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.
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.
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.
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.
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
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.
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
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.
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.
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
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.
Porous microsphere and its applications
Cai, Yunpeng; Chen, Yinghui; Hong, Xiaoyun; Liu, Zhenguo; Yuan, Weien
2013-01-01
Porous microspheres have drawn great attention in the last two decades for their potential applications in many fields, such as carriers for drugs, absorption and desorption of substances, pulmonary drug delivery, and tissue regeneration. The application of porous microspheres has become a feasible way to address existing problems. In this essay, we give a brief introduction of the porous microsphere, its characteristics, preparation methods, applications, and a brief summary of existing problems and research tendencies. PMID:23515359
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)
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
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.
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.
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.
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.
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
NASA Astrophysics Data System (ADS)
Moradi, A.
2015-12-01
To properly model soil thermal performance in unsaturated porous media, for applications such as SBTES systems, knowledge of both soil hydraulic and thermal properties and how they change in space and time is needed. Knowledge obtained from pore scale to macroscopic scale studies can help us to better understand these systems and contribute to the state of knowledge which can then be translated to engineering applications in the field (i.e. implementation of SBTES systems at the field scale). One important thermal property that varies with soil water content, effective thermal conductivity, is oftentimes included in numerical models through the use of empirical relationships and simplified mathematical formulations developed based on experimental data obtained at either small laboratory or field scales. These models assume that there is local thermodynamic equilibrium between the air and water phases for a representative elementary volume. However, this assumption may not always be valid at the pore scale, thus questioning the validity of current modeling approaches. The purpose of this work is to evaluate the validity of the local thermodynamic equilibrium assumption as related to the effective thermal conductivity at pore scale. A numerical model based on the coupled Cahn-Hilliard and heat transfer equation was developed to solve for liquid flow and heat transfer through variably saturated porous media. In this model, the evolution of phases and the interfaces between phases are related to a functional form of the total free energy of the system. A unique solution for the system is obtained by solving the Navier-Stokes equation through free energy minimization. Preliminary results demonstrate that there is a correlation between soil temperature / degree of saturation and equivalent thermal conductivity / heat flux. Results also confirm the correlation between pressure differential magnitude and equilibrium time for multiphase flow to reach steady state conditions
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.
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}.
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
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.
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.
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.
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
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.
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
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.
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.
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.
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
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.
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"
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.
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.
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
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
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
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.
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.
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
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.
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.
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.
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)
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)
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.
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.
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
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)
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
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.
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.
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.
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
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 ...
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
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
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.
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.
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.
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
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
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.
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)
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 Technical Reports Server (NTRS)
Nichols, L. D.
1976-01-01
A fluid flowing in a porous medium heated transversely to the fluid flow is considered. This configuration is applicable to a focused solar energy collector for use in an electric power generating system. A fluidized bed can be regarded as a porous medium with special properties. The solutions presented are valid for describing the effectiveness of such a fluidized bed for collecting concentrated solar energy to heat the working fluid of a heat engine. Results indicate the advantage of high thermal conductivity in the transverse direction and high operating temperature of the porous medium.
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.
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,
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
Functionalization of Biomolecules with Nanostructured Porous Silicon for Biomedical Application
NASA Astrophysics Data System (ADS)
Jeyakumar, P.; Saravanakumar, S. S.; Kulathuraan, K.; Ramadas, V.; Natarajan, B.
2015-02-01
Porous silicon (PS) fabrication, changes in the optical properties and surface modification in the oxidized PS (dipped into the Glucose oxide) due to the infiltration of biomolecules using Luminescence Spectrophotometer [Photoluminescence (PL)], Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscope (SEM) were studied. The surface morphology of oxidized PS (OPS) and treated with Glucose have been studied by SEM. Spontaneous imbibition weight was calculated theoretically using imbibition equation for the porous medium using glucose solution as the wetting liquid. FTIR analysis revealed that, the strong Si-H, Si-O-Si bonds which covered most of the OPS surface. In the glucose treated PS layer, the amide I (C=O) stretch and amide II (C=N) stretch (1690 cm-1 and 1551 cm-1) groups were appeared in the spectrum which confirmed the coupling reaction. Efficient visible Photoluminescence was obtained at around 624 nm from glucose treated porous silicon. The functionalization of glucose with nano structured PS, changes light emission over the surface of OPS. It can be applied in optical biosensor and which can be used in biomedical 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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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,
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 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.
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.
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.
Porous ferroelectrics for energy harvesting applications
NASA Astrophysics Data System (ADS)
Roscow, J.; Zhang, Y.; Taylor, J.; Bowen, C. R.
2015-11-01
This paper provides an overview of energy harvesting using ferroelectric materials, with a particular focus on the energy harvesting capabilities of porous ferroelectric ceramics for both piezo- and pyroelectric harvesting. The benefits of introducing porosity into ferro- electrics such as lead zirconate titanate (PZT) has been known for over 30 years, but the potential advantages for energy harvesting from both ambient vibrations and temperature fluctuations have not been studied in depth. The article briefly discusses piezoelectric and pyro- electric energy harvesting, before evaluating the potential benefits of porous materials for increasing energy harvesting figures of merits and electromechanical/electrothermal coupling factors. Established processing routes are evaluated in terms of the final porous structure and the resulting effects on the electrical, thermal and mechanical properties.
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.
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.
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
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
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
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.
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
27 CFR 19.675 - Medium plant permit applications.
Code of Federal Regulations, 2013 CFR
2013-04-01
... 27 Alcohol, Tobacco Products and Firearms 1 2013-04-01 2013-04-01 false Medium plant permit... Obtaining A Permit § 19.675 Medium plant permit applications. (a) General. Any person wishing to establish a medium plant must file form TTB F 5110.74, Application and Permit for an Alcohol Fuel Producer Under 26...
27 CFR 19.675 - Medium plant permit applications.
Code of Federal Regulations, 2012 CFR
2012-04-01
... 27 Alcohol, Tobacco Products and Firearms 1 2012-04-01 2012-04-01 false Medium plant permit... Obtaining A Permit § 19.675 Medium plant permit applications. (a) General. Any person wishing to establish a medium plant must file form TTB F 5110.74, Application and Permit for an Alcohol Fuel Producer Under 26...
27 CFR 19.675 - Medium plant permit applications.
Code of Federal Regulations, 2014 CFR
2014-04-01
... 27 Alcohol, Tobacco Products and Firearms 1 2014-04-01 2014-04-01 false Medium plant permit... Obtaining A Permit § 19.675 Medium plant permit applications. (a) General. Any person wishing to establish a medium plant must file form TTB F 5110.74, Application and Permit for an Alcohol Fuel Producer Under 26...
27 CFR 19.675 - Medium plant permit applications.
Code of Federal Regulations, 2011 CFR
2011-04-01
... 27 Alcohol, Tobacco Products and Firearms 1 2011-04-01 2011-04-01 false Medium plant permit... Obtaining A Permit § 19.675 Medium plant permit applications. (a) General. Any person wishing to establish a medium plant must file form TTB F 5110.74, Application and Permit for an Alcohol Fuel Producer Under 26...
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.
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)
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.
High-strength porous carbon and its multifunctional applications
Wojtowicz, Marek A; Rubenstein, Eric P; Serio, Michael A; Cosgrove, Joseph E
2013-12-31
High-strength porous carbon and a method of its manufacture are described for multifunctional applications, such as ballistic protection, structural components, ultracapacitor electrodes, gas storage, and radiation shielding. The carbon is produced from a polymer precursor via carbonization, and optionally by surface activation and post-treatment.
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.
Controlled synthesis of porous platinum nanostructures for catalytic applications.
Cao, Yanqin; Zhang, Junwei; Yang, Yong; Huang, Zhengren; Long, Nguyen Viet; Nogami, Masayuki
2014-02-01
Porous platinum, that has outstanding catalytic and electrical properties and superior resistant characteristics to corrosion, has been widely applied in chemical, petrochemical, pharmaceutical, electronic, and automotive industries. As the catalytic activity and selectivity depend on the size, shape and structure of nanomaterials, the strategies for controlling these factors of platinum nanomaterials to get excellent catalytic properties are discussed. Here, recent advances in the design and preparation of various porous platinum nanostructures are reviewed, including wet-chemical synthesis, electro-deposition, galvanic replacement reaction and de-alloying technology. The applications of various platinum nanostructures are also discussed, especially in fuel cells. PMID:24749422
Porous Core-Shell Nanostructures for Catalytic Applications
NASA Astrophysics Data System (ADS)
Ewers, Trevor David
Porous core-shell nanostructures have recently received much attention for their enhanced thermal stability. They show great potential in the field of catalysis, as reactant gases can diffuse in and out of the porous shell while the core particle is protected from sintering, a process in which particles coalesce to form larger particles. Sintering is a large problem in industry and is the primary cause of irreversible deactivation. Despite the obvious advantages of high thermal stability, porous core-shell nanoparticles can be developed to have additional interactive properties from the combination of the core and shell together, rather than just the core particle alone. This dissertation focuses on developing new porous core-shell systems in which both the core and shell take part in catalysis. Two types of systems are explored; (1) yolk-shell nanostructures with reducible oxide shells formed using the Kirkendall effect and (2) ceramic-based porous oxide shells formed using sol-gel chemistry. Of the Kirkendall-based systems, Au FexOy and Cu CoO were synthesized and studied for catalytic applications. Additionally, ZnO was explored as a potential shelling material. Sol-gel work focused on optimizing synthetic methods to allow for coating of small gold particles, which remains a challenge today. Mixed metal oxides were explored as a shelling material to make dual catalysts in which the product of a reaction on the core particle becomes a reactant within the shell.
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
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.
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
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 .
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
Ultralight porous metals: From fundamentals to applications
NASA Astrophysics Data System (ADS)
Tianjian, Lu
2002-10-01
Over the past few years a number of low cost metallic foams have been produced and used as the core of sandwich panels and net shaped parts. The main aim is to develop lightweight structures which are stiff, strong, able to absorb large amount of energy and cheap for application in the transport and construction industries. For example, the firewall between the engine and passenger compartment of an automobile must have adequate mechanical strength, good energy and sound absorbing properties, and adequate fire retardance. Metal foams provide all of these features, and are under serious consideration for this applications by a number of automobile manufacturers (e.g., BMW and Audi). Additional specialized applications for foam-cored sandwich panels range from heat sinks for electronic devices to crash barriers for automobiles, from the construction panels in lifts on aircraft carriers to the luggage containers of aircraft, from sound proofing walls along railway tracks and highways to acoustic absorbers in lean premixed combustion chambers. But there is a problem. Before metallic foams can find a widespread application, their basic properties must be measured, and ideally modeled as a function of microstructural details, in order to be included in a design. This work aims at reviewing the recent progress and presenting some new results on fundamental research regarding the micromechanical origins of the mechanical, thermal, and acoustic properties of metallic foams.
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
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.
Jang, Long-Kuan; Chang, Philip W.; Findley, John E.; Yen, Teh Fu
1983-01-01
This paper presents a bench-scale study on the transport in highly permeable porous rock of three bacterial species—Bacillus subtilis, Pseudomonas putida, and Clostridium acetobutylicum—potentially applicable in microbial-enhanced oil recovery processes. The transport of cells during the injection of bacterial suspension and nutrient medium was simulated by a deep bed filtration model. Deep bed filtration coefficients and the maximum capacity of cells in porous rock were measured. Low to intermediate (∼106/ml) injection concentrations of cellular suspensions are recommended because plugging of inlet surface is less likely to occur. In addition to their resistance to adverse environments, spores of clostridia are strongly recommended for use in microbial-enhanced oil recovery processes since they are easiest among the species tested to push through porous rock. After injection, further transport of bacteria during incubation can occur by growth and mobility through the stagnant nutrient medium which fills the porous rock. We have developed an apparatus to study the migration of bacteria through a Berea sandstone core containing nutrient medium. PMID:16346414
Jang, L K; Chang, P W; Findley, J E; Yen, T F
1983-11-01
This paper presents a bench-scale study on the transport in highly permeable porous rock of three bacterial species-Bacillus subtilis, Pseudomonas putida, and Clostridium acetobutylicum-potentially applicable in microbial-enhanced oil recovery processes. The transport of cells during the injection of bacterial suspension and nutrient medium was simulated by a deep bed filtration model. Deep bed filtration coefficients and the maximum capacity of cells in porous rock were measured. Low to intermediate ( approximately 10/ml) injection concentrations of cellular suspensions are recommended because plugging of inlet surface is less likely to occur. In addition to their resistance to adverse environments, spores of clostridia are strongly recommended for use in microbial-enhanced oil recovery processes since they are easiest among the species tested to push through porous rock. After injection, further transport of bacteria during incubation can occur by growth and mobility through the stagnant nutrient medium which fills the porous rock. We have developed an apparatus to study the migration of bacteria through a Berea sandstone core containing nutrient medium. PMID:16346414
Porous Nanocomposites with Integrated Internal Domains: Application to Separation Membranes
Li, Wenle; Walz, John Y.
2014-01-01
Asymmetric membranes with layered structure have made significant achievements due to their balanced properties and multi-functionalities that come from a combination of multiple layers. However, issues such as delamination and substructure resistance are generated by the intrinsic layered structure. Here, we present a strategy to integrate the traditional layered structure into an asymmetric but continuous porous network. Through infiltrations of microparticles and nanoparticles to targeted regions, active domains are created inside the porous scaffold versus having them applied externally. The fabricated internal active domains are highly adjustable in terms of its dimensions, pore size, and materials. We demonstrate that it is a general method that can be applicable to a wide variety of particles regardless of their material, dimensions, or geometry. By eliminating the external layered structure, problems such as those mentioned above can be eliminated. This integration technique can be extended to other devices required a layered structure, such as solid oxide fuel cells and lithium ion battery. PMID:24646923
Fabrication, properties, and applications of porous metals with directional pores
NAKAJIMA, Hideo
2010-01-01
Lotus-type porous metals with aligned long cylindrical pores are fabricated by unidirectional solidification from the melt with a dissolved gas such as hydrogen, nitrogen, or oxygen. The gas atoms can be dissolved into the melt via a pressurized gas atmosphere or thermal decomposition of gaseous compounds. Three types of solidification techniques have been developed: mold casting, continuous zone melting, and continuous casting techniques. The last method is superior from the viewpoint of mass production of lotus metals. The observed anisotropic behaviors of the mechanical properties, sound absorption, and thermal conductivity are inherent to the anisotropic porous structure. In particular, the remarkable anisotropy in the mechanical strength is attributed to the stress concentration around the pores aligned perpendicular to the loading direction. Heat sinks are a promising application of lotus metals due to the high cooling performance with a large heat transfer. PMID:21084772
Porous Nanocomposites with Integrated Internal Domains: Application to Separation Membranes
NASA Astrophysics Data System (ADS)
Li, Wenle; Walz, John Y.
2014-03-01
Asymmetric membranes with layered structure have made significant achievements due to their balanced properties and multi-functionalities that come from a combination of multiple layers. However, issues such as delamination and substructure resistance are generated by the intrinsic layered structure. Here, we present a strategy to integrate the traditional layered structure into an asymmetric but continuous porous network. Through infiltrations of microparticles and nanoparticles to targeted regions, active domains are created inside the porous scaffold versus having them applied externally. The fabricated internal active domains are highly adjustable in terms of its dimensions, pore size, and materials. We demonstrate that it is a general method that can be applicable to a wide variety of particles regardless of their material, dimensions, or geometry. By eliminating the external layered structure, problems such as those mentioned above can be eliminated. This integration technique can be extended to other devices required a layered structure, such as solid oxide fuel cells and lithium ion battery.
Fabrication, properties, and applications of porous metals with directional pores.
Nakajima, Hideo
2010-01-01
Lotus-type porous metals with aligned long cylindrical pores are fabricated by unidirectional solidification from the melt with a dissolved gas such as hydrogen, nitrogen, or oxygen. The gas atoms can be dissolved into the melt via a pressurized gas atmosphere or thermal decomposition of gaseous compounds. Three types of solidification techniques have been developed: mold casting, continuous zone melting, and continuous casting techniques. The last method is superior from the viewpoint of mass production of lotus metals. The observed anisotropic behaviors of the mechanical properties, sound absorption, and thermal conductivity are inherent to the anisotropic porous structure. In particular, the remarkable anisotropy in the mechanical strength is attributed to the stress concentration around the pores aligned perpendicular to the loading direction. Heat sinks are a promising application of lotus metals due to the high cooling performance with a large heat transfer. PMID:21084772
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)
Adsorption-induced deformation in porous media and application to CO2-injected coal beds
NASA Astrophysics Data System (ADS)
Vandamme, M.; Brochard, L.; Coussy, O.
2010-05-01
An injection of carbon dioxide into a coal bed methane reservoir facilitates the recovery of methane, a process known as enhanced coal bed methane recovery (ECBM). Over the injection process carbon dioxide molecules get adsorbed at the surface of the coal pores, making the coal swell. This swelling leads to a closure of the coal fracture system and thus to a decrease of the permeability of the reservoir, hindering further injection and impairing the economic viability of ECBM. Here we provide a framework in which to calculate adsorption-induced strains in a porous medium. Usual poromechanics equations are extended to take into account surface energies. The calculations performed are valid for a general microstructure and the microstructural features are identified which govern the mechanical response of the porous medium to a change of surface stress. The effect of adsorption on surface stress is also discussed. An application to coal beds is presented. We employ molecular simulations to calculate adsorption isotherms of methane and carbon dioxide in coal. A comparison of our results with experimental data on coal swelling shows that adsorption in micropores (below 2 nm) plays a primary role in the swelling behavior of coal.
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)
Qin, C.; Hassanizadeh, S.
2013-12-01
Multiphase flow and species transport though thin porous layers are encountered in a number of industrial applications, such as fuel cells, filters, and hygiene products. Based on some macroscale models like the Darcy's law, to date, the modeling of flow and transport through such thin layers has been mostly performed in 3D discretized domains with many computational cells. But, there are a number of problems with this approach. First, a proper representative elementary volume (REV) is not defined. Second, one needs to discretize a thin porous medium into computational cells whose size may be comparable to the pore sizes. This suggests that the traditional models are not applicable to such thin domains. Third, the interfacial conditions between neighboring layers are usually not well defined. Last, 3D modeling of a number of interacting thin porous layers often requires heavy computational efforts. So, to eliminate the drawbacks mentioned above, we propose a new approach to modeling multilayers of thin porous media as 2D interacting continua (see Fig. 1). Macroscale 2D governing equations are formulated in terms of thickness-averaged material properties. Also, the exchange of thermodynamic properties between neighboring layers is described by thickness-averaged quantities. In Comparison to previous macroscale models, our model has the distinctive advantages of: (1) it is rigorous thermodynamics-based model; (2) it is formulated in terms of thickness-averaged material properties which are easily measureable; and (3) it reduces 3D modeling to 2D leading to a very significant reduction of computation efforts. As an application, we employ the new approach in the study of liquid water flooding in the cathode of a polymer electrolyte fuel cell (PEFC). To highlight the advantages of the present model, we compare the results of water distribution with those obtained from the traditional 3D Darcy-based modeling. Finally, it is worth noting that, for specific case studies, a
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.
Application of Quenching and Partitioning Processing to Medium Mn Steel
NASA Astrophysics Data System (ADS)
Seo, Eun Jung; Cho, Lawrence; De Cooman, Bruno C.
2015-01-01
The present work analyzes the application of quenching and partitioning processing to medium Mn steel to obtain a new type of ultra-high-strength multiphase medium Mn steel. The selection of the quench temperature makes it possible to vary the ultimate tensile strength within a range of 500 MPa. The processing leads to low-carbon lath martensite matrix with a controlled volume fraction of retained austenite.
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
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
Application of Passive Porous Treatment to Slat Trailing Edge Noise
NASA Technical Reports Server (NTRS)
Khorrami, Mehdi R.; Choudhari, Meelan M.
2003-01-01
Porous trailing-edge treatment is investigated as a passive means for slat noise reduction by using time-accurate simulations based on Reynolds-averaged Navier-Stokes equations. For the model scale high-lift configuration used during previous experiments in the Low-Turbulence Pressure Tunnel at NASA Langley Research Center, application of the proposed treatment over a minute fraction of the slat surface area is shown to mitigate the noise impact of the trailing edge, with no measurable aerodynamic penalty. Assessment of the pressure fluctuations in the vicinity of the treated edge indicates a potential noise reduction in excess of 20 dB. The primary mechanism underlying this reduction is related to the reduced strength of Strouhal shedding from the finite thickness trailing edge. A secondary effect of the treatment involves an upward shift in the Strouhal-shedding frequency to a frequency band of reduced auditory sensitivity in a full-scale application.
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.
Form birefringence in porous semiconductors and dielectrics: A review
Golovan', L. A. Kashkarov, P. K.; Timoshenko, V. Yu.
2007-07-15
The phenomenon of optical anisotropy in porous semiconductors and dielectrics (porous silicon, gallium phosphide, and alumina) and photonic crystal structures formed on their basis is reviewed. It is shown that anisotropic nanostructuring of initially isotropic media leads to the occurrence of strong birefringence. Applicability of the effective-medium model to description of the form birefringence in porous semiconductors and dielectrics is discussed.
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.
Research and development on porous components for MCFC applications
NASA Astrophysics Data System (ADS)
Bergaglio, E.; Sabattini, A.; Capobianco, P.
A fuel cell is a complex system in which every single part must have optimal and long lasting characteristics to assure a good performance. Our research group has focused on a specific section of a cell, the porous components, the elements that directly come into play and more strongly influence the working and performance. Attention has been focused on matrix, in particular trying to improve it by intervening in the first step of raw powder choice. α-LiAlO 2 has been considered a new interesting and promising material to test. The purpose of this work is the study of the possibility of producing an α-LiAlO 2-based matrix with suitable properties for a MCFC cell. The subsequent steps of powder characterisation, tape preparation and final product analysis are presented as well as the various application techniques.
Supported metal nanoparticles on porous materials. Methods and applications.
White, Robin J; Luque, Rafael; Budarin, Vitaliy L; Clark, James H; Macquarrie, Duncan J
2009-02-01
Nanoparticles are regarded as a major step forward to achieving the miniaturisation and nanoscaling effects and properties that have been utilised by nature for millions of years. The chemist is no longer observing and describing the behaviour of matter but is now able to manipulate and produce new types of materials with specific desired physicochemical characteristics. Such materials are receiving extensive attention across a broad range of research disciplines. The fusion between nanoparticle and nanoporous materials technology represents one of the most interesting of these rapidly expanding areas. The harnessing of nanoscale activity and selectivity, potentially provides extremely efficient catalytic materials for the production of commodity chemicals, and energy needed for a future sustainable society. In this tutorial review, we present an introduction to the field of supported metal nanoparticles (SMNPs) on porous materials, focusing on their preparation and applications in different areas. PMID:19169462
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).
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.
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
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.
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.
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
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
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.
Porous silicon ring resonator for compact, high sensitivity biosensing applications
Rodriguez, Gilberto A.; Hu, Shuren; Weiss, Sharon M.
2015-01-01
A ring resonator is patterned on a porous silicon slab waveguide to produce a compact, high quality factor biosensor with a large internal surface area available for enhanced recognition of biological and chemical molecules. The porous nature of the ring resonator allows molecules to directly interact with the guided mode. Quality factors near 10,000 were measured for porous silicon ring resonators with a radius of 25 μm. A bulk detection sensitivity of 380 nm/RIU was measured upon exposure to salt water solutions. Specific detection of nucleic acid molecules was demonstrated with a surface detection sensitivity of 4 pm/nM.
Titanium--hydroxyapatite porous structures for endosseous applications.
Popa, C; Simon, V; Vida-Simiti, I; Batin, G; Candea, V; Simon, S
2005-12-01
Materials for uncemented endosseous implants have to assure an as short as possible osseointegration time. Thus, a material with both surface bioactivity and a porous outer structure can become a preferred choice for this type of applications. This paper presents a class of titanium-base PM composites, reinforced with particulate hydroxyapatite. Raw materials were titanium powder, obtained through hydriding--milling--dehydriding, with the grain size of 63-100 microm, and sol-gel hydroxyapatite (HA) powder, produced by the reaction between Ca(NO3)2 x 4H2O and (NH4)2HPO4. Blends with 5 to 50% HA were prepared and pressed in a rigid die, producing single composition or gradual composition samples. The applied pressure was of 400, 500 or 600 MPa. Sintering was performed in vacuum, at 1160 ( composite function)C. All samples, although well sintered, displayed swelling during sintering, due to diffusion into the matrix. The increase in volume is more severe for higher amounts of HA in the green compacts and for higher applied compaction pressure. Compacts with a gradual increase of the HA content are recommended from the functional and mechanical point of view, but the increase should be slow, not to produce interlayer cracks. The outer surface shows interconnected pores, suitable for the ingrowth of vital new bone. PMID:16362217
Hierarchical Porous Zeolite Structures for Pressure Swing Adsorption Applications.
Besser, Benjamin; Tajiri, Henrique Akira; Mikolajczyk, Gerd; Möllmer, Jens; Schumacher, Thomas C; Odenbach, Stefan; Gläser, Roger; Kroll, Stephen; Rezwan, Kurosch
2016-02-10
Porous adsorbents with hierarchical structured macropores ranging from 1 to 100 μm are prepared using a combination of freeze casting and additional sacrificial templating of polyurethane foams, with a zeolite 13X powder serving as adsorbent. The pore system of the prepared monoliths features micropores assigned to the zeolite 13X particle framework, interparticular pores of ∼1-2 μm, lamellar pores derived from freeze casting of ∼10 μm, and an interconnected pore network obtained from the sacrificial templates ranging from around 100 to 200 μm with a total porosity of 71%. Gas permeation measurements show an increase in intrinsic permeability by a factor of 14 for monoliths prepared with an additional sacrificial templated foam compared to monoliths solely providing freeze casting pores. Cyclic CO2 adsorption and desorption tests where pressure swings between 8 and 140 kPa reveal constant working capacities over multiple cycles. Furthermore, the monoliths feature a high volumetric working capacity of ∼1.34 mmol/cm(3) which is competitive to packed beds made of commercially available zeolite 13X beads (∼1.28 mmol/cm(3)). Combined with the faster CO2 uptake showing an adsorption of 50% within 5-8 s (beads ∼10 s), the monoliths show great potential for pressure swing adsorption applications, where high volumetric working capacities, fast uptakes, and low pressure drops are needed for a high system performance. PMID:26760054
The Effect of Porous Medium Storage on Unstable Density-Driven Solute Transport.
Xie, Yueqing; Graf, Thomas; Simmons, Craig T; Diersch, Hans-Jörg G
2015-01-01
Unstable density-driven groundwater flow and solute transport (i.e., free convection) leads to spatiotemporal variations in pressure. Specific storage (So ) indicates the capability of a confined aquifer to release or store groundwater associated with a pressure change. Although So is known to dampen pressure propagation, So has been implicitly assumed to have a negligible impact on the unstable free convective process in prior studies. This work explores the effect of So on both the classic onset criterion and the fingering process using numerical models. Results show that the classic onset criterion is applicable when So is smaller than 10(-1) m(-1) . Results also demonstrate that So does not play a significant role in the free convective fingering process unless it is greater than 10(-3) m(-1) . For most practical purposes in hydrogeology (large Rayleigh number and small So ), the implicit assumption of small or zero So is appropriate. PMID:25393965
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.
NASA Astrophysics Data System (ADS)
Ramiro-Manzano, Fernando; Fenollosa, Roberto; Xifré-Pérez, Elisabet; Garín, Moises; Meseguer, Francisco
2012-09-01
We have recently developed a new type of porous silicon we name as porous silicon colloids. They consist of almost perfect spherical silicon nanoparticles with a very smooth surface, able to scatter (and also trap) light very efficiently in a large-span frequency range. Porous silicon colloids have unique properties because of the following: (a) they behave as optical microcavities with a high refractive index, and (b) the intrinsic photoluminescence (PL) emission is coupled to the optical modes of the microcavity resulting in a unique luminescence spectrum profile. The PL spectrum constitutes an optical fingerprint identifying each particle, with application for biosensing. In this paper, we review the synthesis of silicon colloids for developing porous nanoparticles. We also report on the optical properties with special emphasis in the PL emission of porous silicon microcavities. Finally, we present the photonic barcode concept.
2012-01-01
We have recently developed a new type of porous silicon we name as porous silicon colloids. They consist of almost perfect spherical silicon nanoparticles with a very smooth surface, able to scatter (and also trap) light very efficiently in a large-span frequency range. Porous silicon colloids have unique properties because of the following: (a) they behave as optical microcavities with a high refractive index, and (b) the intrinsic photoluminescence (PL) emission is coupled to the optical modes of the microcavity resulting in a unique luminescence spectrum profile. The PL spectrum constitutes an optical fingerprint identifying each particle, with application for biosensing. In this paper, we review the synthesis of silicon colloids for developing porous nanoparticles. We also report on the optical properties with special emphasis in the PL emission of porous silicon microcavities. Finally, we present the photonic barcode concept. PMID:22943136
Supported porous carbon and carbon-CNT nanocomposites for supercapacitor applications
NASA Astrophysics Data System (ADS)
Schopf, Dimitri; Es-Souni, Mohammed
2016-03-01
Supported porous carbon and porous carbon-MWCNT-nanocomposite films are produced by pyrolysis of porous polyvinylidene fluoride (PVDF) or porous PVDF-MWCNT-nanocomposite films on thermally resistant substrates. All films are characterized by SEM, RAMAN and XRD. The application of these films as supercapacitors is explored with outstanding supercapacitance values ranging from 80 to 120 F g-1 (up to 70 mF cm-2) in a three-electrode set-up in 1 M KOH, depending on microstructure. Additionally, the implementation of porous nanocarbon-MWCNT-nanocomposite films as electrodes in a symmetrical supercapacitor device is investigated. In all cases, long-term charge-discharge stability is demonstrated.
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.
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.
The processing and potential applications of porous silicon
Syyuan Shieh.
1992-07-01
Stability of a cylindrical pore under the influence of surface energy is important for porous silicon (PS) processing in the integrated circuit industry. Once the zig-zag cylindrical pores of porous silicon or oxidized porous silicon (OPS) are unstable and breakup into rows of isolated spherical pores, oxidation of PS and densification/nitridation of OPS become difficult. Swing to difficulty transport of reactant gas (O{sub 2}, NH{sub 3}) or the trapped gas (for densification of OPS). A first order analysis of the stability of a cylindrical pore or cylinder is considered first. Growth of small sinusoidal perturbations by viscous flow or evaporation/condensation result in dependence of perturbation growth rate on perturbation wavelength. Rapid thermal oxidation (RTO) of porous silicon is proposed as an alternative for the tedious two-step 300 and 800C oxidation process. Transmission electron microscopy, energy dispersive spectroscopy ESCA are used for quality control. Also, rapid thermal nitridation of oxidized porous silicon in ammonia is proposed to enhance OPS resistance to HF solution. Pores breakup of OPS results in a trapped gas problem during densification. Wet helium is proposed as OPS densification ambient gas to shorten densification time. Finally, PS is proposed to be an extrinsic gettering center in silicon wafers. The suppression of oxidation-induced stacking faults is used to demonstrate the gettering ability. Possible mechanism is discussed.
Development and Applications of Porous Tantalum Trabecular Metal Enhanced Titanium Dental Implants
Bencharit, Sompop; Byrd, Warren C.; Altarawneh, Sandra; Hosseini, Bashir; Leong, Austin; Reside, Glenn; Morelli, Thiago; Offenbacher, Steven
2013-01-01
Statement of Problem Porous tantalum trabecular metal has recently been incorporated in titanium dental implants as a new form of implant surface enhancement. However, there is little information on the applications of this material in implant dentistry. Methods We, therefore review the current literature on the basic science and clinical uses of this material. Results Porous tantalum metal is used to improve the contact between osseous structure and dental implants; and therefore presumably facilitate osseointegration. Success of porous tantalum metal in orthopedic implants led to the incorporation of porous tantalum metal in the design of root-from endosseous titanium implants. The porous tantalum three-dimensional enhancement of titanium dental implant surface allows for combining bone ongrowth together with bone ingrowth, or osseoincorporation. While little is known about the biological aspect of the porous tantalum in the oral cavity, there seems to be several possible advantages of this implant design. This article reviews the biological aspects of porous tantalum enhanced titanium dental implants, in particular the effects of anatomical consideration and oral environment to implant designs. Conclusions We propose here possible clinical situations and applications for this type of dental implant. Advantages and disadvantages of the implants as well as needed future clinical studies are discussed. PMID:23527899
Near and medium infrared optical fiber lasers and emerging applications
NASA Astrophysics Data System (ADS)
Prudenzano, F.; Mescia, L.; Allegretti, L.; De Sario, M.; D'Orazio, A.; Di Tommaso, A.; Palmisano, T.; Petruzzelli, V.
2010-02-01
Laser cavities emitting in the near and medium infrared wavelength range, made of rare earth doped optical fibers and suitable pairs of integrated mirrors, are used in a large number of applications. Nowadays, the efficient employment of near and medium infrared laser beams is largely widespread in the field of m*aterial processing, surgery, directed energy, remote sensing, spectroscopy, imaging, and so on. In a lot of cases, the high conversion efficiency, the excellent beam quality, the compactness and, the good heat dissipation capability make fiber lasers competitive and attractive with respect to other light sources, such as ion-doped crystal and bulk glass lasers, optical parametric oscillators, semiconductor and gas lasers. The paper aims to recall and/or briefly illustrate a few among the numerous strategies recently followed by research laboratories and industries to obtain laser sources based on rare earth doped optical fibres. A recall on the host materials and the dopants employed for their construction, and the corresponding applications is given, too. Moreover, an example of near infrared (NIR) fiber optic laser development, by employing available on market components is illustrated by underlining the possibility to easily obtain high beam quality.
Application of porous materials for laminar flow control
NASA Technical Reports Server (NTRS)
Pearce, W. E.
1978-01-01
Fairly smooth porous materials were elected for study Doweave; Fibermetal; Dynapore; and perforated titanium sheet. Factors examined include: surface smoothness; suction characteristics; porosity; surface impact resistance; and strain compatibility. A laminar flow control suction glove arrangement was identified with material combinations compatible with thermal expansion and structural strain.
Surface functionalized hydrophobic porous particles toward water treatment application.
Abbaspourrad, Alireza; Carroll, Nick J; Kim, Shin-Hyun; Weitz, David A
2013-06-18
A microfluidic-based approach for the fabrication of organic contaminants absorbing core-shell particles is demonstrated. The hydrophobic porous core absorbs oil while the hydrophilic surface enables the particles to be well-dispersed in aqueous solutions. These particles can uptake oil from aqueous solution saturated with oil or via direct contact with oil blobs as depicted in the figure. PMID:23649837
Gas sensing using porous materials for automotive applications.
Wales, Dominic J; Grand, Julien; Ting, Valeska P; Burke, Richard D; Edler, Karen J; Bowen, Chris R; Mintova, Svetlana; Burrows, Andrew D
2015-07-01
Improvements in the efficiency of combustion within a vehicle can lead to reductions in the emission of harmful pollutants and increased fuel efficiency. Gas sensors have a role to play in this process, since they can provide real time feedback to vehicular fuel and emissions management systems as well as reducing the discrepancy between emissions observed in factory tests and 'real world' scenarios. In this review we survey the current state-of-the-art in using porous materials for sensing the gases relevant to automotive emissions. Two broad classes of porous material - zeolites and metal-organic frameworks (MOFs) - are introduced, and their potential for gas sensing is discussed. The adsorptive, spectroscopic and electronic techniques for sensing gases using porous materials are summarised. Examples of the use of zeolites and MOFs in the sensing of water vapour, oxygen, NOx, carbon monoxide and carbon dioxide, hydrocarbons and volatile organic compounds, ammonia, hydrogen sulfide, sulfur dioxide and hydrogen are then detailed. Both types of porous material (zeolites and MOFs) reveal great promise for the fabrication of sensors for exhaust gases and vapours due to high selectivity and sensitivity. The size and shape selectivity of the zeolite and MOF materials are controlled by variation of pore dimensions, chemical composition (hydrophilicity/hydrophobicity), crystal size and orientation, thus enabling detection and differentiation between different gases and vapours. PMID:25982991
Porous poly(para-phenylene) scaffolds for load-bearing orthopedic applications.
DiRienzo, Amy L; Yakacki, Christopher M; Frensemeier, Mareike; Schneider, Andreas S; Safranski, David L; Hoyt, Anthony J; Frick, Carl P
2014-02-01
The focus of this study was to fabricate and investigate the mechanical behavior of porous poly(para-phenylene) (PPP) for potential use as a load-bearing orthopedic biomaterial. PPPs are known to have exceptional mechanical properties due to their aromatic backbone; however, the manufacturing and properties of PPP porous structures have not been previously investigated. Tailored porous structures with either small (150-250µm) or large (420-500µm) pore sizes were manufactured using a powder-sintering/salt-leaching technique. Porosities were systematically varied using 50 to 90vol%. Micro-computed tomography (µCT) and scanning electron microscopy (SEM) were used to verify an open-cell structure and investigate pore morphology of the scaffolds. Uniaxial mechanical behavior of solid and porous PPP samples was characterized through tensile and compressive testing. Both modulus and strength decreased with increasing porosity and matched well with foam theory. Porous scaffolds showed a significant decrease in strain-to-failure (<4%) under tensile loading and experienced linear elasticity, plastic deformation, and densification under compressive loading. Over the size ranges tested, pore size did not significantly influence the mechanical behavior of the scaffolds on a consistent basis. These results are discussed in regards to use of porous PPP for orthopedic applications and a prototype porous interbody fusion cage is presented. PMID:24374261
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
A novel architecture for pore network modelling with applications to permeability of porous media
NASA Astrophysics Data System (ADS)
Jivkov, Andrey P.; Hollis, Cathy; Etiese, Friday; McDonald, Samuel A.; Withers, Philip J.
2013-04-01
SummaryNetwork models of porous media are beneficial for predicting the evolution of macroscopic mass transport properties. This work proposes a novel bi-regular network model based on truncated octahedral support. With the model, pore systems with different pore coordination spectra for a given average coordination number can be constructed to match experimental data. This feature and the maximum allowed pore coordination of 14 make the proposed model more realistic and flexible than the existing models based on cubic supports. Limestone is used as a study material to illustrate the model performance. Experimental pore space data for this material obtained by X-ray tomography (CT) are used for constructing microstructure-informed model realisations. It is demonstrated that with these realisations the experimentally measured permeability of the material can be predicted. The model is further used to assess the effects of pore connectivity and porosity on the permeability. It is shown that the effect of pore connectivity is substantially stronger than the effect of porosity. A strategy for calculating the evolution of permeability with damage-related pore space changes is also described. The results reveal the effects of the mechanical properties of the medium on the permeability evolution as a function of damage evolution. Developments of this strategy are suggested for deriving mechanism-based constitutive laws for engineering applications.
Grain reconstruction of porous media: application to a low-porosity Fontainebleau sandstone.
Thovert, J F; Yousefian, F; Spanne, P; Jacquin, C G; Adler, P M
2001-06-01
The fundamental issue of reconstructing a porous medium is examined anew in this paper, thanks to a sample of low-porosity Fontainebleau sandstone that has been analyzed by computed microtomography. Various geometric properties are determined on the experimental sample. A statistical property, namely, the probability density of the covering radius, is determined. This is used in order to reconstruct a porous medium by means of a Poissonian generation of polydisperse spheres. In a second part, the properties of the real experimental sample and of the reconstructed one are compared. The most important success of the present reconstruction technique is the fact that the numerical sample percolates despite its low porosity. Moreover, other geometrical features and conductivity are found to be in good agreement. PMID:11415092
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
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.
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.
NASA Astrophysics Data System (ADS)
Ye, Ke; Zhang, Dongming; Guo, Fen; Cheng, Kui; Wang, Guiling; Cao, Dianxue
2015-06-01
Highly porous nickel@carbon sponge electrode with low cost is synthesized via a facile sponge carbonization method coupled with a direct electrodeposition of Ni. The obtained electrodes are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The catalytic performances of urea electro-oxidation in alkaline medium are investigated by cyclic voltammetry (CV) and chronoamperometry (CA). The Ni@carbon sponge electrode exhibits three-dimensional open network structures with a large surface area. Remarkably, the Ni@carbon sponge electrode shows much higher electrocatalytic activity and lower onset oxidation potential towards urea electro-oxidation compared to a Ni/Ti flat electrode synthesized by the same procedure. The Ni@carbon sponge electrode achieves an onset oxidation potential of 0.24 V (vs. Ag/AgCl) and a peak current density of 290 mA cm-2 in 5 mol L-1 NaOH and 0.10 mol L-1 urea solutions accompanied with a desirable stability. The impressive electrocatalytic activity is largely attributed to the high intrinsic electronic conductivity, superior porous network structures and rich surface Ni active species, which can largely boost the interfacial electroactive sites and charge transfer rates for urea electro-oxidation in alkaline medium, indicating promising applications in fuel cells.
Biophotonic applications of eigenchannels in a scattering medium (Conference Presentation)
NASA Astrophysics Data System (ADS)
Kim, Moonseok; Choi, Wonjun; Choi, Youngwoon; Yoon, Changhyeong; Choi, Wonshik
2016-03-01
When waves travel through disordered media such as ground glass and skin tissues, they are scattered multiple times. Most of the incoming energy bounces back at the superficial layers and only a small fraction can penetrate deep inside. This has been a limiting factor for the working depth of various optical techniques. We present a systematic method to enhance wave penetration to the scattering media. Specifically, we measured the reflection matrix of a disordered medium with wide angular coverage for each orthogonal polarization states. From the reflection matrix, we identified reflection eigenchannels of the medium, and shaped the incident wave into the reflection eigenchannel with smallest eigenvalue, which we call anti-reflection mode. This makes reflectance reduced and wave penetration increased as a result of the energy conservation. We demonstrated transmission enhancement by more than a factor of 3 by the coupling of the incident waves to the anti-reflection modes. Based on the uneven distribution of eigenvalues of reflection eigenchannels, we further developed an iterative feedback control method for finding and coupling light to anti-reflection modes. Since this adaptive control method can keep up with sample perturbation, it promotes the applicability of exploiting reflection eigenchannels. Our approach of delivering light deep into the scattering media will contribute to enhancing the sensitivity of detecting objects hidden under scattering layers, which is universal problem ranging from geology to life science.
Medium Range Ensembles Flood Forecasts for Community Level Applications
NASA Astrophysics Data System (ADS)
Fakhruddin, S.; Kawasaki, A.; Babel, M. S.; AIT
2013-05-01
Early warning is a key element for disaster risk reduction. In recent decades, there has been a major advancement in medium range and seasonal forecasting. These could provide a great opportunity to improve early warning systems and advisories for early action for strategic and long term planning. This could result in increasing emphasis on proactive rather than reactive management of adverse consequences of flood events. This can be also very helpful for the agricultural sector by providing a diversity of options to farmers (e.g. changing cropping pattern, planting timing, etc.). An experimental medium range (1-10 days) flood forecasting model has been developed for Bangladesh which provides 51 set of discharge ensembles forecasts of one to ten days with significant persistence and high certainty. This could help communities (i.e. farmer) for gain/lost estimation as well as crop savings. This paper describe the application of ensembles probabilistic flood forecast at the community level for differential decision making focused on agriculture. The framework allows users to interactively specify the objectives and criteria that are germane to a particular situation, and obtain the management options that are possible, and the exogenous influences that should be taken into account before planning and decision making. risk and vulnerability assessment was conducted through community consultation. The forecast lead time requirement, users' needs, impact and management options for crops, livestock and fisheries sectors were identified through focus group discussions, informal interviews and questionnaire survey.
Application of acoustic bessel beams for handling of hollow porous spheres.
Azarpeyvand, Mahdi; Azarpeyvand, Mohammad
2014-02-01
Acoustic manipulation of porous spherical shells, widely used as drug delivery carriers and magnetic resonance imaging contrast agents, is investigated analytically. The technique used for this purpose is based on the application of high-order Bessel beams as a single-beam acoustic manipulation device, by which particles lying on the axis of the beam can be pulled toward the beam source. The exerted acoustic radiation force is calculated using the standard partial-wave series method, and the wave propagation within the porous media is modeled using Biot's theory of poro-elasticity. Numerical simulations are performed for porous aluminum and silica shells of different thickness and porosity. Results indicate that manipulation of low-porosity shells is possible using Bessel beams with large conical angles, over a number of broadband frequency ranges, whereas manipulation of highly porous shells can occur over both narrowband and broadband frequency domains. PMID:24342912
Dispersion properties in porous media: application to Redox Flow Battery electrodes
NASA Astrophysics Data System (ADS)
Picano, Francesco; Maggiolo, Dario; Marion, Andrea; Guarnieri, Massimo
2015-11-01
Redox Flow Batteries (RFBs) represent a promising technology as a way to store energy. However, in order to improve RFBs performance, some conceptual and technological issues are still open. In particular, a properly designed geometry of flow channels and porous medium is still under investigation in order to uniformly distribute the reacting species all along the electrode. The ideal configuration aims to minimize the drag maximizing the mixing so to increase the overall performance and efficiency. In the present work a Lattice Boltzmann 3D model (LBM) has been used to better understand the dependence of mass and momentum transports on the porosity and carbon fiber preferential orientation. The LBM has been coupled with a Lagrangian particle tracking algorithm in order to investigate the dispersion mechanisms induced by the porous medium on the species flowing in a typical RFB. Results show that the drag is considerably reduced when the medium fibers are preferentially oriented along the streamwise direction. Surprisingly, this configuration shows also the highest transversal dispersion rate characterized by a super-diffusive behavior. Actually, the dispersion features are found to strongly depend on the porous media microstructure showing either anomalous or regular diffusion.
Highly efficient forward osmosis based on porous membranes--applications and implications.
Qi, Saren; Li, Ye; Zhao, Yang; Li, Weiyi; Tang, Chuyang Y
2015-04-01
For the first time, forward osmosis (FO) was performed using a porous membrane with an ultrafiltration (UF)-like rejection layer and its feasibility for high performance FO filtration was demonstrated. Compared to traditional FO membranes with dense rejection layers, the UF-like FO membrane was 2 orders of magnitude more permeable. This gave rise to respectable FO water flux even at ultralow osmotic driving force, for example, 7.6 L/m(2).h at an osmotic pressure of merely 0.11 bar (achieved by using a 0.1% poly(sodium 4-styrene-sulfonate) draw solution). The membrane was applied to oil/water separation, and a highly stable FO water flux was achieved. The adoption of porous FO membranes opens a door to many new opportunities, with potential applications ranging from wastewater treatment, valuable product recovery, and biomedical applications. The potential applications and implications of porous FO membranes are addressed in this paper. PMID:25751713
Macromolecular coatings on porous silicon: Applications in drug delivery, biosensing, and composites
NASA Astrophysics Data System (ADS)
Perelman, Loren Avery
Two classes of macromolecules, proteins and polymers, are coated onto porous Si films in a variety of geometries in order to study fundamental behaviors of these coatings and their potential device applications. The unique preparation control that porous Si allows in both nano-morphology and surface functionalization provides the means for the coatings. In chapter two, a drug delivery platform using bovine serum albumin (BSA) protein as a stimuli-responsive capping layer on porous Si is described and characterized. It was found that the surface chemistry of the porous Si film has a profound influence on both drug loading capacity and drug release kinetics, providing for control over these drug release variables. The BSA is observed to act as a pH-responsive trigger for the release of vancomycin from the porous Si film. The drug is safely stored in the porous matrix at pH 4 and is released after triggering with pH 7.4 phosphate buffered saline. Chapter three discusses a porous SiO2-based biosensor that is prepared by oxidizing a porous Si film, adsorbing BSA to the surface as a coating, and functionalizing the protein with specific target probes for vancomycin. The BSA was observed to adsorb strongly to the surface, resisting desoprtion in both phosphate buffered saline and triton-X buffer solutions. Quantitative binding information for the tripeptide Ac-L-Lysine-D-Alanine-D-Alanine and vancomycin is determined using the optical properties of the porous Si as a transduction methodology. Chapters four and five describe the fabrication of thermoresponsive and multifunctional nanohybrids, respectively, using stimuli-responsive hydrogels to infiltrate and coat oxidized porous Si films. The optical properties of the porous Si films are used to study the response of the hydrogel phase of the hybrids to a variety of stimuli. The optical changes correspond to previously-described physical changes in the hydrogel phase, and it was determined that this platform provides a
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.
Barkay-Olami, Hilla; Zilberman, Meital
2016-08-01
Use of naturally derived materials for biomedical applications is steadily increasing. Soy protein has advantages over various types of natural proteins employed for biomedical applications due to its low price, nonanimal origin, and relatively long storage time and stability. In the current study, blends of soy protein with other polymers (gelatin, alginate, pectin, polyvinyl alcohol, and polyethylene glycol) were developed and studied. The mechanical tensile properties of dense films were studied in order to select the best secondary polymer for porous three-dimensional structures. The porous soy-gelatin and soy-alginate structures were then studied for physical properties, degradation behavior, and microstructure. The results show that these blends can be assembled into porous three-dimensional structures by combining chemical crosslinking with freeze-drying. The soy-alginate blends are advantageous over soy-gelatin blends, demonstrated better stability, and degradation time along with controlled swelling behavior due to more effective crosslinking and higher water uptake than soy-gelatin blends. Water vapor transmission rate experiments showed that all porous blend structures were in the desired range for burn treatment [2000-2500 g/(m(2) d)] and can be controlled by the crosslinking process. We conclude that these novel porous three-dimensional structures have a high potential for use as scaffolds for tissue engineering, especially for skin regeneration applications. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1109-1120, 2016. PMID:26038233
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.
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)
Petkovich, Nicholas Daniel
Materials with nm- and mum-scale pores are important in the design of efficient, safe, and versatile energy conversion and storage systems. In the research detailed in this thesis, the synthesis and testing of porous materials for lithium-ion battery anodes and for thermochemical fuel production are explored. The preparation, modification, and performance of various carbon and transition metal oxide composite materials for lithium-ion battery electrodes are discussed in the first part of this work. Of particular interest are TiO 2/carbon composites that possess a three-dimensionally ordered macroporous (3DOM) structure, and, in some instances, additional mesoporosity. By changing the chelating agent used to stabilize the precursor for TiO2, crystallites of TiO2 can either be localized on the surface of the 3DOM structure or buried within the carbon matrix. This positioning has important ramifications for the electrochemical properties of the materials. In addition, the content of carbon in the composite materials can be altered. For carbon-rich composites, improved Li+ insertion/extraction capacities are attained by changing the voltage window used for cycling. Carbon can also be removed altogether, allowing for the formation 3DOM TiO¬2 with good electrochemical properties Conversion of the 3DOM TiO2 to sodium titanate is demonstrated via the ambient pressure treatment of the 3DOM material in sodium hydroxide. Subsequent ion-exchange with H+ results in the formation of hydrogen titanate materials with extremely high surface areas. A remnant of the 3DOM structure remains in these materials. Cerium oxide, praseodymium oxide and perovskite oxide-based catalysts for the thermochemical conversion of solar energy and abundant feedstocks (H2O and CO2) into useable fuels (H2 and CO) are investigated in the second part of this work. All of these materials possess a 3DOM structure and have moderate surface areas intended to improve reaction kinetics. Mixed oxides containing
Shear dispersion in a capillary tube with a porous wall
NASA Astrophysics Data System (ADS)
Dejam, Morteza; Hassanzadeh, Hassan; Chen, Zhangxin
2016-02-01
An analytical expression is presented for the shear dispersion during solute transport in a coupled system comprised of a capillary tube and a porous medium. The dispersion coefficient is derived in a capillary tube with a porous wall by considering an accurate boundary condition, which is the continuity of concentration and mass flux, at the interface between the capillary tube and porous medium. A comparison of the obtained results with that in a non-coupled system identifies three regimes including: diffusion-dominated, transition, and advection-dominated. The results reveal that it is essential to include the exchange of solute between the capillary tube and porous medium in development of the shear dispersion coefficient for the last two regimes. The resulting equivalent transport equation revealed that due to mass transfer between the capillary tube and the porous medium, the dispersion coefficient is decreased while the effective velocity in the capillary tube increases. However, a larger effective advection term leads to faster breakthrough of a solute and enhances mass delivery to the porous medium as compared with the classical double-porosity model with a non-coupled dispersion coefficient. The obtained results also indicate that the finite porous medium gives faster breakthrough of a solute as compared with the infinite one. These results find applications in solute transport in porous capillaries and membranes.
Shear dispersion in a capillary tube with a porous wall.
Dejam, Morteza; Hassanzadeh, Hassan; Chen, Zhangxin
2016-01-01
An analytical expression is presented for the shear dispersion during solute transport in a coupled system comprised of a capillary tube and a porous medium. The dispersion coefficient is derived in a capillary tube with a porous wall by considering an accurate boundary condition, which is the continuity of concentration and mass flux, at the interface between the capillary tube and porous medium. A comparison of the obtained results with that in a non-coupled system identifies three regimes including: diffusion-dominated, transition, and advection-dominated. The results reveal that it is essential to include the exchange of solute between the capillary tube and porous medium in development of the shear dispersion coefficient for the last two regimes. The resulting equivalent transport equation revealed that due to mass transfer between the capillary tube and the porous medium, the dispersion coefficient is decreased while the effective velocity in the capillary tube increases. However, a larger effective advection term leads to faster breakthrough of a solute and enhances mass delivery to the porous medium as compared with the classical double-porosity model with a non-coupled dispersion coefficient. The obtained results also indicate that the finite porous medium gives faster breakthrough of a solute as compared with the infinite one. These results find applications in solute transport in porous capillaries and membranes. PMID:26845232
Applications of porous tantalum in total hip arthroplasty.
Levine, Brett; Della Valle, Craig J; Jacobs, Joshua J
2006-11-01
Porous tantalum is an alternative metal for total joint arthroplasty components that offers several unique properties. Its high volumetric porosity (70% to 80%), low modulus of elasticity (3 MPa), and high frictional characteristics make it conducive to biologic fixation. Tantalum has excellent biocompatibility and is safe to use in vivo. The low modulus of elasticity allows for more physiologic load transfer and relative preservation of bone stock. Because of its bioactive nature and ingrowth properties, tantalum is used in primary as well as revision total hip arthroplasty components, with good to excellent early clinical results. In revision arthroplasty, standard and custom augments may serve as a structural bone graft substitute. Formation of a bone-like apatite coating in vivo affords strong fibrous ingrowth properties and allows for substantial soft-tissue attachment, indicating potential for use in cases requiring reattachment of muscles and tendons to a prosthesis. Development of modular components and femoral stems also is being evaluated. The initial clinical data and basic science studies support further investigation of porous tantalum as an alternative to traditional implant materials. PMID:17077337
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.
Chavanne, Xavier; Frangi, Jean-Pierre
2014-01-01
This paper describes a sensor dedicated to measuring the vertical profile of the complex permittivity and the temperature of any medium in which sensor electrodes are inserted. Potential applications are the estimate of the humidity and salinity in a porous medium, such as a soil. It consists of vertically-stacked capacitors along two conductive parallel cylinders of 5 cm in diameter and at a 10-cm distance to scan a significant volume of the medium (∼1 L). It measures their admittances owing to a self-balanced impedance bridge operating at a frequency in the range of 1–20 MHz, possibly 30 MHz. Thanks to accurate design and electronic circuit theory-based modeling, the determination of the admittances takes into account all distortions due to lead and bridge electromagnetic effects inside the sensor when working at high frequencies. Calibration procedures and uncertainties are presented. The article also describes developments to make the present sensor autonomous on digital acquisition, basic data treatment and energy, as well as able to transfer stored data by a radio link. These steps in progress are prerequisites for a wireless network of sensors. PMID:25162233
Xia, Wei; Qiu, Bin; Xia, Dingguo; Zou, Ruqiang
2013-01-01
Porous carbon materials have numerous applications due to their thermal and chemical stability, high surface area and low densities. However, conventional preparing porous carbon through zeolite or silica templates casting has been criticized by the costly and/or toxic procedure. Creating three-dimensional (3D) carbon products is another challenge. Here, we report a facile way to prepare porous carbons from metal-organic gel (MOG) template, an extended metal-organic framework (MOF) structure. We surprisingly found that the carbon products inherit the highly porous nature of MOF and combine with gel's integrated character, which results in hierarchical porous architectures with ultrahigh surface areas and quite large pore volumes. They exhibit considerable hydrogen uptake and excellent electrochemical performance as cathode material for lithium-sulfur battery. This work provides a general method to fast and clean synthesis of porous carbon materials and opens new avenues for the application of metal-organic gel in energy storage. PMID:23728472
Porous Cu Nanowire Aerosponges from One-Step Assembly and their Applications in Heat Dissipation.
Jung, Sung Mi; Preston, Daniel J; Jung, Hyun Young; Deng, Zhengtao; Wang, Evelyn N; Kong, Jing
2016-02-17
Highly porous metal nanowire aerosponges are produced by direct assembly of the Cu nanowire in situ during their synthesis. Such a method offers not only great simplicity, but also excellent properties such as extremely low densities, high electrical conductivities, and remarkable mechanical properties. Furthermore, these Cu aerosponges exhibit excellent wicking behavior, suggesting their potential for heat-exchange applications in heat pipes. PMID:26635235
Evaluation of QNI corrections in porous media applications
NASA Astrophysics Data System (ADS)
Radebe, M. J.; de Beer, F. C.; Nshimirimana, R.
2011-09-01
Qualitative measurements using digital neutron imaging has been the more explored aspect than accurate quantitative measurements. The reason for this bias is that quantitative measurements require correction for background and material scatter, and neutron spectral effects. Quantitative Neutron Imaging (QNI) software package has resulted from efforts at the Paul Scherrer Institute, Helmholtz Zentrum Berlin (HZB) and Necsa to correct for these effects, while the sample-detector distance (SDD) principle has previously been demonstrated as a measure to eliminate material scatter effect. This work evaluates the capabilities of the QNI software package to produce accurate quantitative results on specific characteristics of porous media, and its role to nondestructive quantification of material with and without calibration. The work further complements QNI abilities by the use of different SDDs. Studies of effective %porosity of mortar and attenuation coefficient of water using QNI and SDD principle are reported.
NASA Astrophysics Data System (ADS)
Muth, John; Poggie, Matthew; Kulesha, Gene; Michael Meneghini, R.
2013-02-01
Hip and knee replacement can dramatically improve a patient's quality of life through pain relief and restored function. Fixation of hip and knee replacement implants to bone is critical to the success of the procedure. A variety of roughened surfaces and three-dimensional porous surfaces have been used to enhance biological fixation on orthopedic implants. Recently, highly porous metals have emerged as versatile biomaterials that may enhance fixation to bone and are suitable to a number of applications in hip and knee replacement surgery. This article provides an overview of several processes used to create these implant surfaces.
Zhuravleva, K; Chivu, A; Teresiak, A; Scudino, S; Calin, M; Schultz, L; Eckert, J; Gebert, A
2013-05-01
Porous ß-type non-toxic Ti40Nb alloy was prepared by compaction of mechanically alloyed powder mixed with NaCl or Mg particles as space-holder material. The compacts with porosity of 36-80% demonstrated a very low Young's modulus of ~1.5-3 GPa and compression strength of ~10-35 MPa, which is suitable for potential implant material application. Porous samples were electrochemically covered with hydroxyapatite. The influence of the deposition time and of the electrolyte concentrations on the morphology of the hydroxyapatite coating was studied. It is demonstrated that a homogenous coating of hydroxyapatite crystals with different shape and size can be obtained on the surface of the porous samples. PMID:23498259
Porous Ti6Al4V alloys with enhanced normalized fatigue strength for biomedical applications.
Li, Fuping; Li, Jinshan; Kou, Hongchao; Zhou, Lian
2016-03-01
In this paper, porous Ti6Al4V alloys for biomedical applications were fabricated by diffusion bonding of alloy meshes. The compression-compression fatigue behavior was studied. It results that porous Ti6Al4V alloys show enhanced normalized fatigue strength which is in the range of 0.5-0.55 at 10(6)cycles. The porosity has some effect on the absolute S-N curves but minor effect on the normalized S-N curves. The relationship between strain per cycle and number of cycles shows three distinct stages and the value of strain per cycle is constant in stage II. The reasons for the higher normalized fatigue strength of porous Ti6Al4V alloys are discussed based on the fatigue crack initiation and propagation. PMID:26706555
NASA Astrophysics Data System (ADS)
Jodar, B.; Seisson, G.; Hébert, D.; Bertron, I.; Boustie, M.; Berthe, L.
2016-08-01
Because of their shock wave attenuation properties, porous materials and foams are increasingly used for various applications such as graphite in the aerospace industry and polyurethane (PU) foams in biomedical engineering. For these two materials, the absence of residual compaction after compression and release cycles limits the efficiency of the usual numerical dynamic porous models such as P-α and POREQST. In this paper, we suggest a simple enhancement of the latter in order to take into account the compression-release hysteresis behavior experimentally observed for the considered materials. The new model, named H-POREQST, was implemented into a Lagrangian hydrocode and tested for simulating plate impact experiments at moderate pressure onto a commercial grade of porous graphite (EDM3). It proved to be in far better agreement with experimental data than the original model which encourages us to pursue numerical tests and developments.
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
Yu, Yan; Gu, Lin; Zhu, Changbao; van Aken, Peter A; Maier, Joachim
2009-11-11
Tin nanoparticles encapsulated in porous multichannel carbon microtubes (denoted as SPMCTs) were prepared by carbonization of electrospun PAN-PMMA-tin octoate nanofibers fabricated using a single-nozzle electrospinning technique. This material exhibited excellent characteristics for lithium ion battery anode applications in terms of reversible capacities, cycling performance, and rate capability. Undertaking such a production configuration allows the long-existing problem of obtaining a high packing density of tin particles while retaining sufficient spare space to buffer the volume variation during lithium alloying and dealloying processes to be properly addressed. Furthermore, the porous carbon shell preserves both the mechanical and chemical stability of the function-active Sn metal, which also serves as a highly conductive medium allowing Li(+) to access. PMID:19886691
Porous mixed metal oxides: design, formation mechanism, and application in lithium-ion batteries
NASA Astrophysics Data System (ADS)
Wu, Fangfang; Bai, Jing; Feng, Jinkui; Xiong, Shenglin
2015-10-01
The relentless pursuit of new electrode materials for lithium ion batteries (LIBs) has been conducted for decades. Structures with either porous or nanostructure configurations have been confirmed as advantageous candidates for energy storage/conversion applications. The integration of the two features into one structure can provide another chance to improve the electroactivities. Recently, single-phased mixed metal oxides (MMOs) containing different metal cations, in particular, have confirmed high electrochemical activities because of their complex chemical composition, interfacial effects, and the synergic effects of the multiple metal species. In this review, we will focus on recent research advances of MMOs with porous architectures as anode materials in the matter of structural arrangement and compositional manipulation. Moreover, the application of self-supported MMO-based porous structures as LIB anodes is also explained herein. More importantly, investigations on the synthetic system and formation mechanism of porous MMOs will be highlighted. Some future trends for the innovative design of new electrode materials are also discussed in this review. The challenges and prospects will draw many researchers' attention.
Nelson, J.T. . Dept. of Mechanical Engineering Lawrence Berkeley Lab., CA )
1988-11-01
A theoretical model for acoustic emission in a vertically heterogeneous porous layer bounded by semi-infinite solid regions is developed using linearized equations of motion for a fluid/solid mixture and a reflectivity method. Green's functions are derived for both point loads and moments. Numerically integrated propagators represent solutions for intermediate heterogeneous layers in the porous region. These are substituted into a global matrix for solution by Gaussian elimination and back-substitution. Fluid partial stress and seismic responses to dislocations associated with fracturing of a layer of rock with a hydraulically conductive fracture network are computed with the model. A constitutive model is developed for representing the fractured rock layer as a porous material, using commonly accepted relationships for moduli. Derivations of density, tortuosity, and sinuosity are provided. The main results of the model application are the prediction of a substantial fluid partial stress response related to a second mode wave for the porous material. The response is observable for relatively large distances, on the order of several tens of meters. The visco-dynamic transition frequency associated with parabolic versus planar fluid velocity distributions across micro-crack apertures is in the low audio or seismic range, in contrast to materials with small pore size, such as porous rocks, for which the transition frequency is ultrasonic. Seismic responses are predicted for receiver locations both in the layer and in the outlying solid regions. In the porous region, the seismic response includes both shear and dilatational wave arrivals and a second-mode arrival. The second-mode arrival is not observable outside of the layer because of its low velocity relative to the dilatational and shear wave propagation velocities of the solid region.
Applications of porous electrodes to metal-ion removal and the design of battery systems
Trost, G.G.
1983-09-01
This dissertation treats the use of porous electrodes as electrochemical reactors for the removal of dilute metal ions. A methodology for the scale-up of porous electrodes used in battery applications is given. Removal of 4 ..mu..g Pb/cc in 1 M sulfuric acid was investigated in atmospheric and high-pressure, flow-through porous reactors. The atmospheric reactor used a reticulated vitreous carbon porous bed coated in situ with a mercury film. Best results show 98% removal of lead from the feed stream. Results are summarized in a dimensionless plot of Sherwood number vs Peclet number. High-pressure, porous-electrode experiments were performed to investigate the effect of pressure on the current efficiency. Pressures were varied up to 120 bar on electrode beds of copper or lead-coated spheres. The copper spheres showed high hydrogen evolution rates which inhibited lead deposition, even at high cathodic overpotentials. Use of lead spheres inhibited hydrogen evolution but often resulted in the formation of lead sulfate layers; these layers were difficult to reduce back to lead. Experimental data of one-dimensional porous battery electrodes are combined with a model for the current collector and cell connectors to predict ultimate specific energy and maximum specific power for complete battery systems. Discharge behavior of the plate as a whole is first presented as a function of depth of discharge. These results are combined with the voltage and weight penalties of the interconnecting bus and post, positive and negative active material, cell container, etc. to give specific results for the lithium-aluminum/iron sulfide high-temperature battery. Subject to variation is the number of positive electrodes, grid conductivity, minimum current-collector weight, and total delivered capacity. The battery can be optimized for maximum energy or power, or a compromise design may be selected.
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
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.
Ali, Farhad; Khan, Ilyas; Samiulhaq; Shafie, Sharidan
2013-01-01
The aim of this study is to present an exact analysis of combined effects of radiation and chemical reaction on the magnetohydrodynamic (MHD) free convection flow of an electrically conducting incompressible viscous fluid over an inclined plate embedded in a porous medium. The impulsively started plate with variable temperature and mass diffusion is considered. The dimensionless momentum equation coupled with the energy and mass diffusion equations are analytically solved using the Laplace transform method. Expressions for velocity, temperature and concentration fields are obtained. They satisfy all imposed initial and boundary conditions and can be reduced, as special cases, to some known solutions from the literature. Expressions for skin friction, Nusselt number and Sherwood number are also obtained. Finally, the effects of pertinent parameters on velocity, temperature and concentration profiles are graphically displayed whereas the variations in skin friction, Nusselt number and Sherwood number are shown through tables. PMID:23840321
2011-01-01
A boundary layer analysis is presented for the mixed convection past a vertical wedge in a porous medium saturated with a nano fluid. The governing partial differential equations are transformed into a set of non-similar equations and solved numerically by an efficient, implicit, iterative, finite-difference method. A parametric study illustrating the influence of various physical parameters is performed. Numerical results for the velocity, temperature, and nanoparticles volume fraction profiles, as well as the friction factor, surface heat and mass transfer rates have been presented for parametric variations of the buoyancy ratio parameter Nr, Brownian motion parameter Nb, thermophoresis parameter Nt, and Lewis number Le. The dependency of the friction factor, surface heat transfer rate (Nusselt number), and mass transfer rate (Sherwood number) on these parameters has been discussed. PMID:21711715
Yih, K.A.
1997-03-01
Effect of transpiration velocity on the heat and mass transfer characteristics of mixed convection about a permeable vertical plate embedded in a saturated porous medium under the coupled effects of thermal and mass diffusion is numerically analyzed. The plate is maintained at a uniform temperature and species concentration with constant transpiration velocity. The transformed governing equations are solved by Keller box method. Numerical results for the local Nusselt number and local Sherwood number are presented. In general, it has been found for thermally assisted flow that the local surface heat and mass transfer rates increase owing to suction of fluid. This trend reversed for blowing of fluid. It is apparent that the Lewis number has a pronounced effect on the local Sherwood number than it does on the local Nusselt number. Increasing the Lewis number decreases (increases) the local heat (mass) transfer rate.
NASA Astrophysics Data System (ADS)
Khan, Najeeb Alam; Sultan, Faqiha
2015-05-01
This paper devotedly study the double diffusive Darcian convection flow of Eyring-Powell fluid from a cone embedded in a homogeneous porous medium with the effects of Soret and Dufour. Arising set of non-linear partial differential equations are transformed through a suitable self-similar transformation into a set of nonlinear ordinary differential equations. Further, the numerical and the analytical solutions of the governing equations are elucidated by using numerical method as well as non-perturbation scheme. Numerical values are presented through tables for the skin friction coefficients, Nusselt number and Sherwood number. The obtained results are validated by comparing the analytical results with previously published results obtained by bvp4c for the numerical values of physical quantities. The effect of various parameters on the velocity, temperature and concentration profiles is discussed and also shown graphically.
NASA Astrophysics Data System (ADS)
Singh, M.
2016-02-01
The instability of the plane interface between two uniform, superposed and streaming Rivlin-Ericksen elastico-viscous fluids through porous media, including the `effective interfacial tension' effect, is considered. In the absence of the `effective interfacial tension' stability/instability of the system as well as perturbations transverse to the direction of streaming are found to be unaffected by the presence of streaming if perturbations in the direction of streaming are ignored, whereas for perturbation in all other directions, there exists instability for a certain wave number range. The `effective interfacial tension' is able to suppress this Kelvin-Helmholtz instability for small wavelength perturbations, the medium porosity reduces the stability range given in terms of a difference in streaming velocities.
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. PMID:26698873
Two-Phase Flow Within Porous Media Analogies: Application Towards CO2 Sequestration
Crandall, D.M. Clarkson University, Potsdam, NY); Ahmadi, G.; Smith, D.H.
2007-04-20
Geologic carbon dioxide sequestration (GCO2S) involves the capture of large quantities of CO2 from point-source emitters and pumping this greenhouse gas to subsurface reservoirs (USDOE, 2006). The mechanisms of two-phase fluid displacement in GCO2S, where a less viscous fluid displaces a more viscous fluid in a heterogeneous porous domain is similar to enhanced oil recovery activities. Direct observation of gas-liquid interface movement in geologic reservoirs is difficult due to location and opacity. Over the past decades, complex, interconnected pore-throat models have been developed and used to study multiphase flow interactions in porous media, both experimentally (Buckley, 1994) and numerically (Blunt, 2001). This work expands upon previous experimental research with the use of a new type of heterogeneous flowcell, created with stereolithography (SL). Numerical solutions using the Volume-of-Fluid (VOF) model with the same flowcell geometry, are shown to be in good agreement with the drainage experiments, where the defending fluid wets the surface. This computational model is then used to model imbibition, the case of the invading fluid preferentially wetting the surface. Low capillary flows and imbibition conditions are shown to increase the storage volume of the invading fluid in the porous medium.
Utilizing of inner porous structure in injection moulds for application of special cooling method
NASA Astrophysics Data System (ADS)
Seidl, M.; Bobek, J.; Šafka, J.; Habr, J.; Nováková, I.; Běhálek, L.
2016-04-01
The article is focused on impact evaluation of controlled inner structure of production tools and new cooling method on regulation of thermal processes for injection moulding technology. The mould inserts with porous structure were cooled by means of liquid CO2 which is very progressive cooling method and enables very fast and intensive heat transfer among the plastic product, the production tool and cooling medium. The inserts were created using rapid prototype technology (DLSM) and they had a bi-component structure consisting of thin compact surface layer and defined porous inner structure of open cell character where liquid CO2 was flowing through. This analyse includes the evaluation of cooling efficiency for different inner structures and different time profiles for dosing of liquid CO2 into the porous structure. The thermal processes were monitored using thermocouples and IR thermal analyse of product surface and experimental device. Intensive heat removal influenced also the final structure and the shape and dimensional accuracy of the moulded parts that were made of semi-crystalline polymer. The range of final impacts of using intensive cooling method on the plastic parts was defined by DSC and dimensional analyses.
NASA Astrophysics Data System (ADS)
Dittrich, T. M.; Ryan, J. N.
2008-12-01
The presence of mobile colloids (particles between 1 nm and 1 μm in size) in natural soil and groundwater systems has been well established. Colloids generally have a high sorptive capacity resulting from their high surface area to mass ratio, which makes them effective sorbents of low solubility, strongly sorbing contaminants. Mobile colloids that sorb contaminants can increase the apparent solubility and rate of transport of the contaminants when desorption from the colloids is slow relative to the rate of flow. This process is known as colloid-facilitated transport (CFT). The additional transport of contaminants associated with mobile colloids should be accounted for to accurately predict transport rates of strongly-sorbing contaminants in the environment. Some examples of contaminants that have the potential for CFT are hydrophobic pesticides, polycyclic aromatic hydrocarbons (PAHs), actinide cations (e.g., Th, U, Pu, Am), and many metals (e.g, Pb, Cu, Hg). Many low solubility contaminants that have the potential for CFT are also harmful or toxic to humans, underscoring the importance of accurate modeling techniques to protect water sources from contamination. Contaminated Department of Energy (DOE) sites have been particularly valuable research opportunities for studying the transport of radionuclides in the natural environment. The DOE has conducted energy and weapons research and development in thirty-one states and Puerto Rico and has introduced many toxic and radioactive chemicals into surface waters, soils, and groundwater. Field experiments on DOE sites including the Nevada Test Site, the Hanford 200 Area tank farm, Rocky Flats CO, and Oak Ridge TN, have confirmed that metals and radionuclides have moved further than expected due to colloid-facilitated transport. The major goal of this research project is to identify and quantify the effects of sorption kinetics on colloid- facilitated transport in unsaturated porous media. This information will be used
Capillary infiltration rates into porous media with applications to Silcomp processing
Einset, E.O.
1996-02-01
The rate of capillary rise of a liquid into a porous medium made up of consolidated particulates is analyzed. The infiltration distance is parabolic in time and can be modeled using the Washburn analysis. The effective pore radius is measured to be one to two orders of magnitude smaller than the particle size, particle spacing, and the median pore size as measured by mercury porosimetry. This result is interpreted using a modification of the Washburn model which models the porous medium as a single pore with varying diameter. Using a two-sized single pore model, the predicted infiltration rate is consistent with the measured values. In applying the two-sized single pore model to the reactive capillary infiltration of silicon into a carbonaceous preform in the Silcomp process, the effect of pore closure by the conversion of carbon to SiC is predicted. Using pore closure dimensions measured in a partial infiltration experiment, a decrease in the infiltration rate constant is predicted and is consistent with the measured infiltration rate.
NASA Astrophysics Data System (ADS)
Poonoosamy, J.; Curti, E.; Kosakowski, G.; Grolimund, D.; Van Loon, L. R.; Mäder, U.
2016-06-01
A reaction cell experiment was designed to examine mineral dissolution/precipitation processes both at the macroscopic and pore scale. A rectangular flow cell was filled with a reactive porous layer lying between two porous layers composed of quartz sand (SiO2). The reactive layer consisted of celestite (or celestine, SrSO4) with a bimodal grain size distribution (<63 μm and 125-400 μm). A barium chloride solution was then injected into the flow cell, leading to fast dissolution and replacement of celestite by barite (or baryte, BaSO4). Due to the higher molar volume of barite compared to celestite, the porosity decreased in the reactive layer. We concentrated on the refinement of post-mortem analysis and the investigation of the dissolution/precipitation mechanisms at the pore scale (10-100 μm). The sequential evolution of mineral transformations occurring in the reactive layer was determined. Our analytical techniques, combining scanning electron microscopy and synchrotron X-ray microdiffraction/microfluorescence, showed that the small celestite grain fraction dissolved rapidly to form nano-crystalline barite filling the pore space, while large celestite grains were covered with a thin rim of epitaxial micro-crystalline barite. Two distinct nucleation mechanisms for barite precipitation were involved: homogeneous nucleation (nucleation of barite in the pore space) and heterogeneous nucleation (nucleation on the surface of a solid substrate). Classical nucleation theory, using well-established and estimated parameters (e.g. effective interfacial tension) describing barite nucleation, was applied to explain the mineralogical changes occurring in our system.
NASA Astrophysics Data System (ADS)
Wang, B.; Bauer, S.; Pfeiffer, W. T.
2015-12-01
Large scale energy storage will be required to mitigate offsets between electric energy demand and the fluctuating electric energy production from renewable sources like wind farms, if renewables dominate energy supply. Porous formations in the subsurface could provide the large storage capacities required if chemical energy carriers such as hydrogen gas produced during phases of energy surplus are stored. This work assesses the behavior of a porous media hydrogen storage operation through numerical scenario simulation of a synthetic, heterogeneous sandstone formation formed by an anticlinal structure. The structural model is parameterized using data available for the North German Basin as well as data given for formations with similar characteristics. Based on the geological setting at the storage site a total of 15 facies distributions is generated and the hydrological parameters are assigned accordingly. Hydraulic parameters are spatially distributed according to the facies present and include permeability, porosity relative permeability and capillary pressure. The storage is designed to supply energy in times of deficiency on the order of seven days, which represents the typical time span of weather conditions with no wind. It is found that using five injection/extraction wells 21.3 mio sm³ of hydrogen gas can be stored and retrieved to supply 62,688 MWh of energy within 7 days. This requires a ratio of working to cushion gas of 0.59. The retrievable energy within this time represents the demand of about 450000 people. Furthermore it is found that for longer storage times, larger gas volumes have to be used, for higher delivery rates additionally the number of wells has to be increased. The formation investigated here thus seems to offer sufficient capacity and deliverability to be used for a large scale hydrogen gas storage operation.
Development of porous Ti6Al4V/chitosan sponge composite scaffold for orthopedic applications.
Guo, Miao; Li, Xiang
2016-01-01
A novel composite scaffold consisting of porous Ti6Al4V part filled with chitosan sponge was fabricated using a combination of electron beam melting and freeze-drying. The mechanical properties of porous Ti6Al4V part were examined via compressive test. The ultimate compressive strength was 85.35 ± 8.68 MPa and the compressive modulus was 2.26 ± 0.42 GPa. The microstructure of composite scaffold was characterized using scanning electron microscopy. The chitosan sponge filled in Ti6Al4V part exhibited highly porous and well-interconnected micro-pore architecture. The osteoblastic cells were seeded on scaffolds to test their seeding efficiency and biocompatibility. Significantly higher cell seeding efficiency was found on composite scaffold. The biological response of osteoblasts on composite scaffolds was superior in terms of improved cell attachment, higher proliferation, and well-spread morphology in relation to porous Ti6Al4V part. These results suggest that the Ti6Al4V/chitosan composite scaffold is potentially useful as a biomedical scaffold for orthopedic applications. PMID:26478418
NASA Astrophysics Data System (ADS)
Graule, Thomas; Ozog, Paulina; Durif, Caroline; Wilkens-Heinecke, Judit; Kata, Dariusz
2016-06-01
Porous, graded ceramic structures are of high relevance in the field of energy conversion as well as in catalysis, and additionally in filtration technology and in biomedical applications. Among different technologies for the tailored design for such structures we demonstrate here a new environmental friendly UV curing-based concept to prepare laminated structures with pore sizes ranging from a few microns up to 50 microns in diameter and with porosities ranging from 10% up to 75 vol.% porosity.
Correia, Cristina; Bhumiratana, Sarindr; Sousa, Rui A.; Reis, Rui L.
2013-01-01
In native bone, cells experience fluctuating shear forces that are induced by pulsatile interstitial flow associated with habitual loading. We hypothesized that the formation of engineered bone can be augmented by replicating such physiologic stimuli to osteogenic cells cultured in porous scaffolds using bioreactors with medium perfusion. To test this hypothesis, we investigated the effect of fluid flow regime on in vitro bone-like tissue development by human adipose stem cells (hASC) cultivated on porous three-dimensional silk fibroin scaffolds. To this end, we varied the sequential relative durations of steady flow (SF) and pulsatile flow (PF) of culture medium applied over a period of 5 weeks, and evaluated their effect on early stages of bone formation. Porous silk fibroin scaffolds (400–600 μm pore size) were seeded with hASC (30×106 cells/mL) and cultured in osteogenic medium under four distinct fluid flow regimes: (1) PF for 5 weeks; (2) SF for 1 week, PF for 4 weeks; (3) SF for 2 weeks, PF for 3 weeks; (4) SF for 5 weeks. The PF was applied in 12 h intervals, with the interstitial velocity fluctuating between 400 and 1200 μm/s at a 0.5 Hz frequency for 2 h, followed by 10 h of SF. In all groups, SF was applied at 400 μm/s. The best osteogenic outcomes were achieved for the sequence of 2 weeks of SF and 3 weeks of PF, as evidenced by gene expression (including the PGE2 mechanotransduction marker), construct compositions, histomorphologies, and biomechanical properties. We thus propose that osteogenesis in hASC and the subsequent early stage bone development involve a mechanism, which detects and responds to the level and duration of hydrodynamic shear forces. PMID:23259605
Higuita, Mario; Bernal, Claudia; Mesa, Monica
2014-10-01
The porous inorganic materials, with hierarchical structures, find application in many processes where the chemical stability and pore connectivity are key points, such as separation, adsorption and catalysis. Here, we synthesized carbon-silica composite materials, which combine hydrolytic stability of the carbon with the surface chemical reactivity of silica in aqueous media. The polycondensation of carbonaceous and siliceous species from sucrose, Triton X-100 surfactant and tetraethylortosilicate during the hydrothermal synthesis led to the formation of hydrochar composite materials. The subsequent carbonization process of these composite hydrochars gave carbon-silica hierarchical porous materials. The study of the micellar reaction system and the characterization of the derivate materials (carbon-silica composite, carbon and silica) were carried out. The results indicate that synthesis conditions allowed the formation of a silica network interpenetrated with a carbon one, which is produced from the incorporated organic matter. The control of the acidity of the reaction medium and hydrothermal conditions modulated the reaction yield and porous characteristics of the materials. The composite nature in conjunction with the hierarchical porosity increases the interest of these materials for future biological applications, such as lipase immobilization. PMID:25175205
Zhu, Jianhui; Jiang, Jian; Liu, Jingping; Ding, Ruimin; Ding, Hao; Feng, Yamin; Wei, Guangming; Huang, Xintang
2011-03-15
Porous NiO nanowall arrays (NWAs) grown on flexible Fe-Co-Ni alloy have been successfully synthesized by using nullaginite (Ni{sub 2}(OH){sub 2}CO{sub 3}) as precursor and investigated as supercapacitor electrodes. In details, we adopted a simple hydrothermal method to realize Ni{sub 2}(OH){sub 2}CO{sub 3} NWAs and examined their robust mechanical adhesion to substrate via a long-time ultrasonication test. Porous NiO NWAs were then obtained by a post-calcination towards precursors at 500 {sup o}C in nitrogen atmosphere. Electrochemical properties of as-synthesized NiO NWAs were evaluated by cyclic voltammetry and galvanostatic charge/discharge; porous NiO NWAs electrode delivered a specific capacitance of 270 F/g (0.67 A/g); even at high current densities, the electrode could still deliver a high capacitance up to 236 F/g (13.35 A/g). Meanwhile, it exhibited excellent cycle lifetime with {approx}93% specific capacitance kept after 4000 cycles. These results suggest that as-made porous NiO NWAs electrode is a promising candidate for future thin-film supercapacitors and other microelectronic systems. -- Graphical abstract: Porous NiO nanowall arrays (NWAs) grown on alloy substrate have been made using nullaginite as precursor and studied as supercapacitor electrodes. Porous nanowalls interconnected with each other resulting in the formation of extended-network architectures and exhibited excellent capacitor properties. NiO NWAs electrode delivered a capacitance of 270 F/g (0.67 A/g); even at high current density, the electrode could still deliver a high capacitance up to 236 F/g (13.35 A/g). Besides, it exhibited excellent cycle lifetime with {approx}93% capacitance kept after 4000 cycles. These remarkable results made it possible for mass production of NiO NWAs and future thin-film microelectronic applications. Display Omitted Research highlights: {yields} Large-scale nullaginite (Ni{sub 2}(OH){sub 2}CO{sub 3}) nanowall arrays (NWAs) have been synthesized on
Fourar, M.; Bories, S. ); Lenormand, R. ); Persoff, P. )
1993-11-01
Two-phase (air-water) flow experiments were conducted in horizontal artificial fractures. The fractures were between glass plates that were either smooth or artificially roughened by gluing a layer of glass beads to them. One smooth fracture with an aperture of 1 mm and three rough fractures, one with the two surfaces in contact and two without contact, were studied. For both types of fractures, the flow structures are similar to those observed in two-phase flow in a pipe, with structures (bubbles, fingering bubbles, films, and drops) depending on the gas and liquid flow rates. The pressure gradients measured for different liquid and gas velocities were interpreted by three models. First, using Darcy's law leads to relative permeability curves similar to conventional ones for porous media. However, these curves depend not only on saturation but also on flow rats. This effect is caused by inertial forces which are not included in this approach. Second, the standard approach for two-phase flow in pipes (Lockhart and Martinelli's equation) agrees with experimental results, at least for small pressure gradients. Finally, the best fit was obtained by treating the two phases as one homogeneous phase. All the properties are averaged, and the pressure drop is deduced from an empirical correlation between the two-phase Reynolds number and the friction factor. 22 refs., 11 figs.
NASA Astrophysics Data System (ADS)
Shahzad, F.; Hayat, T.
2012-05-01
The unsteady MHD flow of an incompressible micropolar fluid have been considered. The fluid is filling the semi-infinite space z>0 which is in contact with an infinite porous rotating disk at z = 0. The common angular velocity of the disk and fluid at infinity is Ω. The fluid is electrically conducting in presence of an applied constant magnetic field B0. Initially the disk and the fluid are rotating about the z/-axis and at time t = 0, suddenly the disk starts rotating about the z-axis and moving with uniform acceleration, while the fluid at infinity continue to rotate about z/-axis with same angular velocity Ω. The axes of rotation of both the disk and that of the fluid at infinity are assumed to be in the plane x = 0, and distance between axes is l. The governing problem is solved numerically using Newton's method. Numerical results explaining the effects of various parameters associated with the flow are discussed graphically.
Barth, G.R.; Hill, M.C.; Illangasekare, T.H.; Rajaram, H.
2001-01-01
As a first step toward understanding the role of sedimentary structures in flow and transport through porous media, this work deterministically examines how small-scale laboratory-measured values of hydraulic conductivity relate to in situ values of simple, artificial structures in an intermediate-scale (10 m long), two-dimensional, heterogeneous, laboratory experiment. Results were judged based on how well simulations using measured values of hydraulic conductivities matched measured hydraulic heads, net flow, and transport through the tank. Discrepancies were investigated using sensitivity analysis and nonlinear regression estimates of the in situ hydraulic conductivity that produce the best fit to measured hydraulic heads and net flow. Permeameter and column experiments produced laboratory measurements of hydraulic conductivity for each of the sands used in the intermediate-scale experiments. Despite explicit numerical representation of the heterogeneity the laboratory-measured values underestimated net flow by 12-14% and were distinctly smaller than the regression-estimated values. The significance of differences in measured hydraulic conductivity values was investigated by comparing variability of transport predictions using the different measurement methods to that produced by different realizations of the heterogeneous distribution. Results indicate that the variations in measured hydraulic conductivity were more important to transport than variations between realizations of the heterogeneous distribution of hydraulic conductivity.
Deridder, Sander; Desmet, Gert
2011-01-01
The results of a numerical simulation study of the diffusion and retention in fully porous spheres and cylinders are compared with some of the high order accuracy analytical solutions for the effective diffusion coefficient that have been derived from the effective medium theory (EMT) theory in part I of the present study. A variety of different ordered (spheres and cylinders) and disordered (cylinders) packings arrangements has been considered. The agreement between simulations and theory was always excellent, lying within the (very tight) accuracy limits of the simulations over the full range of retention factor and diffusion constant values that is practically relevant for most LC applications. Subsequently filling up the spheres and cylinders with a central solid core, while keeping the same packing geometry and the same mobile phase (same thermodynamic retention equilibrium), it was found that the core induces an additional obstruction which reduces the effective intra-particle diffusion coefficient exactly with a factor γ(part)=2/(2+ρ³) for spherical particles and γ(part)=1/(1+ρ²) for cylinders (ρ is the ratio of the core to the particle diameter, ρ=d(core)/d(part)). These expressions hold independently of the packing geometry, the value of the diffusion coefficients and the equilibrium constant or the size of the core. The expressions also imply that, if considering equal mobile phase conditions, the presence of the solid core will never reduce the particle contribution to the B-term band broadening with more than 33% (50% in case of cylindrical pillars). PMID:21122871
Sviridov, A. P. Osminkina, L. A.; Nikolaev, A. L.; Kudryavtsev, A. A.; Vasiliev, A. N.; Timoshenko, V. Yu.
2015-09-21
A significant decrease of the cavitation threshold in aqueous suspensions of porous silicon nanoparticles (PSi NPs) with sizes about 100 nm as compared with pure water was observed for ultrasound irradiation (USI) with therapeutic frequency (0.88 MHz) and intensities (about 1 W/cm{sup 2}). This effect is explained by porous morphology of PSi NPs, which promotes the nucleation of cavitation bubbles. In vitro experiments revealed a suppression of the proliferation of cancer cells with the introduced PSi NPs after exposure to USI related to the enhanced cavitation processes, which led to the cell destruction. The obtained results demonstrate that PSi NPs are prospective for applications as sonosensitizers in mild cancer therapy.
NASA Technical Reports Server (NTRS)
Park, Junhong; Palumbo, Daniel L.
2004-01-01
For application of porous and granular materials to vibro-acoustic controls, a finite dynamic strength of the solid component (frame) is an important design factor. The primary goal of this study was to investigate structural vibration damping through this frame wave propagation for various poroelastic materials. A measurement method to investigate the vibration characteristics of the frame was proposed. The measured properties were found to follow closely the characteristics of the viscoelastic materials - the dynamic modulus increased with frequency and the degree of the frequency dependence was determined by its loss factor. The dynamic stiffness of hollow cylindrical beams containing porous and granular materials as damping treatment was measured also. The data were used to extract the damping materials characteristics using the Rayleigh-Ritz method. The results suggested that the acoustic structure interaction between the frame and the structure enhances the dissipation of the vibration energy significantly.
Shepodd, Timothy J.
2002-01-01
Highly crosslinked monolithic porous polymer materials for chromatographic applications. By using solvent compositions that provide not only for polymerization of acrylate monomers in such a fashion that a porous polymer network is formed prior to phase separation but also for exchanging the polymerization solvent for a running buffer using electroosmotic flow, the need for high pressure purging is eliminated. The polymer materials have been shown to be an effective capillary electrochromatographic separations medium at lower field strengths than conventional polymer media. Further, because of their highly crosslinked nature these polymer materials are structurally stable in a wide range of organic and aqueous solvents and over a pH range of 2-12.
Creating porous tubes by centrifugal forces for soft tissue application.
Dalto, P D; Shoichet, M S
2001-10-01
Chemically crosslinked poly(2-hydroxyethyl methacrylate) (PHEMA) tubes were synthesized by applying centrifugal forces to propagating polymer chains in solution. Initiated monomer solutions, with a composition typical for PHEMA sponges, were placed into a cylindrical mold that was rotated about its long axis. As polymerization proceeded, phase separated PHEMA formed a sediment at the periphery under centrifugal action. The solvent remained in the center of the mold while the PHEMA phase gelled, resulting in a tube. By controlling the rotational speed and the formulation chemistry (i.e., monomer, initiator and crosslinking agent concentrations), the tube dimensions and wall morphology were manipulated. Tube manufacture was limited by a critical casting concentration [M]c, above which only rods formed. All tubes had an outer diameter of 2.4 mm, reflecting the internal diameter of the mold and a wall thickness of approximately 40-400 microm. Wall morphologies varied from interconnecting polymer and water phases to a closed cell, gel-like, structure. Concentric tubes were successfully prepared by using formulations that enhanced phase separation over gelation/network formation. This was achieved by using formulations with lower concentrations of monomer and crosslinking agent and higher concentrations of initiator. This technique offers a new approach to the synthesis of polymeric tubes for use in soft tissue applications, such as nerve guidance channels. PMID:11519786
Potsika, Vassiliki T; Grivas, Konstantinos N; Protopappas, Vasilios C; Vavva, Maria G; Raum, Kay; Rohrbach, Daniel; Polyzos, Demosthenes; Fotiadis, Dimitrios I
2014-07-01
Quantitative ultrasound has recently drawn significant interest in the monitoring of the bone healing process. Several research groups have studied ultrasound propagation in healing bones numerically, assuming callus to be a homogeneous and isotropic medium, thus neglecting the multiple scattering phenomena that occur due to the porous nature of callus. In this study, we model ultrasound wave propagation in healing long bones using an iterative effective medium approximation (IEMA), which has been shown to be significantly accurate for highly concentrated elastic mixtures. First, the effectiveness of IEMA in bone characterization is examined: (a) by comparing the theoretical phase velocities with experimental measurements in cancellous bone mimicking phantoms, and (b) by simulating wave propagation in complex healing bone geometries by using IEMA. The original material properties of cortical bone and callus were derived using serial scanning acoustic microscopy (SAM) images from previous animal studies. Guided wave analysis is performed for different healing stages and the results clearly indicate that IEMA predictions could provide supplementary information for bone assessment during the healing process. This methodology could potentially be applied in numerical studies dealing with wave propagation in composite media such as healing or osteoporotic bones in order to reduce the simulation time and simplify the study of complicated geometries with a significant porous nature. PMID:24091149
Targeted delivery by smart capsules for controlling two-phase flow in porous media
NASA Astrophysics Data System (ADS)
Fan, Jing; Abbaspourrad, Alireza; Weitz, David; Harvard Weitzgroup Team
2015-11-01
Two-phase flow in porous media is significantly influenced by the physical properties of the fluids and the geometry of the medium. We develop a variety of smart microcapsules that can deliver and release specific substances to the target location in the porous medium, and therefore change the fluid property or medium geometry at certain locations. In this talk, I will present two types of smart capsules for targeted surfactant delivery to the vicinity of oil-water interface and targeted microgel delivery for improving the homogeneity of the porous medium, respectively. We further prove the concept by monitoring the capsule location and the fluid structure in the porous media by micro-CT and confocal microscopy. This technique not only is of particular importance to the relevant industry applications especially in the oil industry but also opens a new window to study the mechanism of two-phase flow in porous media. Advanced Energy Consortium BEG08-027.
NASA Astrophysics Data System (ADS)
Moura, Marcel; Fiorentino, Eve-Agnès; Jørgen Måløy, Knut; Toussaint, Renaud; Schäfer, Gerhard
2015-04-01
We have performed two-phase flow experiments to analyze the drainage from a quasi-2D random porous medium. The medium is transparent, which allows for the visualization of the invasion pattern during the flow and is initially fully saturated with a viscous fluid (a dyed glycerol-water mix). As the pressure in the fluid is gradually reduced, air penetrates from an open inlet, thus displacing the fluid which leaves the system from the outlet in the opposite side. A feedback mechanism was devised to control the experiment: the capillary pressure (difference in pressure between the non-wetting and wetting phases) is continuously increased to be just above the threshold value necessary to drive the invasion process. This mechanism is intended to keep the invasion process slow, in the so-called capillary regime, where capillary forces dominate the dynamics. Pressure measurements and pictures of the flow are recorded and the pressure-saturation relationship is computed. The effects of the boundary conditions to this quantity are verified experimentally by repeatedly performing the analysis using porous media of different sizes. We show that some features of the pressure-saturation curve are strongly affected by boundary effects. The invasion close to the inlet and outlet of the model are particularly influenced by the boundaries and this is reflected in the phases of pressure building up in the pressure-saturation curves, in the beginning and end of the invasion process. Conversely, at the central part of the model (away from the boundaries), the invasion process happens at an essentially constant capillary pressure, which is reflected as a plateau in the pressure-saturation curve. Additionally, the use of a high-resolution camera allows us to analyze the images down to the pore scale. We can directly obtain a distribution of pore-throat sizes in the model (and their associated capillary pressure thresholds) and divide it into distributions of invaded / non-invaded pores
NASA Astrophysics Data System (ADS)
Li, Xia; Sun, Qian; Liu, Jian; Xiao, Biwei; Li, Ruying; Sun, Xueliang
2016-01-01
For the first time, we report a facile approach to fabricate metal organic framework derived carbon (MOF-C) with tunable porous structure. Different from direct pyrolysis of MOFs and blind attempt in application, the in-situ ammonia treatment enables MOF-C with desired porous structure from enriched microporous structure to hierarchically mesoporous structure. Further, NH3 treated MOF-C as carbon host for sulfur loading performing as the cathode for Li-S batteries results in twice higher capacity retention than that of pristine MOF-C. Besides, different Li-S electrochemical mechanisms regarding the different porous structures of carbon are also revealed and investigated in this paper.
Gand, Adeline; Hindié, Mathilde; Chacon, Diane; Van Tassel, Paul R; Pauthe, Emmanuel
2014-01-01
Biomaterials capable of delivering controlled quantities of bioactive agents, while maintaining mechanical integrity, are needed for a variety of cell contacting applications. We describe here a nanotemplating strategy toward porous, polyelectrolyte-based thin films capable of controlled biomolecular loading and release. Films are formed via the layer-by-layer assembly of charged polymers and nanoparticles (NP), then chemically cross-linked to increase mechanical rigidity and stability, and finally exposed to tetrahydrofuran to dissolve the NP and create an intra-film porous network. We report here on the loading and release of the growth factor bone morphogenetic protein 2 (BMP-2), and the influence of BMP-2 loaded films on contacting murine C2C12 myoblasts. We observe nanotemplating to enable stable BMP-2 loading throughout the thickness of the film, and find the nanotemplated film to exhibit comparable cell adhesion, and enhanced cell differentiation, compared with a non-porous cross-linked film (where BMP-2 loading is mainly confined to the film surface). PMID:25482416
NASA Astrophysics Data System (ADS)
Chen, Z.; Xiao, A.; Chen, Y.; Zuo, C.; Zhou, S.; Li, L.
2013-11-01
We report NiO nanowall thin films prepared by a facile hydrothermal synthesis method and their electrochromic application. The as-prepared porous nanowall NiO thin films show a highly porous structure built up by many interconnected nanoflakes with a thickness of about 30 nm. The electrochromic performances of the NiO films are characterized by means of UV-vis spectroscopy and cyclic voltammetry (CV) measurements. The effect of the annealing temperature on electrochromic properties is discussed. The NiO nanowall film annealed at 300 °C exhibits much better electrochromic performance than those counterparts annealed at higher temperature. The film annealed at 300 °C exhibits a noticeable electrochromism with reversible color changes from transparent to brown dark and presents a transmittance variation with 77% at 550 nm. The NiO nanowall film also shows good reaction kinetics with fast switching speed, and the coloration and bleaching times are 3 s and 4 s, respectively. The improved electrochromic performances are due to the porous morphological characteristics with fast ion and electron transfer resulting in fast reaction kinetics and high color contrast.
NASA Astrophysics Data System (ADS)
Sarhadi, Fatemeh; Shafiee Afarani, Mahdi; Mohebbi-Kalhori, Davod; Shayesteh, Masoud
2016-04-01
In the present study, porous alumina scaffolds with specific orientation and anisotropic properties are fabricated for application in bone tissue repair. The scaffolds with double shape pores, tubular oriented and isotropic rounded pores, were prepared using alumina and silica as starting materials by the slip casting route. Milled polyurethane foam and silk fibers were applied as replica materials as well. The effect of fiber types and diameter and number of fibers on the microstructure and pore size was studied. Moreover, different characteristics such as porosity, density, orientation, flexural strength and compressive strength of the samples were investigated. Results showed that various fibers with different diameters and numbers led to forming the pores with different pore sizes, microstructure and consequently changes in the physical and mechanical properties. In addition, the simultaneous presence of fibers and particles led to more porous scaffolds. The oriented tiny micro-tube and rounded pores were observed in all porous ceramic scaffolds. Mechanical testing showed an anisotropy in the mechanical behaviors such that higher strengths were observed in the oriented pore direction than that of transverse. With increasing the number and diameter of silk fibers, the scaffolds with a high porosity up to 68 vol% and proper flexural strength were obtained.
Soret effect due to opposing flow in square porous annulus
NASA Astrophysics Data System (ADS)
Al-Rashed, Abdullah A. A. A.; Athani, Abdulgaphur; Khaleed, H. M. T.
2016-06-01
The present work is undertaken to investigate the behavior of opposing flow in porous medium under the influence of Soret effect in a square porous annulus. The boundary conditions are such that the outer walls of annulus are maintained at higher temperature and concentration as compared to inner walls. This heat and mass transfer phenomenon is governed by three partial differential equations. The differential equations are converted into a matrix form of equations by the application of finite element method and then solved using iterative algorithm. The results are presented in terms of isotherms, iso-concentration and streamlines indicating the thermal energy, concentration and fluid velocity inside the porous medium under applied boundary conditions. It found that the maximum value of stream function in porous medium decreases with decrease in buoyancy ratio.
NASA Astrophysics Data System (ADS)
Wang, M. B.; Wang, G.
2013-03-01
Referring to previous literature, the elastic problem for a deep pressure tunnel with a permeable liner in a saturated elastic porous medium that obeys Terzaghi's effective stress principle is further investigated. In the analysis, the influences of the changes of the pore water pressure around the opening, the construction sequence of the tunnel, and the interaction between the liner and the surrounding geomaterial on the mechanical response of the tunnel are appropriately considered. Also, the influences of the relative liner thickness and rigidity and the relative distance of the point under investigation from the tunnel axis on the stress-displacement fields for various combinations of the mechanical and geometric parameters are numerically evaluated and discussed. The results indicate that both the support pressure and displacement increase monotonically with increasing liner rigidity and thickness. The influence of the tunnel excavation upon the displacement field is significantly larger than upon the stress field. Either too high or too low values for the relative rigidity and thickness of the liner are unfavorable for structural stability.
NASA Astrophysics Data System (ADS)
Javed, Tariq; Siddiqui, Muhammad Arshad; Mehmood, Ziafat; Pop, Ioan
2015-10-01
In this article, numerical simulations are carried out for fluid flow and heat transfer through natural convection in an isosceles triangular cavity under the effects of uniform magnetic field. The cavity is of cold bottom wall and uniformly/non-uniformly heated side walls and is filled with isotropic porous medium. The governing Navier Stoke's equations are subjected to Penalty finite element method to eliminate pressure term and Galerkin weighted residual method is applied to obtain the solution of the reduced equations for different ranges of the physical parameters. The results are verified as grid independent and comparison is made as a limiting case with the results available in literature, and it is shown that the developed code is highly accurate. Computations are presented in terms of streamlines, isotherms, local Nusselt number and average Nusselt number through graphs and tables. It is observed that, for the case of uniform heating side walls, strength of circulation of streamlines gets increased when Rayleigh number is increased above critical value, but increase in Hartmann number decreases strength of streamlines circulations. For non-uniform heating case, it is noticed that heat transfer rate is maximum at corners of bottom wall.
NASA Astrophysics Data System (ADS)
Gray, William G.; Miller, Cass T.
2006-11-01
This work is the third in a series of papers on the thermodynamically constrained averaging theory (TCAT) approach to modeling flow and transport phenomena in multiscale porous medium systems. Building upon the general TCAT framework and the mathematical foundation presented in previous works in this series, we demonstrate the TCAT approach for the case of single-fluid-phase flow. The formulated model is based upon conservation equations for mass, momentum, and energy and a general entropy inequality constraint, which is developed to guide model closure. A specific example of a closed model is derived under limiting assumptions using a linearization approach and these results are compared and contrasted with the traditional single-phase-flow model. Potential extensions to this work are discussed. Specific advancements in this work beyond previous averaging theory approaches to single-phase flow include use of macroscale thermodynamics that is averaged from the microscale, the use of derived equilibrium conditions to guide a flux-force pair approach to simplification, use of a general Lagrange multiplier approach to connect conservation equation constraints to the entropy inequality, and a focus on producing complete, closed models that are solvable.
Abudalo, R.A.; Ryan, J.N.; Harvey, R.W.; Metge, D.W.; Landkamer, L.
2010-01-01
To assess the effect of organic matter on the transport of Cryptosporidium parvum oocysts in a geochemically heterogeneous saturated porous medium, we measured the breakthrough and collision efficiencies of oocysts as a function of dissolved organic matter concentration in a flow-through column containing ferric oxyhydroxide-coated sand. We characterized the surface properties of the oocysts and ferric oxyhydroxide-coated sand using microelectrophoresis and streaming potential, respectively, and the amount of organic matter adsorbed on the ferric oxyhydroxide-coated sand as a function of the concentration of dissolved organic matter (a fulvic acid isolated from Florida Everglades water). The dissolved organic matter had no significant effect on the zeta potential of the oocysts. Low concentrations of dissolved organic matter were responsible for reversing the charge of the ferric oxyhydroxide-coated sand surface from positive to negative. The charge reversal and accumulation of negative charge on the ferric oxyhydroxide-coated sand led to increases in oocyst breakthrough and decreases in oocyst collision efficiency with increasing dissolved organic matter concentration. The increase in dissolved organic matter concentration from 0 to 20 mg L-1 resulted in a two-fold decrease in the collision efficiency. ?? 2009 Elsevier Ltd.
NASA Astrophysics Data System (ADS)
Tham, Leony; Nazar, Roslinda; Pop, Ioan
2015-11-01
The steady laminar mixed convection boundary layer flow from a horizontal circular cylinder in a nanofluid embedded in a porous medium, which is maintained at a constant surface heat flux, has been studied by using the Buongiorno-Darcy nanofluid model for both cases of a heated and cooled cylinder. The resulting system of nonlinear partial differential equations is solved numerically using an implicit finite-difference scheme known as the Keller box method. The solutions for the flow and heat transfer characteristics are evaluated numerically and studied for various values of the governing parameters, namely the Lewis number, Brownian number, mixed convection parameter, buoyancy ratio parameter and thermophoresis parameter. It is also found that the boundary layer separation occurs at the opposing fluid flow, that is when the mixed convection parameter is negative. It is also observed that increasing the mixed convection parameter delays the boundary layer separation and the separation can be completely suppressed for sufficiently large values of the mixed convection parameter. The Brownian and buoyancy ratio parameters appear to affect the fluid flow and heat transfer profiles.
NASA Astrophysics Data System (ADS)
Baqaie Saryazdi, A.; Talebi, F.; Armaghani, T.; Pop, I.
2016-04-01
In this paper, the problem of developing forced convection flow of a nanofluid in a constant-wall-temperature circular tube filled with a porous medium is considered. The flow is steady and Brinkman-Forchheimer-extended Darcy equation model is employed. The thermal-equilibrium model is assumed between nanofluid and solid phase. It is also assumed that nanoparticles are distributed non-uniformly inside the pipe, hence the particles volume fraction equation is also coupled with the governing equations. A numerical study has been performed using the Finite-Volume method to analyze heat transfer coefficient of Al2O3 -water nanofluid. The effects of nanoparticles volume fraction and porosity on fluid flow and heat transfer of nanofluids are studied. The results show that the Nusselt number is increased with increasing particles volume fraction. Moreover, the wall shear stresses are increased. Finally, the effect of porosity on particle volume fraction distribution is studied and discussed in detail. We are confident that the reported results are new and original.
Eco-friendly porous concrete using bottom ash aggregate for marine ranch application.
Lee, Byung Jae; Prabhu, G Ganesh; Lee, Bong Chun; Kim, Yun Yong
2016-03-01
This article presents the test results of an investigation carried out on the reuse of coal bottom ash aggregate as a substitute material for coarse aggregate in porous concrete production for marine ranch applications. The experimental parameters were the rate of bottom ash aggregate substitution (30%, 50% and 100%) and the target void ratio (15%, 20% and 25%). The cement-coated granular fertiliser was substituted into a bottom ash aggregate concrete mixture to improve marine ranch applications. The results of leaching tests revealed that the bottom ash aggregate has only a negligible amount of the ten deleterious substances specified in the Ministry of Environment - Enforcement Regulation of the Waste Management Act of Republic Korea. The large amount of bubbles/air gaps in the bottom ash aggregate increased the voids of the concrete mixtures in all target void ratios, and decreased the compressive strength of the porous concrete mixture; however, the mixture substituted with 30% and 10% of bottom ash aggregate and granular fertiliser, respectively, showed an equal strength to the control mixture. The sea water resistibility of the bottom ash aggregate substituted mixture was relatively equal to that of the control mixture, and also showed a great deal of improvement in the degree of marine organism adhesion compared with the control mixture. No fatality of fish was observed in the fish toxicity test, which suggested that bottom ash aggregate was a harmless material and that the combination of bottom ash aggregate and granular fertiliser with substitution rates of 30% and 10%, respectively, can be effectively used in porous concrete production for marine ranch application. PMID:26687102
Preparation and application of highly porous aerogel-based bioactive materials in dentistry
NASA Astrophysics Data System (ADS)
Kuttor, Andrea; Szalóki, Melinda; Rente, Tünde; Kerényi, Farkas; Bakó, József; Fábián, István; Lázár, István; Jenei, Attila; Hegedüs, Csaba
2014-03-01
In this study, the possibility of preparation and application of highly porous silica aerogel-based bioactive materials are presented. The aerogel was combined with hydroxyapatite and β-tricalcium phosphate as bioactive and osteoinductive agents. The porosity of aerogels was in the mesoporous region with a maximum pore diameter of 7.4 and 12.7 nm for the composite materials. The newly developed bioactive materials were characterized by scanning electron microscopy. The in vitro biological effect of these modified surfaces was also tested on SAOS-2 osteogenic sarcoma cells by confocal laser scanning microscopy.
Supporting data intensive applications with medium grained parallelism
Pfaltz, J.L.; French, J.C.; Grimshaw, A.S.; Son, S.H.
1992-04-01
ADAMS is an ambitious effort to provide new database access paradigms for the kinds of scientific applications that require massively parallel access to very large data sets in order to be effective. Many of the Grand Challenge Problems fall into this category, as well as those kinds of scientific research which depend on widely distributed shared sets of disparate data. The essence of the ADAMS approach is to view data purely in functional terms, rather than the more traditional structural view in which multiple data items are aggregated into records or tuples of flat files. Further, ADAMS has been implemented as an embedded interface so that scientists can develop applications in the host programming language of their choice, often Fortran, Pascal, or C, and still access shared data generated in other environments. The syntax and semantics of ADAMS is essentially complete. The functional nature of the ADAMS data interface paradigm simplifies its implementation in a distributed environment, e.g., the Mentat run-time system, because one must only distribute functional servers, not pieces of data structures. However, this only opens up the possibility of effective parallel database processing; to realize this potential far more work must be done in the areas of data dependence, intra-statement parallelism, parallel query optimization, and maintaining consistency and reliability in concurrent systems. Discovering how to make effective parallel data access an actually in real scientific applications is the point of this research.
NASA Astrophysics Data System (ADS)
Xiong, Qingrong; Baychev, Todor G.; Jivkov, Andrey P.
2016-09-01
Pore network models have been applied widely for simulating a variety of different physical and chemical processes, including phase exchange, non-Newtonian displacement, non-Darcy flow, reactive transport and thermodynamically consistent oil layers. The realism of such modelling, i.e. the credibility of their predictions, depends to a large extent on the quality of the correspondence between the pore space of a given medium and the pore network constructed as its representation. The main experimental techniques for pore space characterisation, including direct imaging, mercury intrusion porosimetry and gas adsorption, are firstly summarised. A review of the main pore network construction techniques is then presented. Particular focus is given on how such constructions are adapted to the data from experimentally characterised pore systems. Current applications of pore network models are considered, with special emphasis on the effects of adsorption, dissolution and precipitation, as well as biomass growth, on transport coefficients. Pore network models are found to be a valuable tool for understanding and predicting meso-scale phenomena, linking single pore processes, where other techniques are more accurate, and the homogenised continuum porous media, used by engineering community.
Xiong, Qingrong; Baychev, Todor G; Jivkov, Andrey P
2016-09-01
Pore network models have been applied widely for simulating a variety of different physical and chemical processes, including phase exchange, non-Newtonian displacement, non-Darcy flow, reactive transport and thermodynamically consistent oil layers. The realism of such modelling, i.e. the credibility of their predictions, depends to a large extent on the quality of the correspondence between the pore space of a given medium and the pore network constructed as its representation. The main experimental techniques for pore space characterisation, including direct imaging, mercury intrusion porosimetry and gas adsorption, are firstly summarised. A review of the main pore network construction techniques is then presented. Particular focus is given on how such constructions are adapted to the data from experimentally characterised pore systems. Current applications of pore network models are considered, with special emphasis on the effects of adsorption, dissolution and precipitation, as well as biomass growth, on transport coefficients. Pore network models are found to be a valuable tool for understanding and predicting meso-scale phenomena, linking single pore processes, where other techniques are more accurate, and the homogenised continuum porous media, used by engineering community. PMID:27442725
NASA Astrophysics Data System (ADS)
Lai, Ming; Gao, Yan; Yuan, Bin; Zhu, Min
2015-01-01
Recently, porous Ti-Nb-based shape memory alloys have been considered as promising implants for biomedical application, because of their non-toxic elements, low elastic modulus, and stable superelasticity. However, the inverse relationship between pore characteristics and superelasticity of porous SMAs will strongly affect their clinical application. Until now, there have been few works specifically focusing on the effect of pore structure on the mechanical properties and superelasticity of porous Ti-Nb-based SMAs. In this study, the pore structure, including porosity and pore size, of porous Ti-22Nb-6Zr alloys was successfully regulated by adjusting the amount and size of space-holder particles. XRD and SEM investigation showed that all these porous alloys had homogeneous composition. Compression tests indicated that porosity played an important role in the mechanical properties and superelasticity of these porous alloys. Those alloys with porosity in the range of 38.5%-49.7% exhibited mechanical properties approaching to cortical bones, with elastic modulus, compressive strength, and recoverable strain in the range of 7.2-11.4 GPa, 188-422 MPa, and 2.4%-2.6%, respectively. Under the same porosity, the alloys with larger pores exhibited lower elastic modulus, while the alloys with smaller pores presented higher compressive strength.
Li, Jun; Ostoja-Starzewski, Martin
2013-11-01
In two recent papers [Phys. Rev. E 85, 025302(R) (2012) and Phys. Rev. E 85, 056314 (2012)], the authors proposed fractal continuum hydrodynamics and its application to model fluid flows in fractally permeable reservoirs. While in general providing a certain advancement of continuum mechanics modeling of fractal media to fluid flows, some results and statements to previous works need clarification. We first show that the nonlocal character those authors alleged in our paper [Proc. R. Soc. A 465, 2521 (2009)] actually does not exist; instead, all those works are in the same general representation of derivative operators differing by specific forms of the line coefficient c(1). Next, the claimed generalization of the volumetric coefficient c(3) is, in fact, equivalent to previously proposed product measures when considering together the separate decomposition of c(3) on each coordinate. Furthermore, the modified Jacobian proposed in the two commented papers does not relate the volume element between the current and initial configurations, which henceforth leads to a correction of the Reynolds' transport theorem. Finally, we point out that the asymmetry of the Cauchy stress tensor resulting from the conservation of the angular momentum must not be ignored; this aspect motivates a more complete formulation of fractal continuum models within a micropolar framework. PMID:24329394
NASA Astrophysics Data System (ADS)
Li, Jun; Ostoja-Starzewski, Martin
2013-11-01
In two recent papers [Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.85.025302 85, 025302(R) (2012) and Phys. Rev. E10.1103/PhysRevE.85.056314 85, 056314 (2012)], the authors proposed fractal continuum hydrodynamics and its application to model fluid flows in fractally permeable reservoirs. While in general providing a certain advancement of continuum mechanics modeling of fractal media to fluid flows, some results and statements to previous works need clarification. We first show that the nonlocal character those authors alleged in our paper [Proc. R. Soc. A1364-502110.1098/rspa.2009.0101 465, 2521 (2009)] actually does not exist; instead, all those works are in the same general representation of derivative operators differing by specific forms of the line coefficient c1. Next, the claimed generalization of the volumetric coefficient c3 is, in fact, equivalent to previously proposed product measures when considering together the separate decomposition of c3 on each coordinate. Furthermore, the modified Jacobian proposed in the two commented papers does not relate the volume element between the current and initial configurations, which henceforth leads to a correction of the Reynolds’ transport theorem. Finally, we point out that the asymmetry of the Cauchy stress tensor resulting from the conservation of the angular momentum must not be ignored; this aspect motivates a more complete formulation of fractal continuum models within a micropolar framework.
Yin, Na; Stilwell, Matthew D; Santos, Thiago M A; Wang, Huaping; Weibel, Douglas B
2015-01-01
Bacterial cellulose (BC) is a biocompatible hydrogel with a three-dimensional (3-D) structure formed by a dense network of cellulose nanofibers. A limitation of using BC for applications in tissue engineering is that the pore size of the material (∼0.02-10μm) is smaller than the dimensions of mammalian cells and prevents cells from penetrating into the material and growing into 3-D structures that mimic tissues. This paper describes a new route to porous bacterial cellulose (pBC) scaffolds by cultivating Acetobacter xylinum in the presence of agarose microparticles deposited on the surface of a growing BC pellicle. Monodisperse agarose microparticles with a diameter of 300-500μm were created using a microfluidic technique, layered on growing BC pellicles and incorporated into the polymer as A. xylinum cells moved upward through the growing pellicle. Removing the agarose microparticles by autoclaving produced BC gels containing a continuous, interconnected network of pores with diameters ranging from 300 to 500μm. Human P1 chondrocytes seeded on the scaffolds, replicated, invaded the 3-D porous network and distributed evenly throughout the substrate. Chondrocytes grown on pBC substrates displayed a higher viability compared to growth on the surface of unmodified BC substrates. The approach described in this paper introduces a new method for creating pBC substrates with user-defined control over the physical dimensions of the pore network, and demonstrates the application of these materials for tissue engineering. PMID:25449918
Porous-wall hollow glass microspheres as novel potential nanocarriers for biomedical applications
Li, Shuyi; Nguyen, Lynsa; Xiong, Hairong; Wang, Meiyao; Hu, Tom C.-C.; She, Jin-Xiong; Serkiz, Steven M.; Wicks, George G.; Dynan, William S.
2011-01-01
Porous-wall hollow glass microspheres (PW-HGMs) are a novel form of glass material consisting of a 10 to 100 micron-diameter hollow central cavity surrounded by a 1 micron-thick silica shell. A tortuous network of nanometer-scale channels completely penetrates the shell. We show here that these channels promote size-dependent uptake and controlled release of biological molecules in the 3–8 nm range, including antibodies and a modified single-chain antibody variable fragment (scFv). In addition, a 6 nm (70 kDa) dextran can be used to gate the porous walls, facilitating controlled release of an internalized small interfering RNA. PW-HGMs remained in place after mouse intratumoral injection, suggesting a possible application for the delivery of anti-cancer drugs. The combination of a hollow central cavity that can carry soluble therapeutic agents with mesoporous walls for controlled release is a unique characteristic that distinguishes PW-HGMs from other glass materials for biomedical applications. PMID:19616128
Rudisill, Stephen G; Wang, Zhiyong; Stein, Andreas
2012-05-15
Nanoporous and nanostructured materials are becoming increasingly important for advanced applications involving, for example, bioactive materials, catalytic materials, energy storage and conversion materials, photonic crystals, membranes, and more. As such, they are exposed to a variety of harsh environments and often experience detrimental morphological changes as a result. This article highlights material limitations and recent advances in porous materials--three-dimensionally ordered macroporous (3DOM) materials in particular--under reactive or high-temperature conditions. Examples include systems where morphological changes are desired and systems that require an increased retention of structure, surface area, and overall material integrity during synthesis and processing. Structural modifications, changes in composition, and alternate synthesis routes are explored and discussed. Improvements in thermal or structural stability have been achieved by the isolation of nanoparticles in porous structures through spatial separation, by confinement in a more thermally stable host, by the application of a protective surface or an adhesive interlayer, by alloy or solid solution formation, and by doping to induce solute drag. PMID:22409622
Planar, Polysilazane-Derived Porous Ceramic Supports for Membrane and Catalysis Applications
Konegger, Thomas; Williams, Lee F.; Bordia, Rajendra K.
2015-01-01
Porous, silicon carbonitride-based ceramic support structures for potential membrane and catalysis applications were generated from a preceramic polysilazane precursor in combination with spherical, ultrahigh-molecular weight polyethylene microparticles through a sacrificial filler approach. A screening evaluation was used for the determination of the impact of both porogen content and porogen size on pore structure, strength, and permeability characteristics of planar specimens. By optimizing both the composition as well as cross-linking parameters, maximum characteristic biaxial flexural strengths of 65 MPa and porosities of 42% were achieved. The evolution of an interconnected, open-pore network during thermal porogen removal and conversion of the preceramic polymer led to air permeabilities in the order of 10−14 m2. The materials were further exposed to long-term heat treatments to demonstrate the stability of properties after 100 h at 800°C in oxidizing, inert, and reducing environments. The determined performance, in combination with the versatile preparation method, illustrates the feasibility of this processing approach for the generation of porous ceramic support structures for applications at elevated temperatures in a variety of fields, including membrane and catalysis science. PMID:26681809
Jahangiri, Elham; Reichelt, Senta; Thomas, Isabell; Hausmann, Kristin; Schlosser, Dietmar; Schulze, Agnes
2014-01-01
The versatile oxidase enzyme laccase was immobilized on porous supports such as polymer membranes and cryogels with a view of using such biocatalysts in bioreactors aiming at the degradation of environmental pollutants in wastewater. Besides a large surface area for supporting the biocatalyst, the aforementioned porous systems also offer the possibility for simultaneous filtration applications in wastewater treatment. Herein a "green" water-based, initiator-free, and straightforward route to highly reactive membrane and cryogel-based bioreactors is presented, where laccase was immobilized onto the porous polymer supports using a water-based electron beam-initiated grafting reaction. In a second approach, the laccase redox mediators 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) and syringaldehyde were cross-linked instead of the enzyme via electron irradiation in a frozen aqueous poly(acrylate) mixture in a one pot set-up, yielding a mechanical stable macroporous cryogel with interconnected pores ranging from 10 to 50 µm in size. The membranes as well as the cryogels were characterized regarding their morphology, chemical composition, and catalytic activity. The reactivity towards waste- water pollutants was demonstrated by the degradation of the model compound bisphenol A (BPA). Both membrane- and cryogel-immobilized laccase remained highly active after electron beam irradiation. Apparent specific BPA removal rates were higher for cryogel- than for membrane-immobilized and free laccase, whereas membrane-immobilized laccase was more stable with respect to maintenance of enzymatic activity and prevention of enzyme leakage from the carrier than cryogel-immobilized laccase. Cryogel-immobilized redox mediators remained functional in accelerating the laccase-catalyzed BPA degradation, and especially ABTS was found to act more efficiently in immobilized than in freely dissolved state. PMID:25111026
Frenzer, Gerald; Frantzen, Andreas; Sanders, Daniel; Simon, Ulrich; Maier, Wilhelm F.
2006-01-01
A method of wet chemical synthesis suitable for high throughput and combinatorial applications has been developed for the synthesis of porous resistive thick-film gas sensors. This method is based on the robot-controlled application of unstable metal oxide suspensions on an array of 64 inter-digital electrodes positioned on an Al2O3 substrate. SnO2, WO3, ZrO2, TiO2, CeO2, In2O3 and Bi2O3 were chosen as base oxides, and were optimised by doping or mixed oxide formation. The parallel synthesis of mixed oxide sensors is illustrated by representative examples. The electrical characteristics and the sensor performance of the films were measured by high-throughput impedance spectroscopy while supplying various test gases (H2, CO, NO, NO2, propene). Data collection, data mining techniques applied and the best potential sensor materials discovered are presented.
Development of a Chitosan-Based Biofoam: Application to the Processing of a Porous Ceramic Material
Mathias, Jean-Denis; Tessier-Doyen, Nicolas; Michaud, Philippe
2011-01-01
Developing biofoams constitutes a challenging issue for several applications. The present study focuses on the development of a chitosan-based biofoam. Solutions of chitosan in acetic acid were dried under vacuum to generate foams with high-order structures. Chitosan concentration influenced significantly the morphology of developed porosity and the organization of pores in the material. Physico-chemical characterizations were performed to investigate the effects of chitosan concentration on density and thermal conductivity of foams. Even if chitosan-based biofoams exhibit interesting insulating properties (typically around 0.06 W·m−1·K−1), it has been shown that their durabilities are limited when submitted to a wet media. So, a way of application consists to elaborate a ceramic material with open porosity from a slurry prepared with an organic solvent infiltrating the porous network of the foam. PMID:21541051
Stafford, P.L.
1996-05-01
Simulations of a tritium tracer experiment in fractured shale saprolite, conducted at the Oak Ridge National Laboratory, were performed using 1D and 2D equivalent porous medium (EPM) and discrete-fracture/matrix-diffusion (DFMD) models. The models successfully reproduced the general shape of the breakthrough curves in down-gradient monitoring wells which are characterized by rapid first arrival, a slow-moving center of mass, and a persistent ``tail`` of low concentration. In plan view, the plume shows a large degree of transverse spreading with the width almost as great as the length. EPM models were sensitive to dispersivity coefficient values which had to be large (relative to the 3.7m distance between the injection and monitoring wells) to fit the tail and transverse spreading. For example, to fit the tail a longitudinal dispersivity coefficient, {alpha}{sub L}, of 0.8 meters for the 2D simulations was used. To fit the transverse spreading, a transverse dispersivity coefficient, {alpha}{sub T}, of 0.8 to 0.08 meters was used indicating an {alpha}{sub L}/{alpha}{sub T} ratio between 10 and 1. Transverse spreading trends were also simulated using a 2D DFMD model using a few larger aperture fractures superimposed onto an EPM. Of the fracture networks studied, only those with truncated fractures caused transverse spreading. Simulated tritium levels in all of the cases were larger than observed values by a factor of approximately 100. Although this is partly due to input of too much tritium mass by the models it appears that dilution in the wells, which were not purged prior to sampling, is also a significant factor. The 1D and 2D EPM models were fitted to monitoring data from the first five years of the experiment and then used to predict future tritium concentrations.
DH Bacon; MD White; BP McGrail
2000-03-07
The Hanford Site, in southeastern Washington State, has been used extensively to produce nuclear materials for the US strategic defense arsenal by the Department of Energy (DOE) and its predecessors, the US Atomic Energy Commission and the US Energy Research and Development Administration. A large inventory of radioactive and mixed waste has accumulated in 177 buried single- and double shell tanks. Liquid waste recovered from the tanks will be pretreated to separate the low-activity fraction from the high-level and transuranic wastes. Vitrification is the leading option for immobilization of these wastes, expected to produce approximately 550,000 metric tons of Low Activity Waste (LAW) glass. This total tonnage, based on nominal Na{sub 2}O oxide loading of 20% by weight, is destined for disposal in a near-surface facility. Before disposal of the immobilized waste can proceed, the DOE must approve a performance assessment, a document that described the impacts, if any, of the disposal facility on public health and environmental resources. Studies have shown that release rates of radionuclides from the glass waste form by reaction with water determine the impacts of the disposal action more than any other independent parameter. This report describes the latest accomplishments in the development of a computational tool, Subsurface Transport Over Reactive Multiphases (STORM), Version 2, a general, coupled non-isothermal multiphase flow and reactive transport simulator. The underlying mathematics in STORM describe the rate of change of the solute concentrations of pore water in a variably saturated, non-isothermal porous medium, and the alteration of waste forms, packaging materials, backfill, and host rocks.
Tam, Shiu-Wing
1998-01-01
An illumination source comprising a porous silicon having a source of electrons on the surface and/or interticies thereof having a total porosity in the range of from about 50 v/o to about 90 v/o. Also disclosed are a tritiated porous silicon and a photovoltaic device and an illumination source of tritiated porous silicon.
Tam, Shiu-Wing
1997-01-01
An illumination source comprising a porous silicon having a source of electrons on the surface and/or interticies thereof having a total porosity in the range of from about 50 v/o to about 90 v/o. Also disclosed are a tritiated porous silicon and a photovoltaic device and an illumination source of tritiated porous silicon.
Tam, S.W.
1997-02-25
Disclosed is an illumination source comprising a porous silicon having a source of electrons on the surface and/or interstices thereof having a total porosity in the range of from about 50 v/o to about 90 v/o. Also disclosed are a tritiated porous silicon and a photovoltaic device and an illumination source of tritiated porous silicon. 1 fig.
Tam, S.W.
1998-06-16
An illumination source is disclosed comprising a porous silicon having a source of electrons on the surface and/or interstices thereof having a total porosity in the range of from about 50 v/o to about 90 v/o. Also disclosed are a tritiated porous silicon and a photovoltaic device and an illumination source of tritiated porous silicon. 1 fig.
Porous Polyimide Membranes Prepared by Wet Phase Inversion for Use in Low Dielectric Applications
Kim, Soohyun; Jang, Keon-Soo; Choi, Hee-Dok; Choi, Seung-Hoon; Kwon, Seong-Ji; Kim, Il-Doo; Lim, Jung Ah; Hong, Jae-Min
2013-01-01
A wet phase inversion process of polyamic acid (PAA) allowed fabrication of a porous membrane of polyimide (PI) with the combination of a low dielectric constant (1.7) and reasonable mechanical properties (Tensile strain: 8.04%, toughness: 3.4 MJ/m3, tensile stress: 39.17 MPa, and young modulus: 1.13 GPa), with further thermal imidization process of PAA. PAA was simply synthesized from purified pyromellitic dianhydride (PMDA) and 4,4-oxydianiline (ODA) in two different reaction solvents such as γ-butyrolactone (GBL) and N-methyl-2-pyrrolidinone (NMP), which produce Mw/PDI of 630,000/1.45 and 280,000/2.0, respectively. The porous PAA membrane was fabricated by the wet phase inversion process based on a solvent/non-solvent system via tailored composition between GBL and NMP. The porosity of PI, indicative of a low electric constant, decreased with increasing concentration of GBL, which was caused by sponge-like formation. However, due to interplay between the low electric constant (structural formation) and the mechanical properties, GBL was employed for further exploration, using toluene and acetone vs. DI-water as a coagulation media. Non-solvents influenced determination of the PAA membrane size and porosity. With this approach, insight into the interplay between dielectric properties and mechanical properties will inform a wide range of potential low-k material applications. PMID:23615465
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.
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
Olami, Hilla; Zilberman, Meital
2016-02-01
Interest in the development of new bioresorbable structures for various tissue engineering applications is on the rise. In the current study, we developed and studied novel soy protein-based porous blends as potential new scaffolds for such applications. Soy protein has several advantages over the various types of natural proteins employed for biomedical applications due to its low price, non-animal origin and relatively long storage time and stability. In the present study, blends of soy protein with other polymers (gelatin, pectin and alginate) were added and chemically cross-linked using the cross-linking agents carbodiimide or glyoxal, and the porous structure was obtained through lyophilization. The resulting blend porous structures were characterized using environmental scanning microscopy, and the cytotoxicity of these scaffolds was examined in vitro. The biocompatibility of the scaffolds was also evaluated in vitro by seeding and culturing human fibroblasts on these scaffolds. Cell growth morphology and adhesion were examined histologically. The results show that these blends can be assembled into porous three-dimensional structures by combining chemical cross-linking with freeze-drying. The achieved blend structures combine suitable porosity with a large pore size (100-300 µm). The pore structure in the soy-alginate scaffolds possesses adequate interconnectivity compared to that of the soy-gelatin scaffolds. However, porous structure was not observed for the soy-pectin blend, which presented a different structure with significantly lower porosities than all other groups. The in vitro evaluation of these porous soy blends demonstrated that soy-alginate blends are advantageous over soy-gelatin blends and exhibited adequate cytocompatibility along with better cell infiltration and stability. These soy protein scaffolds may be potentially useful as a cellular/acellular platform for skin regeneration applications. PMID:26526932
NASA Astrophysics Data System (ADS)
Asano, S.; Makuta, T.; Murasawa, G.
2012-04-01
We used a new method to fabricate salami-type porous metal from glass microcapsules and liquid metal. Each pore of its salami-like structure behaves as a micro-bell. This metal, which is more than 20% lighter than bulk material, also shows a unique characteristic: high-frequency oscillation is greatly attenuated when propagated in its medium. This method offers great potential for size, shape, and conformation control, with changed attenuation characteristics of its salami-like pore structure achieved merely by changing the mixing technique. This study was conducted to measure compressive deformation behavior and attenuation characteristic of salami-type porous SnSbCu. To begin with, we fabricated two salami-type porous metals using 16um or 60um diameter microcapsule, which have different salami structures in its body. Next, compressive loading test was conducted for the metals. Then, the attenuation characteristic was investigated using laser ultrasonic measurement. Thereby, compressive deformation behavior was same between fabricated two salami-type porous metals. In contrast, the attenuation characteristic was different at low frequency range between them.
Code of Federal Regulations, 2012 CFR
2012-07-01
... medium-sized general molded, extruded, and fabricated rubber plants subcategory. 428.60 Section 428.60... (CONTINUED) RUBBER MANUFACTURING POINT SOURCE CATEGORY Medium-Sized General Molded, Extruded, and Fabricated Rubber Plants Subcategory § 428.60 Applicability; description of the medium-sized general...
Code of Federal Regulations, 2014 CFR
2014-07-01
... medium-sized general molded, extruded, and fabricated rubber plants subcategory. 428.60 Section 428.60... (CONTINUED) RUBBER MANUFACTURING POINT SOURCE CATEGORY Medium-Sized General Molded, Extruded, and Fabricated Rubber Plants Subcategory § 428.60 Applicability; description of the medium-sized general...
Code of Federal Regulations, 2013 CFR
2013-07-01
... medium-sized general molded, extruded, and fabricated rubber plants subcategory. 428.60 Section 428.60... (CONTINUED) RUBBER MANUFACTURING POINT SOURCE CATEGORY Medium-Sized General Molded, Extruded, and Fabricated Rubber Plants Subcategory § 428.60 Applicability; description of the medium-sized general...
Enhancement of entangled porous titanium by BisGMA for load-bearing biomedical applications.
Liu, Yan; Jiang, Guofeng; He, Guo
2016-04-01
The Bisphenol A glycidyl methacrylate (BisGMA) was used as binder to fix the free cross wire nodes in the entangled porous titanium for enhancement. The entangled titanium with 60% porosity after infiltrated with 5-20 vol.% BisGMA had the pore size in the range of 100 μm-400 μm. The enhanced materials with the real porosity of 40-55% exhibited the elastic modulus in the range of 0.4-1.4 GPa and the yielding strength in the range of 12.9-52.5 MPa. Such mechanical properties were comparable with those of cancellous bones, suggesting potentials for load-bearing bio applications. PMID:26838821
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
NASA Astrophysics Data System (ADS)
Jiang, Y. G.; Shan, F. K.; Jin, H. M.; Zhou, L. W.; Sheng, Ping
We have designed and constructed a compact cell to measure the electrokinetic coefficients in the frequency range of interest to hydrocarbon exploration, 20 to 100 Hz. Experimental results are presented on the frequency dependence of the electrokinetic coefficients, and dynamic permeability of a porous rock saturated with either 0.1 mole brine or transformer oil. In particular, the brine-saturated electro-osmosis coefficient is found to be two orders of magnitude larger than that saturated with transformer oil; whereas for the streaming potential the ratio of the two cases is in the reverse. These results, when combined with viscosity and electrical conductivity values, lead consistently to the fact that the electrokinetic Onsager coefficient of brine-saturated samples is three orders of magnitude larger than that of oil-saturated samples. This difference provides a strong motivation to further explore the potential application of electrokinetic Onsager coefficient as a hydrocarbon indicator.
Luo, Baiwen; Choong, Cleo
2015-01-01
Natural materials are promising alternatives to synthetic materials used in tissue engineering applications as they have superior biocompatibility and promote better cell attachment and proliferation. Ovalbumin, a natural polymer found in avian egg white, is an example of a nature-derived material. Despite the availability and reported biocompatibility of ovalbumin, limited research has been carried out to investigate the efficacy of ovalbumin-based scaffolds for adipose tissue engineering applications. Hence, the current study was carried out to investigate the effect of different crosslinkers on ovalbumin scaffold properties as first step towards the development of ovalbumin-based scaffolds for adipose tissue engineering applications. In this study, highly porous three-dimensional scaffolds were fabricated by using three different crosslinkers: glutaraldehyde, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and 1,4-butanediol diglycidyl ether. Results showed that the overall scaffold properties such as morphology, pore size and mechanical properties could be modulated based on the type and concentration of crosslinkers used during the fabrication process. Subsequently, the efficacy of the different scaffolds for supporting cell proliferation was investigated. In vitro degradation was also carried on for the best scaffold based on the mechanical and cellular results. Overall, this study is a demonstration of the viability of ovalbumin-based scaffolds as cell carriers for soft tissue engineering applications. PMID:25158688
NASA Astrophysics Data System (ADS)
Safuan, Nadia; Sukmana, Irza; Kadir, Mohammed Rafiq Abdul; Noviana, Deni
2014-04-01
Porous tantalum has been used as an orthopedic implant for bone defects as it has a good corrosion resistance and fatigue behaviour properties. However, there are some reports on the rejection of porous Ta after the implantation. Those clinical cases refer to the less bioactivity of metallic-based materials. This study aims to evaluate hydroxyapatite coated and uncoated porous Tantalum in order to improve the biocompatibility of porous tantalum implant and osseointegration. Porous tantalum was used as metallic-base substrate and hydroxyapatite coating has been done using plasma-spraying technique. Scanning Electron Microscopy (SEM) and Field Emission Scanning Electron Microscopy (FESEM) techniques were utilizes to investigate the coating characteristics while Confocal Raman Microscopy to investigate the interface and image. The effect of coating to the corrosion behaviour was assessed by employing potentiodynamic polarization tests in simulated body fluid at 37±1 °C. Based on SEM and FESEM results, the morphologies as well the weight element consists in the uncoated and hydroxyapatite coated porous tantalum were revealed. The results indicated that the decrease in corrosion current density for HA coated porous Ta compared to the uncoated porous Ta. This study concluded that by coating porous tantalum with HA supports to decrease the corrosion rate of pure porous.
Seth, Saona; Venugopalan, Paloth; Moorthy, Jarugu Narasimha
2015-01-26
Porous coordination polymers (CPs) with partially uncoordinated pyridyl rings based on rationally designed polypyridyl linkers are appealing from the point of view of their application as nucleophilic catalysts. A D2d -symmetric tetradentate organic linker L, that is, 2,2',6,6'-tetramethoxy-3,3',5,5'-tetrakis(4-pyridyl)biphenyl, was designed and synthesized for metal-assisted self-assembly aimed at porous CPs. Depending on the nature of the metal ion and the counter anion, the ligand L is found to function as a 3- or 4-connecting building block leading to porous CPs of diverse topologies. The reaction of L with Zn(NO3 )2 and Cd(NO3 )2 yields porous 2 D CPs of "fes" topology, in which the tetrapyridyl linker L serves as a 3-connecting unit with its free pyridyl rings well exposed into the pores. The functional utility of these porous CPs containing uncoordinated pyridyl rings is demonstrated by employing them as efficient heterogeneous nucleophilic catalysts for acetylation of a number of phenols with varying electronic properties and reactivities. PMID:25430673
NASA Astrophysics Data System (ADS)
Xing, Ruimin; Liu, Shanhu
2012-05-01
Fabrication of intrinsically fluorescent porous nanocarriers that are simultaneously stable in aqueous solutions and photostable is critical for their application in drug delivery and optical imaging but remains a challenge. In this study, fluorescent porous zinc sulfide nanospheres were synthesized by a facile gum arabic-assisted hydrothermal procedure. The morphology, composition and properties of the nanospheres have been characterized by field-emission scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, N2 adsorption-desorption analysis, thermal gravimetric analysis, fourier transform infrared spectrograph, optical measurement, dynamic light scattering, and cytotoxicity assay. They exhibit larger surface area, excellent colloidal stability, photostable fluorescent signals, and good biocompatibility, which makes them promising hosts for drug delivery and cellular imaging. The fluorescent dye safranine-T was employed as a drug model and loaded into the porous nanospheres, which were delivered to human cervical cancer HeLa cells in vitro for live cell imaging.Fabrication of intrinsically fluorescent porous nanocarriers that are simultaneously stable in aqueous solutions and photostable is critical for their application in drug delivery and optical imaging but remains a challenge. In this study, fluorescent porous zinc sulfide nanospheres were synthesized by a facile gum arabic-assisted hydrothermal procedure. The morphology, composition and properties of the nanospheres have been characterized by field-emission scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, N2 adsorption-desorption analysis, thermal gravimetric analysis, fourier transform infrared spectrograph, optical measurement, dynamic light scattering, and cytotoxicity assay. They exhibit larger surface area, excellent colloidal stability, photostable fluorescent signals, and good biocompatibility, which makes them promising
NASA Astrophysics Data System (ADS)
Trahey, Lynn
Bismuth telluride is a well-known thermoelectric material for refrigeration applications. Thermoelectrics possess several advantages over conventional refrigeration and power generation devices, yet are not widely-used due to low efficiencies. It has been predicted and shown experimentally that the efficiency of thermoelectric devices increases when the semiconducting materials have reduced dimensions. Therefore, the aim of this research was to show enhanced thermoelectric efficiency in one-dimensional nanowires. The nanowires were synthesized via electrochemical deposition into porous alumina templates. Electrodeposition is a versatile technique that ensures electrical continuity in the deposited material. The nanowire templates, porous alumina, were made by the double anodization of high-purity aluminum foil in oxalic acid solutions. This technique produces parallel, hexagonally packed, and nanometer-range diameter pores that can reach high aspect ratios (greater than 2000:1). The main anodization variables (electrolyte concentration, applied potential, 2nd anodization time, and temperature) were studied systematically in order to deconvolute their effects on the resulting pores and to obtain high aspect ratio pores. The porous alumina is of great importance because the pore dimensions determine the dimensions of the electrodeposited nanowires, which influence the thermoelectric performance of the nanowire arrays. Nanowire arrays were characterized in several ways. Powder X-ray diffraction was used to assess crystallinity and preferred orientation of the nanowires, revealing that the nanowires are highly crystalline and grow with strong preferred orientation such that the material is suited for optimal thermoelectric performance. Scanning electron microscopy was used to evaluate the nanowire nucleation percentage and growth-front uniformity, both of which were enhanced by pulsed-potential electrodeposition. Compositional analysis via electron microprobe indicates
Hearon, Keith; Singhal, Pooja; Horn, John; Small, Ward; Olsovsky, Cory; Maitland, Kristen C.; Wilson, Thomas S.; Maitland, Duncan J.
2013-01-01
Porous shape memory polymers (SMPs) include foams, scaffolds, meshes, and other polymeric substrates that possess porous three-dimensional macrostructures. Porous SMPs exhibit active structural and volumetric transformations and have driven investigations in fields ranging from biomedical engineering to aerospace engineering to the clothing industry. The present review article examines recent developments in porous SMPs, with focus given to structural and chemical classification, methods of characterization, and applications. We conclude that the current body of literature presents porous SMPs as highly interesting smart materials with potential for industrial use. PMID:23646038
NASA Astrophysics Data System (ADS)
Roberts, S.; Ezzedine, S. M.; Bourcier, W. L.; Hunt, J. D.; Ryerson, F. J.
2012-12-01
Silica gels are abundant in various surface and subsurface applications, yet they have not been evaluated for geothermal and carbon sequestration reservoir management. For example, a) sustaining long term heat extraction from geothermal systems can be achieved by optimizing thermal sweeping of available conductive surface area; b) minimizing supercritical CO2 leaks through caprock can be insured by blocking any possible leakage pathways. Diverting and blocking agents have been effectively used in the petroleum industry to enhance recovery; however, these are often organic polymers that raise environmental concerns. Silicas are inorganic and environmentally friendly. In the current study we have developed a numerical model to simulate the flow mass and heat transport of silica gel in both geothermal and immiscible supercritical CO2 sequestration reservoirs. We illustrate the application of the model for a) maximizing thermal extraction and minimizing water loses for hydrothermal systems by using the gel as a diverter and blocking agent and b) minimizing CO2 leakages to the caprock by using the gel as blocking and coating agent. Several 2D and 3D examples in porous and fractured network will be presented and design criteria for both application will be discussed. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
NASA Astrophysics Data System (ADS)
Nagel, T.; Shao, H.; Linder, M.; Wörner, A.; Kolditz, O.
2013-12-01
Heat processes in industry and for power generation can be made more cost-efficient and climate friendly by the integration of thermal energy storage devices. Due to high storage densities and superior long term storage characteristics, systems relying on thermochemical reactions are of great interest and often based on porous or granular media. As such, they share characteristic features in terms of mass and heat transport that are strongly coupled by physical and chemical phenomena. We have employed the theory of porous media to establish a model featuring reactive multicomponent compressible fluid mass transport through solid particle bed coupled to local thermal nonequilibrium heat transport. The model development has been based on an extensive evaluation of the Clausius-Duhem inequality to derive thermodynamically consistent constitutive relations for secondary variables as well as direct and indirect coupling terms. The model has then been implemented into the open source scientific simulation code OpenGeoSys using the finite element method. Lab and pilot scale thermochemical heat storage reactors with different reaction systems (oxidation reactions, hydration reactions) have been simulated successfully using axisymmetric geometries. The simulations show the strong coupling of pressure, concentration and temperature fields as well as the gas-solid reactions occurring inside the reactors. The effect of certain process parameters, such as mass flow and particle size, on the occurrence of local thermal nonequilibrium is illustrated. It is shown that the reactors can be used in a number of operating modes such as the extraction or release of heat accompanied by significant temperature drops or raises; the buffering or smoothing of temperature fluctuations at the inlet; the up- or downgrading of heat. The developed model therefore represents a useful tool to understand reactor behavior, optimize operating parameters, estimate thermal and parasitic losses, and
Wang, Yichao; Uemura, Toshimasa; Dong, Jian; Kojima, Hiroko; Tanaka, Junzo; Tateishi, Tetsuya
2003-12-01
Composites of bone marrow-derived osteoblasts (BMOs) and porous ceramics have been widely used as a bone graft model for bone tissue engineering. Perfusion culture has potential utility for many cell types in three-dimensional (3D) culture. Our hypothesis was that perfusion of medium would increase the cell viability and biosynthetic activity of BMOs in porous ceramic materials, which would be revealed by increased levels of alkaline phosphate (ALP) activity and osteocalcin (OCN) and enhanced bone formation in vivo. For testing in vitro, BMO/beta-tricalcium phosphate composites were cultured in a perfusion container (Minucells and Minutissue, Bad Abbach, Germany) with fresh medium delivered at a rate of 2 mL/h by a peristaltic pump. The ALP activity and OCN content of composites were measured at the end of 1, 2, 3, and 4 weeks of subculture. For testing in vivo, after subculturing for 2 weeks, the composites were subcutaneously implanted into syngeneic rats. These implants were harvested 4 or 8 weeks later. The samples then underwent a biochemical analysis of ALP activity and OCN content and were observed by light microscopy. The levels of ALP activity and OCN in the composites were significantly higher in the perfusion group than in the control group (p < 0.01), both in vitro and in vivo. Histomorphometric analysis of the hematoxylin- and eosin-stained sections revealed a higher average ratio of bone to pore in BMO/beta-TCP composites of the perfusion group after implantation: 47.64 +/- 6.16 for the perfusion group and 26.22 +/- 4.84 for control at 4 weeks (n = 6, p < 0.01); 67.97 +/- 3.58 for the perfusion group and 47.39 +/- 4.10 for control at 8 weeks (n = 6, p < 0.05). These results show that the application of a perfusion culture system during the subculture of BMOs in a porous ceramic scaffold is beneficial to their osteogenesis. After differentiation culture in vitro with the perfusion culture system, the activity of the osteoblastic cells and the
NASA Astrophysics Data System (ADS)
Bachrata, A.; Fichot, F.; Quintard, M.; Repetto, G.; Fleurot, J.
2012-05-01
A generalized non local-equilibrium, three-equation model was developed for the macroscopic description of two-phase flow heat and mass transfer in porous media subjected to phase change. Six pore-scale closure problems were proposed to determine all the effective transport coefficients for representative unit cells. An improved model is presented in this paper with the perspective of application to intense boiling phenomena. The objective of this paper is to present application of this model to the simulation of reflooding of severely damaged nuclear reactor cores. In case of accident at a nuclear power plant, water sources may not be available for a long period of time and the core heats up due to the residual power. Any attempt to inject water during core degradation can lead to quenching and further fragmentation of the core material. The fragmentation of fuel rods and melting of reactor core materials may result in the formation of a "debris bed". The typical particle size in a debris bed might reach few millimeters (characteristic length-scale: 1 to 5 mm), which corresponds to a high permeability porous medium. The proposed two-phase flow model is implemented in the ICARECATHARE code, developed by IRSN to study severe accident scenarios in pressurized water reactors. Currently, the French IRSN has set up two experimental facilities to study debris bed reflooding, PEARL and PRELUDE, with the objective to validate safety models. The PRELUDE program studies the complex two phase flow of water and steam in a porous medium (diameter 180 mm, height 200 mm), initially heated to a high temperature (400°C or 700°C). The series of PRELUDE experiments achieved in 2010 constitute a significant complement to the database of high temperature bottom reflood experimental data. They provide relevant data to understand the progression of the quench front and the intensity of heat transfer. Modeling accurately these experiments required improvements to the reflooding model
Bachrata, A.; Fichot, F.; Quintard, M.; Repetto, G.; Fleurot, J.
2012-05-15
A generalized non local-equilibrium, three-equation model was developed for the macroscopic description of two-phase flow heat and mass transfer in porous media subjected to phase change. Six pore-scale closure problems were proposed to determine all the effective transport coefficients for representative unit cells. An improved model is presented in this paper with the perspective of application to intense boiling phenomena. The objective of this paper is to present application of this model to the simulation of reflooding of severely damaged nuclear reactor cores. In case of accident at a nuclear power plant, water sources may not be available for a long period of time and the core heats up due to the residual power. Any attempt to inject water during core degradation can lead to quenching and further fragmentation of the core material. The fragmentation of fuel rods and melting of reactor core materials may result in the formation of a {sup d}ebris bed{sup .} The typical particle size in a debris bed might reach few millimeters (characteristic length-scale: 1 to 5 mm), which corresponds to a high permeability porous medium. The proposed two-phase flow model is implemented in the ICARECATHARE code, developed by IRSN to study severe accident scenarios in pressurized water reactors. Currently, the French IRSN has set up two experimental facilities to study debris bed reflooding, PEARL and PRELUDE, with the objective to validate safety models. The PRELUDE program studies the complex two phase flow of water and steam in a porous medium (diameter 180 mm, height 200 mm), initially heated to a high temperature (400 deg. C or 700 deg. C). The series of PRELUDE experiments achieved in 2010 constitute a significant complement to the database of high temperature bottom reflood experimental data. They provide relevant data to understand the progression of the quench front and the intensity of heat transfer. Modeling accurately these experiments required improvements to the
Zhao, Feng; Zhou, Jidong; Han, Siqin; Ma, Fang; Zhang, Ying; Zhang, Jie
2016-04-01
Aerobic production of rhamnolipid by Pseudomonas aeruginosa was extensively studied. But effect of medium composition on anaerobic production of rhamnolipid by P. aeruginosa was unknown. A simplifying medium facilitating anaerobic production of rhamnolipid is urgently needed for in situ microbial enhanced oil recovery (MEOR). Medium factors affecting anaerobic production of rhamnolipid were investigated using P. aeruginosa SG (Genbank accession number KJ995745). Medium composition for anaerobic production of rhamnolipid by P. aeruginosa is different from that for aerobic production of rhamnolipid. Both hydrophobic substrate and organic nitrogen inhibited rhamnolipid production under anaerobic conditions. Glycerol and nitrate were the best carbon and nitrogen source. The commonly used N limitation under aerobic conditions was not conducive to rhamnolipid production under anaerobic conditions because the initial cell growth demanded enough nitrate for anaerobic respiration. But rhamnolipid was also fast accumulated under nitrogen starvation conditions. Sufficient phosphate was needed for anaerobic production of rhamnolipid. SO4(2-) and Mg(2+) are required for anaerobic production of rhamnolipid. Results will contribute to isolation bacteria strains which can anaerobically produce rhamnolipid and medium optimization for anaerobic production of rhamnolipid. Based on medium optimization by response surface methodology and ions composition of reservoir formation water, a simplifying medium containing 70.3 g/l glycerol, 5.25 g/l NaNO3, 5.49 g/l KH2PO4, 6.9 g/l K2HPO4·3H2O and 0.40 g/l MgSO4 was designed. Using the simplifying medium, 630 mg/l of rhamnolipid was produced by SG, and the anaerobic culture emulsified crude oil to EI24 = 82.5 %. The simplifying medium was promising for in situ MEOR applications. PMID:26925616
Tian, Meng; Chen, Feng; Song, Wei; Song, Yancheng; Chen, Yuanwei; Wan, Changxiu; Yu, Xixun; Zhang, Xiaohua
2009-07-01
The purpose of this study was to investigate in vivo biocompatibility and osteogenesis as well as degradability of the porous strontium-doped calcium polyphosphate (SCPP) scaffolds as a biomaterial for bone substitute applications. The evaluation was performed on a rabbit model over a period of 16 weeks by histology combined with image analysis, X-ray microradiography and immunohistochemistry methods. The histological and X-ray microradiographic results showed that the SCPP scaffold exhibited good biocompatibility and extensive osteoconductivity with host bone. Moreover, a significant more bone formation was observed in the SCPP group compared with that in the CPP group, especially at the initial stage after implantation. New bone volumes (NBVs) of the SCPP group determined at week 4, 8 and 16 were 14, 27 and 45%, respectively. Accordingly, NBVs of the CPP group were 10, 19 and 40%. Immunohistochemical results revealed that both the expression of collagen type I and bone morphogenetic proteins in the SCPP group were higher than that in the CPP group, which might be associated with the release of strontium ions during the implantation. In addition, during 16 weeks implantation the SCPP scaffold exhibited similar degradability with the CPP scaffold in vivo. Both scaffolds showed the greatest degradation rate for the first 4 weeks, and then the degradation rate gradually decreased. The results presented in this study demonstrated that SCPP scaffold can be considered as a biocompatible material, making it attractive for bone substitute application purposes. PMID:19267259
Two-dimensional porous anodic alumina for optoelectronics and photocatalytic application
NASA Astrophysics Data System (ADS)
Khoroshko, L. S.
2015-11-01
Fabrication of porous anodic alumina film structures using anodizing, sol-gel synthesis and photolithography is reported. The structures receive interest as planar waveguides due to strong photoluminescence of the embedded trivalent lanthanides. Mesoporous structures comprising sol-gel derived titania in porous anodic alumina play a role of effective catalyst for water purification.
Metal glass vacuum tube solar collectors are approaching lower-medium temperature heat application.
Jiang, Xinian
2010-04-26
Solar thermal collectors are widely used worldwide mainly for hot water preparation at a low temperature (less than 80 degrees C). Applications including many industrial processes and central air conditioning with absorption chillers, instead require lower-medium temperature heat (between 90 degrees C and 150 degrees C) to be driven when using solar thermal energy. The metal absorber glass vacuum tube collectors (MGVT) are developed for this type of applications. Current state-of-art and possible future technology development of MGVT are presented. PMID:20607893
Metal glass vacuum tube solar collectors are approaching lower-medium temperature heat application.
Jiang, Xinian
2010-04-26
Solar thermal collectors are widely used worldwide mainly for hot water preparation at a low temperature (less than 80?C). Applications including many industrial processes and central air conditioning with absorption chillers, instead require lower-medium temperature heat (between 90 degrees C and 150 degrees C) to be driven when using solar thermal energy. The metal absorber glass vacuum tube collectors (MGVT) are developed for this type of applications. Current state-of-art and possible future technology development of MGVT are presented. PMID:20588568
Ruckenstein, E.; Wang, X.B. . Dept. of Chemical Engineering)
1994-06-05
Porous poly(styrene-divinylbenzene) carriers for the immobilization of white rot fungus Phanerochaete chrysosporium have been prepared by the concentrated emulsion polymerization method. The white rot fungus Phanerochaete chrysosporium has been immobilized on porous poly(styrene-divinylbenzene) carriers and used for the batch production and the repeated batch production of lignin peroxidase in shake cultures based on a carbon-limited medium containing veratryl alcohol. The best results were achieved when a spore inoculum was used for immobilization instead of 1-day-old mycelial pellets, for both the batch production and the repeated batch production. The porous poly(styrene-divinylbenzene) immobilized Phanerochaete chrysosporium and freely suspended mycelial pellets were used as biocatalysts for the degradation of 2-chlorophenol in a 2-L bioreactor. The porous poly(styrene-divinylbenzene) particle immobilized spores exhibited a much higher activity in the degradation of 2-chlorophenol than the freely suspended mycelial pellets.
Chen, Feng; Zhu, Ying-Jie; Zhang, Kui-Hua; Wu, Jin; Wang, Ke-Wei; Tang, Qi-Li; Mo, Xiu-Mei
2011-01-01
Calcium phosphate is the most important inorganic constituent of biological tissues, and synthetic calcium phosphate has been widely used as biomaterials. In this study, a facile method has been developed for the fabrication of amorphous calcium phosphate (ACP)/polylactide-block-monomethoxy(polyethyleneglycol) hybrid nanoparticles and ACP porous nanospheres. Europium-doping is performed to enable photoluminescence (PL) function of ACP porous nanospheres. A high specific surface area of the europium-doped ACP (Eu3+:ACP) porous nanospheres is achieved (126.7 m2/g). PL properties of Eu3+:ACP porous nanospheres are investigated, and the most intense peak at 612 nm is observed at 5 mol% Eu3+ doping. In vitro cytotoxicity experiments indicate that the as-prepared Eu3+:ACP porous nanospheres are biocompatible. In vitro drug release experiments indicate that the ibuprofen-loaded Eu3+:ACP porous nanospheres show a slow and sustained drug release in simulated body fluid. We have found that the cumulative amount of released drug has a linear relationship with the natural logarithm of release time (ln(t)). The Eu3+:ACP porous nanospheres are bioactive, and can transform to hydroxyapatite during drug release. The PL properties of drug-loaded nanocarriers before and after drug release are also investigated. PMID:21711603
2011-01-01
Calcium phosphate is the most important inorganic constituent of biological tissues, and synthetic calcium phosphate has been widely used as biomaterials. In this study, a facile method has been developed for the fabrication of amorphous calcium phosphate (ACP)/polylactide-block-monomethoxy(polyethyleneglycol) hybrid nanoparticles and ACP porous nanospheres. Europium-doping is performed to enable photoluminescence (PL) function of ACP porous nanospheres. A high specific surface area of the europium-doped ACP (Eu3+:ACP) porous nanospheres is achieved (126.7 m2/g). PL properties of Eu3+:ACP porous nanospheres are investigated, and the most intense peak at 612 nm is observed at 5 mol% Eu3+ doping. In vitro cytotoxicity experiments indicate that the as-prepared Eu3+:ACP porous nanospheres are biocompatible. In vitro drug release experiments indicate that the ibuprofen-loaded Eu3+:ACP porous nanospheres show a slow and sustained drug release in simulated body fluid. We have found that the cumulative amount of released drug has a linear relationship with the natural logarithm of release time (ln(t)). The Eu3+:ACP porous nanospheres are bioactive, and can transform to hydroxyapatite during drug release. The PL properties of drug-loaded nanocarriers before and after drug release are also investigated. PMID:21711603
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.
Application of Medium and Seasonal Flood Forecasts for Agriculture Damage Assessment
NASA Astrophysics Data System (ADS)
Fakhruddin, Shamsul; Ballio, Francesco; Menoni, Scira
2015-04-01
Early warning is a key element for disaster risk reduction. In recent decades, major advancements have been made in medium range and seasonal flood forecasting. This progress provides a great opportunity to reduce agriculture damage and improve advisories for early action and planning for flood hazards. This approach can facilitate proactive rather than reactive management of the adverse consequences of floods. In the agricultural sector, for instance, farmers can take a diversity of options such as changing cropping patterns, applying fertilizer, irrigating and changing planting timing. An experimental medium range (1-10 day) and seasonal (20-25 days) flood forecasting model has been developed for Thailand and Bangladesh. It provides 51 sets of discharge ensemble forecasts of 1-10 days with significant persistence and high certainty and qualitative outlooks for 20-25 days. This type of forecast could assist farmers and other stakeholders for differential preparedness activities. These ensembles probabilistic flood forecasts have been customized based on user-needs for community-level application focused on agriculture system. The vulnerabilities of agriculture system were calculated based on exposure, sensitivity and adaptive capacity. Indicators for risk and vulnerability assessment were conducted through community consultations. The forecast lead time requirement, user-needs, impacts and management options for crops were identified through focus group discussions, informal interviews and community surveys. This paper illustrates potential applications of such ensembles for probabilistic medium range and seasonal flood forecasts in a way that is not commonly practiced globally today.
Fontana, Flavia; Mori, Michela; Riva, Federica; Mäkilä, Ermei; Liu, Dongfei; Salonen, Jarno; Nicoletti, Giovanni; Hirvonen, Jouni; Caramella, Carla; Santos, Hélder A
2016-01-13
The new frontier in the treatment of chronic nonhealing wounds is the use of micro- and nanoparticles to deliver drugs or growth factors into the wound. Here, we used platelet lysate (PL), a hemoderivative of platelets, consisting of a multifactorial cocktail of growth factors, to modify porous silicon (PSi) microparticles and assessed both in vitro and ex vivo the properties of the developed microsystem. PL-modified PSi was assessed for its potential to induce proliferation of fibroblasts. The wound closure-promoting properties of the microsystem were then assessed in an in vitro wound healing assay. Finally, the PL-modified PSi microparticles were evaluated in an ex vivo experiment over human skin. It was shown that PL-modified PSi microparticles were cytocompatible and enhanced the cell proliferation in different experimental settings. In addition, this microsystem promoted the closure of the gap between the fibroblast cells in the wound healing assay, in periods of time comparable with the positive control, and induced a proliferation and regeneration process onto the human skin in an ex vivo experiment. Overall, our results show that PL-modified PSi microparticles are suitable microsystems for further development toward applications in the treatment of chronic nonhealing wounds. PMID:26652045
Harries, Megan; Bukovsky-Reyes, Santiago; Bruno, Thomas J
2016-01-15
This paper details the sampling methods used with the field portable porous layer open tubular cryoadsorption (PLOT-cryo) approach, described in Part I of this two-part series, applied to several analytes of interest. We conducted tests with coumarin and 2,4,6-trinitrotoluene (two solutes that were used in initial development of PLOT-cryo technology), naphthalene, aviation turbine kerosene, and diesel fuel, on a variety of matrices and test beds. We demonstrated that these analytes can be easily detected and reliably identified using the portable unit for analyte collection. By leveraging efficiency-boosting temperature control and the high flow rate multiple capillary wafer, very short collection times (as low as 3s) yielded accurate detection. For diesel fuel spiked on glass beads, we determined a method detection limit below 1 ppm. We observed greater variability among separate samples analyzed with the portable unit than previously documented in work using the laboratory-based PLOT-cryo technology. We identify three likely sources that may help explain the additional variation: the use of a compressed air source to generate suction, matrix geometry, and variability in the local vapor concentration around the sampling probe as solute depletion occurs both locally around the probe and in the test bed as a whole. This field-portable adaptation of the PLOT-cryo approach has numerous and diverse potential applications. PMID:26726934
NASA Astrophysics Data System (ADS)
Köhler, Christian; Kloke, Arne; Drzyzga, Anna; Zengerle, Roland; Kerzenmacher, Sven
2013-11-01
We present the implementation and optimization of a novel electrodeposition method for the fabrication of highly porous platinum electrodes. It is based on the co-deposition of platinum and copper and the selective dealloying of copper in a pulsed manner. The new process yields mechanically stable platinum electrodes with roughness factors of up to RF = 6500 ± 700, compared to the state-of-the-art cyclic electrodeposition method this corresponds to an improvement in RF by 111%. Furthermore the time demand for fabrication is reduced by 59%, whereas the platinum utilization is increased by 53%. The method is particularly advantageous for applications such as micro fuel cells since it enables the precise deposition of catalytically active electrodes on micro-structured conductive areas. In this context the novel platinum electrodes show higher current densities for the oxidation of formic acid and glucose than state-of-the-art electrodes. In terms of methanol oxidation their catalytic activity is comparable to commercial direct methanol fuel cell (DMFC) electrodes, fabricated from Pt-Ru nanoparticles dispersed on carbon black.
Jiang, Guofeng; Wang, Cunlong; Li, Qiuyan; Dong, Jie; He, Guo
2015-02-01
A kind of Ti-Mg composite was prepared by infiltrating the biodegradable magnesium melt into the porous titanium (p-Ti) with entangled structure. The microstructure and the mechanical properties of the composites were investigated by using the metallographic technique and the compressive testing method. The novelty in the elastic property was discussed based on the experimental results and the referenced data. It was found that as the Ti volume fractions increased from 37.1% to 53.6%, the compressive plateau stress of the p-Ti/Mg composites increased from 175 MPa to 246 MPa, but the Young's modulus decreased from 47 GPa to 22 GPa. When the magnesium matrix was strengthened by adding 0.5 wt.% Zr, the plateau stress and the Young's modulus of the p-Ti/Mg(Zr) composites were reasonably enhanced. The stiffness of the p-Ti/Mg composites is comparable to that of the cortical bone, suggesting their considerable potentials for the load-bearing orthopedic applications. PMID:25492182
Klinzing, Gerard R; Zavaliangos, Antonios
2016-08-01
This work establishes a predictive model that explicitly recognizes microstructural parameters in the description of the overall mass uptake and local gradients of moisture into tablets. Model equations were formulated based on local tablet geometry to describe the transient uptake of moisture. An analytical solution to a simplified set of model equations was solved to predict the overall mass uptake and moisture gradients with the tablets. The analytical solution takes into account individual diffusion mechanisms in different scales of porosity and diffusion into the solid phase. The time constant of mass uptake was found to be a function of several key material properties, such as tablet relative density, pore tortuosity, and equilibrium moisture content of the material. The predictions of the model are in excellent agreement with experimental results for microcrystalline cellulose tablets without the need for parameter fitting. The model presented provides a new method to analyze the transient uptake of moisture into hydrophilic materials with the knowledge of only a few fundamental material and microstructural parameters. In addition, the model allows for quick and insightful predictions of moisture diffusion for a variety of practical applications including pharmaceutical tablets, porous polymer systems, or cementitious materials. PMID:27381910
Application of the heterogeneous complex networks model to porous structure of soils
NASA Astrophysics Data System (ADS)
Benito, R. M.; Santiago, A.; Cárdenas, J. P.
2009-04-01
We present a general formalism for models to study the evolution dynamics of complex networks [1]. It is an extension of the preferential attachment model to heterogeneous networks (HPA), which we define as those where nodes have intrinsic properties that bias their attachment probabilities to other nodes. We would like to emphasize that the proposed class of models is quite general and contains most of the previous heterogeneous network models available in the literature, including the fitness model, as particular cases. Also it should be mentioned that although there are some previous models that incorporate an internal property to nodes (e.g. hidden variables), none of them focuses on growing networks with such heterogeneity. An analytical expression of the degree distribution has been derived for the general class of heterogeneous models presented [2]. It has been shown analytically that all the models in this class present power laws in the degree distribution with different exponents. We have also carried out a numerical simulation of the degree distribution and clustering in the threshold model [1]. This is a particular case in the class of models proposed, where the attachment affinity is inversely related to the distance between node states as given by a space metric. This particular model is introduced in order to provide a benchmark for numerical simulation of heterogeneous networks, while loosing as little generality as possible in the choice. We think that the hypothesis of an inverse relationship between affinity and intrinsic distance (as given by a relevant metric) may be a reasonable proxy for many real networks where preferential attachment can be considered as the most relevant linking mechanism. Finally we present an application of the HPA to quantify the structure of porous soils [3]. Under this perspective pores are represented by nodes and the space for the flow of fluids between them are represented by links. Pore properties such as position
Vázquez, Mercedes; Paull, Brett
2010-06-01
This review critically summarises recent novel and advanced achievements in the application of monolithic materials and related porous polymer gels in micro-fluidic devices appearing within the literature over the period of the last 5 years (2005-2010). The range of monolithic materials has developed rapidly over the past decade, with a diverse and highly versatile class of materials now available, with each exhibiting distinct porosities, pore sizes, and a wide variety of surface functionalities. A major advantage of these materials is their ease of preparation in micro-fluidic channels by in situ polymerisation, leading to monolithic materials being increasingly utilised for a larger variety of purposes in micro-fluidic platforms. Applications of porous polymer monoliths, silica-based monoliths and related homogeneous porous polymer gels in the preparation of separation columns, ion-permeable membranes, preconcentrators, extractors, electrospray emitters, micro-valves, electrokinetic pumps, micro-reactors and micro-mixers in micro-fluidic devices are discussed herein. Procedures used in the preparation of monolithic materials in micro-channels, as well as some practical aspects of the micro-fluidic chip fabrication are addressed. Recent analytical/bioanalytical and catalytic applications of the final micro-fluidic devices incorporating monolithic materials are also reviewed. PMID:20493286
Phenolic resin-based porous carbons for adsorption and energy storage applications
NASA Astrophysics Data System (ADS)
Wickramaratne, Nilantha P.
The main objective of this dissertation research is to develop phenolic resin based carbon materials for range of applications by soft-templating and Stober-like synthesis strategies. Applications Studied in this dissertation are adsorption of CO2, bio-molecular and heavy metal ions, and energy storage devices. Based on that, our goal is to design carbon materials with desired pore structure, high surface area, graphitic domains, incorporated metal nanoparticles, and specific organic groups and heteroatoms. In this dissertation the organic-organic self-assembly of phenolic resins and triblock copolymers under acidic conditions will be used to obtain mesoporous carbons/carbon composites and Stober-like synthesis involving phenolic resins under basic condition will be used to prepare polymer/carbon particles and their composites. The structure of this dissertation consists of an introductory chapter (Chapter 1) discussing the general synthesis of carbon materials, particularly the soft-templating strategy and Stober-like carbon synthesis. Also, Chapter 1 includes a brief outline of applications namely adsorption of CO2, biomolecule and heavy metal ions, and supercapacitors. Chapter 2 discusses the techniques used for characterization of the carbon materials studied. This chapter starts with nitrogen adsorption analysis, which is used to measure the specific surface area, pore volume, distribution of pore sizes, and pore width. In addition to nitrogen adsorption, powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution thermogravimetric analysis (HR-TGA), cyclic voltammetry (CV) and CHNS elemental analysis (EA) are mentioned too. Chapter 3 is focused on carbon materials for CO2 adsorption. There are different types of porous solid materials such as silicate, MOFs, carbons, and zeolites studied for CO2 adsorption. However, the carbon based materials are considered to be the best candidates for CO 2 adsorption to the industrial point of
Cho, Daehwan; Kim, Moonkyoung; Hwang, Jeonghyun; Park, Jay Hoon; Joo, Yong Lak; Jeong, Youngjin
2015-12-01
We report a facile fabrication of porous silicon nanofibers by a simple three-stage procedure. Polymer/silicon precursor composite nanofibers are first fabricated by electrospinning, a water-based spinning dope, which undergoes subsequent heat treatment and then reduction using magnesium to be converted into porous silicon nanofibers. The porous silicon nanofibers are coated with a graphene by using a plasma-enhanced chemical vapor deposition for use as an anode material of lithium ion batteries. The porous silicon nanofibers can be mass-produced by a simple and solvent-free method, which uses an environmental-friendly polymer solution. The graphene-coated silicon nanofibers show an improved cycling performance of a capacity retention than the pure silicon nanofibers due to the suppression of the volume change and the increase of electric conductivity by the graphene. PMID:26510445
NASA Astrophysics Data System (ADS)
Cho, Daehwan; Kim, Moonkyoung; Hwang, Jeonghyun; Park, Jay Hoon; Joo, Yong Lak; Jeong, Youngjin
2015-10-01
We report a facile fabrication of porous silicon nanofibers by a simple three-stage procedure. Polymer/silicon precursor composite nanofibers are first fabricated by electrospinning, a water-based spinning dope, which undergoes subsequent heat treatment and then reduction using magnesium to be converted into porous silicon nanofibers. The porous silicon nanofibers are coated with a graphene by using a plasma-enhanced chemical vapor deposition for use as an anode material of lithium ion batteries. The porous silicon nanofibers can be mass-produced by a simple and solvent-free method, which uses an environmental-friendly polymer solution. The graphene-coated silicon nanofibers show an improved cycling performance of a capacity retention than the pure silicon nanofibers due to the suppression of the volume change and the increase of electric conductivity by the graphene.
Porous media heat transfer for injection molding
Beer, Neil Reginald
2016-05-31
The cooling of injection molded plastic is targeted. Coolant flows into a porous medium disposed within an injection molding component via a porous medium inlet. The porous medium is thermally coupled to a mold cavity configured to receive injected liquid plastic. The porous medium beneficially allows for an increased rate of heat transfer from the injected liquid plastic to the coolant and provides additional structural support over a hollow cooling well. When the temperature of the injected liquid plastic falls below a solidifying temperature threshold, the molded component is ejected and collected.
Mori, Michela; Almeida, Patrick V; Cola, Michela; Anselmi, Giulia; Mäkilä, Ermei; Correia, Alexandra; Salonen, Jarno; Hirvonen, Jouni; Caramella, Carla; Santos, Hélder A
2014-11-01
The wound healing stands as very complex and dynamic process, aiming the re-establishment of the damaged tissue's integrity and functionality. Thus, there is an emerging need for developing biopolymer-based composites capable of actively promoting cellular proliferation and reconstituting the extracellular matrix. The aims of the present work were to prepare and characterize biopolymer-functionalized porous silicon (PSi) microparticles, resulting in the development of drug delivery microsystems for future applications in wound healing. Thermally hydrocarbonized PSi (THCPSi) microparticles were coated with both chitosan and a mixture of chondroitin sulfate/hyaluronic acid, and subsequently loaded with two antibacterial model drugs, vancomycin and resveratrol. The biopolymer coating, drug loading degree and drug release behavior of the modified PSi microparticles were evaluated in vitro. The results showed that both the biopolymer coating and drug loading of the THCPSi microparticles were successfully achieved. In addition, a sustained release was observed for both the drugs tested. The viability and proliferation profiles of a fibroblast cell line exposed to the modified THCPSi microparticles and the subsequent reactive oxygen species (ROS) production were also evaluated. The cytotoxicity and proliferation results demonstrated less toxicity for the biopolymer-coated THCPSi microparticles at different concentrations and time points comparatively to the uncoated counterparts. The ROS production by the fibroblasts exposed to both uncoated and biopolymer-coated PSi microparticles showed that the modified PSi microparticles did not induce significant ROS production at the concentrations tested. Overall, the biopolymer-based PSi microparticles developed in this study are promising platforms for wound healing applications. PMID:25305585
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
Code of Federal Regulations, 2010 CFR
2010-07-01
... medium-sized general molded, extruded, and fabricated rubber plants subcategory. 428.60 Section 428.60... RUBBER MANUFACTURING POINT SOURCE CATEGORY Medium-Sized General Molded, Extruded, and Fabricated Rubber... fabricated rubber plants subcategory. The following provisions of this subpart are applicable to...
Code of Federal Regulations, 2011 CFR
2011-07-01
... medium-sized general molded, extruded, and fabricated rubber plants subcategory. 428.60 Section 428.60... RUBBER MANUFACTURING POINT SOURCE CATEGORY Medium-Sized General Molded, Extruded, and Fabricated Rubber... fabricated rubber plants subcategory. The following provisions of this subpart are applicable to...
Application of a mobile medium voltage sub-cycle transfer switch
Doncker, R.W. de; Maranto, J.A.
1996-11-01
This paper presents the application of a Mobile 3{O} Medium Voltage Sub-Cycle Transfer Switch (MVSTS). This application is a 15 kV class witch rated at a continuous current of 600 A. The function of a sub-cycle switch is to maintain AC electrical power to a critical load by switching between 2 independent sources within 4 ms. This switching time is sufficiently fast to preserve the operation of even the most sensitive customer equipment loads during distribution system disturbances such as voltage sags or swells. The mobile unit will allow a quick installation to a customer`s facility for temporary reliability assurance in a Preferred/Alternate or Split-Bus arrangement. This application also gives a customer the flexibility of trying the MVSTS before committing to a permanent installation.
Applicability of the effective-medium approximation to heterogeneous aerosol particles
NASA Astrophysics Data System (ADS)
Mishchenko, Michael I.; Dlugach, Janna M.; Liu, Li
2016-07-01
The effective-medium approximation (EMA) is based on the assumption that a heterogeneous particle can have a homogeneous counterpart possessing similar scattering and absorption properties. We analyze the numerical accuracy of the EMA by comparing superposition T-matrix computations for spherical aerosol particles filled with numerous randomly distributed small inclusions and Lorenz-Mie computations based on the Maxwell-Garnett mixing rule. We verify numerically that the EMA can indeed be realized for inclusion size parameters smaller than a threshold value. The threshold size parameter depends on the refractive-index contrast between the host and inclusion materials and quite often does not exceed several tenths, especially in calculations of the scattering matrix and the absorption cross section. As the inclusion size parameter approaches the threshold value, the scattering-matrix errors of the EMA start to grow with increasing the host size parameter and/or the number of inclusions. We confirm, in particular, the existence of the effective-medium regime in the important case of dust aerosols with hematite or air-bubble inclusions, but then the large refractive-index contrast necessitates inclusion size parameters of the order of a few tenths. Irrespective of the highly restricted conditions of applicability of the EMA, our results provide further evidence that the effective-medium regime must be a direct corollary of the macroscopic Maxwell equations under specific assumptions.
A new medium for triplet-triplet annihilated upconversion and photocatalytic application.
Ye, Changqing; Wang, Jingjing; Wang, Xiaomei; Ding, Ping; Liang, Zuoqin; Tao, Xutang
2016-02-01
Since the triplet-triplet annihilated upconversion (TTA-UC) materials work efficiently only in degassing organic solvents, it is of significance to find a new medium without toxicity and volatility and that promotes TTA-UC. Here, we firstly reported the effect of an OH-containing medium on low power upconversion and found that in alcohol solvent containing β-cyclodextrin (β-CD), the phosphorescence lifetime (τp) of the sensitizer (PdTPP) and the fluorescence quantum yield (Φf) of the acceptor (DPA) were enhanced with the increase in the number of OH-groups of the medium. A large triplet-triplet quenching constant (kq, 1.91 × 10(9) M(-1) s(-1)) and high upconversion efficiency (ΦUC, ∼ 36%) of PdTPP/DPA were obtained under the excitation of a diode laser (532 nm, 60 mW cm(-2)). Under our green-to-blue upconversion irradiation, in a demonstration experiment the photocurrent was recorded at 0.09 μA cm(-2), resulting from photocatalytic water splitting by a Cd0.7Zn0.3S photoanode and a Pt counter-electrode in a photoelectrochemical cell. The importance of this study suggests that upconversion-powered photoelectrochemistry possesses potential application for hydrogen generation from water under excitation of sun energy. PMID:26580451
Li, Tianwei; Yan, Gang; Wang, Yeyao; Ma, Xiaofan; Nie, Yongfeng
2003-05-01
According to the basic characteristics of municipal solid waste generated from medium or small city of China, the optimal management principles and programs for optimization management model suitable to them were put forward. By application of the model in case study, the optimal scenarios for the disposal of municipal solid waste from the planning system in 1999, 2005 and 2010 were calculated, which adequately validated and accounted for the advantages of optimization model by comparison of costs between optimization scenarios and former scenarios. PMID:12916219
Natural convection in porous media
Prasad, V.; Hussain, N.A.
1986-01-01
This book presents the papers given at a conference on free convection in porous materials. Topics considered at the conference included heat transfer, nonlinear temperature profiles and magnetic fields, boundary conditions, concentrated heat sources in stratified porous media, free convective flow in a cavity, heat flux, laminar mixed convection flow, and the onset of convection in a porous medium with internal heat generation and downward flow.
Sun, Zhixing; Shen, Zhigang; Zhang, Xiaojing; Ma, Shulin
2014-01-01
Nonmetal materials take up about 70 wt% of waste printed wiring boards (WPWB), which are usually recycled as low-value fillers or even directly disposed by landfill dumping and incineration. In this research, a novel reuse ofthe nonmetals to produce porous composites for sound absorbing application was demonstrated. The manufacturing process, absorbing performance and mechanical properties of the composites were studied. The results show that the high porous structure of the composites leads to an excellent sound absorption ability in broad-band frequency range. Average absorption coefficient of above 0.4 can be achievedby the composite in the frequency range from 100 to 6400 Hz. When the particle size is larger than 0.2 mm, the absorption ability of the composite is comparable to that of commercial wood-fibre board and urea-formaldehyde foam. Mechanical analysis indicates that the porous composites possess sufficient structural strength for self-sustaining applications. All the results indicate that producing sound absorbing composite with nonmetal particles from WPWB provides an efficient and profitable way for recycling this waste resource and can resolve both the environment pollution and noise pollution problems. PMID:24701924
Quevedo González, Fernando José; Nuño, Natalia
2016-06-01
The mechanical properties of well-ordered porous materials are related to their geometrical parameters at the mesoscale. Finite element (FE) analysis is a powerful tool to design well-ordered porous materials by analysing the mechanical behaviour. However, FE models are often computationally expensive. This article aims to develop a cost-effective FE model to simulate well-ordered porous metallic materials for orthopaedic applications. Solid and beam FE modelling approaches are compared, using finite size and infinite media models considering cubic unit cell geometry. The model is then applied to compare two unit cell geometries: cubic and diamond. Models having finite size provide similar results than the infinite media model approach for large sample sizes. In addition, these finite size models also capture the influence of the boundary conditions on the mechanical response for small sample sizes. The beam FE modelling approach showed little computational cost and similar results to the solid FE modelling approach. Diamond unit cell geometry appeared to be more suitable for orthopaedic applications than the cubic unit cell geometry. PMID:26260268
NASA Astrophysics Data System (ADS)
Hashemi, Seyed Iman; Fazelabdolabadi, Babak; Moradi, Siyamak; Rashidi, Ali Morad; Shahrabadi, Abbas; Bagherzadeh, Hadi
2016-01-01
Prevention of asphaltene formation in reservoir rocks can result in resolving a severe long-lasting issue in petroleum production. The present research addresses the issue in the context of exploring the potential effect of nickel oxide (NiO) nanoparticles in destabilizing asphaltene deposition in porous media, in the presence of carbon dioxide. To ensure proper distribution within the system and to retain future field-scale applicability, the NiO nanoparticles were exposed to the in situ oil via injection gas stream, in which they had been uniformly dispersed using polydimethylsiloxane (PDMS). The experimental results, established under miscible CO2 state, indicate a considerable improvement in permeability/porosity reduction of core, as well as less asphaltene accumulation in porous media and increased oil recovery factor after applying NiO nanoparticles.
NASA Astrophysics Data System (ADS)
Kang, M.; Bilheux, H. Z.; Voisin, S.; Cheng, C. L.; Perfect, E.; Horita, J.; Warren, J. M.
2013-04-01
Using neutron radiography, the measurement of water thickness was performed using aluminum (Al) water calibration cells at the High Flux Isotope Reactor (HFIR) Cold-Guide (CG) 1D neutron imaging facility at Oak Ridge National Laboratory, Oak Ridge, TN, USA. Calibration of water thickness is an important step to accurately measure water contents in samples of interest. Neutron attenuation by water does not vary linearly with thickness mainly due to beam hardening and scattering effects. Transmission measurements for known water thicknesses in water calibration cells allow proper correction of the underestimation of water content due to these effects. As anticipated, strong scattering effects were observed for water thicknesses greater than 0.2 cm when the water calibration cells were positioned close to the face of the detector/scintillator (0 and 2.4 cm away, respectively). The water calibration cells were also positioned 24 cm away from the detector face. These measurements resulted in less scattering and this position (designated as the sample position) was used for the subsequent experimental determination of the neutron attenuation coefficient for water. Neutron radiographic images of moist Flint sand in rectangular and cylindrical containers acquired at the sample position were used to demonstrate the applicability of the water calibration. Cumulative changes in the water volumes within the sand columns during monotonic drainage determined by neutron radiography were compared with those recorded by direct reading from a burette connected to a hanging water column. In general, the neutron radiography data showed very good agreement with those obtained volumetrically using the hanging water-column method. These results allow extension of the calibration equation to the quantification of unknown water contents within other samples of porous media.
Kang, Misun; Bilheux, Hassina Z; Voisin, Sophie; Cheng, Chu-lin; Perfect, Edmund; Horita, Juske; Warren, Jeffrey
2013-04-01
Using neutron radiography, the measurement of water thickness was performed using aluminum (Al) water calibration cells at the High Flux Isotope Reactor (HFIR) Cold-Guide (CG) 1D neutron imaging facility at Oak Ridge National Laboratory, Oak Ridge, TN, USA. Calibration of water thickness is an important step to accurately measure water contents in samples of interest. Neutron attenuation by water does not vary linearly with thickness mainly due to beam hardening and scattering effects. Transmission measurements for known water thicknesses in water calibration cells allow proper correction of the underestimation of water content due to these effects. As anticipated, strong scattering effects were observed for water thicknesses greater than 2 mm when the water calibration cells were positioned close to the face of the detector / scintillator (0 and 2.4 cm away, respectively). The water calibration cells were also positioned 24 cm away from the detector face. These measurements resulted in less scattering and this position (designated as the sample position) was used for the subsequent experimental determination of the neutron attenuation coefficient for water. Neutron radiographic images of moist Flint sand in rectangular and cylindrical containers acquired at the sample position were used to demonstrate the applicability of the water calibration. Cumulative changes in the water volumes within the sand columns during monotonic drainage determined by neutron radiography were compared with those recorded by direct reading from a burette connected to a hanging water column. In general, the neutron radiography data showed very good agreement with those obtained volumetrically using the hanging water-column method. These results allow extension of the calibration equation to the quantification of unknown water contents within other samples of porous media.
Wei, Yi; Wang, Yuxia; Zhang, Huixia; Zhou, Weiqing; Ma, Guanghui
2016-09-15
A new strategy is developed to prepare porous microspheres with narrow size distribution for peptides controlled release, involving a fabrication of porous microspheres without any porogens followed by a pore closing process. Amphiphilic polymers with different hydrophobic segments (poly(monomethoxypolyethylene glycol-co-d,l-lactide) (mPEG-PLA), poly(monomethoxypolyethylene glycol-co-d,l-lactic-co-glycolic acid) (mPEG-PLGA)) are employed as microspheres matrix to prepare porous microspheres based on a double emulsion-premix membrane emulsification technique combined with a solvent evaporation method. Both microspheres possess narrow size distribution and porous surface, which are mainly caused by (a) hydrophilic polyethylene glycol (PEG) segments absorbing water molecules followed by a water evaporation process and (b) local explosion of microspheres due to fast evaporation of dichloromethane (MC). Importantly, mPEG-PLGA microspheres have a honeycomb like structure while mPEG-PLA microspheres have a solid structure internally, illustrating that the different hydrophobic segments could modulate the affinity between solvent and matrix polymer and influence the phase separation rate of microspheres matrix. Long term release patterns are demonstrated with pore-closed microspheres, which are prepared from mPEG-PLGA microspheres loading salmon calcitonin (SCT). These results suggest that it is potential to construct porous microspheres for drug sustained release using permanent geometric templates as new porogens. PMID:27285778
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
Three-dimensional porous graphene-Co3O4 nanocomposites for high performance photocatalysts
NASA Astrophysics Data System (ADS)
Bin, Zeng; Hui, Long
2015-12-01
Novel three-dimensional porous graphene-Co3O4 nanocomposites were synthesized by freeze-drying methods. Scanning and transmission electron microscopy revealed that the graphene formed a three-dimensional porous structure with Co3O4 nanoparticles decorated surfaces. The as-obtained product showed high photocatalytic efficiency and could be easily separated from the reaction medium by magnetic decantation. This nanocomposite may be expected to have potential in water purification applications.
Problems of applications of high power IR radiation in aquatic medium under high pressure
NASA Astrophysics Data System (ADS)
Sorokin, Yurii V.; Kuzyakov, Boris A.
2004-06-01
In this work the effects that appear in the optical breakdown are analyzed in water and the time dependences received also for the velocities and pressures at the wave fronts. The application of acoustic waves, generated by high power laser pulses in the aqueous medium, has quite serious perspectives for sounding. It is shown in the work that under comparatively low power density of radiation, as a result of a surface layer heating, the thermoelastic sresses arise, leading to the excitation of the acoustic waves. The analysis showed that the prognostic evaluations of the values of a light deflagration area are possible for a clear aqueous medium with the pressures up to 400 kg/cm2. With the presence of microinhomogeneities, it is necessary to know their total physical and chemical properties and detailed trustworthy data by their spatial distribution. A principally new approach was developed to the problem of videoinformation transmission from the object surfaces by the fiber-optic channel. The application of a precision measuring TV-camera with a color format in the range 0.3 - 0.98 μm allows to raise the information capacity of the transmitted information. The optimization of vision module choice are considered also.
NASA Astrophysics Data System (ADS)
Yang, Xia; Tang, Yong-Bing; Huang, Xing; Xue, Hong Tao; Kang, Wen Pei; Li, Wen Yue; Ng, Tsz-Wai; Lee, Chun-Sing
2015-06-01
Prussian Blue (PB, Fe4[Fe(CN)6]3) is utilized to synthesize bimetallic metal-organic frameworks (MOFs) (Fe4[Fe(CN)6]3/Mx[Fe(CN)6], M = Cu, Ni, Co, etc.) by cation exchange, driven by differences in solubility product constant (Ksp) of monometallic MOFs. Upon decomposition, the bimetallic MOFs convert to porous composite metal oxides (Fe2O3/MOx, M = Cu, Ni, Co, etc.) while keeping the original cubic morphology. This study demonstrates a general approach for preparing bimetallic MOFs and porous composite oxides. We also demonstrate the good electrochemical performance (specific capacity of 774 mAh g-1 after 120 cycles at 500 mA g-1) of the synthesized porous Fe2O3-CuO composite as an anode material for lithium ion batteries. And according to references, this composite exhibit better or comparable rate capability and cycle stability compared with other hybrid transition metal oxides.
NASA Astrophysics Data System (ADS)
Bestem'yanov, K. P.; Gordienko, Vyacheslav M.; Ivanov, Anatoliy A.; Konovalov, Aleksei N.; Podshivalov, Alexey A.
2004-07-01
A system is devised for optical heterodyning based on a femtosecond Cr:forsterite laser using a balance scheme for the laser noise compensation. The dependence of a heterodyne signal on the time delay is measured by detecting backscattered laser radiation from a strongly scattering porous object (a sheet of paper). It is found that the backscattered signal contains 'a long tail' with an exponential decay caused by multiple scattering. The exponent of the exponential is determined by the lifetime of photons in a scattering layer. The absorption and scattering coefficients for different types of paper are measured by the photon lifetime.
Polymer Replicas of Photonic Porous Silicon for Sensing and Drug Delivery Applications
NASA Astrophysics Data System (ADS)
Li, Yang Yang; Cunin, Frédérique; Link, Jamie R.; Gao, Ting; Betts, Ronald E.; Reiver, Sarah H.; Chin, Vicki; Bhatia, Sangeeta N.; Sailor, Michael J.
2003-03-01
Elaborate one-dimensional photonic crystals are constructed from a variety of organic and biopolymers, which can be dissolved or melted, by templating the solution-cast or injection-molded materials in porous silicon or porous silicon dioxide multilayer (rugate dielectric mirror) structures. After the removal of the template by chemical dissolution, the polymer castings replicate the photonic features and the nanostructure of the master. We demonstrate that these castings can be used as vapor sensors, as deformable and tunable optical filters, and as self-reporting, bioresorbable materials.
Polymer replicas of photonic porous silicon for sensing and drug delivery applications.
Li, Yang Yang; Cunin, Frédérique; Link, Jamie R; Gao, Ting; Betts, Ronald E; Reiver, Sarah H; Chin, Vicki; Bhatia, Sangeeta N; Sailor, Michael J
2003-03-28
Elaborate one-dimensional photonic crystals are constructed from a variety of organic and biopolymers, which can be dissolved or melted, by templating the solution-cast or injection-molded materials in porous silicon or porous silicon dioxide multilayer (rugate dielectric mirror) structures. After the removal of the template by chemical dissolution, the polymer castings replicate the photonic features and the nanostructure of the master. We demonstrate that these castings can be used as vapor sensors, as deformable and tunable optical filters, and as self-reporting, bioresorbable materials. PMID:12663921
NASA Astrophysics Data System (ADS)
Xu, Rui; Wang, Jiawei; Li, Qiuyu; Sun, Guoying; Wang, Enbo; Li, Siheng; Gu, Jianmin; Ju, Mingliang
2009-11-01
We developed a facile synthetic route of porous cobalt oxide (Co 3O 4) nanorods via a microemulsion-based method in combination with subsequent calcination process. The porous structure was formed by controlled decomposition of the microemulsion-synthesized precursor CoC 2O 4 nanorods without destruction of the original morphology. The as-prepared Co 3O 4 nanorods, consisting of small nanoparticles with diameter of 80-150 nm, had an average diameter of 200 nm and a length of 3-5 μm. The morphology and structure of synthesized samples were characterized by transmission electron microscopy and scanning electron microscopy. The phase and composition were investigated by X-ray powder diffraction and X-ray photoelectron spectroscopy. The optical property of Co 3O 4 nanorods was investigated. Moreover, the porous Co 3O 4 nanorods exhibited high electrochemical performance when applied as cathode materials for lithium-ion batteries, which gives them good potential applications.
Tripathi, D; Anwar Bég, O
2014-02-01
A mathematical study of the peristaltic flow of complex rheological viscoelastic fluids using the generalized fractional Burgers' model through a non-uniform channel is presented. This model is designed to study the movement of chyme and undigested chyme (biophysical waste materials) through the small intestine to the large intestine. To simulate blockages and impedance of debris generated by cell shedding, infections, adhesions on the wall and undigested material, a drag force porous media model is utilized. This effectively mimicks resistance to chyme percolation generated by solid matrix particles in the regime. The conduit geometry is mathematically simulated as a sinusoidal propagation with linear increment in shape of the bolus along the length of channel. A modified Darcy-Brinkman model is employed to simulate the generalized flows through isotropic, homogenous porous media, a simplified but physically robust approximation to actual clinical situations. To model the rheological properties of chyme, a viscoelastic Burgers' fluid formulation is adopted. The governing equations are simplified by assuming long wavelength and low Reynolds number approximations. Numerical and approximate analytical solutions are obtained with two semi-numerical techniques, namely the homotopy perturbation method and the variational iteration method. Visualization of the results is achieved with Mathematica software. The influence of the dominant hydromechanical and geometric parameters such as fractional viscoelastic parameters, wave number, non-uniformity constant, permeability parameter, and material constants on the peristaltic flow characteristics are depicted graphically. PMID:24300568
Sotomayor, María Eugenia Ospina, Liliana María Levenfeld, Belén Várez, Alejandro
2013-12-15
The characterization of 430L stainless steel planar porous supports obtained by powder extrusion moulding was performed in this work. A thermoplastic multicomponent binder based on high density polyethylene and paraffin wax was selected for the process. Green supports were shaped by extrusion moulding, and subsequently the binder was removed by a thermal cycle previously optimized. Sintering was carried out at different temperatures in low vacuum. Density of sintered parts was measured by Archimedes' method and porosity was also evaluated through a microstructural analysis by optical microscopy. The porosity degree of samples sintered at low temperature was close to 35% which is a very suitable value for their application in SOFCs. Tensile tests were carried out in order to determine mechanical strength as a function of porosity degree. Based on these results, the best feedstock composition and processing parameters were selected. The oxidation behaviour in static air at high temperature was studied, and formed oxides were characterized in a scanning electron microscope equipped with energy dispersive analysis of X-rays. X-ray diffraction experiments were performed in order to identify the formed oxides based on formula Fe{sub 2−x}Cr{sub x}O{sub 3}. The results of these studies showed that this kind of ferritic stainless steel would be more suitable to be used as anodic supports where a rich hydrogen atmosphere is employed. Preliminary deposition tests allowed obtaining a homogeneous Ni–YSZ anode layer with a thickness of 10 μm on the porous metallic substrates. - Highlights: • 430L stainless steel porous supports were obtained by powder extrusion moulding. • Porosity degree was controlled sintering at different temperatures in low vacuum. • Tensile tests allowed determining mechanical strength of porous supports. • A study about its oxidation behaviour in static air at high temperature was realized. • After oxidation, formed oxides were
NASA Astrophysics Data System (ADS)
Fauzi, Nur Fatihah; Ahmad, Syakila; Pop, Ioan
2014-07-01
The steady mixed convection flow of an incompressible viscous fluid over an isoflux sphere embedded in a porous medium with the existence of heat source/sink is theoretically considered for both the assisting and opposing flow cases with small Prandtl number. The transformed equations of the non-similar boundary layer at the lower stagnation point of the sphere are solved numerically using a finite-difference method known as the Keller-box scheme. Numerical results are presented for the skin friction coefficient and the local wall temperature, as well as the velocity and temperature profiles for different values of the porosity parameter, the heat source/sink parameter and the mixed convection parameter for air. It is noticed that the solution has two branches in a certain range of the mixed convection parameter.
Xia, Youyi; Hu, Hongxia; Shen, Tong; Bai, Linyi; Xiang, Siyuan; Lei, Yilong; Xiao, Hongping
2016-08-21
With the help of rhodamine B base (RBB), novel Pd nanospheres were synthesized by a facile one-step approach. Owing to their hierarchically porous characteristics, these nanospheres exhibited highly catalytic activity for HCOOH electrooxidation (∼1.84 times and 1.67 times higher than those of a commercial Pd/C catalyst for mass and specific activity, respectively). PMID:27453963
Xiong, Guangyao; Luo, Honglin; Zuo, Guifu; Ren, Kaijing; Wan, Yizao
2015-09-15
Graphene oxide (GO) and hydroxyapatite (HAp) are frequently used as reinforcements in polymers to improve mechanical and biological properties. In this work, novel porous hybrid nanocomposites consisting of GO, HAp, and sodium alginate (SA) have been prepared by facile solution mixing and freeze drying in an attempt to obtain a scaffold with desirable mechanical and biological properties. The as-prepared porous GO/HAp/SA hybrid nanocomposites were characterized by SEM, XRD, FTIR, TGA, and mechanical testing. In addition, preliminary cell behavior was assessed by CCK8 assay. It is found that the GO/HAp/SA nanocomposites show improved compressive strength and modulus over neat SA and HAp/SA nanocomposites. CCK8 results reveal that the GO/HAp/SA nanocomposites show enhanced cell proliferation over neat SA and GO/SA nanocomposite. It has been demonstrated that GO/HAp20/SA holds promise in bone tissue engineering. - Graphical abstract: Display Omitted - Highlights: • Graphene oxide (GO), hydroxyapatite (HAp), and alginate (SA) nanocomposites were fabricated. • The novel porous composites were prepared by solution mixture and freeze drying. • The GO/HAp/SA had porous structure with porosity > 85% and pore size > 150 μm. • The GO/HAp/SA exhibited improved mechanical properties over HAp/SA counterparts. • The GO/HAp/SA showed enhanced cell proliferation over GO/SA counterparts.
Shape Memory Alloy Modeling and Applications to Porous and Composite Structures
NASA Astrophysics Data System (ADS)
Zhu, Pingping
underlying mechanism of pore interactions in the SMA foams. Additionally, the influence of geometric features including the number, size and locations of pores are studied to guide the design and optimization of porous SMAs. Thirdly, modeling and simulation are performed on a series of cracked self-healing SMA composite systems. These composites are to be applied in aeronautic structures where fatigue crack initiation and propagation is a significant safety and economic concern, based on a liquid-assisted SMA self-healing technology. We develop a modeling approach in Abaqus to create composite models with the as-is or pre-strained SMA wires. The modeling approach is validated by two simulation cases following the experiment setups. The amount of crack closure in the SMA-reinforced MMC is then focused, especially on the role of the SMA reinforcement, the softening property of the matrix, and the effect of pre-strain in the SMA. Composites with various geometric configurations of SMA are also created to study how the number, location, length and orientation of the SMA wires would affect the crack closure and self-healing behavior. These studies, from three aspects, provide deep insights to SMA and its related applications from the modeling and simulation point of view, which can further guide the development and application of this unique material.
NASA Astrophysics Data System (ADS)
Kiang, Y.-W.; Liu, C. H.
1985-02-01
Plane wave scattering by an irregularity slab embedded in a linearly stratified isotropic medium is studied under the single scatter approximation. In addition to regular reflection from the stratified background, both the incident and the reflected waves are scattered by the random irregularities. The behavior of the unperturbed field in the neighborhood of the turning point is accurately taken into account by using the full wave solution. The scattered fields can be interpreted in terms of the Bragg condition similar to the case of the well-known Booker-Gordon form, but with four terms accounting for the reflection effect of the turning point on both the unperturbed and scattered waves. The case of elongated irregularities is studied in detail. Analytical expression for the angular spectrum of the average scattered field intensity is derived, and its physical meaning discussed. In comparison with the case where the background medium is homogeneous, the relation to the two-dimensional Booker-Gordon formula is clarified. Applications to high-frequency propagation in the disturbed ionosphere are discussed.
LeGoy, P.R.
1999-11-01
Variable speed hydraulic turbine power generation has become a useful tool in the chemical processing industry. The technology that preceded and led to the use of variable speed hydraulic turbines was Variable Speed Constant Frequency (VSCF) drives for power generation. The current state of the art in the VSCF technology is the Insulated Gate Bipolar Transistor (IGBT), voltage source, Pulse Width Modulation (PWM) drive. A new PWM switch has been created. The new switch is the Integrated Gate-Commutated Thyristor (IGCT), PWM device. The drives produced with this technology are current source therefore the operational voltages of the drives are easily configured for medium voltage range. Medium voltage power makes the new drives desirable because of the size of the generators. A common power range for variable speed Hydraulic Power Generation is 1MW and applications for the chemical processing industry have a trend toward higher powers. For this type generator: if the operational voltage falls below 2300V the size of the generator becomes too large, bulky and expensive. Windings are no longer wires; they become bussbars. The current solution to the voltage problem is to include a transformer in the generator/drive connection.
Peterson, D.; Haase, S.
2009-07-01
This report provides a market assessment of gasification and direct combustion technologies that use wood and agricultural resources to generate heat, power, or combined heat and power (CHP) for small- to medium-scale applications. It contains a brief overview of wood and agricultural resources in the U.S.; a description and discussion of gasification and combustion conversion technologies that utilize solid biomass to generate heat, power, and CHP; an assessment of the commercial status of gasification and combustion technologies; a summary of gasification and combustion system economics; a discussion of the market potential for small- to medium-scale gasification and combustion systems; and an inventory of direct combustion system suppliers and gasification technology companies. The report indicates that while direct combustion and close-coupled gasification boiler systems used to generate heat, power, or CHP are commercially available from a number of manufacturers, two-stage gasification systems are largely in development, with a number of technologies currently in demonstration. The report also cites the need for a searchable, comprehensive database of operating combustion and gasification systems that generate heat, power, or CHP built in the U.S., as well as a national assessment of the market potential for the systems.
Inverse electromagnetic scattering in a two-layered medium with an application to mine detection
NASA Astrophysics Data System (ADS)
Delbary, Fabrice; Erhard, Klaus; Kress, Rainer; Potthast, Roland; Schulz, Jochen
2008-02-01
The detection of metallic objects is an important application in state-of-the-art security technology. In particular, for humanitarian mine detection the task is to detect objects that are buried in soil. Usually hand-held mine detectors create an electromagnetic pulse via a current in some wire loop and evaluate the scattered electromagnetic field via induction in a receiver loop that is moved together with the sender loop. This receiver signal can then be employed in identifying the location and the shape of metallic objects. Here, we model the full electromagnetic scattering problem in a two-layered medium from a perfectly conducting obstacle using boundary integral equations. The scattered field is modeled via a boundary layer approach and for its kernel the Green's matrix for the two-layered medium is constructed. We establish uniqueness and existence for the solution of the corresponding boundary integral equation. In the second part of the paper, we employ a direct search method for parameter estimation to find the location and size of some simple metallic objects from measurements of the induced voltage for a number of sender-receiver-loop positions.
NASA Astrophysics Data System (ADS)
Prabhakar, Neeraj; Näreoja, Tuomas; von Haartman, Eva; Karaman, Didem Şen; Jiang, Hua; Koho, Sami; Dolenko, Tatiana A.; Hänninen, Pekka E.; Vlasov, Denis I.; Ralchenko, Victor G.; Hosomi, Satoru; Vlasov, Igor I.; Sahlgren, Cecilia; Rosenholm, Jessica M.
2013-04-01
Recent advances within materials science and its interdisciplinary applications in biomedicine have emphasized the potential of using a single multifunctional composite material for concurrent drug delivery and biomedical imaging. Here we present a novel composite material consisting of a photoluminescent nanodiamond (ND) core with a porous silica (SiO2) shell. This novel multifunctional probe serves as an alternative nanomaterial to address the existing problems with delivery and subsequent tracing of the particles. Whereas the unique optical properties of ND allows for long-term live cell imaging and tracking of cellular processes, mesoporous silica nanoparticles (MSNs) have proven to be efficient drug carriers. The advantages of both ND and MSNs were hereby integrated in the new composite material, ND@MSN. The optical properties provided by the ND core rendered the nanocomposite suitable for microscopy imaging in fluorescence and reflectance mode, as well as super-resolution microscopy as a STED label; whereas the porous silica coating provided efficient intracellular delivery capacity, especially in surface-functionalized form. This study serves as a demonstration how this novel nanomaterial can be exploited for both bioimaging and drug delivery for future theranostic applications.Recent advances within materials science and its interdisciplinary applications in biomedicine have emphasized the potential of using a single multifunctional composite material for concurrent drug delivery and biomedical imaging. Here we present a novel composite material consisting of a photoluminescent nanodiamond (ND) core with a porous silica (SiO2) shell. This novel multifunctional probe serves as an alternative nanomaterial to address the existing problems with delivery and subsequent tracing of the particles. Whereas the unique optical properties of ND allows for long-term live cell imaging and tracking of cellular processes, mesoporous silica nanoparticles (MSNs) have proven
Li, Fuping; Li, Jinshan; Kou, Hongchao; Huang, Tingting; Zhou, Lian
2015-09-01
Porous titanium and its alloys are believed to be promising materials for bone implant applications, since they can reduce the "stress shielding" effect by tailoring porosity and improve fixation of implant through bone ingrowth. In the present work, porous Ti6Al4V alloys for biomedical application were fabricated by diffusion bonding of alloy meshes. Compressive mechanical behavior and compatibility in the range of physiological strain rate were studied under quasi-static and dynamic conditions. The results show that porous Ti6Al4V alloys possess anisotropic structure with elongated pores in the out-of-plane direction. For porous Ti6Al4V alloys with 60-70 % porosity, more than 40 % pores are in the range of 200-500 μm which is the optimum pore size suited for bone ingrowth. Quasi-static Young's modulus and yield stress of porous Ti6Al4V alloys with 30-70 % relative density are in the range of 6-40 GPa and 100-500 MPa, respectively. Quasi-static compressive properties can be quantitatively tailored by porosity to match those of cortical bone. Strain rate sensitivity of porous Ti6Al4V alloys is related to porosity. Porous Ti6Al4V alloys with porosity higher than 50 % show enhanced strain rate sensitivity, which is originated from that of base materials and micro-inertia effect. Porous Ti6Al4V alloys with 60-70 % porosity show superior compressive mechanical compatibility in the range of physiological strain rate for cortical bone implant applications. PMID:26384823
Kartsakli, Elli; Antonopoulos, Angelos; Alonso, Luis; Verikoukis, Christos
2014-01-01
Relay sensor networks are often employed in end-to-end healthcare applications to facilitate the information flow between patient worn sensors and the medical data center. Medium access control (MAC) protocols, based on random linear network coding (RLNC), are a novel and suitable approach to efficiently handle data dissemination. However, several challenges arise, such as additional delays introduced by the intermediate relay nodes and decoding failures, due to channel errors. In this paper, we tackle these issues by adopting a cloud architecture where the set of relays is connected to a coordinating entity, called cloud manager. We propose a cloud-assisted RLNC-based MAC protocol (CLNC-MAC) and develop a mathematical model for the calculation of the key performance metrics, namely the system throughput, the mean completion time for data delivery and the energy efficiency. We show the importance of central coordination in fully exploiting the gain of RLNC under error-prone channels. PMID:24618727
Synthesis and characterization of Fe3O4: Porous carbon nanocomposites for biosensor application
NASA Astrophysics Data System (ADS)
Arora, Manju; Zargar, R. A.
2015-08-01
Fe3O4:Porous carbon (Fe3O4:PC) nano-magnetic composites were prepared by using different weight fractions of acid treated PC by the chemical co-precipitation route and annealed at 573 K, 773 K and 973 K temperatures in inert N2 gas atmosphere for 2 hrs to obtain desired stoichiometry of nanocomposites. The structural, morphological and magnetic properties of these composites were characterized by powder XRD, TEM, EPR and VSM analytical techniques. The crystallinity of the composites, g-value and spin concentration increases with increasing annealing temperature. TEM images confirmed the formation of nanosized ferrite nanoprticles whose size increases from 23 nm to 54 nm on increasing annealing temperature. Porous carbon increases porosity, coercivity and reduces saturation magnetization of these prepared nanocomposites.
Wacker, Josias B; Parashar, Virendra K; Gijs, Martin A M
2011-04-19
We report the microfluidic chip-based assembly of colloidal silanol-functionalized silica nanoparticles using monodisperse water-in-oil droplets as templates. The nanoparticles are linked via silica bridges, thereby forming superstructures that range from doublets to porous spherical or rod-like micro-objects. Adding magnetite nanoparticles to the colloid generates micro-objects that can be magnetically manipulated. We functionalized such magnetic porous assemblies with horseradish peroxidase and demonstrate the catalytic binding of fluorescent dye-labeled tyramide over the complete effective surface of the superstructure. Such nanoparticle assemblies permit easy manipulation and recovery after a heterogeneous catalytic process while providing a large surface similar to that of the individual nanoparticles. PMID:21417232
Fabrication of Porous TiO2 Hollow Spheres and Their Application in Gas Sensing
2010-01-01
In this work, porous TiO2 hollow spheres with an average diameter of 100 nm and shell thickness of 20 nm were synthesized by a facile hydrothermal method with NH4HCO3 as the structure-directing agent, and the formation mechanism for this porous hollow structure was proved to be the Ostwald ripening process by tracking the morphology of the products at different reaction stages. The product was characterized by SEM, TEM, XRD and BET analyses, and the results show that the as-synthesized products are anatase phase with a high surface area up to 132.5 m2/g. Gas-sensing investigation reveals that the product possesses sensitive response to methanal gas at 200°C due to its high surface area. PMID:20730129
NASA Astrophysics Data System (ADS)
Babaei, Hasan; Wilmer, Christopher E.
2016-01-01
We have studied the mechanisms of heat transfer in a porous crystal-gas mixture system, motivated by the not insignificant challenge of quickly dissipating heat generated in metal-organic frameworks (MOFs) due to gas adsorption. Our study reveals that the thermal conductance of the system (crystal and gas) is dominated by lattice thermal conductivity in the crystal, and that conductance is reduced as the concentration of gas in the pores increases. This mechanism was observed from classical molecular simulations of a monatomic gas in an idealized porous crystal structure. We show that the decreased conductivity associated with increased gas concentration is due to phonon scattering in the crystal due to interactions with gas molecules. Calculations of scattering rates for two phonon modes reveal that scattering of the lowest frequency mode scales linearly with gas density. This result suggests that the probability of a phonon-gas collision is simply proportional to the number of gas molecules in the pore.
Cobalt monoxide-doped porous graphitic carbon microspheres for supercapacitor application
Yang, Zheng-Chun; Tang, Chun-Hua; Zhang, Yu; Gong, Hao; Li, Xu; Wang, John
2013-01-01
A novel design and facile synthesis process for carbon based hybrid materials, i.e., cobalt monoxide (CoO)-doped graphitic porous carbon microspheres (Co-GPCMs), have been developed. With the synthesis strategy, the mixture of cobalt gluconate, α-cyclodextrin and poly (ethylene oxide)106-poly (propylene oxide)70-poly (ethylene oxide)106 is treated hydrothermally, followed by pyrolysis in argon. The resultant Co-GPCMs exhibits a porous carbon matrix with localized graphitic structure while CoO nanodots are embedded in the carbon frame. Thus, the Co-GPCMs effectively combine the electric double-layer capacitance and pseudo-capacitance when used as the electrode in supercapacitor, which lead to a higher operation voltage (1.6 V) and give rise to a significantly higher energy density. This study provides a new research strategy for electrode materials in high energy density supercapacitors. PMID:24113335
Zhang, Kai; Qin, Furong; Lai, Yanqing; Li, Jie; Lei, Xiaoke; Wang, Mengran; Lu, Hai; Fang, Jing
2016-03-01
Hierarchically porous carbon/graphene aerogel (CGA) with relatively high surface area and pore volume is synthesized through an efficient fabrication strategy, which involves forming hydrothermal carbon layer on the pore wall as upholder and directly carbonizing the wet hydrogel from hydrothermal reaction, without using any special drying techniques. Cassava powder is used as carbon precursor which enables sustainable synthesis. Carbonizing the wet hydrothermal product is found to be a self-activation process, through which abundant pores are generated. The aerogel is used as host to encapsulate sulfur for lithium sulfur battery. Graphene, served as highly conductive scaffold, accelerates the transport of the electrons. The hierarchically porous structure is in favor of improving the electrochemical performance of lithium sulfur battery. Therefore, the cathode with high sulfur loading and high sulfur content can deliver very good performance. PMID:26885723
Recent developments in neutron imaging with applications for porous media research
NASA Astrophysics Data System (ADS)
Kaestner, A. P.; Trtik, P.; Zarebandkouki, M.; Kazantsev, D.; Snehota, M.; Dobson, K. J.; Lehmann, E. H.
2015-12-01
Computed tomography has become a standard method to probe processes in porous media. Neutrons enabled us to better study the dynamics of hydrogeneous fluids in the matrix of dense and opaque materials. We review recent instrumentation and method improvements to the neutron imaging facilities NEUTRA and ICON at Paul Scherrer Institute. The improvements give us higher spatial resolution making it possible to follow finer details and faster acquisition to increase the CT volume capture rate. The combination with new reconstruction techniques improve the information output with less acquired projection data and hence providing higher volume rates. Bi-modality is a further option to provide more information about the sample and the processes taking place. These features make new neutron imaging experiments to investigate the fluid distribution in porous samples possible. We demonstrate the performance on a selection of experiments performed at our neutron imaging instruments.
[The application of air-lift loop column filling with porous carrier in wastewater treatment].
Fan, Y; Ding, F; Yang, H; Chen, S; Zhang, W; Xing, X
2001-09-01
An air lift loop reactor filling with porous carrier particles was utilized as aeration column. Experiments were carried out in wide operating conditions. The experimental results showed that in the range of gas flow rate from 0.117 to 0.156 m3/(min.m3), a higher efficiency of removal of ammonium-N was achieved, and when the gas flow rate was above 0.039 m3/(min.m3), the COD was completely degraded in about 1 h. The filling ratio of the porous carriers in the column was an important factor for the removal of C and N compounds, and a filling ratio of 15% was proved to be most suitable in the operation ranges. The experimental results also indicated that the effect of aeration temperature on the removal efficiency was significant and the highest efficiency was obtained at around 25 degrees C. PMID:11769236
Method of dispensing droplets to penetration-resistive mediums. [Patent application
Fowler, V.L.; Ryon, A.D.; Haas, P.A.
1982-06-10
Uniform, monosized microspheroids are produced in a gelation medium characterized by a high resistance to surface penetration by reducing the effect of impact on entry of the droplets into the medium by contacting the droplet with a stream of medium and by introducing the resulting stream into a gelation column.
Preparation of porous nickel-titania cermets and their application to anode materials
Taimatsu, H.; Kudo, K.; Kaneko, H.; Matsukaze, N.; Iwata, T.
1995-12-31
Porous nickel-titania cermets have been prepared as new-type anode materials for solid oxide fuel cells using the solid-state displacement reaction method. The microstructures of the cermets were interwoven aggregate-type, differently from those of conventional nickel-YSZ cermets: nickel and titania phases three-dimensionally entangled each other. These cermets revealed good properties in compatibility of thermal expansion with YSZ, strength, gas permeation and electrical conduction.
Thermally modulated porous silica multispectral filters and their application in remote imaging.
Garcia Sega, Adrian; King, Brian H; Lee, Jessica Y; Sailor, Michael J; Miskelly, Gordon M
2013-09-24
We report a thermally tunable multispectral imaging filter based on reversible condensation of volatile organic fluids within a nanoporous one-dimensional photonic crystal. The photonic crystal (optical rugate filter) comprises oxidized porous silicon, prepared by electrochemical etch of silicon and subsequent air oxidation (porous silica rugate filter, pSiF). The reflectance spectrum of the pSiF is designed and constructed to match two of the red emission bands of the luminescent complex europium(III) tris-dipicolinate, [Eu(dpa)3](3-), which has been used as an indicator for anthrax spores. When the pSiF is fitted with a thermoelectric Peltier cooler/heater and sealed in a container with 2-propanol vapor, microcapillary effects drive the temperature-dependent condensation/evaporation of 2-propanol into/out of the porous nanostructure. Thermal cycling experiments show that the wavelengths of the spectral bands of the pSiF are reversibly tuned by ±35 nm for a temperature change of ±40 °C. Difference images of a UV-illuminated scene containing the [Eu(dpa)3](3-) target, obtained by reflection from pSiF that is continuously thermally cycled through the emission bands of the dye, show that the target can be discriminated from the background or from control targets with overlapping but dissimilar luminescence spectra. PMID:23968219