance indicating its great potential as a promising anode material for Li-ion batteries.A facile and efficient synthesis was developed to fabricate a 3D-porous LiNbO3 nanocomposite by microwave-induced auto-combustion. Such a material shows a high reversible capacity, excellent rate performance and stable cycle performance indicating its great potential as a promising anode material for Li-ion batteries. Electronic supplementary information (ESI) available: Experimental details and additional supporting figures. See DOI: 10.1039/c4nr00232f
Dense, Viscous Brine Behavior in Heterogeneous Porous Medium Systems
Wright, D. Johnson; Pedit, J.A.; Gasda, S.E.; Farthing, M.W.; Murphy, L.L.; Knight, S.R.; Brubaker, G.R.
2010-01-01
The behavior of dense, viscous calcium bromide brine solutions used to remediate systems contaminated with dense nonaqueous phase liquids (DNAPLs) is considered in laboratory and field porous medium systems. The density and viscosity of brine solutions are experimentally investigated and functional forms fit over a wide range of mass fractions. A density of 1.7 times, and a corresponding viscosity of 6.3 times, that of water is obtained at a calcium bromide mass fraction of 0.53. A three-dimensional laboratory cell is used to investigate the establishment, persistence, and rate of removal of a stratified dense brine layer in a controlled system. Results from a field-scale experiment performed at the Dover National Test Site are used to investigate the ability to establish and maintain a dense brine layer as a component of a DNAPL recovery strategy, and to recover the brine at sufficiently high mass fractions to support the economical reuse of the brine. The results of both laboratory and field experiments show that a dense brine layer can be established, maintained, and recovered to a significant extent. Regions of unstable density profiles are shown to develop and persist in the field-scale experiment, which we attribute to regions of low hydraulic conductivity. The saturated-unsaturated, variable-density ground-water flow simulation code SUTRA is modified to describe the system of interest, and used to compare simulations to experimental observations and to investigate certain unobserved aspects of these complex systems. The model results show that the standard model formulation is not appropriate for capturing the behavior of sharp density gradients observed during the dense brine experiments. PMID:20444520
NASA Astrophysics Data System (ADS)
He, Shuijian; Hou, Haoqing; Chen, Wei
2015-04-01
3D porous and self-supported carbon hybrids are promising electrode materials for supercapacitor application attributed to their prominent properties such as binder-free electrode fabrication process, excellent electric conductivity and high power density etc. We present here a facile chemical vapor deposition method to fabricate a novel 3D flexible carbon hybrid nanostructure by growing a monolayer of nitrogen-doped carbon nanotubes on the skeleton of carbon foam (N-CNTs/CF) with Fe nanoparticle as catalyst. With such 3D porous, flexible and ultralight carbon nanostructure as binder-free electrode material, large surface area is available and fast ionic transport is facilitated. Moreover, the carbon-based network can provide excellent electronic conductivity. The electrochemical studies demonstrate that the supercapacitor constructed from the N-CNTs/CF hybrid exhibit high power density of 69.3 kW kg-1 and good stability with capacitance retention ration above 95% after cycled at 50 A g-1 for 5000 cycles. Therefore, the prepared porous N-CNTs/CF nanostructure is expected to be a type of excellent electrode material for electrical double layer capacitors.
NASA Astrophysics Data System (ADS)
Wargo, E. A.; Kotaka, T.; Tabuchi, Y.; Kumbur, E. C.
2013-11-01
Focused ion beam-scanning electron microscopy (FIB-SEM) and nano-scale X-ray computed tomography (nano-CT) have emerged as two popular nanotomography techniques for quantifying the 3-D microstructure of porous materials. The objective of this study is to assess the unique features and limitations of FIB-SEM and nano-CT in capturing the 3-D microstructure and structure-related transport properties of porous fuel cell materials. As a test case, a sample of a micro-porous layer used in polymer electrolyte fuel cells is analyzed to obtain 3-D microstructure datasets using these two nanotomography techniques. For quantitative comparison purposes, several key transport properties are determined for these two datasets, including the porosity, pore connectivity, tortuosity, structural diffusivity coefficient, and chord length (i.e., void size) distributions. The results obtained for both datasets are evaluated against each other and experimental data when available. Additionally, these two techniques are compared qualitatively in terms of the acquired images, image segmentation, and general systems operation. The particular advantages and disadvantages of both techniques are highlighted, along with suggestions for best practice.
A Two-Dimensional Model for the Analysis of Contaminant Transport in a Fractured Porous Medium.
1991-03-05
CHAINT-MC is a two-dimensional finite element model applicable to the transport of a dissolved radionuclide in a fractured porous medium along with radioactive chain decay and subsequent transport of the dissolved daughters.
Analysis of Fractional Flow for Transient Two-Phase Flow in Fractal Porous Medium
NASA Astrophysics Data System (ADS)
Lu, Ting; Duan, Yonggang; Fang, Quantang; Dai, Xiaolu; Wu, Jinsui
2016-03-01
Prediction of fractional flow in fractal porous medium is important for reservoir engineering and chemical engineering as well as hydrology. A physical conceptual fractional flow model of transient two-phase flow is developed in fractal porous medium based on the fractal characteristics of pore-size distribution and on the approximation that porous medium consist of a bundle of tortuous capillaries. The analytical expression for fractional flow for wetting phase is presented, and the proposed expression is the function of structural parameters (such as tortuosity fractal dimension, pore fractal dimension, maximum and minimum diameters of capillaries) and fluid properties (such as contact angle, viscosity and interfacial tension) in fractal porous medium. The sensitive parameters that influence fractional flow and its derivative are formulated, and their impacts on fractional flow are discussed.
A New Contraction Family for Porous Medium and Fast Diffusion Equations
NASA Astrophysics Data System (ADS)
Chmaycem, G.; Jazar, M.; Monneau, R.
2016-08-01
In this paper, we present a surprising two-dimensional contraction family for porous medium and fast diffusion equations. This approach provides new a priori estimates on the solutions, even for the standard heat equation.
Ioannidis, M.; Kwiecien, M.; Chatzis, I.
1995-12-31
This paper describes a new method for the computer generation of 3-D stochastic realizations of porous media using geostatistical information obtained from high-contrast 2-D images of pore casts. The stochastic method yields model porous media with statistical properties identical to those of their real counterparts. Synthetic media obtained in this manner can form the basis for a number of studies related to the detailed characterization of the porous microstructure and, ultimately, the prediction of important petrophysical and reservoir engineering properties. In this context, direct computer estimation of the formation resistivity factor is examined using a discrete random walk algorithm. The dependence of formation factor on measureable statistical properties of the pore space is also investigated.
Effect of thermal stratification on free convection within a porous medium
Nakayama, A.; Koyama, H.
1987-07-01
Free convection over a vertical flat plate embedded in a thermally stratified porous medium is analyzed by exploiting the similarity transformation procedure. Numerical integration results are presented for a series of wall and ambient temperature distributions which permit similarity solutions. The conjugate conduction connection problems of a free convection fin embedded in a thermally stratified porous medium is examined, and it is shown that the influence of the thermal stratification on the heat transfer is quite significant. 8 references.
Sharifi, Tiva; Gracia-Espino, Eduardo; Jia, Xueen; Sandström, Robin; Wågberg, Thomas
2015-12-30
We report efficient electrolysis of both water-splitting half reactions in the same medium by a bifunctional 3D electrode comprising Co3O4 nanospheres nucleated on the surface of nitrogen-doped carbon nanotubes (NCNTs) that in turn are grown on conductive carbon paper (CP). The resulting electrode exhibits high stability and large electrochemical activity for both oxygen and hydrogen evolution reactions (OER and HER). We obtain a current density of 10 mA/cm(2) in 0.1 M KOH solution at overpotentials of only 0.47 and 0.38 V for OER and HER, respectively. Additionally, the experimental observations are understood and supported by analyzing the Co3O4:NCNT and NCNT:CP interfaces by ab initio calculations. Both the experimental and the theoretical studies indicate that firm and well-established interfaces along the electrode play a crucial role on the stability and electrochemical activity for both OER and HER. PMID:26629887
Duan, Shasha; Yang, Ke; Wang, Zhihui; Chen, Mengting; Zhang, Ling; Zhang, Hongbo; Li, Chunzhong
2016-01-27
The combination of carbon nanomaterial with three-dimensional (3D) porous polymer substrates has been demonstrated to be an effective approach to manufacture high-performance stretchable conductive materials (SCMs). However, it remains a challenge to fabricate 3D-structured SCMs with outstanding electrical conductivity capability under large strain in a facile way. In this work, the 3D printing technique was employed to prepare 3D porous poly(dimethylsiloxane) (O-PDMS) which was then integrated with carbon nanotubes and graphene conductive network and resulted in highly stretchable conductors (OPCG). Two types of OPCG were prepared, and it has been demonstrated that the OPCG with split-level structure exhibited both higher electrical conductivity and superior retention capability under deformations, which was illustrated by using a finite element method. The specially designed split-level OPCG is capable of sustaining both large strain and repeated deformations showing huge potential in the application of next-generation stretchable electronics. PMID:26713456
Study of flow at the interface of a porous medium using particle image velocimetry
NASA Astrophysics Data System (ADS)
Shams Saryazdi, Masoud
This thesis reports the results of an experimental study of the flow at the interface of a fibrous porous medium and a freely flowing fluid. The model for the porous medium was a square array of parallel rods, and arrays with three different solid volume fractions were tested; namely 2.5%, 5.2%, and 10%. The flow adjacent to the porous medium was a shear flow perpendicular to the interface. It was created by generating circular Couette flow in a narrow channel outside the porous medium. Comprehensive velocity measurements were made inside and outside the various porous media using a PIV system that was developed for the experiment. An adverse pressure gradient in the streamwise direction was found to exist between the rods for the media with solid volume fractions of 5.2% and 10%. However no such pressure gradient was found for the 2.5% medium. The fluid motion corresponding to the adverse pressure gradients inside the medium was circulatory. The slip coefficient proposed by Beavers and Joseph was found directly by measuring the local velocity near the boundary of the porous medium. The slip coefficient for the media tested was found to be approximately 3. Comparisons show that Brinkman's equation in its original form (with the same viscosity inside the porous medium mu* and outside mu) did not produce results that matched the measured velocity field. Furthermore, Brinkman's equation did not produce results that matched the experimental velocity fields using any value of the viscosity ratio, mu*/mu. The measurements show that the slip velocity is small, and that Brinkman's equation with mu*/mu ≈ 9 predicts slip velocities quite well. The shear penetration length decreases as the solid volume fraction increases, and for a porous medium with a solid volume fraction of around 10%, the penetration length is smaller than all length scales of the medium. Therefore, for the higher solid volume fractions tested, shear penetration is practically negligible. Penetration of
Yin, Bo; Ma, Pei; Chen, Jun; Wang, Hai; Wu, Gui; Li, Bo; Li, Qiang; Huang, Zhifeng; Qiu, Guixing; Wu, Zhihong
2016-01-01
Porous titanium is a kind of promising material for bone substitution, while its bio-inert property results in demand of modifications to improve the osteointegration capacity. In this study, gelatin (Gel) and nano-hydroxyapatite (nHA) were used to construct 3D micro-scaffolds in the pores of porous titanium in the ratios of Gel:nHA = 1:0, Gel:nHA = 1:1, and Gel:nHA = 1:3, respectively. Cell attachment and proliferation, and gene and protein expression levels of osteogenic markers were evaluated in MC3T3-E1 cells, followed by bone regeneration assessment in a rabbit radius defect model. All hybrid scaffolds with different composition ratio were found to have significant promotional effects in cell adhesion, proliferation and differentiation, in which the group with Gel:nHA = 1:1 showed the best performance in vitro, as well as the most bone regeneration volume in vivo. This 3D micro-scaffolds modification may be an innovative method for porous titanium ornamentation and shows potential application values in clinic. PMID:27092492
Luo, Wen-Bin; Gao, Xuan-Wen; Shi, Dong-Qi; Chou, Shu-Lei; Wang, Jia-Zhao; Liu, Hua-Kun
2016-06-01
Pt-Gd alloy polycrystalline thin film is deposited on 3D nickel foam by pulsed laser deposition method serving as a whole binder/carbon-free air electrode, showing great catalytic activity enhancement as an efficient bifunctional catalyst for the oxygen reduction and evolution reactions in lithium oxygen batteries. The porous structure can facilitate rapid O2 and electrolyte diffusion, as well as forming a continuous conductive network throughout the whole energy conversion process. It shows a favorable cycle performance in the full discharge/charge model, owing to the high catalytic activity of the Pt-Gd alloy composite and 3D porous nickel foam structure. Specially, excellent cycling performance under capacity limited mode is also demonstrated, in which the terminal discharge voltage is higher than 2.5 V and the terminal charge voltage is lower than 3.7 V after 100 cycles at a current density of 0.1 mA cm(-2) . Therefore, this electrocatalyst is a promising bifunctional electrocatalyst for lithium oxygen batteries and this depositing high-efficient electrocatalyst on porous substrate with polycrystalline thin film by pulsed laser deposition is also a promising technique in the future lithium oxygen batteries research. PMID:27120699
Farzadi, Arghavan; Solati-Hashjin, Mehran; Asadi-Eydivand, Mitra; Abu Osman, Noor Azuan
2014-01-01
Powder-based inkjet 3D printing method is one of the most attractive solid free form techniques. It involves a sequential layering process through which 3D porous scaffolds can be directly produced from computer-generated models. 3D printed products' quality are controlled by the optimal build parameters. In this study, Calcium Sulfate based powders were used for porous scaffolds fabrication. The printed scaffolds of 0.8 mm pore size, with different layer thickness and printing orientation, were subjected to the depowdering step. The effects of four layer thicknesses and printing orientations, (parallel to X, Y and Z), on the physical and mechanical properties of printed scaffolds were investigated. It was observed that the compressive strength, toughness and Young's modulus of samples with 0.1125 and 0.125 mm layer thickness were more than others. Furthermore, the results of SEM and μCT analyses showed that samples with 0.1125 mm layer thickness printed in X direction have more dimensional accuracy and significantly close to CAD software based designs with predefined pore size, porosity and pore interconnectivity. PMID:25233468
NASA Astrophysics Data System (ADS)
Peng, Yuncheng; Wang, Yao; Deng, Yuan
2016-08-01
With the ever increasing level of performance of energy conversion micro-devices, such as thin-film solar cells and thermoelectric micro-generators or coolers, their reliability and stability still remain a challenge. The high electrical and mechanical stability of an electrode is two of the critical factors that affect the long-term life of devices. Here we show that these factors can be achieved by constructing a 3D porous network of nanostructures in copper film using facile magnetron sputtering technology without any templates. The constructed 3D porous network of nanostructures in Cu film provides not only the advantages of light weight, prominently high conductivity, and large elastic deformation, but also the ability to absorb stress, preventing crack propagation, which is crucial for electrodes to maintain stable electrical and mechanical properties under working conditions. The nanopores inside the 3D network are capable of unrestrained deformation under applied stress resulting in strong elastic recovery. This work puts forward a feasible solution for manufacturing electrodes with excellent electrical and mechanical properties for micro-energy devices.
Khan, Sami Ullah; Ali, Nasir; Abbas, Zaheer
2015-01-01
An analysis is carried out to study the heat transfer in unsteady two-dimensional boundary layer flow of a magnetohydrodynamics (MHD) second grade fluid over a porous oscillating stretching surface embedded in porous medium. The flow is induced due to infinite elastic sheet which is stretched periodically. With the help of dimensionless variables, the governing flow equations are reduced to a system of non-linear partial differential equations. This system has been solved numerically using the finite difference scheme, in which a coordinate transformation is used to transform the semi-infinite physical space to a bounded computational domain. The influence of the involved parameters on the flow, the temperature distribution, the skin-friction coefficient and the local Nusselt number is shown and discussed in detail. The study reveals that an oscillatory sheet embedded in a fluid-saturated porous medium generates oscillatory motion in the fluid. The amplitude and phase of oscillations depends on the rheology of the fluid as well as on the other parameters coming through imposed boundary conditions, inclusion of body force term and permeability of the porous medium. It is found that amplitude of flow velocity increases with increasing viscoelastic and mass suction/injection parameters. However, it decreases with increasing the strength of the applied magnetic field. Moreover, the temperature of fluid is a decreasing function of viscoelastic parameter, mass suction/injection parameter and Prandtl number. PMID:26657931
Khan, Sami Ullah; Ali, Nasir; Abbas, Zaheer
2015-01-01
An analysis is carried out to study the heat transfer in unsteady two-dimensional boundary layer flow of a magnetohydrodynamics (MHD) second grade fluid over a porous oscillating stretching surface embedded in porous medium. The flow is induced due to infinite elastic sheet which is stretched periodically. With the help of dimensionless variables, the governing flow equations are reduced to a system of non-linear partial differential equations. This system has been solved numerically using the finite difference scheme, in which a coordinate transformation is used to transform the semi-infinite physical space to a bounded computational domain. The influence of the involved parameters on the flow, the temperature distribution, the skin-friction coefficient and the local Nusselt number is shown and discussed in detail. The study reveals that an oscillatory sheet embedded in a fluid-saturated porous medium generates oscillatory motion in the fluid. The amplitude and phase of oscillations depends on the rheology of the fluid as well as on the other parameters coming through imposed boundary conditions, inclusion of body force term and permeability of the porous medium. It is found that amplitude of flow velocity increases with increasing viscoelastic and mass suction/injection parameters. However, it decreases with increasing the strength of the applied magnetic field. Moreover, the temperature of fluid is a decreasing function of viscoelastic parameter, mass suction/injection parameter and Prandtl number. PMID:26657931
Methyl alcohol used as penetrant inspection medium for porous materials
NASA Technical Reports Server (NTRS)
Hendron, J. A.
1971-01-01
Porous material thoroughly wetted with alcohol shows persistent wet line or area at locations of cracks or porosity. Inspection is qualitative and repeatable, but is used quantitatively with select samples to grade density variations in graphite blocks. Photography is employed to achieve permanent record of results.
Effective parameters for two-phase flow in a porous medium with periodic heterogeneities
NASA Astrophysics Data System (ADS)
Ataie-Ashtiani, B.; Hassanizadeh, S. M.; Oostrom, M.; Celia, M. A.; White, M. D.
2001-05-01
Computational simulations of two-phase flow in porous media are used to investigate the feasibility of replacing a porous medium containing heterogeneities with an equivalent homogeneous medium. Simulations are performed for the case of infiltration of a dense nonaqueous phase liquid (DNAPL) in a water-saturated, heterogeneous porous medium. For two specific porous media, with periodic and rather simple heterogeneity patterns, the existence of a representative elementary volume (REV) is studied. Upscaled intrinsic permeabilities and upscaled nonlinear constitutive relationships for two-phase flow systems are numerically calculated and the effects of heterogeneities are evaluated. Upscaled capillary pressure-saturation curves for drainage are found to be distinctly different from the lower-scale curves for individual regions of heterogeneity. Irreducible water saturation for the homogenized medium is found to be much larger than the corresponding lower-scale values. Numerical simulations for both heterogeneous and homogeneous representations of the considered porous media are carried out. Although the homogenized model simulates the spreading behavior of DNAPL reasonably well, it still fails to match completely the results form the heterogeneous simulations. This seems to be due, in part, to the nonlinearities inherent to multiphase flow systems. Although we have focussed on a periodic heterogeneous medium in this study, our methodology is applicable to other forms of heterogeneous media. In particular, the procedure for identification of a REV, and associated upscaled constitutive relations, can be used for randomly heterogeneous or layered media as well.
Lewallen, Eric A; Jones, Dakota L; Dudakovic, Amel; Thaler, Roman; Paradise, Christopher R; Kremers, Hilal M; Abdel, Matthew P; Kakar, Sanjeev; Dietz, Allan B; Cohen, Robert C; Lewallen, David G; van Wijnen, Andre J
2016-05-01
Integration of porous metal prosthetics, which restore form and function of irreversibly damaged joints, into remaining healthy bone is critical for implant success. We investigated the biological properties of adipose-tissue-derived mesenchymal stromal/stem cells (AMSCs) and addressed their potential to alter the in vitro microenvironment of implants. We employed human AMSCs as a practical source for musculoskeletal applications because these cells can be obtained in large quantities, are multipotent, and have trophic paracrine functions. AMSCs were cultured on surgical-grade porous titanium disks as a model for orthopedic implants. We monitored cell/substrate attachment, cell proliferation, multipotency, and differentiation phenotypes of AMSCs upon osteogenic induction. High-resolution scanning electron microscopy and histology revealed that AMSCs adhere to the porous metallic surface. Compared to standard tissue culture plastic, AMSCs grown in the porous titanium microenvironment showed differences in temporal expression for genes involved in cell cycle progression (CCNB2, HIST2H4), extracellular matrix production (COL1A1, COL3A1), mesenchymal lineage identity (ACTA2, CD248, CD44), osteoblastic transcription factors (DLX3, DLX5, ID3), and epigenetic regulators (EZH1, EZH2). We conclude that metal orthopedic implants can be effectively seeded with clinical-grade stem/stromal cells to create a pre-conditioned implant. PMID:26774799
Numerical modeling of fresh concrete flow through porous medium
NASA Astrophysics Data System (ADS)
Kolařík, F.; Patzák, B.; Zeman, J.
2016-06-01
The paper focuses on a numerical modeling of a non-Newtonian fluid flow in a porous domain. It presents combination of a homogenization approach to obtain permeability from the underlying micro-structure with coupling of a Stokes and Darcy flow through the interface on the macro level. As a numerical method we employed the Finite Element method. The results obtained from the homogenization approach are validated against fully resolved solution computed by direct numerical simulation.
A comparison of measured and modeled velocity fields for a laminar flow in a porous medium
NASA Astrophysics Data System (ADS)
Wood, B. D.; Apte, S. V.; Liburdy, J. A.; Ziazi, R. M.; He, X.; Finn, J. R.; Patil, V. A.
2015-11-01
Obtaining highly-resolved velocity data from experimental measurements in porous media is a significant challenge. The goal of this work is to compare the velocity fields measured in a randomly-packed porous medium obtained from particle image velocimetry (PIV) with corresponding fields predicted from direct numerical simulation (DNS). Experimentally, the porous medium was comprised of 15 mm diameter spherical beads made of optical glass placed in a glass flow cell to create the packed bed. A solution of ammonium thiocyanate was refractive-index matched to the glass creating a medium that could be illuminated with a laser sheet without distortion. The bead center locations were quantified using the imaging system so that the geometry of the porous medium was known very accurately. Two-dimensional PIV data were collected and processed to provide high-resolution velocity fields at a single plane within the porous medium. A Cartesian-grid-based fictitious domain approach was adopted for the direct numerical simulation of flow through the same geometry as the experimental measurements and without any adjustable parameters. The uncertainties associated with characterization of the pore geometry, PIV measurements, and DNS predictions were all systematically quantified. Although uncertainties in bead position measurements led to minor discrepancies in the comparison of the velocity fields, the axial and normal velocity deviations exhibited normalized root mean squared deviations (NRMSD) of only 11.32% and 4.74%, respectively. The high fidelity of both the experimental and numerical methods have significant implications for understanding and even for engineering the micro-macro relationship in porous materials. The ability to measure and model sub-pore-scale flow features also has relevance to the development of upscaled models for flow in porous media, where physically reasonable closure models must be developed at the sub-pore scale. These results provide valuable data
Instabilities of a free bilayer flowing on an inclined porous medium
NASA Astrophysics Data System (ADS)
Praveen Kumar, A. Ananth; Usha, R.; Banerjee, Tamal; Bandyopadhyay, Dipankar
2013-12-01
The instabilities of a free bilayer flowing on an inclined Darcy-Brinkman porous layer have been explored. The bilayer is composed of a pair of immiscible liquid films with a deformable liquid-liquid interface and a liquid-air free surface. An Orr-Sommerfeld analysis of the governing equations and boundary conditions uncovers that this configuration can be unstable by a pair of long-wave interfacial modes at the free surface and at the interface together with a couple of finite wave-number shear modes originating from the inertial influences at the liquid layers. In particular, one of the shear modes originates beyond a threshold flow rate owing to the slippage at the porous-liquid interface and is found to be the dominant one even when the porous medium is moderately thin, porous, and permeable. The strength of the porous media mediated mode (a) grows with increase in porosity, (b) grows and then remains invariant with increase in thickness, and (c) initially grows and then decays with increase in the permeability of the porous layer. Further, the presence of a lower layer with smaller viscosity and a thicker upper layer is found to facilitate the growth of this newly identified porous media mode. Importantly, beyond a threshold upper to lower thickness and viscosity ratios and the angle of inclination the porous media mode dominates over all the other interfacial or shear modes, highlighting its importance in the bilayer flows down an inclined porous medium. The study showcases the importance of a porous layer in destabilizing a free bilayer flow down an inclined plane, which can be of importance to improve mixing, emulsification, and heat and mass transfer characteristics in the microscale devices.
Formation of bubbly horizon in liquid-saturated porous medium by surface temperature oscillation.
Goldobin, Denis S; Krauzin, Pavel V
2015-12-01
We study nonisothermal diffusion transport of a weakly soluble substance in a liquid-saturated porous medium in contact with a reservoir of this substance. The surface temperature of the porous medium half-space oscillates in time, which results in a decaying solubility wave propagating deep into the porous medium. In this system, zones of saturated solution and nondissolved phase coexist with ones of undersaturated solution. The effect is first considered for the case of annual oscillation of the surface temperature of water-saturated ground in contact with the atmosphere. We reveal the phenomenon of formation of a near-surface bubbly horizon due to temperature oscillation. An analytical theory of the phenomenon is developed. Further, the treatment is extended to the case of higher frequency oscillations and the case of weakly soluble solids and liquids. PMID:26764828
Formation of bubbly horizon in liquid-saturated porous medium by surface temperature oscillation
NASA Astrophysics Data System (ADS)
Goldobin, Denis S.; Krauzin, Pavel V.
2015-12-01
We study nonisothermal diffusion transport of a weakly soluble substance in a liquid-saturated porous medium in contact with a reservoir of this substance. The surface temperature of the porous medium half-space oscillates in time, which results in a decaying solubility wave propagating deep into the porous medium. In this system, zones of saturated solution and nondissolved phase coexist with ones of undersaturated solution. The effect is first considered for the case of annual oscillation of the surface temperature of water-saturated ground in contact with the atmosphere. We reveal the phenomenon of formation of a near-surface bubbly horizon due to temperature oscillation. An analytical theory of the phenomenon is developed. Further, the treatment is extended to the case of higher frequency oscillations and the case of weakly soluble solids and liquids.
NASA Astrophysics Data System (ADS)
Wang, Hongbin; Wang, Ning; Hang, Tao; Li, Ming
2016-05-01
Three-dimensional porous micro-nano hierarchical structure Cu films were prepared by electrochemical deposition with the Hydrogen bubble dynamic template. The morphologies of the deposited films characterized by Scanning Electronic Microscopy (SEM) exhibit a porous micro-nano hierarchical structure, which consists of three levels in different size scales, namely the honeycomb-like microstructure, the dendritic substructure and the nano particles. Besides, the factors which influenced the microscopic morphology were studied, including the deposition time and the additive Ethylene diamine. By measuring the water contact angle, the porous copper films were found to be super-hydrophobic. The maximum of the contact angles could reach as high as 162.1°. An empirical correlation between morphologies and wetting properties was revealed for the first time. The pore diameter increased simultaneously with the deposition time while the contact angle decreased. The mechanism was illustrated by two classical models. Such super-hydrophobic three-dimensional hierarchical micro-nano structure is expected to have practical application in industry.
Critical diameter for the transmission of a detonation wave into a porous medium
Makris, A.; Oh, T.J.; Lee, J.H.S.; Knystautas, R.
1994-12-31
An experimental investigation has been undertaken to elucidate the existence of a critical diameter for the transmission of gaseous detonation into a porous medium. A Chapman-Jouguet (CJ) detonation is first established in a tube and allowed to transmit through an orifice plate into a porous medium comprised of inert spheres of equal diameter. It is found that detonation can successfully transmit past the orifice for diameters much smaller than the normal critical diameter (d{sub c}) of the mixture. An immediate transition from detonation to quasi-detonation normally takes place upon wave entry in the porous medium. Failure of detonation is observed to take place downstream of the orifice in the near-limit regime and is followed by deflagration to detonation transition (DDT) within the porous medium. Wave velocities in the porous medium are found to be identical to the corresponding values measured for direct transmission (without an orifice). For subcritical conditions, there is complete quenching of combustion in the pores. The critical composition (lean and rich) for mixtures with high activation energy is found to be practically the same as the propagation limits in the porous medium without an orifice. This indicates that the phenomenon is governed by the smallest physical dimension of the pore size, and thus a local failure mechanism exists. In mixtures highly diluted with argon, i.e., (C{sub 2}H{sub 2}-O{sub 2}) + 75% Ar, which have, a lower activation energy and for which the ``d{sub c} = 13{lambda}`` correlation (where {lambda} is the cell size) is known to break down, the critical composition appears to depend on the orifice diameter. The orifice now introduces a larger controlling length scale at the limits compared to the pore size, indicating that a global failure mechanism may prevail for such mixtures. Present findings are consistent with a local and global failure mechanism for normal detonation failure recently proposed by Lee.
2015-01-01
One-dimensional (1D) boron nitride nanotube (BNNT) and 2D hexagonal BN (h-BN) are attractive for demonstrating fundamental physics and promising applications in nano-/microscale devices. However, there is a high anisotropy associated with these BN allotropes as their excellent properties are either along the tube axis or in-plane directions, posing an obstacle in their widespread use in technological and industrial applications. Herein, we report a series of 3D BN prototypes, namely, pillared boron nitride (PBN), by fusing single-wall BNNT and monolayer h-BN aimed at filling this gap. We use density functional theory and molecular dynamics simulations to probe the diverse mechano-mutable properties of PBN prototypes. Our results demonstrate that the synergistic effect of the tubes, junctions, and sheets imparts cooperative deformation mechanisms, which overcome the intrinsic limitations of the PBN constituents and provide a number of superior characteristics including 3D balance of strength and toughness, emergence of negative Poisson’s ratio, and elimination of strain softening along the armchair orientation. These features, combined with the ultrahigh surface area and lightweight structure, render PBN as a 3D multifunctional template for applications in graphene-based nanoelectronics, optoelectronics, gas storage, and functional composites with fascinating in-plane and out-of-plane tailorable properties. PMID:25289114
NASA Astrophysics Data System (ADS)
Jadhav, Harsharaj S.; Thorat, Gaurav M.; Mun, Junyoung; Seo, Jeong Gil
2016-01-01
Transition metal oxides have attracted great attention as an anode material for next generation lithium ion batteries. Here we report the preparation of self-assembled hierarchical 3D-NiO microspheres with ultra-thin porous nanoflakes by simple and cost effective urea assisted chemical co-precipitation method followed by annealing at different temperature. It is noteworthy that the annealing temperature has an impact on the formation of different morphologies and resultantly on the electrochemical performance. This hierarchical 3D-NiO microspheres with ultra-thin porous nanoflakes shows enhanced electrochemical performance with a large reversible capacity, superior cyclic performance, high rate capability, and improved ionic conductivity as an anode material for lithium ion batteries. A high reversible capacity up to 795 mA h g-1 after 150 cycles at a rate of 0.5 C, and a capacity higher than 460.2 mA h g-1 at a rate as high as 10 C were obtained for optimized NiO sample. In particular, enhancement of the electrochemical performance was attributed to the high specific surface area, good electric contact among the particles, and easier lithium ion diffusion.
Kim, Hye-Na; Moon, Jun Hyuk
2012-11-01
This paper describes the use of Nb₂O₅-coated TiO₂ 3D ordered porous electrodes in dye-sensitized solar cells. We employed bilayer inverse opal structures as a backbone of 3D porous structures, and the number of Nb₂O₅ coatings was controlled, determining the concentration of Nb₂O₅ coating. XPS measurements confirmed the formation of Nb₂O₅. The uniformity of the Nb₂O₅ coating was characterized by elemental mapping using SEM and TEM measurements. Photovoltaic measurement on dye-sensitized solar cells (DSSCs) that incorporated Nb₂O₅/TiO₂ inverse opal electrodes yielded a maximum efficiency of 7.23% for a 3.3 wt % Nb₂O₅ coating on a TiO₂ IO structure. The Nb₂O₅ significantly increased the short-circuit current density (J(SC)). Electrochemical impedance spectroscopy was used to measure the J(SC), revealing an enhanced electron injection upon deposition of the Nb₂O₅ coating. PMID:23153118
Heat transfer in porous medium embedded with vertical plate: Non-equilibrium approach - Part A
NASA Astrophysics Data System (ADS)
Badruddin, Irfan Anjum; Quadir, G. A.
2016-06-01
Heat transfer in a porous medium embedded with vertical flat plate is investigated by using thermal non-equilibrium model. Darcy model is employed to simulate the flow inside porous medium. It is assumed that the heat transfer takes place by natural convection and radiation. The vertical plate is maintained at isothermal temperature. The governing partial differential equations are converted into non-dimensional form and solved numerically using finite element method. Results are presented in terms of isotherms and streamlines for various parameters such as heat transfer coefficient parameter, thermal conductivity ratio, and radiation parameter
In vitro and in vivo evaluations of 3D porous TCP-coated and non-coated alumina scaffolds.
Kim, Young-Hee; Anirban, Jyoti M; Song, Ho-Yeon; Seo, Hyung-Seok; Lee, Byong-Taek
2011-02-01
Both tricalcium phosphate (TCP) and alumina have been extensively studied and shown to have high biocompatibility. Tricalcium phosphate has improved biodegradability and a higher solubility than hydroxyapatite. In contrast, alumina (Al(2)O(3)) is almost completely inert at physiological conditions and has been used as a biomaterial due to its wear resistance, high surface finish, and excellent hardness. Thus, the combination of these two implants would result in greater biocompatibility and phenotype maintenance. A polyurethane (PU) foam replica method was employed in this study to coat TCP on an alumina scaffold. The TCP-coated alumina scaffold was then sintered to generate a porous surface morphology. The pore sizes obtained using this approach ranged between 100-600 µm, which is ideal for cellular proliferation. The cytotoxicity, cellular proliferation, differentiation, and ECM deposition on the coated scaffold resulted in longer-term viability of osteogenic markers compared to the non-coated scaffold. Moreover, the osteogenic properties of porous TCP-coated Al(2)O(3) scaffolds were reported in this study using rabbit models. The TCP/Al(2)O( 3) scaffold and control Al(2)O(3) scaffolds were implanted in the rabbit femur. The bone tissue response was analyzed with micro-computed tomography (micro CT) at 12 and 24 weeks after implantation. The porous scaffolds exhibited favorable hard and soft tissue responses at both time points. At 24 weeks, a three-fold increase in bone tissue ingrowth was observed in defects containing TCP-coated Al(2)O(3) scaffolds compared to control Al(2)O(3) scaffolds. PMID:20207781
NASA Astrophysics Data System (ADS)
Liao, M. W.; Chung, C. K.
2014-08-01
The porous anodic aluminum oxide (AAO) with high-aspect-ratio pore channels is widely used as a template for fabricating nanowires or other one-dimensional (1D) nanostructures. The high specific surface area of AAO can also be applied to the super capacitor and the supporting substrate for catalysis. The rough surface could be helpful to enhance specific surface area but it generally results in electrical field concentration even to ruin AAO. In this article, the aluminum (Al) films with the varied 2D-3D morphology on Si substrates were prepared using magnetron sputtering at a power of 50 W-185 W for 1 h at a working pressure of 2.5 × 10-1 Pa. Then, AAO was fabricated from the different Al films by means of one-step hybrid pulse anodizing (HPA) between the positive 40 V and the negative -2 V (1 s:1 s) for 3 min in 0.3 M oxalic acid at a room temperature. The microstructure and morphology of Al films were characterized by X-ray diffraction, scanning electron microscope and atomic force microscope, respectively. Some hillocks formed at the high target power could be attributed to the grain texture growth in the normal orientation of Al(1 1 1). The 3D porous AAO structure which is different from the conventional 2D planar one has been successfully demonstrated using HPA on the film with greatly rough hillock-surface formed at the highest power of 185 W. It offers a potential application of the new 3D AAO to high specific surface area devices.
Pan, David; Ombaba, Matthew; Zhou, Zhi-You; Liu, Yang; Chen, Shaowei; Lu, Jennifer
2012-12-21
For carbon nanotube-based electronics to achieve their full performance potential, it is imperative to minimize the contact resistance between macroscale metal contacts and the carbon nanotube (CNT) nanoelectrodes. We have developed a three-dimensional electrode platform that consists of carbon nanofibers (CNFs) that are directly grown on a metal contact, such as copper (Cu). Carbon nanofiber morphology can be tailored by adjusting the annealing time of a thin electrochemically deposited nickel catalyst layer on copper. We demonstrate that increasing the annealing time increases the amount of copper infused into the nickel catalyst layer. This reduces the carbon deposition rate, and consequently a more well-defined CNF 3D architecture can be fabricated. This direct growth of CNFs on a Cu substrate yields an excellent electron transfer pathway, with contact resistance between CNFs and Cu being comparable to that of a Cu-Cu interface. Furthermore, the excellent bonding strength between CNFs and Cu can be maintained over prolonged periods of ultrasonication. The porous 3D platform affixed with intertwined CNFs allows facile surface functionalization. Using a simple solution soaking procedure, the CNF surface has been successfully functionalized with iron(II) phthalocyanine (FePc). FePc functionalized CNFs exhibit excellent oxygen reduction capability, equivalent to platinum-carbon electrodes. This result demonstrates the technological promise of this new 3D electrode platform that can be exploited in other applications that include sensing, battery, and supercapacitors. PMID:23171171
NASA Astrophysics Data System (ADS)
Thakur, R. C.; Rana, G. C.
2013-06-01
In this paper, we investigate the effect of a vertical magnetic field on thermal instability of an Oldroydian visco-elastic rotating fluid in a porous medium. By applying the normal mode analysis method, the dispersion relation governing the effects of rotation, magnetic field and medium permeability is derived and solved analytically and numerically. For the case of stationary convection, the Oldroydian viscoelastic fluid behaves like an ordinary Newtonian fluid and it is observed that rotation has a stabilizing effect while the magnetic field and medium permeability have a stabilizing/destabilizing effect under certain conditions on thermal instability of the Oldroydian viscoelastic fluid in a porous medium. The oscillatory modes are introduced due to the presence of rotation, the magnetic field and gravity field. It is also observed that the `principle of exchange of stability' is invalid in the presence of rotation and the magnetic field.
NASA Astrophysics Data System (ADS)
MacKinnon, David K.; Cournoyer, Luc; Beraldin, J.-Angelo
2015-05-01
Within the context of the ASTM E57 working group WK12373, we compare the two methods that had been initially proposed for calculating the relative range error of medium-range (2 m to 150 m) optical non-contact 3D imaging systems: the first is based on a single plane (single-plane assembly) and the second on an assembly of three mutually non-orthogonal planes (three-plane assembly). Both methods are evaluated for their utility in generating a metric to quantify the relative range error of medium-range optical non-contact 3D imaging systems. We conclude that the three-plane assembly is comparable to the single-plane assembly with regard to quantification of relative range error while eliminating the requirement to isolate the edges of the target plate face.
NASA Astrophysics Data System (ADS)
Halder, Aditi; Patra, S.; Viswanath, B.; Munichandraiah, N.; Ravishankar, N.
2011-02-01
We present a simple template-free method for the synthesis of interconnected hierarchical porous palladium nanostructures by controlling the aggregation of nanoparticles in organic media. The interaction between the nanoparticles is tuned by varying the dielectric constant of the medium consistent with DLVO calculations. The reaction products range from discrete nanoparticles to compact porous clusters with large specific surface areas. The nanoclusters exhibit hierarchical porosity and are found to exhibit excellent activity towards the reduction of 4-nitrophenol into 4-aminophenol and hydrogen oxidation. The method opens up possibilities for synthesizing porous clusters of other functional inorganics in organic media.We present a simple template-free method for the synthesis of interconnected hierarchical porous palladium nanostructures by controlling the aggregation of nanoparticles in organic media. The interaction between the nanoparticles is tuned by varying the dielectric constant of the medium consistent with DLVO calculations. The reaction products range from discrete nanoparticles to compact porous clusters with large specific surface areas. The nanoclusters exhibit hierarchical porosity and are found to exhibit excellent activity towards the reduction of 4-nitrophenol into 4-aminophenol and hydrogen oxidation. The method opens up possibilities for synthesizing porous clusters of other functional inorganics in organic media. Electronic supplementary information (ESI) available: Additional figures of the Pd nanostructures. See DOI: 10.1039/c0nr00640h
NASA Astrophysics Data System (ADS)
Minale, Mario
2014-12-01
The momentum balance on the solid skeleton of a porous medium like porous rocks, foam metals, or porous brushes is, here, theoretically derived with the volume averaging method. It is derived for both homogeneous and non-homogeneous porous media and for the latters no length scales constraints are invoked. The momentum balance on the solid skeleton holds in the whole porous medium and contains volume averaged stresses and velocity. For heterogeneous porous media, it is coupled with the fluid momentum balance through a general averaged quantity, while in the homogeneous case, it is coupled with Darcy's equation, corrected with the first and the second Brinkman's term, through a geometrically rescaled Darcy's term. This latter equation coincides with Biot's equation for poro-elasticity, but it is here derived with a different formalism. This approach gives the opportunity to derive a new stress boundary condition at the interface between a porous medium and a homogeneous fluid.
Smoothed Particle Hydrodynamics Modeling of Gravity Currents on a Dry Porous Medium
NASA Astrophysics Data System (ADS)
Daly, E.; Grimaldi, S.; Bui, H.
2014-12-01
Gravity currents flowing over porous media occur in many environmental processes and industrial applications, such as irrigation, benthic boundary layers, and oil spills. The coupling of the flow over the porous surface and the infiltration of the fluid in the porous media is complex and difficult to model. Of particular interest is the prediction of the position of the runoff front and the depth of the infiltration front. We present here a model for the flow of a finite volume of a highly viscous Newtonian fluid over a dry, homogenous porous medium. The Navier-Stokes equations describing the runoff flow are coupled to the Volume Averaged Navier-Stokes equations for the infiltration flow. The numerical solution of these equations is challenging because of the presence of two free surfaces (runoff and infiltration waves), the lack of fixed boundary conditions at the runoff front, and the difficulties in defining appropriate conditions at the surface of the porous medium. The first two challenges were addressed by using Smoothed Particle Hydrodynamics, which is a Lagrangian, mesh-free particle method particularly suitable for modelling free surface flows. Two different approaches were used to model the flow conditions at the surface of the porous medium. The Two Domain Approach (TDA) assumes that runoff and infiltration flows occur in two separate homogenous domains; here, we assume the continuity of velocity and stresses at the interface of the two domains. The One Domain Approach (ODA) models runoff and infiltration flows as occurring through a medium whose hydraulic properties vary continuously in space. The transition from the hydraulic properties of the atmosphere and the porous medium occur in a layer near the surface of the porous medium. Expressions listed in literature were used to compute the thickness of this transition layer and the spatial variation of porosity and permeability within it. Our results showed that ODA led to slower velocities of the runoff
Westdickenberg, Michael; Wilkening, Jon
2008-12-10
We introduce variational particle schemes for the porous medium equation and the system of isentropic Euler equations in one space dimension. The methods are motivated by the interpretation of each of these partial differential equations as a 'steepest descent' on a suitable abstract manifold. We show that our methods capture very well the nonlinear features of the flows.
DETERMINISTIC AND STOCHASTIC ANALYSES OF DISPERSION IN AN UNBOUNDED STRATIFIED POROUS MEDIUM
The dispersion of a conservative solute released instantaneously from a finite or point source in an unbounded, nonrandom periodically stratified porous medium is examined theoretically by applying the moment method of R. Aris (1956) and P.G. Saffman (1962). The governing moment ...
Pyka, Grzegorz; Kerckhofs, Greet
2014-01-15
In material science microfocus X-ray computed tomography (micro-CT) is one of the most popular non-destructive techniques to visualise and quantify the internal structure of materials in 3D. Despite constant system improvements, state-of-the-art micro-CT images can still hold several artefacts typical for X-ray CT imaging that hinder further image-based processing, structural and quantitative analysis. For example spatial resolution is crucial for an appropriate characterisation as the voxel size essentially influences the partial volume effect. However, defining the adequate image resolution is not a trivial aspect and understanding the correlation between scan parameters like voxel size and the structural properties is crucial for comprehensive material characterisation using micro-CT. Therefore, the objective of this study was to evaluate the influence of the spatial image resolution on the micro-CT based morphological analysis of three-dimensional (3D) open porous structures with a high surface complexity. In particular the correlation between the local surface properties and the accuracy of the micro-CT-based macro-morphology of 3D open porous Ti6Al4V structures produced by selective laser melting (SLM) was targeted and revealed for rough surfaces a strong dependence of the resulting structure characteristics on the scan resolution. Reducing the surface complexity by chemical etching decreased the sensitivity of the overall morphological analysis to the spatial image resolution and increased the detection limit. This study showed that scan settings and image processing parameters need to be customized to the material properties, morphological parameters under investigation and the desired final characteristics (in relation to the intended functional use). Customization of the scan resolution can increase the reliability of the micro-CT based analysis and at the same time reduce its operating costs. - Highlights: • We examine influence of the image resolution
Saalfrank, Rolf W; Scheurer, Andreas
2012-01-01
Supramolecular coordination cages and polymers bear exceptional advantages over their organic counterparts. They are available in one-pot reactions and in high yields and display physical properties that are generally inaccessible with organic species. Moreover, their weak, reversible, noncovalent bonding interactions facilitate error checking and self-correction. This review emphasizes the achievements in supramolecular coordination container as well as polymer chemistry initiated by serendipity and their materialization based on rational design. The recognition of similarities in the synthesis of different supramolecular assemblies allows prediction of potential structures in related cases. The combination of detailed symmetry considerations with the basic rules of coordination chemistry has only recently allowed for the design of rational strategies for the construction of a variety of nanosized spherical containers, bowls, 1D-, 2D-, and 3D-coordination polymers with specified size and shape. PMID:22160460
NASA Astrophysics Data System (ADS)
Hou, Yang; Li, Jianyang; Gao, Xianfeng; Wen, Zhenhai; Yuan, Chris; Chen, Junhong
2016-04-01
Although lithium-sulfur (Li-S) batteries have attracted much attention due to their high theoretical specific energy and low cost, their practical applications have been severely hindered by poor cycle life, inadequate sulfur utilization, and the insulating nature of sulfur. Here, we report a rationally designed Li-S cathode with a dual-confined configuration formed by confining sulfur in 2D carbon nanosheets with an abundant porous structure followed by 3D graphene aerogel wrapping. The porous carbon nanosheets act as the sulfur host and suppress the diffusion of polysulfide, while the graphene conductive networks anchor the sulfur-adsorbed carbon nanosheets, providing pathways for rapid electron/ion transport and preventing polysulfide dissolution. As a result, the hybrid electrode exhibits superior electrochemical performance, including a large reversible capacity of 1328 mA h g-1 in the first cycle, excellent cycling stability (maintaining a reversible capacity of 647 mA h g-1 at 0.2 C after 300 cycles) with nearly 100% Coulombic efficiency, and a high rate capability of 512 mA h g-1 at 8 C for 30 cycles, which is among the best reported rate capabilities.Although lithium-sulfur (Li-S) batteries have attracted much attention due to their high theoretical specific energy and low cost, their practical applications have been severely hindered by poor cycle life, inadequate sulfur utilization, and the insulating nature of sulfur. Here, we report a rationally designed Li-S cathode with a dual-confined configuration formed by confining sulfur in 2D carbon nanosheets with an abundant porous structure followed by 3D graphene aerogel wrapping. The porous carbon nanosheets act as the sulfur host and suppress the diffusion of polysulfide, while the graphene conductive networks anchor the sulfur-adsorbed carbon nanosheets, providing pathways for rapid electron/ion transport and preventing polysulfide dissolution. As a result, the hybrid electrode exhibits superior
Fractal continuum model for tracer transport in a porous medium.
Herrera-Hernández, E C; Coronado, M; Hernández-Coronado, H
2013-12-01
A model based on the fractal continuum approach is proposed to describe tracer transport in fractal porous media. The original approach has been extended to treat tracer transport and to include systems with radial and uniform flow, which are cases of interest in geoscience. The models involve advection due to the fluid motion in the fractal continuum and dispersion whose mathematical expression is taken from percolation theory. The resulting advective-dispersive equations are numerically solved for continuous and for pulse tracer injection. The tracer profile and the tracer breakthrough curve are evaluated and analyzed in terms of the fractal parameters. It has been found in this work that anomalous transport frequently appears, and a condition on the fractal parameter values to predict when sub- or superdiffusion might be expected has been obtained. The fingerprints of fractality on the tracer breakthrough curve in the explored parameter window consist of an early tracer breakthrough and long tail curves for the spherical and uniform flow cases, and symmetric short tailed curves for the radial flow case. PMID:24483554
Numerical simulation of seismo-electromagnetic fields associated with a fault in a porous medium
NASA Astrophysics Data System (ADS)
Ren, Hengxin; Huang, Qinghua; Chen, Xiaofei
2016-04-01
In this work, we carry out numerical simulations of the seismo-electromagnetic fields associated with a fault in a porous medium by considering the electrokinetic effect. In addition to porous materials, the adopted layered models comprise solid materials in which the electrokinetic effect is inoperative. First, sensitivity study is performed for the evanescent and direct radiation electromagnetic (EM) waves generated by a double couple point source embedded in a porous half-space below a solid half-space. Results suggest that both the evanescent and direct radiation EM waves are sensitive to some medium properties, e.g., porosity, salinity, fluid viscosity, and conductivity of solid layer. Then, adopting an eight-layer half-space model, we simulate the seismic and EM wavefields generated by the rupture process of a finite fault. It is shown that the electrokinetic effect is able to generate observable co-rupture EM signals, but the observability depends on some factors such as the epicentral distance, properties of the medium where the fault is located, and local activity levels of EM noise. Time synchronization coseismic EM signals are recorded when the receiver is close to the ground water level but located in a solid medium. In addition to the post-seismic electric field, our results also show the post-seismic magnetic field which has not been identified in previous simulation studies on the electrokinetic effect. The generation of the post-seismic magnetic field probably requires a sufficiently strong medium heterogeneity or fluid-pressure gradient.
Numerical simulation of seismo-electromagnetic fields associated with a fault in a porous medium
NASA Astrophysics Data System (ADS)
Ren, Hengxin; Huang, Qinghua; Chen, Xiaofei
2016-07-01
In this work, we carry out numerical simulations of the seismo-electromagnetic fields associated with a fault in a porous medium by considering the electrokinetic effect. In addition to porous materials, the adopted layered models comprise solid materials in which the electrokinetic effect is inoperative. First, sensitivity study is performed for the evanescent and direct radiation electromagnetic (EM) waves generated by a double couple point source embedded in a porous half-space below a solid half-space. Results suggest that both the evanescent and direct radiation EM waves are sensitive to some medium properties, for example porosity, salinity, fluid viscosity, and conductivity of solid layer. Then, adopting an eight-layer half-space model, we simulate the seismic and EM wavefields generated by the rupture process of a finite fault. It is shown that the electrokinetic effect is able to generate observable corupture EM signals, but the observability depends on some factors such as the epicentral distance, properties of the medium where the fault is located, and local activity levels of EM noise. Time synchronization coseismic EM signals are recorded when the receiver is close to the ground water level but located in a solid medium. In addition to the post-seismic electric field, our results also show the post-seismic magnetic field which has not been identified in previous simulation studies on the electrokinetic effect. The generation of the post-seismic magnetic field probably requires a sufficiently strong medium heterogeneity or fluid-pressure gradient.
Modeling of porous scaffold deformation induced by medium perfusion.
Podichetty, Jagdeep T; Madihally, Sundararajan V
2014-05-01
In this study, we tested the possibility of calculating permeability of porous scaffolds utilized in soft tissue engineering using pore size and shape. We validated the results using experimental measured pressure drop and simulations with the inclusion of structural deformation. We prepared Polycaprolactone (PCL) and Chitosan-Gelatin (CG) scaffolds by salt leaching and freeze drying technique, respectively. Micrographs were assessed for pore characteristics and mechanical properties. Porosity for both scaffolds was nearly same but the permeability varied 10-fold. Elastic moduli were 600 and 9 kPa for PCL and CG scaffolds, respectively, while Poisson's ratio was 0.3 for PCL scaffolds and ∼1.0 for CG scaffolds. A flow-through bioreactor accommodating a 10 cm diameter and 0.2 cm thick scaffold was used to determine the pressure-drop at various flow rates. Additionally, computational fluid dynamic (CFD) simulations were performed by coupling fluid flow, described by Brinkman equation, with structural mechanics using a dynamic mesh. The experimentally obtained pressure drop matched the simulation results of PCL scaffolds. Simulations were extended to a broad range of permeabilities (10(-10) m(2) to 10(-14) m(2) ), elastic moduli (10-100,000 kPa) and Poisson's ratio (0.1-0.49). The results showed significant deviation in pressure drop due to scaffold deformation compared to rigid scaffold at permeabilities near healthy tissues. Also, considering the scaffold as a nonrigid structure altered the shear stress profile. In summary, scaffold permeability can be calculated using scaffold pore characteristics and deformation could be predicted using CFD simulation. These relationships could potentially be used in monitoring tissue regeneration noninvasively via pressure drop. PMID:24259467
Kumar, Rajesh; Oh, Jung-Hwan; Kim, Hyun-Jun; Jung, Jung-Hwan; Jung, Chan-Ho; Hong, Won G; Kim, Hae-Jin; Park, Jeong-Young; Oh, Il-Kwon
2015-07-28
Atomic-scale defects on carbon nanostructures have been considered as detrimental factors and critical problems to be eliminated in order to fully utilize their intrinsic material properties such as ultrahigh mechanical stiffness and electrical conductivity. However, defects that can be intentionally controlled through chemical and physical treatments are reasonably expected to bring benefits in various practical engineering applications such as desalination thin membranes, photochemical catalysts, and energy storage materials. Herein, we report a defect-engineered self-assembly procedure to produce a three-dimensionally nanohole-structured and palladium-embedded porous graphene hetero-nanostructure having ultrahigh hydrogen storage and CO oxidation multifunctionalities. Under multistep microwave reactions, agglomerated palladium nanoparticles having diameters of ∼10 nm produce physical nanoholes in the basal-plane structure of graphene sheets, while much smaller palladium nanoparticles are readily impregnated inside graphene layers and bonded on graphene surfaces. The present results show that the defect-engineered hetero-nanostructure has a ∼5.4 wt % hydrogen storage capacity under 7.5 MPa and CO oxidation catalytic activity at 190 °C. The defect-laden graphene can be highly functionalized for multipurpose applications such as molecule absorption, electrochemical energy storage, and catalytic activity, resulting in a pathway to nanoengineering based on underlying atomic scale and physical defects. PMID:26061778
Zhang, Long; Zhang, Fan; Yang, Xi; Long, Guankui; Wu, Yingpeng; Zhang, Tengfei; Leng, Kai; Huang, Yi; Ma, Yanfeng; Yu, Ao; Chen, Yongsheng
2013-01-01
Until now, few sp2 carbon materials simultaneously exhibit superior performance for specific surface area (SSA) and electrical conductivity at bulk state. Thus, it is extremely important to make such materials at bulk scale with those two outstanding properties combined together. Here, we present a simple and green but very efficient approach using two standard and simple industry steps to make such three-dimensional graphene-based porous materials at the bulk scale, with ultrahigh SSA (3523 m2/g) and excellent bulk conductivity. We conclude that these materials consist of mainly defected/wrinkled single layer graphene sheets in the dimensional size of a few nanometers, with at least some covalent bond between each other. The outstanding properties of these materials are demonstrated by their superior supercapacitor performance in ionic liquid with specific capacitance and energy density of 231 F/g and 98 Wh/kg, respectively, so far the best reported capacitance performance for all bulk carbon materials. PMID:23474952
Momentum transfer at the interface between a porous medium and a pure fluid
NASA Astrophysics Data System (ADS)
Hu, Howard; Zhang, Songpeng
2015-11-01
We examine the flow parallel to the interface between a porous medium and a liquid, focusing on the boundary conditions at the interface. When Darcy's law is used to describe the momentum transport in the porous layer, the classic Beavers-Joseph condition relates the shear rate and the slip velocity at the interface with a slip parameter that depends on the structure of the porous surface. When the Brinkman equation is used, the averaged velocity is continuous at the interface, however the fluid shear stress across the interface commonly experiences a jump. This shear stress jump can be expressed in terms of the slip velocity at the interface divided by a length characterized by the square root of the permeability, and a dimensionless stress jump coefficient. In this work, we study the momentum transfer from the clear fluid onto the solid structure at the interface, and proposed a stress partition parameter that characterizes the stress transfer from the clear fluid to the fluid (and solid) phase of the porous medium. Simple models are developed to formulate this stress partition parameter for porous media that are brush-like, long fibers, and random, respectively. Our model predictions are compared with numerical and experimental results in the literature.
NASA Astrophysics Data System (ADS)
Xie, D.; Tang, W. J.; Xia, X. H.; Wang, D. H.; Zhou, D.; Shi, F.; Wang, X. L.; Gu, C. D.; Tu, J. P.
2015-11-01
Scrupulous design and fabrication of advanced anode materials are of great importance for developing high-performance lithium ion batteries. Herein, we report a facile strategy for construction of free-standing and free-binder 3D porous carbon coated MoS2/nitrogen-doped graphene (C-MoS2/N-G) integrated electrode via a hydrothermal-induced self-assembly process. The preformed carbon coated MoS2 is strongly anchored on the porous nitrogen-doped graphene aerogel architecture. As an anode for lithium ion batteries, the C-MoS2/N-G electrode delivers a high first discharge capacity of 1600 mAh g-1 and maintains 900 mAh g-1 after 500 cycles at a current density of 200 mA g-1. Impressively, superior high-rate capability is achieved for the C-MoS2/N-G with a reversible capacity of 500 mAh g-1 at a high current density of 4000 mA g-1. Furthermore, the lithium storage mechanism of the obtained integrated electrode is investigated by ex-situ X-ray photoelectron spectroscopy and transmission electron microscopy in detail.
Hou, Yang; Li, Jianyang; Gao, Xianfeng; Wen, Zhenhai; Yuan, Chris; Chen, Junhong
2016-04-21
Although lithium-sulfur (Li-S) batteries have attracted much attention due to their high theoretical specific energy and low cost, their practical applications have been severely hindered by poor cycle life, inadequate sulfur utilization, and the insulating nature of sulfur. Here, we report a rationally designed Li-S cathode with a dual-confined configuration formed by confining sulfur in 2D carbon nanosheets with an abundant porous structure followed by 3D graphene aerogel wrapping. The porous carbon nanosheets act as the sulfur host and suppress the diffusion of polysulfide, while the graphene conductive networks anchor the sulfur-adsorbed carbon nanosheets, providing pathways for rapid electron/ion transport and preventing polysulfide dissolution. As a result, the hybrid electrode exhibits superior electrochemical performance, including a large reversible capacity of 1328 mA h g(-1) in the first cycle, excellent cycling stability (maintaining a reversible capacity of 647 mA h g(-1) at 0.2 C after 300 cycles) with nearly 100% Coulombic efficiency, and a high rate capability of 512 mA h g(-1) at 8 C for 30 cycles, which is among the best reported rate capabilities. PMID:27029963
NASA Astrophysics Data System (ADS)
Zhang, Luojiang; Hui, Kwun Nam; San Hui, Kwan; Lee, Haiwon
2016-06-01
The synthesis of layered double hydroxide (LDH) as electroactive material has been well reported; however, fabricating an LDH electrode with excellent electrochemical performance at high current density remains a challenge. In this paper, we report a 3D hierarchical porous flower-like NiAl-LDH grown on nickel foam (NF) through a liquid-phase deposition method as a high-performance binder-free electrode for energy storage. With large ion-accessible surface area as well as efficient electron and ion transport pathways, the prepared LDH-NF electrode achieves high specific capacity (1250 C g-1 at 2 A g-1 and 401 C g-1 at 50 A g-1) after 5000 cycles of activation at 20 A g-1 and high cycling stability (76.7% retention after another 5000 cycles at 50 A g-1), which is higher than those of most previously reported NiAl-LDH-based materials. Moreover, a hybrid supercapacitor with LDH-NF as the positive electrode and porous graphene nanosheet coated on NF (GNS-NF) as the negative electrode, delivers high energy density (30.2 Wh kg-1 at a power density of 800 W kg-1) and long cycle life, which outperforms the other devices reported in the literature. This study shows that the prepared LDH-NF electrode offers great potential in energy storage device applications.
NASA Astrophysics Data System (ADS)
Shishkovsky, I.; Volchkov, S.
2013-11-01
The objective of the investigation was to test the biocompatibility of 3D porous biopolymer matrices (tissue-cellular scaffolds), made of biocompatible and bioresorbable polymers (polycarbonate, polyetheretherketone /PEEK/, polycaprolactone), including the materials with biocompatible oxide ceramics additive (TiO2, Al2O3, ZrO2 and hydroxyapatite) of micron and nano sizes, for tissue-engineering purposes. The porous samples were prepared via a layer-by-layer SLS method. The surface microstructures and their roughness were analyzed by the optical microscopy equipped with the cell analysis software. The cellular morphology, proliferative activity and adhesion of the polymeric and ceramopolymeric matrices were the subjects for comparison. The study showed that all the tested materials posessed biocompatible properties. The experimentally estimated cell duplication speed per day turned out to be maximal for polycarbonate (0.279 duplications per day) and for PEEK + Al2O3 = 3:1 group (0.30 dupl/day) against 0.387 dupl/day for the reference sample and 0.270 dupl/day for the group of cells placed close to the pure titanium samples.
Hibi, Yoshihiko; Tomigashi, Akira; Hirose, Masafumi
2015-12-01
Numerical simulations that couple flow in a surface fluid with that in a porous medium are useful for examining problems of pollution that involve interactions among the atmosphere, surface water and groundwater, including, for example, saltwater intrusion along coasts. We previously developed a numerical simulation method for simulating a coupled atmospheric gas, surface water, and groundwater system (called the ASG method) that employs a saturation equation for flow in a porous medium; this equation allows both the void fraction of water in the surface system and water saturation in the porous medium to be solved simultaneously. It remained necessary, however, to evaluate how global pressure, including gas pressure, water pressure, and capillary pressure, should be specified at the boundary between the surface and the porous medium. Therefore, in this study, we derived a new equation for global pressure and integrated it into the ASG method. We then simulated water saturation in a porous medium and the void fraction of water in a surface system by the ASG method and reproduced fairly well the results of two column experiments. Next, we simulated water saturation in a porous medium (sand) with a bank, by using both the ASG method and a modified Picard (MP) method. We found only a slight difference in water saturation between the ASG and MP simulations. This result confirmed that the derived equation for global pressure was valid for a porous medium, and that the global pressure value could thus be used with the saturation equation for porous media. Finally, we used the ASG method to simulate a system coupling atmosphere, surface water, and a porous medium (110m wide and 50m high) with a trapezoidal bank. The ASG method was able to simulate the complex flow of fluids in this system and the interaction between the porous medium and the surface water or the atmosphere. PMID:26583741
NASA Astrophysics Data System (ADS)
Hibi, Yoshihiko; Tomigashi, Akira; Hirose, Masafumi
2015-12-01
Numerical simulations that couple flow in a surface fluid with that in a porous medium are useful for examining problems of pollution that involve interactions among the atmosphere, surface water and groundwater, including, for example, saltwater intrusion along coasts. We previously developed a numerical simulation method for simulating a coupled atmospheric gas, surface water, and groundwater system (called the ASG method) that employs a saturation equation for flow in a porous medium; this equation allows both the void fraction of water in the surface system and water saturation in the porous medium to be solved simultaneously. It remained necessary, however, to evaluate how global pressure, including gas pressure, water pressure, and capillary pressure, should be specified at the boundary between the surface and the porous medium. Therefore, in this study, we derived a new equation for global pressure and integrated it into the ASG method. We then simulated water saturation in a porous medium and the void fraction of water in a surface system by the ASG method and reproduced fairly well the results of two column experiments. Next, we simulated water saturation in a porous medium (sand) with a bank, by using both the ASG method and a modified Picard (MP) method. We found only a slight difference in water saturation between the ASG and MP simulations. This result confirmed that the derived equation for global pressure was valid for a porous medium, and that the global pressure value could thus be used with the saturation equation for porous media. Finally, we used the ASG method to simulate a system coupling atmosphere, surface water, and a porous medium (110 m wide and 50 m high) with a trapezoidal bank. The ASG method was able to simulate the complex flow of fluids in this system and the interaction between the porous medium and the surface water or the atmosphere.
Theoretical/experimental considerations about oil displacement by water in a fractured porous medium
Perez-Rosales, C.; Cruz-Hernandez, J.; Samaniego-V., F.
1994-12-31
Based upon observations made with a two-dimension porous cell, which allows direct visualization of fluid displacement processes, theoretical formulations were established for explaining oil displacement by water in a fractured porous medium. The theory rests on the idea that fluids are transported essentially through the fractures by a convective process, whereas water inflow to the matrix blocks is carried out by a dispersive process which depends on the difference between fracture and matrix water saturation. With these considerations, a derivation is presented of an expression for water saturation as a function of distance and time. Agreement between theory and experiment is reasonably good.
Magneto-polar fluid flow through a porous medium of variable permeability in slip flow regime
NASA Astrophysics Data System (ADS)
Gaur, P. K.; Jha, A. K.; Sharma, R.
2016-05-01
A theoretical study is carried out to obtain an analytical solution of free convective heat transfer for the flow of a polar fluid through a porous medium with variable permeability bounded by a semi-infinite vertical plate in a slip flow regime. A uniform magnetic field acts perpendicular to the porous surface. The free stream velocity follows an exponentially decreasing small perturbation law. Using the approximate method the expressions for the velocity, microrotation, and temperature are obtained. Further, the results of the skin friction coefficient, the couple stress coefficient and the rate of heat transfer at the wall are presented with various values of fluid properties and flow conditions.
Quantifying Light, Medium, and Heavy Crude Oil Distribution in Homogeneous Porous Media
NASA Astrophysics Data System (ADS)
Ghosh, J.; Tick, G. R.
2008-12-01
Crude oil recovery is highly dependent upon the physical heterogeneity of media and resulting distribution of the oil-phase within the pore spaces. Factors such as capillary force, the geometry of the pore spaces, and interfacial tension between the oil blobs and water-wet porous media will ultimately control the recovery process. Pore scale studies were conducted to study the distribution and the morphology of various fractions of crude oil in increasingly heterogeneous porous media. In addition, experiments were also carried out to characterize the temporal changes in distribution and morphology of the oil phase after a series of surfactant flooding events. Specifically, columns were packed with three different porous media with increasing heterogeneity and distributed with three different fractions (light, medium, and heavy) of crude oil. The columns were imaged using synchrotron X-ray microtomography before and after a series of surfactant floods to quantify the resulting crude oil distributions over time. Preliminary results show that the light crude oil was more heterogeneously distributed than the medium fraction crude oil within the same porous media type both before and throughout the series of surfactant floods. It was also observed that approximately 95% of the medium fraction crude oil blob-size distribution was smaller (<0.0008 cu mm) than that of the light crude oil, encompassing a significant number of blob singlets. The lighter crude oil fraction has the median blob diameter approximately 20 times greater than that of the medium crude oil fraction. These results further reveal that that oil extraction and recovery is highly dependent upon the oil fraction, the presence of small- sized blob singlets, and the resulting distributions present within porous media before and during surfactant flooding. This research will not only be helpful in understanding the factors controlling crude oil mobilization at the pore scale but also test the utility of
NASA Astrophysics Data System (ADS)
Koh, Joo Hwan; Koh, Jong Kwan; Seo, Jin Ah; Shin, Jong-Shik; Kim, Jong Hak
2011-09-01
Porous TiO2 nanotube arrays with three-dimensional (3D) interconnectivity were prepared using a sol-gel process assisted by poly(vinyl chloride-graft-4-vinyl pyridine), PVC-g-P4VP graft copolymer and a ZnO nanorod template. A 7 µm long ZnO nanorod array was grown from the fluorine-doped tin oxide (FTO) glass via a liquid phase deposition method. The TiO2 sol-gel solution templated by the PVC-g-P4VP graft copolymer produced a random 3D interconnection between the adjacent ZnO nanorods during spin coating. Upon etching of ZnO, TiO2 nanotubes consisting of 10-15 nm nanoparticles were generated, as confirmed by wide-angle x-ray scattering (WAXS), energy-filtering transmission electron microscopy (EF-TEM) and field-emission scanning electron microscopy (FE-SEM). The ordered and interconnected nanotube architecture showed an enhanced light scattering effect and increased penetration of polymer electrolytes in dye-sensitized solar cells (DSSC). The energy conversion efficiency reached 1.82% for liquid electrolyte, and 1.46% for low molecular weight (Mw) and 0.74% for high Mw polymer electrolytes.
Nellore, Bhanu Priya Viraka; Kanchanapally, Rajashekhar; Pedraza, Francisco; Sinha, Sudarson Sekhar; Pramanik, Avijit; Hamme, Ashton T; Arslan, Zikri; Sardar, Dhiraj; Ray, Paresh Chandra
2015-09-01
More than a billion people lack access to safe drinking water that is free from pathogenic bacteria and toxic metals. The World Health Organization estimates several million people, mostly children, die every year due to the lack of good quality water. Driven by this need, we report the development of PGLa antimicrobial peptide and glutathione conjugated carbon nanotube (CNT) bridged three-dimensional (3D) porous graphene oxide membrane, which can be used for highly efficient disinfection of Escherichia coli O157:H7 bacteria and removal of As(III), As(V), and Pb(II) from water. Reported results demonstrate that versatile membrane has the capability to capture and completely disinfect pathogenic pathogenic E. coli O157:H7 bacteria from water. Experimentally observed disinfection data indicate that the PGLa attached membrane can dramatically enhance the possibility of destroying pathogenic E. coli bacteria via synergistic mechanism. Reported results show that glutathione attached CNT-bridged 3D graphene oxide membrane can be used to remove As(III), As(V), and Pb(II) from water sample at 10 ppm level. Our data demonstrated that PGLa and glutathione attached membrane has the capability for high efficient removal of E. coli O157:H7 bacteria, As(III), As(V), and Pb(II) simultaneously from Mississippi River water. PMID:26273843
Yuan, Xiaoya; Zhou, Chou; Jin, Yanrong; Jing, Qiuye; Yang, Yaling; Shen, Xu; Tang, Qi; Mu, Yuanhua; Du, An-Ke
2016-04-15
3D porous framework composed of exfoliated ultrathin nanosheets is a hot topic in the field of energy storage and conversion. A facile method to prepare 3D mesoporous C3N4 with few-layered nanosheets interconnected in large quantity via H2SO4 intercalation and subsequent thermal treatment was described herein. The obtained thermally-exfoliated C3N4 (TE-C3N4) was thoroughly characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), UV-Vis diffuse reflectance spectroscopy (DRS) and Brunauer-Emmett-Teller (BET) measurements. The detailed analysis indicated that TE-C3N4 possessed enlarged inter-layer space, enhanced UV-light adsorption and high specific surface area with 3D interconnected structure composed of ultrathin 2D nanosheets. Compared to bulk C3N4, TE-C3N4 showed an enhanced photocatalytic activity for photodegradation of Rhodamine B under UV-light irradiation and exhibited no significant loss of photocatalytic activity after 11 recycled runs. The pseudo-first reaction rate constant for TE-C3N4 was about four times higher than that for pure bulk-C3N4. The better photocatalytic performance could be attributed to more active catalytic sites, prolonged photo-excited carrier lifetime and shorted pathway of the carriers to the reaction sites. PMID:26851454
Ma, Xue; Tian, Jing; Yang, Hong-Y.; Zhao, Kai; Li, Xia
2013-05-01
The reaction of RE(NO)₃·6H₂O and formamide yielded the coordination polymers, [RE(HCOO)₄]⁻[NH₂CHNH₂]⁺ (RE=Y 1, Eu 2, Gd 3, Tb 4, Dy 5, Er 6, and Yb 7). They possess 3D porous frameworks with the 1D rhombic channels occupied by [NH₂CHNH₂]⁺ cations. Complexes 2 and 4 display the characteristic down-conversion emissions corresponding to ⁵D₀→⁷F_{J} (J=1–4) transitions of Eu(III) ion and ⁵D₄→⁷F_{J} (J=6–3) transitions of Tb(III) ion, respectively. Longer lifetime values of 2.128±0.002 ms (⁵D₀) for 2 and 2.132±0.002 ms (⁵D₄) for 4 have been observed. The up-conversion spectra of the Y:Yb,Er and Gd:Yb,Er codoped complexes exhibit three emission bands around 410 (⁴H_{9/2}→⁴I_{15/2}, blue), 518–570 (⁴S_{3/2}, ²H_{11/2}→⁴I_{15/2}, green), and 655 nm (⁴F_{9/2}→⁴I_{15/2}, red). - Graphical Abstract: The complexes [RE(HCOO)₄]⁻[NH₂CHNH₂]⁺ possess 3D porous frameworks. Eu(III) and Tb(III) complexes show characteristic emission of Ln(III) ions. The up-conversion emission of the Y:Yb,Er and Gd:Yb,Er codoped complexes was observed. Highlights: •The reaction of RE(NO)₃·6H₂O and formamide produced complexes [RE(HCOO)₄]⁻[NH₂CHNH₂]⁺. • The complexes possess 3D frameworks with the 1D channels occupied by [NH₂CHNH₂]^{+} cations. • Eu(III)/Tb(III) complexes display the characteristic down-conversion emission of Ln(III) ions. • The Y:Yb,Er and Gd:Yb,Er doped complexes exhibit the up-conversion emission.
Chappard, Daniel; Terranova, Lisa; Mallet, Romain; Mercier, Philippe
2015-01-01
The 3D arrangement of porous granular biomaterials usable to fill bone defects has received little study. Granular biomaterials occupy 3D space when packed together in a manner that creates a porosity suitable for the invasion of vascular and bone cells. Granules of beta-tricalcium phosphate (β-TCP) were prepared with either 12.5 or 25 g of β-TCP powder in the same volume of slurry. When the granules were placed in a test tube, this produced 3D stacks with a high (HP) or low porosity (LP), respectively. Stacks of granules mimic the filling of a bone defect by a surgeon. The aim of this study was to compare the porosity of stacks of β-TCP granules with that of cores of trabecular bone. Biomechanical compression tests were done on the granules stacks. Bone cylinders were prepared from calf tibia plateau, constituted high-density (HD) blocks. Low-density (LD) blocks were harvested from aged cadaver tibias. Microcomputed tomography was used on the β-TCP granule stacks and the trabecular bone cores to determine porosity and specific surface. A vector-projection algorithm was used to image porosity employing a frontal plane image, which was constructed line by line from all images of a microCT stack. Stacks of HP granules had porosity (75.3 ± 0.4%) and fractal lacunarity (0.043 ± 0.007) intermediate between that of HD (respectively 69.1 ± 6.4%, p < 0.05 and 0.087 ± 0.045, p < 0.05) and LD bones (respectively 88.8 ± 1.57% and 0.037 ± 0.014), but exhibited a higher surface density (5.56 ± 0.11 mm2/mm3 vs. 2.06 ± 0.26 for LD, p < 0.05). LP granular arrangements created large pores coexisting with dense areas of material. Frontal plane analysis evidenced a more regular arrangement of β-TCP granules than bone trabecule. Stacks of HP granules represent a scaffold that resembles trabecular bone in its porous microarchitecture. PMID:26528240
NASA Astrophysics Data System (ADS)
Hidri, F.; Sghaier, N.; Eloukabi, H.; Prat, M.; Nasrallah, S. Ben
2013-12-01
We study the distribution of ions in a drying porous medium up to the formation of first crystals at the surface. The study is based on comparisons between numerical simulations and experiments with packings of glass beads. The experimental configuration, which is representative of many previous drying experiments, is characterized by the formation of an efflorescence fairy ring at the surface of the porous medium. The preferential formation of crystals at the periphery is explained by the combined effect of higher evaporation fluxes at the surface periphery, as in the classical coffee ring problem, and variations in the porosity near the wall bordering the packing. It is shown that both effects have a great impact on the time marking the occurrence of first crystals, which is referred to as the first crystallization time. The experiments indicate that the first crystallization time increases with a decreasing bead size for a given initial ion concentration. This is explained by the variation with bead size of the characteristic size of the near wall region where a preferential desaturation of the sample occurs as a result of the porosity increase near the wall. The study also reveals a significant salt supersaturation effect. This represents a noticeable fact in relation with salt weathering issues.
Quenching of a highly superheated porous medium by injection of water
NASA Astrophysics Data System (ADS)
Fichot, F.; Bachrata, A.; Repetto, G.; Fleurot, J.; Quintard, M.
2012-11-01
Understanding of two-phase flow through porous medium with intense phase change is of interest in many situations, including nuclear, chemical or geophysical applications. Intense boiling occurs when the liquid is injected into a highly superheated medium. Under such conditions, the heat flux extracted by the fluid from the porous medium is mainly governed by the nucleation of bubbles and by the evaporation of thin liquid films. Both configurations are possible, depending on local flow conditions and on the ratio of bubble size to pore size. The present study is motivated by the safety evaluation of light water nuclear reactors in case of a severe accident scenario, such as the one that happened in Fukushima Dai-ichi plant in March, 2011. If water sources are not available for a long period of time, the reactor core heats up due to the residual power and eventually becomes significantly damaged due to intense oxidation of metals and fragmentation of fuel rods resulting in the formation of a porous medium where the particles have a characteristic length-scale of 1 to 5 mm. The coolability of the porous medium will depend on the water flow rate which can enter the medium under the available driving head and on the geometrical features of the porous matrix (average pore size, porosity). Therefore, it is of high interest to evaluate the conditions for which the injection of water in such porous medium is likely to stop the progression of the accident. The present paper addresses the issue of modelling two-phase flow and heat transfers in a porous medium initially dry, where water is injected. The medium is initially at a temperature well above the saturation temperature of water. In a first part, a summary of existing knowledge is provided, showing the scarcity of models and experimental data. In a second part, new experimental results obtained in an IRSN facility are analysed. The experiment consists in a bed of steel particles that are heated up to 700
NASA Astrophysics Data System (ADS)
Monga, O.; Garnier, P.; Pot, V.; Coucheney, E.; Nunan, N.; Otten, W.; Chenu, C.
2014-04-01
This paper deals with the simulation of microbial degradation of organic matter in soil within the pore space at a microscopic scale. Pore space was analysed with micro-computed tomography and described using a sphere network coming from a geometrical modelling algorithm. The biological model was improved regarding previous work in order to include the transformation of dissolved organic compounds and diffusion processes. We tested our model using experimental results of a simple substrate decomposition experiment (fructose) within a simple medium (sand) in the presence of different bacterial strains. Separate incubations were carried out in microcosms using five different bacterial communities at two different water potentials of -10 and -100 cm of water. We calibrated the biological parameters by means of experimental data obtained at high water content, and we tested the model without changing any parameters at low water content. Same as for the experimental data, our simulation results showed that the decrease in water content caused a decrease of mineralization rate. The model was able to simulate the decrease of connectivity between substrate and microorganism due the decrease of water content.
Thermal consolidation of porous medium with a rheological kelvin-voigt skeleton
NASA Astrophysics Data System (ADS)
Bartlewska-Urban, Monika; Strzelecki, Tomasz
2012-10-01
This study presents calculations results of thermal consolidation process of the porous medium with the rheological Kelvin-Voigt skeleton, obtained numerically with the use of Flex.PDE software. The investigated calculation scheme consisted of the porous column filled with a liquid. The vertical load was applied to the top surface of the column through a porous plate allowing the free flow of liquid through this surface. Numerical solution is based on compression of the sample at appropriately defined boundary conditions. The aim of this study was to describe the influence of external load and temperature gradient on the deformation tests progress at different values of three parameters: λ,
Chen, J.D.; Wada, N.
1986-04-01
A new technique for visualizing the distribution and structure of oil, water, and quartz particles in a transparent, three-dimensional (3D), porous medium is presented. A laser light sheet illuminates a slice of a rectangular cell containing a mixture of oil, water, and quartz particles. All three phases have the same refractive index. The quartz particles do not fluoresce. From the different fluorescence colors of water and oil, the cross-sectional distribution of the three phases can be visualized. Photographs of different cross sections are presented that show both the solid grain structure and trapped oil blobs. This technique can be used to study two-phase flow in porous media.
New porous medium Poisson-Nernst-Planck equations for strongly oscillating electric potentials
NASA Astrophysics Data System (ADS)
Schmuck, M.
2013-02-01
We consider the Poisson-Nernst-Planck system which is well-accepted for describing dilute electrolytes as well as transport of charged species in homogeneous environments. Here, we study these equations in porous media whose electric permittivities show a strong contrast compared with the electric permittivity of the electrolyte phase. Our main result is the derivation of convenient low-dimensional equations, that is, of effective macroscopic porous media Poisson-Nernst-Planck equations, which reliably describe ionic transport. The contrast in the electric permittivities between liquid and solid phase and the heterogeneity of the porous medium induce strongly oscillating electric potentials (fields). In order to account for this specific physical scenario, we introduce a modified asymptotic multiple-scale expansion which takes advantage of the nonlinearly coupled structure of the ionic transport equations. This allows for a systematic upscaling resulting in a new effective porous medium formulation which shows a new transport term on the macroscale. Solvability of all arising equations is rigorously verified. The emergence of a new transport term indicates promising physical insights into the influence of the microscale material properties on the macroscale. Hence, systematic upscaling strategies provide a source and a prospective tool to capitalize intrinsic scale effects for scientific, engineering, and industrial applications.
Oostrom, Martinus; Freedman, Vicky L.; Wietsma, Thomas W.; Dane, Jacob H.; Truex, Michael J.
2012-11-01
Soil desiccation (drying), involving water evaporation induced by dry gas injection, is a potentially robust vadose zone remediation process to limit contaminant transport through the vadose zone. A series of four intermediate-scale flow cell experiments was conducted in homogeneous and simple layered heterogeneous porous medium systems to investigate the effects of heterogeneity on desiccation of unsaturated porous media. The permeability ratios of porous medium layers ranged from about five to almost two orders of magnitude. The insulated flow cell was equipped with twenty humidity and temperature sensors and a dual-energy gamma system was used to determine water saturations at various times. The multiphase code STOMP was used to simulate the desiccation process. Results show that injected dry gas flowed predominantly in the higher permeability layer and delayed water removal from the lower permeability material. For the configurations tested, water vapor diffusion from the lower to the higher permeability zone was considerable over the duration of the experiments, resulting in much larger relative humidity values of the outgoing air than based on permeability ratios alone. Acceptable numerical matches with the experimental data were obtained when an extension of the saturation-capillary pressure relation below the residual water saturation was used. The agreements between numerical and experimental results suggest that the correct physics are implemented in the simulator and that the thermal and hydraulic properties of the porous media, flow cell wall and insulation materials were properly represented.
Jeong, Seung-Woo; Corapcioglu, M Yavuz
2005-11-11
Governing mechanisms of dense non-aqueous phase liquid (DNAPL) removal during surfactant and surfactant-foam (SF) flooding were studied by porous-patterned glass model experiments. Physical forces, viscous forces and capillary forces, acting on trichloroethylene (TCE) blobs were quantified to understand DNAPL removal mechanisms during the floods, simultaneously visualizing the removal mechanisms. The viscous force of the remedial fluid was intimately related to TCE removal from the porous medium. The remedial fluid with a high viscous force displaced more TCE blobs. Displacement of residual TCE by the remedial fluid began as viscous pressure of flooding was closed to the capillary pressure of the porous medium. In the region of viscous pressure less than the capillary pressure, residual TCE was either retained or solubilized, not displaced, implying that TCE solubilization was the dominant TCE removal process. Glass porous model visualization validated a dominance of the capillary forces during a surfactant flush and a dominance of the viscous forces of the displacing fluid during a SF flood. PMID:16054295
Effect of supermolecular structure on oil filtration in a porous medium
Gal`tsev, V.E.; Ametov, I.M.; Dzyubenko, E.M.
1995-09-01
The formation of supermolecular structures during the adsorption of a tar-asphaltene fraction on the surface of grains of rock-forming materials in a porous medium was studied. The effect of these structures on the character of oil filtration in a porous medium is established. The filamentary structures formed have a diameter of 20 to 40 {angstrom}, corresponding to the size of asphaltene associates, and exhibit preferred orientation with a tilt in the direction opposite to the direction of flow. Some residual orientation of filaments is retained upon a change in the direction of flow. On the basis of ENDOR data, a model of a spatially anisotropic asphaltene micelle in oil was developed, which explains the observed character of coagulation and the formation of filamentary structures.
Temporal behavior of a solute cloud in a fractal heterogeneous porous medium at different scales
NASA Astrophysics Data System (ADS)
Ross, Katharina; Attinger, Sabine
2010-05-01
Water pollution is still a very real problem and the need for efficient models for flow and solute transport in heterogeneous porous or fractured media is evident. In our study we focus on solute transport in heterogeneous fractured media. In heterogeneous fractured media the shape of the pores and fractures in the subsurface might be modeled as a fractal network or a heterogeneous structure with infinite correlation length. To derive explicit results for larger scale or effective transport parameters in such structures is the aim of this work. To describe flow and transport we investigate the temporal behavior of transport coefficients of solute movement through a spatially heterogeneous medium. It is necessary to distinguish between two fundamentally different quantities characterizing the solute dispersion: The effective dispersion coefficient Deff(t) represents the physical (observable) dispersion in one given realization of the medium. It is conceptually different from the mathematically simpler ensemble dispersion coefficient Dens(t) which characterizes the (abstract) dispersion with respect to the set of all possible realizations of the medium. In the framework of a stochastic approach DENTZ ET AL. (2000 I[2] & II[3]) derive explicit expressions for the temporal behavior of the center-of-mass velocity and the dispersion of the concentration distribution, using a second order perturbation expansion. In their model the authors assume a finite correlation length of the heterogeneities and use a GAUSSIAN correlation function. In a first step, we model the fractured medium as a heterogeneous porous medium with infinite correlation length and neglect single fractures. ZHAN & WHEATCRAFT (1996[4]) analyze the macrodispersivity tensor in fractal porous media using a non-integer exponent which consists of the HURST coefficient and the fractal dimension D. To avoid this non-integer exponent for numerical reasons we extend the study of DENTZ ET AL. (2000 I[2] & II[3
Samiulhaq; Ahmad, Sohail; Vieru, Dumitru; Khan, Ilyas; Shafie, Sharidan
2014-01-01
Magnetic field influence on unsteady free convection flow of a second grade fluid near an infinite vertical flat plate with ramped wall temperature embedded in a porous medium is studied. It has been observed that magnitude of velocity as well as skin friction in case of ramped temperature is quite less than the isothermal temperature. Some special cases namely: (i) second grade fluid in the absence of magnetic field and porous medium and (ii) Newtonian fluid in the presence of magnetic field and porous medium, performing the same motion are obtained. Finally, the influence of various parameters is graphically shown. PMID:24785147
Samiulhaq; Ahmad, Sohail; Vieru, Dumitru; Khan, Ilyas; Shafie, Sharidan
2014-01-01
Magnetic field influence on unsteady free convection flow of a second grade fluid near an infinite vertical flat plate with ramped wall temperature embedded in a porous medium is studied. It has been observed that magnitude of velocity as well as skin friction in case of ramped temperature is quite less than the isothermal temperature. Some special cases namely: (i) second grade fluid in the absence of magnetic field and porous medium and (ii) Newtonian fluid in the presence of magnetic field and porous medium, performing the same motion are obtained. Finally, the influence of various parameters is graphically shown. PMID:24785147
Thermal conductivity in porous media: Percolation-based effective-medium approximation
NASA Astrophysics Data System (ADS)
Ghanbarian, Behzad; Daigle, Hugh
2016-01-01
Knowledge of porosity and saturation-dependent thermal conductivities is necessary to investigate heat and water transfer in natural porous media such as rocks and soils. Thermal conductivity in a porous medium is affected by the complicated relationship between the topology and geometry of the pore space and the solid matrix. However, as water content increases from completely dry to fully saturated, the effect of the liquid phase on thermal conductivity may increase substantially. Although various methods have been proposed to model the porosity and saturation dependence of thermal conductivity, most are empirical or quasiphysical. In this study, we present a theoretical upscaling framework from percolation theory and the effective-medium approximation, which is called percolation-based effective-medium approximation (P-EMA). The proposed model predicts the thermal conductivity in porous media from endmember properties (e.g., air, solid matrix, and saturating fluid thermal conductivities), a scaling exponent, and a percolation threshold. In order to evaluate our porosity and saturation-dependent models, we compare our theory with 193 porosity-dependent thermal conductivity measurements and 25 saturation-dependent thermal conductivity data sets and find excellent match. We also find values for the scaling exponent different than the universal value of 2, in insulator-conductor systems, and also different from 0.76, the exponent in conductor-superconductor mixtures, in three dimensions. These results indicate that the thermal conductivity under fully and partially saturated conditions conforms to nonuniversal behavior. This means the value of the scaling exponent changes from medium to medium and depends not only on structural and geometrical properties of the medium but also characteristics (e.g., wetting or nonwetting) of the saturating fluid.
Thermal instability of a fluid-saturated porous medium bounded by thin fluid layers
Pillatsis, G.; Taslim, M.E.; Narusawa, U. )
1987-08-01
A linear stability analysis is performed for a horizontal Darcy porous layer of depth 2d{sub m} sandwiched between two fluid layers of depth d (each) with the top and bottom boundaries being dynamically free and kept at fixed temperatures. The Beavers-Joseph condition is employed as one of the interfacial boundary conditions between the fluid and the porous layer. The critical Rayleigh number and the horizontal wave number for the onset of convective motion depend on the following four dimensional parameters: {cflx d} (= d{sub m}/d, the depth ratio), {delta} (= {radical}K/d{sub m} with K being the permeability of the porous medium) {alpha} (the proportionality constant in the Beavers-Joseph condition), and k/k{sub m} (the thermal conductivity ratio). In order to analyze the effect of these parameters on the stability condition, a set of numerical solutions is obtained in terms of a convergent series for the respective layers, for the case in which the thickness of the porous layer is much greater than that of the fluid layer. A comparison of this study with the previously obtained exact solution for the case of constant heat flux boundaries is made to illustrate quantitative effects of the interfacial and the top/bottom boundaries on the thermal instability of a combined system of porous and fluid layers.
A numerical inversion of a the Laplace transform solution to radial dispersion in a porous medium.
Moench, A.F.; Ogata, A.
1981-01-01
A special form of the numerical inversion of the Laplace transform described by Stehfest (1970) is applied to the transformed solution of dispersion in a radial flow system in a porous medium. The inversion is extremely simple to use because the weighting coefficients depend only on the number of terms used in the computation and not upon the transform solution as required by most numerical inversion techniques.-from Authors
Nonlinear hydro-magnetic convection at a permeable cylinder in a porous medium
NASA Astrophysics Data System (ADS)
van Gorder, Robert A.; Vajravelu, K.
2011-10-01
We consider the longitudinal steady nonlinear hydromagnetic convection flow over a permeable vertical cylinder in a porous medium. We assume that both the mainstream velocity at the outer edge of the boundary layer and the surface temperature of the cylinder vary linearly with axial distance from the leading edge, and extend the existing literature by including the nonlinear density temperature variation, magnetic field, and heat source/sink.
Specific features of gas absorption in a rotating permeable porous medium
NASA Astrophysics Data System (ADS)
Bazhaikin, A. N.
2014-01-01
The absorption of gaseous ammonia (NH3), sulfur dioxide (SO2), and carbon dioxide (CO2) by water in a rotating cellular-porous disk medium has been experimentally studied. Data on the degree of air cleaning from these impurities are obtained, which are indicative of an anomalously high solubility (exceeding equilibrium values) of indicated gases in water under conditions studied. The results show the possibility of creating effective absorbers for air cleaning from gaseous impurities.
Development of the 3-D Track Imager for Medium and High-Energy Gamma-Ray Telescopes
NASA Technical Reports Server (NTRS)
Hunter, Stanley D.
2006-01-01
The Advanced Compton Telescope (ACT) and Advanced Pair Telescope (APT) are envisioned as the next medium (0.3 ^ 50 MeV) and high-energy (30 MeV - greater than 100 GeV) gamma-ray missions. These missions will address many research focus areas of the Structure and Evolution of the Universe Roadmap. These areas include: element formation, matter, energy, & magnetic field interactions in galaxies, AGN & GRB emission, and behavior of matter in extreme environments of black holes & pulsars. Achieving these science goals requires a substantial increases in telescope sensitivity and angular resolution. This talk will discuss how these goals can be met with the three-dimensional track imager (3-DTI), a large volume, low density, time projection chamber with two-dimensional micro-well detector readout and report on our development of a 10 cm x 10 cm x 30 prototype instrument.
Coupled consolidation of a porous medium with a cylindrical or a spherical cavity
NASA Astrophysics Data System (ADS)
Zhou, Y.; Rajapakse, R. K. N. D.; Graham, J.
1998-06-01
This paper presents a theoretical approach to analyse coupled, linear thermoporoelastic fields in a saturated porous medium under radial and spherical symmetry. The governing equations account for compressibility and thermal expansion of constituents, heat sink due to thermal dilatation of water and thermal expansion of the medium, and thermodynamically coupled heat-water flow. It has been reported in the literature that thermodynamically coupled heat-water flows known as thermo-osmosis and thermal filtration have the potential to significantly alter the flow fields in clay-rich barriers in the near field of a underground waste containment scheme. This study presents a mathematical model and examines the effects of thermo-osmosis and thermal-filtration on coupled consolidation fields in a porous medium with a cavity. Analytical solutions of the governing equations are presented in the Laplace transform space. A numerical inversion scheme is used to obtain the time-domain solutions for a cylindrical cavity in a homogeneous or a non-homogeneous medium. A closed form time-domain solution is presented for a spherical cavity in a homogeneous medium. Selected numerical solutions for homogeneous and non-homogeneous media show a significant increase in pore pressure and displacements due to the presence of thermodynamically coupled flows and a negligible influence on temperature.
NASA Astrophysics Data System (ADS)
Taylor, Stewart W.; Milly, P. C. D.; Jaffé, Peter R.
1990-09-01
Growth of a biofilm in a porous medium reduces the total volume and the average size of the pores. The change in the pore size distributions is easily quantified when certain geometric assumptions are made. Existing models of permeability or of relative permeability can be manipulated to yield estimates of the resulting reduction in permeability as a function of biofilm thickness. The associated reductions in porosity and specific surface can be estimated as well. Based on a sphere model of the medium, the Kozeny-Carman permeability model predicts physically realistic results for this problem. Using a cut-and-random-rejoin-type model of the medium, the permeability model of Childs and Collis-George yields qualitatively reasonable results for this problem, as does a generalization of the relative permeability model of Mualem. Permeability models of Kozeny-Carman and of Millington and Quirk lead to unrealistic results for a cut-and-random-rejoin-type medium. The Childs and Collis-George and the Mualem models predict that the permeability reduction for a given volume of biomass is greatest when the porous medium has uniform pore sizes.
NASA Astrophysics Data System (ADS)
Li, Tingting; Li, Na; Liu, Jiawei; Cai, Kai; Foda, Mohamed F.; Lei, Xiaomin; Han, Heyou
2014-12-01
In this work, a high-capacity supercapacitor material based on functionalized three-dimensional (3D) porous graphene was fabricated by low temperature hydrothermal treatment of graphene oxide (GO) using both ionic liquid (IL) and SiO2 spheres as ``spacers''. In the synthesis, the introduction of dual ``spacers'' effectively enlarged the interspace between graphene sheets and suppressed their re-stacking. In addition, the IL also acted as a structure-directing agent playing a crucial role in inducing the formation of unique 3D architectures. Consequently, fast electron/ion transport channels were successfully constructed and numerous oxygen-containing groups on graphene sheets were effectively reserved, which had unique advantages in decreasing ion diffusion resistance and providing additional pseudocapacitance. As expected, the obtained material exhibited superior specific capacitance and rate capability compared to single ``spacer'' designed electrodes and simultaneously maintained excellent cycling stability. In particular, there was nearly no loss of its initial capacitance after 3000 cycles. In addition, we further assembled a symmetric two-electrode device using the material, which showed outstanding flexibility and low equivalent series resistance (ESR). More importantly, it was capable of yielding a maximum power density of about 13.3 kW kg-1 with an energy density of about 7.0 W h kg-1 at a voltage of 1.0 V in 1 M H2SO4 electrolyte. All these impressive results demonstrate that the material obtained by this approach is greatly promising for application in high-performance supercapacitors.In this work, a high-capacity supercapacitor material based on functionalized three-dimensional (3D) porous graphene was fabricated by low temperature hydrothermal treatment of graphene oxide (GO) using both ionic liquid (IL) and SiO2 spheres as ``spacers''. In the synthesis, the introduction of dual ``spacers'' effectively enlarged the interspace between graphene sheets
NASA Astrophysics Data System (ADS)
Geistlinger, Helmut; Ataei-Dadavi, Iman; Mohammadian, Sadjad; Vogel, Hans-Jörg
2015-11-01
We study the impact of pore structure and surface roughness on capillary trapping of nonwetting gas phase during imbibition with water for capillary numbers between 10-7 and 5 × 10-5, within glass beads, natural sands, glass beads monolayers, and 2-D micromodels. The materials exhibit different roughness of the pore-solid interface. We found that glass beads and natural sands, which exhibit nearly the same grain size distribution, pore size distribution, and connectivity, showed a significant difference of the trapped gas phase of about 15%. This difference can be explained by the microstructure of the pore-solid interface. Based on the visualization of the trapping dynamics within glass beads monolayers and 2-D micromodels, we could show that bypass trapping controls the trapping process in glass beads monolayers, while snap-off trapping controls the trapping process in 2-D micromodels. We conclude that these different trapping processes are the reason for the different trapping efficiency, when comparing glass beads packs with natural sand packs. Moreover, for small capillary numbers of 10-6, we found that the cluster size distribution of trapped gas clusters of all 2-D and 3-D porous media can be described by a universal power law behavior predicted from percolation theory. This cannot be expected a priori for 2-D porous media, because bicontinuity of the two bulk phases is violated. Obviously, bicontinuity holds for the thin-film water phase and the bulk gas phase. The snap-off trapping process leads to ordinary bond percolation in front of the advancing bulk water phase and is the reason for the observed universal power law behavior in 2-D micromodels with rough surfaces.
Li, Tingting; Li, Na; Liu, Jiawei; Cai, Kai; Foda, Mohamed F; Lei, Xiaomin; Han, Heyou
2015-01-14
In this work, a high-capacity supercapacitor material based on functionalized three-dimensional (3D) porous graphene was fabricated by low temperature hydrothermal treatment of graphene oxide (GO) using both ionic liquid (IL) and SiO2 spheres as "spacers". In the synthesis, the introduction of dual "spacers" effectively enlarged the interspace between graphene sheets and suppressed their re-stacking. In addition, the IL also acted as a structure-directing agent playing a crucial role in inducing the formation of unique 3D architectures. Consequently, fast electron/ion transport channels were successfully constructed and numerous oxygen-containing groups on graphene sheets were effectively reserved, which had unique advantages in decreasing ion diffusion resistance and providing additional pseudocapacitance. As expected, the obtained material exhibited superior specific capacitance and rate capability compared to single "spacer" designed electrodes and simultaneously maintained excellent cycling stability. In particular, there was nearly no loss of its initial capacitance after 3000 cycles. In addition, we further assembled a symmetric two-electrode device using the material, which showed outstanding flexibility and low equivalent series resistance (ESR). More importantly, it was capable of yielding a maximum power density of about 13.3 kW kg(-1) with an energy density of about 7.0 W h kg(-1) at a voltage of 1.0 V in 1 M H2SO4 electrolyte. All these impressive results demonstrate that the material obtained by this approach is greatly promising for application in high-performance supercapacitors. PMID:25427664
NASA Astrophysics Data System (ADS)
Strijker, Geertje; Beekman, Fred; Bertotti, Giovanni; Luthi, Stefan M.
2013-05-01
Stress distributions and deformation patterns in a medium with a pre-existing fracture set are analyzed as a function of the remote compressive stress orientation (σH) using finite element models with increasingly complex fracture configurations. Slip along the fractures causes deformation localization at the tips as wing cracks or shear zones. The deformation intensity is proportional to the amount of slip, attaining a peak value for α = 45° (α: angle between the fracture strike and σH) and slip is linearly proportional with fracture length. Wing cracks develop for high deformation intensities for 30° < α < 60°, whereas primary plastic shear zones develop for low deformation intensities. Additionally, two types of secondary shear zones develop for α < 30° and α > 60°, with constant angles of 135° and - 60° with σH, respectively. Mechanical interaction between fractures in a fracture zone, quantified as change in slip compared to an isolated fracture, decreases with increasing fracture separation. Fracture underlap elongates the fracture length and therefore increases the amount of slip, while fracture overlap exhibits the opposite effect. Fracture slip decreases with an increasing amount of directly adjacent fractures. Mechanical interaction becomes negligible for fracture configurations with spacing-to-length and spacing-to-overlap ratios exceeding 0.5 and that in this case fractures are decoupled. Independent of the pre-existing fracture configuration, the development of a secondary systematic fracture set driven by a remote stress rotation is dominated by σH; development of wing cracks or shear zones is restricted to the fracture tips. Blocks with tapered geometries are present in models with a variable fracture strike, where the maximum principal stress (σ1, applying the geological convention that compressive stresses are positive) trajectories consistently deviate from σH; the presence of two systematic σ1 trajectory orientations suggests
Magneto-rotatory compressible couple-stress fluid heated from below in porous medium
NASA Astrophysics Data System (ADS)
Mehta, Chander Bhan
2016-03-01
The study is aimed at analysing thermal convection in a compressible couple stress fluid in a porous medium in the presence of rotation and magnetic field. After linearizing the relevant equations, the perturbation equations are analysed in terms of normal modes. A dispersion relation governing the effects of rotation, magnetic field, couple stress parameter and medium permeability have been examined. For a stationary convection, the rotation postpones the onset of convection in a couple stress fluid heated from below in a porous medium in the presence of a magnetic field. Whereas, the magnetic field and couple stress postpones and hastens the onset of convection in the presence of rotation and the medium permeability hastens and postpones the onset of convection with conditions on Taylor number. Further the oscillatory modes are introduced due to the presence of rotation and the magnetic field which were non-existent in their absence, and hence the principle of exchange stands valid. The sufficient conditions for nonexistence of over stability are also obtained.
Effective parameters for two-phase flow in a porous medium with periodic heterogeneities
Ataie-Ashtiani, B; Hassanizadeh, S M.; Oostrom, Martinus ); Celia, M A.; White, Mark D. )
2000-12-01
The study of non-aqueous phase liquid (NAPL) transport in groundwater requires a correct description of multiphase flow in porous media. For the simulation of multiphase flow a number of material-dependent parameters have to be known. These include relationships between capillary pressure, relative permeability, and saturation. One of the major difficulties in characterizing a porous medium is the presence of small-scale heterogeneities, which have distinctly different multiphase flow properties than the main medium. Such heterogeneities can considerably affect the spreading behavior of non-aqueous liquids. They are often sources of localized pools of pollutants. For most practical purposes, the details of fluid distribution in such a medium are not of interest. It is also computationally not feasible to discretise a compositional multiphase model at such small scales. Even if a detailed numerical model is constructed, it is virtually impossible to obtain data for these heterogeneities. Thus, instead of modeling the subsurface at the scale of micro-heterogeneities, it is desirable to model it at a higher scale, as a homogenized medium, with effective properties.
NASA Astrophysics Data System (ADS)
Deng, Weina; Hu, Aiping; Chen, Xiaohua; Zhang, Shiying; Tang, Qunli; Liu, Zheng; Fan, Binbin; Xiao, Kuikui
2016-08-01
A rational 3D hierarchical porous nitrogen-doped aligned carbon nanotubes (HPNACNTs) with well-directed 1D conductive electron paths is designed as scaffold to load sulfur. The HPNACNTs have abundant micropores, mesopores and macropores with a relatively high specific surface area and a large total pore volume. The sulfur-HPNACNTs composite is synthesized for lithium-sulfur batteries by a melt-diffusion of sulfur powders into HPNACNTs scaffolds. Electrochemical tests reveal that the sulfur-HPNACNTs (68.8 wt% sulfur) composite exhibits a high initial discharge capacity of 1340 mAh g-1 at 0.1 C and retains as high as 979 mAh g-1 at 0.2 C after 200 cycles. More importantly, it shows high reversible capacity at high rates (817 mAh g-1 at 5 C). Its enhanced electrochemical performance can be attributed to the excellent electrical conductivity of aligned carbon nanotubes, the synergetic effect of its hierarchical porosity and the restraint of the shuttle effect due to the SxLi … N interactions via the N lone-pair electron.
Hou, Yang; Cui, Shumao; Wen, Zhenhai; Guo, Xiaoru; Feng, Xinliang; Chen, Junhong
2015-11-25
A novel 3D nanoarchitecture comprising in situ-formed N-doped CoNi alloy-encapsulated carbon nanotubes (CoNi-NCNTs) grown on N-doped porous carbon nanosheets (NPCNs) is designed and constructed for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). When evaluated as an electrocatalyst for ORR, the hybrid shows efficient catalytic activity, high selectivity, superior durability, and strong tolerance against methanol crossover compared with the commercial Pt/C catalyst. Such good oxygen reduction reaction performance is comparable to most of the previously reported results and the synergistic effect is found to boost the catalytic performance. Moreover, the constructed hybrid exhibits an excellent ORR activity with a current density of 10 mA cm(-2) at 1.59 V and an onset potential of 1.57 V, even beyond the state-of-the-art Ir/C catalyst in alkaline media. The enhancement in electrochemical performance can be attributed to the unique morphology and defect structures, high porosity, good conductive networks, and strongly interacting CoNi-NCNT and NPCN in the hybrid. These results suggest the possibility for the development of effective nanocarbon electrocatalysts to replace commercial noble metal catalysts for direct use in fuel cells and water splitting devices. PMID:26449376
Wang, Kui; Kievit, Forrest M; Florczyk, Stephen J; Stephen, Zachary R; Zhang, Miqin
2015-10-12
Cationic nanoparticles (NPs) for targeted gene delivery are conventionally evaluated using 2D in vitro cultures. However, this does not translate well to corresponding in vivo studies because of the marked difference in NP behavior in the presence of the tumor microenvironment. In this study, we investigated whether prostate cancer (PCa) cells cultured in three-dimensional (3D) chitosan-alginate (CA) porous scaffolds could model cationic NP-mediated gene targeted delivery to tumors in vitro. We assessed in vitro tumor cell proliferation, formation of tumor spheroids, and expression of marker genes that promote tumor malignancy in CA scaffolds. The efficacy of NP-targeted gene delivery was evaluated in PCa cells in 2D cultures, PCa tumor spheroids grown in CA scaffolds, and PCa tumors in a mouse TRAMP-C2 flank tumor model. PCa cells cultured in CA scaffolds grew into tumor spheroids and displayed characteristics of higher malignancy as compared to those in 2D cultures. Significantly, targeted gene delivery was only observed in cells cultured in CA scaffolds, whereas cells cultured on 2D plates showed no difference in gene delivery between targeted and nontarget control NPs. In vivo NP evaluation confirmed targeted gene delivery, indicating that only CA scaffolds correctly modeled NP-mediated targeted delivery in vivo. These findings suggest that CA scaffolds serve as a better in vitro platform than 2D cultures for evaluation of NP-mediated targeted gene delivery to PCa. PMID:26347946
Reaction fronts in a porous medium. Approximation techniques versus numerical solution
Escobedo, F.; Viljoen, H.J.
1995-03-01
The combustion of a gas fuel inside a porous media, as found in radiant porous burners (PRB), is one of the most promising novel combustion concepts. The flame sheet approximation (FS) and a novel polynomial approximation technique (PA) are compared in terms of their capability to describe reaction fronts of highly exothermic reactions in a porous medium. A one-phase model and a two-phase model of a system with adiabatic walls and a radiant output (to approximate the case of a porous radiant burner) are included in the analysis. By matching the reaction zone solution found by either the FS or PA method with the solutions of the nonreacting zones, the temperature, conversion, and position of the reaction zone were determined. Numerical solutions for catalytic and noncatalytic oxidation reactions were used to compare the predictions of both approaches. It was found that although both techniques yielded good approximations to the solutions, the PA technique proved to be more accurate, producing results with 3.5% of the numerical results. Both methods can find useful application in the analysis of this class of problems.
Non-Darcian effects on double-diffusive convection within a porous medium
Karimi-Fard, M.; Charrier-Mojtabi, M.C.; Vafai, K.
1997-06-01
Natural convection in porous media is widely encountered in nature and technological processes. Water movement in geothermal reservoirs, underground spreading of chemical wastes and other pollutants, thermal insulation, and solidification are just a few examples where the thermal natural convection or the combined thermosolutal natural convection in porous media are observed. This work describes a numerical study of double-diffusive natural convection in a square cavity filled with a porous medium. The flow is driven by a combined buoyancy effect due to both temperature and concentration variations. Several different flow models for porous media, such as Darcy flow, Forchheimer`s extension, Brinkman`s extension, and the generalized flow are considered. The coupled equations are solved using a finite volume approach with a projection algorithm for the momentum equation. Non-Darcian effects are analyzed through investigating the average heat and mass transfer rates. This study consists of a global analysis of each model and the comparison between them when the Darcy number varies. This work also focuses on the influence of the Lewis number on the inertial and boundary effects. It is shown that the inertial and boundary effects have a profound effect on the double-diffusive convection.
Transport of bare and capped zinc oxide nanoparticles is dependent on porous medium composition.
Kurlanda-Witek, H; Ngwenya, B T; Butler, I B
2014-07-01
Zinc oxide (ZnO) nanoparticles are one of the most frequently used nanoparticles in industry and hence are likely to be introduced to the groundwater environment. The mobility of these nanoparticles in different aquifer materials has not been assessed. While some studies have been published on the transport of ZnO nanoparticles in individual porous media, these studies do not generally account for varying porous medium composition both within and between aquifers. As a first step towards understanding the impact of this variability, this paper compares the transport of bare ZnO nanoparticles (bZnO-NPs) and capped ZnO nanoparticles, coated with tri-aminopropyltriethoxysilane (cZnO-NPs), in saturated columns packed with glass beads, fine grained sand and fine grained calcite, at near-neutral pH and groundwater salinity levels. With the exception of cZnO-NPs in sand columns, ZnO nanoparticles are highly immobile in all three types of studied porous media, with most retention taking place near the column inlet. Results are in general agreement with DLVO theory, and the deviation in experiments with cZnO-NPs flowing through columns packed with sand is linked to variability in zeta potential of the capped nanoparticles and sand grains. Therefore, differences in surface charge of nanoparticles and porous media are demonstrated to be key drivers in nanoparticle transport. PMID:24796515
Natural convection heat transfer of nanofluids along a vertical plate embedded in porous medium
2013-01-01
The unsteady natural convection heat transfer of nanofluid along a vertical plate embedded in porous medium is investigated. The Darcy-Forchheimer model is used to formulate the problem. Thermal conductivity and viscosity models based on a wide range of experimental data of nanofluids and incorporating the velocity-slip effect of the nanoparticle with respect to the base fluid, i.e., Brownian diffusion is used. The effective thermal conductivity of nanofluid in porous media is calculated using copper powder as porous media. The nonlinear governing equations are solved using an unconditionally stable implicit finite difference scheme. In this study, six different types of nanofluids have been compared with respect to the heat transfer enhancement, and the effects of particle concentration, particle size, temperature of the plate, and porosity of the medium on the heat transfer enhancement and skin friction coefficient have been studied in detail. It is found that heat transfer rate increases with the increase in particle concentration up to an optimal level, but on the further increase in particle concentration, the heat transfer rate decreases. For a particular value of particle concentration, small-sized particles enhance the heat transfer rates. On the other hand, skin friction coefficients always increase with the increase in particle concentration and decrease in nanoparticle size. PMID:23391481
Natural convection heat transfer of nanofluids along a vertical plate embedded in porous medium
NASA Astrophysics Data System (ADS)
Uddin, Ziya; Harmand, Souad
2013-02-01
The unsteady natural convection heat transfer of nanofluid along a vertical plate embedded in porous medium is investigated. The Darcy-Forchheimer model is used to formulate the problem. Thermal conductivity and viscosity models based on a wide range of experimental data of nanofluids and incorporating the velocity-slip effect of the nanoparticle with respect to the base fluid, i.e., Brownian diffusion is used. The effective thermal conductivity of nanofluid in porous media is calculated using copper powder as porous media. The nonlinear governing equations are solved using an unconditionally stable implicit finite difference scheme. In this study, six different types of nanofluids have been compared with respect to the heat transfer enhancement, and the effects of particle concentration, particle size, temperature of the plate, and porosity of the medium on the heat transfer enhancement and skin friction coefficient have been studied in detail. It is found that heat transfer rate increases with the increase in particle concentration up to an optimal level, but on the further increase in particle concentration, the heat transfer rate decreases. For a particular value of particle concentration, small-sized particles enhance the heat transfer rates. On the other hand, skin friction coefficients always increase with the increase in particle concentration and decrease in nanoparticle size.
NASA Astrophysics Data System (ADS)
Sadovskii, V. M.; Sadovskaya, O. V.
2015-10-01
Based on the generalized rheological method, the mathematical model describing small deformations of a single-phase porous medium without regard to the effects of a fluid or gas in pores is constructed. The change in resistance of a material to the external mechanical impacts at the moment of pore collapse is taken into account by means of the von Mises-Schleicher strength condition. In order to consider irreversible deformations, alongside with the classical yield conditions by von Mises and Tresca- Saint-Venant, the special condition modeling the plastic loss of stability of a porous skeleton is used. The random nature of the pore size distribution is taken into account. It is shown that the proposed mathematical model satisfies the principles of thermodynamics of irreversible processes. Phenomenological parameters of the model are determined on the basis of the approximate calculation of the problem on quasi-static loading of a cubic periodicity cell with spherical voids. In the framework of the obtained model, the process of propagation of plane longitudinal waves of the compression in a homogenous porous medium, accompanied by the plastic deformation of a skeleton and the collapse of pores, is analyzed.
Sadovskii, V. M. Sadovskaya, O. V.
2015-10-28
Based on the generalized rheological method, the mathematical model describing small deformations of a single-phase porous medium without regard to the effects of a fluid or gas in pores is constructed. The change in resistance of a material to the external mechanical impacts at the moment of pore collapse is taken into account by means of the von Mises–Schleicher strength condition. In order to consider irreversible deformations, alongside with the classical yield conditions by von Mises and Tresca– Saint-Venant, the special condition modeling the plastic loss of stability of a porous skeleton is used. The random nature of the pore size distribution is taken into account. It is shown that the proposed mathematical model satisfies the principles of thermodynamics of irreversible processes. Phenomenological parameters of the model are determined on the basis of the approximate calculation of the problem on quasi-static loading of a cubic periodicity cell with spherical voids. In the framework of the obtained model, the process of propagation of plane longitudinal waves of the compression in a homogenous porous medium, accompanied by the plastic deformation of a skeleton and the collapse of pores, is analyzed.
Xiu, Peng; Jia, Zhaojun; Lv, Jia; Yin, Chuan; Cheng, Yan; Zhang, Ke; Song, Chunli; Leng, Huijie; Zheng, Yufeng; Cai, Hong; Liu, Zhongjun
2016-07-20
3D printed porous titanium (Ti) holds enormous potential for load-bearing orthopedic applications. Although the 3D printing technique has good control over the macro-sturctures of porous Ti, the surface properties that affect tissue response are beyond its control, adding the need for tailored surface treatment to improve its osseointegration capacity. Here, the one step microarc oxidation (MAO) process was applied to a 3D printed porous Ti6Al4V (Ti64) scaffold to endow the scaffold with a homogeneous layer of microporous TiO2 and significant amounts of amorphous calcium-phosphate. Following the treatment, the porous Ti64 scaffolds exhibited a drastically improved apatite forming ability, cyto-compatibility, and alkaline phosphatase activity. In vivo test in a rabbit model showed that the bone in-growth at the untreated scaffold was in a pattern of distance osteogenesis by which bone formed only at the periphery of the scaffold. In contrast, the bone in-growth at the MAO-treated scaffold exhibited a pattern of contact osteogenesis by which bone formed in situ on the entire surface of the scaffold. This pattern of bone in-growth significantly increased bone formation both in and around the scaffold possibly through enhancement of bone formation and disruption of bone remodeling. Moreover, the implant surface of the MAO-treated scaffold interlocked with the bone tissues through the fabricated microporous topographies to generate a stronger bone/implant interface. The increased osteoinetegration strength was further proven by a push out test. MAO exhibits a high efficiency in the enhancement of osteointegration of porous Ti64 via optimizing the patterns of bone in-growth and bone/implant interlocking. Therefore, post-treatment of 3D printed porous Ti64 with MAO technology might open up several possibilities for the development of bioactive customized implants in orthopedic applications. PMID:27341499
NASA Astrophysics Data System (ADS)
King, Brian H.; Sailor, Michael J.
2011-01-01
Porous silicon optical rugate filters are electrochemically fabricated to display reflectance peaks in the medium-wavelength infrared (MWIR) region from 4 to 8 μm. Etching conditions are adjusted to create filters with single and multiple infrared reflectance peaks overlapping specific infrared chemical absorbance bands. Additional infrared reflectance peaks are designed into the structures to provide internal optical reference channels. Samples containing optical reflectance features matching the absorbance band of CO2 at 2350 cm-1 are used to demonstrate gas sensing with optical filters, and a structure with a photonic stop band tuned to match the infrared absorbance band of the P=O functional group, found in G-series chemical warfare agents, is fabricated. With adequate electrolyte replenishment, the calibrated etch conditions generated reproducible spectral band features even for relatively long etch durations. This work represents the first example of a porous Si spectral filter prepared to match specific spectral features of molecules in the MWIR (``fingerprint'') region.
MHD flow of Burger's fluid over an off-centered rotating disk in a porous medium
NASA Astrophysics Data System (ADS)
Khan, Najeeb Alam; Khan, Sidra; Ullah, Saif
2015-08-01
In this study, off-centered stagnation flow of three dimensional Burger's fluid over an infinite rotating disk in a porous medium with a uniform magnetic field, which is applying normal to the disk, is investigated. A uniform suction/injection is applied through the surface of the porous disk. The structure has been modeled in the form of ordinary differential equations, which are reduced from partial differential equations by using the similarity transformation. Analytical solution is obtained by non-perturbation technique of homotopy analysis method (HAM). The influence of non-dimensional parameters on velocity profile is presented in graphical form and the numerical comparison is made with the viscous fluid as a special case.
Li, Ching-Wen; Pan, Wei-Ting; Ju, Jyh-Cherng; Wang, Gou-Jen
2016-01-01
In this study, we have developed a microporous poly(lactic-co-glycolic acid) (PLGA) scaffold that combines a continuous release property and a three-dimensional (3D) scaffolding technique for the precise and efficient formation of endothelial cell lineage from embryonic stem cells (ESCs). Eight PLGA scaffolds (14.29%, 16.67%, 20% and 25% concentrations of PLGA solutions) mixed with two crystal sizes of sodium chloride (NaCl) were fabricated by leaching. Then, vascular endothelial cell conditioned medium (ECCM) mixed with gelatin was embedded into the scaffold for culturing of mouse embryonic stem cells (mESCs). The 14.29% PLGA scaffolds fabricated using non-ground NaCl particles (NG-PLGA) and the 25% PLGA containing scaffolds fabricated using ground NaCl particles (G-PLGA) possessed minimum and maximum moisture content and bovine serum albumin (BSA) content properties, respectively. These two groups of scaffolds were used for future experiments in this study. Cell culture results demonstrated that the proposed porous scaffolds without growth factors were sufficient to induce mouse ESCs to differentiate into endothelial-like cells in the early culture stages, and combined with embedded ECCM could provide a long-term inducing system for ESC differentiation. PMID:27068738
Desmet, Gert; Deridder, Sander
2011-01-01
Using the permeability analogue of the diffusion and partitioning processes occurring in a chromatographic column, the different Effective Medium Theory (EMT) models that exist in literature for the electrical and thermal conductivity have been transformed into expressions that accurately predict the B-term band broadening in chromatographic columns. The expressions are written in such a form that they hold for both fully porous and porous-shell particles, and both spherical and cylindrical particles are considered. Mutually comparing the established EMT-expressions, it has been found that the most basic variant, i.e., the Maxwell-based expression, is already accurate to within 5% for the typical conditions encountered in liquid phase chromatography, independently of the exact microscopic morphology of the packing. For most typical values of the intra-particle diffusion rate and the species retention factors, it is even accurate to within 1%. If even higher accuracies are needed, more elaborate EMT-expressions are available. The modelling accuracy of all explicit EMT-expressions is much better than the residence time weighted (RTW) B-term expressions that have been used up to now in the field of chromatography, where the error is typically on the order of 10% and more. The EMT-models have also been used to establish expressions for the obstruction and tortuosity factor in packings of non-porous particles. The EMT has also been applied to the meso-porous zone only, yielding an expression for the intra-particle diffusion coefficient that can be used without having to specify any obstruction factor. It has also been shown that the EMT also provides a very simple but exact expression to represent the way in which the solid core obstructs the effective intra-particle diffusion in the case of porous-shell particles. This obstruction factor is given by γ(part)=2/(2+ρ³) for spherical particles and γ(part)=1/(1+ρ³) for cylinders. Back-transforming the obtained
NASA Astrophysics Data System (ADS)
Amiaz, Yanai; Ronen, Zeev; Adar, Eilon; Weisbrod, Noam
2015-04-01
A chalk fractured aquitard beneath an industrial site is subjected to intense contamination due to percolation of contaminants from the different facilities operating at the site. In order to reduce further contamination, draining trenches were excavated and filled with coarse gravel (3-4 cm in diameter) forming a porous medium, to which the contaminated groundwater discharges from the fractures surrounding the trenches. This research is aimed at establishing a biodegrading process of high efficiency and performance within the draining trenches. The research includes both field and laboratory experiments. An experimental setup of five columns (50 cm length and 4.5 cm in diameter) was constructed under highly controlled conditions. Over the course of the experiments, the columns were filled with different particle sizes and placed in a temperature controlled chamber. Filtered groundwater (0.2 µm) from the site groundwater, enriched by a model contaminant carbofuran (CRF), was injected to the columns; as two of the columns were inoculated by CRF degrading microorganisms native in the site's groundwater, two columns were inoculated by CRF degrading bacteria from the external environment, and one column was used as a control. During the experiment, measurements were taken from different locations along each column. These include: (a) CRF concentration and (b) hydraulic pressure and solution viscosity (in order to obtain the changes in permeability). A tracer test using uranine was carried out in parallel, in order to obtain the changes in hydraulic parameters. Correlating CRF concentration variations to changes of hydraulic parameters enable the deduction due to the effect that biological activity (under different temperature regimes) has on the hydraulic properties of the porous medium and its effect on the process of contaminant groundwater bodies' remediation. Preliminary results suggest that although biodegradation occurs, microbial activity has minor effect on
Iontophoresis From a Micropipette into a Porous Medium Depends on the ζ-Potential of the Medium
Guy, Yifat; Faraji, Amir H.; Gavigan, Colleen A.; Strein, Timothy G.; Weber, Stephen G.
2012-01-01
Iontophoresis uses electricity to deliver solutes into living tissue. Often, iontophoretic ejections from micropipettes into brain tissue are confined to millisecond pulses for highly localized delivery, but longer pulses are common. As hippocampal tissue has a ζ-potential of approximately –22 mV, we hypothesized that, in the presence of the electric field resulting from the iontophoretic current, electroosmotic flow in the tissue would carry solutes considerably farther than diffusion alone. A steady state solution to this mass transport problem predicts a spherically symmetrical solute concentration profile with the characteristic distance of the profile depending on the ζ-potential of the medium, the current density at the tip, the tip size and the solute electrophoretic mobility and diffusion coefficient. Of course, the ζ-potential of the tissue is defined by immobilized components of the extracellular matrix as well as cell-surface functional groups. As such, it cannot be changed at will. Therefore, the effect of the ζ-potential of the porous medium on ejections is examined using poly(acrylamide-co-acrylic acid) hydrogels with various magnitudes of ζ-potential, including that similar to hippocampal brain tissue. We demonstrated that nearly neutral fluorescent dextran (3 and 70 kD) solute penetration distance in the hydrogels and OHSCs depends on the magnitude of the applied current, solute properties, and, in the case of the hydrogels, the ζ-potential of the matrix. Steady state solute ejection profiles can be predicted semi-quantitatively. PMID:22264102
Liekens, Anuschka; Denayer, Joeri; Desmet, Gert
2011-07-15
The difference in B-term diffusion between fully porous and porous-shell particles is investigated using the physically sound diffusion equations originating from the Effective Medium Theory (EMT). Experimental data of the B-term diffusion obtained via peak parking measurements on six different commercial particle types have been analyzed (3 porous and 3 non porous). All particles were investigated using the same experimental design and test analytes, over a very broad range of retention factor values. First, the B-term reducing effect of the solid core (inducing an additional obstruction compared to fully porous particles) has been quantified using the Hashin-Shtrikman expression, showing that the presence of a solid core can account for a reduction of about 11% when the core diameter makes up 63% of the total particle diameter (Halo and Poroshell-particles) and a reduction of 16% when the core diameter makes up 73% (Kinetex). Remaining differences can be attributed to differences in the microscopic structure of the meso-porous material (meso-pore diameter, internal porosity or relative void volume). The much lower B-term diffusion of Halo and Kinetex particles compared to the fully porous Acquity particles (some 20-40% difference, of which about 10-15% can be attributed to the presence of the solid core) can hence largely be attributed to the much smaller internal porosity and the smaller pore size of the meso-porous material making up the shell of these particles. PMID:21628063
The effect of thermal losses on traveling waves for in-situ combustion in porous medium
NASA Astrophysics Data System (ADS)
Chapiro, G.; Marchesin, D.
2015-09-01
We study a model for the injection of air into an underground porous medium that contains a solid fuel. In our previous works the model was simplified and all wave sequences for the Riemann problem solution were obtained without taking into account thermal losses to the surrounding rock. In this work the first step is made to understand the effect of heat losses, which are important especially in laboratory experiments. In order to simplify the proof of the existence and uniqueness of the traveling wave solution, we disregard diffusion effects and the dependence of gas density on temperature.
Three-dimensional radiative flow with variable thermal conductivity and porous medium
NASA Astrophysics Data System (ADS)
Hayat, T.; Shehzad, S. A.; Alsaadi, F. E.; Alsaedi, A.
2013-06-01
This investigation deals with the three-dimensional boundary layer flow in a porous medium. The flow is induced by an exponentially stretching surface. Analysis is presented in the presence of heat transfer. Two cases, namely prescribed surface temperature (PST) and prescribed surface heat flux (PHF), are considered. Effects of thermal radiation are also present. The nonlinear partial differential equations are reduced into the ordinary differential equations. Series solutions are developed for the velocities and temperatures. Convergence of series solutions is checked via graphs and numerical values. Results are displayed and discussed for both PST and PHF cases.
Long, Thomas J.; Sprenger, Cynthia C.; Plymate, Stephen R.; Ratner, Buddy D.
2014-01-01
Synthetic biomaterial scaffolds show promise for in vitro and in vivo 3D cancer models. Tumors engineered in biomaterial scaffolds have shown evidence of being more physiologically relevant than some traditional preclinical model systems, and synthetic biomaterials provide the added benefit of defined and consistent microenvironmental control. Here, we examine sphere-templated poly(2-hydroxyethyl methacrylate) (pHEMA) scaffolds as the basis for engineering xenografts from multiple human prostate cancer cell lines. pHEMA scaffolds seeded and pre-cultured with tumorigenic M12 cells prior to implantation generated tumors in athymic nude mice, demonstrating the ability of the scaffolds to be used as a synthetic vehicle for xenograft generation. pHEMA scaffolds seeded with LNCaP C4-2 cells, which require Matrigel or stromal cell support for tumor formation, were poorly tumorigenic up to twelve weeks after implantation even when Matrigel was infused into the scaffold, demonstrating a lack of necessary pro-tumorigenic signaling within the scaffolds. Finally, M12mac25 cells, which are ordinarily rendered non-tumorigenic through the expression of the tumor suppressor insulin-like growth factor binding protein 7 (IGFBP7), displayed a tumorigenic response when implanted within porous pHEMA scaffolds. These M12mac25 tumors showed a significantly higher macrophage infiltration within the scaffolds driven by the foreign body response to the materials. These findings show the potential for this biomaterials-based model system to be used in the study of prostate cancer tumorigenesis and dormancy escape. PMID:24942815
Seismoelectric reflection and transmission at a fluid/porous-medium interface.
Schakel, Menne; Smeulders, David
2010-01-01
The dispersion relation for seismoelectric wave propagation in poroelastic media is formulated in terms of effective densities comprising all viscous and electrokinetic coupling effects. Using Helmholtz decomposition, two seismoelectric conversion coefficients are derived, for an incident P-wave upon an interface between a compressible fluid and a poroelastic medium. These coefficients relate the incident P-wave to a reflected electromagnetic wave in the fluid, and a transmitted electromagnetic wave in the porous medium. The dependency on angle of incidence and frequency is computed. Using orthodox and interference fluxes, it is shown that energy conservation is satisfied. A sensitivity analysis indicates that electrolyte concentration, viscosity, and permeability highly influence seismoelectric conversion. PMID:20058946
Downscaling Method from Macroscopic to Microscopic Scale in a Periodic Two-Dimensional Porous Medium
NASA Astrophysics Data System (ADS)
Angeli, Pierre-Emmanuel; Ducros, Frédéric; Cioni, Olivier; Goyeau, Benoît
2010-05-01
A downscaling procedure applied to the steady laminar convective heat transfer through a two-dimensional homogeneous porous medium is proposed. Local conservation equations are numerically solved. A filtering procedure applied on the computed local fields gives the macroscopic dynamic and thermal behavior of the fluid. Our interest is to reconstruct the fields at microscopic scale in one or more arbitrary sub-areas of the medium. To this end, numerical simulations of the chosen sub-areas are carried out using the Trio_U CFD code. Cell-averaged quantities deduced from the reference volume averages are used as constraints on the solutions. A periodicity assumption is used for velocity and temperature spatial deviation. Reconstructed fields are compared to reference fields.
NASA Astrophysics Data System (ADS)
Ghanbarian, Behzad; Hunt, Allen G.; Skinner, Thomas E.; Ewing, Robert P.
2015-02-01
Accurate prediction of the saturation dependence of different modes of transport in porous media, such as those due to conductivity, air permeability, and diffusion, is of broad interest in engineering and natural resources management. Most current predictions use a "bundle of capillary tubes" concept, which, despite its widespread use, is a severely distorted idealization of natural porous media. In contrast, percolation theory provides a reliable and powerful means to model interconnectivity of disordered networks and porous materials. In this study, we invoke scaling concepts from percolation theory and effective medium theory to predict the saturation dependence of modes of transport — hydraulic and electrical conductivity, air permeability, and gas diffusion — in two disturbed soils. Universal scaling from percolation theory predicts the saturation dependence of air permeability and gas diffusion accurately, even when the percolation threshold for airflow is estimated from the porosity. We also find that the non-universal scaling obtained from the critical path analysis (CPA) of percolation theory can make excellent predictions of hydraulic and electrical conductivity under partially saturated conditions.
Flow of an aqueous foam through a two-dimensional porous medium: a pore scale investigation
NASA Astrophysics Data System (ADS)
Meheust, Y.; Jones, S. A.; Dollet, B.; Cox, S.; Cantat, I.
2012-12-01
Flowing foams are used in many engineering and technical applications. A well-known application is oil recovery. Another one is the remediation of polluted soil: the foam is injected into the ground in order to mobilize chemical species present in the medium. Apart from potential interesting physico-chemical and biochemical properties, foams have peculiar flow properties that might be of benefit to the application. We address here this physical aspect of the topic. As a precursor to the study of foam flow through a complex porous material, we first study the behavior of an aqueous two-dimensional foam flowing through a medium consisting of two parallel channels with different widths, at fixed medium porosity, that is, at fixed total combined width of the two channels. The flow velocity, and hence flux, in each channel is measured by analyzing images of the flowing foam. It is then compared to a theoretical model, the basic assumption of which is that the pressure drop along a channel is identical for both channels. This pressure drop both consists of (i) a dynamic pressure drop, which is controlled by bubble-wall friction and depends on the foam velocity in the channel, and (ii) a capillary pressure drop over the bubble films that emerge at the channel outlet, the latter pressure drop being controlled by the radius of curvature of the bubble film. Based on this assumption, the dependence of the ratio of the foam velocities in the two channels is inferred as a function of the channel width ratio. It compares well to the measurements and shows that the flow behavior is highly dependent on the foam structure within the narrowest of the two channels, especially when a "bamboo" structure is obtained. Consequently, the flux in a channel is found to have a more complicated relation to the channel width than expected for the flow of a standard Newtonian fluid in the same geometry. We provide a comparison to this reference configuration. We then study the flow of the same
Green, R.T.; Manteufel, R.D.; Dodge, F.T.; Svedeman, S.J.
1993-07-01
The performance of a geologic repository for high-level nuclear waste will be influenced to a large degree by thermohydrologic phenomena created by the emplacement of heat-generating radioactive waste. The importance of these phenomena is manifest in that they can greatly affect the movement of moisture and the resulting transport of radionuclides from the repository. Thus, these phenomena must be well understood prior to a definitive assessment of a potential repository site. An investigation has been undertaken along three separate avenues of analysis: (i) laboratory experiments, (ii) mathematical models, and (iii) similitude analysis. A summary of accomplishments to date is as follows. (1) A review of the literature on the theory of heat and mass transfer in partially saturated porous medium. (2) A development of the governing conservation and constitutive equations. (3) A development of a dimensionless form of the governing equations. (4) A numerical study of the importance and sensitivity of flow to a set of dimensionless groups. (5) A survey and evaluation of experimental measurement techniques. (6) Execution of laboratory experiments of nonisothermal flow in a porous medium with a simulated fracture.
Laboratory investigations of the physics of steam flow in a porous medium
Herkelrath, W.N.; Moench, A.F.
1982-01-01
Experiments were carried out in the laboratory to test a theory of transient flow of pure steam in a uniform porous medium. This theory is used extensively in modeling pressure-transient behavior in vapor-dominated geothermal systems. Transient, superheated steam-flow experiments were run by bringing a cylinder of porous material to a uniform initial pressure, and then making a step increase in pressure at one end of the sample, while monitoring the pressure-transient breakthrough at the other end. It was found in experiments run at 100?, 125?, and 146?C that the time required for steam-pressure transients to propagate through an unconsolidated material containing sand, silt, and clay was 10 to 25 times longer than predicted by theory. It is hypothesized that the delay in the steam-pressure transient was caused by adsorption of steam in the porous sample. In order to account for steam adsorption, a sink term was included in the conservation of mass equation. In addition, energy transfer in the system has to be considered because latent heat is released when steam adsorption occurs, increasing the sample temperature by as much as 10?C. Finally, it was recognized that the steam pressure was a function of both the temperature and the amount of adsorption in the sample. For simplicity, this function was assumed to be in equilibrium adsorption isotherm, which was determined by experiment. By solving the modified mass and energy equations numerically, subject to the empirical adsorption isotherm relationship, excellent theoretical simulation of the experiments was achieved. The experiments support the hypothesis that adsorption of steam can strongly influence steam pressure-transient behavior in porous media; the results suggest that the modified steam-flow theory, which includes steam adsorption terms, should be used in modeling steam flow in vapor-dominated geothermal systems.
Two-dimensional network simulation of diffusion driven coarsening of foam inside a porous medium
Cohen, D.; Patzek, T.W.; Radke, C.J.
1996-04-01
In order to use foams in subsurface applications, it is necessary to understand their stability in porous media. Diffusion driven coarsening of a stationary or nonflowing foam in a porous medium results in changing gas pressures and a coarsening of the foam texture. A two-dimensional network simulation has been created that predicts the behavior of foam in a porous medium by physically specifying the locations of all the lamellae in the system and by solving the complete set of Young-Laplace and diffusion equations. An hourglass approximates the shape of the pores, and the pore walls are considered to be highly water wet. A singularity arises in the system of differential algebraic equations due to the curvature of the pore walls. This singularity is a signal that the system must undergo oscillations or sudden lamellar rearrangements before the diffusion process can continue. Newton-Raphson iteration is used along with Keller`s method of arc-length continuation and a new jump resolution technique to locate and resolve bifurcations in the system of coupled lamellae. Gas bubbles in pore throats are regions of encapsulated pressure. As gas is released from these bubbles during diffusion, the pressure of the bubbles in the pore bodies increases. When the pressure increase is scaled by the characteristic Young-Laplace pressure, the equilibrium time for the diffusion process is scaled by the ratio of the square of the characteristic length to the gas diffusivity and two dimensionless groups. One describes the ease with which gas can diffuse through a lamella, the second represents the amount of gas encapsulated within the pore throats initially. Given this scaling, the resulting plots of pressure versus time and normalized lamellae positions versus time are universal for all system sizes and characteristics. This is true as long as the initial lamella distribution is the same in each case.
Instability of uniform gas flow within liquid-saturated porous medium
NASA Astrophysics Data System (ADS)
Tsiberkin, Kirill
2014-05-01
Problem of flow instability in porous media are important for applied fields like mining, water supply, etc. There is a fundamental interest to mechanisms are influence on flow too. E.g., a viscous fingering is typical phenomenon of displacement processes in porous medium [1,2]. The instability of gas flow in liquid-saturated domain have no wide studies but it can make significant influence on heat and mass transport. If the one phase have a high saturation, the other phase will form the droplets are break and captured within pores due to the capillary forces [2-4]. It is possible to neglect the capillarity if the saturation of both fluids exceed a percolation thresholds [5,6]. We consider an infinite flat layer of uniform porous medium is saturated with gas and liquid have close saturation. Its upper boundary is impermeable for liquid phase and gas can pass freely through the border, and the down boundary is permeable for both phases. The temperature and pressure are fixed at the top while their gradients are fixed at the bottom side. Neglecting the capillarity, gas solubility, liquid evaporation and any phase transitions, we obtain a steady solution and study its' stability. The governing parameter of the flow is α = αgAPe, αg = (ρwCg )/(ρsCs), A = ρstatvstat (1) where Pe is the thermal Peclet number determines a ratio between convective and conductive heat transfer, αg is ratio of thermal capacities of fluid and matrix, and A is determined by gas density and velocity in the steady state. Analyzing the perturbations, we found that a long-wave instability realizes in the system. The critical value of parameter is: αc = a1 + k2a2 + O(ρg/ρw), (2) where a1,a2 are positive coefficients are calculated using thermal perturbations combinations and k is wave number along horizontal direction. The minimal αc equals 2.47, and it correspond the critical Peclet number near 200 in the methane-water system. An error of the dependence is of order of gas to water
The flow of a foam in a two-dimensional porous medium
NASA Astrophysics Data System (ADS)
Géraud, Baudouin; Jones, Siân. A.; Cantat, Isabelle; Dollet, Benjamin; Méheust, Yves
2016-02-01
Foams have been used for decades as displacing fluids for enhanced oil recovery and aquifer remediation, and more recently, for remediation of the vadose zone, in which case foams carry chemical amendments. Foams are better injection fluids than aqueous solutions due to their low sensitivity to gravity and because they are less sensitive to permeability heterogeneities, thus allowing a more uniform sweep. The latter aspect results from their peculiar rheology, whose understanding motivates the present study. We investigate foam flow through a two-dimensional porous medium consisting of circular obstacles positioned randomly in a horizontal transparent Hele-Shaw cell. The local foam structure is recorded in situ, which provides a measure of the spatial distribution of bubble velocities and sizes at regular time intervals. The flow exhibits a rich phenomenology including preferential flow paths and local flow nonstationarity (intermittency) despite the imposed permanent global flow rate. Moreover, the medium selects the bubble size distribution through lamella division-triggered bubble fragmentation. Varying the mean bubble size of the injected foam, its water content, and mean velocity, we characterize those processes systematically. In particular, we measure the spatial evolution of the distribution of bubble areas, and infer the efficiency of bubble fragmentation depending on the various control parameters. We furthermore show that the distributions of bubble sizes and velocities are correlated. This study sheds new light on the local rheology of foams in porous media and opens the way toward quantitative characterization of the relationship between medium geometry and foam flow properties. It also suggests that large-scale models of foam flows in the subsurface should account for the correlation between bubble sizes and velocities.
Velocity and stress jump conditions between a porous medium and a fluid
NASA Astrophysics Data System (ADS)
Valdés-Parada, Francisco J.; Aguilar-Madera, Carlos G.; Ochoa-Tapia, J. Alberto; Goyeau, Benoît
2013-12-01
Modeling transport phenomena in hierarchical systems can be carried out by either a one domain approach or a two domain approach. The first one involves assuming the system as a pseudo-continuum and is expressed in terms of position-dependent effective medium coefficients. In the two domain approach, the differential equations have position-independent coefficients but require accounting for the corresponding boundary conditions that couple the equations between each homogeneous region. For momentum transport between a porous medium and a fluid, stress boundary conditions have been derived in terms of a jump coefficient that needs to be predicted within a two-domain approach formulation. However, continuity of the velocity is postulated at the dividing surface. In this work, we propose a methodology for the derivation of boundary conditions for both the velocity and the stress. These conditions are expressed in terms of jump coefficients that are computed from the solution of an ancillary macroscopic closure problem. This problem accounts for the deviations from the one and two domain approaches. From the closure problem solution we were also able to determine the position at which the jump conditions should be applied, i.e., the dividing surface position. In addition, we used this methodology adopting the assumptions proposed by Ochoa-Tapia and Whitaker as well as those by Beavers and Joseph. We found that any version of the two domain approach was in agreement with the one domain approach in the bulk of the porous medium and the fluid. However, the same is not true for the process of capturing the essential information of the inter-region.
NASA Astrophysics Data System (ADS)
Ghanbarian, Behzad; Daigle, Hugh; Hunt, Allen G.; Ewing, Robert P.; Sahimi, Muhammad
2015-01-01
Understanding and accurate prediction of gas or liquid phase (solute) diffusion are essential to accurate prediction of contaminant transport in partially saturated porous media. In this study, we propose analytical equations, using concepts from percolation theory and the Effective Medium Approximation (EMA) to model the saturation dependence of both gas and solute diffusion in porous media. The predictions of our theoretical approach agree well with the results of nine lattice Boltzmann simulations. We find that the universal quadratic scaling predicted by percolation theory, combined with the universal linear scaling predicted by the EMA, describes diffusion in porous media with both relatively broad and extremely narrow pore size distributions.
NASA Astrophysics Data System (ADS)
Sadovskaya, O. V.; Sadovskii, V. M.
2015-10-01
The parallel computational algorithm for analysis of the processes of elastic-plastic deformation of a porous medium under the action of external dynamic loads is developed. This algorithm is based on the mathematical model taking into account threshold nature of change in the strength of a material under the collapse of pores. The algorithm is implemented in Fortran by means of functions of the MPI library. The parallel program system has been tested on clusters in computations of the propagation of plane longitudinal shock waves of the compression and in computations of the expansion of a cylindrical cavity in an infinite porous medium. The comparison of numerical results and exact solutions has shown their good qualitative and quantitative correspondence. Using the obtained algorithm, the process of propagation of elastic-plastic waves of the compression in a homogenous porous medium, accompanied by the deformation of a skeleton and the collapse of pores, is analyzed.
Investigation of NO{sub x} conversion characteristics in a porous medium
Afsharvahid, S.; Ashman, P.J.; Dally, B.B.
2008-03-15
The conversion of nitric oxide (using CNG/air as fuel/oxidizer) inside a porous medium is investigated in this study. Unlike freely propagating flames, porous burners provide a solid medium that facilitates heat exchange with the gaseous phase. The heat exchange allows the stabilization of a variety of fuel mixtures from lean to rich and with a variety of calorific values. In addition, it allows the control of the reaction zone temperature and thus the control of pollutant formation while maintaining flame stability. An experimental porous burner was designed and manufactured for this purpose. The effects of equivalence ratio and flow velocity on the flame stabilization, NO{sub x} and TFN (total fixed nitrogen) conversion ratios, and temperature profiles along the burner are investigated. In addition, numerical calculations using the PLUG flow simulator model and the GRI 3.0 kinetic mechanism reveals the key reactions which control the conversion efficiency. It was found that under slightly fuel-rich conditions ({phi}{<=}1.3) NO{sub x} mostly converts to N{sub 2} with a maximum conversion ratio of 65%, while for higher equivalence ratios ({phi}>1.3) a large proportion of NO{sub x} converts to NH{sub 3}. Results from experiments and numerical modeling showed that the temperature profile along the burner has significant effects on the NO{sub x} and TFN conversion ratios. It was also found that temperatures between 1000 and 1500 K are most desirable for NO{sub x} and TFN conversion in the porous burner. Analysis of the chemical paths for the low- and high-equivalence-ratio cases showed that the formation of nitrogen-containing species under very rich conditions ({phi}>1.3) is due to the increased importance of the HCNO path as compared to the HNO path. The latter is the dominant path at low equivalence ratios ({phi}{<=}1.3) and leads to the formation of N{sub 2}. The NO concentration in the initial mixture was found to improve the conversion by up to 20% at low
On two mathematical models of nonequilibrium two-phase flow in a porous medium
NASA Astrophysics Data System (ADS)
Tarakanov, A.; Konyukhov, A.
2013-05-01
Nonequilibrium effects in the displacement in a porous medium which manifest themselves in dependence of relative phase permeabilities and capillary pressure on the rate of the displacement are well known (see, for example, [1-2]). There are at least two different approaches to account for this phenomenon in mathematical models. The first one is based on the use of dynamic relations f(S, ∂S/∂t) instead of equilibrium functions of saturation. The model of this type was developed by Barenblatt and his co-workers [1]. Its great advantage is a small number of additional empirical parameters. Under some suggestions the characteristic time of capillary relaxation f(S, ∂S/∂t)=fe(S+τ∂S/∂t) is the only additional parameter of the model and dynamic relative permeability has the following form , where subscript 'e' denotes equilibrium functions of saturation. Another approach (see, [2]) is based on principles of nonequilibrium thermodynamics. In the framework of this approach a new thermodynamic parameter being an argument of thermodynamic potential is introduced to parameterize nonequilibrium states. For this parameter (hereafter denoted as ξ) the kinetic equation is formulated which provides non-negativity of dissipation of capillary forces. Relative phase permeabilities and capillary pressure are suggested to be functions of this parameter and saturation f=f(S,ξ), Pc=Pc(S,ξ) (1) This way of modeling starts from relation between the thermodynamical potential and its arguments and even the simplest models include a relatively large number of empirical parameters. Development of the permeability function requires additional argumentation. In the present paper the dependence of the phase permeabilities on ξ is introduced such that the resulting model is compatible with Barenblatt's model at small relaxation time i.e. f→fe(S+τ∂S/∂t) as τ→0 . (2) On the other hand the functions (1) can not be represented by the dynamic relations of the form f(S,
NASA Astrophysics Data System (ADS)
Chen, Xingxin; Cai, Qipeng; Ding, Jianwen; Guo, Liqun
2016-02-01
identified that could explain the rate change: (1) only particles deposited in the porous medium by fouling mechanisms could be released by ultrasound stimulations at power levels below a certain critical value, or (2) ultrasound stimulations at power levels above a certain critical value are sufficient to change the structure of the porous medium, producing more dead-end pore openings that allow particle flow through the porous medium. The results presented are unique in indicating that successive particle release can be induced using increasing ultrasound stimulation.
Oxygen Transfer in a Fluctuating Capillary Fringe: Impact of Porous Medium Heterogeneity
NASA Astrophysics Data System (ADS)
Haberer, C.; Rolle, M.; Cirpka, O. A.; Grathwohl, P.
2013-12-01
Mass transfer of oxygen from the atmosphere, across the capillary fringe, to anoxic groundwater is of primary importance for many biogeochemical processes affecting groundwater quality. The controlling mechanisms for oxygen transfer across the capillary fringe are the diffusive/dispersive transport as well as mass exchange between entrapped air and groundwater. In addition, the presence of physical heterogeneity in the porous medium may strongly affect the oxygen fluxes. We performed quasi two-dimensional flow-through experiments at the laboratory bench-scale to study the effect of a coarse-material inclusion, located in proximity of the water table, on flow and oxygen transfer in the capillary fringe. Flow and transport were monitored under both steady-state and transient flow conditions, the latter obtained by fluctuating the water table. We visually inspected the complex flow field using a dye tracer solution, measured vertical oxygen profiles across the capillary fringe at high spatial resolution, and determined oxygen fluxes in the effluent of the flow-through chamber. Our results show that the coarse-material inclusion significantly affected oxygen transfer during the different phases of the experiments. At steady state, the oxygen flux across the unsaturated/saturated interface was considerably enhanced due to flow focusing in the fully water-saturated coarse lens. During drainage, the capillary barrier effect prevented water to drain from the fine material overlying the coarse lens. The entrapped oxygen-rich aqueous phase contributed to the total amount of oxygen supplied to the system when the water table was raised back to its initial level. In case of imbibition, also pronounced entrapment of air occurred in the coarse lens, causing oxygen to partition between the aqueous and gaseous phases. Thus, we found that oxygen transfer across the capillary fringe was significantly enhanced by the coarse-material inclusion due to flow focusing, the capillary
NASA Astrophysics Data System (ADS)
Pandey, S. K.; Chaube, M. K.
2011-09-01
This paper presents an analytical study of the MHD flow of a micropolar fluid through a porous medium induced by sinusoidal peristaltic waves traveling down the channel walls. Low Reynolds number and long wavelength approximations are applied to solve the non-linear problem in the closed form and expressions for axial velocity, pressure rise per wavelength, mechanical efficiency and stream function are obtained. The impacts of pertinent parameters on the aforementioned quantities are examined by plotting graphs on the basis of computational results. It is found that the pumping improves with Hartman number but degrades with permeability of the porous medium.
Modeling the Effect of Fluid Flow on a Growing Network of Fractures in a Porous Medium
NASA Astrophysics Data System (ADS)
Alhashim, Mohammed; Koch, Donald
2015-11-01
The injection of a viscous fluid at high pressure in a geological formation induces the fracturing of pre-existing joints. Assuming a constant solid-matrix stress field, a weak joint saturated with fluid is fractured when the fluid pressure exceeds a critical value that depends on the joint's orientation. In this work, the formation of a network of fractures in a porous medium is modeled. When the average length of the fractures is much smaller than the radius of a cluster of fractured joints, the fluid flow within the network can be described as Darcy flow in a permeable medium consisting of the fracture network. The permeability and porosity of the medium are functions of the number density of activated joints and consequently depend on the fluid pressure. We demonstrate conditions under which these relationships can be derived from percolation theory. Fluid may also be lost from the fracture network by flowing into the permeable rock matrix. The solution of the model shows that the cluster radius grows as a power law with time in two regimes: (1) an intermediate time regime when the network contains many fractures but fluid loss is negligible; and (2) a long time regime when fluid loss dominates. In both regimes, the power law exponent depends on the Euclidean dimension and the injection rate dependence on time.
Variation in Hydraulic Conductivity with Decreasing pH in a Biologically-Clogged Porous Medium
NASA Astrophysics Data System (ADS)
Kirk, M. F.; Santillan, E.; McGrath, L. K.; Altman, S. J.
2011-12-01
Biological clogging can significantly lower the hydraulic conductivity of porous media, potentially helping to limit CO2 transport from geological carbon storage reservoirs. How clogging is affected by CO2 injection, however, is unclear. We used column experiments to examine how decreasing pH, a geochemical change associated with CO2 injection, will affect the hydraulic conductivity (K) of biologically clogged porous medium. Four biologically-active experiments and two control experiments were performed. Columns consisted of 1 mm2 capillary tubes filled with 105-150 μm diameter glass beads. Artificial groundwater medium containing 1 mM glucose was pumped through the columns at a rate of 0.015 mL/min (q = 21.6 m/day; Re = 0.045). Each column was inoculated with 10^8 CFU of Pseudomonas fluorescens tagged with a green fluorescent protein; cells introduced to control columns were heat sterilized. Biomass distribution and transport was monitored using scanning laser confocal microscopy and effluent plating. Growth was allowed to occur for 5 days in medium with pH 7 in the biologically active columns. During that time, K decreased to values ranging from 10 to 27% of the average control K and effluent cell levels increased to about 10^8 CFU/mL. Next, the pH of the inflowing medium was lowered to 4 in three experiments and 5.5 in one experiment. After pH 4 medium was introduced, K increased to values ranging from 21 to 64% of the average control K and culturable cell levels in the effluent fell by about 4 log units. Confocal images show that clogging persisted in the columns at pH 4 because most of the microbial biomass remained attached to bead surfaces. In the experiment where pH was lowered to 5.5, K changed little because biological clogging remained entirely intact. The concentration of culturable cells in the effluent was also invariant. These results suggest that biomass in porous medium will largely remain in place following exposure to acidic water in a CO2
Identification of the Permeability Field of Porous Medium from the Injection of Passive Tracer
Zhan, Lang; Yortsos, Y.C.
1999-10-18
In this paper, a method was proposed which focused on the question, namely on how to invert data on arrival times at various (and numerous) points in the porous medium to map the permeability field. The method, elements of which were briefly described in (9), is based on a direct inversion of the data, as will be described below , rather than on the optimization of initial random (or partly constrained) guesses of the permeability field, to match the available data, as typically done in the analogous problem of pressure transients. The direct inversion is based on two conditions, that Darcy's law for single-phase flow in porous media is valid, and that dispersion of the concentration of the injected tracer is negligible. While the former is a well-accepted premise, the latter depends on injection and field conditions, and may not necessarily apply in all cases. Based on these conditions, we formulate a nonlinear boundary value problem, the coefficients of which depend on the experimental arrival time data.
Oostrom, Martinus; Wietsma, Thomas W.; Strickland, Christopher E.; Freedman, Vicky L.; Truex, Michael J.
2012-02-01
Soil desiccation, in conjunction with surface infiltration control, is considered at the Hanford Site as a potential technology to limit the flux of technetium and other contaminants in the vadose zone to the groundwater. An intermediate-scale experiment was conducted to test the response of a series of instruments to desiccation and subsequent rewetting of porous media. The instruments include thermistors, thermocouple psychrometers, dual-probe heat pulse sensors, heat dissipation units, and humidity probes. The experiment was simulated with the multifluid flow simulator STOMP, using independently obtained hydraulic and thermal porous medium properties. All instrument types used for this experiment were able to indicate when the desiccation front passed a certain location. In most cases the changes were sharp, indicating rapid changes in moisture content, water potential, or humidity. However, a response to the changing conditions was recorded only when the drying front was very close to a sensor. Of the tested instruments, only the heat dissipation unit and humidity probes were able to detect rewetting. The numerical simulation results reasonably match the experimental data, indicating that the simulator captures the pertinent gas flow and transport processes related to desiccation and rewetting and may be useful in the design and analysis of field tests.
A one-domain approach for modeling and simulation of free fluid over a porous medium
NASA Astrophysics Data System (ADS)
Chen, Huangxin; Wang, Xiao-Ping
2014-02-01
We propose a one-domain approach based on the Brinkman model for the modeling and simulation of the transport phenomenon between free fluid and a porous medium. A thin transition layer is introduced between the free fluid region and the porous media region, across which the porosity and permeability undergo a rapid but continuous change. We study the behavior of the solution to the one-domain model analytically and numerically. Using the method of matched asymptotic expansion, we recover the Beavers-Joseph-Saffman (BJS) interface condition as the thickness of the transition layer goes to zero. We also calculate the error estimates between the leading order solution of the one-domain model and the standard Darcy-Stokes model of two-domain model with BJS condition. Numerical methods are developed for both the one-domain model and the two-domain model. Numerical results are presented to support the analytical results, thereby justifying the one-domain model as a good approximation to the two domain Stokes-Darcy model.
Micromorphic homogenization of a porous medium: elastic behavior and quasi-brittle damage
NASA Astrophysics Data System (ADS)
Hütter, Geralf; Mühlich, Uwe; Kuna, Meinhard
2015-11-01
Today it is well known that the classical Cauchy continuum theory is insufficient to describe the deformation behavior of solids if gradients occur over distances which are comparable to the microstructure of the material. This becomes crucial e.g., for small specimens or during localization of deformation induced by material degradation (damage). Higher-order continuum approaches like micromorphic theories are established to address such problems. However, such theories require the formulation of respective constitutive laws, which account for the microstructural interactions. Especially in damage mechanics such laws are mostly formulated in a purely heuristic way, which leads to physical and numerical problems. In the present contribution, the fully micromorphic constitutive law for a porous medium is obtained in closed form by homogenization based on the minimal boundary conditions concept. It is shown that this model describes size effects of porous media like foams adequately. The model is extended toward quasi-brittle damage overcoming the physical and numerical limitations of purely heuristic approaches.
BISQ model based on a Kelvin-Voigt viscoelastic frame in a partially saturated porous medium
NASA Astrophysics Data System (ADS)
Nie, Jian-Xin; Ba, Jing; Yang, Ding-Hui; Yan, Xin-Fei; Yuan, Zhen-Yu; Qiao, Hai-Peng
2012-06-01
Taking into account three important porous media mechanisms during wave propagation (the Biot-flow, squirt-flow, and solid-skeleton viscoelastic mechanisms), we introduce water saturation into the dynamic governing equations of wave propagation by analyzing the effective medium theory and then providing a viscoelastic Biot/squirt (BISQ) model which can analyze the wave propagation problems in a partially viscous pore fluid saturated porous media. In this model, the effects of pore fluid distribution patterns on the effective bulk modulus at different frequencies are considered. Then we derive the wave dynamic equations in the time-space domain. The phase velocity and the attenuation coefficient equations of the viscoelatic BISQ model in the frequency-wavenumber domain are deduced through a set of plane harmonic solution assumptions. Finally, by means of numerical simulations, we investigate the effects of water saturation, permeability, and frequency on compressional wave velocity and attenuation. Based on tight sandstone and carbonate experimental observed data, the compressional wave velocities of partially saturated reservoir rocks are calculated. The compressional wave velocity in carbonate reservoirs is more sensitive to gas saturation than in sandstone reservoirs.
Experimental Investigation of Dissolution-Driven Convection in Heterogeneous Porous Medium
NASA Astrophysics Data System (ADS)
Ni, Rui; Salibindla, Ashwanth K. R.; Masuk, Ashik Ullah Mohammad; Shen, Jikang
2015-11-01
Subsurface carbon sequestration in saline aquifers has emerged as one promising method to mitigate anthropogenic emission of CO2 because of the potential storage capacity of the accessible formations. Being injected into the porous formation underground, the buoyant CO2 will start to migrate upward and may eventually leak back to the surface through faults in the overlying caprock. This leaking process may be hindered or even completely stopped due to the dissolution of CO2 into the brine. For those locations, where the supercritical CO2 is above the brine, the dissolution between the two fluids leads to a mixture with higher density than both CO2 and brine; and thus the resultant solution on the interface is unstable, drawing the CO2 -rich mixture downward and rendering the sequestration significantly more stable. Previous laboratory experiments on dissolution-driven convection were mostly limited to a simplified case where the porous medium was assumed to be homogenous. To account for the heterogeneity existing in the actual formations, we designed a series of experiments in controlled ways to introduce spatial variations of permeability. By measuring the mass transfer efficiency under different conditions, our experiments provide a new way to assess the
Modeling spatial competition for light in plant populations with the porous medium equation.
Beyer, Robert; Etard, Octave; Cournède, Paul-Henry; Laurent-Gengoux, Pascal
2015-02-01
We consider a plant's local leaf area index as a spatially continuous variable, subject to particular reaction-diffusion dynamics of allocation, senescence and spatial propagation. The latter notably incorporates the plant's tendency to form new leaves in bright rather than shaded locations. Applying a generalized Beer-Lambert law allows to link existing foliage to production dynamics. The approach allows for inter-individual variability and competition for light while maintaining robustness-a key weakness of comparable existing models. The analysis of the single plant case leads to a significant simplification of the system's key equation when transforming it into the well studied porous medium equation. Confronting the theoretical model to experimental data of sugar beet populations, differing in configuration density, demonstrates its accuracy. PMID:24623311
Radiation Effect On Three Dimensional Vertical Channel Flow Through Porous Medium
NASA Astrophysics Data System (ADS)
Guria, M.
2015-12-01
The flow of a viscous incompressible fluid through a vertical channel in the presence of radiation immersed in a porous medium has been studied. Approximate solutions have been obtained for the velocity and temperature fields, shear stresses and rate of heat transfer using the perturbation technique. It is found that the primary velocity decreases with an increase in the radiation parameter as well as the Prandtl number for cooling of the plate. It is also found that with an increase in the permeability parameter, the primary velocity increases for cooling of the plate. The magnitude of the secondary velocity decreases near the plate y = 0 and increases near the plate y = d with an increase in the permeability parameter. The temperature distribution decreases with an increase of the radiation parameter as wall as the Prandtl number for cooling of the plate. The shear stresses and the rate of heat transfer, which are of physical interest, are presented in the form of tables.
Qayyum, Mubashir; Khan, Hamid; Rahim, M Tariq; Ullah, Inayat
2015-01-01
The aim of this article is to model and analyze an unsteady axisymmetric flow of non-conducting, Newtonian fluid squeezed between two circular plates passing through porous medium channel with slip boundary condition. A single fourth order nonlinear ordinary differential equation is obtained using similarity transformation. The resulting boundary value problem is solved using Homotopy Perturbation Method (HPM) and fourth order Explicit Runge Kutta Method (RK4). Convergence of HPM solution is verified by obtaining various order approximate solutions along with absolute residuals. Validity of HPM solution is confirmed by comparing analytical and numerical solutions. Furthermore, the effects of various dimensionless parameters on the longitudinal and normal velocity profiles are studied graphically. PMID:25738864
Fractional Cahn-Hilliard, Allen-Cahn and porous medium equations
NASA Astrophysics Data System (ADS)
Akagi, Goro; Schimperna, Giulio; Segatti, Antonio
2016-09-01
We introduce a fractional variant of the Cahn-Hilliard equation settled in a bounded domain Ω ⊂RN and complemented with homogeneous Dirichlet boundary conditions of solid type (i.e., imposed in the whole of RN ∖ Ω). After setting a proper functional framework, we prove existence and uniqueness of weak solutions to the related initial-boundary value problem. Then, we investigate some significant singular limits obtained as the order of either of the fractional Laplacians appearing in the equation is let tend to 0. In particular, we can rigorously prove that the fractional Allen-Cahn, fractional porous medium, and fractional fast-diffusion equations can be obtained in the limit. Finally, in the last part of the paper, we discuss existence and qualitative properties of stationary solutions of our problem and of its singular limits.
NASA Astrophysics Data System (ADS)
Chew, J. V. L.; Sulaiman, J.
2016-06-01
This paper considers Newton-MSOR iterative method for solving 1D nonlinear porous medium equation (PME). The basic concept of proposed iterative method is derived from a combination of one step nonlinear iterative method which known as Newton method with Modified Successive Over Relaxation (MSOR) method. The reliability of Newton-MSOR to obtain approximate solution for several PME problems is compared with Newton-Gauss-Seidel (Newton-GS) and Newton-Successive Over Relaxation (Newton-SOR). In this paper, the formulation and implementation of these three iterative methods have also been presented. From four examples of PME problems, numerical results showed that Newton-MSOR method requires lesser number of iterations and computational time as compared with Newton-GS and Newton-SOR methods.
A study of the propagation of compression waves in porous medium filled with steam
Sutrisno; Djoko Wintolo; Samsul Kamal; Sudarman, S.
1996-01-24
A preliminary investigation on the propagation of compression waves through a radial system of porous medium filled with steam has been conducted for the case of uniform and non-uniform basic temperature distributions. When a relatively weak pressure disturbance is introduced as a signal source in a uniform temperature system, it is found that the pressure disturbance decays away and smears out as time progresses. However, for the case of a nonuniform basic temperature distribution, the temperature gradient and fluid viscosity give significant effects on the reduction of pressure signal attenuation. The attenuation of the compression waves depends on the wave frequencies. For higher frequencies the strength of the signal decays rapidly, and for lower frequencies the signal could propagate farther away. It is found also that porosity and permeability distributions gives significant effects on the amplitude and the wave profiles.
A numerical model of controlled bioinduced mineralization in a porous medium to prevent corrosion
NASA Astrophysics Data System (ADS)
Afanasyev, Michael; van Paassen, Leon; Heimovaara, Timo
2013-04-01
This paper presents a numerical model of controlled bioinduced mineralization in a porous medium as a possible corrosion protection mechanism. Corrosion is a significant economic problem - recent reports evaluate the annual cost of metal corrosion as 3-4% of the gross domestic product (GDP), in both developed and developing countries. Corrosion control methods currently used are costly and unsustainable as they require the use of larger volumes of materials, hazardous chemicals and regular inspections. As an alternative corrosion control method, bioinduced deposition of protective mineral layers has been proposed. Bioinduced precipitation of calcite has already been investigated for CO2 geological sequestration and soil improvement. To our knowledge, though, no numerical study of biomineralization for corrosion protection has been described yet. Our model includes three phases - solid, biofilm and mobile water. In the latter the reactive elements are dissolved, which are involved in the precipitation and the biofilm growth. The equations that describe the pore water flow, chemical reactions in the mobile water, consumption of substrate and expulsion of metabolic products by the biofilm are briefly presented. Also, the changes in porosity and permeability of the porous medium through biofilm growth and solids precipitation are included. Our main assumptions are that the biofilm is uniform, has a constant density and composition, that all chemical reactions except for substrate consumption occur in the mobile water, and that the precipitates are uniformly distributed on the surface of the solids. We validate the model with simple analytical solutions and against experimental data. The metabolism of the micro-organisms introduces changes in the physical and chemical characteristics of the environment, such as concentrations of chemicals and pH levels. As an extension to the model, we couple these changes to the rates of biofilm growth and precipitation rates. The
Darcy Flow in a Wavy Channel Filled with a Porous Medium
Gray, Donald D; Ogretim, Egemen; Bromhal, Grant S
2013-05-17
Flow in channels bounded by wavy or corrugated walls is of interest in both technological and geological contexts. This paper presents an analytical solution for the steady Darcy flow of an incompressible fluid through a homogeneous, isotropic porous medium filling a channel bounded by symmetric wavy walls. This packed channel may represent an idealized packed fracture, a situation which is of interest as a potential pathway for the leakage of carbon dioxide from a geological sequestration site. The channel walls change from parallel planes, to small amplitude sine waves, to large amplitude nonsinusoidal waves as certain parameters are increased. The direction of gravity is arbitrary. A plot of piezometric head against distance in the direction of mean flow changes from a straight line for parallel planes to a series of steeply sloping sections in the reaches of small aperture alternating with nearly constant sections in the large aperture bulges. Expressions are given for the stream function, specific discharge, piezometric head, and pressure.
Natural convection on a vertical plate in a saturated porous medium with internal heat generation
NASA Astrophysics Data System (ADS)
Guedda, M.; Sriti, M.; Achemlal, D.
2014-08-01
The main goal of this paper is to re-exam a class of exact solutions for the two-dimensional free convection boundary layers induced by a heated vertical plate embedded in a saturated porous medium with an exponential decaying heat generation. The temperature distribution of the plate has been assumed to vary as a power of the axial coordinate measured from the leading edge of the plate and subjected to an applied lateral mass flux. The boundary layer equations are solved analytically and numerically using a fifth-order Runge-Kutta scheme coupled with the shooting iteration method. As for the classical problem without internal heat generation, it is proved that multiple (unbounded) solutions arise for any and for any suction/injection parameter. For such solutions, the asymptotic behavior as the similarity variable approaches infinity is determined.
NASA Astrophysics Data System (ADS)
Markicevic, B.; Navaz, H. K.
2010-12-01
The fate of a wetting liquid sessile droplet imbibed by a porous medium is formulated as a multiphase flow problem and a numerical solution is developed using the capillary network model with a microforce balance at the liquid ∣gas interface. The liquid phase capillary flow and evaporation are solved simultaneously. An exclusive evidence for a multiphase flow is already found in the capillary flow, as a liquid wets a much larger volume of porous medium compared to the wetted volume, calculated by assuming that the medium imbibes the liquid in the single-phase flow. The physics of the multiphase capillary flow includes the formation of local gas clusters and liquid ganglia. The clusters and ganglia distribution is further altered by evaporation. The evaporation tends to shrink the ganglia sizes and open the gas clusters, both due to the liquid mass loss from the porous medium. Still, the capillarity tends to disperse the liquid back into the regions from where the liquid previously evaporated. These changes in the liquid saturation produce the changes in vapor concentration within the porous medium and changes in the mass fluxes. The imprint shape varies, where, for more spherical imprints, the evaporation is enhanced due to the capillary flow. The opposite is true for the elongated imprints for which the capillarity hinders the evaporation rate. Comparing the spherical and elongated imprints, the liquid dispersion differs and the capillary flow the into protrusion direction is pronounced for the elongated imprints. The changes in the liquid dispersion and imprint shape influence the vapor concentration within the porous medium, vapor phase mass fluxes, and liquid persistence time. Finally, the previous behavior is observed for hazardous materials and warfare agents, where predicting the fate of such kind of liquids and their vapors become especially important due to their harmful effects.
NASA Astrophysics Data System (ADS)
Pham, Ngoc; Papavassiliou, Dimitrios
2014-11-01
Pore surface charge heterogeneity has been found to affect particle retention in flow through porous media. In this study, retention of nanoparticles under different surface blocking conditions is numerically investigated. Micro-CT scanning is used to reconstruct the 3D geometry of sandstone and image-based analysis is used to characterize the pore space and the mineral composition of the rock. Flow of water through the sample is simulated with the lattice Boltzmann method. The motion of nanoparticles is modeled by injection of particles moving under convection and molecular diffusion and recording their trajectories in time. When interacting with the pore surface, particles can be retained onto the surface with a particular deposition rate. As deposited particles hinder the retention of other particles by blocking occupied sites, the deposition is considered to be a second order process. Particle breakthrough under different modeled and real distributions of surface heterogeneity as a function of various surface blocking conditions is investigated. The effect is stronger when parts of the surface are much more favorable for deposition than others. Acknowledgements: Advanced Energy Consortium (AEC BEG08-022) & XSEDE (CTS090017).
NASA Astrophysics Data System (ADS)
Wen, Baole
Buoyancy-driven convection in fluid-saturated porous media is a key environmental and technological process, with applications ranging from carbon dioxide storage in terrestrial aquifers to the design of compact heat exchangers. Porous medium convection is also a paradigm for forced-dissipative infinite-dimensional dynamical systems, exhibiting spatiotemporally chaotic dynamics if not "true" turbulence. The objective of this dissertation research is to quantitatively characterize the dynamics and heat transport in two-dimensional horizontal and inclined porous medium convection between isothermal plane parallel boundaries at asymptotically large values of the Rayleigh number Ra by investigating the emergent, quasi-coherent flow. This investigation employs a complement of direct numerical simulations (DNS), secondary stability and dynamical systems theory, and variational analysis. The DNS confirm the remarkable tendency for the interior flow to self-organize into closely-spaced columnar plumes at sufficiently large Ra (up to Ra ≃ 105), with more complex spatiotemporal features being confined to boundary layers near the heated and cooled walls. The relatively simple form of the interior flow motivates investigation of unstable steady and time-periodic convective states at large Ra as a function of the domain aspect ratio L. To gain insight into the development of spatiotemporally chaotic convection, the (secondary) stability of these fully nonlinear states to small-amplitude disturbances is investigated using a spatial Floquet analysis. The results indicate that there exist two distinct modes of instability at large Ra: a bulk instability mode and a wall instability mode. The former usually is excited by long-wavelength disturbances and is generally much weaker than the latter. DNS, strategically initialized to investigate the fully nonlinear evolution of the most dangerous secondary instability modes, suggest that the (long time) mean inter-plume spacing in
Modeling of seismic field in porous medium:Simulation study of single pore and pore ensemble effects
NASA Astrophysics Data System (ADS)
Shatskaya, A. A.; Nemirovich-Danchenko, M. M.; Terre, D. A.
2015-11-01
The article considers the effect of porous media on elastic wave field. Based on numerical modeling, diffraction pattern of the wave propagating through a single pore in carbonates has been produced. Matrix properties (calcite and dolomite) and fluid (water) are modeled based on thin core section image. The qualitative comparison with the available computational data has been performed. Provided that ensemble of pores is involved, the effect of porous medium on seismic field has been studied. For comparison with experimental data the model of porous sintered aluminum Al-6061 has been considered. The processing of numerical modeling results made it possible to estimate average velocities in the model of porous aluminum and compare them with physical modeling data. The provided estimates have indicated qualitative (single pore) and quantitative (ensemble of pores) correlation of simulation and experiment results.
Map of fluid flow in fractal porous medium into fractal continuum flow.
Balankin, Alexander S; Elizarraraz, Benjamin Espinoza
2012-05-01
This paper is devoted to fractal continuum hydrodynamics and its application to model fluid flows in fractally permeable reservoirs. Hydrodynamics of fractal continuum flow is developed on the basis of a self-consistent model of fractal continuum employing vector local fractional differential operators allied with the Hausdorff derivative. The generalized forms of Green-Gauss and Kelvin-Stokes theorems for fractional calculus are proved. The Hausdorff material derivative is defined and the form of Reynolds transport theorem for fractal continuum flow is obtained. The fundamental conservation laws for a fractal continuum flow are established. The Stokes law and the analog of Darcy's law for fractal continuum flow are suggested. The pressure-transient equation accounting the fractal metric of fractal continuum flow is derived. The generalization of the pressure-transient equation accounting the fractal topology of fractal continuum flow is proposed. The mapping of fluid flow in a fractally permeable medium into a fractal continuum flow is discussed. It is stated that the spectral dimension of the fractal continuum flow d(s) is equal to its mass fractal dimension D, even when the spectral dimension of the fractally porous or fissured medium is less than D. A comparison of the fractal continuum flow approach with other models of fluid flow in fractally permeable media and the experimental field data for reservoir tests are provided. PMID:23004869
Map of fluid flow in fractal porous medium into fractal continuum flow
NASA Astrophysics Data System (ADS)
Balankin, Alexander S.; Elizarraraz, Benjamin Espinoza
2012-05-01
This paper is devoted to fractal continuum hydrodynamics and its application to model fluid flows in fractally permeable reservoirs. Hydrodynamics of fractal continuum flow is developed on the basis of a self-consistent model of fractal continuum employing vector local fractional differential operators allied with the Hausdorff derivative. The generalized forms of Green-Gauss and Kelvin-Stokes theorems for fractional calculus are proved. The Hausdorff material derivative is defined and the form of Reynolds transport theorem for fractal continuum flow is obtained. The fundamental conservation laws for a fractal continuum flow are established. The Stokes law and the analog of Darcy's law for fractal continuum flow are suggested. The pressure-transient equation accounting the fractal metric of fractal continuum flow is derived. The generalization of the pressure-transient equation accounting the fractal topology of fractal continuum flow is proposed. The mapping of fluid flow in a fractally permeable medium into a fractal continuum flow is discussed. It is stated that the spectral dimension of the fractal continuum flow ds is equal to its mass fractal dimension D, even when the spectral dimension of the fractally porous or fissured medium is less than D. A comparison of the fractal continuum flow approach with other models of fluid flow in fractally permeable media and the experimental field data for reservoir tests are provided.
Monodisperse and Polydisperse Particle Flow over a Backward Facing Step Preceding a Porous Medium
NASA Astrophysics Data System (ADS)
Chambers, Frank; Dange, Alok
2011-11-01
Computational Fluid Dynamic predictions were performed for the flow of monodisperse and polydisperse particles over a backward facing step with and without a porous medium downstream. The carrier fluid was air and the particles had a density of 500 kg/m3. Monodisperse particles with diameters of 10 and 40 microns and polydispersed particles from 1 to 50 microns with a Rosin-Rammler size distribution were used. The step had an expansion ratio of 2 and the step Reynolds numbers were 6550 and 10000. The k-epsilon RNG model with standard wall functions was used with FLUENT's discrete phase model for the particles. Velocity and particle residence time tracks were examined. The placement of the medium at 4.25h from the step was found to control the velocity profiles and the length of the recirculation zone while placement at 6.75h had negligible effects. The particle tracks show that more particles with lower Stokes number enter the recirculation zone while the particles with higher Stokes number tend to bypass the recirculation zone and move directly to the filter. The results for the monodispersed and the polydispersed particles appear virtually the same at low particle concentrations, but the polydispersed results provide a very good view of the phenomena.
Leis, Andrew P.; Schlicher, Sven; Franke, Hilmar; Strathmann, Martin
2005-01-01
We describe a novel and noninvasive, microscopy-based method for visualizing the structure and dynamics of microbial biofilms, individual fluorescent microbial cells, and inorganic colloids within a model porous medium. Biofilms growing in flow cells packed with granules of an amorphous fluoropolymer could be visualized as a consequence of refractive index matching between the solid fluoropolymer grains and the aqueous immersion medium. In conjunction with the capabilities of confocal microscopy for nondestructive optical sectioning, the use of amorphous fluoropolymers as a solid matrix permits observation of organisms and dynamic processes to a depth of 2 to 3 mm, whereas sediment biofilms growing in sand-filled flow cells can only be visualized in the region adjacent to the flow cell wall. This method differs fundamentally from other refractive index-matching applications in that optical transparency was achieved by matching a solid phase to water (and not vice versa), thereby permitting real-time microscopic studies of particulate-containing, low-refractive-index media such as biological and chromatographic systems. PMID:16085878
NASA Astrophysics Data System (ADS)
Mosthaf, K.; Baber, K.; Flemisch, B.; Helmig, R.; Leijnse, A.; Rybak, I.; Wohlmuth, B.
2011-10-01
Domains composed of a porous part and an adjacent free-flow region are of special interest in many fields of application. So far, the coupling of free flow with porous-media flow has been considered only for single-phase systems. Here we extend this classical concept to two-component nonisothermal flow with two phases inside the porous medium and one phase in the free-flow region. The mathematical modeling of flow and transport phenomena in porous media is often based on Darcy's law, whereas in free-flow regions the (Navier-) -Stokes equations are used. In this paper, we give a detailed description of the employed subdomain models. The main contribution is the developed coupling concept, which is able to deal with compositional (miscible) flow and a two-phase system in the porous medium. It is based on the continuity of fluxes and the assumption of thermodynamic equilibrium, and uses the Beavers-Joseph-Saffman condition. The phenomenological explanations leading to a simple, solvable model, which accounts for the physics at the interface, are laid out in detail. Our model can account for evaporation and condensation processes at the interface and is used to model evaporation from soil influenced by a wind field in a first numerical example.
An Amorphous Network Model for Capillary Flow and Dispersion in a Partially Saturated Porous Medium
NASA Astrophysics Data System (ADS)
Simmons, C. S.; Rockhold, M. L.
2013-12-01
Network models of capillary flow are commonly used to represent conduction of fluids at pore scales. Typically, a flow system is described by a regular geometric lattice of interconnected tubes. Tubes constitute the pore throats, while connection junctions (nodes) are pore bodies. Such conceptualization of the geometry, however, is questionable for the pore scale, where irregularity clearly prevails, although prior published models using a regular lattice have demonstrated successful descriptions of the flow in the bulk medium. Here a network is allowed to be amorphous, and is not subject to any particular lattice structure. Few network flow models have treated partially saturated or even multiphase conditions. The research trend is toward using capillary tubes with triangular or square cross sections that have corners and always retain some fluid by capillarity when drained. In contrast, this model uses only circular capillaries, whose filled state is controlled by a capillary pressure rule for the junctions. The rule determines which capillary participate in the flow under an imposed matric potential gradient during steady flow conditions. Poiseuille's Law and Laplace equation are used to describe flow and water retention in the capillary units of the model. A modified conjugate gradient solution for steady flow that tracks which capillary in an amorphous network contribute to fluid conduction was devised for partially saturated conditions. The model thus retains the features of classical capillary models for determining hydraulic flow properties under unsaturated conditions based on distribution of non-interacting tubes, but now accounts for flow exchange at junctions. Continuity of the flow balance at every junction is solved simultaneously. The effective water retention relationship and unsaturated permeability are evaluated for an extensive enough network to represent a small bulk sample of porous medium. The model is applied for both a hypothetically
Mass transport at the interface between a highly permeable porous medium and an open channel flow
NASA Astrophysics Data System (ADS)
Moretto, C.; Pokrajac, D.
2012-04-01
Hyporheic exchange has been extensively studied in the literature. The majority of papers present the results of field studies and the associated engineering simulation models. The number of laboratory studies is smaller. Most of them are focused on the bulk scale effects, since the measurements within the bed at the grain scale are difficult and therefore rare. Measurement within the pores of a permeable bed becomes possible for some idealized pore configurations. Pokrajac and Manes (2009) and Manes et al. (2009) use constant diameter spheres packed in a cubic pattern, which form straight pores (with variable cross-sectional area) in three orthogonal directions. Their results include detailed velocity measurements and the characteristics of turbulence at the fluid/porous interface, but not the mass transport. The experimental study reported here uses the same porous medium and extends this work by including grain-scale mass transport measurements. The results presented involve the hydrodynamics and the mass transport at the fluid/pore interface and within the first pore under the surface of the medium. The experiments are carried out in a 11m long and 40cm wide tilting flume. The porous medium, placed on the flume bed, is composed of 5 layers of 12mm diameter plastic spheres packed in a cubic pattern. This arrangement was chosen in order to have a regular matrix, thereby allowing measurements of the velocities and solute concentration within a pore. The measurement window covers a central section of a longitudinal pore which is visible through a lateral pore. The velocity field is measured by means of the Particle Image Velocimetry (PIV), and the concentration field is measured using the Laser Induced Fluorescence (LIF). These two techniques allow simultaneous non-intrusive measurements within a single pore. The experiments involved uniform, fully developed turbulent flow. The experimental conditions were: bed slope = 0.01, water depth = 45mm, depth
NASA Astrophysics Data System (ADS)
Gastone, Francesca; Tosco, Tiziana; Sethi, Rajandrea
2014-10-01
The present work is the first part of a comprehensive study on the use of guar gum to improve delivery of microscale zero-valent iron particles in contaminated aquifers. Guar gum solutions exhibit peculiar shear thinning properties, with high viscosity in static conditions and lower viscosity in dynamic conditions: this is beneficial both for the storage of MZVI dispersions, and also for the injection in porous media. In the present paper, the processes associated with guar gum injection in porous media are studied performing single-step and multi-step filtration tests in sand-packed columns. The experimental results of single-step tests performed by injecting guar gum solutions prepared at several concentrations and applying different dissolution procedures evidenced that the presence of residual undissolved polymeric particles in the guar gum solution may have a relevant negative impact on the permeability of the porous medium, resulting in evident clogging. The most effective preparation procedure which minimizes the presence of residual particles is dissolution in warm water (60 °C) followed by centrifugation (procedure T60C). The multi-step tests (i.e. injection of guar gum at constant concentration with a step increase of flow velocity), performed at three polymer concentrations (1.5, 3 and 4 g/l) provided information on the rheological properties of guar gum solutions when flowing through a porous medium at variable discharge rates, which mimic the injection in radial geometry. An experimental protocol was defined for the rheological characterization of the fluids in porous media, and empirical relationships were derived for the quantification of rheological properties and clogging with variable injection rate. These relationships will be implemented in the second companion paper (Part II) in a radial transport model for the simulation of large-scale injection of MZVI-guar gum slurries.
Gastone, Francesca; Tosco, Tiziana; Sethi, Rajandrea
2014-10-01
The present work is the first part of a comprehensive study on the use of guar gum to improve delivery of microscale zero-valent iron particles in contaminated aquifers. Guar gum solutions exhibit peculiar shear thinning properties, with high viscosity in static conditions and lower viscosity in dynamic conditions: this is beneficial both for the storage of MZVI dispersions, and also for the injection in porous media. In the present paper, the processes associated with guar gum injection in porous media are studied performing single-step and multi-step filtration tests in sand-packed columns. The experimental results of single-step tests performed by injecting guar gum solutions prepared at several concentrations and applying different dissolution procedures evidenced that the presence of residual undissolved polymeric particles in the guar gum solution may have a relevant negative impact on the permeability of the porous medium, resulting in evident clogging. The most effective preparation procedure which minimizes the presence of residual particles is dissolution in warm water (60°C) followed by centrifugation (procedure T60C). The multi-step tests (i.e. injection of guar gum at constant concentration with a step increase of flow velocity), performed at three polymer concentrations (1.5, 3 and 4g/l) provided information on the rheological properties of guar gum solutions when flowing through a porous medium at variable discharge rates, which mimic the injection in radial geometry. An experimental protocol was defined for the rheological characterization of the fluids in porous media, and empirical relationships were derived for the quantification of rheological properties and clogging with variable injection rate. These relationships will be implemented in the second companion paper (Part II) in a radial transport model for the simulation of large-scale injection of MZVI-guar gum slurries. PMID:25065767
Hrabe, Nikolas W.; Heinl, Peter; Bordia, Rajendra K.; Körner, Carolin; Fernandes, Russell J.
2013-01-01
Regular 3D periodic porous Ti-6Al-4 V structures were fabricated by the selective electron beam melting method (EBM) over a range of relative densities (0.17–0.40) and pore sizes (500–1500 μm). Structures were seeded with human osteoblast-like cells (SAOS-2) and cultured for four weeks. Cells multiplied within these structures and extracellular matrix collagen content increased. Type I and type V collagens typically synthesized by osteoblasts were deposited in the newly formed matrix with time in culture. High magnification scanning electron microscopy revealed cells attached to surfaces on the interior of the structures with an increasingly fibrous matrix. The in-vitro results demonstrate that the novel EBM-processed porous structures, designed to address the effect of stress-shielding, are conducive to osteoblast attachment, proliferation and deposition of a collagenous matrix characteristic of bone. PMID:23869614
Hayat, Tasawar; Rafiq, Maimona; Ahmad, Bashir
2016-01-01
The objective of present paper is to examine the peristaltic flow of magnetohydrodynamic (MHD) Jeffrey fluid saturating porous space in a channel through rotating frame. Unlike the previous attempts, the flow formulation is based upon modified Darcy's law porous medium effect in Jeffrey fluid situation. In addition the impacts due to Soret and Dufour effects in the radiative peristaltic flow are accounted. Rosseland's approximation has been utilized for the thermal radiative heat flux. Lubrication approach is implemented for the simplification. Resulting problems are solved for the stream function, temperature and concentration. Graphical results are prepared and analyzed for different parameters of interest entering into the problems. PMID:26808387
NASA Astrophysics Data System (ADS)
Das, K.
2014-03-01
This paper is devoted to investigate the influences of thermal radiation and temperature-dependent fluid properties on convective slip flow of slightly rarefied fluids over a porous wedge plate embedded in a Darcy-Forchheimer porous medium. Using the similarity transformation, the governing system of non-linear partial differential equations is transformed into similarity non-linear ordinary differential equations which are solved by employing a numerical shooting technique with a fourth-order Runge-Kutta integration scheme. Numerical results are analyzed for the effect of different pertinent parameters on the flow and heat transfer characteristics.
Hayat, Tasawar; Rafiq, Maimona; Ahmad, Bashir
2016-01-01
The objective of present paper is to examine the peristaltic flow of magnetohydrodynamic (MHD) Jeffrey fluid saturating porous space in a channel through rotating frame. Unlike the previous attempts, the flow formulation is based upon modified Darcy's law porous medium effect in Jeffrey fluid situation. In addition the impacts due to Soret and Dufour effects in the radiative peristaltic flow are accounted. Rosseland’s approximation has been utilized for the thermal radiative heat flux. Lubrication approach is implemented for the simplification. Resulting problems are solved for the stream function, temperature and concentration. Graphical results are prepared and analyzed for different parameters of interest entering into the problems. PMID:26808387
The flow of an aqueous foam through a two-dimensional porous medium
NASA Astrophysics Data System (ADS)
Dollet, B.; Jones, S. A.; Géraud, B.; Meheust, Y.; Cox, S. J.; Cantat, I.
2013-12-01
Flowing foams are used in many engineering and technical applications. A well-known application is oil recovery. Another one is the remediation of polluted soils: the foam is injected into the ground in order to mobilize chemical species present in the medium. Apart from potential interesting physico-chemical and biochemical properties, foams have peculiar flow properties that applications might benefit of. In particular, viscous dissipation arises mostly from the contact zones between the soap films and the walls, which results in peculiar friction laws allowing the foam to invade narrow pores more efficiently than Newtonian fluids would. We investigate the flow of a two-dimensional foam in three geometrical configurations. The flow velocity field and pressure field can both be reconstructed from the kinematics of the foam bubbles. We first consider a medium consisting of two parallel channels with different widths, at fixed medium porosity, that is, at fixed total combined width of the two channels. The flow behavior is highly dependent on the foam structure within the narrowest of the two channels [1]; consequently, the flux ratio between the two channels exhibits a non-monotonic dependence on the ratio of their widths. We then consider two parallel channels that are respectively convergent and divergent. The resulting flow kinematics imposes asymmetric bubble deformations in the two channels; these deformations strongly impact the foam/wall friction, and consequently the flux distribution between the two channels, causing flow irreversibility. We quantitatively predict the flux ratio as a function of the channel widths by modeling pressure drops of both viscous and capillary origins. This study reveals the crucial importance of boundary-induced bubble deformation on the mobility of a flowing foam. We then study how film-wall friction, capillary pressures and bubble deformation impact the flow of a foam in a two-dimensional porous medium consisting of randomly
Variation in Biofilm Stability with Decreasing pH Affects Porous Medium Hydraulic Properties
NASA Astrophysics Data System (ADS)
Kirk, M. F.; Santillan, E. F.; McGrath, L. K.; Altman, S. J.
2010-12-01
Changes to microbial communities caused by subsurface CO2 injection may have many consequences, including possible impacts to CO2 transport. We used column experiments to examine how decreasing pH, a geochemical change associated with CO2 injection, will affect biofilm stability and ultimately the hydraulic properties of porous media. Columns consisted of 1 mm2 square capillary tubes filled with 105-150 µm diameter glass beads. Artificial groundwater medium containing 1 mM glucose was pumped through the columns at a rate of 0.01 mL/min (q = 14.4 m/day; Re = 0.03). Columns were inoculated with 3 × 10^8 CFU (avg.) of Pseudomonas fluorescens, a model biofilm former, transformed with a green fluorescent protein. Biomass distribution and transport was examined using scanning laser confocal microscopy and effluent plating. Variation in the bulk hydraulic properties of the columns was measured using manometers. In an initial experiment, biofilm growth was allowed to occur for seven days in medium with pH 7.3. Within this period, cells uniformly coated bead surfaces, effluent cell numbers stabilized at 1 × 10^9 CFU/mL, and hydraulic conductivity (K) decreased 77%. Next, medium with pH 4 was introduced. As a result, biomass within the reactor redistributed from bead surfaces to pores, effluent cell numbers decreased to 3 × 10^5 CFU/mL, and K decreased even further (>94% reduction). This decreased K was maintained until the experiment was terminated, seven days after introducing low pH medium. These results suggest that changes in biomass distribution as a result of decreased pH may initially limit transport of solubility-trapped CO2 following CO2 injection. Experiments in progress and planned will test this result in more detail and over longer periods of time. This material is based upon work supported as part of the Center for Frontiers of Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office
NASA Astrophysics Data System (ADS)
Turkaya, Semih; Toussaint, Renaud; Eriksen, Fredrik; Zecevic, Megan; Daniel, Guillaume; Flekkøy, Eirik; Måløy, Knut Jørgen
2015-09-01
The characterization and understanding of rock deformation processes due to fluid flow is a challenging problem with numerous applications. The signature of this problem can be found in Earth Science and Physics, notably with applications in natural hazard understanding, mitigation or forecast (e.g. earthquakes, landslides with hydrological control, volcanic eruptions), or in industrial applications such as hydraulic-fracturing, steam-assisted gravity drainage, CO sequestration operations or soil remediation. Here we investigate the link between the visual deformation and the mechanical wave signals generated due to fluid injection into porous media. In a rectangular Hele-Shaw Cell, side air injection causes burst movement and compaction of grains along with channeling (creation of high permeability channels empty of grains). During the initial compaction and emergence of the main channel, the hydraulic fracturing in the medium generates a large non-impulsive low frequency signal in the frequency range 100 Hz - 10 kHz. When the channel network is established, the relaxation of the surrounding medium causes impulsive aftershock-like events, with high frequency (above 10 kHz) acoustic emissions, the rate of which follows an Omori Law. These signals and observations are comparable to seismicity induced by fluid injection. Compared to the data obtained during hydraulic fracturing operations, low frequency seismicity with evolving spectral characteristics have also been observed. An Omori-like decay of microearthquake rates is also often observed after injection shut-in, with a similar exponent p≃0.5 as observed here, where the decay rate of aftershock follows a scaling law dN/dt ∝(t-t₀ )-p . The physical basis for this modified Omori law is explained by pore pressure diffusion affecting the stress relaxation.
NASA Astrophysics Data System (ADS)
Mehta, C. B.; Singh, M.; Kumar, S.
2016-02-01
An investigation is made on the effect of Hall currents on thermal instability of a compressible couple-stress fluid in the presence of a horizontal magnetic field saturated in a porous medium. The analysis is carried out within the framework of the linear stability theory and normal mode technique. A dispersion relation governing the effects of viscoelasticity, Hall currents, compressibility, magnetic field and porous medium is derived. For the stationary convection a couple-stress fluid behaves like an ordinary Newtonian fluid due to the vanishing of the viscoelastic parameter. Compressibility, the magnetic filed and couple-stress parameter have stabilizing effects on the system whereas Hall currents and medium permeability have a destabilizing effect on the system, but in the absence of Hall current couple-stress has a destabilizing effect on the system. It has been observed that oscillatory modes are introduced due to the presence of viscoelasticity, magnetic field porous medium and Hall currents which were non-existent in their absence.
NASA Astrophysics Data System (ADS)
Mayer, Alex S.; Miller, Cass T.
1992-11-01
A series of experiments was performed to characterize the morphologic distribution of nonaqueous-phase liquids (NAPL's) at residual saturation, as a function of porous medium size. Morphologic characterization of NAPL distributions was accomplished using a novel in situ polymerization technique. The porous medium consisted of glass beads. Blob length, volume and shape characteristics were determined for each experiment, and pore size distributions were determined through capillary pressure-saturation experiments. Both the blob lenght and pore size distributions were fitted to a van Genuchten function. Both blob lenght and pressure-saturation data could be scaled with the same averaged porous medium characteristics. The blob length distributions were found to be wider than the pore size distributions. Estimates of representative elementary volumes (REV's) were generated from statistical analysis using a van Genuchten cumulative frequency distribution function for blob lenght and an empirical function for blob volume as a function of blob length. Simulations were also performed using a Monte Carlo method. The size of the REV needed for a given level of prediction of the residual saturation level was found to increase as a function of mean particle volume for the similar used in this study. Extrapolation of the REV analysis suggests that the size of an REV will increase rapidly as uniformity of the medium decreases. If this extrapolation holds true, significant uncertainty would exist in most determination of residual saturation for poorly sorted media that have been reported to date.
Aziz, Asim; Siddique, J. I.; Aziz, Taha
2014-01-01
In this paper, a simplified model of an incompressible fluid flow along with heat and mass transfer past a porous flat plate embedded in a Darcy type porous medium is investigated. The velocity, thermal and mass slip conditions are utilized that has not been discussed in the literature before. The similarity transformations are used to transform the governing partial differential equations (PDEs) into a nonlinear ordinary differential equations (ODEs). The resulting system of ODEs is then reduced to a system of first order differential equations which was solved numerically by using Matlab bvp4c code. The effects of permeability, suction/injection parameter, velocity parameter and slip parameter on the structure of velocity, temperature and mass transfer rates are examined with the aid of several graphs. Moreover, observations based on Schmidt number and Soret number are also presented. The result shows, the increase in permeability of the porous medium increase the velocity and decrease the temperature profile. This happens due to a decrease in drag of the fluid flow. In the case of heat transfer, the increase in permeability and slip parameter causes an increase in heat transfer. However for the case of increase in thermal slip parameter there is a decrease in heat transfer. An increase in the mass slip parameter causes a decrease in the concentration field. The suction and injection parameter has similar effect on concentration profile as for the case of velocity profile. PMID:25531301
Parameters analysis of a porous medium model for treatment with hyperthermia using OpenMP
NASA Astrophysics Data System (ADS)
Freitas Reis, Ruy; dos Santos Loureiro, Felipe; Lobosco, Marcelo
2015-09-01
Cancer is the second cause of death in the world so treatments have been developed trying to work around this world health problem. Hyperthermia is not a new technique, but its use in cancer treatment is still at early stage of development. This treatment is based on overheat the target area to a threshold temperature that causes cancerous cell necrosis and apoptosis. To simulate this phenomenon using magnetic nanoparticles in an under skin cancer treatment, a three-dimensional porous medium model was adopted. This study presents a sensibility analysis of the model parameters such as the porosity and blood velocity. To ensure a second-order solution approach, a 7-points centered finite difference method was used for space discretization while a predictor-corrector method was used to time evolution. Due to the massive computations required to find the solution of a three-dimensional model, this paper also presents a first attempt to improve performance using OpenMP, a parallel programming API.
An adaptive lattice Boltzmann scheme for modeling two-fluid-phase flow in porous medium systems
NASA Astrophysics Data System (ADS)
Dye, Amanda L.; McClure, James E.; Adalsteinsson, David; Miller, Cass T.
2016-04-01
We formulate a multiple-relaxation-time (MRT) lattice-Boltzmann method (LBM) to simulate two-fluid-phase flow in porous medium systems. The MRT LBM is applied to simulate the displacement of a wetting fluid by a nonwetting fluid in a system corresponding to a microfluidic cell. Analysis of the simulation shows widely varying time scales for the dynamics of fluid pressures, fluid saturations, and interfacial curvatures that are typical characteristics of such systems. Displacement phenomena include Haines jumps, which are relatively short duration isolated events of rapid fluid displacement driven by capillary instability. An adaptive algorithm is advanced using a level-set method to locate interfaces and estimate their rate of advancement. Because the displacement dynamics are confined to the interfacial regions for a majority of the relaxation time, the computational effort is focused on these regions. The proposed algorithm is shown to reduce computational effort by an order of magnitude, while yielding essentially identical solutions to a conventional fully coupled approach. The challenges posed by Haines jumps are also resolved by the adaptive algorithm. Possible extensions to the advanced method are discussed.
Larabi, Mohamed Aziz; Mutschler, Dimitri; Mojtabi, Abdelkader
2016-06-28
Our present work focuses on the coupling between thermal diffusion and convection in order to improve the thermal gravitational separation of mixture components. The separation phenomenon was studied in a porous medium contained in vertical columns. We performed analytical and numerical simulations to corroborate the experimental measurements of the thermal diffusion coefficients of ternary mixture n-dodecane, isobutylbenzene, and tetralin obtained in microgravity in the international space station. Our approach corroborates the existing data published in the literature. The authors show that it is possible to quantify and to optimize the species separation for ternary mixtures. The authors checked, for ternary mixtures, the validity of the "forgotten effect hypothesis" established for binary mixtures by Furry, Jones, and Onsager. Two complete and different analytical resolution methods were used in order to describe the separation in terms of Lewis numbers, the separation ratios, the cross-diffusion coefficients, and the Rayleigh number. The analytical model is based on the parallel flow approximation. In order to validate this model, a numerical simulation was performed using the finite element method. From our new approach to vertical separation columns, new relations for mass fraction gradients and the optimal Rayleigh number for each component of the ternary mixture were obtained. PMID:27369539
Nilson, R.H.; Lie, K.H. )
1987-12-01
A double-porosity model is used to describe the oscillatory gas motion and associated contaminant transport induced by cyclical variations in the barometric pressure at the surface of a fractured porous medium. Flow along the fractures and within the permeable matrix blocks is locally one-dimensional. The interaction between fractures and blocks includes the Darcian seepage of fluid as well as the Fickian diffusion of contaminant. To guard against artificial numerical diffusion, the FRAM filtering remedy and methodology of Chapman is used in calculating the advective fluxes along fractures and within blocks. The entire system of equations, including the fracture/matrix interaction terms, is solved by a largely implicit non-computational time step is large compared to the cross-block transit time of Darcian pressure waves. The numerical accuracy is tested by comparison with exact solutions for oscillatory and unidirectional flows, some of which include Darcian seepage or Fickian diffusion interaction between the fracture and the matrix. The method is used to estimate the rate of transport of radioactive gases through the rubblized chimney produced by an underground nuclear explosion.
Convection and reaction in a diffusive boundary layer in a porous medium: Nonlinear dynamics
NASA Astrophysics Data System (ADS)
Andres, Jeanne Therese H.; Cardoso, Silvana S. S.
2012-09-01
We study numerically the nonlinear interactions between chemical reaction and convective fingering in a diffusive boundary layer in a porous medium. The reaction enhances stability by consuming a solute that is unstably distributed in a gravitational field. We show that chemical reaction profoundly changes the dynamics of the system, by introducing a steady state, shortening the evolution time, and altering the spatial patterns of velocity and concentration of solute. In the presence of weak reaction, finger growth and merger occur effectively, driving strong convective currents in a thick layer of solute. However, as the reaction becomes stronger, finger growth is inhibited, tip-splitting is enhanced and the layer of solute becomes much thinner. Convection enhances the mass flux of solute consumed by reaction in the boundary layer but has a diminishing effect as reaction strength increases. This nonlinear behavior has striking differences to the density fingering of traveling reaction fronts, for which stronger chemical kinetics result in more effective finger merger owing to an increase in the speed of the front. In a boundary layer, a strong stabilizing effect of reaction can maintain a long-term state of convection in isolated fingers of wavelength comparable to that at onset of instability.
Effect of first-order chemical reaction on gravitational instability in a porous medium.
Kim, Min Chan; Choi, Chang Kyun
2014-11-01
To understand the CO_{2} sequestration in the saline aquifer, the effect of a first-order chemical reaction on the onset of the buoyancy-driven instability in an isotropic reactive porous medium is analyzed theoretically. Under the linear stability theory, the stability equations are derived in the semi-infinite domain and they are solved with and without the quasi-steady-state approximation. We also considered the stability of the reactive system at a steady-state limit. The analysis for the steady-state case proposed that the onset of instability motion can occur during the transient period even if the system is stable at the steady state. Through the initial growth rate analysis the most unstable initial disturbance is determined, and it is found that initially the system is unconditionally stable regardless of the Damköhler number D_{a} and the Darcy-Rayleigh number Ra. Based on the results of the initial growth rate analysis, the direct numerical simulation is also conducted by using the Fourier pseudospectral method. The present theoretical and numerical analyses suggest that the chemical reaction makes the system stable and no convective motion can be expected for D_{a}/Ra^{2}>2.5×10^{-3}. PMID:25493890
NASA Astrophysics Data System (ADS)
Larabi, Mohamed Aziz; Mutschler, Dimitri; Mojtabi, Abdelkader
2016-06-01
Our present work focuses on the coupling between thermal diffusion and convection in order to improve the thermal gravitational separation of mixture components. The separation phenomenon was studied in a porous medium contained in vertical columns. We performed analytical and numerical simulations to corroborate the experimental measurements of the thermal diffusion coefficients of ternary mixture n-dodecane, isobutylbenzene, and tetralin obtained in microgravity in the international space station. Our approach corroborates the existing data published in the literature. The authors show that it is possible to quantify and to optimize the species separation for ternary mixtures. The authors checked, for ternary mixtures, the validity of the "forgotten effect hypothesis" established for binary mixtures by Furry, Jones, and Onsager. Two complete and different analytical resolution methods were used in order to describe the separation in terms of Lewis numbers, the separation ratios, the cross-diffusion coefficients, and the Rayleigh number. The analytical model is based on the parallel flow approximation. In order to validate this model, a numerical simulation was performed using the finite element method. From our new approach to vertical separation columns, new relations for mass fraction gradients and the optimal Rayleigh number for each component of the ternary mixture were obtained.
NASA Astrophysics Data System (ADS)
Dobberschütz, Sören; Böhm, Michael
2010-02-01
The behaviour of a free fluid flow above a porous medium, both separated by a curved interface, is investigated. By carrying out a coordinate transformation, we obtain the description of the flow in a domain with a straight interface. Using periodic homogenisation, the effective behaviour of the transformed partial differential equations in the porous part is given by a Darcy law with non-constant permeability matrix. Then the fluid behaviour at the porous-liquid interface is obtained with the help of generalised boundary-layer functions: Whereas the velocity in normal direction is continuous across the interface, a jump appears in tangential direction. Its magnitude seems to be related to the slope of the interface. Therefore the results indicate a generalised law of Beavers and Joseph.
NASA Astrophysics Data System (ADS)
Ciriello, Valentina; Longo, Sandro; Chiapponi, Luca; Di Federico, Vittorio
2016-06-01
We develop a model to grasp the combined effect of rheology and spatial stratifications on two-dimensional non-Newtonian gravity-driven flow in porous media. We consider a power-law constitutive equation for the fluid, and a monomial variation of permeability and porosity along the vertical direction (transverse to the flow) or horizontal direction (parallel to the flow). Under these assumptions, similarity solutions are derived in semi-analytical form for thin gravity currents injected into a two-dimensional porous medium and having constant or time-varying volume. The extent and shape of the porous domain affected by the injection is significantly influenced by the interplay of model parameters. These describe the fluid (flow behaviour index n), the spatial heterogeneity (coefficients β, γ, δ, ω for variations of permeability and porosity in the horizontal or vertical direction), and the type of release (volume exponent α). Theoretical results are validated against two sets of experiments with α = 1 (constant inflow) conducted with a stratified porous medium (simulated by superimposing layers of glass beads of different diameter) and a Hele-Shaw analogue for power-law fluid flow, respectively. In the latter case, a recently established Hele-Shaw analogy is extended to the variation of properties parallel to the flow direction. Comparison with experimental results shows that the proposed model is able to capture the propagation of the current front and the current profile.
pH-dependent transport of metals through a reactive porous medium
NASA Astrophysics Data System (ADS)
Prigiobbe, V.; Bryant, S. L.
2013-12-01
Here we present a study on the effect of pH-dependent adsorption and hydrodynamic dispersion on metal transport through a reactive porous medium with hydrophilic surface. We investigate how the migration of a certain fraction of a metal can be facilitated by its competitive adsorption with protons. We performed laboratory experiments using a chromatographic column filled with silica beads coated with hydrous ferric oxide (HFO) and flooded initially with an acidic solution (pH 3) and then with an alkaline solution (pH > 7) containing either sodium, potassium, lithium, calcium, magnesium, strontium, or barium cations. Concentrations were chosen for which nonclassical transport is predicted. Highly resolved breakthrough curves measured with inline ion chromatography allowed us to observe in all cases the formation of a fast wave/pulse traveling at the interstitial fluid velocity and a retarded front. Classical theory of reactive transport through porous media predicts the formation of only the retarded front and assumes that hydrodynamic dispersion only smooths it without introducing an additional wave. Therefore, the fast wave is a notable exception to this theory. The mechanism responsible for this phenomenon is due to the interplay between hydrodynamic dispersion and pH-dependent adsorption. Hydrodynamic dispersion broadens the metal concentration front at the inlet of the column and creates a mixing zone where the high-pH solution containing the metal mixes with the low-pH solution initially present in the system. The resulting pH of the mixing zone spans a range where both the adsorption and the retardation of the metal are negligible. This leads to the formation of a metal plume, which then separates from the retarded front traveling at the interstitial fluid velocity as an isolated pulse. This fast transport phenomenon operates independently of other modes of rapid transport, such as colloid-facilitated transport and flow in fractures. A one
Doughty, C.; Pruess, K.
1991-06-01
Over the past few years the authors have developed a semianalytical solution for transient two-phase water, air, and heat flow in a porous medium surrounding a constant-strength linear heat source, using a similarity variable {eta} = r/{radical}t. Although the similarity transformation approach requires a simplified geometry, all the complex physical mechanisms involved in coupled two-phase fluid and heat flow can be taken into account in a rigorous way, so that the solution may be applied to a variety of problems of current interest. The work was motivated by adverse to predict the thermohydrological response to the proposed geologic repository for heat-generating high-level nuclear wastes at Yucca Mountain, Nevada, in a partially saturated, highly fractured volcanic formation. The paper describes thermal and hydrologic conditions near the heat source; new features of the model; vapor pressure lowering; and the effective-continuum representation of a fractured/porous medium.
NASA Astrophysics Data System (ADS)
Singh, M.; Mehta, C. B.
2015-05-01
Rayleigh-Taylor instability of two superposed Walters' B has elastico-viscous fluids in a uniform magnetic field through a porous medium with different permeability been studied to include the suspended (dust) particles effect. Using normal mode technique a dispersion relation has been derived. The stability analysis has been carried out. The magnetic field stabilizes the unstable configuration for the wave number band K > K* in which the system is unstable in the absence of the magnetic field. It is also found that for a potential stable arrangement for Walters B' elastico-viscous fluids of different permeabilities in the presence of suspended particles through a porous medium the system is stable, whereas in the potentially unstable case instability of the system occurs.
NASA Astrophysics Data System (ADS)
Jackson, A. S.; Rybak, I.; Helmig, R.; Gray, W. G.; Miller, C. T.
2012-06-01
This work is the ninth in a series of papers on the thermodynamically constrained averaging theory (TCAT) approach for modeling flow and transport phenomena in multiscale porous medium systems. A fundamental approach is developed to model the transition region between a two-fluid-phase porous medium system and a single-fluid-phase system, including species transport. A general model formulation is developed along with an entropy inequality to guide the specification of closure relations. The general model formulation and entropy inequality are then used to specify a closed system. The transition region model developed in this work is a generalization and extension of coupling conditions commonly used in sharp interface models. The theoretical framework has multiple areas of potential applicability including terrestrial-atmospheric contact zones, surface water-sediment interface zones, and industrial drying processes.
NASA Astrophysics Data System (ADS)
Sharma, Mukesh Kumar; Bansal, Kuldip; Bansal, Seema
2012-09-01
The periodic nature of the cardiac cycle induces a pulsatile, unsteady flow within the circulatory system. The pulsatile model of blood flow provides data to analyse the physiological situation in close proximity. The distribution of fatty cholesterol and artery-clogging blood clots in the lumen of the coronary artery is assumed as a porous medium. A mathematical model for pulsatile flow through an stenosed artery filled with porous medium in the presence of transverse static magnetic field has been formulated under the consideration of hematocrit dependent viscosity of blood that governed by Einstein equation. The velocity profile, volume flux, pressure gradient and wall shear stress are obtained and the effects of magnetic number, Darcy number, Womersely number are computed and represented through graphs.
Mojtabi, A. ); Charrier-Mojtabi, M.C. )
1992-11-01
Natural convection flows in a cylindrical annular porous medium have been studied extensively over the last twenty years. The main results concern the two-dimensional steady state. Several techniques have been developed, such as the finite difference method (Caltagirone, 1976), the finite element method (Mojtabi et al., 1987), and the spectral method (Charrier-Mojtabi and Caltagirone, 1980; Rao et al., 1987; Himasekhar and Bau, 1988; Charrier-Mojtabi et al., 1991). 6 refs., 3 tabs.
NASA Astrophysics Data System (ADS)
Timoumi, M.; Chérif, B.; Sifaoui, M. S.
2005-12-01
In this paper, heat transfer problem through a semi-transparent porous medium in a cylindrical enclosure is investigated. The governing equations for this problem and the boundary conditions are non-linear differential equations depending on the dimensionless radial coordinate, Planck number N, scattering albedo ω, walls emissivity and thermal conductivity ratio kr. The set of differential equations are solved by a numerical technique taken from the IMSL MATH/LIBRARY. Various results are obtained for the dimensionless temperature profiles in the solid and fluid phases and the radiative heat flux. The effects of some radiative properties of the medium on the heat transfer rate are examined.
Free convection flow of non-Newtonian fluids along a vertical plate embedded in a porous medium
Han-Taw Chen; Cha'o-Kuang Chen )
1988-02-01
The problem of free convection flow of a non-Newtonian power law fluid along an isothermal vertical flat plate embedded in the porous medium is considered in the present study. The physical coordinate system is shown schematically in Fig 1. In the present study, it is assumed that the modified Darcy law and the boundary layer approximation are applicable. This implies that the present solutions are valid at a high Rayleigh number. With these simplifications, the governing partial nonlinear differential equations can be transformed into a set of coupled ordinary differential equations which can be solved by the fourth-order Runge-Kutta method. Algebraic equations for heat transfer rate and boundary layer thickness as a function of the prescribed wall temperature and physical properties of liquid-porous medium are obtained. The similarity solutions can be applied to problems in geophysics and engineering. The primary purpose of the present study is to predict the characteristics of steady natural convection heat transfer using the model of the flow of a non-Newtonian power law fluid in a porous medium given by Dharmadhikari and Kale (1985). Secondly, the effects of the new power law index n on heat transfer are investigated.
Bubbling behaviors induced by gas-liquid mixture permeating through a porous medium
NASA Astrophysics Data System (ADS)
Hu, Liang; Li, Mingbo; Chen, Wenyu; Xie, Haibo; Fu, Xin
2016-08-01
This paper investigates the bubbling behaviors induced by gas-liquid mixture permeating through porous medium (PM), which was observed in developing immersion lithography system and was found having great differences with traditional bubbling behaviors injected with only gas phase through the PM. An experimental setup was built up to investigate the bubbling characteristics affected by the mixed liquid phase. Both the flow regimes of gas-liquid mixture in micro-channel (upstream of the PM) and the bubbling flow regimes in water tank (downstream of the PM) were recorded synchronously by high-speed camera. The transitions between the flow regimes are governed by gas and liquid Weber numbers. Based on the image analysis, the characteristic parameters of bubbling region, including the diameter of bubbling area on PM surface, gas-phase volume flux, and dispersion angle of bubbles in suspending liquid, were studied under different proportions of gas and liquid flow rate. Corresponding empirical correlations were developed to describe and predict these parameters. Then, the pertinent bubble characteristics in different bubbling flow regimes were systematically investigated. Specifically, the bubble size distribution and the Sauter mean diameter affected by increasing liquid flow rate were studied, and the corresponding analysis was given based on the hydrodynamics of bubble-bubble and bubble-liquid interactions. According to dimensionless analysis, the general prediction equation of Sauter mean diameter under different operating conditions was proposed and confirmed by experimental data. The study of this paper is helpful to improve the collection performance of immersion lithography and aims to reveal the differences between the bubbling behaviors on PM caused by only gas flow and gas-liquid mixture flow, respectively, for the researches of fluid flow.
NASA Astrophysics Data System (ADS)
Hauswirth, Scott C.; Miller, Cass T.
2014-10-01
The remediation of former manufactured gas plant (FMGP) sites contaminated with tar DNAPLs (dense non-aqueous phase liquids) presents a significant challenge. The tars are viscous mixtures of thousands of individual compounds, including known and suspected carcinogens. This work investigates the use of combinations of mobilization, solubilization, and chemical oxidation approaches to remove and degrade tars and tar components in porous medium systems. Column experiments were conducted using several flushing solutions, including an alkaline-polymer (AP) solution containing NaOH and xanthan gum (XG), a surfactant-polymer (SP) solution containing Triton X-100 surfactant (TX100) and XG, an alkaline-surfactant-polymer (ASP) solution containing NaOH, TX100, and XG, and base-activated sodium persulfate both with and without added TX100. The effectiveness of the flushing solutions was assessed based on both removal of polycyclic aromatic hydrocarbon (PAH) mass and on the reduction of dissolved-phase PAH concentrations. SP flushes of 6.6 to 20.9 PV removed over 99% of residual PAH mass and reduced dissolved-phase concentrations by up to two orders of magnitude. ASP flushing efficiently removed 95-96% of residual PAH mass within about 2 PV, and significantly reduced dissolved-phase concentrations of several low molar mass compounds, including naphthalene, acenaphthene, fluorene, and phenanthrene. AP flushing removed a large portion of the residual tar (77%), but was considerably less effective than SP and ASP in terms of the effect on dissolved PAH concentrations. Persulfate was shown to oxidize tar components, primarily those with low molar mass, however, the overall degradation was relatively low (30-50% in columns with low initial tar saturations), and the impact on dissolved-phase concentrations was minimal.
NASA Astrophysics Data System (ADS)
Roux, N.; Costard, F.; Grenier, C. F.
2013-12-01
In permafrost-affected regions, hydrological changes due to global warming are still under investigation. But yet, we can already foresee from recent studies that for example, the variability and intensity of surface/subsurface flow are likely to be affected by permafrost degradation. And the feedback induced by such changes on permafrost degradation is still not clearly assessed. Of particular interest are lake and river-taliks. A talik is a permanently unfrozen zone that lies below rivers or lake. They should play a key role in these interactions given that they are the only paths for groundwater flow in permafrost regions. Thus heat transfers on a regional scale are potentially influenced by groundwater circulation. The aim of our study is therefore to investigate the evolution of river taliks. We developed a multidisciplinary approach coupling field investigation, experimental studies in a cold room and numerical modeling. In Central Yakutia, Siberia, where permafrost is continuous, we recently installed instruments to monitor ground temperature and water pressure in a river talik between two thermokarst lakes. We present here the coupling of numerical modeling and laboratory experiments in order to look after the main parameters controlling river-talik installation. In a cold room at IDES, where a metric scale channel is filled with sand as a porous medium, we are able to control air, water and permafrost temperature, but also water flow, so that we can test various parameter sets for a miniaturized river. These results are confronted with a numerical model developed at the LSCE with Cast3m (www-cast3m.cea.fr), that couples heat and water transfer. In particular, expressions for river-talik heat exchange terms are investigated. A further step will come in the near future with results from field investigation providing the full complexity of a natural system. Keywords: Talik, River, Numerical Modeling, Cold Room, Permafrost.
Co-symmetry breakdown in problems of thermal convection in porous medium
NASA Astrophysics Data System (ADS)
Bratsun, Dmitry A.; Lyubimov, Dmitry V.; Roux, Bernard
We investigate two-dimensional thermal convection of saturating incompressible fluid in a horizontal cylinder filled with porous medium. The temperature distribution on the boundaries is time-independent and corresponds to the heating from below. At supercritical parameter values the problem has infinite number of stationary solutions for arbitrary shape of the region. This degeneracy is connected with the so-called co-symmetry property: the existence of the vector field which is orthogonal to the considered one. Non-coincidence of zeroes of these two fields leads generally speaking, to the degeneracy of the solutions. To destroy the degeneracy we add weak fluid seeping of the fluid through the boundaries either in vertical or in the horizontal direction. The breakdown of the family of the stationary solutions at high supercritical values of the Rayleigh number is studied in detail with the help of the corresponding normal form. Several limit cycles with the twisted leading manifolds appear as a result of the family destruction. To investigate the dynamical behavior the finite-dimensional models of the convection which maintain the breakdown of co-symmetry, are constructed on the base of the Galerkin approximation. The same scenario of the transition to chaos which seems to be connected with the co-symmetry breakdown, is recovered for both kinds of seeping. The quasi-periodic solution branches from the limit cycle. The further increase of the Peclet number leads to mode-locking, which is followed by the appearance of the homoclinic surface formed by the unstable manifold of the saddle periodic orbit; destruction of the latter surface leaves in the phase space the object with torus-like shape and non-integer fractal dimension.
Nonlinear instability of an Oldroyd elastico–viscous magnetic nanofluid saturated in a porous medium
Moatimid, Galal M.; Alali, Elham M. M. Ali, Hoda S. M.
2014-09-15
Through viscoelastic potential theory, a Kelvin-Helmholtz instability of two semi-infinite fluid layers, of Oldroydian viscoelastic magnetic nanofluids (MNF), is investigated. The system is saturated by porous medium through two semi-infinite fluid layers. The Oldroyd B model is utilized to describe the rheological behavior of viscoelastic MNF. The system is influenced by uniform oblique magnetic field that acts at the surface of separation. The model is used for the MNF incorporated the effects of uniform basic streaming and viscoelasticity. Therefore, a mathematical simplification must be considered. A linear stability analysis, based upon the normal modes analysis, is utilized to find out the solutions of the equations of motion. The onset criterion of stability is derived; analytically and graphs have been plotted by giving numerical values to the various parameters. These graphs depict the stability characteristics. Regions of stability and instability are identified and discussed in some depth. Some previous studies are recovered upon appropriate data choices. The stability criterion in case of ignoring the relaxation stress times is also derived. To relax the mathematical manipulation of the nonlinear approach, the linearity of the equations of motion is taken into account in correspondence with the nonlinear boundary conditions. Taylor's theory is adopted to expand the governing nonlinear characteristic equation according to of the multiple time scales technique. This analysis leads to the well-known Ginzburg–Landau equation, which governs the stability criteria. The stability criteria are achieved theoretically. To simplify the mathematical manipulation, a special case is considered to achieve the numerical estimations. The influence of orientation of the magnetic fields on the stability configuration, in linear as well as nonlinear approaches, makes a dual role for the magnetic field strength in the stability graphs. Stability diagram is plotted for
Shi, Jia-Le; Tang, Cheng; Peng, Hong-Jie; Zhu, Lin; Cheng, Xin-Bing; Huang, Jia-Qi; Zhu, Wancheng; Zhang, Qiang
2015-10-21
A nanostructured carbon with high specific surface area (SSA), tunable pore structure, superior electrical conductivity, mechanically robust framework, and high chemical stability is an important requirement for electrochemical energy storage. Porous graphene fabricated by chemical activation and liquid etching has a high surface area but very limited volume of electrochemically accessible mesopores. Herein, an effective strategy of in situ formation of hierarchically mesoporous oxide templates with small pores induced by Kirkendall diffusion and large pores attributed to evaporation of deliberately introduced volatile metal is proposed for chemical vapor deposition assembly of porous graphene frameworks (PGFs). The PGFs inherit the hierarchical mesoporous structure of the templates. A high SSA of 1448 m(2) g(-1), 91.6% of which is contributed by mesopores, and a mesopore volume of 2.40 cm(3) g(-1) are attained for PGFs serving as reservoirs of ions or active materials in electrochemical energy storage applications. When the PGFs are applied in lithium-sulfur batteries, a very high sulfur utilization of 71% and a very low fading rate of ≈0.04% per cycle after the second cycle are achieved at a current rate of 1.0 C. This work provides a general strategy for the rational construction of mesoporous structures induced by a volatile metal, with a view toward the design of hierarchical nanomaterials for advanced energy storage. PMID:26265205
Zhang, Qingchun; Tan, Ke; Zhang, Yan; Ye, Zhaoyang; Tan, Wen-Song; Lang, Meidong
2014-01-13
In tissue engineering, incorporation of bone morphogenetic protein-2 (BMP-2) into biomaterial scaffolds is an attractive strategy to stimulate bone repair. However, suboptimal release of BMP-2 remains a great concern, which may cause unfavorable bone formation as well as severe inflammation. In this study, genipin-cross-linked gelatin entrapped with recombinant human BMP-2 (rhBMP-2) was exploited to decorate the interior surface of three-dimensional porous poly(ε-caprolactone) (PCL) scaffolds. With gelatin-coating, PCL scaffolds demonstrated enhanced water uptake and improved compressive moduli. Intriguingly, a unique release profile of rhBMP-2 composed of a transient burst release followed by a sustained release was achieved in coated scaffolds. These coated scaffolds well supported growth and osteogenesis of human mesenchymal stem cells (hMSCs) in vitro, indicating the retaining of rhBMP-2 bioactivity. When hMSCs-seeded scaffolds were implanted subcutaneously in nude mice for 4 weeks, better bone formation was observed in gelatin/rhBMP-2-coated scaffolds. Specifically, the spatial distribution of newly formed bone was more uniform in gelatin-coated scaffolds than in uncoated scaffolds, which displayed preferential bone formation at the periphery. These results collectively demonstrated that gelatin-coating of porous PCL scaffolds is a promising approach for delivering rhBMP-2 to stimulate improved bone regeneration. PMID:24266740
Huang, Wei E; Oswald, Sascha E; Lerner, David N; Smith, Colin C; Zheng, Chunmiao
2003-05-01
A novel combination of noninvasive imaging with an oxygen sensitive fluorescent indicator was developed to investigate the biodegradation processes occurring at the fringe of a solute plume, where the supply of oxygen was limited. A thin transparent porous matrix (156 x 120 x 3 mm) was made from quartz plates and quartz sand (212-300 microm) and enriched with acetate-degrading bacteria. A degrading plume developed from a continuous acetate source in the uniform flow field containing dissolved oxygen. Ruthenium (II)-dichlorotris(1,10-phenanthroline) (Ru(phen)3Cl2), a water-soluble fluorescent dye, was used as an indicator of dissolved oxygen. The fluorescence intensity was dependent on the concentration of oxygen because the dissolved oxygen acted as collisional quencher. The oxygen distribution was interpreted from images recorded by a CCD camera. These two-dimensional experimental results showed quantitatively how the oxygen concentrations decreased strongly at the narrow plume fringe and that oxygen was depleted at the core of the plume. Separately, dispersivity was measured in a series of nonreactive transport experiments, and biodegradation parameters were evaluated by batch experiments. Two-dimensional numerical simulations with MT3D/RT3D used these parameters, and the predicted oxygen distributions were compared with the experimental results. This measurement method provides a novel approach to investigate details of solute transport and biodegradation in porous media. PMID:12775064
Huang, Shao-Zhuan; Jin, Jun; Cai, Yi; Li, Yu; Deng, Zhao; Zeng, Jun-Yang; Liu, Jing; Wang, Chao; Hasan, Tawfique; Su, Bao-Lian
2015-01-01
Bicontinuous hierarchically porous Mn2O3 single crystals (BHP-Mn2O3-SCs) with uniform parallelepiped geometry and tunable sizes have been synthesized and used as anode materials for lithium-ion batteries (LIBs). The monodispersed BHP-Mn2O3-SCs exhibit high specific surface area and three dimensional interconnected bimodal mesoporosity throughout the entire crystal. Such hierarchical interpenetrating porous framework can not only provide a large number of active sites for Li ion insertion, but also good conductivity and short diffusion length for Li ions, leading to a high lithium storage capacity and enhanced rate capability. Furthermore, owing to their specific porosity, these BHP-Mn2O3-SCs as anode materials can accommodate the volume expansion/contraction that occurs with lithium insertion/extraction during discharge/charge processes, resulting in their good cycling performance. Our synthesized BHP-Mn2O3-SCs with a size of ~700 nm display the best electrochemical performance, with a large reversible capacity (845 mA h g(-1) at 100 mA g(-1) after 50 cycles), high coulombic efficiency (>95%), excellent cycling stability and superior rate capability (410 mA h g(-1) at 1 Ag(-1)). These values are among the highest reported for Mn2O3-based bulk solids and nanostructures. Also, electrochemical impedance spectroscopy study demonstrates that the BHP-Mn2O3-SCs are suitable for charge transfer at the electrode/electrolyte interface. PMID:26439102
NASA Astrophysics Data System (ADS)
Huang, Shao-Zhuan; Jin, Jun; Cai, Yi; Li, Yu; Deng, Zhao; Zeng, Jun-Yang; Liu, Jing; Wang, Chao; Hasan, Tawfique; Su, Bao-Lian
2015-10-01
Bicontinuous hierarchically porous Mn2O3 single crystals (BHP-Mn2O3-SCs) with uniform parallelepiped geometry and tunable sizes have been synthesized and used as anode materials for lithium-ion batteries (LIBs). The monodispersed BHP-Mn2O3-SCs exhibit high specific surface area and three dimensional interconnected bimodal mesoporosity throughout the entire crystal. Such hierarchical interpenetrating porous framework can not only provide a large number of active sites for Li ion insertion, but also good conductivity and short diffusion length for Li ions, leading to a high lithium storage capacity and enhanced rate capability. Furthermore, owing to their specific porosity, these BHP-Mn2O3-SCs as anode materials can accommodate the volume expansion/contraction that occurs with lithium insertion/extraction during discharge/charge processes, resulting in their good cycling performance. Our synthesized BHP-Mn2O3-SCs with a size of ~700 nm display the best electrochemical performance, with a large reversible capacity (845 mA h g-1 at 100 mA g-1 after 50 cycles), high coulombic efficiency (>95%), excellent cycling stability and superior rate capability (410 mA h g-1 at 1 Ag-1). These values are among the highest reported for Mn2O3-based bulk solids and nanostructures. Also, electrochemical impedance spectroscopy study demonstrates that the BHP-Mn2O3-SCs are suitable for charge transfer at the electrode/electrolyte interface.
Huang, Shao-Zhuan; Jin, Jun; Cai, Yi; Li, Yu; Deng, Zhao; Zeng, Jun-Yang; Liu, Jing; Wang, Chao; Hasan, Tawfique; Su, Bao-Lian
2015-01-01
Bicontinuous hierarchically porous Mn2O3 single crystals (BHP-Mn2O3-SCs) with uniform parallelepiped geometry and tunable sizes have been synthesized and used as anode materials for lithium-ion batteries (LIBs). The monodispersed BHP-Mn2O3-SCs exhibit high specific surface area and three dimensional interconnected bimodal mesoporosity throughout the entire crystal. Such hierarchical interpenetrating porous framework can not only provide a large number of active sites for Li ion insertion, but also good conductivity and short diffusion length for Li ions, leading to a high lithium storage capacity and enhanced rate capability. Furthermore, owing to their specific porosity, these BHP-Mn2O3-SCs as anode materials can accommodate the volume expansion/contraction that occurs with lithium insertion/extraction during discharge/charge processes, resulting in their good cycling performance. Our synthesized BHP-Mn2O3-SCs with a size of ~700 nm display the best electrochemical performance, with a large reversible capacity (845 mA h g−1 at 100 mA g−1 after 50 cycles), high coulombic efficiency (>95%), excellent cycling stability and superior rate capability (410 mA h g−1 at 1 Ag−1). These values are among the highest reported for Mn2O3-based bulk solids and nanostructures. Also, electrochemical impedance spectroscopy study demonstrates that the BHP-Mn2O3-SCs are suitable for charge transfer at the electrode/electrolyte interface. PMID:26439102
Instability of plane-parallel flow of incompressible liquid over a saturated porous medium
NASA Astrophysics Data System (ADS)
Lyubimova, T. P.; Lyubimov, D. V.; Baydina, D. T.; Kolchanova, E. A.; Tsiberkin, K. B.
2016-07-01
The linear stability of plane-parallel flow of an incompressible viscous fluid over a saturated porous layer is studied to model the instability of water flow in a river over aquatic plants. The saturated porous layer is bounded from below by a rigid plate and the pure fluid layer has a free, undeformable upper boundary. A small inclination of the layers is imposed to simulate the riverbed slope. The layers are inclined at a small angle to the horizon. The problem is studied within two models: the Brinkman model with the boundary conditions by Ochoa-Tapia and Whitaker at the interface, and the Darcy-Forchheimer model with the conditions by Beavers and Joseph. The neutral curves and critical Reynolds numbers are calculated for various porous layer permeabilities and relative thicknesses of the porous layer. The results obtained within the two models are compared and analyzed.
Instability of plane-parallel flow of incompressible liquid over a saturated porous medium.
Lyubimova, T P; Lyubimov, D V; Baydina, D T; Kolchanova, E A; Tsiberkin, K B
2016-07-01
The linear stability of plane-parallel flow of an incompressible viscous fluid over a saturated porous layer is studied to model the instability of water flow in a river over aquatic plants. The saturated porous layer is bounded from below by a rigid plate and the pure fluid layer has a free, undeformable upper boundary. A small inclination of the layers is imposed to simulate the riverbed slope. The layers are inclined at a small angle to the horizon. The problem is studied within two models: the Brinkman model with the boundary conditions by Ochoa-Tapia and Whitaker at the interface, and the Darcy-Forchheimer model with the conditions by Beavers and Joseph. The neutral curves and critical Reynolds numbers are calculated for various porous layer permeabilities and relative thicknesses of the porous layer. The results obtained within the two models are compared and analyzed. PMID:27575214
NASA Astrophysics Data System (ADS)
Roux, Nicolas; Grenier, Christophe; Costard, François
2015-04-01
In permafrost-affected regions, hydrological changes due to global warming are still under investigation. But yet, we can already foresee from recent studies that for example, the variability and intensity of surface/subsurface flow are likely to be affected by permafrost degradation. The feedback induced by such changes on permafrost degradation is still not clearly assessed. Of particular interest are lake and river's taliks. A talik is a permanently unfrozen zone that lies below rivers or lakes. They are likely to play a key role in the formerly presented interactions, given that they are the only paths for groundwater flow in permafrost regions. Thus heat transfers on a regional scale are influenced by groundwater circulation. The aim of our study is therefore to investigate the evolution of river's taliks. In addition, they are the only perennial liquid water resources in continuous permafrost environments. The issue associated is to what extent can taliks develop into the future because of climate change and how likely are they to become open taliks, connecting sub-permafrost water with surface water with potentially strong geochemical changes? We developed a multidisciplinary approach coupling field investigation, experimental studies in a cold room and numerical modeling. The field investigation concerns Central Yakutia, Siberia, where we have installed instruments to monitor ground temperatures and water pressure in a small river's talik between two thermokarst lakes. We present here the results corresponding to the cold room experimental work, associating numerical modeling and laboratory experiments in order to look after the main parameters controlling river's talik installation and validate our numerical simulation approach. In a cold room at GEOPS, where a metric scale channel is filled with a porous medium (sand or silty-clay), we are able to control air, water and permafrost initial temperature, but also water flow. At initial time, the "river
Nikom, Jaru; Charoonpatrapong-Panyayong, Kanokwan; Kedjarune-Leggat, Ureporn; Stevens, Ron; Kosachan, Nudthakarn; Jaroenworaluck, Angkhana
2013-08-01
3D interconnected porous scaffolds of HA and HA with various additions of SiO2 were fabricated using a polymeric template technique, to make bioceramic scaffolds consisting of macrostructures of the interconnected macropores. Three different sizes of the polyurethane template were used in the fabrication process to form different size interconnected macropores, to study the effect of pore size on human osteoblast cell viability. The template used allowed fabrication of scaffolds with pore sizes of 45, 60, and 75 ppi, respectively. Scanning microscopy was used extensively to observe the microstructure of the sintered samples and the characteristics of cells growing on the HA surfaces of the interconnected macropores. It has been clearly demonstrated that the SiO2 addition has influenced both the phase transformation of HA to TCP (β-TCP and α-TCP) and also affected the human osteoblast cell viability grown on these scaffolds. PMID:23355495
Sadiasa, Alexander; Nguyen, Thi Hiep; Lee, Byong-Taek
2014-01-01
Three dimensional porous scaffolds composed of various ratios of polycaprolactone and poly(L-lactic acid) (PLLA) were prepared using salt leaching method for bone regeneration applications. Surfaces of the scaffolds were visualized using scanning electron microscope (SEM) and the combination of the polymers was confirmed by FT-IR. Addition of PLLA increased the porosity and pore sizes of the scaffolds and also the scaffolds' compressive strength initially. Osteoblast-like cells were used and it was found that the samples' cell biocompatibility was further promoted with the increase in PLLA content as observed via cell proliferation assays using MTT, gene expression with RT-PCR, and micrographs from SEM and confocal microscopy. Samples were then implanted into male rabbits for 2 months, and histological staining and micro-CT histomorphometry show that new bone formations were detected in the site containing the implants of the scaffolds and that bone regeneration was further promoted with the increased concentration of PLLA in the scaffold. PMID:24138179
Xie, Xiuqiang; Chen, Shuangqiang; Sun, Bing; Wang, Chengyin; Wang, Guoxiu
2015-09-01
Low-cost and sustainable sodium-ion batteries are regarded as a promising technology for large-scale energy storage and conversion. The development of high-rate anode materials is highly desirable for sodium-ion batteries. The optimization of mass transport and electron transfer is crucial in the discovery of electrode materials with good high-rate performances. Herein, we report the synthesis of 3 D interconnected SnO2 /graphene aerogels with a hierarchically porous structure as anode materials for sodium-ion batteries. The unique 3 D architecture was prepared by a facile in situ process, during which cross-linked 3 D conductive graphene networks with macro-/meso-sized hierarchical pores were formed and SnO2 nanoparticles were dispersed uniformly on the graphene surface simultaneously. Such a 3 D functional architecture not only facilitates the electrode-electrolyte interaction but also provides an efficient electron pathway within the graphene networks. When applied as anode materials in sodium-ion batteries, the as-prepared SnO2 /graphene aerogel exhibited high reversible capacity, improved cycling performance compared to SnO2 , and promising high-rate capability. PMID:26079600
Ma, Rui; Lai, Yu-xiao; Li, Long; Tan, Hong-lue; Wang, Jia-li; Li, Ye; Tang, Ting-ting; Qin, Ling
2015-01-01
Bone infections are common in trauma-induced open fractures with bone defects. Therefore, developing anti-infection scaffolds for repairing bone defects is desirable. This study develoepd novel Mg-based porous composite scaffolds with a basal matrix composed of poly(lactic-co-glycolicacid) (PLGA) and tricalcium phosphate (TCP). A unique low-temperature rapid prototyping technology was used to fabricate the scaffolds, including PLGA/TCP (PT), PLGA/TCP/5%Mg (PT5M), PLGA/TCP/10%Mg (PT10M), and PLGA/TCP/15%Mg (PT15M). The bacterial adhesion and biofilm formation of Staphylococcus aureus were evaluated. The results indicated that the Mg-based scaffolds significantly inhibited bacterial adhesion and biofilm formation compared to PT, and the PT10M and PT15M exhibited significantly stronger anti-biofilm ability than PT5M. In vitro degratation tests revealed that the degradation of the Mg-based scaffolds caused an increase of pH, Mg2+ concentration and osmolality, and the increased pH may be one of the major contributing factors to the antibacterial function of the Mg-based scaffolds. Additionally, the PT15M exhibited an inhibitory effect on cell adhesion and proliferation of MC3T3-E1 cells. In conclusion, the PLGA/TCP/Mg scaffolds could inhibit bacterial adhesion and biofilm formation, and the PT10M scaffold was considered to be an effective composition with considerable antibacterial ability and good cytocompatibility. PMID:26346217
NASA Astrophysics Data System (ADS)
Zubair Akbar, Muhammad; Ashraf, Muhammad; Farooq Iqbal, Muhammad; Ali, Kashif
2016-04-01
The paper presents the numerical study of heat and mass transfer analysis in a viscous unsteady MHD nanofluid flow through a channel with porous walls and medium in the presence of metallic nanoparticles. The two cases for effective thermal conductivity are discussed in the analysis through H-C model. The impacts of the governing parameters on the flow, heat and mass transfer aspects of the issue are talked about. Under the patronage of small values of permeable Reynolds number and relaxation/contraction parameter, we locate that, when wall contraction is together with suction, flow turning is encouraged close to the wall where the boundary layer is shaped. On the other hand, when the wall relaxation is coupled with injection, the flow adjacent to the porous walls decreased. The outcome of the exploration may be beneficial for applications of biotechnology. Numerical solutions for the velocity, heat and mass transfer rate at the boundary are obtained and analyzed.
NASA Astrophysics Data System (ADS)
Hasan, Raisul
2016-07-01
In this research paper firstly theoretical analysis and design of the porous matrix for filtration and selection of associated liquid (highly viscous and low viscous liquid) is carried out. Hence, porosity of the bed has been found out followed by a detailed CFD analysis of the flow to identify displacement structure (fingering: due to the nonlinear interactions among viscous, capillary and gravitational forces). Moreover, an experiment will be with synthetic porous medium consists of a single layer of glass beads which are then positioned homogeneously or non-homogeneously between two Perspex sheets and then fluid displacement structure/fingering will be photographed. Then the effort will be made to validate results with the experiment based photograph and then the CFD model will be extended to microgravity condition KEYWORDS: CFD, Fingering, microgravity, Non-homogeneously, Capillary .
Jianu, Dana; Tumbar, Tudorita
2015-01-01
Cartilage has limited regeneration potential. Thus, there is an imperative need to develop new strategies for cartilage tissue engineering (CTE) amenable for clinical use. Recent CTE approaches rely on optimal cell-scaffold interactions, which require a great deal of optimization. In this study we attempt to build a novel gelatin- (G-) alginate- (A-) polyacrylamide (PAA) 3D interpenetrating network (IPN) with superior performance in promoting chondrogenesis from human adipose-derived stem cells (hADSCs). We show that our G-A-PAA scaffold is capable of supporting hADSCs proliferation and survival, with no apparent cytotoxic effect. Moreover, we find that after exposure to prochondrogenic conditions a key transcription factor known to induce chondrogenesis, namely, Sox9, is highly expressed in our hADSCs/G-A-PAA bioconstruct, along with cartilage specific markers such as collagen type II, CEP68, and COMP extracellular matrix (ECM) components. These data suggest that our G-A-PAA structural properties and formulation might enable hADSCs conversion towards functional chondrocytes. We conclude that our novel G-A-PAA biomatrix is a good candidate for prospective in vivo CTE applications. PMID:26106422
Hibi, Yoshihiko; Tomigashi, Akira
2015-09-01
Numerical simulations that couple flow in a surface fluid with that in a porous medium are useful for examining problems of pollution that involve interactions among atmosphere, water, and groundwater, including saltwater intrusion along coasts. Coupled numerical simulations of such problems must consider both vertical flow between the surface fluid and the porous medium and complicated boundary conditions at their interface. In this study, a numerical simulation method coupling Navier-Stokes equations for surface fluid flow and Darcy equations for flow in a porous medium was developed. Then, the basic ability of the coupled model to reproduce (1) the drawdown of a surface fluid observed in square-pillar experiments, using pillars filled with only fluid or with fluid and a porous medium and (2) the migration of saltwater (salt concentration 0.5%) in the porous medium using the pillar filled with fluid and a porous medium was evaluated. Simulations that assumed slippery walls reproduced well the results with drawdowns of 10-30 cm when the pillars were filled with packed sand, gas, and water. Moreover, in the simulation of saltwater infiltration by the method developed in this study, velocity was precisely reproduced because the experimental salt concentration in the porous medium after saltwater infiltration was similar to that obtained in the simulation. Furthermore, conditions across the boundary between the porous medium and the surface fluid were satisfied in these numerical simulations of square-pillar experiments in which vertical flow predominated. Similarly, the velocity obtained by the simulation for a system coupling flow in surface fluid with that in a porous medium when horizontal flow predominated satisfied the conditions across the boundary. Finally, it was confirmed that the present simulation method was able to simulate a practical-scale surface fluid and porous medium system. All of these numerical simulations, however, required a great deal of
NASA Astrophysics Data System (ADS)
Meisenheimer, D.; Brueck, C. L.; Wildenschild, D.
2015-12-01
X-ray microtomography imaging of fluid-fluid interfaces in three-dimensional porous media allows for the testing of thermodynamically derived predictions that seek a unique relationship between capillary pressure, fluid saturation, and specific interfacial area (Pc-Sw-Anw). Previous experimental studies sought to test this functional dependence under quasi-equilibrium conditions (assumed static on the imaging time-scale); however, applying predictive models developed under static conditions for dynamic scenarios can lead to substantial flaws in predicted outcomes. Theory and models developed using dynamic data can be verified using fast x-ray microtomography which allows for the unprecedented measurement of developing interfacial areas, curvatures, and trapping behaviors of fluid phases in three-dimensional systems. We will present results of drainage and imbibition experiments of air and water within a mixture of glass beads. The experiments were performed under both quasi-equilibrium and dynamic conditions at the Advanced Photon Source (APS) at Argonne National Laboratory. Fast x-ray microtomography was achieved by utilizing the high brilliance of the x-ray beam at the APS under pink-beam conditions where the white beam is modified with a 4 mm Al absorber and a 0.8 mrad Pt-coated mirror to eliminate low and high-energy photons, respectively. We present a comparison of the results from the quasi-equilibrium and dynamic experiments in an effort to determine if the Pc-Sw-Anw relationship is comparable under either experimental condition and to add to the discussion on whether the Pc-Sw-Anw relationship is unique as hypothesized by existing theory.
Moortgat, Joachim Firoozabadi, Abbas
2013-10-01
Numerical simulation of multiphase compositional flow in fractured porous media, when all the species can transfer between the phases, is a real challenge. Despite the broad applications in hydrocarbon reservoir engineering and hydrology, a compositional numerical simulator for three-phase flow in fractured media has not appeared in the literature, to the best of our knowledge. In this work, we present a three-phase fully compositional simulator for fractured media, based on higher-order finite element methods. To achieve computational efficiency, we invoke the cross-flow equilibrium (CFE) concept between discrete fractures and a small neighborhood in the matrix blocks. We adopt the mixed hybrid finite element (MHFE) method to approximate convective Darcy fluxes and the pressure equation. This approach is the most natural choice for flow in fractured media. The mass balance equations are discretized by the discontinuous Galerkin (DG) method, which is perhaps the most efficient approach to capture physical discontinuities in phase properties at the matrix-fracture interfaces and at phase boundaries. In this work, we account for gravity and Fickian diffusion. The modeling of capillary effects is discussed in a separate paper. We present the mathematical framework, using the implicit-pressure-explicit-composition (IMPEC) scheme, which facilitates rigorous thermodynamic stability analyses and the computation of phase behavior effects to account for transfer of species between the phases. A deceptively simple CFL condition is implemented to improve numerical stability and accuracy. We provide six numerical examples at both small and larger scales and in two and three dimensions, to demonstrate powerful features of the formulation.
Instability modes of a two-layer Newtonian plane Couette flow past a porous medium
NASA Astrophysics Data System (ADS)
Praveen Kumar, A. Ananth; Goyal, Himanshu; Banerjee, Tamal; Bandyopadhyay, Dipankar
2013-06-01
We explore the salient features of the different instability modes of a pressure-driven two-layer plane Couette flow confined between a moving wall and a Darcy-Brinkman porous layer. A linear stability analysis of the conservation laws leads to an Orr-Sommerfeld system, which is solved numerically with appropriate boundary conditions to identify the time and length scales of the instability modes. The study reveals that the movement of the confining wall together with the slippage at the porous-liquid interface originating from the flow inside the porous layer can stimulate a pair of finite-wave-number shear modes in addition to the long-wave interfacial mode of instability. The shear modes dominate the interfacial mode, especially when the frictional influence at the liquid layers is smaller due to the movement of the confining plate or due to the larger slippage at the porous-liquid interface. The shear modes are found to be present under all combinations of the viscosity μr and thickness hr ratios of the liquid layers. This is in stark contrast to the two-layer flow confined between nonporous plates where the interfacial (shear) mode is observed only when μr>hr2 (μr
Cheng, Alice; Humayun, Aiza; Cohen, David J.; Boyan, Barbara D.; Schwartz, Zvi
2014-01-01
Additive manufacturing by laser sintering is able to produce high resolution metal constructs for orthopaedic and dental implants. In this study, we used a human trabecular bone template to design and manufacture Ti-6Al-4V constructs with varying porosity via laser sintering. Characterization of constructs revealed interconnected porosities ranging from 15–70% with compressive moduli of 2063–2954 MPa. These constructs with macro porosity were further surface-treated to create a desirable multi-scale micro-/nano-roughness, which has been shown to enhance the osseointegration process. Osteoblasts (MG63 cells) exhibited high viability when grown on the constructs. Proliferation (DNA) and alkaline phosphatase specific activity (ALP), an early differentiation marker, decreased as porosity increased, while osteocalcin (OCN), a late differentiation marker, as well as osteoprotegerin (OPG), vascular endothelial growth factor (VEGF) and bone morphogenetic proteins 2 and 4 (BMP2, BMP4) increased with increasing porosity. 3D constructs with the highest porosity and surface modification supported the greatest osteoblast differentiation and local factor production. These results indicate that additively manufactured 3D porous constructs mimicking human trabecular bone and produced with additional surface treatment can be customized for increased osteoblast response. Increased factors for osteoblast maturation and differentiation on high porosity constructs suggest the enhanced performance of these surfaces for increasing osseointegration in vivo. PMID:25287305
NASA Astrophysics Data System (ADS)
Devaux, Fabrice; Lantz, Eric
2014-05-01
In this paper we present a three dimensional numerical model, based on a Pseudo-Spectral Time Domain algo- rithm (PSTD), that simulates the propagation of light carrying an image through a scattering medium and the back propagation of the scattered light which is re ected back by a phase conjugate mirror, modelled thanks to the nonlinear optical process of three-wave-mixing. We show how the phase conjugate wave retraces the scattering path and retrieves the spatial information of the input image with a signal to noise ratio that depends on the lateral dimensions of the phase conjugate mirror and of the number of realizations cumulated. Moreover, we show that the image restoration is not precluded by the polarization change between the phase conjugate wave and the scattered light exiting the complex medium.
NASA Astrophysics Data System (ADS)
Butt, A. S.; Tufail, M. N.; Ali, Asif
2016-03-01
A three-dimensional flow of a magnetohydrodynamic Casson fluid over an unsteady stretching surface placed into a porous medium is examined. Similarity transformations are used to convert time-dependent partial differential equations into nonlinear ordinary differential equations. The transformed equations are then solved analytically by the homotopy analysis method and numerically by the shooting technique combined with the Runge-Kutta-Fehlberg method. The results obtained by both methods are compared with available reported data. The effects of the Casson fluid parameter, magnetic field parameter, and unsteadiness parameter on the velocity and local skin friction coefficients are discussed in detail.
Ismail, Zulkhibri; Khan, Ilyas; Nasir, Nadirah Mohd; Awang, Rahimah Jusoh; Salleh, Mohd Zuki; Shafie, Sharidan
2015-02-03
An analysis of the exact solutions of second grade fluid problem for unsteady magnetohydrodynamic (MHD) flows past an infinite inclined plate in a porous medium is presented. It is assumed that the bounding infinite inclined plate has a constant temperature with radiation effects. Based on Boussinesq approximation the expressions for dimensionless velocity, temperature and concentration are obtained by using Laplace transform method. The derived solutions satisfying the involved differential equations, and all the boundary and initial conditions. The influence of various parameters on the velocity has been illustrated graphically and analyzed.
Rauf, A. Meraj, M. A.; Ashraf, M.; Batool, K.; Hussain, M.
2015-07-15
This article studies the simultaneous impacts of heat and mass transfer of an incompressible electrically conducting micropolar fluid generated by the stretchable disk in presence of porous medium. The thermal radiation effect is accounted via Rosseland’s approximation. The governing boundary layer equations are reduced into dimensionless form by employing the suitable similarity transformations. A finite difference base algorithm is utilized to obtain the solution expressions. The impacts of physical parameters on dimensionless axial velocity, radial velocity, micro-rotation, temperature and concentrations profiles are presented and examined carefully. Numerical computation is performed to compute shear stress, couple stress, heat and mass rate at the disk.
NASA Astrophysics Data System (ADS)
Rauf, A.; Ashraf, M.; Batool, K.; Hussain, M.; Meraj, M. A.
2015-07-01
This article studies the simultaneous impacts of heat and mass transfer of an incompressible electrically conducting micropolar fluid generated by the stretchable disk in presence of porous medium. The thermal radiation effect is accounted via Rosseland's approximation. The governing boundary layer equations are reduced into dimensionless form by employing the suitable similarity transformations. A finite difference base algorithm is utilized to obtain the solution expressions. The impacts of physical parameters on dimensionless axial velocity, radial velocity, micro-rotation, temperature and concentrations profiles are presented and examined carefully. Numerical computation is performed to compute shear stress, couple stress, heat and mass rate at the disk.
NASA Astrophysics Data System (ADS)
Mustafaev, R. A.
2008-02-01
Dorodnicyn's generalized method of integral relations is used to compute a Verigin-type single-phase unsteady flow in a porous medium. This problem describes the pumping of a gas through a gallery in a bounded horizontal aquifer and is associated with underground gas storage in aquifers. The case of an isothermal process and an ideal gas are considered. The viscosity of the gas is neglected. Sines are used as smoothing functions. The results obtained in the first and third approximations are presented and analyzed. The solution is compared with a finite-difference solution and that produced by the method of integral relations. The results are given in a table.
Hayat, Tasawar; Awais, Muhammad; Imtiaz, Amna
2016-01-01
This communication deals with the properties of heat source/sink in a magneto-hydrodynamic flow of a non-Newtonian fluid immersed in a porous medium. Shrinking phenomenon along with the permeability of the wall is considered. Mathematical modelling is performed to convert the considered physical process into set of coupled nonlinear mathematical equations. Suitable transformations are invoked to convert the set of partial differential equations into nonlinear ordinary differential equations which are tackled numerically for the solution computations. It is noted that dual solutions for various physical parameters exist which are analyzed in detail. PMID:27598314
On the stability and uniqueness of the flow of a fluid through a porous medium
NASA Astrophysics Data System (ADS)
Hill, A. A.; Rajagopal, K. R.; Vergori, L.
2016-06-01
In this short note, we study the stability of flows of a fluid through porous media that satisfies a generalization of Brinkman's equation to include inertial effects. Such flows could have relevance to enhanced oil recovery and also to the flow of dense liquids through porous media. In any event, one cannot ignore the fact that flows through porous media are inherently unsteady, and thus, at least a part of the inertial term needs to be retained in many situations. We study the stability of the rest state and find it to be asymptotically stable. Next, we study the stability of a base flow and find that the flow is asymptotically stable, provided the base flow is sufficiently slow. Finally, we establish results concerning the uniqueness of the flow under appropriate conditions, and present some corresponding numerical results.
NASA Astrophysics Data System (ADS)
Ramachandra Prasad, V.; Gaffar, S. Abdul; Keshava Reddy, E.; Bég, O. Anwar
2014-07-01
Polymeric enrobing flows are important in industrial manufacturing technology and process systems. Such flows are non-Newtonian. Motivated by such applications, in this article we investigate the nonlinear steady state boundary layer flow, heat, and mass transfer of an incompressible Jefferys non-Newtonian fluid past a vertical porous plate in a non-Darcy porous medium. The transformed conservation equations are solved numerically subject to physically appropriate boundary conditions using a versatile, implicit, Keller-box finite-difference technique. The numerical code is validated with previous studies. The influence of a number of emerging non-dimensional parameters, namely Deborah number (De), Darcy number (Da), Prandtl number (Pr), ratio of relaxation to retardation times (λ), Schmidt number (Sc), Forchheimer parameter (Λ), and dimensionless tangential coordinate (ξ) on velocity, temperature, and concentration evolution in the boundary layer regime are examined in detail. Furthermore, the effects of these parameters on surface heat transfer rate, mass transfer rate, and local skin friction are also investigated. It is found that the boundary layer flow is decelerated with increasing De and Forchheimer parameter, whereas temperature and concentration are elevated. Increasing λ and Da enhances the velocity but reduces the temperature and concentration. The heat transfer rate and mass transfer rates are found to be depressed with increasing De and enhanced with increasing λ. Local skin friction is found to be decreased with a rise in De, whereas it is elevated with increasing λ. An increasing Sc decreases the velocity and concentration but increases temperature.
NASA Astrophysics Data System (ADS)
Nandeppanavar, M. M.; Siddalingappa, M. N.
2013-06-01
In this present paper, we have discussed the effects of viscous dissipation and thermal radiation on heat transfer over a non-linear stretching sheet through a porous medium. Usual similarity transformations are considered to convert the non-linear partial differential equation of motion and heat transfer into ODE's. Solutions of motion and heat transfer are obtained by the Runge-Kutta integration scheme with most efficient shooting technique. The graphical results are presented to interpret various physical parameters of interest. It is found that the velocity profile decreases with an increase of the porous parameter asymptotically. The temperature field decreases with an increase in the parametric values of the Prandtl number and thermal radiation while with an increase in parameters of the Eckert number and porous parameter, the temperature field increases in both PST (power law surface temperature) and PHF (power law heat flux) cases. The numerical values of the non-dimensional wall temperature gradient and wall temperature are tabulated and discussed.
Nonlinear Stress/Strain Behavior of a Synthetic Porous Medium at Seismic Frequencies
NASA Astrophysics Data System (ADS)
Roberts, P. M.; Ibrahim, R. H.
2008-12-01
Laboratory experiments on porous core samples have shown that seismic-band (100 Hz or less) mechanical, axial stress/strain cycling of the porous matrix can influence the transport behavior of fluids and suspended particles during steady-state fluid flow through the cores. In conjunction with these stimulated transport experiments, measurements of the applied dynamic axial stress/strain were made to investigate the nonlinear mechanical response of porous media for a poorly explored range of frequencies from 1 to 40 Hz. A unique core-holder apparatus that applies low-frequency mechanical stress/strain to 2.54-cm-diameter porous samples during constant-rate fluid flow was used for these experiments. Applied stress was measured with a load cell in series with the source and porous sample, and the resulting strain was measured with an LVDT attached to the core face. A synthetic porous system consisting of packed 1-mm-diameter glass beads was used to investigate both stress/strain and stimulated mass-transport behavior under idealized conditions. The bead pack was placed in a rubber sleeve and static confining stresses of 2.4 MPa radial and 1.7 MPa axial were applied to the sample. Sinusoidal stress oscillations were applied to the sample at 1 to 40 Hz over a range of RMS stress amplitude from 37 to 275 kPa. Dynamic stress/strain was measured before and after the core was saturated with deionized water. The slope of the linear portion of each stress/strain hysteresis loop was used to estimate Young's modulus as a function of frequency and amplitude for both the dry and wet sample. The modulus was observed to increase after the dry sample was saturated. For both dry and wet cases, the modulus decreased with increasing dynamic RMS stress amplitude at a constant frequency of 23 Hz. At constant RMS stress amplitude, the modulus increased with increasing frequency for the wet sample but remained constant for the dry sample. The observed nonlinear behavior of Young's modulus
NASA Astrophysics Data System (ADS)
Swarnalathamma, B. V.; Krishna, M. Veera
2016-05-01
In this paper, we discussed the theoretical and computational study of peristaltic hemodynamic flow of couple stress fluids through a porous medium under the influence of magnetic field with wall slip condition. Actually this study is motivated towards the physiological flow of the blood in the micro circulatory system by taking account of the particle size effect. We consider the Reynolds number is small enough and the wave length to diameter ratio is large enough to negate inertial effects. The governing equations for the couple stress fluid flow through porous medium based on stoke constitutive equations and Brinkman model. The exact solutions for axial velocity, pressure gradient, frictional force, stream function and mechanical efficiency are obtained analytically, its behaviour computationally discussed with reference to different physical parameters reflecting couple stress parameter, Hartmann number, permeability parameter, slip parameter as well as amplitude ratio on pumping characteristics and frictional force, stream lines pattern and trapping of peristaltic flow pattern are studied with particular emphasis making use of graphs.
Source-like solution for radial imbibition into a homogeneous semi-infinite porous medium.
Xiao, Junfeng; Stone, Howard A; Attinger, Daniel
2012-03-01
We describe the imbibition process from a point source into a homogeneous semi-infinite porous material. When body forces are negligible, the advance of the wetting front is driven by capillary pressure and resisted by viscous forces. With the assumption that the wetting front assumes a hemispherical shape, our analytical results show that the absorbed volume flow rate is approximately constant with respect to time, and that the radius of the wetting evolves in time as r ≈ t(1/3). This cube-root law for the long-time dynamics is confirmed by experiments using a packed cell of glass microspheres with average diameter of 42 μm. This result complements the classical one-dimensional imbibition result where the imbibition length l ≈ t(1/2), and studies in axisymmetric porous cones with small opening angles where l ≈ t(1/4) at long times. PMID:22283599
Impact of porous medium on the high cycle temperature fluctuations in a mixing tee
Bu, L.; Zhao, J.
2012-07-01
Temperature fluctuations occur in the region where hot and cold fluids mix turbulently in the nuclear power plants. Temperature fluctuations cause thermal fatigue of piping systems. In the design of generation IV nuclear power plants, supercritical fluids are supposed to be used widely. This paper investigated the thermal striping phenomenon caused by the turbulent mixing in a supercritical water Tee. There are two key issues in the study of thermal striping phenomenon: One is to find the region which experiences the peak temperature fluctuation; the other is how to attenuate it. Porous media was used to attenuate the temperature fluctuations in this paper. The results show that porous media with proper parameters in a tee can reduce the temperature fluctuations magnificently. (authors)
NASA Astrophysics Data System (ADS)
Yang, PeiPei; Wen, Zhi; Dou, RuiFeng; Liu, Xunliang
2016-08-01
Flow and heat transfer through a 2D random porous medium are studied by using the lattice Boltzmann method (LBM). For the random porous medium, the influence of disordered cylinder arrangement on permeability and Nusselt number are investigated. Results indicate that the permeability and Nusselt number for different cylinder locations are unequal even with the same number and size of cylinders. New correlations for the permeability and coefficient b‧Den of the Forchheimer equation are proposed for random porous medium composed of Gaussian distributed circular cylinders. Furthermore, a general set of heat transfer correlations is proposed and compared with existing experimental data and empirical correlations. Our results show that the Nu number increases with the increase of the porosity, hence heat transfer is found to be accurate considering the effect of porosity.
NASA Astrophysics Data System (ADS)
Sheremet, M. A.; Pop, Ioan
2015-06-01
This paper deals with a numerical study of natural convection flow and heat transfer inside a concentric horizontal annulus filled with a porous medium saturated by a cuprum (Cu)-water nanofluid. The inner and outer cylinders are kept at different constant temperatures. First, the governing partial differential equations in dimensional formulation in a polar coordinate system for the physical domain are transformed in dimensionless form in terms of stream function-temperature formulation. These equations along with the corresponding boundary conditions were solved numerically by the finite difference method. Particular efforts have been focused on the effects of the Rayleigh number, porosity of the porous medium, solid volume fraction parameter of nanoparticles, annulus radius ratio, and the solid matrix of the porous medium (glass balls and aluminum foam) on the local and average Nusselt numbers, streamlines and isotherms. It is found that a very good agreement exists between the present results and those from the open literature.
NASA Astrophysics Data System (ADS)
Pletinckx, D.
2011-09-01
The current 3D hype creates a lot of interest in 3D. People go to 3D movies, but are we ready to use 3D in our homes, in our offices, in our communication? Are we ready to deliver real 3D to a general public and use interactive 3D in a meaningful way to enjoy, learn, communicate? The CARARE project is realising this for the moment in the domain of monuments and archaeology, so that real 3D of archaeological sites and European monuments will be available to the general public by 2012. There are several aspects to this endeavour. First of all is the technical aspect of flawlessly delivering 3D content over all platforms and operating systems, without installing software. We have currently a working solution in PDF, but HTML5 will probably be the future. Secondly, there is still little knowledge on how to create 3D learning objects, 3D tourist information or 3D scholarly communication. We are still in a prototype phase when it comes to integrate 3D objects in physical or virtual museums. Nevertheless, Europeana has a tremendous potential as a multi-facetted virtual museum. Finally, 3D has a large potential to act as a hub of information, linking to related 2D imagery, texts, video, sound. We describe how to create such rich, explorable 3D objects that can be used intuitively by the generic Europeana user and what metadata is needed to support the semantic linking.
NASA Astrophysics Data System (ADS)
Chand, Ramesh
2015-12-01
Thermal instability in a horizontal layer of Oldroydian visco-elastic fluid in a porous medium is investigated. For porous medium the Brinkman-Darcy model is considered. A linear stability analysis based upon perturbation method and normal mode technique is used to find solution of the fluid layer confined between two free-free boundaries. The onset criterion for stationary and oscillatory convection is derived analytically. The influence of the Brinkman-Darcy, Prandtl-Darcy number, stress relaxation parameter on the stationary and oscillatory convection is studied both analytically and graphically. The sufficient condition for the validity of PES has also been derived.
Dynamics of a liquid drop in porous medium saturated by another liquid under gravity
NASA Astrophysics Data System (ADS)
Ivantsov, A. O.; Lyubimova, T. P.
2016-02-01
The work deals with numerical simulations of settling or ascension process of a liquid drop in porous media saturated by another liquid. The calculations were carried out using the Darcy model by Level set method with adaptive mesh refinement algorithm that dynamically refines computational mesh near interface. It is shown that the drop is unstable and the finger instability develops at the forefront of moving drop for any ratio of the viscosities of liquids. Under modulated pressure gradient small-scale perturbations of interface are suppressed and in the case of modulation with large enough intensity drop becomes stable.
Grančič, Peter; Štěpánek, František
2011-08-01
The multibody dynamics of a system of chemical swarm robots in a porous environment is investigated. The chemical swarm robots are modeled as brownian particles capable of delivering an encapsulated chemical payload toward a given target location and releasing it in response to an external stimulus. The presence of chemical signals (chemo-attractant) in the system plays a crucial role in coordinating the collective movement of the particles via chemotaxis. For a number of applications, such as distributed chemical processing and targeted drug delivery, the understanding of factors that govern the collective behavior of the particles, especially their ability to localize a given target, is of immense importance. A hybrid modeling methodology based on the combination of the brownian dynamics method and diffusion problem coupled through the chemotaxis phenomena is used to analyze the impact of a varying signaling threshold and the strength of chemotaxis on the ability of the chemical robots to fulfill their target localization mission. The results demonstrate that the selected performance criteria (the localization half time and the success rate) can be improved when an appropriate signaling process is chosen. Furthermore, for an optimum target localization strategy, the topological complexity of the porous environment needs to be reflected. PMID:21929036
NASA Astrophysics Data System (ADS)
Grančič, Peter; Štěpánek, František
2011-08-01
The multibody dynamics of a system of chemical swarm robots in a porous environment is investigated. The chemical swarm robots are modeled as Brownian particles capable of delivering an encapsulated chemical payload toward a given target location and releasing it in response to an external stimulus. The presence of chemical signals (chemo-attractant) in the system plays a crucial role in coordinating the collective movement of the particles via chemotaxis. For a number of applications, such as distributed chemical processing and targeted drug delivery, the understanding of factors that govern the collective behavior of the particles, especially their ability to localize a given target, is of immense importance. A hybrid modeling methodology based on the combination of the Brownian dynamics method and diffusion problem coupled through the chemotaxis phenomena is used to analyze the impact of a varying signaling threshold and the strength of chemotaxis on the ability of the chemical robots to fulfill their target localization mission. The results demonstrate that the selected performance criteria (the localization half time and the success rate) can be improved when an appropriate signaling process is chosen. Furthermore, for an optimum target localization strategy, the topological complexity of the porous environment needs to be reflected.
Vapour-liquid phase diagram for an ionic fluid in a random porous medium.
Holovko, M F; Patsahan, O; Patsahan, T
2016-10-19
We study the vapour-liquid phase behaviour of an ionic fluid confined in a random porous matrix formed by uncharged hard sphere particles. The ionic fluid is modelled as an equimolar binary mixture of oppositely charged equisized hard spheres, the so-called restricted primitive model (RPM). Considering the matrix-fluid system as a partly-quenched model, we develop a theoretical approach which combines the method of collective variables with the extension of the scaled-particle theory (SPT) for a hard-sphere fluid confined in a disordered hard-sphere matrix. The approach allows us to formulate the perturbation theory using the SPT for the description of the thermodynamics of the reference system. The phase diagrams of the RPM in matrices of different porosities and for different size ratios of matrix and fluid particles are calculated in the random-phase approximation and also when the effects of higher-order correlations between ions are taken into account. Both approximations correctly reproduce the basic effects of porous media on the vapour-liquid phase diagram, i.e. with a decrease of porosity the critical point shifts towards lower fluid densities and lower temperatures and the coexistence region gets narrower. For the fixed matrix porosity, both the critical temperature and the critical density increase with an increase of size of matrix particles and tend to the critical values of the bulk RPM. PMID:27548356
Chamkha, A.J.; Khaled, A.R.A.
1999-08-27
Simultaneous heat and mass transfer from different geometries embedded in porous media has many engineering and geophysical applications, such as migration of water in geothermal reservoirs, underground spreading of chemical wastes and other pollutants, thermal insulation, enhanced oil recovery, packed-bed catalytic reactors, cooling of nuclear reactors, grain storage, and evaporative cooling and solidification. This work considers steady, laminar, hydromagnetic simultaneous heat and mass transfer by mixed convection flow over a permeable vertical plate immersed in a uniform porous medium for the cases of power law variations of both the wall temperature and concentration and the wall heat flux and mass flux. Appropriate transformations are employed to transform the governing differential equations to a nonsimilar form. The transformed equations are solved numerically by an accurate, implicit, iterative, finite difference method. The obtained results are validated by favorable comparisons with previously published work on special cases of the problem. A parametric study illustrating the influence of all involved parameters on the local Nusselt and Sherwood numbers is conducted. The results of this parametric study are shown graphically, and the physical aspects of the problem are discussed.
NASA Astrophysics Data System (ADS)
Rauf, A.; Shahzad, S. A.; Siddiq, M. K.; Raza, J.; Meraj, M. A.
2016-03-01
A numerical study is carried out for two dimensional steady incompressible mixed convective flow of electrically conductive micro nanofluid in a stretchable channel. The flow is generated due to the stretching walls of the channel immersed in a porous medium. The magnetic field is applied perpendicular to the walls. The impact of radiation, viscous dissipation, thermophoretic and Brownian motion of nanoparticles appear in the energy equation. A numerical technique based on Runge-Kutta-Fehlberg fourth-fifth order (RFK45) method is used to express the solutions of velocity, microrotation, temperature and concentration fields. The dimensionless physical parameters are discussed both in tabular and graphical forms. The results are also found in a good agreement with previously published literature work.
NASA Astrophysics Data System (ADS)
Khalid Aurangzaib, M.; Bhattacharyya, Krishnendu; Shafie, Sharidan
2016-06-01
The characteristics of the unsteady boundary layer flow with melting heat transfer near a stagnation-point towards a flat plate embedded in a DarcyBrinkman porous medium with thermal radiation are investigated. The governing partial differential equations are transformed into self-similar ordinary differential equations by similarity transformations. The transformed self-similar equations are solved numerically using bvp4c from Matlab for several values of the flow parameters. The study reveals that the multiple solutions exist for the decelerating (A < 0) flow, whereas for the accelerating (A ≥ 0) flow, the solution is unique. The results also indicate that the melting phenomenon increases the rate of heat transfer and delays the boundary layer separation. To validate the current numerical results, comparison with available results is made and found to be in a good agreement.
NASA Astrophysics Data System (ADS)
Sharma, Rajesh; Bhargava, Rama
2015-07-01
In this article, the two-dimensional boundary layer problem of Hiemenz flow (two-dimensional flow of a fluid near a stagnation point) of an incompressible micropolar fluid towards a nonlinear stretching surface placed in a porous medium in the presence of transverse magnetic field is examined. The resulting nonlinear differential equations governing the problem have been transformed by a similarity transformation into a system of nonlinear ordinary differential equations which are solved numerically by the Element Free Galerkin method. The influence of various parameters on the velocity, microrotation, temperature, and concentration is shown. Some of the results are compared with the Finite Element Method. Finally, validation of the numerical results is demonstrated for local skin friction ? for hydrodynamic micropolar fluid flow on a linearly stretching surface.
NASA Astrophysics Data System (ADS)
Postelnicu, Adrian
2010-10-01
Dufour and Soret effects on flow at a stagnation point in a fluid-saturated porous medium are studied in this paper. A two dimensional stagnation-point flow with suction/injection of a Darcian fluid is considered. By using an appropriate similarity transformation, the boundary layer equations of momentum, energy and concentration are reduced to a set of ordinary differential equations, which are solved numerically using the Keller-box method, which is a very efficient finite differences technique. Nusselt and Sherwood numbers are obtained, together with the velocity, temperature and concentration profiles in the boundary layer. For the large suction case, asymptotic analytical solutions of the problem are obtained, which compare favourably with the numerical solutions. A critical view of the problem is presented finally.
NASA Astrophysics Data System (ADS)
Miller, Cass T.; Gray, William G.
2008-03-01
This work is the fourth in a series of papers on the thermodynamically constrained averaging theory (TCAT) approach for modeling flow and transport phenomena in multiscale porous medium systems. The general TCAT framework and the mathematical foundation presented in previous works are built upon by formulating macroscale models for conservation of mass, momentum, and energy, and the balance of entropy for a species in a phase volume, interface, and common curve. In addition, classical irreversible thermodynamic relations for species in entities are averaged from the microscale to the macroscale. Finally, we comment on alternative approaches that can be used to connect species and entity conservation equations to a constrained system entropy inequality, which is a key component of the TCAT approach. The formulations detailed in this work can be built upon to develop models for species transport and reactions in a variety of multiphase systems.
NASA Astrophysics Data System (ADS)
Mabood, F.; Shateyi, S.; Khan, W. A.
2015-09-01
This paper deals with a theoretical investigation of flow and heat transfer of a Casson fluid from a horizontal circular cylinder in a non-Darcy porous medium under the action of slips and thermal radiation parameters. A model of Casson fluid flow for a circular cylinder has been developed to simulate the transport phenomena. The numerical solution has been obtained for the dimensionless velocity and temperature of the Casson fluid. The effects of various important parameters on the dimensionless velocity, temperature as well as on the skin friction and the dimensionless heat transfer rates are investigated and presented graphically. A comparison with previous published data has been done and we found a good agreement with them.
Marangoni boundary layer flow and heat transfer of copper-water nanofluid over a porous medium disk
NASA Astrophysics Data System (ADS)
Lin, Yanhai; Zheng, Liancun
2015-10-01
In this paper we present a study of the Marangoni boundary layer flow and heat transfer of copper-water nanofluid over a porous medium disk. It is assumed that the base fluid water and the nanoparticles copper are in thermal equilibrium and that no slippage occurs between them. The governing partial differential equations are transformed into a set of ordinary differential equations by generalized Kármán transformation. The corresponding nonlinear two-point boundary value problem is solved by the Homotopy analysis method and the shooting method. The effects of the solid volume fraction, the permeability parameter and the Marangoni parameter on the velocity and temperature fields are presented graphically and analyzed in detail.
NASA Astrophysics Data System (ADS)
Ramesh, K.; Devakar, M.
2015-11-01
In the present paper, the effects of magnetic field and heat transfer on the peristaltic flow of an incompressible couple stress fluid through porous medium in an inclined asymmetric channel have been studied under the long wavelength approximation. The exact solutions of the resultant governing equations have been obtained for the stream function, pressure gradient, temperature and heat transfer coefficients. The pressure difference and frictional forces have been computed numerically. The effects of Hartmann number, Darcy number, Grashof number, couple stress parameter, heat generation parameter and inclination angle on the heat characteristics, velocity characteristics, pumping characteristics and trapping phenomena are discussed in detail. It is found that the pressure gradient increases from horizontal channel to vertical channel. The best pumping can be seen at higher Hartmann number. The size of trapped bolus decreases with the increase of couple stress parameter and the strength of the magnetic flied. Increase of heat generation parameter increases the pressure gradient, temperature and the size of the bolus.
Khan, Arshad; Khan, Ilyas; Ali, Farhad; ulhaq, Sami; Shafie, Sharidan
2014-01-01
This study investigates the effects of an arbitrary wall shear stress on unsteady magnetohydrodynamic (MHD) flow of a Newtonian fluid with conjugate effects of heat and mass transfer. The fluid is considered in a porous medium over a vertical plate with ramped temperature. The influence of thermal radiation in the energy equations is also considered. The coupled partial differential equations governing the flow are solved by using the Laplace transform technique. Exact solutions for velocity and temperature in case of both ramped and constant wall temperature as well as for concentration are obtained. It is found that velocity solutions are more general and can produce a huge number of exact solutions correlative to various fluid motions. Graphical results are provided for various embedded flow parameters and discussed in details. PMID:24621775
3d-3d correspondence revisited
NASA Astrophysics Data System (ADS)
Chung, Hee-Joong; Dimofte, Tudor; Gukov, Sergei; Sułkowski, Piotr
2016-04-01
In fivebrane compactifications on 3-manifolds, we point out the importance of all flat connections in the proper definition of the effective 3d {N}=2 theory. The Lagrangians of some theories with the desired properties can be constructed with the help of homological knot invariants that categorify colored Jones polynomials. Higgsing the full 3d theories constructed this way recovers theories found previously by Dimofte-Gaiotto-Gukov. We also consider the cutting and gluing of 3-manifolds along smooth boundaries and the role played by all flat connections in this operation.
Evaluation of Porous Medium Permeability by Acoustic Logging Finds Geothermal Applications
Conche, B.; Lebreton, F.; Rojas, J.
1986-01-21
In a well, after an acoustic waveform has circulated through the surrounding porous media, the study of its alteration can help in evaluating their permeability. The treatment of the acoustic compressional wave's first three cycles yields a unique parameter called I-c. The recording of this I-c log all along any open hole interval is now possible by respecting some practical rules known by logging companies. Large flows of fluid found in geothermal low-enthalpy operations have provided an opportunity to check the validity of this method. Cumulative I-c derived permeability with depth (''EXAFLO'' log) correlates with the flowmeter log, as examples will show. Some new aspects of the theory underlying the I-c/permeability relationship have been developed and are described here.
Swarming behavior of gradient-responsive Brownian particles in a porous medium.
Grančič, Peter; Štěpánek, František
2012-07-01
Active targeting by Brownian particles in a fluid-filled porous environment is investigated by computer simulation. The random motion of the particles is enhanced by diffusiophoresis with respect to concentration gradients of chemical signals released by the particles in the proximity of a target. The mathematical model, based on a combination of the Brownian dynamics method and a diffusion problem is formulated in terms of key parameters that include the particle diffusiophoretic mobility and the signaling threshold (the distance from the target at which the particles release their chemical signals). The results demonstrate that even a relatively simple chemical signaling scheme can lead to a complex collective behavior of the particles and can be a very efficient way of guiding a swarm of Brownian particles towards a target, similarly to the way colonies of living cells communicate via secondary messengers. PMID:23005461
Swarming behavior of gradient-responsive Brownian particles in a porous medium
NASA Astrophysics Data System (ADS)
Grančič, Peter; Štěpánek, František
2012-07-01
Active targeting by Brownian particles in a fluid-filled porous environment is investigated by computer simulation. The random motion of the particles is enhanced by diffusiophoresis with respect to concentration gradients of chemical signals released by the particles in the proximity of a target. The mathematical model, based on a combination of the Brownian dynamics method and a diffusion problem is formulated in terms of key parameters that include the particle diffusiophoretic mobility and the signaling threshold (the distance from the target at which the particles release their chemical signals). The results demonstrate that even a relatively simple chemical signaling scheme can lead to a complex collective behavior of the particles and can be a very efficient way of guiding a swarm of Brownian particles towards a target, similarly to the way colonies of living cells communicate via secondary messengers.
Drift of a polymer chain in a porous medium —A Monte Carlo study
NASA Astrophysics Data System (ADS)
Avramova, K.; Milchev, A.
2002-01-01
We investigate the drift of an end-labeled telehelic polymer chain in a frozen disordered medium under the action of a constant force applied to the one end of the macromolecule by means of an off-lattice bead spring Monte Carlo model. The length of the polymers N is varied in the range 8
Dual-function growth medium and structural soil for use as porous pavement.
Sloan, John J; Hegemann, Mary Ann; George, Steve A
2008-01-01
Permeable grass-covered surfaces can reduce the quantity of storm water runoff and filter out potentially harmful chemicals. The objective of this study was to develop permeable structural soils that sustained healthy turf growth and filtered heavy metals from contaminated pavement runoff. The basic soil medium was a 50:50 mixture (v/v) of expanded shale (ExSh) and quartz sand (QS). The ExSh component consisted of (i) large-diameter particles (3-6 mm), (ii) small-diameter particles (1-3 mm), or (iii) a 50:50 mixture (v/v) of the two. The basic blends were mixed with 0, 10, and 20% sphagnum peat moss (v/v) and 0, 10, and 20% natural zeolites (v/v) and placed in 15-cm-diameter pots in a greenhouse. Bermudagrass plugs were planted in each pot. The addition of sphagnum peat moss to the basic ExSh/QS blend increased bermudagrass growth and improved plant response to added fertilizer. Zeolites had no significant effect on plant growth in the absence of sphagnum peat moss. Growing mediums that contained 10 to 20% sphagnum peat moss and 10 to 20% zeolites consistently produced more bermudagrass biomass than the unamended ExSh/QS mixture. Changing the ratio of small- to large-diameter ExSh in the basic medium did not affect bermudagrass yield. Very low amounts of Cd, Cu, Pb, and Zn were recovered in leachate after the addition of 10 mg metal per pot, suggesting that most heavy metals (>99%) were retained in the growing mediums. Zeolites reduced the amount of Cd and Pb in leachate water, but not Cu or Zn. PMID:18948478
NASA Astrophysics Data System (ADS)
Minale, Mario
2016-02-01
In this paper, a stress boundary condition at the interface between a porous medium saturated by a viscoelastic fluid and the free viscoelastic fluid is derived. The volume averages are used to upscale the problem. The boundary condition is obtained on the assumption that the free fluid stress is transferred partially to the fluid within the porous medium and partially to the solid skeleton. To this end the momentum balance on the solid skeleton saturated by the viscoelastic fluid is derived and a generalised Biot's equation is obtained, which is coupled with the generalised Brinkman's equation derived in Part I of the paper. They together state that the whole stress carried by the porous medium, sum of that of the fluid and that of the solid skeleton, is not dissipated. The boundary condition here derived does not show any stress jump and as in Part I, to emphasize the effect of elasticity, a second order fluid of Coleman and Noll is considered as viscoelastic fluid. Also the stress boundary condition at the interface between a homogeneous solid and the porous medium saturated by the viscoelastic fluid is obtained.
NASA Astrophysics Data System (ADS)
Meulien Ohlmann, Odile
2013-02-01
Today the industry offers a chain of 3D products. Learning to "read" and to "create in 3D" becomes an issue of education of primary importance. 25 years professional experience in France, the United States and Germany, Odile Meulien set up a personal method of initiation to 3D creation that entails the spatial/temporal experience of the holographic visual. She will present some different tools and techniques used for this learning, their advantages and disadvantages, programs and issues of educational policies, constraints and expectations related to the development of new techniques for 3D imaging. Although the creation of display holograms is very much reduced compared to the creation of the 90ies, the holographic concept is spreading in all scientific, social, and artistic activities of our present time. She will also raise many questions: What means 3D? Is it communication? Is it perception? How the seeing and none seeing is interferes? What else has to be taken in consideration to communicate in 3D? How to handle the non visible relations of moving objects with subjects? Does this transform our model of exchange with others? What kind of interaction this has with our everyday life? Then come more practical questions: How to learn creating 3D visualization, to learn 3D grammar, 3D language, 3D thinking? What for? At what level? In which matter? for whom?
Heat transfer in porous medium embedded with vertical plate: Non-equilibrium approach - Part B
NASA Astrophysics Data System (ADS)
Quadir, G. A.; Badruddin, Irfan Anjum
2016-06-01
This work is continuation of the paper Part A. Due to large number of results, the paper is divided into two section with section-A (Part A) discussing the effect of various parameters such as heat transfer coefficient parameter, thermal conductivity ratio etc. on streamlines and isothermal lines. Section-B highlights the heat transfer characteristics in terms of Nusselt number The Darcy model is employed to simulate the flow inside the medium. It is assumed that the heat transfer takes place by convection and radiation. The governing partial differential equations are converted into non-dimensional form and solved numerically using finite element method.
Anomalously slow relaxation of interacting liquid nanoclusters confined in a porous medium
NASA Astrophysics Data System (ADS)
Borman, V. D.; Belogorlov, A. A.; Tronin, V. N.
2016-02-01
Anomalously slow relaxation of clusters of a liquid confined in a disordered system of pores has been studied for the (water-L23 nanoporous medium) system. The evolution of the system of confined liquid clusters consists of a fast formation stage followed by slow relaxation of the system and its decay. The characteristic time for the formation of the initial state is τp˜10 s after the reduction of excess pressure after complete filling. Anomalously slow relaxation has been observed for times of 101- 105 s, and decay has been observed at times of >105 s. The time dependence of the volume fraction θ of pores filled with the confined liquid is described by a power law θ ˜t-α with the exponent α <0.15 . The exponent α and temperature dependence α (T ) are qualitatively described theoretically for the case of a slightly polydisperse medium in a mean-field approximation with the inclusion of the interaction of liquid clusters and averaging over various degenerate local configurations of clusters. In this approximation, slow relaxation is represented as a continuous transition through a sequence of metastable states of the system of clusters with a decreasing barrier.
A simple, effective-medium model for water saturation in porous rocks
Berg, C.R.
1995-07-01
A general equation for water saturation is derived from effective-medium theory. A simpler low-frequency equation is also derived. Both equations are directly solvable for water saturation. The model should be applicable to any granular, water-wet formation. Additional relationships are derived specifically for application to shaly sandstones, but the model should be applicable to a wide range of rock types, water conductivities, and tool frequencies. In the derivation, hydrocarbons are included in the matrix component of the equation and the combined ``matrix`` elements are treated as resistors in parallel. The low-frequency equation is compared to various approaches to calculation of water saturation, such as Dual-Water, Waxman-Smits, and Bussian. The general equation is compared to three-component effective medium, porosity index, and complex refractive index models (CRIM). The model is proven to work on experimental data under a wide range of frequencies and water conductivities. It is recommended that the new saturation model be used for nearly all types of electrical saturation calculation, whether the measurements are from standard resistivity tools or from dielectric tools.
Impact of kinetic mass transfer on free convection in a porous medium
NASA Astrophysics Data System (ADS)
Lu, Chunhui; Shi, Liangsheng; Chen, Yiming; Xie, Yueqing; Simmons, Craig T.
2016-05-01
We investigate kinetic mass transfer effects on unstable density-driven flow and transport processes by numerical simulations of a modified Elder problem. The first-order dual-domain mass transfer model coupled with a variable-density-flow model is employed to describe transport behavior in porous media. Results show that in comparison to the no-mass-transfer case, a higher degree of instability and more unstable system is developed in the mass transfer case due to the reduced effective porosity and correspondingly a larger Rayleigh number (assuming permeability is independent on the mobile porosity). Given a constant total porosity, the magnitude of capacity ratio (i.e., immobile porosity/mobile porosity) controls the macroscopic plume profile in the mobile domain, while the magnitude of mass transfer timescale (i.e., the reciprocal of the mass transfer rate coefficient) dominates its evolution rate. The magnitude of capacity ratio plays an important role on the mechanism driving the mass flux into the aquifer system. Specifically, for a small capacity ratio, solute loading is dominated by the density-driven transport, while with increasing capacity ratio local mass transfer dominated solute loading may occur at later times. At significantly large times, however, both mechanisms contribute comparably to solute loading. Sherwood Number could be a nonmonotonic function of mass transfer timescale due to complicated interactions of solute between source zone, mobile zone and immobile zone in the top boundary layer, resulting in accordingly a similar behavior of the total mass. The initial assessment provides important insights into unstable density-driven flow and transport in the presence of kinetic mass transfer.
Molnar, Ian L; Willson, Clinton S; O'Carroll, Denis M; Rivers, Mark L; Gerhard, Jason I
2014-01-21
Attempts at understanding nanoparticle fate and transport in the subsurface environment are currently hindered by an inability to quantify nanoparticle behavior at the pore scale (within and between pores) within realistic pore networks. This paper is the first to present a method for high resolution quantification of silver nanoparticle (nAg) concentrations within porous media under controlled experimental conditions. This method makes it possible to extract silver nanoparticle concentrations within individual pores in static and quasi-dynamic (i.e., transport) systems. Quantification is achieved by employing absorption-edge synchrotron X-ray computed microtomography (SXCMT) and an extension of the Beer-Lambert law. Three-dimensional maps of X-ray mass linear attenuation are converted to SXCMT-determined nAg concentration and are found to closely match the concentrations determined by ICP analysis. In addition, factors affecting the quality of the SXCMT-determined results are investigated: 1) The acquisition of an additional above-edge data set reduced the standard deviation of SXCMT-determined concentrations; 2) X-ray refraction at the grain/water interface artificially depresses the SXCMT-determined concentrations within 18.1 μm of a grain surface; 3) By treating the approximately 20 × 10(6) voxels within each data set statistically (i.e., averaging), a high level of confidence in the SXCMT-determined mean concentrations can be obtained. This novel method provides the means to examine a wide range of properties related to nanoparticle transport in controlled laboratory porous medium experiments. PMID:24354304
Clement, T.P.; Jones, N.L.
1998-02-01
RT3D (Reactive Transport in 3-Dimensions) is a computer code that solves coupled partial differential equations that describe reactive-flow and transport of multiple mobile and/or immobile species in a three dimensional saturated porous media. RT3D was developed from the single-species transport code, MT3D (DoD-1.5, 1997 version). As with MT3D, RT3D also uses the USGS groundwater flow model MODFLOW for computing spatial and temporal variations in groundwater head distribution. This report presents a set of tutorial problems that are designed to illustrate how RT3D simulations can be performed within the Department of Defense Groundwater Modeling System (GMS). GMS serves as a pre- and post-processing interface for RT3D. GMS can be used to define all the input files needed by RT3D code, and later the code can be launched from within GMS and run as a separate application. Once the RT3D simulation is completed, the solution can be imported to GMS for graphical post-processing. RT3D v1.0 supports several reaction packages that can be used for simulating different types of reactive contaminants. Each of the tutorials, described below, provides training on a different RT3D reaction package. Each reaction package has different input requirements, and the tutorials are designed to describe these differences. Furthermore, the tutorials illustrate the various options available in GMS for graphical post-processing of RT3D results. Users are strongly encouraged to complete the tutorials before attempting to use RT3D and GMS on a routine basis.
Characterization of porous indium tin oxide thin films using effective medium theory
NASA Astrophysics Data System (ADS)
Ederth, J.; Niklasson, G. A.; Hultâker, A.; Heszler, P.; Granqvist, C. G.; van Doorn, A. R.; Jongerius, M. J.; Burgard, D.
2003-01-01
Effective medium theory was used to model optical properties in the 0.3 - 30 μm wavelength range for films comprised of nanoparticles of a transparent conducting oxide that are connected in a percolating network characterized by a filling factor f. The model is based on charge carrier density ne and resistivity ρ of the particles, and it enables analyses of these microscopic parameters upon posttreatment of the film. The theory was used to interpret data on spin coated layers consisting of nanoparticles of indium tin oxide (i.e., In2O3:Sn) with f close to the percolation limit. It showed that the as-deposited film contained nanoparticles with ne as large as ˜5×1020cm-3 and ρ≈5×10-4 Ω cm. The model also provided important data on f, ne, and ρ after heat treatment of the film.
ERIC Educational Resources Information Center
Hastings, S. K.
2002-01-01
Discusses 3 D imaging as it relates to digital representations in virtual library collections. Highlights include X-ray computed tomography (X-ray CT); the National Science Foundation (NSF) Digital Library Initiatives; output peripherals; image retrieval systems, including metadata; and applications of 3 D imaging for libraries and museums. (LRW)
NASA Astrophysics Data System (ADS)
Lokajíček, T.; Kern, H.; Svitek, T.; Ivankina, T.
2014-06-01
Ultrasonic measurements of the 3D velocity distribution of P- and S-waves were performed on a spherical sample of a biotite gneiss from the Outokumpu scientific drill hole. Measurements were done at room temperature and pressures up to 400 and 70 MPa, respectively, in a pressure vessel with oil as a pressure medium. A modified transducer/sample assembly and the installation of a new mechanical system allowed simultaneous measurements of P- and S-wave velocities in 132 independent directions of the sphere on a net in steps of 15°. Proper signals for P- and S-waves could be recorded by coating the sample surface with a high-viscosity shear wave gel and by temporal point contacting of the transmitter and receiver transducers with the sample surface during the measurements. The 3D seismic measurements revealed a strong foliation-related directional dependence (anisotropy) of P- and S-wave velocities, which is confirmed by measurements in a multi-anvil apparatus on a cube-shaped specimen of the same rock. Both experimental approaches show a marked pressure sensitivity of P- and S-wave velocities and velocity anisotropies. With increasing pressure, P- and S-wave velocities increase non-linearly due to progressive closure of micro-cracks. The reverse is true for velocity anisotropy. 3D velocity calculations based on neutron diffraction measurements of crystallographic preferred orientation (CPO) of major minerals show that the intrinsic bulk anisotropy is basically caused by the CPO of biotite constituting about 23 vol.% of the rock. Including the shape of biotite grains and oriented low-aspect ratio microcracks into the modelling increases bulk anisotropy. An important finding from this study is that the measurements on the sample sphere and on the sample cube displayed distinct differences, particularly in shear wave velocities. It is assumed that the differences are due to the different geometries of the samples and the configuration of the transducer-sample assembly
NASA Astrophysics Data System (ADS)
Ibrahim, F. S.; Hassanien, I. A.; Bakr, A. A.
2004-10-01
In this work, the effects of a temperature-dependent heat source on the hydromagnetic free-convective flow (set up due to temperature as well as species concentration) of an electrically conducting micropolar fluid past a steady vertical porous plate through a highly porous medium has been analyzed when the free stream oscillates in magnitude. A uniform magnetic field acts perpendicularly to the porous surface, which absorbs the micropolar fluid with constant suction velocity. The method of solution can be applied for a small perturbation approximation. The numerical results of velocity and temperature distributions of micropolar fluids are compared with the corresponding flow problems for a Newtonian fluid. The effects of the material parameters on velocity, angular momentum, concentration, and temperature fields across the boundary layer are investigated. In addition, the skin-friction coefficient and Nusselt number are shown in tabular form.
Antraygues, P.; Aubert, M.
1993-12-01
In order to characterize the relationships between self-potential generation and hydrothermal convection, laboratory measurements of electric potential and temperature are made along a vertical cylindrical column of porous material where a two-phase flow (wet steam) occurs. For steady state convection, the vertical distributions of vapor and water flow rates are calculated from thermal balance. At the initiation of convection, a positive electrical charge flux is related to the convective front. For isothermal and steady state columns, a positive electric potential gradient is observed along the vapor flow direction. These electric potentials are mainly a function of the vapor flow rates and of the medium permeability. A sudden and large increase in the vapor flow rate and in the volume fraction of vapor can induce a large and long-lived increase in the potential differences along the vapor flow direction. An electrokinetic effect related to the saturated vapor flow is the best candidate for this electric potential generation. The experimental resutls obtained in the present study are applied to self-potential generation in rising two-phase convective cells on active volcanoes. The observed positive self-potential anomalies close to active fissures depend on the electrical charge flux related to the upward saturated vapor flow. These results also demonstrate the value of self-potential monitoring in the early stages preceding a volcanic eruption.
NASA Astrophysics Data System (ADS)
Lal, Sreeyuth; Lucci, Francesco; Defraeye, Thijs; Poulikakos, Lily; Partl, Manfred; Derome, Dominique; Carmeliet, Jan
2015-11-01
Forced convective drying of a macroporous medium is a complex interplay of enhanced air-vapor mixing due to turbulent airflow at the air-solid interface and the momentum transfer resulting from air infiltration into the material. Such air infiltration is expected to have a non-trivial effect on the drying rate of a material like porous asphalt (PA), which is characterized by large, interconnected pores open to the surface. Through a series of CFD simulations performed on an original PA geometry extracted from CT scans, we quantify the relative impacts of interior material resistance and boundary layer resistance on moisture transport in PA. At wind speeds below 1 m/s, the effect of material resistance on the total moisture transfer is found to be high due to low air infiltration. At higher wind speeds, air infiltration increases by which the material resistance decreases. Similar simulations are performed on an idealized PA geometry made from randomized Kelvin cells (KC) since they are computationally less expensive, and thus ideal for parametric studies. However, in KC cells, drying from air infiltration is stronger than diffusive drying even at low wind speeds. This shows the need to fine-tune the pore connectivity of KC to better match the air infiltration observed in PA. This research was supported by a Swiss National Science Foundation (SNSF) Grant (200021-143651).
NASA Astrophysics Data System (ADS)
Sulochana, C.; Sandeep, N.; Sugunamma, V.; Rushi Kumar, B.
2016-06-01
In this paper, we investigated the effects of aligned magnetic field, thermal radiation, heat generation/absorption, cross-diffusion, viscous dissipation, heat source and chemical reaction on the flow of a nanofluid past an exponentially stretching sheet in porous medium. The governing partial differential equations are transformed to set of ordinary differential equations using self-similarity transformation, which are then solved numerically using bvp4c Matlab package. Finally the effects of various non-dimensional parameters on velocity, temperature, concentration, skin friction, local Nusselt and Sherwood numbers are thoroughly investigated and presented through graphs and tables. We observed that an increase in the aligned angle strengthens the applied magnetic field and decreases the velocity profiles of the flow. Soret and Dufour numbers are helpful to enhance the heat transfer rate. An increase in the heat source parameter, radiation parameter and Eckert number increases the mass transfer rate. Mixed convection parameter has tendency to enhance the friction factor along with the heat and mass transfer rate.
NASA Astrophysics Data System (ADS)
Marneni, Narahari; Tippa, Sowmya; Pendyala, Rajashekhar
2015-12-01
Analytical investigation of the unsteady natural convection flow along an infinite vertical plate embedded in a porous medium subjected to a ramped temperature boundary condition has been performed in the presence of magnetic field, thermal radiation, heat generation or absorption, chemical reaction and Dufour effect. The governing equations for momentum, energy and concentration have been solved using the Laplace transform technique. The closed-form exact solutions for the velocity, temperature and concentration fields as well as the skin-friction, Nusselt and Sherwood numbers are obtained without any restrictions. The influence of pertinent parameters on the fluid velocity, temperature, skin-friction and Nusselt number have been discussed in detailed through graphs. The natural convection due to ramped wall temperature (RWT) has also been compared with that of the constant wall temperature (CWT). It is observed that the fluid velocity and temperature profiles are greater in case of CWT than the case of RWT. Also it is noticed that the flow accelerates with increasing values of heat source parameter, permeability parameter and Dufour number while the flow retardation is observed with increasing values of radiation parameter, magnetic field parameter and Schmidt number.
NASA Astrophysics Data System (ADS)
Sulochana, C.; Sandeep, N.; Sugunamma, V.; Rushi Kumar, B.
2015-07-01
In this paper, we investigated the effects of aligned magnetic field, thermal radiation, heat generation/absorption, cross-diffusion, viscous dissipation, heat source and chemical reaction on the flow of a nanofluid past an exponentially stretching sheet in porous medium. The governing partial differential equations are transformed to set of ordinary differential equations using self-similarity transformation, which are then solved numerically using bvp4c Matlab package. Finally the effects of various non-dimensional parameters on velocity, temperature, concentration, skin friction, local Nusselt and Sherwood numbers are thoroughly investigated and presented through graphs and tables. We observed that an increase in the aligned angle strengthens the applied magnetic field and decreases the velocity profiles of the flow. Soret and Dufour numbers are helpful to enhance the heat transfer rate. An increase in the heat source parameter, radiation parameter and Eckert number increases the mass transfer rate. Mixed convection parameter has tendency to enhance the friction factor along with the heat and mass transfer rate.
NASA Astrophysics Data System (ADS)
Kim, Min Chan
2014-11-01
To simulate a CO2 sequestration process, some researchers employed a water/propylene glycol (PPG) system which shows a non-monotonic density profile. Motivated by this fact, the stability of the diffusion layer of two miscible fluids saturated in a porous medium is analyzed. For a non-monotonic density profile system, linear stability equations are derived in a global domain, and then transformed into a system of ordinary differential equations in an infinite domain. Initial growth rate analysis is conducted without the quasi-steady state approximation (QSSA) and shows that initially the system is unconditionally stable for the least stable disturbance. For the time evolving case, the ordinary differential equations are solved applying the eigen-analysis and numerical shooting scheme with and without the QSSA. To support these theoretical results, direct numerical simulations are conducted using the Fourier spectral method. The results of theoretical linear stability analyses and numerical simulations validate one another. The present linear and nonlinear analyses show that the water/PPG system is more unstable than the CO2/brine one, and the flow characteristics of these two systems are quite different from each other.
Waheed, Shimaa E
2016-01-01
A problem of flow and heat transfer in a non-Newtonian Maxwell liquid film over an unsteady stretching sheet embedded in a porous medium in the presence of a thermal radiation is investigated. The unsteady boundary layer equations describing the problem are transformed to a system of non-linear ordinary differential equations which is solved numerically using the shooting method. The effects of various parameters like the Darcy parameter, the radiation parameter, the Deborah number and the Prandtl number on the flow and temperature profiles as well as on the local skin-friction coefficient and the local Nusselt number are presented and discussed. It is observed that increasing values of the Darcy parameter and the Deborah number cause an increase of the local skin-friction coefficient values and decrease in the values of the local Nusselt number. Also, it is noticed that the local Nusselt number increases as the Prandtl number increases and it decreases with increasing the radiation parameter. However, it is found that the free surface temperature increases by increasing the Darcy parameter, the radiation parameter and the Deborah number whereas it decreases by increasing the Prandtl number. PMID:27462509
Papini, M.P.; Kahie, Y.D.; Troia, B.; Majone, M.
1999-12-15
The surface complexation approach has been applied to describe the adsorption of lead and proton onto a heterogeneous natural porous medium at constant ionic strength. Acid-base titration experiments were used to determine the minimum number of sites needed to describe the surface heterogeneity. Lead adsorption tests at several pH and total lead concentration were used to complete the model structure, whose adjustable parameters (site concentration and apparent formation constants) were determined by nonlinear multivariate regression of titration and adsorption data. The final model represents the acid-base properties of the surface by the presence of two amphoteric sites, SOH and TOH, and a monoprotic one, MOH; whereas lead adsorption is considered only onto SOH and MOH sites. The model allows a good representation of the experimental behavior in the whole experimental range. Theoretical surface speciation shows that lead adsorption occurs mostly onto site MOH at low pH level and on both SOH and MOH sites at higher values. The model was independently validated by simulating Pb and pH breakthrough experiments performed in small chromatographic columns. Experimental breakthroughs are well predicted by an advection-dispersion transport model coupled with the chemical equilibrium routine (IMPACT), without any parameter adjustment. A large spreading of Pb and pH breakthroughs was calculated and experimentally observed, even in the absence of any kinetic effect. That spreading is explained in terms of the concomitant presence of competitive adsorption and surface heterogeneity.
3-D Relativistic MHD Simulations
NASA Astrophysics Data System (ADS)
Nishikawa, K.-I.; Frank, J.; Koide, S.; Sakai, J.-I.; Christodoulou, D. M.; Sol, H.; Mutel, R. L.
1998-12-01
We present 3-D numerical simulations of moderately hot, supersonic jets propagating initially along or obliquely to the field lines of a denser magnetized background medium with Lorentz factors of W = 4.56 and evolving in a four-dimensional spacetime. The new results are understood as follows: Relativistic simulations have consistently shown that these jets are effectively heavy and so they do not suffer substantial momentum losses and are not decelerated as efficiently as their nonrelativistic counterparts. In addition, the ambient magnetic field, however strong, can be pushed aside with relative ease by the beam, provided that the degrees of freedom associated with all three spatial dimensions are followed self-consistently in the simulations. This effect is analogous to pushing Japanese ``noren'' or vertical Venetian blinds out of the way while the slats are allowed to bend in 3-D space rather than as a 2-D slab structure.
Chamkha, A.J.
1997-10-01
There has been considerable interest in studying natural or buoyancy-induced flows in fluid-saturated porous media adjacent to surfaces in recent years. This interest stems from numerous possible industrial and technological applications. Examples of some applications include geothermal reservoirs, drying of porous solids, heat exchanger design, petroleum production, filtration, chemical catalytic reactor, nuclear waste repositories, and geophysical flows. Here, continuum equations governing steady, laminar, buoyancy-induced flow and heat transfer of a power-law fluid over a horizontal surface immersed in a uniform porosity and permeability porous medium are developed. These partial differential equations are transformed into ordinary differential equations by using a general similarity transformation for variable surface temperature and constant heat flux cases. The resulting equations are solved numerically by an implicit finite-difference method. Numerical results for typical velocity and temperature profiles are presented and discussed.
NASA Astrophysics Data System (ADS)
Chen-Wiegart, Yu-chen Karen; DeMike, Ross; Erdonmez, Can; Thornton, Katsuyo; Barnett, Scott A.; Wang, Jun
2014-03-01
A distance propagation method is presented for calculating tortuosity with relatively low computation time from three-dimensional (3D) tomographic data. Moreover, a novel concept of tortuosity distribution is developed to provide a more comprehensive picture of inhomogeneous microstructures where tortuosity depends on the actual 3D paths. Instead of using one single tortuosity value, the tortuosity distribution both as spatial distribution map and also statistic histogram can provide a more complete description. The method, which can be applied to any porous medium, is tested against a diffusion-based tortuosity calculation on two 3D microstructures: a LiCoO2 cathode electrode of lithium ion battery measured by x-ray nano-tomography and a lanthanum strontium manganite-yttria-stabilized zirconia, solid oxide fuel cells cathode measured using focused ion beam-scanning electron microscopy serial sectioning. The present method is shown to provide good-agreement with the effective diffusion-based tortuosity values.
Crandall, K.R.
1987-08-01
TRACE 3-D is an interactive beam-dynamics program that calculates the envelopes of a bunched beam, including linear space-charge forces, through a user-defined transport system. TRACE 3-D provides an immediate graphics display of the envelopes and the phase-space ellipses and allows nine types of beam-matching options. This report describes the beam-dynamics calculations and gives detailed instruction for using the code. Several examples are described in detail.
Saiers, James E.; Ryan, Joseph
2003-06-15
During the past year (June 2003 to June 2004), work at Yale has centered on investigating the influences of porewater pH, flow transients, and the presence of natural organic matter (NOM) on the deposition and mobilization of clay colloids (kaolinite and illite) within columns packed with unsaturated porous media. The experiments on pH and flow-transient effects were described in our First-Term Progress Report (which covered the initial 18 months of the study) and will not be repeated here. More recent experiments on the role of NOM in colloid transport proved equally as interesting. Even at porewater concentrations as low as 0.2 mg/L, soil-humic acid substantially lowered clay-colloid deposition rates compared to the case in which soil-humic acid was absent from the porewater. We attribute this to adsorption of the humic acid to the positively charged edge sites of the clay colloids, which effectively reduced the colloid affinity for negatively charged air- and solid-water interfaces. Comparison of the results of the column experiments to calculations of a new mathematical model has sharpened our inferences regarding mechanisms that govern the rate-limited deposition and mobilization of colloids. We are testing these inferences by carrying out flow-and-transport visualization experiments. We have constructed a semi-transparent representation of a porous medium, consisting of a rectangular parallel-plate chamber that encloses 3-5 layers of uniformly sized sand grains. Ceramic plates fused to the ends of the chamber maintain the capillary tension and syringe pumps (located at the inlet and outlet ends) regulate the flow of water and colloids through the partially saturated sand. By placing the chamber beneath a microscope, we can examine the distribution of colloids between air-water and solid-water interfaces, directly measure the kinetics of deposition onto these interfaces, and observe the mechanisms that contribute to the release of immobile colloids. To date
NASA Astrophysics Data System (ADS)
Srinivasacharya, D.; Surender, Ontela
2015-01-01
The effect of thermal and mass stratification on mixed convection boundary layer flow over a vertical flat plate embedded in a porous medium saturated by a nanofluid has been investigated. The vertical plate is maintained at uniform and constant heat, mass and nanoparticle fluxes, and the behavior of the porous medium is described by the Darcy model. The model considered for nanofluids incorporates the effects of Brownian motion and thermophoresis. In addition, the thermal energy equations include regular diffusion and cross-diffusion terms. A suitable coordinate transformation is introduced, and the obtained system of non-similar, coupled and non-linear partial differential equations is solved numerically. The influence of pertinent parameters on the non-dimensional velocity, temperature, concentration and nanoparticle volume fraction are discussed. In addition, the variation of heat, mass and nanoparticle transfer rates at the plate are exhibited graphically for different values of physical parameters.
Suresh, M.; Manglik, A.
2014-01-01
This paper proposes the exact solution for unsteady flow of a viscous incompressible electrically conducting fluid past a impulsively started infinite horizontal surface which is rotating with an angular velocity embedded in a saturated porous medium under the influence of strong magnetic field with hall effect. Our study focuses on the change of direction of the external magnetic field on the flow system which leads to change in the flow behavior and skin frictional forces at the boundary. Systems of flow equations are solved using Laplace transform technique. The impacts of control parameters Hartman number, rotation of the system, hall effect, inclination of the magnetic field, and Darcy number on primary and secondary velocities are shown graphically, skin friction at horizontal boundary in tabular form. For validating our results, in the absence of permeability of the porous medium and inclination of the magnetic field the results are in good agreement with the published results.
NASA Astrophysics Data System (ADS)
Srinivasacharya, D.; Surender, O.
2015-07-01
In this paper, non-similarity solutions for natural convection heat and mass transfer along a vertical plate with a uniform wall temperature and concentration in a doubly stratified porous medium saturated by a fluid are obtained. The Darcy-Forchheimer-based model is employed to describe the flow in the porous medium. The nonlinear governing equations and their associated boundary conditions are initially cast into dimensionless forms by using pseudo-similarity variables. The resulting system of nonlinear partial differential equations is then solved numerically by using the Keller-box method. The effects of the buoyancy parameter, Forchheimer number, and thermal and solutal stratification parameters on the dimensionless velocity, temperature, concentration, and heat and mass transfer coefficients are studied.
Fauske, H.K.; Cash, R.J.
1993-11-01
The conditions under which ferrocyanide waste sludge flows as a homogeneous non-Newtonian two-phase (solid precipitate-liquid) mixture rather than as a liquid through a porous medium (of stationary precipitate) are examined theoretically, based on the notion that the preferred rheological behavior of the sludge is the one which imposes the least resistance to the sludge flow. The homogeneous two-phase mixture is modeled as a power-law fluid and simple criteria are derived that show that the homogeneous power-law sludge-flow is a much more likely flow situation than the porous medium model of sludge flow. The implication of this finding is that the formation of a hot spot or the drainage of sludge from a waste tank are not likely to result in the uncovering (drying) and subsequent potential overheating of the reactive-solid component of the sludge.
Kieft, T.L.; Ringelberg, D.B.; White, D.C.
1994-09-01
Ester-linked phospholipid fatty acid (PLFA) profiles of a Pseudomonas aureofaciens strain and an Arthrobacter protophormiae strain, each isolated from a subsurface sediment, were quantified in a starvation experiment in a silica sand porous medium under moist and dry conditions. Washed cells were added to sand microcosms and maintained under saturated conditions or subjected to desiccation by slow drying over a period of 16 days. In a third treatment, cells were added to saturated microcosms along with organic nutrients and maintained under saturated conditions. The numbers of culturable cells of both bacterial strains declined to below detection level within 16 days in both the moist and dried nutrient-deprived conditions, while direct counts and total PLFAs remained relatively constant. Both strains of bacteria maintained culturability in the nutrient-amended microcosms. The dried P. aureofaciens cells showed increased ratios of saturated to unsaturated fatty acids, increased ratios of trans- to cis-monoenoic fatty acids, and increased ratios of cyclopropyl fatty acids to their monoenoic precursors. P. aureofaciens starved under moist conditions showed few changes in PLFA profiles during the 16-day incubation, whereas cells incubated in the presence of nutrients showed decreases in the ratios of both saturated fatty acids to unsaturated fatty acids and cyclopropyl fatty acids to their monoenoic precursors. The PLFA profiles of A. protophormiae changed very little in response to either nutrient deprivation or desiccation. Diglyceride fatty acids, proposedindicators of dead or lysed cells, remained relatively constant throughout the experiment. The results of this laboratory experiment can be useful for interpreting PLFA profiles of subsurface communities of microorganisms for the purpose of determining their physiological status. 43 refs., 8 figs.
Bolton, E.W.; Lasaga, A.C.; Rye, D.M.
1999-01-01
The kinetics of dissolution and precipitation is of central importance to understanding the long-term evolution of fluid flows in crustal environments, with implications for problems as diverse as nuclear waste disposal and crustal evolution. The authors examine the dynamics of such evolution for several geologically relevant permeability distributions (models for en-echelon cracks, an isolated sloping fractured zone, and two sloping high-permeability zones that are close enough together to interact). Although the focus is on a simple quartz matrix system, generic features emerge from this study that can aid in the broader goal of understanding the long-term feedback between flow and chemistry, where dissolution and precipitation is under kinetic control. Examples of thermal convection in a porous medium with spatially variable permeability reveal features of central importance to water-rock interaction. After a transient phase, an accelerated rate of change of porosity may be used with care to decrease computational time, as an alternative to the quasi-stationary state approximation (Lichtner, 1988). Kinetic effects produce features not expected by traditional assumptions made on the basis of equilibrium, for example, that cooling fluids are oversaturated and heating fluids are undersaturated with respect to silicic acid equilibrium. Indeed, the authors observe regions of downwelling oversaturated fluid experiencing heating and regions of upwelling, yet cooling, undersaturated fluid. When oscillatory convection is present, the amplitudes of oscillation generally increase with time in near-surface environments, whereas amplitudes tend to decrease over long times near the heated lower boundary. The authors examine the scaling behavior of characteristic length scales, of terms in the solute equation, and of the typical deviation from equilibrium, each as a function of the kinetic rate parameters.
NASA Astrophysics Data System (ADS)
Oldham, Mark
2015-01-01
Radiochromic materials exhibit a colour change when exposed to ionising radiation. Radiochromic film has been used for clinical dosimetry for many years and increasingly so recently, as films of higher sensitivities have become available. The two principle advantages of radiochromic dosimetry include greater tissue equivalence (radiologically) and the lack of requirement for development of the colour change. In a radiochromic material, the colour change arises direct from ionising interactions affecting dye molecules, without requiring any latent chemical, optical or thermal development, with important implications for increased accuracy and convenience. It is only relatively recently however, that 3D radiochromic dosimetry has become possible. In this article we review recent developments and the current state-of-the-art of 3D radiochromic dosimetry, and the potential for a more comprehensive solution for the verification of complex radiation therapy treatments, and 3D dose measurement in general.
Wicks, George G; Serkiz, Steven M.; Zidan, Ragaiy; Heung, Leung K.
2014-06-24
Porous wall hollow glass microspheres are provided as a template for formation of nanostructures such as carbon nanotubes, In addition, the carbon nanotubes in combination with the porous wall hollow glass microsphere provides an additional reaction template with respect to carbon nanotubes.
NASA Astrophysics Data System (ADS)
Iliesiu, Luca; Kos, Filip; Poland, David; Pufu, Silviu S.; Simmons-Duffin, David; Yacoby, Ran
2016-03-01
We study the conformal bootstrap for a 4-point function of fermions < ψψψψ> in 3D. We first introduce an embedding formalism for 3D spinors and compute the conformal blocks appearing in fermion 4-point functions. Using these results, we find general bounds on the dimensions of operators appearing in the ψ × ψ OPE, and also on the central charge C T . We observe features in our bounds that coincide with scaling dimensions in the GrossNeveu models at large N . We also speculate that other features could coincide with a fermionic CFT containing no relevant scalar operators.
Small scale flow processes in aqueous heterogeneous porous media
Rashidi, M.; Dickenson, E.
1996-04-01
Small scale flow processes in aqueous heterogeneous porous systems have been studied experimentally via novel nonintrusive fluorescence imaging techniques. The techniques involve 3D visualization and quantification of flow fields within a refractive index-matched transparent porous column. The refractive index-matching yields a transparent porous medium, free from any scattering and refraction at the solid-liquid interfaces, as a result allowing direct optical probing at any point within the porous system. By illuminating the porous regions within the column with a planar sheet of laser beam, flow processes through the porous medium can be observed microscopically, and qualitative and quantitative in-pore transport information can be obtained at a good resolution and a good accuracy. A CCD camera is used to record the fluorescent images at every vertical plane location while sweeping back and forth across the column. These digitized flow images are then analyzed and accumulated over a 3D volume within the column. Series of flow experiments in aqueous, refractive index-matched, porous systems packed with natural mineral particles have been performed successfully in these laboratories.
NASA Astrophysics Data System (ADS)
Altman, S. J.; Kirk, M. F.; Santillan, E. U.; McGrath, L. K.
2013-12-01
Microbial biomass can clog porous media and ultimately affect both structural and mineral trapping of CO2 in geological carbon storage reservoirs. Whether biomass can remain intact following a sudden decrease in groundwater pH, a geochemical change associated with CO2 injection, is unclear. We examined this question using twelve biologically-active and three control column-reactor experiments. Cell abundance and distribution was monitored using confocal microscopy, plating, and direct counting. Hydraulic conductivity (K) was monitored using pressure sensors. Growth occurred for four days at neutral pH. During that time, K within the clogged portion of the reactors decreased from 0.013 to 0.0006 cm s-1 on average, a 1.47 log reduction. Next, the pH of the inflowing aqueous medium was lowered to pH 4 in six experiments and pH 5.7 in six experiments. As a result, K increased in five of the pH 4 experiments and two of the pH 5.7 experiments. Despite this increase, however, the columns remained largely clogged. Compared to pre-inoculation K values, log reductions averaged 1.13 and 1.44 in pH 4 and pH 5.7 experiments, respectively. Our findings show that biomass can largely remain intact following acidification and continue to reduce K, even when considerable cell stress and death occurs. This material is based upon work supported as part of the Center for Frontiers of Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001114. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Kieft, T. L.; Ringelberg, D. B.; White, D. C.
1994-01-01
Ester-linked phospholipid fatty acid (PLFA) profiles of a Pseudomonas aureofaciens strain and an Arthrobacter protophormiae strain, each isolated from a subsurface sediment, were quantified in a starvation experiment in a silica sand porous medium under moist and dry conditions. Washed cells were added to sand microcosms and maintained under saturated conditions or subjected to desiccation by slow drying over a period of 16 days to final water potentials of approximately - 7.5 MPa for the P. aureofaciens and - 15 MPa for the A. protophormiae. In a third treatment, cells were added to saturated microcosms along with organic nutrients and maintained under saturated conditions. The numbers of culturable cells of both bacterial strains declined to below detection level within 16 days in both the moist and dried nutrient-deprived conditions, while direct counts and total PLFAs remained relatively constant. Both strains of bacteria maintained culturability in the nutrient-amended microcosms. The dried P. aureofaciens cells showed changes in PLFA profiles that are typically associated with stressed gram-negative cells, i.e., increased ratios of saturated to unsaturated fatty acids, increased ratios of trans- to cis-monoenoic fatty acids, and increased ratios of cyclopropyl fatty acids to their monoenoic precursors. P. aureofaciens starved under moist conditions showed few changes in PLFA profiles during the 16-day incubation, whereas cells incubated in the presence of nutrients showed decreases in the ratios of both saturated fatty acids to unsaturated fatty acids and cyclopropyl fatty acids to their monoenoic precursors. The PLFA profiles of A. protophormiae changed very little in response to either nutrient deprivation or desiccation. Diglyceride fatty acids, which have been proposed to be indicators of dead or lysed cells, remained relatively constant throughout the experiment. Only the A. protophormiae desiccated for 16 days showed an increase in the ratio of
NASA Astrophysics Data System (ADS)
Iizuka, Keigo
2008-02-01
In order to circumvent the fact that only one observer can view the image from a stereoscopic microscope, an attachment was devised for displaying the 3D microscopic image on a large LCD monitor for viewing by multiple observers in real time. The principle of operation, design, fabrication, and performance are presented, along with tolerance measurements relating to the properties of the cellophane half-wave plate used in the design.
Chamkha, A.J.
1998-07-01
Continuum boundary layer equations are derived for governing steady, laminar, hydromagnetic, mixed convection flow along a vertical semi-infinite permeable plate maintained at constant heat flux and embedded in a uniform porous medium with heat generation and magnetic dissipation. A mixed-convection parameter covering the entire range from pure forced convection to pure free convection is introduced. The governing equations are transformed using a non-similarity transformation and solved numerically by an implicit finite difference method. Typical results for the skin friction coefficient and the wall heat transfer are presented and discussed for various parametric conditions. The investigation of forced, mixed, and free convection heat transfer from surfaces embedded in porous media has received considerable attention in view of its importance in the petroleum industries, filtration, heat exchanger design, thermal insulation, chemical catalytic reactors, burying of drums containing heat-generating chemicals in the earth, and underground spread of pollutants.
Aziz, Asim; Ali, Yasir; Aziz, Taha; Siddique, J I
2015-01-01
In this paper, we investigate the slip effects on the boundary layer flow and heat transfer characteristics of a power-law fluid past a porous flat plate embedded in the Darcy type porous medium. The nonlinear coupled system of partial differential equations governing the flow and heat transfer of a power-law fluid is transformed into a system of nonlinear coupled ordinary differential equations by applying a suitable similarity transformation. The resulting system of ordinary differential equations is solved numerically using Matlab bvp4c solver. Numerical results are presented in the form of graphs and the effects of the power-law index, velocity and thermal slip parameters, permeability parameter, suction/injection parameter on the velocity and temperature profiles are examined. PMID:26407162
Aziz, Asim; Ali, Yasir; Aziz, Taha; Siddique, J. I.
2015-01-01
In this paper, we investigate the slip effects on the boundary layer flow and heat transfer characteristics of a power-law fluid past a porous flat plate embedded in the Darcy type porous medium. The nonlinear coupled system of partial differential equations governing the flow and heat transfer of a power-law fluid is transformed into a system of nonlinear coupled ordinary differential equations by applying a suitable similarity transformation. The resulting system of ordinary differential equations is solved numerically using Matlab bvp4c solver. Numerical results are presented in the form of graphs and the effects of the power-law index, velocity and thermal slip parameters, permeability parameter, suction/injection parameter on the velocity and temperature profiles are examined. PMID:26407162
Vasco, D.W.
2011-10-01
Using an asymptotic technique, valid when the medium properties are smoothly-varying, I derive a semi-analytic expression for the propagation velocity of a quasi-static disturbance traveling within a nonlinear-elastic porous medium. The phase, a function related to the propagation time, depends upon the properties of the medium, including the pressure-sensitivities of the medium parameters, and on pressure and displacement amplitude changes. Thus, the propagation velocity of a disturbance depends upon its amplitude, as might be expected for a nonlinear process. As a check, the expression for the phase function is evaluated for a poroelastic medium, when the material properties do not depend upon the fluid pressure. In that case, the travel time estimates agree with conventional analytic estimates, and with values calculated using a numerical simulator. For a medium with pressure-dependent permeability I find general agreement between the semi-analytic estimates and estimates from a numerical simulation. In this case the pressure amplitude changes are obtained from the numerical simulator.
Simulation of contaminant flow ina laboratory-scale porous system
Rashidi, M.
1995-12-01
The microscopic movement of contaminants in a porous medium has been simulated in an experiment. The approach has been to study the microscale transport processes using a novel nonintrusive fluorescence imaging technique developed in our laboratories. The system studied consists of a packed porous column with a refractive index-matched fluid seeded with fluorescent tracer particles (for flow measurements) or an organic dye (for contaminant concentration measurements). Microscopic measurements of contaminant concentration, contaminant velocity, and pore geometry were obtained in a full three-dimensional volume of the test section at a good accuracy and a high resolution. 3D plots of these measurements show the complex geometry of the porous medium. It is also seen that near the contaminant front there is a significant correlation between the flow and the contaminant concentration. The goal is to use these and future results toward better understanding of contaminant flow and report thorough natural porous media.
Visualizing 3D fracture morphology in granular media
NASA Astrophysics Data System (ADS)
Dalbe, Marie-Julie; Juanes, Ruben
2015-11-01
Multiphase flow in porous media plays a fundamental role in many natural and engineered subsurface processes. The interplay between fluid flow, medium deformation and fracture is essential in geoscience problems as disparate as fracking for unconventional hydrocarbon production, conduit formation and methane venting from lake and ocean sediments, and desiccation cracks in soil. Recent work has pointed to the importance of capillary forces in some relevant regimes of fracturing of granular materials (Sandnes et al., Nat. Comm. 2011), leading to the term hydro-capillary fracturing (Holtzman et al., PRL 2012). Most of these experimental and computational investigations have focused, however, on 2D or quasi-2D systems. Here, we develop an experimental set-up that allows us to observe two-phase flow in a 3D granular bed, and control the level of confining stress. We use an index matching technique to directly visualize the injection of a liquid in a granular media saturated with another, immiscible liquid. We determine the key dimensionless groups that control the behavior of the system, and elucidate different regimes of the invasion pattern. We present result for the 3D morphology of the invasion, with particular emphasis on the fracturing regime.
Visualizing 3D Fracture Morphology in Granular Media
NASA Astrophysics Data System (ADS)
Dalbe, M. J.; Juanes, R.
2015-12-01
Multiphase flow in porous media plays a fundamental role in many natural and engineered subsurface processes. The interplay between fluid flow, medium deformation and fracture is essential in geoscience problems as disparate as fracking for unconventional hydrocarbon production, conduit formation and methane venting from lake and ocean sediments, and desiccation cracks in soil. Recent work has pointed to the importance of capillary forces in some relevant regimes of fracturing of granular materials (Sandnes et al., Nat. Comm. 2011), leading to the term hydro-capillary fracturing (Holtzman et al., PRL 2012). Most of these experimental and computational investigations have focused, however, on 2D or quasi-2D systems. Here, we develop an experimental set-up that allows us to observe two-phase flow in a 3D granular bed, and control the level of confining stress. We use an index matching technique to directly visualize the injection of a liquid in a granular media saturated with another, immiscible liquid. We determine the key dimensionless groups that control the behavior of the system, and elucidate different regimes of the invasion pattern. We present result for the 3D morphology of the invasion, with particular emphasis on the fracturing regime.
3-D Relativistic MHD Simulations
NASA Astrophysics Data System (ADS)
Nishikaw, K.-I.; Frank, J.; Christodoulou, D. M.; Koide, S.; Sakai, J.-I.; Sol, H.; Mutel, R. L.
1998-12-01
We present 3-D numerical simulations of moderately hot, supersonic jets propagating initially along or obliquely to the field lines of a denser magnetized background medium with Lorentz factors of W=4.56 and evolving in a four-dimensional spacetime. The new results are understood as follows: Relativistic simulations have consistently shown that these jets are effectively heavy and so they do not suffer substantial momentum losses and are not decelerated as efficiently as their nonrelativistic counterparts. In addition, the ambient magnetic field, however strong, can be pushed aside with relative ease by the beam, provided that the degrees of freedom associated with all three spatial dimensions are followed self-consistently in the simulations. This effect is analogous to pushing Japanese ``noren'' or vertical Venetian blinds out of the way while the slats are allowed to bend in 3-D space rather than as a 2-D slab structure. We also simulate jets with the more realistic initial conditions for injecting jets for helical mangetic field, perturbed density, velocity, and internal energy, which are supposed to be caused in the process of jet generation. Three possible explanations for the observed variability are (i) tidal disruption of a star falling into the black hole, (ii) instabilities in the relativistic accretion disk, and (iii) jet-related PRocesses. New results will be reported at the meeting.
NASA Astrophysics Data System (ADS)
Kostrzewski, Andrew A.; Aye, Tin M.; Kim, Dai Hyun; Esterkin, Vladimir; Savant, Gajendra D.
1998-09-01
Physical Optics Corporation has developed an advanced 3-D virtual reality system for use with simulation tools for training technical and military personnel. This system avoids such drawbacks of other virtual reality (VR) systems as eye fatigue, headaches, and alignment for each viewer, all of which are due to the need to wear special VR goggles. The new system is based on direct viewing of an interactive environment. This innovative holographic multiplexed screen technology makes it unnecessary for the viewer to wear special goggles.
NASA Technical Reports Server (NTRS)
1992-01-01
Ames Research Center research into virtual reality led to the development of the Convolvotron, a high speed digital audio processing system that delivers three-dimensional sound over headphones. It consists of a two-card set designed for use with a personal computer. The Convolvotron's primary application is presentation of 3D audio signals over headphones. Four independent sound sources are filtered with large time-varying filters that compensate for motion. The perceived location of the sound remains constant. Possible applications are in air traffic control towers or airplane cockpits, hearing and perception research and virtual reality development.
Tsimpanogiannis, Ioannis N.; Yortsos, Yanis C.
2001-08-15
This report describes the development of an effective continuum model to describe the nucleation and subsequent growth of a gas phase from a supersaturated, slightly compressible binary liquid in a porous medium, driven by solute diffusion.This report also focuses on the processes resulting from the withdrawal of the liquid at a constant rate. As before, the model addresses two stages before the onset of bulk gas flow, nucleation and gas phase growth. Because of negligible gradients due to gravity or viscous forces, the critical gas saturation, is only a function of the nucleation fraction.
NASA Astrophysics Data System (ADS)
Hari, Niranjan; Sivasankaran, S.; Bhuvaneswari, M.; Siri, Zailan
2015-12-01
The aim of the present study is to analyze the effects of chemical reaction on MHD mixed convection with the stagnation point flow towards a vertical plate embedded in a porous medium with radiation and internal heat generation. The governing boundary layer equations are transformed into a set of ordinary differential equations using similarity transformations. Then they are solved by shooting technique with Runge-Kutta fourth order iteration. The obtained numerical results are illustrated graphically and the heat and mass transfer rates are given in tabular form. The velocity and temperature profiles overshoot near the plate on increasing the chemical reaction parameter, Richardson number and magnetic field parameter.
Choudhury, Rita; Dhar, Paban
2014-01-01
This paper presents the study of convective heat and mass transfer characteristics of an incompressible MHD viscoelastic fluid past an infinite vertical plate immersed in a porous medium with chemical reaction and ion slip effects. Highly nondimensional governing equations are solved analytically by perturbation scheme. The analytical expressions for velocity, shearing stress, temperature, concentration, rate of heat transfer, and mass transfer are obtained. Also, graphical representations have been carried out for velocity field and shearing stress to investigate the effects of viscoelasticity and the effects of ion slip on the fluid flow in combination with other physical parameters involved in the solution. PMID:27379282
NASA Astrophysics Data System (ADS)
Srinivasacharya, D.; Pranitha, J.; RamReddy, Ch.
2012-05-01
In this paper, effects of magnetic field and double dispersion on free convection heat and mass transfer along a vertical plate embedded in a doubly stratified non-Darcy porous medium saturated with power-law fluid is considered. The governing partial differential equations are transformed into ordinary differential equations using similarity transformations and then solved numerically. The numerical results are compared and found to be in good agreement with previously published results as special cases of the present investigation. The effects of magnetic parameter, dispersion parameters, and power-law index on the velocity, temperature, and concentration are illustrated graphically.
NASA Astrophysics Data System (ADS)
RamReddy, Chetteti; Pradeepa, Teegala
2016-05-01
Based on the nonlinear variation of density with temperature (NDT) in the buoyancy term, the mixed convection flow along a vertical plate of a micropolar fluid saturated porous medium is considered. In addition, the effect of homogeneous-heterogeneous reaction and convective boundary condition has been taken into account. Using lie scaling group transformations, the similarity representation is attained for the system of partial differential equations, prior to being solved by a spectral quasilinearization method. The results show that in the presence of aiding and opposing flow situations, both the species concentration and mass transfer rate decreases when the strength of homogeneous and heterogeneous reaction parameters are enhanced.
NASA Astrophysics Data System (ADS)
Harfash, Akil J.; Alshara, Ahmed K.
2015-05-01
The linear and nonlinear stability analysis of the motionless state (conduction solution) and of a vertical throughflow in an anisotropic porous medium are tested. In particular, the effect of a nonhomogeneous porosity and a constant anisotropic thermal diffusivity have been taken into account. Then, the accuracy of the linear instability thresholds are tested using a three dimensional simulation. It is shown that the strong stabilising effect of gravity field. Moreover, the results support the assertion that the linear theory, in general, is accurate in predicting the onset of convective motion, and thus, regions of stability.
Cevidanes, Lucia; Tucker, Scott; Styner, Martin; Kim, Hyungmin; Chapuis, Jonas; Reyes, Mauricio; Proffit, William; Turvey, Timothy; Jaskolka, Michael
2009-01-01
This paper discusses the development of methods for computer-aided jaw surgery. Computer-aided jaw surgery allows us to incorporate the high level of precision necessary for transferring virtual plans into the operating room. We also present a complete computer-aided surgery (CAS) system developed in close collaboration with surgeons. Surgery planning and simulation include construction of 3D surface models from Cone-beam CT (CBCT), dynamic cephalometry, semi-automatic mirroring, interactive cutting of bone and bony segment repositioning. A virtual setup can be used to manufacture positioning splints for intra-operative guidance. The system provides further intra-operative assistance with the help of a computer display showing jaw positions and 3D positioning guides updated in real-time during the surgical procedure. The CAS system aids in dealing with complex cases with benefits for the patient, with surgical practice, and for orthodontic finishing. Advanced software tools for diagnosis and treatment planning allow preparation of detailed operative plans, osteotomy repositioning, bone reconstructions, surgical resident training and assessing the difficulties of the surgical procedures prior to the surgery. CAS has the potential to make the elaboration of the surgical plan a more flexible process, increase the level of detail and accuracy of the plan, yield higher operative precision and control, and enhance documentation of cases. Supported by NIDCR DE017727, and DE018962 PMID:20816308
ERIC Educational Resources Information Center
Matsuda, Hiroshi; Shindo, Yoshiaki
2006-01-01
The 3D computer graphics (3D-CG) animation using a virtual actor's speaking is very effective as an educational medium. But it takes a long time to produce a 3D-CG animation. To reduce the cost of producing 3D-CG educational contents and improve the capability of the education system, we have developed a new education system using Virtual Actor.…
Deridder, Sander; Desmet, Gert
2012-02-01
Using computational fluid dynamics (CFD), the effective B-term diffusion constant γ(eff) has been calculated for four different random sphere packings with different particle size distributions and packing geometries. Both fully porous and porous-shell sphere packings are considered. The obtained γ(eff)-values have subsequently been used to determine the value of the three-point geometrical constant (ζ₂) appearing in the 2nd-order accurate effective medium theory expression for γ(eff). It was found that, whereas the 1st-order accurate effective medium theory expression is accurate to within 5% over most part of the retention factor range, the 2nd-order accurate expression is accurate to within 1% when calculated with the best-fit ζ₂-value. Depending on the exact microscopic geometry, the best-fit ζ₂-values typically lie in the range of 0.20-0.30, holding over the entire range of intra-particle diffusion coefficients typically encountered for small molecules (0.1 ≤ D(pz)/D(m) ≤ 0.5). These values are in agreement with the ζ₂-value proposed by Thovert et al. for the random packing they considered. PMID:22236565
Preferential water and solute fluxes in a model macropored porous medium as a function of flow rate
NASA Astrophysics Data System (ADS)
batany, stephane; Peyneau, Pierre-Emmanuel; Lassabatere, Laurent; Bechet, Beatrice; Faure, Pamela; Dangla, Patrick
2016-04-01
Macropores in soils can induce preferential flow and increase solute transport. Close to water saturation, most of the water flows through macropores at a much higher rate than it would in the same soil without any macropore. Preferential flow and water infiltration in soils with macropores have been investigated with different modeling approaches. Most of these are based on dual porosity or dual permeability approaches. These approaches consider that macropored soils are constituted by the association of two regions exchanging water, a matrix and a macropore domain, both of them obeying Darcy's law. Nevertheless, these approaches restrict preferential flow to the macropore domain and cannot simulate any enhancement of flow in the matrix surrounding the macropores. However, this hypothesis has been strongly questioned by several studies that had investigated solute transfer in macropored soils for which solute breakthrough curves (BTCs) were in complete disagreement with the flow restriction to the macropore domain. Thus, the understanding of water infiltration in soils requires more investigations regarding the effect of macropore and cracks in soils. The proposed paper aims at investigating water flow and tracer transport in a water saturated model macropored system as a function of the flow rate. Various solutes were injected in a 5 cm diameter, 14.5 cm high column filled with 425-800 μm diameter glass beads glued together. A 3 mm diameter Teflon rod inserted along the axis of the column during the preparation of the system was removed after the consolidation of the porous medium to create a macropore. Several flow rates - always ensuring a laminar flow - were tested, from values for which the diffusion transport rate is similar to the advective transport rate to values several orders of magnitude higher for which advection dominates. For all flow rates, solute BTCs were analyzed using the moment method and MIM model to quantify the volume of water visited by
NASA Astrophysics Data System (ADS)
Ferrante, Aldo Pedro; Fallico, Carmine; Rios, Ana C.; Fernanda Rivera, Maria; Santillan, Patricio; Salazar, Mario
2013-04-01
The contamination of large areas and correspondent aquifers often imposes to implement some recovery operations which are generally complex and very expensive. Anyway, these interventions necessarily require the preventive characterization of the aquifers to be reclaimed and in particular the knowledge of the relevant hydrodispersive parameters. The determination of these parameters requires the implementation tracer tests for the specific site (Sauty JP, 1978). To reduce cost and time that such test requires tracer tests on undisturbed soil samples, representative of the whole aquifer, can be performed. These laboratory tests are much less expensive and require less time, but the results are certainly less reliable than those obtained by field tests for several reasons, including the particular scale of investigation. In any case the hydrodispersive parameters values, obtained by tests carried out in laboratory, can provide useful information on the considered aquifer, allowing to carry out initial verifications on the transmission and propagation of the pollutants in the aquifer considered. For this purpose, tracer tests with inlet of short time were carried out in the Soil Physics Laboratory of the Department of Soil Protection (University of Calabria), on a series of sandy soil samples with six different lengths, repeating each test with three different water flow velocities (5 m/d; 10 m/s and 15 m/d) (J. Feyen et al., 1998). The lengths of the samples taken into account are respectively 15 cm, 24 cm, 30 cm, 45 cm, 60 cm and 75 cm, while the solution used for each test was made of 100 ml of water and NaCl with a concentration of this substance corresponding to 10 g/L. For the porous medium taken into consideration a particle size analysis was carried out, resulting primarily made of sand, with total porosity equal to 0.33. Each soil sample was placed in a flow cell in which was inlet the tracer from the bottom upwards, measuring by a conductivimeter the
NASA Astrophysics Data System (ADS)
Garg, B. P.; Singh, K. D.; Bansal, A. K.
2015-02-01
An analysis of an oscillatory magnetohydrodynamic (MHD) convective flow of a second order (viscoelastic), incompressible, and electrically conducting fluid through a porous medium bounded by two infinite vertical parallel porous plates is presented. The two porous plates with slip-flow condition and the no-slip condition are subjected respectively to a constant injection and suction velocity. The pressure gradient in the channel varies periodically with time. A magnetic field of uniform strength is applied in the direction perpendicular to the planes of the plates. The induced magnetic field is neglected due to the assumption of a small magnetic Reynolds number. The temperature of the plate with no-slip condition is non-uniform and oscillates periodically with time and the temperature difference of the two plates is assumed high enough to induce heat radiation. The entire system rotates in unison about the axis perpendicular to the planes of the plates. Adopting complex variable notations, a closed form solution of the problem is obtained. The analytical results are evaluated numerically and then presented graphically to discuss in detail the effects of different parameters of the problem. The velocity, temperature and the skin-friction in terms of its amplitude and phase angle have been shown graphically to observe the effects of the viscoelastic parameter γ, rotation parameter Ω, suction parameter λ , Grashof number Gr, Hartmann number M, the pressure A, Prandtl number Pr, radiation parameter N and the frequency of oscillation ω .
NASA Astrophysics Data System (ADS)
Gil, José J.; San José, Ignacio
2010-11-01
From our previous definition of the indices of polarimetric purity for 3D light beams [J.J. Gil, J.M. Correas, P.A. Melero and C. Ferreira, Monogr. Semin. Mat. G. de Galdeano 31, 161 (2004)], an analysis of their geometric and physical interpretation is presented. It is found that, in agreement with previous results, the first parameter is a measure of the degree of polarization, whereas the second parameter (called the degree of directionality) is a measure of the mean angular aperture of the direction of propagation of the corresponding light beam. This pair of invariant, non-dimensional, indices of polarimetric purity contains complete information about the polarimetric purity of a light beam. The overall degree of polarimetric purity is obtained as a weighted quadratic average of the degree of polarization and the degree of directionality.
Caspi, S.; Helm, M.; Laslett, L.J.
1991-03-30
We have developed an harmonic representation for the three dimensional field components within the windings of accelerator magnets. The form by which the field is presented is suitable for interfacing with other codes that make use of the 3D field components (particle tracking and stability). The field components can be calculated with high precision and reduced cup time at any location (r,{theta},z) inside the magnet bore. The same conductor geometry which is used to simulate line currents is also used in CAD with modifications more readily available. It is our hope that the format used here for magnetic fields can be used not only as a means of delivering fields but also as a way by which beam dynamics can suggest correction to the conductor geometry. 5 refs., 70 figs.
NASA Technical Reports Server (NTRS)
2004-01-01
The Mars Exploration Rover Spirit took this 3-D navigation camera mosaic of the crater called 'Bonneville' after driving approximately 13 meters (42.7 feet) to get a better vantage point. Spirit's current position is close enough to the edge to see the interior of the crater, but high enough and far enough back to get a view of all of the walls. Because scientists and rover controllers are so pleased with this location, they will stay here for at least two more martian days, or sols, to take high resolution panoramic camera images of 'Bonneville' in its entirety. Just above the far crater rim, on the left side, is the rover's heatshield, which is visible as a tiny reflective speck.
NASA Astrophysics Data System (ADS)
Ray, Nadja; Rupp, Andreas; Knabner, Peter
2016-04-01
Soil is arguably the most prominent example of a natural porous medium that is composed of a porous matrix and a pore space. Within this framework and in terms of soil's heterogeneity, we first consider transport and fluid flow at the pore scale. From there, we develop a mechanistic model and upscale it mathematically to transfer our model from the small scale to that of the mesoscale (laboratory scale). The mathematical framework of (periodic) homogenization (in principal) rigorously facilitates such processes by exactly computing the effective coefficients/parameters by means of the pore geometry and processes. In our model, various small-scale soil processes may be taken into account: molecular diffusion, convection, drift emerging from electric forces, and homogeneous reactions of chemical species in a solvent. Additionally, our model may consider heterogeneous reactions at the porous matrix, thus altering both the porosity and the matrix. Moreover, our model may additionally address biophysical processes, such as the growth of biofilms and how this affects the shape of the pore space. Both of the latter processes result in an intrinsically variable soil structure in space and time. Upscaling such models under the assumption of a locally periodic setting must be performed meticulously to preserve information regarding the complex coupling of processes in the evolving heterogeneous medium. Generally, a micro-macro model emerges that is then comprised of several levels of couplings: Macroscopic equations that describe the transport and fluid flow at the scale of the porous medium (mesoscale) include averaged time- and space-dependent coefficient functions. These functions may be explicitly computed by means of auxiliary cell problems (microscale). Finally, the pore space in which the cell problems are defined is time- and space dependent and its geometry inherits information from the transport equation's solutions. Numerical computations using mixed finite
NASA Astrophysics Data System (ADS)
Ezzat, M. A.; El-Bary, A. A.; Hatem, A. S.
2014-07-01
A technique of the state space approach and the inversion of the Laplace transform method are applied to dimensionless equations of an unsteady one-dimensional boundary-layer flow due to heat and mass transfer through a porous medium saturated with a viscoelastic fluid bounded by an infinite vertical plate in the presence of a uniform magnetic field is described. Complete analytical solutions for the temperature, concentration, velocity, and induced magnetic and electric fields are presented. The inversion of the Laplace transforms is carried out by using a numerical approach. The proposed method is used to solve two problems: boundary-layer flow in a viscoelastic fluid near a vertical wall subjected to the initial conditions of a stepwise temperature and concentration and viscoelastic fluid flow between two vertical walls. The solutions are found to be dependent on the governing parameters including the Prandtl number, the Schmidt number, the Grashof number, reaction rate coefficient, viscoelastic parameter, and permeability of the porous medium. Effects of these major parameters on the transport behavior are investigated methodically, and typical results are illustrated to reveal the tendency of the solutions. Representative results are presented for the velocity, temperature, concentration, and induced magnetic and electric field distributions, as well as the local skin-friction coefficient and the local Nusselt and Sherwood numbers.
Gray, William G.; Miller, Cass T.
2010-01-01
This work is the eighth in a series that develops the fundamental aspects of the thermodynamically constrained averaging theory (TCAT) that allows for a systematic increase in the scale at which multiphase transport phenomena is modeled in porous medium systems. In these systems, the explicit locations of interfaces between phases and common curves, where three or more interfaces meet, are not considered at scales above the microscale. Rather, the densities of these quantities arise as areas per volume or length per volume. Modeling of the dynamics of these measures is an important challenge for robust models of flow and transport phenomena in porous medium systems, as the extent of these regions can have important implications for mass, momentum, and energy transport between and among phases, and formulation of a capillary pressure relation with minimal hysteresis. These densities do not exist at the microscale, where the interfaces and common curves correspond to particular locations. Therefore, it is necessary for a well-developed macroscale theory to provide evolution equations that describe the dynamics of interface and common curve densities. Here we point out the challenges and pitfalls in producing such evolution equations, develop a set of such equations based on averaging theorems, and identify the terms that require particular attention in experimental and computational efforts to parameterize the equations. We use the evolution equations developed to specify a closed two-fluid-phase flow model. PMID:21197134
NASA Astrophysics Data System (ADS)
Narter, Matt; Brusseau, Mark L.
2010-08-01
Fluid-fluid interfacial area for porous media systems can be measured with the aqueous phase interfacial partitioning tracer test (IPTT) method or with high-resolution microtomography. The results of prior studies have shown that interfacial areas measured with the IPTT method are larger than values measured with microtomography. The observed disparity has been hypothesized to result from the impact of porous medium surface roughness on film-associated interfacial area, wherein the influence of surface roughness is characterized to some extent by the IPTT method but not by microtomography due to resolution constraints. This hypothesis was tested by using the two methods to measure interfacial area between an organic immiscible liquid and water for an ideal glass beads medium that has no measurable surface roughness. The tracer tests yielded a mean interfacial area of 2.8 (±5 cm-1), while microtomography produced an interfacial area of 2.7 (±2 cm-1). Maximum specific interfacial areas, equivalent to areas normalized by nonwetting fluid volume, were calculated and compared to measures of the specific solid surface area. The normalized interfacial areas were similar to the specific solid surface area calculated using the smooth sphere assumption and to the specific solid surface area measured using the N2/Brunauer, Emmett, and Teller (BET) method. The results presented herein indicate that both the IPTT and microtomography methods provide robust characterization of fluid-fluid interfacial area and that they are comparable in the absence of the impact of surface roughness.
Narter, Matt; Brusseau, Mark L
2010-08-01
Fluid-fluid interfacial area for porous-media systems can be measured with the aqueous-phase interfacial partitioning tracer test (IPTT) method or with high-resolution microtomography. The results of prior studies have shown that interfacial areas measured with the IPTT method are larger than values measured with microtomography. The observed disparity has been hypothesized to result from the impact of porous-medium surface roughness on film-associated interfacial area, wherein the influence of surface roughness is characterized to some extent by the IPTT method but not by microtomography due to resolution constraints. This hypothesis was tested by using the two methods to measure interfacial area between an organic immiscible liquid and water for an ideal glass-beads medium that has no measurable surface roughness. The tracer tests yielded a mean interfacial area of 2.8 (± 5 cm(-1)), while microtomography produced an interfacial area of 2.7 (± 2 cm(-1)). Maximum specific interfacial areas, equivalent to areas normalized by non-wetting fluid volume, were calculated and compared to measures of the specific solid surface area. The normalized interfacial areas were similar to the specific solid surface area calculated using the smooth-sphere assumption, and to the specific solid surface area measured using the N2/BET method. The results presented herein indicate that both the IPTT and microtomography methods provide robust characterization of fluid-fluid interfacial area, and that they are comparable absent the impact of surface roughness. PMID:24604925
NASA Astrophysics Data System (ADS)
Gray, William G.; Miller, Cass T.
2009-05-01
This work is the fifth in a series of papers on the thermodynamically constrained averaging theory (TCAT) approach for modeling flow and transport phenomena in multiscale porous medium systems. The general TCAT framework and the mathematical foundation presented in previous works are used to develop models that describe species transport and single-fluid-phase flow through a porous medium system in varying physical regimes. Classical irreversible thermodynamics formulations for species in fluids, solids, and interfaces are developed. Two different approaches are presented, one that makes use of a momentum equation for each entity along with constitutive relations for species diffusion and dispersion, and a second approach that makes use of a momentum equation for each species in an entity. The alternative models are developed by relying upon different approaches to constrain an entropy inequality using mass, momentum, and energy conservation equations. The resultant constrained entropy inequality is simplified and used to guide the development of closed models. Specific instances of dilute and non-dilute systems are examined and compared to alternative formulation approaches.
Microscale transport in porous media
Rashidi, M.; Rinker, R.
1996-04-01
In-pore transport processes in homogeneous and heterogeneous porous media have been investigated using novel 3D imaging techniques. The experimental system consists of a clear column packed with clear particles and a refractive index-matched fluid seeded with fluorescent tracers and an organic solute dye. By illuminating the porous regions within the column with a planar sheet of laser beam, flow and transport processes through the porous medium can be observed microscopically, and qualitative and quantitative in-pore transport information can be obtained at a good resolution and a high accuracy. Fluorescent images are captured and recorded at every vertical plane location while sweeping back and forth across the test section. These digitized transport images are then analyzed and accumulated over a 3D volume within the column. This paper reports on pore-scale observations of velocity, chemical concentration, and fluxes. Tests were undertaken with two separate columns. One is a rectangular column for chemical transport and bioremediation studies in aqueous heterogeneous systems and the other is a cylindrical column for flow and transport investigations in nonaqueous homogeneous systems.
NASA Technical Reports Server (NTRS)
1997-01-01
Many prominent rocks near the Sagan Memorial Station are featured in this image, taken in stereo by the Imager for Mars Pathfinder (IMP) on Sol 3. 3D glasses are necessary to identify surface detail. Wedge is at lower left; Shark, Half-Dome, and Pumpkin are at center. Flat Top, about four inches high, is at lower right. The horizon in the distance is one to two kilometers away.
Mars Pathfinder is the second in NASA's Discovery program of low-cost spacecraft with highly focused science goals. The Jet Propulsion Laboratory, Pasadena, CA, developed and manages the Mars Pathfinder mission for NASA's Office of Space Science, Washington, D.C. JPL is an operating division of the California Institute of Technology (Caltech). The Imager for Mars Pathfinder (IMP) was developed by the University of Arizona Lunar and Planetary Laboratory under contract to JPL. Peter Smith is the Principal Investigator.
Click below to see the left and right views individually. [figure removed for brevity, see original site] Left [figure removed for brevity, see original site] Right
NASA Technical Reports Server (NTRS)
2004-01-01
This 3-D, microscopic imager mosaic of a target area on a rock called 'Diamond Jenness' was taken after NASA's Mars Exploration Rover Opportunity ground into the surface with its rock abrasion tool for a second time.
Opportunity has bored nearly a dozen holes into the inner walls of 'Endurance Crater.' On sols 177 and 178 (July 23 and July 24, 2004), the rover worked double-duty on Diamond Jenness. Surface debris and the bumpy shape of the rock resulted in a shallow and irregular hole, only about 2 millimeters (0.08 inch) deep. The final depth was not enough to remove all the bumps and leave a neat hole with a smooth floor. This extremely shallow depression was then examined by the rover's alpha particle X-ray spectrometer.
On Sol 178, Opportunity's 'robotic rodent' dined on Diamond Jenness once again, grinding almost an additional 5 millimeters (about 0.2 inch). The rover then applied its Moessbauer spectrometer to the deepened hole. This double dose of Diamond Jenness enabled the science team to examine the rock at varying layers. Results from those grindings are currently being analyzed.
The image mosaic is about 6 centimeters (2.4 inches) across.
Nam, Sunyoung; Won, Jong-Eun; Kim, Cheol-Hwan; Kim, Hae-Won
2011-01-01
Effects of three-dimensional (3D) calcium phosphate (CaP) porous granules on the growth and odontogenic differentiation of human dental pulp stem cells (hDPSCs) were examined for dental tissue engineering. hDPSCs isolated from adult human dental pulps were cultured for 3-4 passages, and populated on porous granules. Cell growth on the culture dish showed an ongoing increase for up to 21 days, whereas the growth on the 3D granules decreased after 14 days. This reduction in proliferative potential on the 3D granules was more conspicuous under the osteogenic medium conditions, indicating that the 3D granules may induce the odontogenic differentiation of hDPSCs. Differentiation behavior on the 3D granules was confirmed by the increased alkaline phosphatase activity, up-regulation of odontoblast-specific genes, including dentin sialophosphoprotein (DSPP) and dentin matrix protein 1 (DMP1) by quantitative polymerase chain reaction, and greater level of dentin sialoprotein synthesis by western blot. Moreover, the cellular mineralization, as assessed by Alizarin red S and calcium quantification, was significantly higher in the 3D CaP granules than in the culture dish. Taken all, the 3D CaP porous granules should be useful for dental tissue engineering in combination with hDPSCs by providing favorable 3D substrate conditions for cell growth and odontogenic development. PMID:21772958
NASA Astrophysics Data System (ADS)
Meheust, Y.; Toussaint, R.; Lovoll, G.; Maloy, K. J.
2015-12-01
P.G. Saffman & G. Taylor (1958) studied the stability of the interface between two immiscible fluids of different densities and viscosities when one displaces the other inside a Hele-Shaw (HS) cell. They showed that with a horizontal cell and if the displaced fluid is the more viscous, the interface is unstable and leads to a viscous fingering which they nearly fully modeled [1]. The HS geometry was introduced as a geometry imposing the same flow behavior as the Darcy-scale flow in a two-dimensional (2D) porous medium, and therefore allowing an analogy between the two configurations. This is however not obvious, since capillary forces act at very different scales in the two. Later, researchers performing unstable displacement experiments in HS cells containing random 2D porous media also observed viscous fingering at large viscosity ratios, but with invasion patterns very different from those of Saffman and Taylor (ST) [2-3]. It was however considered that the two processes were both Laplacian growth processes, i.e., processes in which the invasion probability density is proportional to the pressure gradient. Ten years ago, we investigated viscously-unstable drainage in 2D porous media experimentally and measured the growth activity as well as occupation probability maps for the invasion process [4-5]. We concluded that in viscous fingering in 2D porous media, the activity was rather proportional to the square of the pressure gradient magnitude (a so-called DBM model of exponent 2), so that the universality class of the growth/invasion process was different from that of ST viscous fingering. We now strengthen our claim with new results based on the comparison of (i) pressure measurements with the pressure field around a finger such as described by the ST analytical model, and (ii) branching angles in the invasion patterns with those expected for DBMs of various exponents. [1] Saffman, P. G. and Taylor, G. Proc. Soc. London 1958(Ser A 245), 312-329. [2] Lenormand, R
James Saiers
2006-06-28
Radionuclides, metals, and dense non-aqueous phase liquids have contaminated about six billion cubic meters of soil at Department of Energy (DOE) sites. The subsurface transport of many of these contaminants is facilitated by colloids (i.e., microscopic, waterborne particles). The first step in the transport of contaminants from their sources to off-site surface water and groundwater is migration through the vadose zone. Developing our understanding of the migration of colloids and colloid-associated contaminants through the vadose zone is critical to assessing and controlling the release of contaminants from DOE sites. In this study, we examined the mobilization, transport, and filtration (retention) of mineral colloids and colloid-associated radionuclides within unsaturated porous media. This investigation involved laboratory column experiments designed to identify properties that affect colloid mobilization and retention and pore-scale visualization experiments designed to elucidate mechanisms that govern these colloid-mass transfer processes. The experiments on colloid mobilization and retention were supplemented with experiments on radionuclide transport through porous media and on radionuclide adsorption to mineral colloids. Observations from all of these experiments – the column and visualization experiments with colloids and the experiments with radionuclides – were used to guide the development of mathematical models appropriate for describing colloids and colloid-facilitated radionuclide transport through the vadose zone.
James Saiers; Joseph Ryan
2006-07-02
Radionuclides, metals, and dense non-aqueous phase liquids have contaminated about six billion cubic meters of soil at Department of Energy (DOE) sites. The subsurface transport of many of these contaminants is facilitated by colloids (i.e., microscopic, waterborne particles). The first step in the transport of contaminants from their sources to off-site surface water and groundwater is migration through the vadose zone. Developing our understanding of the migration of colloids and colloid-associated contaminants through the vadose zone is critical to assessing and controlling the release of contaminants from DOE sites. In this study, we examined the mobilization, transport, and filtration (retention) of mineral colloids and colloidassociated radionuclides within unsaturated porous media. This investigation involved laboratory column experiments designed to identify properties that affect colloid mobilization and retention and pore-scale visualization experiments designed to elucidate mechanisms that govern these colloid-mass transfer processes. The experiments on colloid mobilization and retention were supplemented with experiments on radionuclide transport through porous media and on radionuclide adsorption to mineral colloids. Observations from all of these experiments – the column and visualization experiments with colloids and the experiments with radionuclides – were used to guide the development of mathematical models appropriate for describing colloids and colloid-facilitated radionuclide transport through the vadose zone.
Saiers, James; Ryan, Joseph
2005-06-01
Our research is guided by an EMSP objective to improve conceptual and predictive models of contaminant movement in vadose-zone environments. As described in the report National Roadmap for Vadose-Zone Science and Technology [DOE, 2001], soil-water colloids are capable of adsorbing contaminants, such as radionuclides and metals, and facilitating their migration through the vadose zone and towards groundwater reservoirs. Our research centers on advancing understanding of this phenomenon. In particular, we are combining mathematical modeling with laboratory experimentation at pore and column scales to (1) elucidate the effects of porewater-flow transients on colloid mobilization in unsaturated porous media; (2) explore the sensitivity of colloid deposition rates to changes in porewater chemistry and colloid mineralogy; (3) develop mathematical models appropriate for simulating colloid mobilization, transport, and deposition under both steady-flow and transient-flow conditions; (4) identify mechanisms that govern mineral-colloid mobilization and deposition in unsaturated porous media; (5) quantify the effects of mineral-grain geometry and surface roughness on colloid-filtration rates; and (6) evaluate the influences of colloids on the transport of strontium and cesium (i.e., DOE-contaminants-of-concern) through soils and sediments.
NASA Astrophysics Data System (ADS)
Rashidi, S.; Dehghan, M.; Ellahi, R.; Riaz, M.; Jamal-Abad, M. T.
2015-03-01
A mathematical model for two-dimensional fluid flow under the influence of stream wise transverse magnetic fields in laminar regime is simulated in this study. Heat transfer past a square diamond shaped porous obstacle is also taken into account. The attention is focused to investigate the effects of intensity and direction of magnetic field, Darcy and Reynolds numbers on the mechanism of convective heat transfer and flow structures. The Darcy-Brinkman-Forchheimer model along with the Maxwell equations is used. The nonlinear coupled equations using a finite volume approach (FVA) are solved numerically. The calculations are performed for different governing parameters such as Reynolds number, Nusselt number, Stuart number and Prandtl Number. The physical interpretation of velocity and isothermal contours is assigned through graphs. It is shown that the effects of a transverse magnetic field on flow behavior and heat transfer mechanism are more than that of the stream wise magnetic field. The configuration of streamlines and vorticity contours phenomena are also presented for porous diamond obstacle. Comparison of the numerical solutions with existing literature is also made.
NASA Astrophysics Data System (ADS)
Khader, M. M.; Megahed, Ahmed M.
2014-01-01
This paper is devoted to introduce a numerical simulation using the implicit finite difference method (FDM) with the theoretical study for the effect of viscous dissipation on the steady flow with heat transfer of Newtonian fluid towards a permeable stretching surface embedded in a porous medium with a second-order slip. The governing non-linear partial differential equations are converted into non-linear ordinary differential equations (ODEs) by using similarity variables. Exact solutions corresponding to momentum and energy equations for the case of no slip conditions are obtained. The resulting ODEs are successfully solved numerically with the help of FDM. Graphically results are shown for non-dimensional velocities and temperature. The effects of the porous parameter, the suction (injection) parameter, Eckert number, first- and second-order velocity slip parameter and the Prandtl number on the flow and temperature profiles are presented. Moreover, the local skin friction and Nusselt numbers are presented. Comparison of numerical results is made with the earlier published results under limiting cases.
Zhong, Hua; Liu, Guansheng; Jiang, Yongbing; Brusseau, Mark L; Liu, Zhifeng; Liu, Yang; Zeng, Guangming
2016-03-01
The success of effective bioaugmentation processes for remediation of soil and groundwater contamination requires effective transport of the injected microorganisms in the subsurface environment. In this study, the effect of low concentrations of monorhamnolipid biosurfactant solutions on transport of Pseudomonas aeruginosa in an ideal porous medium (glass beads) with hydrophilic or hydrophobic surfaces was investigated by conducting miscible-displacement experiments. Transport behavior was examined for both glucose-grown and hexadecane-grown cells, with low and high surface hydrophobicity, respectively. A clean-bed colloid deposition model was used for determination of deposition rate coefficients. Results show that cells with high surface hydrophobicity exhibit greater retention than cells with low surface hydrophobicity. Rhamnolipid affects cell transport primarily by changing cell surface hydrophobicity, with an additional minor effect by increasing solution ionic strength. There is a good linear relation between k and rhamnolipid-regulated cell surface hydrophobicity presented as bacterial-adhesion-to-hydrocarbon (BATH) rate of cells (R(2)=0.71). The results of this study show the importance of hydrophobic interaction for transport of bacterial cells in silica-based porous media, and the potential of using low-concentration rhamnolipid solutions for facilitating bacterial transport in bioaugmentation efforts. PMID:26722821
NASA Astrophysics Data System (ADS)
Lin, Yanhai; Zheng, Liancun; Zhang, Xinxin
2015-11-01
We present a research for the MHD Marangoni boundary layer flow and heat transfer in pseudo-plastic power law nanofluids over a porous medium driven by temperature gradient. A variable magnetic field is considered. Four different types of nanoparticles, copper, aluminum oxide, copper oxide, and titanium oxide are considered with pseudo-plastic power-law carboxy methyl cellulose (CMC)-water used as base fluids. A generalized Fourier law proposed by Zheng for varying thermal conductivity of nanofluids is taken into account, and the surface tension is assumed a quadratic function of the temperature. The governing partial differential equations (PDEs) are formulated, and similarity solutions are obtained numerically using shooting technique combined with Runge-Kutta iteration program and Newton's scheme. The effects of various physical parameters on horizontal velocity component and temperature curves are discussed and graphically illustrated in details.
NASA Astrophysics Data System (ADS)
Aaiza, Gul; Khan, Ilyas; Shafie, Sharidan
2015-12-01
Energy transfer in mixed convection unsteady magnetohydrodynamic (MHD) flow of an incompressible nanofluid inside a channel filled with saturated porous medium is investigated. The channel with non-uniform walls temperature is taken in a vertical direction under the influence of a transverse magnetic field. Based on the physical boundary conditions, three different flow situations are discussed. The problem is modelled in terms of partial differential equations with physical boundary conditions. Four different shapes of nanoparticles of equal volume fraction are used in conventional base fluids, ethylene glycol (EG) ( C 2 H 6 O 2 ) and water ( H 2 O). Solutions for velocity and temperature are obtained discussed graphically in various plots. It is found that viscosity and thermal conductivity are the most prominent parameters responsible for different results of velocity and temperature. Due to higher viscosity and thermal conductivity, C 2 H 6 O 2 is regarded as better convectional base fluid compared to H 2 O.