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.
NASA Astrophysics Data System (ADS)
Miller, C. T.; Gray, W. G.; McClure, J. E.; Dye, A. L.; Weigand, T. M.; Hauswirth, S.; Schultz, P. B.
2015-12-01
The thermodynamically constrained averaging theory (TCAT) has been developed over the last decade as a rigorous, formal method of deriving mechanistic mathematical models that describe a wide range of porous medium systems. TCAT models are consistent across length scales and provide explicit linkages between important physics known to be operative at the microscale and larger scale models. This produces a straightforward mechanism to evaluate macroscale quantities based on information generated from microscale simulations or experiments as way to inform model development. TCAT models inherently include interface, common curve, and common point properties in models that admit such entities. Elements of the TCAT theory are discussed, model hierarchies are derived and summarized, and specific aspects of TCAT models are examined in detail. Comparisons of TCAT model constructs with both experimental data and high-resolution microscale simulations illustrate that, contrary to common belief, virtually all capillary pressure vs. saturation data that is available for two-fluid-phase systems is not equilibrium data. Agreement between theory and observation for TCAT models is demonstrated, and aspects of the models posed are validated.
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.
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.
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
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.
Momentum transfer within a porous medium. II. Stress boundary condition
NASA Astrophysics Data System (ADS)
Minale, Mario
2014-12-01
In this paper, we derive a boundary condition at the interface between a free fluid and a porous medium stating that the stress is transferred both to the fluid within the porous medium and to the solid skeleton. A zero stress jump is obtained so that the total stress is preserved at the interface. The boundary condition is obtained with the volume averaging method following the approach of Ochoa-Tapia and Whitaker ["Momentum transfer at the boundary between a porous medium and a homogeneous fluid—I. Theoretical development," Int. J. Heat Mass Transfer 38(14), 2635-2646 (1995)], but starting from the momentum balances written on the fluid and on the solid of the porous region, the latter was derived in part I of this paper. In the same way, also the boundary condition at the interface between a porous medium and a homogeneous solid is obtained. Both boundary conditions describe the equilibrium of forces at the interface, where part of the stress is carried by the solid skeleton and part by the fluid within the porous medium. With the derived boundary conditions, together with the stress transfer equation within the solid skeleton, it is now possible to satisfy the overall force equilibrium on a shear cell partially filled with a porous medium.
Features of saturates mixture filtration in porous medium
NASA Astrophysics Data System (ADS)
Kachalov, V. V.; Maikov, I. L.; Molchanov, D. A.; Torchinsky, V. M.; Zaichenko, V. M.
2015-11-01
Consideration is given to the filtration process of the two-phase multicomponent mixture in the porous. It is shown that “mixture-porous medium” system becomes self- oscillating one during filtration process under special conditions when there is a region of retrograde condensation on the phase diagram of the mixture. A mathematical model of the hydrocarbon mixtures filtration process of the methane series has been developed and a computer program for calculating hydrodynamic and thermodynamic characteristics of this process under isothermal conditions with phase transitions has been created. Consideration is given to the basic mechanisms influencing the filtration dynamics. Limits of the model applicability are discussed. Condition range for occurring self-oscillatory properties in “mixture-porous medium” system is determined by medium permeability, viscosity of the mixture, initial and boundary filtration conditions. Experimental filtration research of mixtures “methane-n-butane”, “methane-propane-butane”, “methane-pentane” under the thermodynamic conditions corresponding retrograde condensation region on the phase diagram have shown validity of this model. It is argued that any multicomponent mixture having a retrograde condensation region on the phase diagram appears as self-oscillating system under right conditions.
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
Estimation of Porous Medium Tortuosity Directly from Flow Path Lines
NASA Astrophysics Data System (ADS)
Pakalapati, Suryanarayana; Celik, Ismail
2013-11-01
A thorough understanding of transport processes inside porous materials is vital for improving the efficiency of energy devices such as fuel cells and batteries. Continuum simulations of porous media make use of parameters such as porosity and tortuosity to account for the influence of the actual pore geometry and orientation on the transport processes. In most studies the tortuosity is treated as an adjustable parameter which is calibrated to match the predictions with the experiments. In this study a direct method is utilized to estimate the tortuosity of a porous medium. The actual geometry of a fuel cell electrode is obtained from an experimental study where the porous structure is reconstructed from slice images. The detailed geometry of porous medium is used to simulate fully resolved fluid flow through the pores. Stream lines are then generated which show the actual paths taken by the fluid flowing through the porous medium. The lengths of these path lines are then used to calculate the tortuosity of the porous medium by employing the actual definition of the tortuosity. It is shown that the tortuosities obtained in this way are smaller than the typical values reported in literature.
Studying Cracking and Oil Invasion in Porous Medium During Drying
NASA Astrophysics Data System (ADS)
Jin, Qiu
We study two interesting phenomena occurred during the evaporation of solvent in porous medium: first, the cracking behavior; and second, the expanding mechanism and the collecting methods of the non-evaporative phase. In the first part of this thesis, we visualize the cracking behavior of colloidal suspensions during drying by a confocal microscope. We develop an effective method which can completely eliminate cracking during drying: by adding emulsion droplets into colloidal suspensions, we can systematically decrease the amount of cracking, and eliminate it completely above a critical droplet concentration. We also find another effect that the emulsion droplets can bring: it varies the speed of air invasion and provides a powerful method to adjust drying rate. Besides, we investigate the samples' fundamental mechanical properties with a rheometer and clarify the underlying physical mechanism for the decreasing of crack amounts. With the effective control over cracking and drying rate, our study may find important applications in many drying and cracking related industrial processes. In the second part of the thesis, we conduct a study on the expanding mechanism and collecting methods of the non-evaporative phase in porous medium, which is inspired by a practical pollution problem that occurs when oil spills to the sandy beach. We build a system in a smaller scale to mimic the practical pollution and investigate the distribution change of the polluting phase as the flushing cycle increases. We find an obvious expansion of the polluting phase after several flushing cycles in both hydrophilic and hydrophobic porous media, but with different distributions and expanding behaviors. We explained this difference by analyzing the pressure distribution in the system at the pore level. Finally, we develop two methods to concentrate the polluting phase in some particular regions, which is beneficial to collect and solve the practical pollution problem.
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
Visualization studies of turbulent transition flows in a porous medium
NASA Technical Reports Server (NTRS)
Bilardo, V. J.
1983-01-01
Results are reported for flow-visualization studies of the flow regimes of water passing through a porous medium consisting of cylindrical glass and plexiglas rods arranged in a complex and fixed three-dimensional geometry. The Reynolds number (Re) varied from 50 to 700; the flow was visualized by injecting a 5% potassium permanganate dye solution into the pores and photographing the resulting dye streaklines with both a still camera and a movie camera. The results indicate that four distinct flow regimes exist in the porous medium: (1) Darcy or creeping flow up to Re = 3; (2) steady inertia-dominated laminar flow for Re = 3-150; (3) unsteady transitional laminar flow for Re = 150-250; and (4) fully turbulent flow for Re greater than 250. It is concluded that a laminar wake instability mechanism typical of the external flow about bluff bodies may be responsible for the overall transition from laminar to turbulent flow in porous media.
Sherwood, Juli L; Sung, James C; Ford, Roseanne M; Fernandez, Erik J; Maneval, James E; Smith, James A
2003-02-15
In this study, we demonstrate the application of immunomagnetic labeling and magnetic resonance imaging (MRI) for the noninvasive visualization of changes in bacterial density distributions as a function of time in a water-saturated porous medium. Magnetite particles (50-60 nm diameter) were attached via a monoclonal antibody to the surface' of Escherichia coli K12 NR50 cells. The cells maintained their motility after labeling, and the presence of the magnetite did not significantly alter cell swimming speed. Diffusive migration for both motile and nonmotile E. coli through a porous medium with a particle-diameter distribution of 250-300 microm was compared. The movement of the nonmotile cells was described by an effective random motility coefficient consistent with Brownian diffusion of a nonmotile colloid. An effective coefficient determined a priori from bacterial motility in an aqueous medium and properties of the porous medium adequately described the movement of the motile cells. The ability to noninvasively visualize bacterial concentrations within an opaque porous medium in real time provides researchers with a powerful tool for studying bacterial transport in porous media. This is important for understanding the impact of bacterial transport on remediation strategies for environmental cleanup of polluted groundwater.
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.
A generalization of averaging theorems for porous medium analysis
NASA Astrophysics Data System (ADS)
Gray, William G.; Miller, Cass T.
2013-12-01
The contributions of Stephen Whitaker to the rigorous analysis of porous medium flow and transport are built on the use of temporal and spatial averaging theorems applied to phases in representative elementary volumes. Here, these theorems are revisited, common point theorems are considered, extensions of existing theorems are developed to include the effects of lower dimensional entities represented as singularities, and a unified form of the theorems for phases, interfaces, common curves, and common points is established for both macroscale and mixed macroscale-megascale systems. The availability of the full set of theorems facilitates detailed analysis of a variety of porous medium systems. Explicit modeling of the physical processes associated with interfaces, common curves, and common points, as well as the kinematics of these entities, can be undertaken at both the macroscale and megascale based on these theorems.
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
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
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
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
Conservations laws for a porous medium equation through nonclassical generators
NASA Astrophysics Data System (ADS)
Gandarias, M. L.
2014-02-01
In Ibragimov (2007) [13] a general theorem on conservation laws was proved. In Gandarias (2011) and Ibragimov (2011) [7,15] the concepts of self-adjoint and quasi self-adjoint equations were generalized and the definitions of weak self-adjoint equations and nonlinearly self-adjoint equations were introduced. In this paper, we find the subclasses of nonlinearly self-adjoint porous medium equations. By using the property of nonlinear self-adjointness, we construct some conservation laws associated with classical and nonclassical generators of the differential equation.
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.
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
Laboratory Investigations of Steam Flow in a Porous Medium
NASA Astrophysics Data System (ADS)
Herkelrath, W. N.; Moench, A. F.; O'Neal, C. F., II
1983-08-01
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 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 10-25 times longer than predicted by conventional superheated steam flow 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. This function was assumed to be an 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.
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.
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.
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
Nonlinear self-adjointness and conservation laws for a porous medium equation with absorption
NASA Astrophysics Data System (ADS)
Gandarias, M. L.; Bruzón, M. S.
2013-10-01
We give conditions for a general porous medium equation to be nonlinear self-adjoint. By using the property of nonlinear self-adjointness we construct some conservation laws associated with classical and nonclassical generators of a porous medium equation with absorption.
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.
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
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; Miller, C T
2010-06-25
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 groundwater 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.
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
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
DeAngelis, D.L.; Yeh, G.T.; Huff, D.D.
1984-10-01
This report documents a model, FRACPORT, that simulates the transport of a solute through a fractured porous matrix. The model should be useful in analyzing the possible transport of radionuclides from shallow-land burial sites in humid environments. The use of the model is restricted to transport through saturated zones. The report first discusses the general modeling approach used, which is based on the Integrated Compartmental Method. The basic equations of solute transport are then presented. The model, which assumes a known water velocity field, solves these equations on two different time scales; one related to rapid transport of solute along fractures and the other related to slower transport through the porous matrix. FRACPORT is validated by application to a simple example of fractured porous medium transport that has previously been analyzed by other methods. Then its utility is demonstrated in analyzing more complex cases of pulses of solute into a fractured matrix. The report serves as a user's guide to FRACPORT. A detailed description of data input, along with a listing of input for a sample problem, is provided. 16 references, 18 figures, 3 tables.
Linear stability of a Berman flow in a channel partially filled with a porous medium
NASA Astrophysics Data System (ADS)
Deng, Chuntao; Martinez, D. Mark
2005-02-01
The temporal stability of similarity solutions for an incompressible fluid moving in a channel partially filled with a porous medium is analyzed. A constant wall suction acting on the bottom surface of the porous medium drives the fluid; the upper wall of the channel is impermeable. This work extends the work of King and Cox ["Asymptotic analysis of the steady-state and time-dependent Berman problem," J. Eng. Math. 39, 87 (2001)] to a wider class of similarity solutions where coupled flow, both above and through a porous medium, is considered. In this work, a similarity transform is proposed which satisfies both the Navier-Stokes equation in the clear fluid portion of the domain and the Brinkman extended Darcy law relationship in the porous medium. The boundary conditions between the clear fluid and porous regions are those outlined by Ochoa-Tapia and Whitaker ["Momentum transfer at the boundary between a porous medium and a homogeneous fluid I: theoretical development," Int. J. Heat Mass Transfer 38, 2635 (1995)]. The solutions of the steady flow are approximated analytically, in the limit of small wall suction, and numerically. Multiple steady-state solutions were found. The temporal stability of the solutions indicates turning-point bifurcations and instability only occurred with reverse flows.
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.
Migration of salt bands through a porous medium
NASA Astrophysics Data System (ADS)
Gitelman, E. M.; Dragila, M. I.
2010-12-01
In order to improve agricultural conditions in saline and sodic soils, we must better understand salt precipitation dynamics and the limiting kinetic mechanisms associated with the salinization process. We used laboratory techniques to monitor salt crystal formation in porous media cells under highly controlled conditions to examine the temporal evolution of salt crystallization. We found that salt crusts first precipitate on the surface and then move down through the porous media towards the water source forming bands collinear with equipotential moisture planes. We compare the kinetic data with a salt crystal formation and transport model and conclude that salt band formation and transport occurs via a cycle of vapor transport, osmotic deposition and deliquescence in the moving front, followed by evaporation and recrystallization in the receding front. Vapor density gradients and deliquescence kinetics controls the transport rate of salt bands through porous media.
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.
Thermal analysis of porous medium with ellipsoidal pores using a homogenization method
NASA Astrophysics Data System (ADS)
Asakuma, Yusuke; Yamamoto, Tsuyoshi
2016-10-01
Effective thermal conductivity including radiation is analyzed using a homogenization method. This method can precisely represent the microstructure of a porous medium with ellipsoidal pores. Here, the effects of parameters such as porosity, pore shape, pore distribution, and temperature of the porous medium on the conductivity are estimated to clarify the mechanisms in complex pore structures. For example, heat transfer by radiation does not dominate if the medium has pores of less than 1 mm in size. Moreover, the anisotropy of the effective thermal conductivity is found to depend on temperature, pore shape, pore size, and pore distribution.
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.
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.
Ordered porous materials for emerging applications.
Davis, Mark E
2002-06-20
"Space--the final frontier." This preamble to a well-known television series captures the challenge encountered not only in space travel adventures, but also in the field of porous materials, which aims to control the size, shape and uniformity of the porous space and the atoms and molecules that define it. The past decade has seen significant advances in the ability to fabricate new porous solids with ordered structures from a wide range of different materials. This has resulted in materials with unusual properties and broadened their application range beyond the traditional use as catalysts and adsorbents. In fact, porous materials now seem set to contribute to developments in areas ranging from microelectronics to medical diagnosis.
Analysis of shape of porous cooled medium for an imposed surface heat flux and temperature
NASA Technical Reports Server (NTRS)
Siegel, R.
1973-01-01
The surface of a porous cooled medium is to be maintained at a specified design temperature while being subjected to uniform heating by an external source. An analytical method is given for determining the shape of the medium surface that will satisfy these boundary conditions. The analysis accounts for temperature dependent variations of fluid density and viscosity and for temperature dependent matrix thermal conductivity. The energy equation is combined with Darcy's law in such a way that a potential can be defined that satisfies Laplace's equation. All of the heat-transfer and flow quantities are expressed in terms of this potential. The determination of the shape of the porous cooled region is thereby reduced to a free-boundary problem such as in inviscid free jet theory. Two illustrative examples are carried out: a porous leading edge with coolant supplied through a slot and a porous cooled duct with a rectangular outer boundary.
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.
The Analytical Solutions for Magnetohydrodynamic Flow of a Third Order Fluid in a Porous Medium
NASA Astrophysics Data System (ADS)
Hayat, Tasawar; Ellahi, Rahmat; Mahomed, Fazal Mehmood
2009-10-01
An analysis has been carried out for flow and heat transfer characteristics in a third grade fluid between two porous plates. The electrically conducting fluid fills the porous medium. The solutions have been developed for small porosity and magnetic field. Three flow problems are investigated and analytical expressions for the velocity field and temperature distribution are given for each case. Moreover, we recover and extend the results of Siddiqui et al. [1] by presenting exact solutions for the governing equations derived in [1].
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.
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
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.
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
Studying the flow dynamics of a karst aquifer system with an equivalent porous medium model.
Abusaada, Muath; Sauter, Martin
2013-01-01
The modeling of groundwater flow in karst aquifers is a challenge due to the extreme heterogeneity of its hydraulic parameters and the duality in their discharge behavior, that is, rapid response of highly conductive karst conduits and delayed drainage of the low-permeability fractured matrix after recharge events. There are a number of different modeling approaches for the simulation of the karst groundwater dynamics, applicable to different aquifer as well as modeling problem types, ranging from continuum models to double continuum models to discrete and hybrid models. This study presents the application of an equivalent porous model approach (EPM, single continuum model) to construct a steady-state numerical flow model for an important karst aquifer, that is, the Western Mountain Aquifer Basin (WMAB), shared by Israel and the West-Bank, using MODFLOW2000. The WMAB was used as a catchment since it is a well-constrained catchment with well-defined recharge and discharge components and therefore allows a control on the modeling approach, a very rare opportunity for karst aquifer modeling. The model demonstrates the applicability of equivalent porous medium models for the simulation of karst systems, despite their large contrast in hydraulic conductivities. As long as the simulated saturated volume is large enough to average out the local influence of karst conduits and as long as transport velocities are not an issue, EPM models excellently simulate the observed head distribution. The model serves as a starting basis that will be used as a reference for developing a long-term dynamic model for the WMAB, starting from the pre-development period (i.e., 1940s) up to date.
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.
Modification of Surface Density of a Porous Medium
NASA Technical Reports Server (NTRS)
Stackpoole, Margaret M. (Inventor); Espinoza, Christian (Inventor)
2016-01-01
A method for increasing density of a region of a porous, phenolic bonded ("PPB") body adjacent to a selected surface to increase failure tensile strength of the adjacent region and/or to decrease surface recession at elevated temperatures. When the surface-densified PPB body is brought together with a substrate, having a higher failure tensile strength, to form a composite body with a PPB body/substrate interface, the location of tensile failure is moved to a location spaced apart from the interface, the failure tensile strength of the PPB body is increased, and surface recession of the material at elevated temperature is reduced. The method deposits and allows diffusion of a phenolic substance on the selected surface. The PPB body and the substrate may be heated and brought together to form the composite body. The phenolic substance is allowed to diffuse into the PPB body, to volatilize and to cure, to provide a processed body with an increased surface density.
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
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.
Regularity for the porous medium equation with variable exponent: The singular case
NASA Astrophysics Data System (ADS)
Henriques, Eurica
We extend to the singular case the results of [E. Henriques, J.M. Urbano, Intrinsic scaling for PDEs with an exponential nonlinearity, Indiana Univ. Math. J. 55 (5) (2006) 1701-1721] concerning the regularity of weak solutions of the porous medium equation with variable exponent. The method of intrinsic scaling is used to show that local weak solutions are locally continuous.
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.
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.
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.
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
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.
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.
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
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.
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.
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.
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.
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,
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.
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.
Sanya, Arthur S O; Akowanou, Christian; Sanya, Emile A; Degan, Gerard
2014-01-01
The problems of steady film condensation on a vertical surface embedded in a thin porous medium with anisotropic permeability filled with pure saturated vapour are studied analytically by using the Brinkman-Darcy flow model. The principal axes of anisotropic permeability are oriented in a direction that non-coincident with the gravity force. On the basis of the flow permeability tensor due to the anisotropic properties and the Brinkman-Darcy flow model adopted by considering negligible macroscopic and microscopic inertial terms, boundary-layer approximations in the porous liquid film momentum equation is solved analytically. Scale analysis is applied to predict the order-of-magnitudes involved in the boundary layer regime. The first novel contribution in the mathematics consists in the use of the anisotropic permeability tensor inside the expression of the mathematical formulation of the film condensation problem along a vertical surface embedded in a porous medium. The present analytical study reveals that the anisotropic permeability properties have a strong influence on the liquid film thickness, condensate mass flow rate and surface heat transfer rate. The comparison between thin and thick porous media is also presented. PMID:26034679
The Diffusion Eigenstates in a Periodic Porous Medium with a Strong Surface Absorption
NASA Astrophysics Data System (ADS)
Bergman, D. J.; Dunn, K. J.; Latorraca, G. A.
1997-03-01
The Bloch diffusion eigenstates of a periodic porous medium, but with an otherwise arbitrary microstructure, and with strong absorption at the pore/matrix interface, have been calculated by expanding them in a series of eigenfunctions of an unphysical porous medium which has the same microstructure but no interface absorption, and where the diffusion also takes place inside the matrix with a diffusion coefficient that approaches infinity. The results are especially simple in the case where the interface absorption coefficient is infinite and for the q=0 eigenstates, but are very accurate also for large but finite rho and arbitrary q-vectors. The results of such calculations are compared with previous calculations that were limited to the regime of low interface absorption.
Experimental investigations of heat transport dynamics in a 1D porous medium column
NASA Astrophysics Data System (ADS)
Cherubini, Claudia; Pastore, Nicola; Giasi, Concetta I.; Allegretti, Nicoletta M.
2016-04-01
A laboratory physical model has been set up to analyse the forced convective flow and the related heat transport dynamics through a 1d porous medium column. In particular, the experiments regard the observation of thermal breakthrough curves obtained through a continuous flow injection in correspondence of eight thermocouple positioned uniformly along a thermally isolated column of porous medium. The experiment has been conducted for different flow rates in order to investigate the critical issues regarding heat transport phenomena such as the influence of non-linear flow regime, the relationship between the thermal dispersion with the flow velocity and the validity of the local thermal equilibrium assumption between the fluid and solid phase. The results emphasize the magnitude of the errors of the commonly used assumptions in the numerical modelling of heat transport.
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.
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
Dynamics of shear layers at the interface of a highly porous medium and a pure fluid
NASA Astrophysics Data System (ADS)
Antoniadis, P. D.; Papalexandris, M. V.
2015-01-01
In this paper, we report on shear flows in domains that contain a macroscopic interface between a highly porous medium and a pure fluid. Our study is based on the single-domain approach, according to which, the same set of governing equations is employed for both inside the porous medium and in the pure-fluid domain. In particular, we introduce a mathematical model for the flows of interest that is derived directly from a continuum theory for fluid-saturated granular materials. The resulting set of equations is a variation of the well-known unsteady Darcy-Brinkman model. First, we employ this model to perform a linear stability analysis of inviscid shear layers over a highly porous medium. Our analysis shows that such layers are unconditionally unstable. Next, we present results from numerical simulations of temporally evolving shear layers in both two and three dimensions. The simulations are performed via a recently designed algorithm that employs a predictor-corrector time-marching scheme and a projection method for the computation of the pressure field on a collocated grid. According to our numerical predictions, the onset of the Kelvin-Helmholtz instability leads to the formation of vortices that extend to both sides of the material interface, thus producing substantial recirculation inside the porous medium. These vortices eventually merge, leading to significant growth of the shear layer and, in three dimensional flows, transition to turbulence. The dynamics of the shear layers, including growth rate and self-similarity, is presented and analysed. Finally, the structure of these layers is described in detail and compared to the one of plain mixing layers.
NASA Astrophysics Data System (ADS)
Walker, R. C.; Hofstee, C.; Dane, J. H.; Hill, W. E.
1998-10-01
Although surfactant enhanced remediation of nonaqueous phase liquids (NAPLs) by pump-and-treat technology has been studied extensively in the laboratory with one-dimensional columns, very few multi-dimensional investigations have been reported. In this study we focus on the removal of perchloroethylene (PCE) from a two-dimensional, saturated porous medium containing a low permeability sand layer situated in an otherwise high permeability sand. A PCE spill was applied at the surface of the porous medium and allowed to redistribute until static equilibrium was achieved. The porous medium was then flushed with various surfactant and co-solvent formulations injected at the PCE source location and extracted at the bottom of the porous medium using a configuration similar to that of Abdul and Ang [Abdul, S.A., Ang, C.C., 1994. In situ surfactant washing of polychlorinated biphenyls and oils from a contaminated field site: Phase II. Pilot study. Ground Water 32, 727-734]. Effluent samples were analyzed for dissolved PCE concentrations. Volumetric water and PCE content values were determined at a number of locations by means of dual-energy gamma radiation measurements. Once surfactant flushing had started, PCE moved as a distinct separate phase ahead of the surfactant front. Most of this downward moving PCE accumulated on top of the low permeability sand layer. Some PCE, however, passed quickly through this layer and subsequently through the high permeability sand below it. Movement of some of the PCE into and through the low permeability sand layer was attributed to local heterogeneities combined with reduced interfacial tensions associated with the surfactant formulation. Clean-up of PCE in most of the high permeability sand was considered to be effective. PCE accumulated on top of the fine layer, however, posed a significant challenge to remediation and required several pumping configurations and surfactant/co-solvent formulations before most of it was removed.
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.
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.
Bleyer, J; Coussot, P
2014-06-01
We study the flow, through a model two-dimensional porous medium, of Newtonian fluids, power-law fluids, and viscoplastic fluids in the laminar regime and with moderate or dominant effects of the yielding term. A numerical technique able to take properly into account yielding effects in viscoplastic flows without any regularization is used to determine the detailed flow characteristics. We show that as soon as the distance between the disks forming the porous medium is sufficiently small, the velocity field and in particular the distribution function of the velocity of these different fluids in a wide range of flow regimes are similar. Moreover, the volume fraction of fluid at rest is negligible even at low flow rate. Thus the non-Newtonian character of a fluid flowing through such a complex geometry tends to be broken. We suggest that this is due to the fact that in a flow through a channel of rapidly varying cross section, the deformation, and thus the flow field, is imposed on the fluid, a situation that is encountered almost everywhere in a porous medium. These results make it possible to deduce a general expression for Darcy's law of these fluid types and estimate the parameters appearing in this expression.
Migration of Air Flow in Non-Fixed Saturated Porous Medium
NASA Astrophysics Data System (ADS)
Kong, X.; Fritz, S.; Kinzelbach, W.
2008-12-01
Two phase flow in porous media is of importance in a number of processes relevant in environmental engineering. The study of gas movement following injection into liquid saturated porous media is an active area of exploration for theoretical and practical reasons, e.g., in air-sparging, oil recovery, and bio-filter. A set of two-dimensional laboratory visualization experiments reveals a previously unrecognized gas-flow instability in a liquid-saturated porous medium packed by its own weight. The medium is made of crushed fused silica glass and saturated with a glycerine-water solution for refractive-index-matching. The interaction of the air flow injected at the bottom and the matrix (porous medium) structure leads to mobilization of the matrix and an instability, which causes the air channel to migrate. The instability of air-channel migration differs significantly from the gas-flow instability in a fixed matrix described in previous research. The migration of the air channel appears as a sequence of former channels collapsing and new channels opening. This process is characterized by the reorganization of the matrix, and the switching between channelized flow and pulsating slug flow. The channel migration comes to a stop after some time, leaving one thin and stable channel. The process is studied by calculating the cumulated lateral movement distance of channel and the lateral width of the area affected by the migration. A dimensionless number is defined to describe the migration. It is observed to be a function of grain size, height of bed, and air flow rate.
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.
On NaCl efflorescence formation and growth at the surface of a porous medium
NASA Astrophysics Data System (ADS)
Veran-Tissoires, S.; Marcoux, M.; Prat, M.
2012-04-01
Rocks or building materials are often altered by the presence of dissolved salts. Salt precipitation is one of the main processes damaging the porous matrix. In this context, our study focuses on salt crystallization which results from evaporation at the surface of porous media. These crystallized salt structures are called efflorescence. Efflorescence is an important issue for the conservation of old paintings and frescoes. The challenge is to understand why these structures do not form everywhere at the porous medium surface but at some specific locations and why there exists an exclusion distance around an efflorescence structure where no new efflorescence forms. These behaviours are explained from a visualization experiment, pore-network simulations and a simple efflorescence growth model. A wicking/evaporating experiment is conducted on packings of glass beads (~1mm diameter) contained in a hollow cylinder. The porous sample is open at the bottom where it is in contact with a brine solution. The upper surface is open to external dry air. In this configuration, the sample remains fully saturated and salt precipitation takes place at the sample surface. This setup is set in an enclosure where temperature is kept constant and dry air is maintained, which imposes a nearly uniform evaporation flux over the sample surface. After a few days of evaporation, efflorescence structures appear, grow and remain discrete, i.e. continue to form individual halite structures. Simulations with a 3D pore network model enable us to show that discrete location of efflorescence results from small scale heterogeneities of the beads packing. Locally some menisci are connected to smaller pores which enhance salt transport by advection. The second objective of the study is to understand the mechanism which makes the efflorescence to growth under the form of a set of individual structures. By studying numerically the growth of one efflorescence structure, we observe a global increase of
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.
Transport of bare and capped zinc oxide nanoparticles is dependent on porous medium composition
NASA Astrophysics Data System (ADS)
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.
Natural convection heat transfer of nanofluids along a vertical plate embedded in porous medium.
Uddin, Ziya; Harmand, Souad
2013-02-07
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.
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)
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.
[Applications of Porous Scaffolds in Muscle Tissue Engineering].
Sun, Yan; Zou, Ling; Liu, Jun
2015-12-01
Scaffold is one of the key elements required for tissue engineering. Porous scaffolds have several special advantages for muscle tissue engineering, and they are beneficial to cell survival, myogenic differentiation, and vascular ingrowth. The performance of porous scaffolds is closely related to the property of the biomaterials used. Additionally, the pore size and porosity may affect cell adhesion, proliferation, and differentiation. This review focuses on the application of porous scaffolds in muscle tissue engineering, including their categories, application, and advantages.
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.
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.
Hall effects on peristaltic flow of a Maxwell fluid in a porous medium
NASA Astrophysics Data System (ADS)
Hayat, T.; Ali, N.; Asghar, S.
2007-04-01
This work is concerned with the peristaltic transport of an incompressible, electrically conducting Maxwell fluid in a planar channel. The flow in the porous space is due to a sinusoidal wave traveling on the channel walls. The Hall effect is taken into account and permeability of porous medium is considered uniform. Modified Darcy's law has been used to model the governing equation. An analytical solution is obtained, which satisfies the momentum equation for the case in which the amplitude ratio is small. The present theoretical model may be considered as mathematical representation to the case of gall bladder and bile duct with stones and dynamics of blood flow in living creatures. Finally, the graphical results are reported and discussed for various values of the physical parameters of interest.
Intracranial stents being modeled as a porous medium: flow simulation in stented cerebral aneurysms.
Augsburger, L; Reymond, P; Rufenacht, D A; Stergiopulos, N
2011-02-01
Intracranial aneurysms may be treated by flow diverters, alternatively to stents and coils combination. Numerical simulation allows the assessment of the complex nature of aneurismal flow. Endovascular devices present a rather dense and fine strut network, increasing the complexity of the meshing. We propose an alternative strategy, which is based on the modeling of the device as a porous medium. Two patient-specific aneurysm data sets were reconstructed using conventional clinical setups. The aneurysms selection was done so that intra-aneurismal flow was shear driven in one and inertia driven in the other. Stents and their porous medium analog were positioned at the aneurysm neck. Physiological flow and standard boundary conditions were applied. The comparison between both approaches was done by analyzing the velocity, vorticity, and shear rate magnitudes inside the aneurysm as well as the wall shear stress (WSS) at the aneurysm surface. Simulations without device were also computed. The average flow reduction reaches 76 and 41% for the shear and inertia driven flow models, respectively. When comparing the two approaches, results show a remarkable similarity in the flow patterns and magnitude. WSS, iso-velocity surfaces and velocity on a trans-sectional plane are in fairly good agreement. The root mean squared error on the investigated parameters reaches 20% for aneurysm velocity, 30.6% for aneurysm shear rate, and 47.4% for aneurysm vorticity. It reaches 20.6% for WSS computed on the aneurysm surface. The advantages of this approach reside in its facility to implement and in the gain in computational time. Results predicted by the porous medium approach compare well with the real stent geometry model and allow predicting the main effects of the device on intra-aneurismal flow, facilitating thus the analysis.
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
NASA Astrophysics Data System (ADS)
Naftaly, Aviv; Dror, Ishai; Berkowitz, Brian
2016-07-01
A continuous time random walk particle tracking (CTRW-PT) method was employed to model flow cell experiments that measured transport of engineered nanoparticles (ENPs) in a reactive porous medium. The experiments involved a water-saturated medium containing negatively charged, polyacrylamide beads, resembling many natural soils and aquifer materials, and having the same refraction index as water. Negatively and positively charged ENPs were injected into a uniform flow field in a 3-D horizontal flow cell, and the spatial and temporal concentrations of the evolving ENP plumes were obtained via image analysis. As a benchmark, and to calibrate the model, Congo red tracer was employed in 1-D column and 3-D flow cell experiments, containing the same beads. Negatively charged Au and Ag ENPs demonstrated migration patterns resembling those of the tracer but were slightly more dispersive; the transport was well represented by the CTRW-PT model. In contrast, positively charged AgNPs displayed an unusual behavior: establishment of an initial plume of essentially immobilized ENPs, followed by development of a secondary, freely migrating plume. The mobile plume was found to contain ENPs that, with aging, exhibited aggregation and charge inversion, becoming negatively charged and mobile. In this case, the CTRW-PT model was modified to include a probabilistic law for particle immobilization, to account for the decreasing tendency (over distance and time) of the positively charged AgNPs to attach to the porous medium. The agreement between experimental results and modeling suggests that the CTRW-PT framework can account for the non-Fickian and surface-charge-dependent transport and aging exhibited by ENPs in porous media.
Iontophoresis from a micropipet 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
2012-03-01
Iontophoresis uses electricity to deliver solutes into living tissue. Often, iontophoretic ejections from micropipets 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 in gels and cultures of hippocampus can be predicted semiquantitatively.
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
Numerical solutions for steady thermal convection from a concentrated source in a porous medium
Hickox, C.E.; Watts, H.A.
1980-06-01
Solutions for the steady, axisymmetric velocity and temperature fields associated with a point source of thermal energy in a fluid-saturated porous medium are obtained numerically through use of similarity transformations. The two cases considered are those of a point source located on the lower, insulated boundary of a semi-infinite region and a point source embedded in an infinite region. Numerical results are presented from which complete descriptions of the velocity and temperature fields can be constructed for Rayleigh numbers ranging from 10/sup -3/ to 10/sup 2/.
Weak self-adjointness and conservation laws for a porous medium equation
NASA Astrophysics Data System (ADS)
Gandarias, M. L.
2012-06-01
The concepts of self-adjoint and quasi self-adjoint equations were introduced by Ibragimov (2006, 2007) [4,7]. In Ibragimov (2007) [6] a general theorem on conservation laws was proved. In Gandarias (2011) [3] we generalized the concept of self-adjoint and quasi self-adjoint equations by introducing the definition of weak self-adjoint equations. In this paper we find the subclasses of weak self-adjoint porous medium equations. By using the property of weak self-adjointness we construct some conservation laws associated with symmetries of the differential equation.
When Air is Injected into Mobile Liquid-saturated Porous Medium
NASA Astrophysics Data System (ADS)
Kong, X.-Z.; Kinzelbach, W.; Stauffer, F.
2009-04-01
The study of gas movement following injection into liquid saturated porous media is an active area of exploration for theoretical and practical reasons, e.g., in air-sparging, oil recovery, and bio-filter. Here, we report a set of two-dimensional laboratory visualization experiments by injecting air into a vertically placed granular medium. The medium is made of crushed fused silica glass and saturated with a glycerine-water solution for refractive-index-matching. We learn that: i) A previously unrecognized gas-flow instability was observed. The interaction of the injected air flow and the medium structure leads to mobilization of the medium and an instability, which causes the air channel to migrate. This instability is dominated by a dimensionless number α, which can be interpreted as a normalization of a critical velocity with a dipole velocity for saturated conditions. The channel migration appears as a sequence of previous channels collapsing and new channels opening. ii) The channel migration comes to a stop after some time, leaving one stable preferential channel for air flow. Furthermore, the grains' packing is compacted due to a rearrangement process. The compacted process is indicated by a set of tracing experiments. iii) Due to a mobilization of the granular medium, segregation on grain size occurs depending on a critical grain size, below which the coarser grains tend to accumulate at the downstream end of the preferred air pathway, and above which the finer grains tend to accumulate there.
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.
Tsimpanogiannis, Ioannis N.; Yortsos, Yanis C.
2001-08-15
This report, focuses on the isothermal gas phase growth from a supersaturated, slightly compressible, binary liquid in a porous medium. This is driven by mass transfer, the extent of which is controlled by the application of either a constant-rate decline of the system pressure or the withdrawal of the liquid at a constant rate. This report deals with the first process. Pressure depletion due to constant-rate liquid withdrawal is analyzed in a companion report .
The effect of critical pH on virus fate and transport in saturated porous medium.
Guan, Huade; Schulze-Makuch, Dirk; Schaffer, Steve; Pillai, Suresh D
2003-01-01
Several viral transport experiments were conducted in a model aquifer 1 m long, using bacteriophages MS2 and phiX174 at various pH (4.6 to 8.3) conditions, to increase our understanding of virus behavior in ground water. The results indicate the existence of a critical pH at which the virus behavior changes abruptly. This is supported by data from field and batch experiments. The critical pH is determined to be 0.5 unit below the highest isoelectric point of the virus and porous medium. When water pH is below the critical pH, the virus has an opposite charge to at least one component of the porous medium, and is almost completely and irreversibly removed from the water. This suggests that electrostatic attraction at a subcritical water pH condition is an important factor controlling virus attenuation in ground water. The concept of critical pH can assist in the design of geologic barriers for preventing viral contamination in ground water.
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.
NASA Astrophysics Data System (ADS)
Tsiberkin, K. B.
2016-08-01
The structure of a homogeneous liquid flow at the interface with a porous medium saturated with the same liquid has been studied in the boundary layer approximation. The porous medium is described by the Brinkman model. Self-similar equations of motion in the form of Blasius equation have been found, and their numerical solutions have been presented. An expression for the force exerted by the flow on the porous medium is derived.
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
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.
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.
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.
NASA Astrophysics Data System (ADS)
Degan, Gérard; Sanya, Arthur; Akowanou, Christian
2016-10-01
This work analytically investigates the problem of steady film condensation along a vertical surface embedded in an anisotropic porous medium filled with a dry saturated vapor. The porous medium is anisotropic in permeability whose principal axes are oriented in a direction which is oblique to the gravity vector. On the basis of the generalized Darcy's law and within the boundary layer approximations, similar solutions have been obtained for the temperature and flow patterns in the condensate. Moreover, closed form solutions for the boundary layer thickness and heat transfer rate have been obtained in terms of the governing parameters of the problem.
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.
Modeling tree water flow as an unsaturated flow through a porous medium.
Aumann, Craig A; Ford, E David
2002-12-21
The electric circuit analogy has had a profound influence on how tree physiologists measure, model and think about tree water flow. For example, previous models that attempt to account for changes in saturation use the electric circuit analogy to define capacitance as the change in saturation per change in pressure. Given that capacitance is constant, this relationship implies that subjecting a block of wood to a pressure of -2.5 MPa for 2 min results in the same change in saturation as subjecting the same block to the same pressure for 2 days. Given the definition of capacitance, it is unclear how the electric circuit analogy could be used to predict changes in saturation separately from changes in pressure. The inadequacies in the electric circuit analogy discussed in this paper necessitate a new theory of tree water flow that recognizes the sapwood as being a porous medium and explicitly deals with the full implications of the unsaturated flow occurring in the sapwood. The theory proposed in this paper combines the Cohesion theory with a mathematical theory of multiphase flow through porous media. Based on this theory, both saturated and unsaturated tree water flow models are presented. Previous partial differential equation models of tree water flow based on the electric circuit analogy are shown to be mathematically equivalent to the model of saturated porous flow. The unsaturated model of tree water flow explicitly models the pressure profile and the rates of change in saturation and specific interfacial area (a measure of how the water in the unsaturated sapwood is partitioned between mobile and immobile components). The unsaturated model highlights the differences between saturated and unsaturated flow and the need to measure the variables governing tree water flow at higher spatial and temporal resolutions. PMID:12425977
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
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.
Film Flow Dominated Simultaneous Flow of Two Viscous Incompressible Fluids Through a Porous Medium
NASA Astrophysics Data System (ADS)
Aursjø, Olav; Erpelding, Marion; Tallakstad, Ken; Flekkøy, Eirik; Hansen, Alex; Måløy, Knut Jørgen
2014-11-01
We present an experimental study of two-phase flow in a quasi-two-dimensional porous medium. The two phases, a water-glycerol solution and a commercial food grade rapeseed/canola oil, having an oil to water-glycerol viscosity ratio of 1.3, are injected simultaneously into a Hele-Shaw cell with a mono-layer of randomly distributed glass beads. The two liquids are injected into the model from alternating point inlets. Initially, the porous model is filled with the water-glycerol solution. We observe that after an initial transient state, an overall static cluster configuration is obtained. While the oil is found to create a connected system spanning cluster, a large part of the water-glycerol clusters left behind the initial invasion front is observed to remain immobile throughout the rest of the experiment. This could suggest that the water-glycerol flow-dynamics is largely dominated by film flow. The flow pathways are thus given through the dynamics of the initial invasion. This behavior is quite different from that observed in systems with large viscosity differences between the two fluids, and where compressibility plays an important part of the process.
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.
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.
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
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.
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
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.
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
A Newton-Krylov solution to the porous medium equations in the agree code
Ward, A. M.; Seker, V.; Xu, Y.; Downar, T. J.
2012-07-01
In order to improve the convergence of the AGREE code for porous medium, a Newton-Krylov solver was developed for steady state problems. The current three-equation system was expanded and then coupled using Newton's Method. Theoretical behavior predicts second order convergence, while actual behavior was highly nonlinear. The discontinuous derivatives found in both closure and empirical relationships prevented true second order convergence. Agreement between the current solution and new Exact Newton solution was well below the convergence criteria. While convergence time did not dramatically decrease, the required number of outer iterations was reduced by approximately an order of magnitude. GMRES was also used to solve problem, where ILU without fill-in was used to precondition the iterative solver, and the performance was slightly slower than the direct solution. (authors)
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.
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.
Breaking of non-Newtonian character in flows through a porous medium.
Chevalier, T; Rodts, S; Chateau, X; Chevalier, C; Coussot, P
2014-02-01
From NMR measurements we show that the velocity field of a yield stress fluid flowing through a disordered well-connected porous medium is very close to that for a Newtonian fluid. In particular, it is shown that no arrested regions exist even at very low velocities, for which the solid regime is expected to be dominant. This suggests that these results obtained for strongly nonlinear fluid can be extrapolated to any nonlinear fluid. We deduce a generalized form of Darcy's law for such materials and provide insight into the physical origin of the coefficients involved in this expression, which are shown to be moments of the second invariant of the strain rate tensor.
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.
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.
Magnetic field nonuniformities and NMR of protons diffusing in a porous medium.
Bergman, D J; Dunn, K J; LaTorraca, G A
1996-01-01
Magnetic field inhomogeneity can arise either because of an externally applied field gradient or because of spatial variations in magnetic susceptibility. The latter are most important when the solid matrix includes paramagnetic substances and when the uniform applied field, and, consequently, also the Larmor precession frequency are very large. Both types of field inhomogeneity add extra phase shifts to the precessing spins. These phase shifts vary with time and position in a complex and random fashion as a result of the diffusive motion of the spins. We have studied these effects by performing detailed calculations for the case of a fluid filled porous medium with a periodic microstructure. Special attention was devoted to the question of whether the statistical distribution of the phase shifts encountered in a Hahn spin echo experiment or in a Carr-Purcell-Meiboom-Gill (CPMG) spin-echo train can be approximated as a Gaussian. The mean square phase shift is measured in such experiments as an enhanced relaxation rate of the precessing transverse magnetization. We determine this mean square phase shift for periodic composites from the diffusion eigenstates, which were calculated using a previously developed Fourier expansion method. The enhanced relaxation rate depends on the echo spacing time tau in a way that can be correlated with important length scales of the porous microstructure. Those correlations can be extended also to disordered microstructures, like the ones that are found in natural rocks. We compare these theoretically predicted correlations with CPMG measurements performed on protons in laboratory samples of brine saturated sandstone. PMID:8970094
Park, Byung Hyun; Lee, Myong-Hwa; Kim, Sang Bum; Kim, Gyung Soo; Jo, Young Min
2010-02-01
The high costs of ceramic and Teflon filter media for hot gas cleaning has limited their industrial applications. This paper presents a foam coating technology that can be used to produce an inexpensive and highly efficient filter for industrial applications. A new apparatus was designed and built that coats porous glass mats with liquid-phase polytetrafluoroethylene (PTFE). The machine generates bubbles, enables the formation of uniform micropores less than 45 microm in diameter, and produces a product with air permeability greater than 5.5 cm3/cm2/sec. The resulting filter was found to be thermally stable up to 270 degrees C without any visible distortion and was comparable in dust collection efficiency to other commercial filter media. In addition, its de-dusting efficiency was greater than 85%, which is similar to that of other test filter media.
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
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.
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
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)
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
Nakayama, A. )
1993-05-01
Convection problems associated with concentrated heat sources within fluid-saturated porous media are of great practical significance, for there are a number of practical applications in geophysics and energy-related problems, such as recovery of petroleum resources, geophysical flows, cooling of underground electric cables, and environmental impact of buried heat generating waste. In this note, a boundary layer analysis is presented for free convection from a point heat source embedded in a porous medium saturated with a non-Newtonian power-law fluid. The governing equations are found to possess a similarity solution for an arbitrary value of the power-law index. Closed-form solutions are presented for both flow and temperature fields, and the effects of pseudoplasticity on the plumes are examined. 17 refs., 5 figs.
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.
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.
Dependence of the conductivity of a porous medium on electrolyte conductivity
NASA Astrophysics Data System (ADS)
Johnson, David Linton; Sen, Pabitra N.
1988-03-01
For an arbitrary geometry of insulating, but charged, objects immersed in an electrolyte for which diffusion currents are important, the mathematical problem of the dc electrical conductivity can be mapped onto that of an ordinary conduction problem without diffusion currents but with a conductive surface layer. As a result, using variational arguments we can prove two general theorems which hold irrespective of the geometry of the porous medium: (a) At high salinities, so that the conductivity of the pore fluid, σf, is large, the conductivity of the system as a whole, σeff, is a linear function of σf, with a slope of 1/F and with an offset proportional to 1/Λ. (b) For lower values of salinity, σeff as a function of σf is convex-up as long as the conductivity within the double-layer region is independent of the salinity of the pore fluid. The parameters F and Λ introduced previously [D. L. Johnson, J. Koplik, and L. M. Schwartz, Phys. Rev. Lett. 57, 2564 (1986); D. L. Johnson, J. Koplik, and R. Dashen, J. Fluid Mech. 176, 379 (1987)] are hereby shown to be relevant to the electrolyte problem. An illustration of an ordered suspension is given to show how to implement these ideas.
Interstitial fluid flow in tendons or ligaments: a porous medium finite element simulation.
Butler, S L; Kohles, S S; Thielke, R J; Chen, C; Vanderby, R
1997-11-01
The purpose of this study is to describe interstitial fluid flow in axisymmetric soft connective tissue (ligaments or tendons) when they are loaded in tension. Soft hydrated tissue was modelled as a porous medium (using Darcy's Law), and the finite element method was used to solve the resulting equations governing fluid flow. A commercially available computer program (FiDAP) was used to create an axisymmetric model of a biomechanically tested rat ligament. The unknown variables at element nodes were pressure and velocity of the interstitial fluid (Newtonian and incompressible). The effect of variations in fluid viscosity and permeability of the solid matrix was parametrically explored. A transient loading state mimicking a rat ligament mechanical experiment was used in all simulations. The magnitude and distribution of pressure, stream lines, shear (stress) rate, vorticity and velocity showed regular patterns consistent with extension flow. Parametric changes of permeability and viscosity strongly affected fluid flow behaviour. When the radial permeability was 1000 times less than the axial permeability, shear rate and vorticity increased (approximately 5-fold). These effects (especially shear stress and pressure) suggested a strong interaction with the solid matrix. Computed levels of fluid flow suggested a possible load transduction mechanism for cells in the tissue.
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
NASA Astrophysics Data System (ADS)
Saller, S. P.; Ronayne, M. J.; Long, A. J.
2013-12-01
Karst conduits are commonly treated as high-conductivity zones in equivalent porous medium (EPM) models. In this study, an EPM model for a Paleozoic age carbonate aquifer was updated to include discrete conduits, and flow was simulated using the coupled continuum pipe-flow method. The modeled area, encompassing 2000 square km of the Madison aquifer in western South Dakota (USA), includes four karst springs with contributing conduit networks. The updated model considered the same observation data that were used to calibrate the EPM model: measured hydraulic heads at matrix observation wells and estimated springflow. Adjusted parameters included the conduit locations and hydraulic properties, as well as the matrix hydraulic conductivity distribution. Inferred karst pathways from environmental tracer analysis were used to guide the placement of conduits. The new coupled continuum pipe-flow model is characterized by a simpler conductivity distribution; extreme high-K values used in the EPM model are not necessary when conduit flow is explicitly simulated. Results are presented to illustrate the influence of conduits on simulated flow behavior.
NASA Astrophysics Data System (ADS)
Chen, Daiquan
Wood's metal injection method is used to perform imbibitions and drainage of ethylene glycol into natural samples of Berea sandstone. Results on the measurement of interfacial area per volume (IAV) in this natural three-dimensional porous medium by the method of image analysis are presented. In Wood's metal injection experiments, Wood's metal was used to represent a non-wetting fluid and ethylene glycol (EG) was used to represent a wetting phase fluid. To determine the IAV for a Wood's metal injected sample, images of the Wood's-metal-injected core were taken with a Scanning Electron Microscope (SEM). This is the first attempt to perform IAV measurements within Berea sandstone based on a large quantity of SEM images. Measurements were performed on two-dimensional micro-models to quantify interfacial area per volume for known pore geometry as a function of fluid pressure and saturation. The transparent micro-models make it possible to visualize and quantify the fluid distributions within the samples and study the detailed capillary pressure-saturation-IAV relationship of each micro-model. The results have shown that as porosity increases, the hysteresis of IAV-saturation relationship decreases. The difference between the drainage and imbibition surfaces from the same sample is small. The theoretical capillary pressure values based on a theoretical equation cannot fit the measured values well and changes need to be made to this equation.
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}.
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.
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.
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.
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
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.
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...
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...
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)
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.
Ren, Dianjun; Smith, James A
2013-04-16
The retention and transport of silver nanoparticles (Ag-NPs) through a ceramic porous medium used for point-of-use drinking water purification is investigated. Two general types of experiments were performed: (i) pulse injections of suspensions of Ag-NPs in aqueous MgSO4 solutions were applied to the ceramic medium, and effluent silver was quantified over time; (ii) Ag-NPs were applied directly to the porous medium during fabrication using a paint-on, dipping, or fire-in method, a synthetic, moderately hard water sample with monovalent and divalent inorganic ions was applied to the ceramic medium, and effluent silver was quantified over time. These latter experiments were performed to approximate real-world use of the filter medium. For experiments with Ag-NPs suspended in the inflow solution, the percentage of applied Ag-NPs retained in the ceramic porous medium ranged from about 13 to 100%. Ag-NP mobility decreased with increasing ionic strength for all cases and to a lesser extent with increasing nanoparticle diameter. Citrate-capped particles were slightly less mobile than proteinate-capped particles. For ceramic disks fabricated with Ag-NPs by the paint-on and dipping methods (where the Ag-NPs are applied to the disks after firing), significant release of nanoparticles into the filter disk effluent was observed relative to the fire-in method (where the nanoparticles are combined with the clay, water, grog, and flour before firing). These results suggest that the fire-in method may be a new and significant improvement to ceramic filter design.
Borman, Vladimir D; Belogorlov, Anton A; Byrkin, Victor A; Tronin, Vladimir N
2013-11-01
An approach has been proposed for the description of the dispersion transition of a nonwetting liquid in confinement. This approach describes intrusion and extrusion processes for the ground state of a disordered porous medium, which is characterized by the formation of a fractal percolation cluster. The observed transition of the system of liquid nanoclusters in confinement to a metastable state in a narrow range of degrees of filling and temperatures has been explained by the appearance of a potential barrier owing to fluctuations of the collective "multiparticle interaction" of liquid nanoclusters in neighboring pores of different sizes on the shell of the fractal percolation cluster of filled pores. The energy of the metastable state forms a potential relief in the space of the porous medium with many maxima and minima. The volume of the dispersed liquid in the metastable state has been calculated within the analytical percolation theory for the ground state with the infinite percolation cluster. The extrusion-time distribution function of pores has been calculated. It has been found that the volume of the nonwetting liquid remaining in the porous medium decreases with time according to a power law. Relaxation in the system under study is a multistep process involving discontinuous equilibrium and overcoming of many local maxima of the potential relief. The formation of the metastable state of the trapped nonwetting liquid has been attributed to the nonergodicity of the disordered porous medium. The model reproduces the observed dependence of the volume of the dispersed liquid both on the degree of filling and on the temperature. PMID:24329223
Borman, Vladimir D; Belogorlov, Anton A; Byrkin, Victor A; Tronin, Vladimir N
2013-11-01
An approach has been proposed for the description of the dispersion transition of a nonwetting liquid in confinement. This approach describes intrusion and extrusion processes for the ground state of a disordered porous medium, which is characterized by the formation of a fractal percolation cluster. The observed transition of the system of liquid nanoclusters in confinement to a metastable state in a narrow range of degrees of filling and temperatures has been explained by the appearance of a potential barrier owing to fluctuations of the collective "multiparticle interaction" of liquid nanoclusters in neighboring pores of different sizes on the shell of the fractal percolation cluster of filled pores. The energy of the metastable state forms a potential relief in the space of the porous medium with many maxima and minima. The volume of the dispersed liquid in the metastable state has been calculated within the analytical percolation theory for the ground state with the infinite percolation cluster. The extrusion-time distribution function of pores has been calculated. It has been found that the volume of the nonwetting liquid remaining in the porous medium decreases with time according to a power law. Relaxation in the system under study is a multistep process involving discontinuous equilibrium and overcoming of many local maxima of the potential relief. The formation of the metastable state of the trapped nonwetting liquid has been attributed to the nonergodicity of the disordered porous medium. The model reproduces the observed dependence of the volume of the dispersed liquid both on the degree of filling and on the temperature.
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.
Guzman, Juan; Maximov, Serguei; Escarela-Perez, Rafael; López-García, Irvin; Moranchel, Mario
2015-01-01
The diffusion and distribution coefficients are important parameters in the design of barrier systems used in radioactive repositories. These coefficients can be determined using a two-reservoir configuration, where a saturated porous medium is allocated between two reservoirs filled by stagnant water. One of the reservoirs contains a high concentration of radioisotopes. The goal of this work is to obtain an analytical solution for the concentration of all radioisotopes in the decay chain of a two-reservoir configuration. The analytical solution must be obtained by taking into account the diffusion and sorption processes. Concepts such as overvalued concentration, diffusion and decay factors are employed to this end. It is analytically proven that a factor of the solution is identical for all chains (considering a time scaling factor), if certain parameters do not change. In addition, it is proven that the concentration sensitivity, due to the distribution coefficient variation, depends of the porous medium thickness, which is practically insensitive for small porous medium thicknesses. The analytical solution for the radioisotope concentration is compared with experimental and numerical results available in literature.
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.
Nonlinear instability of an Oldroyd elastico-viscous magnetic nanofluid saturated in a porous medium
NASA Astrophysics Data System (ADS)
Moatimid, Galal M.; Alali, Elham M. M.; Ali, Hoda S. M.
2014-09-01
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
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.
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.
Hauswirth, Scott C; Miller, Cass T
2014-10-15
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.
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
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.
NASA Astrophysics Data System (ADS)
Cooper, Gene R.
1988-06-01
White Phosphorous (WP) impregnated felt wedges are used as a payload in the M825 improved smoke projectile. An assumption made in this work in that the WP is in a liquid state (i.e., temperature greater than 44 degrees C) where such payloads have been seen to cause flight instabilities. The analytical results given here formulate an initial effort to gain an understanding of the dynamics of a projectile interacting with a WP/felt payload. The analytical methods used here are a simple extension of previous methods used to describe bulk-filled liquid payloads. Moments are predicted due to an inviscid liquid moving through a ridged porous medium which is confined to a spinning cylindrical cavity undergoing coning motion. A drag term is added to the classical Stewartson theory which is used to describe the flow in the porous media. The cylindrical cavity is assumed to consist of several chambers of circular cross section and uniform height, each separated by solid endcaps. This porous media theory is used to calculate the total liquid side moments exerted by all the chambers in the cylinder. Results are presented for a range of coning frequencies, fineness ratios, and porous drag coefficients.
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
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.
Hindered nanoparticle diffusion and void accessibility in a three-dimensional porous medium.
Skaug, Michael J; Wang, Liang; Ding, Yifu; Schwartz, Daniel K
2015-02-24
The inherent pore-scale heterogeneity of many natural and synthetic porous materials can make it difficult to model and predict porous transport because the underlying microscopic processes are often poorly understood. Here we present the results of single-particle tracking experiments in which we followed the pore-scale diffusion of individual nanoparticles, deep within a three-dimensional porous material of moderate porosity. We observed significant hydrodynamic damping of particle motion at subpore length scales, resulting in heterogeneous and spatially dependent mobility. The accessibility of the void space was strongly dependent on particle size, and related to the heterogeneous hydrodynamics. Our results suggest that pore-scale diffusion is more heterogeneous and volume accessibility more limited than previously expected. The method demonstrated here will enable studies of a broad new class of materials including porous polymers of technological interest.
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
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.
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
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.
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.
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
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.
NASA Astrophysics Data System (ADS)
Filo, Ján; Hundertmark-Zaušková, Anna
2016-10-01
The aim of this paper is to design a rescaling algorithm for the numerical solution to the system of two porous medium equations defined on two different components of the real line, that are connected by the nonlinear contact condition. The algorithm is based on the self-similarity of solutions on different scales and it presents a space-time adaptable method producing more exact numerical solution in the area of the interface between the components, whereas the number of grid points stays fixed.
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.
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.
Determining Pore Pressures Along a Slip Surface Within a Saturated Elastic-Plastic Porous Medium
NASA Astrophysics Data System (ADS)
Viesca, R. C.; Rice, J. R.; Dunham, E. M.
2008-12-01
Here we consider shear rupture along a slip surface in a fluid-saturated elastic-plastic porous medium, like in landslide and earthquake modeling, and assume that there are different poro-elasto-plastic response properties on the two sides of the slip surface. This different response may be because the fault bordering materials are dissimilar, or just because one side is actively yielding and the other is not, or is yielding but in a different mode. In effect, we are representing a core about a slip surface that divides two similar or contrasting materials. This representation is especially relevant in earthquake rupture dynamics. Studies of mature fault zones have noted a trend of fractured host rock extending 10--100m from the fault, with an ultracataclastic core ~100mm about or to one side of the principal slip surface (e.g., Chester and Chester, Tectonophys, 1998; Chester et al., Columbia Univ Pr, 2004). Furthermore, there is likely to exist a material contrast that may come from accumulating km of slip and a bias in accumulated damage. The local pore pressure at the slip surface influences the rupture dynamics because, through the effective stress concept, it controls the local shear strength along the fault, a feature neglected as a simplification in our preliminary poro-elasto-plastic modeling of dynamic rupture (Viesca et al., JGR, 2008). To determine pore pressures at the slip surface under locally elastic-plastic response, we must consider pore pressure discontinuities about that surface that arise in an undrained treatment of off-fault material and their amelioration within resulting thin diffusive boundary layers, such that pore pressure and fluid mass flux in the normal direction are continuous at the slip surface. Our approach builds on previous work considering the effect of contrasts in poroelastic properties on rupture propagation (Rudnicki and Rice, JGR, 2006; Dunham and Rice, JGR, 2008). Here we find expressions for the undrained pore pressure
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.
Study of the fluid flow characteristics in a porous medium for CO2 geological storage using MRI.
Song, Yongchen; Jiang, Lanlan; Liu, Yu; Yang, Mingjun; Zhou, Xinhuan; Zhao, Yuechao; Dou, Binlin; Abudula, Abuliti; Xue, Ziqiu
2014-06-01
The objective of this study was to understand fluid flow in porous media. Understanding of fluid flow process in porous media is important for the geological storage of CO2. The high-resolution magnetic resonance imaging (MRI) technique was used to measure fluid flow in a porous medium (glass beads BZ-02). First, the permeability was obtained from velocity images. Next, CO2-water immiscible displacement experiments using different flow rates were investigated. Three stages were obtained from the MR intensity plot. With increasing CO2 flow rate, a relatively uniform CO2 distribution and a uniform CO2 front were observed. Subsequently, the final water saturation decreased. Using core analysis methods, the CO2 velocities were obtained during the CO2-water immiscible displacement process, which were applied to evaluate the capillary dispersion rate, viscous dominated fractional flow, and gravity flow function. The capillary dispersion rate dominated the effects of capillary, which was largest at water saturations of 0.5 and 0.6. The viscous-dominant fractional flow function varied with the saturation of water. The gravity fractional flow reached peak values at the saturation of 0.6. The gravity forces played a positive role in the downward displacements because they thus tended to stabilize the displacement process, thereby producing increased breakthrough times and correspondingly high recoveries. Finally, the relative permeability was also reconstructed. The study provides useful data regarding the transport processes in the geological storage of CO2.
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
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.
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
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)
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.
Chen, Jui-Sheng; Liu, Chen-Wuing
2004-08-01
A reactive fluid circulating within a porous medium can dissolve minerals with which it is out of equilibrium and modify the porosity and permeability. The positive feedback between fluid transport and mineral dissolution causes complex reaction front morphologies such as fingers or wormholes. This study presents a numerical model to investigate reaction front instability, temporal aquifer porosity, and species concentration evolution during reactive transport in a homogeneous porous medium with two small, initially local non-uniformities. Simulation results indicate that a stable planar front develops for a small upstream pressure gradient while the growth of two non-uniformities becomes unstable for a large upstream pressure gradient. Moreover, the unstable reaction front may be either double- or single-finger in shape. Reaction front shape selection depends on the spacing of the two local non-uniformities and the upstream pressure gradients. A behavior diagram is constructed to identify a planar, single- or double-front morphology. The critical non-uniformities spacing at which a reaction front begins to merge into a single-finger decreases with increasing upstream pressure gradient.
Gray, William G.; Miller, Cass T.
2009-01-01
This work is the seventh in a series that introduces and employs the thermodynamically constrained averaging theory (TCAT) for modeling flow and transport in multiscale porous medium systems. This paper expands the previous analyses in the series by developing models at a scale where spatial variations within the system are not considered. Thus the time variation of variables averaged over the entire system is modeled in relation to fluxes at the boundary of the system. This implementation of TCAT makes use of conservation equations for mass, momentum, and energy as well as an entropy balance. Additionally, classical irreversible thermodynamics is assumed to hold at the microscale and is averaged to the megascale, or system scale. The fact that the local equilibrium assumption does not apply at the megascale points to the importance of obtaining closure relations that account for the large-scale manifestation of small-scale variations. Example applications built on this foundation are suggested to stimulate future work. PMID:20436941
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.
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)
Sakaguchi, Shigeru
2002-01-01
In previous papers we considered the Cauchy problem for the one-dimensional evolution p-Laplacian equation for nonzero, bounded, and nonnegative initial data having compact support, and showed that after a finite time the set of spatial critical points of the nonnegative solution u=u(x, t) in {u>0} consists of one point, the spatial maximum point of u, and the curve of the spatial maximum points is continuous with respect to the time variable. Since the spatial derivative ∂xu satisfies the porous medium equation with sign changes, the curve of the spatial maximum points is regarded as an interface with sign changes of ∂xu. On the other hand, in a paper by M. Bertsch and D. Hilhorst (1991, Appl. Anal.41, 111-130) the interfaces where the solutions change their sign were studied in detail for the initial-boundary value problems of the generalized porous medium equation over two-dimensional cylinders. But the monotonicity of the initial data is assumed there. As is noted in Section 4 of our earlier work (1996, J. Math. Anal. Appl.203, 78-103), the monotonicity of ∂xu(ċ, t) in some neighborhood of the spatial maximum point of u(ċ, t) cannot be assumed, and therefore, if this monotonicity for some large t>0 is proved, then by the method of Bertsch and Hilhorst (cited above) one may get more precise regularity properties of the curve of the spatial maximum points. The purpose of the present paper is twofold. One is to remove some monotonicity assumption for initial data in Bertsch and Hilhorst's theorem concerning the regularity of the interfaces with sign changes of solutions of the one-dimensional generalized porous medium equation. By comparing the solution with appropriate symmetric nonnegative solutions we shall get the monotonicity of the solution near the interface after a finite time. The other is as a by-product of the method to get C1 regularity of the curves of the spatial maximum points of nonnegative solutions of the Cauchy problem for the evolution
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.
Porous silicon nanoparticles for nanomedicine: preparation and biomedical applications.
Santos, Hélder A; Mäkilä, Ermei; Airaksinen, Anu J; Bimbo, Luis M; Hirvonen, Jouni
2014-04-01
The research on porous silicon (PSi) materials for biomedical applications has expanded greatly since the early studies of Leigh Canham more than 25 years ago. Currently, PSi nanoparticles are receiving growing attention from the scientific biomedical community. These nanostructured materials have emerged as promising multifunctional and versatile platforms for nanomedicine in drug delivery, diagnostics and therapy. The outstanding properties of PSi, including excellent in vivo biocompatibility and biodegradability, have led to many applications of PSi for delivery of therapeutic agents. In this review, we highlight current advances and recent efforts on PSi nanoparticles regarding the production properties, efficient drug delivery, multidrug delivery, permeation across biological barriers, biosafety and in vivo tracking for biomedical applications. The constant boost on successful preclinical in vivo data reported so far makes this the 'golden age' for PSi, which is expected to finally be translated into the clinic in the near future.
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
Vapour-liquid phase diagram for an ionic fluid in a random porous medium
NASA Astrophysics Data System (ADS)
Holovko, M. F.; Patsahan, O.; Patsahan, T.
2016-10-01
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.
New medium wave infrared stimulable phosphor for image intensifier applications
NASA Astrophysics Data System (ADS)
Soltani, Peter K.; Pierce, Gregory; Storti, George M.; Wrigley, Charles Y.
1990-07-01
A great deal of effort is presently being focused on developing high resolution, high sensitivity medium wavelength IR (MWIR) imaging systems for a variety of applications. These range from thermal imaging for industrial applications to military applications for detecting vehicles, missiles, etc. The present state-of-the-art method for MWIR imaging consists of fabricating linear and two-dimensional arrays of semiconductor detectors, such as HgCdTe, InSb, etc., and incorporating these into an appropriate optical imaging system. However, such devices are difficult to make and are very expensive. A new detector medium is described which can be fabricated at low cost for use in MWIR imaging. Specifically, the new medium is an electron trapping material capable of up-converting MWIR to visible wavelengths, which can be easily detected with a commercial camera system. This paper will describe the specific performance characteristics of the new phosphor material and its application in MWIR imaging.
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
NASA Astrophysics Data System (ADS)
Govardhan, K.; Kaladhar, K.; Nagaraju, G.; Balaswamy, B.
2014-12-01
This paper examines the effect of MHD, and injection through one side of a long vertical channel embedded in porous medium with transpiration cooling. The governing nonlinear partial differential equations have been transformed by similarity transformation into a set of ordinary differential equations, which are solved numerically by Adam-moultan Predictor-Corrector method with Newton-Raphson Method for missing initial conditions. Proflles of dimensionless velocity, temperature and concentration are shown graphically for different parameters entering into the analysis. Also the effects of the pertinent parameters on the heat transfer rates are tabulated. An analysis of the results obtained shows that the flow field is influenced appreciably by emerging parameters of the present study.
Gray, William G.
2008-01-01
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. PMID:19255613
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.
Taylor, S.W.; Jaffe, P.R. )
1990-09-01
An experimental investigaton was conducted to quantify the permeability reduction caused by enhanced biological growth in a porous medium. Studies were conducted using sand-packed column reactors for which variations in piezometric head, substrate concentration, and biomass measured as organic carbon were monitored in space and time. Methanol was used as a growth substrate. Permeability reductions by factors of order 10{sup {minus}3} were observed. The data show that a limit on permeability reduction exists, having a magnitude of 5 {times} 10{sup {minus}4} in the present study. The limit on permeability reduction and the existence of high densities of bacteria in substrate depleted zones are explained with an open pore model. Permeability reduction was observed to correlate well with biomass density for values less than about 0.4 mg/cm{sup 3}, and exhibited independence at higher densities.
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.
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.
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.
Experiment and theory for heterogeneous nucleation of protein crystals in a porous medium
NASA Astrophysics Data System (ADS)
Chayen, Naomi E.; Saridakis, Emmanuel; Sear, Richard P.
2006-01-01
The determination of high-resolution structures of proteins requires crystals of suitable quality. Because of the new impetus given to structural biology by structural genomics/proteomics, the problem of crystallizing proteins is becoming increasingly acute. There is therefore an urgent requirement for the development of new efficient methods to aid crystal growth. Nucleation is the crucial step that determines the entire crystallization process. Hence, the holy grail is to design a "universal nucleant," a substrate that induces the nucleation of crystals of any protein. We report a theory for nucleation on disordered porous media and its experimental testing and validation using a mesoporous bioactive gel-glass. This material induced the crystallization of the largest number of proteins ever crystallized using a single nucleant. The combination of the model and the experimental results opens up the scope for the rational design of nucleants, leading to alternative means of controlling crystallization. protein crystallization | phase diagram | microbatch | vapor diffusion
NASA Astrophysics Data System (ADS)
Slob, E. C.; Grobbe, N.
2014-12-01
The theory of coupled elastic waves and electromagnetic fields in porous media exists for two decades. Several modeling codes have been developed and some field work has been carried out with mixed success. Modeling the so-called electroseismic and seismo-electromagnetic wavefields is tricky because of the strong elastic fields generated by mechanical sources and strong electromagnetic fields generated by electromagnetic sources, while the coupled fields have relatively small amplitudes. A second difficulty is the fact that the elastic field is essentially a wavefield, while the electromagnetic field is a diffusive field. The slow P-wave is usually also a diffusive field depending on the frequency bandwidth of the data. On the other hand, for porous soils and rocks, laboratory measurements have been carried out to experimentally validate the current theoretical model and to some extent this has been successful. To be able to understand measured data it is crucially important that we have good control on the accuracy of modeled data. Today we don't have this control, which makes it hard to judge the quality of the modeled data and trust the experimental validation of the theory. It is therefore important that exact solutions are found to validate modeling codes in simple configurations. These modeling codes can then numerically validate the theory by matching the results obtained in laboratory or field experiments. The simplest configuration is the homogeneous space and we show exact solutions for the governing equations for point sources and point receivers. These Green's functions are obtained for any type of point source and any type of receiver. We reduce the coupled equations to two scalar equations for the electric field and the particle velocity vectors. Solutions for longitudinal and transverse waves are obtained separately and these are combined to obtain the Green's functions for the electric field and the particle velocity, from which the solutions for
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.
NASA Astrophysics Data System (ADS)
Parand, K.; Rad, J. A.; Ahmadi, M.
2016-09-01
Natural convective heat transfer in porous media which is of importance in the design of canisters for nuclear waste disposal has received considerable attention during the past few decades. This paper presents a comparison between two different analytical and numerical methods, i.e. pseudospectral and Adomian decomposition methods. The pseudospectral approach makes use of the orthogonal rational Jacobi functions; this method reduces the solution of the problem to a solution of a system of algebraic equations. Numerical results are compared with each other, showing that the pseudospectral method leads to more accurate results and is applicable on similar problems.
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.
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.
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.
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.
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
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.
Comparison of theory and experiment for solute transport in highly heterogeneous porous medium
NASA Astrophysics Data System (ADS)
Golfier, Fabrice; Quintard, Michel; Cherblanc, Fabien; Zinn, Brendan A.; Wood, Brian D.
2007-11-01
In this work we compare the recently developed two-region mass transfer theory reported by Ahmadi et al. [A. Ahmadi, M. Quintard, S. Whitaker (1998), Transport in chemically and mechanically heterogeneous porous media, V, two-equation model for solute transport with adsorption, Adv. Water Resour. 1998;22:59-86] with experimental results reported by Zinn et al. [Zinn, B., L. C. Meigs, C. F. Harvey, R. Haggerty, W. J. Peplinski, C. F. Von Schwerin. Experimental visualization of solute transport and mass transfer processes in two-dimensional conductivity fields with connected regions of high conductivity. Environ Sci Technol 2004;38:3916-3926]. We find that the constant mass transfer coefficient predicted by the steady-state closure to the theory, when used with the macroscale transport equation, provides a reasonable prediction of the observed breakthrough curve. However, the use of a constant mass transfer coefficient does not allow good representation of the tailing that is observed in the data. We show that the mass transfer coefficient can be represented in terms of the eigenvalue expansion of a Green's function. For a steady solution to the closure problem, this expansion leads to the effective mass transfer coefficient being defined in terms of the harmonic average of the eigenvalues of the expansion; this is consistent with previous work on this topic. To further investigate the influence of using a single, constant value for the mass transfer coefficient, we examine the solution to the mass transfer problem in terms of a mixed model, where the eigenvalues of one region (the inclusions) are kept, while the second region (the matrix) is treated as a homogenized material. The results from this comparison indicate that the mass transfer coefficient predicted via volume averaging using a quasi-steady closure could potentially be improved upon by development of new methods that retain more of the eigenvalues of the system.
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
Sharmin, Rumana; Ioannidis, Marios A; Legge, Raymond L
2006-01-01
At concentrations above the critical micelle concentration, surfactants can significantly enhance the solubilization of residual nonaqueous phase liquids (NAPL) and, for this reason, are the focus of research on surfactant-enhanced aquifer remediation (SEAR). As a consequence of their amphiphilic nature, surfactants may also partition to various extents between the organic and aqueous phases, thereby affecting SEAR performance. We report here on the observation and analysis of the effect of surfactant partitioning on the dissolution kinetics of residual perchloroethylene (PCE) by aqueous solutions (1000 mg/L) of the non-ionic surfactant Triton X-100 in a model porous medium. For this fluid system, batch equilibration experiments showed that the surfactant partitions strongly into the NAPL (NAPL-water partition coefficient equal to 12.5). Dynamic interfacial tension (IFT) measurements were employed to study surfactant diffusion and interfacial adsorption. The dynamic IFT measurements were consistent with partitioning of the surfactant between the two liquid phases. PCE dissolution experiments, conducted in a transparent glass micromodel using an aqueous surfactant solution, were contrasted to experiments using clean water. Surfactant partitioning was observed to delay significantly the onset of micellar solubilization of PCE, an observation reproduced by a numerical model. This effect is attributed to the reduction of surfactant concentration in the immediate vicinity of the NAPL-water interface, which accompanies transport of the surfactant into the NAPL. Accordingly, it is suggested that both the rate and the extent of diffusion of the surfactant into the NAPL affect the onset of and the driving force for micellar solubilization. While many surfactants do not readily partition in NAPL, this possibility must be considered when selecting non-ionic surfactants for the enhanced solubilization of residual chlorinated solvents in porous media.
Pore Scale Modeling of Competitive Adsorption of a Plume in a Porous Medium
Ryan, Emily M.; Tartakovsky, Alexandre M.; Amon, Cristina
2010-06-30
In this paper we present a smoothed particle hydrodynamics (SPH) pore scale reactive transport model of competitive adsorption of a binary system in a porous media. SPH is a Lagrangian, particle based modeling method which uses the particles as interpolation points to directly discretize the governing equations of the system. The theory and details of the SPH pore scale model are presented along with a novel method for handling surface reactions based on the continuum surface force model [1]. The numerical accuracy of the model is validated with analytical and finite difference solutions, and the effects of spatial and temporal resolution on the accuracy of the model are also discussed. The pore scale model is used to study competitive adsorption for different Damköhler and Peclet numbers in a binary system where a plume of species B is introduced into a system which initially contains species A. The pore scale model results are compared with a Darcy scale model to investigate the accuracy of a Darcy scale reactive transport model for a wide range of Damköhler and Peclet numbers. The results demonstrate that the Darcy model is able to accurately predict the total mass of aqueous and adsorbed species of both species A and B for low Damköhler numbers. For high Damköhler numbers the Darcy model is able to accurately model the aqueous and absorbed mass of species A, but is unable to accurately predict the total mass of aqueous and adsorbed species B, which moves through the domain as a plume. At high Peclet numbers, the Darcy model was able to accurately predict the aqueous and adsorbed masses of species A and B at higher Damköhler numbers then low Peclet number simulations, however at both high and low Peclet numbers the Darcy model was not able to accurately predict the total mass of species B at high Damköhler numbers. The simulation results demonstrate the limitations of simple Darcy scale models with constant transport coefficients.
Novel-porous-Ag0 nanocomposite hydrogels via green process for advanced antibacterial applications.
Vimala, Kanikireddy; Kanny, K; Varaprasad, Kokkarachedu; Kumar, N Mithil; Reddy, G S M
2014-12-01
Silver nanoparticles (NPs) antibacterial characteristics were depends on its particle stabilization, particles size and nucleation agent. In this study, we report on green process of porous silver nanocomposite hydrogels for advanced antibacterial applications. The porous poly(acrylamide) (PAM) hydrogels were developed employing sucrose as porogenator. Silver NPs were nucleated with natural biomass Neem (Azadirachta indica) leaf extracts within the porous hydrogel networks. The formation of silver NPs in the porous hydrogels was confirmed by ultraviolet-visible spectroscopy, fourier transform infrared spectroscopy, X-ray diffraction, and thermo gravimetric analysis. Morphological studies done by scanning electron microscopy and transmission electron microscopy showed that the hydrogels were porous in nature and stabilization of NPs, size, and particles shape. The porous PAM silver nanoparticle hydrogels demonstrated excellent antimicrobial activity with significant effect against Escherichia coli, Micrococcus, and Candida albicus. Hence, it was clear that the developed hydrogels can be used effectively for preventing and treating infections.
NASA Astrophysics Data System (ADS)
Oostrom, M.; Dane, J. H.; Wietsma, T. W.
2004-12-01
An intermediate-scale flow cell experiment was conducted to study the behavior of a multicomponent DNAPL at structural interfaces and subsequent remediation using two different forms of the soil vapor extraction (SVE) technique. The flow cell (100-cm long, 5-cm wide, and 80 cm high), was packed under saturated conditions with sloped layers of Hanford silt and coarse sand, embedded in a matrix of a medium-grained laboratory sand. After packing, the water table was lowered to 2 cm above the bottom of the flow cell to establish variably saturated conditions. A finite amount of a volatile multicomponent DNAPL, mimicking the organic liquid disposed at the Hanford Site, was then injected from a small source zone. The infiltration and redistribution processes were visually recorded. In addition, a dual-energy gamma radiation system was used to determine DNAPL and water saturation at more than 1000 locations. Results indicate that lateral spreading of the DNAPL is greatly enhanced by the heterogeneities. The silt layers, by virtue of their substantial non-wetting fluid entry pressures and high water saturations, completely diverted the DNAPL laterally. The relatively dry coarse-sand layers forced some of the DNAPL to move laterally but also allowed some infiltration.
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.
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
2016-04-01
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
NASA Astrophysics Data System (ADS)
Kumari, Vinita; Mishra, Prabhash; Islam, S. S.
2012-10-01
Electrectrochemical immunosensors have diverse applications in areas like medical diagnostics, food industry, environmental monitoring etc. The conductive materials like Indium Tin oxide coated glass (ITO), glassy carbon, porous silicon (PS) etc. can be useful as working electrode for electrochemical immunosensor applications. But the porous silicon is particularly attractive for this application due to its modified properties like very large surface area to volume ratio, surface dependent properties (electrical and optical), photoluminescence at room temperature and biocompatibility. In this paper porous silicon is investigated for development as working electrode for label free model immunosensor based on Human IgG.
Uncertainty estimation in one-dimensional heat transport model for heterogeneous porous medium.
Chang, Ching-Min; Yeh, Hund-Der
2014-01-01
In many practical applications, the rates for ground water recharge and discharge are determined based on the analytical solution developed by Bredehoeft and Papadopulos (1965) to the one-dimensional steady-state heat transport equation. Groundwater flow processes are affected by the heterogeneity of subsurface systems; yet, the details of which cannot be anticipated precisely. There exists a great deal of uncertainty (variability) associated with the application of Bredehoeft and Papadopulos' solution (1965) to the field-scale heat transport problems. However, the quantification of uncertainty involved in such application has so far not been addressed, which is the objective of this wok. In addition, the influence of the statistical properties of log hydraulic conductivity field on the variability in temperature field in a heterogeneous aquifer is also investigated. The results of the analysis demonstrate that the variability (or uncertainty) in the temperature field increases with the correlation scale of the log hydraulic conductivity covariance function and the variability of temperature field also depends positively on the position.
On the movement of a liquid front in an unsaturated, fractured porous medium, Part 1
Nitao, J.J.; Buscheck, T.A.
1989-06-01
The primary aim of this paper is to present approximate analytical solutions of the fracture flow which gives the position of the liquid fracture front as a function of time. These solutions demonstrate that the liquid movement in the fracture can be classified into distinctive time periods, or flow regimes. It is also shown that when plotted versus time using a log-log scale, the liquid fracture front position asymptotically approaches a series of line segments. Two-dimensional numerical simulations were run utilizing input data applicable to the densely welded, fractured tuff found at Yucca Mountain in order to confirm these observations. 19 refs., 15 figs., 8 tabs.
On the infiltration of a liquid front in an unsaturated, fractured porous medium
Nitao, J.; Buscheck, T.
1989-08-01
The unsaturated zone at Yucca Mountain, Nevada, is currently under scientific investigation as a proposed site for the permanent storage of high-level nuclear waste. A deeper understanding of fracture-matrix interaction needed for the prediction of water movement around an in the repository. We show that the liquid front movement can be classified into physically interpretable, distinctive flow regimes. Asymptotic solutions for the front movement are given for each flow period and comparisons with numerical solutions are made. In addition to applications in nuclear waste storage, the results of our study is relevant to hazardous waste disposal, petroleum recovery, and flow in soil macropores. 17 refs., 13 figs., 6 tabs.
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.
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.
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.
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
Investigation of Ice-Templated Porous Electrodes for Application in Organic Batteries.
Stolze, Christian; Janoschka, Tobias; Flauder, Stefan; Müller, Frank A; Hager, Martin D; Schubert, Ulrich S
2016-09-14
Application and investigation of porous composite electrodes for organic batteries fabricated by an ice-templating method are reported for the first time. The possibility to produce polymer composite electrodes with highly aligned, parallel pores is demonstrated and electrochemical investigations are presented to examine their suitability for application in organic batteries. The performance of such ice-templated porous electrodes is experimentally compared with planar electrodes of similar composition against zinc and lithium counter electrodes, respectively. Fundamental properties limiting the performance of ice-templated porous electrodes are discussed and further means to overcome those limitations are proposed. PMID:27570872
Investigation of Ice-Templated Porous Electrodes for Application in Organic Batteries.
Stolze, Christian; Janoschka, Tobias; Flauder, Stefan; Müller, Frank A; Hager, Martin D; Schubert, Ulrich S
2016-09-14
Application and investigation of porous composite electrodes for organic batteries fabricated by an ice-templating method are reported for the first time. The possibility to produce polymer composite electrodes with highly aligned, parallel pores is demonstrated and electrochemical investigations are presented to examine their suitability for application in organic batteries. The performance of such ice-templated porous electrodes is experimentally compared with planar electrodes of similar composition against zinc and lithium counter electrodes, respectively. Fundamental properties limiting the performance of ice-templated porous electrodes are discussed and further means to overcome those limitations are proposed.
NASA Astrophysics Data System (ADS)
Oostrom, M.; Hofstee, C.; Walker, R. C.; Dane, J. H.
1999-04-01
An intermediate-scale flow cell experiment was conducted to remove a liquid trichloroethylene (TCE) spill from a saturated, heterogeneous porous medium using pump-and-treat (P&T) as well as surfactant flushing (SF) techniques. Dissolved TCE concentrations were measured at 20 locations, while fluid saturations were obtained with a dual-energy gamma scanner. The behavior of the TCE spill has been described by Oostrom et al. (1998b) [Oostrom, M., Hofstee, C., Walker, R.C., Dane, J.H., 1998b. Movement and remediation of TCE in a saturated heterogeneous porous medium: 1. Spill behavior and initial dissolution, this issue.]. A total of six alternating P&T and SF periods were used to remediate the flow cell. A two-well system, consisting of an injection and an extraction well, was used during the first five remediation periods. For the last SF period, a three-well system was employed with two injection wells and one extraction well. During the first P&T period, most entrapped TCE was removed, but TCE saturations in a substantial pool on top of a fine-grained sand layer were largely unaffected. During the first SF period, a dense plume was formed containing solubilized TCE which partially sank into the fine-grained sand. In addition, unstable fingers developed below the liquid TCE in the pool. In several samples, small TCE droplets were found, indicating mobilization of TCE. Most of the samples with concentrations larger than 5000 ppm had a milky, emulsion-like appearance. The SF considerably reduced the amount of TCE in the pool on top of the fine-grained sand. During the second P&T period, plume sinking and instabilities were not observed. After starting the second SF period, some unstable fingering and plume sinking resumed, starting at the upstream end of the TCE in the pool. The saturation distribution obtained after the second SF period was quite similar to the one obtained after the first SF period, indicating that additional removal of TCE through SF was difficult
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.
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.
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.
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.
Zheng, Leo Y; Farnam, Dylan S; Homentcovschi, Dorel; Sammakia, Bahgat G
2012-05-01
The presence of bacterial biofilms is detrimental in a wide range of healthcare situations especially wound healing. Physical debridement of biofilms is a method widely used to remove them. This study evaluates the use of microfluidic jet impingement to debride biofilms. In this case, a biofilm is treated as a saturated porous medium also having linear elastic properties. A numerical modeling approach is used to calculate the von Mises stress distribution within a porous medium under fluid-structure interaction (FSI) loading to determine the initial rupture of the biofilm structure. The segregated model first simulates the flow field to obtain the FSI interface loading along the fluid-solid interface and body force loading within the porous medium. A stress-strain model is consequently used to calculate the von Mises stress distribution to obtain the biofilm deformation. Under a vertical jet, 60% of the deformation of the porous medium can be accounted for by treating the medium as if it was an impermeable solid. However, the maximum deformation in the porous medium corresponds to the point of maximum shear stress which is a different position in the porous medium than that of the maximum normal stress in an impermeable solid. The study shows that a jet nozzle of 500 μm internal diameter (ID) with flow of Reynolds number (Re) of 200 can remove the majority of biofilm species.
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
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.
NASA Astrophysics Data System (ADS)
Ghanbarian, Behzad; Sahimi, Muhammad; Daigle, Hugh
2016-07-01
Accurate prediction of the relative permeability to water under partially saturated condition has broad applications and has been studied intensively since the 1940s by petroleum, chemical, and civil engineers, as well as hydrologists and soil scientists. Many models have been developed for this purpose, ranging from those that represent the pore space as a bundle of capillary tubes, to those that utilize complex networks of interconnected pore bodies and pore throats with various cross-section shapes. In this paper, we propose an approach based on the effective-medium approximation (EMA) and percolation theory in order to predict the water relative permeability. The approach is general and applicable to any type of porous media. We use the method to compute the water relative permeability in porous media whose pore-size distribution follows a power law. The EMA is invoked to predict the relative permeability from the fully saturated pore space to some intermediate water saturation that represents a crossover from the EMA to what we refer to as the "critical region." In the critical region below the crossover water saturation Swx, but still above the critical water saturation Swc (the residual saturation or the percolation threshold of the water phase), the universal power law predicted by percolation theory is used to compute the relative permeability. To evaluate the accuracy of the approach, data for 21 sets of undisturbed laboratory samples were selected from the UNSODA database. For 14 cases, the predicted relative permeabilities are in good agreement with the data. For the remaining seven samples, however, the theory underestimates the relative permeabilities. Some plausible sources of the discrepancy are discussed.
4-Nitrobenzene Grafted in Porous Silicon: Application to Optical Lithography
NASA Astrophysics Data System (ADS)
Tiddia, Mariavitalia; Mula, Guido; Sechi, Elisa; Vacca, Annalisa; Cara, Eleonora; De Leo, Natascia; Fretto, Matteo; Boarino, Luca
2016-09-01
In this work, we report a method to process porous silicon to improve its chemical resistance to alkaline solution attacks based on the functionalization of the pore surface by the electrochemical reduction of 4-nitrobenzendiazonium salt. This method provides porous silicon with strong resistance to the etching solutions used in optical lithography and allows the fabrication of tailored metallic contacts on its surface. The samples were studied by chemical, electrochemical, and morphological methods. We demonstrate that the grafted samples show a resistance to harsh alkaline solution more than three orders of magnitude larger than that of pristine porous silicon, being mostly unmodified after about 40 min. The samples maintained open pores after the grafting, making them suitable for further treatments like filling by polymers. Optical lithography was performed on the functionalized samples, and electrochemical characterization results are shown.
4-Nitrobenzene Grafted in Porous Silicon: Application to Optical Lithography.
Tiddia, Mariavitalia; Mula, Guido; Sechi, Elisa; Vacca, Annalisa; Cara, Eleonora; De Leo, Natascia; Fretto, Matteo; Boarino, Luca
2016-12-01
In this work, we report a method to process porous silicon to improve its chemical resistance to alkaline solution attacks based on the functionalization of the pore surface by the electrochemical reduction of 4-nitrobenzendiazonium salt. This method provides porous silicon with strong resistance to the etching solutions used in optical lithography and allows the fabrication of tailored metallic contacts on its surface. The samples were studied by chemical, electrochemical, and morphological methods. We demonstrate that the grafted samples show a resistance to harsh alkaline solution more than three orders of magnitude larger than that of pristine porous silicon, being mostly unmodified after about 40 min. The samples maintained open pores after the grafting, making them suitable for further treatments like filling by polymers. Optical lithography was performed on the functionalized samples, and electrochemical characterization results are shown. PMID:27686091
McClure, James E.; Berrill, Mark A.; Gray, William G.; Miller, Cass T.
2016-09-02
Here, multiphase flow in porous medium systems is typically modeled using continuum mechanical representations at the macroscale in terms of averaged quantities. These models require closure relations to produce solvable forms. One of these required closure relations is an expression relating fluid pressures, fluid saturations, and, in some cases, the interfacial area between the fluid phases, and the Euler characteristic. An unresolved question is whether the inclusion of these additional morphological and topological measures can lead to a non-hysteretic closure relation compared to the hysteretic forms that are used in traditional models, which typically do not include interfacial areas, ormore » the Euler characteristic. We develop a lattice-Boltzmann (LB) simulation approach to investigate the equilibrium states of a two-fluid-phase porous medium system, which include disconnected now- wetting phase features. The proposed approach is applied to a synthetic medium consisting of 1,964 spheres arranged in a random, non-overlapping, close-packed manner, yielding a total of 42,908 different equilibrium points. This information is evaluated using a generalized additive modeling approach to determine if a unique function from this family exists, which can explain the data. The variance of various model estimates is computed, and we conclude that, except for the limiting behavior close to a single fluid regime, capillary pressure can be expressed as a deterministic and non-hysteretic function of fluid saturation, interfacial area between the fluid phases, and the Euler characteristic. This work is unique in the methods employed, the size of the data set, the resolution in space and time, the true equilibrium nature of the data, the parameterizations investigated, and the broad set of functions examined. The conclusion of essentially non-hysteretic behavior provides support for an evolving class of two-fluid-phase flow in porous medium systems models.« less
Compact superferric FFAG accelerators for medium energy hadron applications
NASA Astrophysics Data System (ADS)
Qin, B.; Mori, Y.
2011-08-01
Medium energy hadron beams are desirable in various applications such as accelerator-driven subcritical systems (ADSR), high intensity neutron sources and carbon therapy. Compactness and easy operation characters are important for this energy region, especially in the case of medical use purposes. This paper introduces a novel superferric scheme with scaling fixed-field alternating gradient (FFAG) accelerators, which can provide 400 MeV/u carbon ions for cancer therapy. By employing a maximum field of 5 T with a high field index, 8.5 m diameter with 85 cm radius excursion is achieved in a single FFAG ring. The lattice configuration and design of superferric magnet sectors with high permeability materials were described in detail. This scheme can also be extended to other hadron applications.
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.
Aziz, Asim; Ali, Yasir; Aziz, Taha; Siddique, J. I.
2015-01-01
In this paper, we investigate the slip effects on the boundary layer flow and heat transfer characteristics of a power-law fluid past a porous flat plate embedded in the Darcy type porous medium. The nonlinear coupled system of partial differential equations governing the flow and heat transfer of a power-law fluid is transformed into a system of nonlinear coupled ordinary differential equations by applying a suitable similarity transformation. The resulting system of ordinary differential equations is solved numerically using Matlab bvp4c solver. Numerical results are presented in the form of graphs and the effects of the power-law index, velocity and thermal slip parameters, permeability parameter, suction/injection parameter on the velocity and temperature profiles are examined. PMID:26407162
Aziz, Asim; Ali, Yasir; Aziz, Taha; Siddique, J I
2015-01-01
In this paper, we investigate the slip effects on the boundary layer flow and heat transfer characteristics of a power-law fluid past a porous flat plate embedded in the Darcy type porous medium. The nonlinear coupled system of partial differential equations governing the flow and heat transfer of a power-law fluid is transformed into a system of nonlinear coupled ordinary differential equations by applying a suitable similarity transformation. The resulting system of ordinary differential equations is solved numerically using Matlab bvp4c solver. Numerical results are presented in the form of graphs and the effects of the power-law index, velocity and thermal slip parameters, permeability parameter, suction/injection parameter on the velocity and temperature profiles are examined.
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
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.
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.
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.
NASA Astrophysics Data System (ADS)
Anwar Bég, O.; Zueco, J.; Takhar, H. S.; Bég, T. A.; Sajid, A.
2009-11-01
A boundary-layer model is described for the two-dimensional nonlinear transient thermal convection heat and mass transfer in an optically-thick fluid in a Darcian porous medium adjacent to an impulsively started vertical surface, in the presence of significant thermal radiation and buoyancy forces in an (X∗,Y∗,t∗) coordinate system. An algebraic approximation is employed to simplify the integro-differential equation of radiative transfer for unidirectional flux normal to the plate into the boundary-layer regime, by incorporating this flux term in the energy conservation equation. The conservation equations are non-dimensionalized into an (X,Y,T) coordinate system and solved using the Network Simulation Method (NSM), a robust numerical technique which demonstrates high efficiency and accuracy. The transient variation of non-dimensional streamwise velocity component (u) and temperature (T) and concentration (C) functions is computed for various selected values of Stark number (radiation-conduction interaction parameter) and Darcy number. Transient velocity (u) and steady-state local skin friction (τX) are also studied for various thermal Grashof number (Gr), species Grashof number (Gm), Schmidt number (Sc) and Stark number (N) values. These computations for the infinite permeability case (Da → ∞) are compared with previous finite difference solutions [Prasad et al. Int J Therm Sci 2007;46(12):1251-8] and shown to be in excellent agreement. An increase in Darcy number is seen to accelerate the flow and boost velocity. A decrease in Stark number (corresponding to an increase in thermal radiation heat transfer contribution) is shown to increase the velocity values. Temperature function is observed to fall in value with a rise in Da and increase with decrease in N (corresponding to an increase in thermal radiation heat transfer contribution). Applications of the study include rocket combustion chambers, astrophysical flows, spacecraft thermal fluid dynamics in
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
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.
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.
Simple fabrication of porous gold-film electrodes and their electroanalytical applications.
Hyun, Myeounghee; Choi, Suhee; Kim, Jongwon
2010-01-01
A simple strategy to fabricate porous three-dimensional gold-film electrodes using gold-coated microspheres (AuMS) is presented. The AuMS deposited on gold (AuMS/Au) are electrically interconnected, and show unique electrochemical properties indicating porous surface structures. The AuMS/Au electrodes exhibit electrocatalytic activities for oxygen reduction and peroxide oxidation, which indicates that the apparent macroporous structures also retain porous regions with nanometer-scale dimensions. The porous structures on AuMS/Au electrodes also provide a selective voltammetric response for glucose against ascorbic acid due to the different electron-transfer kinetics. Since AuMS/Au electrodes are simple to prepare compared with previously suggested systems, the present system could offer potential in electroanalytical applications as new gold-based substrates for further modifications of surfaces.
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.
NASA Astrophysics Data System (ADS)
McClure, James E.; Berrill, Mark A.; Gray, William G.; Miller, Cass T.
2016-09-01
Multiphase flows in porous medium systems are typically modeled at the macroscale by applying the principles of continuum mechanics to develop models that describe the behavior of averaged quantities, such as fluid pressure and saturation. These models require closure relations to produce solvable forms. One of these required closure relations is an expression relating the capillary pressure to fluid saturation and, in some cases, other topological invariants such as interfacial area and the Euler characteristic (or average Gaussian curvature). The forms that are used in traditional models, which typically consider only the relationship between capillary pressure and saturation, are hysteretic. An unresolved question is whether the inclusion of additional morphological and topological measures can lead to a nonhysteretic closure relation. Relying on the lattice Boltzmann (LB) method, we develop an approach to investigate equilibrium states for a two-fluid-phase porous medium system, which includes disconnected nonwetting phase features. A set of simulations are performed within a random close pack of 1964 spheres to produce a total of 42 908 distinct equilibrium configurations. This information is evaluated using generalized additive models to quantitatively assess the degree to which functional relationships can explain the behavior of the equilibrium data. The variance of various model estimates is computed, and we conclude that, except for the limiting behavior close to a single fluid regime, capillary pressure can be expressed as a deterministic and nonhysteretic function of fluid saturation, interfacial area between the fluid phases, and the Euler characteristic. To our knowledge, this work is unique in the methods employed, the size of the data set, the resolution in space and time, the true equilibrium nature of the data, the parametrizations investigated, and the broad set of functions examined. The conclusion of essentially nonhysteretic behavior provides
NASA Astrophysics Data System (ADS)
Lazarev, Y.; Petrov, P.; Tartakovsky, D. M.
2002-12-01
In this paper the problem of vacuum-incompressible fluid interface moving in a porous medium by treating conductivity of a medium as a random field with known statistics is considered. The flow is described by a combination of mass conservation and Darcy' law. The use of a coordinate system tied with the moving fluid allows reducing the problem to the well-explored class of problems with fixed boundaries and an effective conductivity tensor instead of the initial scalar conductivity. The hydraulic head is represented as a series in powers of effective conductivity fluctuations. The applied procedure is close to the perturbation theory procedure in the amplitude of the hydraulic conductivity fluctuations ˜ K when searching the solution with accuracy up to ˜ K2 . In both cases physical quantity variance is considered to be proportional to its reason: ˜ V = A ṡ ˜ K ( A is a linear operator). Yet unlike perturbation theory, where it is considered that A depends only on undisturbed flow parameters A = A(¯ K), in the approach being used A is considered to be dependent on averaged flow parameters A = A( ¯ K,< ˜ K2 > ). Equations of the mean hydraulic head and mean flux and expressions for respective variances as well are derived in the 2-D case. For 1-D flow the derived solution agrees with the exact one within terms of σ K2 -order at any free surface fluctuations. Within this approach the free surface moving, evolution in time of the mean hydraulic head spatial distribution, mean flux and relative correlation functions are described by the set of first-order partial differential equations. The conjugate gradient method with preconditioning is proposed to be used as the general method of equation numerical solving to find hydraulic head statistic moments. The problem matrix symmetry and its positive definiteness serve the foundation of the method applicability. RFLOW code has been elaborated to solve this set of equations numerically. Testing data of the
NASA Astrophysics Data System (ADS)
Reddy, Ch. Ram; Kaladhar, K.; Srinivasacharya, D.; Pradeepa, T.
2016-02-01
This paper analyzes the laminar, incompressible mixed convective transport inside vertical channel in an electrically conducting fluid saturated porous medium. In addition, this model incorporates the combined effects of Soret, Hall current and Joule heating. The nonlinear governing equations and their related boundary conditions are initially cast into a dimensionless form using suitable similarity transformations and hence solved using Adomian Decomposition Method (ADM). In order to explore the influence of various parameters on fluid flow properties, quantitative analysis is exhibited graphically and shown in tabular form.
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)
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.
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.
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.
Gelatin functionalised porous titanium alloy implants for orthopaedic applications.
Vanderleyden, E; Van Bael, S; Chai, Y C; Kruth, J-P; Schrooten, J; Dubruel, P
2014-09-01
In the present work, we studied the immobilisation of the biopolymer gelatin onto the surface of three dimensional (3D) regular Ti6Al4V porous implants to improve their surface bio-activity. The successful immobilisation of the gelatin coating was made possible by a polydopamine interlayer, a polymer coating inspired by the adhesive nature of mussels. The presence of both coatings was first optimised on two dimensional titanium (2D Ti) substrates and confirmed by different techniques including X-ray photelectron spectroscopy, contact angle measurements, atomic force microscopy and fluorescence microscopy. Results showed homogeneous coatings that are stable for at least 24h in phosphate buffer at 37°C. In a next step, the coating procedure was successfully transferred to 3D Ti6Al4V porous implants, which indicates the versatility of the applied coating procedure with regard to complex surface morphologies. Furthermore, the bio-activity of these stable gelatin coatings was enhanced by applying a third and final coating using the cell-attractive protein fibronectin. The reproducible immobilisation process allowed for a controlled biomolecule presentation to the surrounding tissue. This newly developed coating procedure outperformed the previously reported silanisation procedure for immobilising gelatin. In vitro cell adhesion and culture studies with human periosteum-derived cells showed that the investigated coatings did not compromise the biocompatible nature of Ti6Al4V porous implants, but no distinct biological differences between the coatings were found.
Gelatin functionalised porous titanium alloy implants for orthopaedic applications.
Vanderleyden, E; Van Bael, S; Chai, Y C; Kruth, J-P; Schrooten, J; Dubruel, P
2014-09-01
In the present work, we studied the immobilisation of the biopolymer gelatin onto the surface of three dimensional (3D) regular Ti6Al4V porous implants to improve their surface bio-activity. The successful immobilisation of the gelatin coating was made possible by a polydopamine interlayer, a polymer coating inspired by the adhesive nature of mussels. The presence of both coatings was first optimised on two dimensional titanium (2D Ti) substrates and confirmed by different techniques including X-ray photelectron spectroscopy, contact angle measurements, atomic force microscopy and fluorescence microscopy. Results showed homogeneous coatings that are stable for at least 24h in phosphate buffer at 37°C. In a next step, the coating procedure was successfully transferred to 3D Ti6Al4V porous implants, which indicates the versatility of the applied coating procedure with regard to complex surface morphologies. Furthermore, the bio-activity of these stable gelatin coatings was enhanced by applying a third and final coating using the cell-attractive protein fibronectin. The reproducible immobilisation process allowed for a controlled biomolecule presentation to the surrounding tissue. This newly developed coating procedure outperformed the previously reported silanisation procedure for immobilising gelatin. In vitro cell adhesion and culture studies with human periosteum-derived cells showed that the investigated coatings did not compromise the biocompatible nature of Ti6Al4V porous implants, but no distinct biological differences between the coatings were found. PMID:25063133
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.
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
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
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
A Diffuse Interface Model for solid-liquid-air dissolution problems based on a porous medium theory
NASA Astrophysics Data System (ADS)
Luo, H.; Quintard, M.; Debenest, G.; Laouafa, F.
2011-12-01
The underground cavities may be dissolved by the flows of groundwater where the dissolution mainly happens at the liquid-solid interface. In many real cases, the cavities are not occupied only by the water, but also the gas phase, e.g., air, or other gases. In this case, there are solid-liquid-gas three phases. Normally, the air does not participate the dissolution. However, it may influence the dissolution as the position of the solid-liquid interface may gradually lower down with the dissolution process. Simulating the dissolution problems with multi- moving interfaces is a difficult task but rather interesting to study the evolution of the underground cavities. In this paper, we propose a diffuse interface model (DIM) to simulate the three-phase dissolution problem, based on a porous medium theory and a volume averaging theory te{Whitaker1999,Golfier2002,Quintard1994}. The interface is regarded as a continuous layer where the phase indicator (mainly for solid-liquid interface) and phase saturation (mainly for liquid-gas interface) vary rapidly but smoothly. The DIM equations enable us to simulate the moving interface under a fixed mesh system, instead of a deformed or moving mesh. Suppose we have three phases, solid, liquid and gas. The solid phase contains only species A. The gas phase contains only the air. The volume averaging theory is used to upscale the balance equations. The final DIM equations are presented below. The balance equation of solid phase can be written as {partialrho_{s}(1-\\varepsilon_{f})}/{partial t}=-K_{sl} where \\varepsilonf represents the volume fraction of the fluids (liquid+gas) and Ksl refers to the mass exchange between the solid phase and the liquid phase. Ksl cam be expressed as K_{sl}=rho_{l}alpha(omega_{eq}-Omega_{Al}). The balance equations of liquid phase can be written as {partialrho_{l}\\varepsilon_{f}S_{l}}/{partial t}+nabla\\cdot(rho_{l}{V}_{l})= K_{sl}. The balance equation of liquid phase can be written as {partialrho
NASA Astrophysics Data System (ADS)
Borman, V. D.; Belogorlov, A. A.; Bortnikova, S. A.; Tronin, V. N.
2016-09-01
The relaxation of a confined nonwetting liquid dispersed in a disordered nanoporous medium has been experimentally studied in the system consisting of water and the L23 hydrophobized silica gel. Discovered that the relaxation of these states to study the system occurs as a result of the relaxation of local metastable configurations of filled and empty pores of the porous medium. Such relaxation occurs abnormally slowly back to the power law with the exponent α < 0.16. The observed anomalously slow relaxation of such a system and comparison with the time dependence of the volume of the confined liquid obtained in confirm the correctness of the description of disordered media on the basis of the notion of local metastable structures.
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 .
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.
Li, Fuping; Li, Jinshan; Xu, Guangsheng; Liu, Gejun; Kou, Hongchao; Zhou, Lian
2015-06-01
Porous titanium with average pore size of 100-650 μm and porosity of 30-70% was fabricated by diffusion bonding of titanium meshes. Pore structure was characterized by Micro-CT scan and SEM. Compressive behavior of porous titanium in the out-of-plane direction was studied. The effect of porosity and pore size on the compressive properties was also discussed based on the deformation mode. The results reveal that the fabrication process can control the porosity precisely. The average pore size of porous titanium can be tailored by adjusting the pore size of titanium meshes. The fabricated porous titanium possesses an anisotropic structure with square pores in the in-plane direction and elongated pores in the out-of-plane direction. The compressive Young's modulus and yield stress are in the range of 1-7.5 GPa and 10-110 MPa, respectively. The dominant compressive deformation mode is buckling of mesh wires, but some uncoordinated buckling is present in porous titanium with lower porosity. Relationship between compressive properties and porosity conforms well to the Gibson-Ashby model. The effect of pore size on compressive properties is fundamentally ascribed to the aspect ratio of titanium meshes. Porous titanium with 60-70% porosity has potential for trabecular bone implant applications.
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.
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
Miller, Cass T.
2009-01-01
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. PMID:22563137
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.
Gas storage in porous metal-organic frameworks for clean energy applications.
Ma, Shengqian; Zhou, Hong-Cai
2010-01-01
Depletion of fossil oil deposits and the escalating threat of global warming have put clean energy research, which includes the search for clean energy carriers such as hydrogen and methane as well as the reduction of carbon dioxide emissions, on the urgent agenda. A significant technical challenge has been recognized as the development of a viable method to efficiently trap hydrogen, methane and carbon dioxide gas molecules in a confined space for various applications. This issue can be addressed by employing highly porous materials as storage media, and porous metal-organic frameworks (MOFs) which have exceptionally high surface areas as well as chemically-tunable structures are playing an unusual role in this respect. In this feature article we provide an overview of the current status of clean energy applications of porous MOFs, including hydrogen storage, methane storage and carbon dioxide capture. PMID:20024292
Pokki, J; Ergeneman, O; Sivaraman, K M; Ozkale, B; Zeeshan, M A; Lühmann, T; Nelson, B J; Pané, S
2012-05-21
Porous nanostructures of polypyrrole (Ppy) were fabricated using colloidal lithography and electrochemical techniques for potential applications in drug delivery. A sequential fabrication method was developed and optimized to maximize the coverage of the Ppy nanostructures and to obtain a homogeneous layer over the substrate. This was realized by masking with electrophoretically-assembled polystyrene (PS) nanospheres and then electroplating. Drug/biomolecule adsorption and the release characteristics for the porous nanostructures of Ppy were investigated using rhodamine B (Rh-B). Rh-B is an easily detectable small hydrophobic molecule that is used as a model for many drugs or biological substances. The porous Ppy nanostructures with an enhanced surface area exhibited higher Rh-B loading capacity than bulk planar films of Ppy. Moreover, tunability of surface morphology for further applications (e.g., sensing, cell adhesion) was demonstrated.
Gas storage in porous metal-organic frameworks for clean energy applications.
Ma, Shengqian; Zhou, Hong-Cai
2010-01-01
Depletion of fossil oil deposits and the escalating threat of global warming have put clean energy research, which includes the search for clean energy carriers such as hydrogen and methane as well as the reduction of carbon dioxide emissions, on the urgent agenda. A significant technical challenge has been recognized as the development of a viable method to efficiently trap hydrogen, methane and carbon dioxide gas molecules in a confined space for various applications. This issue can be addressed by employing highly porous materials as storage media, and porous metal-organic frameworks (MOFs) which have exceptionally high surface areas as well as chemically-tunable structures are playing an unusual role in this respect. In this feature article we provide an overview of the current status of clean energy applications of porous MOFs, including hydrogen storage, methane storage and carbon dioxide capture.
Sun, Ming-Hui; Huang, Shao-Zhuan; Chen, Li-Hua; Li, Yu; Yang, Xiao-Yu; Yuan, Zhong-Yong; Su, Bao-Lian
2016-06-13
Over the last decade, significant effort has been devoted to the applications of hierarchically structured porous materials owing to their outstanding properties such as high surface area, excellent accessibility to active sites, and enhanced mass transport and diffusion. The hierarchy of porosity, structural, morphological and component levels in these materials is key for their high performance in all kinds of applications. The introduction of hierarchical porosity into materials has led to a significant improvement in the performance of materials. Herein, recent progress in the applications of hierarchically structured porous materials from energy conversion and storage, catalysis, photocatalysis, adsorption, separation, and sensing to biomedicine is reviewed. Their potential future applications are also highlighted. We particularly dwell on the relationship between hierarchically porous structures and properties, with examples of each type of hierarchically structured porous material according to its chemical composition and physical characteristics. The present review aims to open up a new avenue to guide the readers to quickly obtain in-depth knowledge of applications of hierarchically porous materials and to have a good idea about selecting and designing suitable hierarchically porous materials for a specific application. In addition to focusing on the applications of hierarchically porous materials, this comprehensive review could stimulate researchers to synthesize new advanced hierarchically porous solids.
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
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.
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
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.
Hierarchically assembled porous ZnO microstructures and applications in a gas sensor
NASA Astrophysics Data System (ADS)
Li, Benxia; Wang, Yanfen
2011-04-01
This paper presents a facile, low-cost and pollution-free route to prepare porous metal oxide nanomaterials. Hierarchically assembled ZnO microstructures with multi-scaled porosity were obtained by calcining the flower-like assembly of a basic zinc carbonate (BZC) precursor which was synthesized by a facile low-temperature (100 ∘C) homogenous precipitation without using any organic solvent or surfactant. A gas sensor based on the porous ZnO sample exhibited higher response to ethanol and formaldehyde gases than commercial ZnO powder. The facile preparation method and the improved property derived from the hierarchically porous microstructure are of great significance in the synthesis and application of nanomaterials.
Review of porous silicon preparation and its application for lithium-ion battery anodes.
Ge, M; Fang, X; Rong, J; Zhou, C
2013-10-25
Silicon is of great interest for use as the anode material in lithium-ion batteries due to its high capacity. However, certain properties of silicon, such as a large volume expansion during the lithiation process and the low diffusion rate of lithium in silicon, result in fast capacity degradation in limited charge/discharge cycles, especially at high current rate. Therefore, the use of silicon in real battery applications is limited. The idea of using porous silicon, to a large extent, addresses the above-mentioned issues simultaneously. In this review, we discuss the merits of using porous silicon for anodes through both theoretical and experimental study. Recent progress in the preparation of porous silicon through the template-assisted approach and the non-template approach have been highlighted. The battery performance in terms of capacity and cyclability of each structure is evaluated.
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.
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.
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.
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.
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.
Optical properties of porous chalcogenide films for sensor application
NASA Astrophysics Data System (ADS)
Lalova, A.; Todorov, R.
2012-12-01
The object of the present work is investigation of the optical properties of obliquely deposited thin films from As - S - Ge system. Aiming to obtain high porous coatings the deposition rate was varied in the range of 0.05-10 nm/s. The conditions for deposition of thin As - S - Ge films with columnar structure and high porosity were established. The role of the actual deposition conditions on the optical properties is examined. The optical constants (refractive index, n and absorption coefficient, α) and thickness, d as well as the optical band gap, Eg, and slope parameter B in dependence of the deposition angle and rate are determined from specrophotometric measurements in the spectral range 400-2000 nm applying the Swanepoel's envelope method and Tauc's procedure. Increasing of the value of n from 2.40 to 1.83 for thin film with composition As10Ge30S60 with increasing deposition angle from 0° to 75° is observed. The possibility of using the thin films for optical sensing of SO2 and H2S was examined. Reversible changes of the refractive index, Δn = 0.015 were observed as a consequence of treatment virgin - exposure to H2SO4 vapors- annealing at 120 °C.
Piezoelectricity of fluorine-system porous electret and its application
NASA Astrophysics Data System (ADS)
Kaimori, Shingo; Sugawara, Jun; Watanabe, Keisuke; Sugitani, Hideki; Hayashi, Syota; Nakiri, Takuo; Tajitsu, Yoshiro
2014-09-01
We developed a piezoelectric polymer film that was an electret using a porous poly(tetrafluoroethylene) (p-PTFE) film with high piezoelectricity and high heat resistance. First, we found that the p-PTFE electret had a piezoelectric constant d33 of 100 pC/N after the optimization of its pore size. This value was about five times as large as that of poly(vinylidene fluoride) (PVDF) and was retained up to a temperature of as high as 120 °C. Then a new device using the laminated film with perfluoroalkoxy (PFA) laminated on one side of the p-PTFE electret was developed for the demonstration of pressure sensing. A new flexible device with a large area was realized. Then, for the demonstration of pressure sensing, a plastic touch pen for a touch panel was traced on the surface of the device at a constant speed of 80 mm/s under a compressive load of 0.05 N. The results confirmed that the device exhibited superior sensing responsiveness.
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
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.
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.
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.
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
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.
NASA Astrophysics Data System (ADS)
Singh, K. D.
2016-08-01
An unsteady mixed convection flow of a visco-elastic, incompressible and electrically conducting fluid in a hot vertical channel is analyzed. The vertical channel is filled with a porous medium. The temperature of one of the channel plates is considered to be fluctuating span-wise cosinusoidally, i.e., T^* ( {y^* ,z^* ,t^* } ) = T_1 + ( {T_2} - {T_ 1} ) cos ( {{{π z^* } over d} - ω ^* t^* } ). A magnetic field of uniform strength is applied perpendicular to the planes of the plates. The magnetic Reynolds number is assumed very small so that the induced magnetic field is neglected. It is also assumed that the conducting fluid is gray, absorbing/emitting radiation and non-scattering. Governing equations are solved exactly for the velocity and the temperature fields. The effects of various flow parameters on the velocity, temperature and the skin friction and the Nusselt number in terms of their amplitudes and phase angles are discussed with the help of figures.
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
Gorla, Rama Subba Reddy; Chamkha, Ali Jawad; Rashad, Ahmed Mohamed
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.
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.
Oostrom, Mart; Dane, Jacob H.; Wietsma, Thomas W.
2005-11-14
A two-dimensional flow cell experiment was conducted to study the removal of the carbon tetrachloride component of a DNAPL mixture from a layered porous medium through soil vapor extraction (SVE) with moist and dry air. A dual-energy gamma radiation system was used at various times to non-intrusively determine fluid saturations. The mixture, which contained the volatile organic carbon tetrachloride, mimics the DNAPL disposed at the Hanford Site in Washington State. The flow cell, which is 100 cm long, 75 cm high and 5.5 cm wide, was packed with two sloped coarse sand and two sloped silt layers in an otherwise uniform matrix of medium-grained sand. A V-shaped fine sand layer was placed at the bottom of the flow cell to prevent DNAPL from exiting the flow cell. The water table was located 2 cm from the bottom, creating variably saturated conditions. A 500-mL spill was introduced at the top of the flow cell from a small source area. It was observed that the DNAPL largely by-passed the silt layers but easily moved into the coarse sand layers. Residual DNAPL was formed in the medium-grained sand matrix. The DNAPL caused a distinct reduction of the capillary fringe. Most of the DNAPL ended up in a pool on top of the V-shaped fine sand. Through four treatments with moist air soil vapor extraction, most residual carbon tetrachloride was removed from the medium-grained matrix and the coarse sand layers. However, soil vapor extraction with moist air was not able to remove the carbon tetrachloride from the silt layers and the pool. Through a water table reduction and subsequent soil vapor extraction with dry air, the carbon tetrachloride in the silt layers and the pool was effectively removed. Based on gamma measurements and carbon tetrachloride vapor concentration data, it was estimated that after the final remediation treatment, almost 90% of the total mass was removed.
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)
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
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.
Yan, Zhengquan; Yao, Wenli; Hu, Lei; Liu, Dandan; Wang, Chundong; Lee, Chun-Sing
2015-03-19
Due to high specific surface area, excellent conductivity, low mass density, good compatibility and elegant flexibility, three-dimensional graphene composites with interconnected porous structures possess unusual and novel physical and electronic properties, unsurpassed chemical functionalities and other attractive features. Therefore, different three-dimensional graphene-based nanoporous scaffolds have been extensively designed, prepared and investigated for practical applications in lithium-ion batteries, super-capacitors, solar cells, catalysis, thermal management, environment pollution enrichment and separation, and chemical sensors with high performance from both fundamental and technological viewpoints. To present readers with a better understanding of this kind of important porous material, in this feature article, we will highlight the main achievements made in the preparation of 3D graphene micro- and/or nano-architectures and their potential applications in the aforementioned fields.
NASA Astrophysics Data System (ADS)
Yan, Zhengquan; Yao, Wenli; Hu, Lei; Liu, Dandan; Wang, Chundong; Lee, Chun-Sing
2015-03-01
Due to high specific surface area, excellent conductivity, low mass density, good compatibility and elegant flexibility, three-dimensional graphene composites with interconnected porous structures possess unusual and novel physical and electronic properties, unsurpassed chemical functionalities and other attractive features. Therefore, different three-dimensional graphene-based nanoporous scaffolds have been extensively designed, prepared and investigated for practical applications in lithium-ion batteries, super-capacitors, solar cells, catalysis, thermal management, environment pollution enrichment and separation, and chemical sensors with high performance from both fundamental and technological viewpoints. To present readers with a better understanding of this kind of important porous material, in this feature article, we will highlight the main achievements made in the preparation of 3D graphene micro- and/or nano-architectures and their potential applications in the aforementioned fields.
Chen, Haining; Zhu, Liqun; Hou, Qin; Liu, Huicong; Li, Weiping
2013-06-01
Changing the sheets: Hollow TiO₂ porous nanosheets (HTPNs) are prepared on ITO glass through an improved TiO₂ polycrystalline shell-assisted cation exchange by using ZnO porous nanosheets (grown by using indirect electrodeposition) as a template. Quantum dot-sensitized solar cells based on HTPNs exhibit a high performance, and other photoelectrochemical devices are expected to be prepared based on HTPNs.
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.
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.
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.
Study of viscoplastic deformation in porous organosilicate thin films for ultra low-k applications
NASA Astrophysics Data System (ADS)
Zin, Emil H.; Bang, W. H.; Todd Ryan, E.; King, Sean W.; Kim, Choong-Un
2013-06-01
This letter reports experimental observations evidencing the viscoplasticity of porous organosilicate glass thin films under conditions pertinent to their application in advanced low-k/Cu interconnect technology. Specifically, it is found that porous SiCOH thin films exhibit a significant level of viscoplasticity with a rate sensitive to the porosity, the degree of plasma damage, and hydration reaction when tested using a ball indenter at 150-400 °C. The activation energy of the viscosity (1.25-1.45 eV) is measured to be far lower than the bulk glass (>4 eV), suggesting that the viscous flow is affected by the presence of defective bond-network such as Si-OH or Si-H bonds.
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.
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.
Multi-particle assembled porous nanostructured MgO: its application in fluoride removal
NASA Astrophysics Data System (ADS)
Gangaiah, Vijayakumar; Siddaramanna, Ashoka; Thimanna Chandrappa, Gujjarahalli
2014-12-01
In this article, a simple and economical route based on ethylene glycol mediated process was developed to synthesize one-dimensional (1D) multiparticle assembled nanostructured MgO using magnesium acetate and urea as reactants. Porous multiparticle chain-like MgO has been synthesized by the calcination of a solvothermally derived single nanostructured precursor. The prepared products were characterized by an x-ray diffraction (XRD) pattern, thermogravimetry, scanning/transmission electron microscopy (SEM/TEM) and N2 adsorption (BET). As a proof of concept, the porous multiparticle chain-like MgO has been applied in a water treatment for isolated and rural communities, and it has exhibited an excellent adsorption capability to remove fluoride in waste water. In addition, this method could be generalized to prepare other 1D nanostructures with great potential for various attractive applications.
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.
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.
Oostrom, Mart; Dane, J H.; Wietsma, Thomas W.
2005-11-16
A two-dimensional flow cell experiment was conducted to study the removal of the carbon tetrachloride component of a DNAPL mixture from a layered porous medium through soil vapor extraction (SVE) with moist and dry air. A dual-energy gamma radiation system was used at various times to non-intrusively determine fluid saturations. The mixture, which contained the volatile organic carbon tetrachloride, mimics the DNAPL disposed at the Hanford Site in Washington State. The flow cell, which is 100 cm long, 75 cm high and 5.5 cm wide, was packed with two sloped coarse sand and two sloped silt layers in an otherwise uniform matrix of medium-grained sand. A V-shaped fine sand layer was placed at the bottom of the flow cell to prevent DNAPL from exiting the flow cell. The water table was located 2 cm from the bottom, creating variably saturated conditions. A 500-mL spill was introduced at the top of the flow cell from a small source area. It was observed that the DNAPL largely by-passed the silt layers but easily moved into the coarse sand layers. Residual DNAPL was formed in the medium-grained sand matrix. The DNAPL caused a distinct reduction of the capillary fringe. Most of the DNAPL ended up in a pool on top of the V-shaped fine sand. Through four treatments with moist air soil vapor extraction, most residual carbon tetrachloride was removed from the medium-grained matrix and the coarse sand layers. However, soil vapor extraction with moist air was not able to remove the carbon tetrachloride from the silt layers and the pool. Through a water table reduction and subsequent soil vapor extraction with dry air, the carbon tetrachloride in the silt layers and the pool was effectively removed. Based on gamma measurements and carbon tetrachloride vapor concentration data, it was estimated that after the final remediation treatment, almost 90% of the total mass was removed. Key Words: DNAPL; soil vapor extraction; desiccation; remediation
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.
Kang, Hyun Goo; Kim, So Yeon; Lee, Young Moo
2006-11-01
Porous gelatin scaffolds were prepared using a modified overrun process, which is a novel method for preparing a porous matrix by injecting air and mixing polymer solution at low temperature. The pores in the scaffolds formed by the overrun process exhibited a dual-pore structure due to the injection of air bubbles and ice recrystallization. However, the morphology of the overrun-processed gelatin scaffolds had closed pore structures. The closed pore structure was reformed into a uniformly distributed and interconnected open structure by the combination of the overrun process and a particle-leaching technique (NaCl and sucrose). The mechanical strength and biodegradation rate of gelatin scaffolds were controlled by the matrix porosity and concentration of gelatin solution. Despite higher porosity, overrun processed gelatin scaffolds showed similar mechanical strength to freeze-dried scaffolds. After 1 week of in vitro culturing, the fibroblasts in overrun-processed scaffolds were widely distributed on the surface of the scaffold pores, whereas cells seeded in freeze-dried scaffolds were mainly placed on the top and bottom of the scaffolds. Therefore, the overrun process combined with a particle-leaching technique can be applied to fabricate porous scaffolds with a desirable cellular structure for tissue engineering applications.
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)
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.
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.
Urmann, Karina; Lazzaro, Anna; Gandolfi, Isabella; Schroth, Martin H; Zeyer, Josef
2009-08-01
Microbial methane oxidation is a key process in the global methane cycle. In the context of global warming, it is important to understand the responses of the methane-oxidizing microbial community to temperature changes in terms of community structure and activity. We studied microbial methane oxidation in a laboratory-column system in which a diffusive CH(4)/O(2) counter gradient was maintained in an unsaturated porous medium at temperatures between 4 and 20 degrees C. Methane oxidation was highly efficient at all temperatures, as on average 99 +/- 0.5% of methane supplied to the system was oxidized. The methanotrophic community that established in the model system after initial inoculation appeared to be able to adapt quickly to different temperatures, as methane emissions remained low even after the system was subjected to abrupt temperature changes. FISH showed that Type I as well as Type II methanotrophs were probably responsible for the observed activity in the column system, with a dominance of Type I methanotrophs. Cloning and sequencing suggested that Type I methanotrophs were represented by the genus Methylobacter while Type II were represented by Methylocystis. The results suggest that in an unsaturated system with diffusive substrate supply, direct effects of temperature on apparent methanotrophic activity and community may be of minor importance. However, this remains to be verified in the field.
NASA Astrophysics Data System (ADS)
Tham, Leony; Nazar, Roslinda; Pop, Ioan
2016-09-01
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)
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.
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)
VeeraKrishna, M.; Subba Reddy, G.
2016-09-01
In this paper, we make an initial vale investigation of hydromagnetic convective flow of a viscous electrically conducting second grade fluid through a porous medium in a rotating parallel plate channel in the presence of a temperature dependent heat source. The perturbations in the flow are created by a constant pressure gradient along the plates in addition to non-torsional oscillations of the lower plate. The exact solutions of the velocity and the temperature fields consist of the steady state and the transient components using Laplace transform technique. The time required for the transient effects to decay is discussed in detail and the ultimate steady state consists of boundary layers on the plates and an interior. Attention is focused on the physical nature of the solutions, and the structure of the various kinds of boundary layers formed on the plates. The final steady state velocity and temperature fields are numerically discussed for different values of the governing parameters. The shear stresses and the Nusselt number are tabulated. Particular case when both the plates are at rest has also been computed and analyzed.
Yan, Lesan; Higbee, Elizabeth; Tsourkas, Andrew
2015-01-01
Because of their low membrane permeability the use of polymeric vesicles in certain drug delivery and molecular imaging applications and as bioreactors is less than ideal. Here, we report a simple method to prepare porous polymeric vesicles that possess high membrane permeability. Specifically, porous vesicles were produced from the aqueous assembly of the diblock copolymer PEG-PBD, and the triblock copolymer PEG-PPO-PEG. It was found that PEG-PPO-PEG-doped polymersomes exhibited improved membrane permeability to molecules less than 5 kDa. Further, these porous vesicles retained molecules ≥10 kDa within their aqueous interiors with no significant leakage. To demonstrate its application, highly efficient magnetic resonance contrast agents were produced from porous polymersomes by encapsulating macromolecules labeled with gadolinium. Due to a fast water exchange rate with surrounding bulk water, these paramagnetic porous polymersomes exhibited higher r1 relaxivity compared with Gd-encapsulated vesicles with no pores. Due to their simplicity, the porous polymersomes prepared with this method are expected to have additional useful applications. PMID:26693022
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.
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.
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.
Application of vigilance research - Rare, medium, or well done?
NASA Technical Reports Server (NTRS)
Wiener, Earl L.
1987-01-01
In the years since Mackworth (1950) initiated research into problems of human vigilance, automated systems have become more complex and costly, with greater repercussions upon failure; this has led to a paradoxical enhancement of human monitoring's importance. Applications of vigilance research to well-designed systems that take human monitoring into account are rare, although the outlook for future systems is improving. Attention is presently given to problems encountered in considerations of signal rate, length of vigil, time decrements, and two examples of implementation from commercial aviation.
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.
Chadwick, E G; Clarkin, O M; Raghavendra, R; Tanner, D A
2014-01-01
The properties of porous silicon make it a promising material for a host of applications including drug delivery, molecular and cell-based biosensing, and tissue engineering. Porous silicon has previously shown its potential for the controlled release of pharmacological agents and in assisting bone healing. Hydroxyapatite, the principle constituent of bone, allows osteointegration in vivo, due to its chemical and physical similarities to bone. Synthetic hydroxyapatite is currently applied as a surface coating to medical devices and prosthetics, encouraging bone in-growth at their surface and improving osseointegration. This paper examines the potential for the use of an economically produced porous silicon particulate-polytetrafluoroethylene sheet for use as a guided bone regeneration device in periodontal and orthopaedic applications. The particulate sheet is comprised of a series of microparticles in a polytetrafluoroethylene matrix and is shown to produce a stable hydroxyapatite on its surface under simulated physiological conditions. The microstructure of the material is examined both before and after simulated body fluid experiments for a period of 1, 7, 14 and 30 days using Scanning Electron Microscopy. The composition is examined using a combination of Energy Dispersive X-ray Spectroscopy, Thin film X-ray diffraction, Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy and the uptake/release of constituents at the fluid-solid interface is explored using Inductively Coupled Plasma-Optical Emission Spectroscopy. Microstructural and compositional analysis reveals progressive growth of crystalline, 'bone-like' apatite on the surface of the material, indicating the likelihood of close bony apposition in vivo.
Babu, Ponnivalavan; Kumar, Rajnish; Linga, Praveen
2013-11-19
In this work, the performance of a new porous medium, polyurethane (PU) foam in a fixed bed reactor for carbon dioxide separation from fuel gas mixture using the hydrate based gas separation process is evaluated. The kinetics of hydrate formation in the presence of 2.5 mol % propane as thermodynamic promoter was investigated at 4.5, 5.5, and 6.0 MPa and 274.2 K. Significantly higher gas consumption and water conversion to hydrate was achieved when PU foam was employed. PU foam as a porous medium can help convert 54% of water to hydrate in two hours of hydrate formation. In addition the induction times were very low (<3.67 min at 6.0 MPa). A normalized rate of hydrate formation of 64.48 (±3.82) mol x min(-1) x m(-3) was obtained at 6.0 MPa and 274.2 K. Based on a morphological study, the mechanism of hydrate formation from water dispersed in interstitial pore space of the porous medium is presented. Finally, we propose a four step operation of the hydrate based gas separation process to scale up.
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
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.
Jahangiri, Elham; Reichelt, Senta; Thomas, Isabell; Hausmann, Kristin; Schlosser, Dietmar; Schulze, Agnes
2014-08-08
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.
Ding, Guan-Jun; Zhu, Ying-Jie; Qi, Chao; Lu, Bing-Qiang; Wu, Jin; Chen, Feng
2015-04-01
Amorphous calcium phosphate (ACP) microspheres with a porous and hollow structure have been prepared using an aqueous solution containing CaCl2 as a calcium source, adenosine triphosphate disodium salt (Na2ATP) as a phosphorus source in the presence of a block copolymer methoxyl poly(ethylene glycol)-block-poly(D,L-lactide) (mPEG-PLA) by the microwave-assisted hydrothermal method. The effects of microwave hydrothermal temperature and the concentrations of CaCl2 and Na2ATP on the crystal phase and morphology of the product are investigated. The as-prepared ACP porous hollow microspheres have a relatively high specific surface area of 232.9 m(2) g(-1) and an average pore size of 9.9 nm. A typical anticancer drug, docetaxel, is used to evaluate the drug loading ability and drug release behavior of ACP porous hollow microspheres in phosphate buffered saline (PBS) with different pH values of 4.5 and 7.4. The experiments reveal that the ACP porous hollow microspheres have a high drug loading capacity and favorable pH-responsive drug release property, and the ACP porous hollow microsphere drug delivery system shows a high ability to damage tumor cells. It is expected that the as-prepared ACP porous hollow microspheres are promising for the applications in various biomedical fields such as drug delivery.
Ding, Guan-Jun; Zhu, Ying-Jie; Qi, Chao; Lu, Bing-Qiang; Wu, Jin; Chen, Feng
2015-04-01
Amorphous calcium phosphate (ACP) microspheres with a porous and hollow structure have been prepared using an aqueous solution containing CaCl2 as a calcium source, adenosine triphosphate disodium salt (Na2ATP) as a phosphorus source in the presence of a block copolymer methoxyl poly(ethylene glycol)-block-poly(D,L-lactide) (mPEG-PLA) by the microwave-assisted hydrothermal method. The effects of microwave hydrothermal temperature and the concentrations of CaCl2 and Na2ATP on the crystal phase and morphology of the product are investigated. The as-prepared ACP porous hollow microspheres have a relatively high specific surface area of 232.9 m(2) g(-1) and an average pore size of 9.9 nm. A typical anticancer drug, docetaxel, is used to evaluate the drug loading ability and drug release behavior of ACP porous hollow microspheres in phosphate buffered saline (PBS) with different pH values of 4.5 and 7.4. The experiments reveal that the ACP porous hollow microspheres have a high drug loading capacity and favorable pH-responsive drug release property, and the ACP porous hollow microsphere drug delivery system shows a high ability to damage tumor cells. It is expected that the as-prepared ACP porous hollow microspheres are promising for the applications in various biomedical fields such as drug delivery. PMID:25535849
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
Development of a chitosan-based biofoam: application to the processing of a porous ceramic material.
Mathias, Jean-Denis; Tessier-Doyen, Nicolas; Michaud, Philippe
2011-02-16
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.
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, 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.
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.
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.
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.
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.
A Porous TiAl6V4 Implant Material for Medical Application.
Deing, Axel; Luthringer, Bérengère; Laipple, Daniel; Ebel, Thomas; Willumeit, Regine
2014-01-01
Increased durability of permanent TiAl6V4 implants still remains a requirement for the patient's well-being. One way to achieve a better bone-material connection is to enable bone "ingrowth" into the implant. Therefore, a new porous TiAl6V4 material was produced via metal injection moulding (MIM). Specimens with four different porosities were produced using gas-atomised spherical TiAl6V4 with different powder particle diameters, namely, "Small" (<45 μm), "Medium" (45-63 μm), "Mix" (90% 125-180 μm + 10% <45 μm), and "Large" (125-180 μm). Tensile tests, compression tests, and resonant ultrasound spectroscopy (RUS) were used to analyse mechanical properties. These tests revealed an increasing Young's modulus with decreasing porosity; that is, "Large" and "Mix" exhibit mechanical properties closer to bone than to bulk material. By applying X-ray tomography (3D volume) and optical metallographic methods (2D volume and dimensions) the pores were dissected. The pore analysis of the "Mix" and "Large" samples showed pore volumes between 29% and 34%, respectively, with pore diameters ranging up to 175 μm and even above 200 μm for "Large." Material cytotoxicity on bone cell lines (SaOs-2 and MG-63) and primary cells (human bone-derived cells, HBDC) was studied by MTT assays and highlighted an increasing viability with higher porosity.
Code of Federal Regulations, 2010 CFR
2010-07-01
... treatment steps to small, medium-size and large water systems. 141.81 Section 141.81 Protection of... to small, medium-size and large water systems. (a) Systems shall complete the applicable corrosion...) or (b)(3) of this section. (2) A small system (serving ≤3300 persons) and a medium-size...
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 Plants Subcategory § 428.60 Applicability; description of the medium-sized general molded, extruded,...
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, 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, 2012 CFR
2012-07-01
... treatment steps to small, medium-size and large water systems. 141.81 Section 141.81 Protection of... to small, medium-size and large water systems. (a) Systems shall complete the applicable corrosion...) or (b)(3) of this section. (2) A small system (serving ≤3300 persons) and a medium-size...
Code of Federal Regulations, 2013 CFR
2013-07-01
... treatment steps to small, medium-size and large water systems. 141.81 Section 141.81 Protection of... to small, medium-size and large water systems. (a) Systems shall complete the applicable corrosion...) or (b)(3) of this section. (2) A small system (serving ≤3300 persons) and a medium-size...
Code of Federal Regulations, 2014 CFR
2014-07-01
... treatment steps to small, medium-size and large water systems. 141.81 Section 141.81 Protection of... to small, medium-size and large water systems. (a) Systems shall complete the applicable corrosion...) or (b)(3) of this section. (2) A small system (serving ≤3300 persons) and a medium-size...
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 Plants Subcategory § 428.60 Applicability; description of the medium-sized general molded, extruded,...
Code of Federal Regulations, 2011 CFR
2011-07-01
... treatment steps to small, medium-size and large water systems. 141.81 Section 141.81 Protection of... to small, medium-size and large water systems. (a) Systems shall complete the applicable corrosion...) or (b)(3) of this section. (2) A small system (serving ≤3300 persons) and a medium-size...
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...
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.
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
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
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.
Targeted Delivery by Smart Capsules for Controlling Two-phase Flow in Porous Media
NASA Astrophysics Data System (ADS)
Fan, J.; Weitz, D.
2015-12-01
Understanding and controlling two-phase flow in porous media are of particular importance to the relevant industry applications, such as enhanced oil recovery, CO2 sequestration, and groundwater remediation. 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 (a) delivering surfactant to the vicinity of oil-water interface and (b) delivering microgels to the high permeability region and therefore blocking the pore space there, respectively. We also show that flooding these two capsules into porous media effectively reduces the trapped oil and improves the homogeneity of the medium, respectively. Besides of its industrial applications, this technique also opens a new window to study the mechanism of two-phase flow in porous media.
Mixed convection aiding flow in a vertical porous annulus-two temperature model
NASA Astrophysics Data System (ADS)
Salman Ahmed, N. J.; AAAl-Rashed, Abdullah A.; Kamangar, Sarfaraz; Khaleed, H. M. T.; YunusKhan, T. M.; Athani, Abdulgaphur
2016-09-01
The effect of convective heat transfer on mixed convection flow in a vertical porous annulus embedded with fluid saturated porous medium for aiding flow is studied. The inner surface of the annular cylinder is heated with constant temperature whereas the outer surface remains at ambient temperature. The governing partial differential equations are solved using Finite Element Method (FEM). It is assumed that the Darcy law is applicable and thermal nonequilibrium TNE exists between solid and fluid phases of porous medium. The aiding flow behavior of heat transfer with respect to Radius ratioRr, Aspect ratio ArandRadiation parameter Rd for different values of Peclet number Peare investigated.
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)
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
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
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.
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
A Highly Ion-Selective Zeolite Flake Layer on Porous Membranes for Flow Battery Applications.
Yuan, Zhizhang; Zhu, Xiangxue; Li, Mingrun; Lu, Wenjing; Li, Xianfeng; Zhang, Huamin
2016-02-24
Zeolites are crystalline microporous aluminosilicates with periodic arrangements of cages and well-defined channels, which make them very suitable for separating ions of different sizes, and thus also for use in battery applications. Herein, an ultra-thin ZSM-35 zeolite flake was introduced onto a poly(ether sulfone) based porous membrane. The pore size of the zeolite (ca. 0.5 nm) is intermediary between that of hydrated vanadium ions (>0.6 nm) and protons (<0.24 nm). The resultant membrane can thus be used to perfectly separate vanadium ions and protons, making this technology useful in vanadium flow batteries (VFB). A VFB with a zeolite-coated membrane exhibits a columbic efficiency of >99 % and an energy efficiency of >81 % at 200 mA cm(-2), which is by far the highest value ever reported. These convincing results indicate that zeolite-coated membranes are promising in battery applications.
A Highly Ion-Selective Zeolite Flake Layer on Porous Membranes for Flow Battery Applications.
Yuan, Zhizhang; Zhu, Xiangxue; Li, Mingrun; Lu, Wenjing; Li, Xianfeng; Zhang, Huamin
2016-02-24
Zeolites are crystalline microporous aluminosilicates with periodic arrangements of cages and well-defined channels, which make them very suitable for separating ions of different sizes, and thus also for use in battery applications. Herein, an ultra-thin ZSM-35 zeolite flake was introduced onto a poly(ether sulfone) based porous membrane. The pore size of the zeolite (ca. 0.5 nm) is intermediary between that of hydrated vanadium ions (>0.6 nm) and protons (<0.24 nm). The resultant membrane can thus be used to perfectly separate vanadium ions and protons, making this technology useful in vanadium flow batteries (VFB). A VFB with a zeolite-coated membrane exhibits a columbic efficiency of >99 % and an energy efficiency of >81 % at 200 mA cm(-2), which is by far the highest value ever reported. These convincing results indicate that zeolite-coated membranes are promising in battery applications. PMID:26822866
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
Fabrication of porous hollow silica nanoparticles and their applications in drug release control.
Li, Zhu-Zhu; Wen, Li-Xiong; Shao, Lei; Chen, Jian-Feng
2004-08-11
Preparation and characterization of porous hollow silica nanoparticles (PHSN) for controlled release applications were investigated. Through orthogonally designed experiments, the optimal synthesis conditions for the preparation of PHSN were obtained and the produced PHSN were characterized by BET, SEM, TEM and IR. Scanning and transmission electron microscopy images revealed their hollow shell-core structure and also demonstrated that the size and shape of PHSN are determined by the templating CaCO3 nanoparticles. The produced PHSN were applied as a carrier to study the controlled release behaviors of Brilliant Blue F (BB), which was used as a model drug. Being loaded into the inner core and on the surfaces of the nanoparticles, BB was released slowly into a bulk solution for about 1140 min as compared to only 10 min for the normal SiO2 nanoparticles, thus exhibited a typical sustained release pattern without any burst effect. In addition, higher BET of the carriers, lower pH value and lower temperature prolonged BB release from PHSN, while stirring speed showed little influence on the release behavior. It showed that PHSN have a promising future in controlled drug delivery applications.
Porous silicon-cyclodextrin based polymer composites for drug delivery applications.
Hernandez-Montelongo, J; Naveas, N; Degoutin, S; Tabary, N; Chai, F; Spampinato, V; Ceccone, G; Rossi, F; Torres-Costa, V; Manso-Silvan, M; Martel, B
2014-09-22
One of the main applications of porous silicon (PSi) in biomedicine is drug release, either as a single material or as a part of a composite. PSi composites are attractive candidates for drug delivery systems because they can display new chemical and physical characteristics, which are not exhibited by the individual constituents alone. Since cyclodextrin-based polymers have been proven efficient materials for drug delivery, in this work β-cyclodextrin-citric acid in-situ polymerization was used to functionalize two kinds of PSi (nanoporous and macroporous). The synthesized composites were characterized by microscopy techniques (SEM and AFM), physicochemical methods (ATR-FTIR, XPS, water contact angle, TGA and TBO titration) and a preliminary biological assay was performed. Both systems were tested as drug delivery platforms with two different model drugs, namely, ciprofloxacin (an antibiotic) and prednisolone (an anti-inflammatory), in two different media: pure water and PBS solution. Results show that both kinds of PSi/β-cyclodextrin-citric acid polymer composites, nano- and macro-, provide enhanced release control for drug delivery applications than non-functionalized PSi samples.
Blanchet, Elise; Desmond, Elie; Erable, Benjamin; Bridier, Arnaud; Bouchez, Théodore; Bergel, Alain
2015-06-01
The objective was to replace synthetic medium by wastewater as a strategy to design low-cost scalable bioanodes. The addition of activated sludge was necessary to form primary bioanodes that were then used as the inoculum to form the secondary bioanodes. Bioanodes formed in synthetic medium with acetate 10mM provided current densities of 21.9±2.1A/m(2), while bioanodes formed in wastewater gave 10.3±0.1A/m(2). The difference was explained in terms of biofilm structure, electrochemical kinetics and redox charge content of the biofilms. In both media, current densities were straightforwardly correlated with the biofilm enrichment in Geobacteraceae but, inside this family, Geobacter sulfurreducens and an uncultured Geobacter sp. were dominant in the synthetic medium, while growth of another Geobacter sp. was favoured in wastewater. Finally, the primary/secondary procedure succeeded in designing bioanodes to treat food wastes by using wastewater as dilution medium, with current densities of 7±1.1A/m(2).
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.
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.
Rame, M.
1990-01-01
Flows in highly heterogeneous porous media arise in a variety of processes including enhanced oil recovery, in situ bioremediation of underground contaminants, transport in underground aquifers and transport through biological membranes. The common denominator of these processes is the transport (and possibly reaction) of a multi-component fluid in several phases. A new numerical methodology for the analysis of flows in heterogeneous porous media is presented. Cases of miscible and immiscible displacement are simulated to investigate the influence of the local heterogeneities on the flow paths. This numerical scheme allows for a fine description of the flowing medium and the concentration and saturation distributions thus generated show low numerical dispersion. If the size of the area of interest is a square of a thousand feet per side, geological information on the porous medium can be incorporated to a length scale of about one to two feet. The technique here introduced, Operator Splitting on Multiple Grids, solves the elliptic operators by a higher-order finite-element technique on a coarse grid that proves efficient and accurate in incorporating different scales of heterogeneities. This coarse solution is interpolated to a fine grid by a splines-under-tension technique. The equations for the conservation of species are solved on this fine grid (of approximately half a million cells) by a finite-difference technique yielding numerical dispersions of less than ten feet. Cases presented herein involve a single phase miscible flow, and liquid-phase immiscible displacements. Cases are presented for model distributions of physical properties and for porosity and permeability data taken from a real reservoir. Techniques for the extension of the methods to compressible flow situations and compositional simulations are discussed.
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)
Chen, Feng; Zhu, Ying-Jie; Zhang, Kui-Hua; Wu, Jin; Wang, Ke-Wei; Tang, Qi-Li; Mo, Xiu-Mei
2011-12-01
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.
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.
Unoxidized porous Si as an isolation material for mixed-signal integrated circuit applications
NASA Astrophysics Data System (ADS)
Kim, Han-Su; Xie, Ya-Hong; DeVincentis, Marc; Itoh, Tatsuo; Jenkins, Keith A.
2003-04-01
An isolation technology for radio frequency (rf) applications based on unoxidized porous Si (PS) is demonstrated. This study examines all the important issues pertinent to incorporating PS with Si very-large-scale integration (VLSI) technology, where PS is used as a semi-insulating material. Specifically, the issues on rf isolation performance of PS as a function of porosity [from coplanar waveguide (CPW) line measurements] and PS thickness (from on-chip inductors) and the stress generated from incorporating PS regions by anodization are discussed in detail. CPW line measurements show that the relative dielectric constant of PS films decreases from 9 to 3 with increasing porosity from 24% to 78%. PS is a very low loss material with loss tangent <0.001 at 20 GHz when its porosity is above 51%. rf crosstalk through a Si substrate can be reduced to that through air by inserting a PS trench between noise generating circuit and noise sensing circuit. On-chip spiral inductors fabricated on top of PS regions of through-the-wafer thickness have Qmax of about 29 at 7 GHz and resonant frequency higher than 20 GHz. With the additional advantage of planar topography and mechanical integrity, we show that unoxidized PS is an outstanding material for rf isolation in Si VLSI.
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.
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
Yang, Likai; Luo, Jing; Shi, Sanjun; Zhang, Qiang; Sun, Xun; Zhang, Zhirong; Gong, Tao
2013-07-15
As a non-invasive administration route, pulmonary peptide delivery for systemic application has shown great promise. However, many barriers exist that prevent effective peptide delivery. The use of porous nanoparticle-aggregate particles (PNAPs) is an excellent option because of their proper aerodynamic size and maximal deposition. However, in most cases, the spray drying heating process for PNAPs has been challenging in regard to maintaining peptide stability and activity. To overcome these issues, we developed a spray freeze-drying method for PNAP preparation. To solve the low entrapment efficiency problem of nanostructured lipid carriers, we used hydrophobic ion pair complexes to increase the lipophilicity of the peptide, thus increasing entrapment efficiency and drug loading. Here, we used a model peptide, octreotide acetate, for PNAP preparation, which has a high entrapment efficiency (>95%) and proper aerodynamic size (~3 μm). In addition, after intrapulmonary administration, we evaluated the pharmacokinetics and pharmacodynamics in a rat preventive hepatic ischemia-reperfusion injury model. Our in vivo data showed significantly increased area under the curve and improved plasma aspartate aminotransferase levels for our PNAP intrapulmonary delivery system vs. the clinically used octreotide acetate delivery via subcutaneous injection. Together, PNAPs may have great potential for carrying peptide drugs for pulmonary delivery.
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.
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.
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
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
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
Jaya, S; Durance, T D
2008-01-01
Many methods are available for developing three-dimensional porous scaffolds using various polymeric materials for tissue-engineering applications. Each has its own advantages and disadvantages. Some of the available methods and their limitations were discussed briefly. This paper focuses on the scope of novel technology called radiant energy application under vacuum for the fabrication of three-dimensional porous scaffolds for tissue engineering applications. Radiant energy application in the form of microwave under vacuum has been shown to develop and maintain the porous structure in fruits and vegetables after dehydration, which produced the microstructure similar to the freeze dried materials. Same principle of applying radiant energy under vacuum was used on the biopolymeric gels to create tailor-made, porous scaffolds for biomedical purposes. It has many advantages over the other existing methods of scaffold fabrication. This paper also reviews the scaffolds design recently fabricated by the authors using radiant energy under vacuum.
Resurgence flows in porous media
NASA Astrophysics Data System (ADS)
Adler, Pierre; Mityushev, Vladimir
2010-05-01
Porous media are generally described by the Darcy equation when the length scales are sufficiently large with respect to the pore scale. This approach is also applicable when the media are heterogeneous, i.e., when permeability varies with space which is the most common case. In addition, real media are very often fractured; for a long time, this complex physical problem has been schematized by the double porosity model devised by Barenblatt. More recently, these fractured media have been addressed with a detailed description of the fractures and of their hydrodynamic interaction with the surrounding porous medium. This approach will be briefly summarized and the main recent progress surveyed (2). There is another situation which occurs frequently in underground studies. One well is connected to a distant well while it is not connected to closer wells. Such a situation can only be understood if there is a direct link between the two connected wells and if this link has little if any hydrodynamic interaction with the porous medium that it crosses. This link can be a fracture or more likely a set of fractures. This phenomenon is called resurgence because of the obvious analogy with rivers which suddenly disappear underground and go out at the ground surface again. Similar ideas have already been developed in other fields. In Physics, random networks limited to nearest neighbors have been recently extended to small world models where distant vertices can be related directly by a link. The electrical testing of porous media by electrical probes located at the walls (electrical tomography) has been used frequently in Geophysics since it is a non-invasive technique; this classical technique corresponds exactly to the situation addressed here from a different perspective. Media with resurgences consist of a double structure (3). The first one which is continuous is described by Darcy law as usual. The second one models the resurgences by capillaries with impermeable walls
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.
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
NASA Astrophysics Data System (ADS)
Haslam, Jeffery John
1998-12-01
The need for improved fuel economy and reduced environmental emissions from power turbines has prompted the development of high temperature fiber composite materials. One use of these materials is for liners of the hot combustion regions of jet engines and land based power turbines. Stability of the composite materials against oxidative damage during long term use at high temperatures has motivated recent research into fiber composite materials composed entirely of oxide ceramics. All-oxide fiber reinforced composites containing porous, strongly bonded matrices have become of interest. The porosity provides for crack deflection along the fibers to prevent catastrophic failure of the fiber reinforcements. A new application of a processing method that produces evaporation/condensation sintering was employed to prevent shrinkage of the matrix. This processing method and the properties of the matrix, fibers, and composite were evaluated in this work. Producing a matrix without shrinkage is important to prevent undesirable crack-like voids from forming in the matrix. These voids are caused by constraint against shrinkage by the fiber reinforcements. Dry hydrogen chloride gas produced a reactive gas atmosphere that was used to sinter the zirconia particles with minimal shrinkage because the gas promotes evaporation/condensation sintering with zirconia. Sintering of samples that did not contain fiber reinforcements was studied to evaluate the properties of the matrix material. The sintering of monoclinic, tetragonal, and cubic zirconias in the reactive gas atmosphere was compared. Additions of mullite (which did not sinter significantly at processing temperatures) further reduced the shrinkage. The effects of the processing conditions on the sintering shrinkage, microstructure development, and mechanical properties were studied. Cubic and monoclinic zirconia coarsened significantly in the HCl gas sintering atmosphere. The coarsening of the particles during the sintering
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
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.
Preparation of porous Cu 2O octahedron and its application as L-Tyrosine sensors
NASA Astrophysics Data System (ADS)
Zhang, Xiaojun; Wang, Guangfeng; Gu, Aixia; Wu, Huaqiang; Fang, Bin
2008-12-01
Highly uniform porous cuprous oxide (Cu 2O) octahedra with an average size of 1 μm were first successfully prepared with high yield by a facile one-step seed-mediated approach, employing cupreous acetate and sodium sulfite as the reactants, and citric acid as the assistant vesicant. The crucial influence of citric acid and poly(vinylpyrrolidone) (PVP) on the morphology of porous octahedron in the synthesis has also been discussed. Electrochemical impendance spectrum (EIS) and cyclic voltammetry (CV) shows that the porous cuprous oxide octahedra have a stronger ability to promote electron transfer than both the Cu 2O octahedral and the Cu 2O nanoparticles resulting from such porous nanostructures, which potentially not only have high surface area but also can supply more efficient transport passage for the probe molecules to get to the active sites. The porous Cu 2O octahedra were successfully used to modify the gold electrode to detect L-Tyrosine (Tyr) with differential pulse voltammetry (DPV). The result shows that the porous cuprous oxide octahedra may be of great potential as L-Tyrosine electrochemical sensor.
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.
NASA Astrophysics Data System (ADS)
Tran Ngoc, T.; Lewandowska, J.; Vauclin, M.; Bertin, H.; Gentier, S.
2009-12-01
The complex processes of water flow and solute transport occurring in subsurface environment have to be well modeled in order to be able to protect the water aquifers against contamination, for security of nuclear waste depositories or CO2 sequestration, in the problem of extraction of geothermal energy. Since natural geological formations are often heterogeneous at different scales, it leads to preferential flow and transport observed in the breakthrough curves which is difficult to model. In such a case the concept of “double-porosity medium” originally introduced by Barenblatt et al. (1960), can be used. In this paper it was applied to a class of heterogeneous media (aggregated soils, fractured porous rocks) in which a strong contrast in the local pore size characteristics is manifested. It was assumed that the interactions/exchanges between the macro- and micro-porosity are responsible for solute spreading in the local non equilibrium conditions and contribute to the non Fickian behaviour. This study presents a macroscopic dispersion model associated with the unsaturated water flow, which was developped using the asymptotic homogenization method. This model consists of two equations describing the processes of solute transfer in the macro- and micro-porosity domains. A coupling between two concentration fields can be seen in the model, which gives an early breakthrough and a long tail effect. In order to enable the two-scale computations, the model was implemented using the commercial code COMSOL Multiphysics®. A particular strategy was proposed to take into account the micro-macro coupling. Finally, a series of experiments of tracer dispersion in a double-porosity physical model was performed under unsaturated steady-state flow conditions. The double-porosity medium presenting the periodic microstructure was composed of a regular assemblage between sintered clayey spheres and a fine sand. The model validation was carried out in two different stages. In
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.
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.
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
2016-01-01
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.
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.
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.
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
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.
Resurgence flows in porous media
NASA Astrophysics Data System (ADS)
Adler, P. M.; Mityushev, V.
2009-12-01
Porous media are generally described by the Darcy equation when the length scales are sufficiently large with respect to the pore scale. This approach is also applicable when the media are heterogeneous, i.e., when permeability varies with space which is the most common case. In addition, real media are very often fractured; for a long time, this complex physical problem has been schematized by the double porosity model devised by Barenblatt. More recently, these fractured media have been addressed with a detailed description of the fractures and of their hydrodynamic interaction with the surrounding porous medium. There is another situation which occurs frequently in underground studies. One well is connected to a distant well while it is not connected to closer wells. Such a situation can only be understood if there is a direct link between the two connected wells and if this link has little if any hydrodynamic interaction with the porous medium that it crosses. This link can be a fracture or more likely a set of fractures. This phenomenon is called resurgence because of the obvious analogy with rivers which suddenly disappear underground and go out at the ground surface again. Similar ideas have already been developed in other fields. In Physics, random networks limited to nearest neighbors have been recently extended to small world models where distant vertices can be related directly by a link. The electrical testing of porous media by electrical probes located at the walls (electrical tomography) has been used frequently in Geophysics since it is a non-invasive technique; this classical technique corresponds exactly to the situation addressed here from a different perspective. Media with resurgences consist of a double structure. The first one which is continuous is described by Darcy law as usual. The second one models the resurgences by capillaries with impermeable walls which relate distant points of the continuous medium. These two structures have already
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.
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
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.
An experimental evaluation of slots versus porous strips for laminar-flow applications
NASA Technical Reports Server (NTRS)
Cornelius, Kenneth C.
1987-01-01
Detailed mean velocity and disturbance amplitude measurements were conducted in a Blasius boundary-layer flow with wall suction applied at three downstream locations. The main emphasis was a direct comparison of the growth rate of the instability wave with discrete spanwise slots versus wide porous strips. The results demonstrate that the local effects of suction through slots or very narrow porous strips have a greater beneficial effect on the stability of the boundary-layer flow relative to the suction influence of a wide porous strip. Codes which use continuous suction for the growth rates of the instability waves to determine the suction quantities for a multiple series of slots will be quite conservative in the estimation of the suction quantity. Guidelines were provided for suction-chamber design and flow rates to minimize internal oscillations which propagate into the boundary-layer flow.
Application of a portable nuclear magnetic resonance surface probe to porous media.
Marko, Andriy; Wolter, Bernd; Arnold, Walter
2007-03-01
A portable nuclear magnetic resonance (NMR) surface probe was used to determine the time-dependent self-diffusion coefficient D(t) of water molecules in two fluid-filled porous media. The measuring equipment and the inhomogeneous magnetic fields in the sensitive volume of the probe are described. It is discussed how to evaluate D(t) using a surface probe from the primary and stimulated echoes generated in three-pulse experiments. Furthermore, the evaluation of D(t) allows one to determine the geometrical structure of porous materials.
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.
Properties of a porous Ti-6Al-4V implant with a low stiffness for biomedical application.
Li, X; Wang, C-T; Zhang, W-G; Li, Y-C
2009-02-01
Porous Ti-6Al-4V alloy was fabricated using the electron beam melting (EBM) process. The phases of the as-received powder and fabricated samples were characterized using X-ray diffraction (XRD) analysis. The XRD peaks of both diffraction patterns agree well, which indicated that the EBM process has not changed the composition of Ti-6Al-4V. The fabricated samples exhibited a Vickers microhardness value of around 428 HV. The compression and three-point bending tests were performed to evaluate the mechanical properties of the porous Ti-6Al-4V implant with a porosity of around 60 per cent. The compressive yield strength, Young's modulus, and ultimate compressive strength were 194.6 MPa, 4.25 GPa, and 222.6 MPa respectively. The bending stiffness and bending strength were 3.7 GPa and 126.3 MPa respectively. These results demonstrated that the porous Ti-6Al-4V implant with a low stiffness and high porosity could be a promising biomaterial for biomedical applications.
Evaporation Limited Radial Capillary Penetration in Porous Media.
Liu, Mingchao; Wu, Jian; Gan, Yixiang; Hanaor, Dorian A H; Chen, C Q
2016-09-27
The capillary penetration of fluids in thin porous layers is of fundamental interest in nature and various industrial applications. When capillary flows occur in porous media, the extent of penetration is known to increase with the square root of time following the Lucas-Washburn law. In practice, volatile liquid evaporates at the surface of porous media, which restricts penetration to a limited region. In this work, on the basis of Darcy's law and mass conservation, a general theoretical model is developed for the evaporation-limited radial capillary penetration in porous media. The presented model predicts that evaporation decreases the rate of fluid penetration and limits it to a critical radius. Furthermore, we construct a unified phase diagram that describes the limited penetration in an annular porous medium, in which the boundaries of outward and inward liquid are predicted quantitatively. It is expected that the proposed theoretical model will advance the understanding of penetration dynamics in porous media and facilitate the design of engineered porous architectures.
Evaporation Limited Radial Capillary Penetration in Porous Media.
Liu, Mingchao; Wu, Jian; Gan, Yixiang; Hanaor, Dorian A H; Chen, C Q
2016-09-27
The capillary penetration of fluids in thin porous layers is of fundamental interest in nature and various industrial applications. When capillary flows occur in porous media, the extent of penetration is known to increase with the square root of time following the Lucas-Washburn law. In practice, volatile liquid evaporates at the surface of porous media, which restricts penetration to a limited region. In this work, on the basis of Darcy's law and mass conservation, a general theoretical model is developed for the evaporation-limited radial capillary penetration in porous media. The presented model predicts that evaporation decreases the rate of fluid penetration and limits it to a critical radius. Furthermore, we construct a unified phase diagram that describes the limited penetration in an annular porous medium, in which the boundaries of outward and inward liquid are predicted quantitatively. It is expected that the proposed theoretical model will advance the understanding of penetration dynamics in porous media and facilitate the design of engineered porous architectures. PMID:27583455
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)
Luo, Jiang
1993-01-01
Technological and theoretical aspects of the development and application of ISFET based coulometric sensor-actuator systems are described. An application of such a system to the characterization of proteins is suggested. Diffusion and migration processes at the coulometric sensor-actuator systems with a planar actuator in the application of acid base titration were studied. To minimize the delay time and to limit the diffusion of the species, a porous noble metal actuator is proposed, instead of a planar one, closely covering the gate of the ISFET. The adaptation of the conventional ISFET technology, by which a flat ISFET is proposed and fabricated, is described. An analytical model to describe the developed ISFET based coulometric sensor-actuator systems with gate-covering porous actuator is proposed. A way to operate the developed coulometric sensor-actuator system for a dynamical measurement of the buffer capacity of an analyte is introduced. The buffer capacity as a distinct parameter to characterize proteins was measured. The preliminary results obtained from the measurement of lysozyme and ribonuclease showed different buffer capacities at different pH values. More studies are necessary to further investigate the applicability of this method to characterize proteins.
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
Chitrattha, Sasiprapa; Phaechamud, Thawatchai
2016-01-01
Poly(lactic acid) (PLA) is polymeric biomaterial that has been used for wound dressing due to its biodegradability and biocompatibility. However, PLA has some limitations including poor toughness, low degradation rate and high hydrophobicity. The aim of this study is to develop an antibiotic drug-loaded PLA porous film as wound dressing with antibacterial activity. PLA porous film was fabricated by temperature change technique using solvent casting method. Polyethylene glycol (PEG) 400 was added for improving the pore interconnectivity of film. Gentamicin sulfate (GS) or metronidazole (MZ) was incorporated into PLA porous films. PLA containing PEG 400 exhibited the more amorphous form than plain PLA film and contained 55.31 ± 2.85% porosity and 20 μm of the pore size which significantly improved the water vapor transmission rate, oxygen transmission rate, degradation rate and percentage of drug release, respectively. Drug-loaded porous films efficiently inhibited the bacteria growth. GS-loaded film inhibited Staphylococcus aureus, Proteus mirabilis, Pseudomonas aeruginosa, whereas MZ-loaded film inhibited Bacteroides fragilis and the sustainable antibacterial activity was attained for 7 days.
Chitrattha, Sasiprapa; Phaechamud, Thawatchai
2016-01-01
Poly(lactic acid) (PLA) is polymeric biomaterial that has been used for wound dressing due to its biodegradability and biocompatibility. However, PLA has some limitations including poor toughness, low degradation rate and high hydrophobicity. The aim of this study is to develop an antibiotic drug-loaded PLA porous film as wound dressing with antibacterial activity. PLA porous film was fabricated by temperature change technique using solvent casting method. Polyethylene glycol (PEG) 400 was added for improving the pore interconnectivity of film. Gentamicin sulfate (GS) or metronidazole (MZ) was incorporated into PLA porous films. PLA containing PEG 400 exhibited the more amorphous form than plain PLA film and contained 55.31 ± 2.85% porosity and 20 μm of the pore size which significantly improved the water vapor transmission rate, oxygen transmission rate, degradation rate and percentage of drug release, respectively. Drug-loaded porous films efficiently inhibited the bacteria growth. GS-loaded film inhibited Staphylococcus aureus, Proteus mirabilis, Pseudomonas aeruginosa, whereas MZ-loaded film inhibited Bacteroides fragilis and the sustainable antibacterial activity was attained for 7 days. PMID:26478412
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)
Saripalli, K. P.; Serne, R. J.; Khaleel, R.
2003-04-01
Tortuosity is the single most important characteristic of flow through porous media that determines several flow and transport phenomena. Currently available definitions of tortuosity are empirical, and do not lend themselves to direct and independent measurement. We present a new definition for the tortuosity factor of saturated media as the ratio of specific surface of real porous medium to that of an idealized capillary bundle. For unsaturated media, tortuosity factor is defined as the ratio of the specific air-water interfacial area of real and the corresponding idealized porous medium. This tortuosity factor is suitably measured using sorptive tracers (e.g., nitrogen adsorption method) for saturated media and interfacial tracers for unsaturated media. New models based on this approach are presented for the prediction of several fundamental phenomena in unsaturated porous media, such as diffusion, unsaturated water flow and anisotropy, that are influenced by changes in tortuosity with a changing water content. Diffusion coefficients and diffusive resistances measured in a number of saturated and unsaturated granular porous media agree well with the predictions of the model. Trends in the prediction of tortuosity as a function water saturation are in agreement with similar recent predictions based on diffusion theory (Moldrup et al., 2001). Unsaturated hydraulic conductivities measured for a number of coarse-textured sediments agree well with predictions based on a modified Kozeny-Carman relation. Results indicate that the alternative definition of tortuosity is useful to the understanding and prediction of multiphase flow and transport. By defining the tortuosity factor as the phase interfacial area ratio, one overcomes the need to base its definition on the length dimensions of flow through the idealized capillary bundles, which is the most serious deficiency in the tortuosity-based approaches to modeling flow through porous media (Dullien, 1979; Epstein, 1989).
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.
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.
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
NASA Astrophysics Data System (ADS)
Cora, Ömer N.; Usta, Yusuf; Koç, Muammer
2009-04-01
Integrated and compact products necessitate the use of advanced thermal management systems with reduced footprint and cost as well as increased efficiency. Micro-scale, porous and modulated (i.e. channels, pyramids, etc) surfaces offer increased surface area for a given volume and lead to two-phase heat transfer conditions with efficiency enhancements up to 300%. Such surfaces made of copper powders were demonstrated to be quite effective by several researchers after they were produced in controlled lab environments. Similar surfaces made of high temperature resistant materials such as stainless steel, nickel and titanium can also be used in fuel processor, SOFC and PEM fuel cell applications as bipolar/interconnect plates. However, their fabrication under mass-production conditions for marketable and cost-effective products requires well-established process parameters. In this study, warm compaction of copper powders onto thin copper solid substrates was experimented with under different compaction pressure (15-50 MPa), temperature (350-500 °C) and surface geometry (flat, large and small channeled) parameters using a design of experiment (DOE) approach to determine the proper process conditions. Porosity and bonding strength of compacted samples were measured to characterize their feasibility for compact and/or micro-scale heat/mass transfer applications. Results showed that a minimum 350 °C temperature and 15 MPa pressure level is necessary to obtain sound porous and micro-channeled surface layers. It was also found that at higher pressure levels (50 MPa), fabrication of micro-scale surface structures is highly repeatable with enhanced bonding strength characteristics. DOE findings will be used to establish proper process conditions to produce such porous surfaces using a continuous roll compaction process in the future.
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.
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.
Laser surface treatment of porous ceramic substrate for application in solid oxide fuel cells
NASA Astrophysics Data System (ADS)
Mahmod, D. S. A.; Khan, A. A.; Munot, M. A.; Glandut, N.; Labbe, J. C.
2016-08-01
Laser has offered a large number of benefits for surface treatment of ceramics due to possibility of localized heating, very high heating/cooling rates and possibility of growth of structural configurations only produced under non-equilibrium high temperature conditions. The present work investigates oxidation of porous ZrB2-SiC sintered ceramic substrates through treatment by a 1072 ± 10 nm ytterbium fiber laser. A multi-layer structure is hence produced showing successively oxygen rich distinct layers. The porous bulk beneath these layers remained unaffected as this laser-formed oxide scale and protected the substrate from oxidation. A glassy SiO2 structure thus obtained on the surface of the substrate becomes subject of interest for further research, specifically for its utilization as solid protonic conductor in Solid Oxide Fuel Cells (SOFCs).
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
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.
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
NASA Astrophysics Data System (ADS)
Ali, M.; Alim, M. A.; Nasrin, R.; Alam, M. S.
2016-07-01
An analysis is performed to study the free convection heat and mass transfer flow of an electrically conducting incompressible viscous fluid about a semi-infinite inclined porous plate under the action of radiation, chemical reaction in presence of magnetic field with variable viscosity. The dimensionless governing equations are steady, two-dimensional coupled and non-linear ordinary differential equation. Nachtsgeim-Swigert shooting iteration technique along with Runge-Kutta integration scheme is used to solve the non-dimensional governing equations. The effects of magnetic parameter, viscosity parameter and chemical reaction parameter on velocity, temperature and concentration profiles are discussed numerically and shown graphically. Therefore, the results of velocity profile decreases for increasing values of magnetic parameter and viscosity parameter but there is no effect for reaction parameter. The temperature profile decreases in presence of magnetic parameter, viscosity parameter and Prandtl number but increases for radiation parameter. Also, concentration profile decreases for the increasing values of magnetic parameter, viscosity parameter and reaction parameter. All numerical calculations are done with respect to salt water and fixed angle of inclination of the plate.
Porous silicon-based scaffolds for tissue engineering and other biomedical applications
NASA Astrophysics Data System (ADS)
Coffer, Jeffery L.; Whitehead, Melanie A.; Nagesha, Dattatri K.; Mukherjee, Priyabrata; Akkaraju, Giridhar; Totolici, Mihaela; Saffie, Roghieh S.; Canham, Leigh T.
2005-06-01
This work describes the formation of porous composite materials based on a combination of bioactive mesoporous silicon and bioerodible polymers such as poly-caprolactone (PCL). The fabrication of a range of composites prepared by both salt leaching and microemulsion techniques are discussed. Particular attention to the influence of Si content in the composite on in vitro calcification assays are assessed. For each system, cytotoxicity and cellular proliferation are explicitly evaluated through fibroblast cell culture assays.