Infiltration Front Research Articles

Interface study by dual‐beam FIB‐TEM in a pressureless infiltrated Al(Mg)–Al2O3 interpenetrating composite

This paper considers the microstructures of an Al(Mg)-Al(2)O(3) interpenetrating composite produced by a pressureless infiltration technique. It is well known that the governing principle in pressureless infiltration in Al-Al(2)O(3) system is the wettability between the molten metal and the ceramic phase; however, the infiltration mechanism is still not well understood. The objective of this research was to observe the metal-ceramic interface to understand the infiltration mechanism better. The composite was produced using an Al-8 wt% Mg alloy and 15% dense alumina foams at 915 degrees C in a flowing N(2) atmosphere. After infiltration, the composite was characterized by a series of techniques. Thin-film samples, specifically produced across the Al(Mg)-Al(2)O(3) interface, were prepared using a dual-beam focussed ion beam and subsequently observed using transmission electron microscopy. XRD scan analysis shows that Mg(3)N(2) formed in the foam at the molten alloy-ceramic infiltration front, whereas transmission electron microscopy analysis revealed that fine AlN grains formed at the metal-ceramic interface and MgAl(2)O(4) and MgSi(2) grains formed at specific points. It is concluded that it is the reactions between Al, Mg and the N(2) atmosphere that improve the wettability between molten Al and Al(2)O(3) and induce spontaneous infiltration.

Quick Method for Estimating Furrow Infiltration

This paper presents a simple and quick method for estimating furrow infiltration using a single advance point based on the volume balance equation. The furrow infiltration and water front advance along the furrow are assumed to follow the modified Kostiakov infiltration and power advance equations, respectively. The volume balance equation, including these equations, is simplified to a function containing two parameters, i.e., the exponents of power advance and Kostiakov infiltration equation (with a prior-known basic infiltration rate). These parameters are estimated by minimizing the function to zero using a quasi-Newton search algorithm, provided with Excel Solver. The estimated exponents are used to determine the Kostiakov infiltration parameters. The proposed one-point method is tested with seven independent furrow irrigation evaluation data sets and the estimated cumulative infiltration is compared with the observed counterparts. Performance of the proposed method was evaluated using the root-mean-s...

P16 INK4a Is a β-Catenin Target Gene and Indicates Low Survival in Human Colorectal Tumors

Human colorectal carcinomas display an infiltrative front of invasion where tumor cells undergo an epithelomesenchymal transition associated with low survival. Epithelomesenchymal transition is regulated by a nuclear beta-catenin accumulation, and subsequently, activation of beta-catenin/TCF4 target genes similar to CYCLIN D(1). Unexpectedly, these tumor cells are characterized by low proliferation, which correlates with the expression of the cell cycle inhibitor p16(INK4A). Therefore, we investigated the molecular mechanism of the transcriptional regulation of p16(INK4A) in colorectal cancer and its correlation with survival. Molecular biological techniques were used for investigating the transcriptional mechanisms of the p16(INK4A) gene regulation. Moreover, p16(INK4A) expression was correlated with the 10-year survival of patients with colorectal carcinomas. In colorectal carcinomas, expression of the p16(INK4A) gene is regulated by beta-catenin/TCF4 and correlates with low survival rates of patients with tumors displaying an infiltrative front of invasion. beta-catenin/TCF4 regulates cell cycle promoting (c-MYC, CYCLIN D(1)) and inhibiting genes (p16(INK4A)) at the same time in the mesenchymally differentiated tumor cells at the front of invasion. The function of p16(INK4A) seems to supersede in this context thus leading to low proliferation. Moreover, these tumor cells seem to govern the outcome of colorectal cancer independently of their proliferation.

Locally conservative, stabilized finite element methods for variably saturated flow

Standard Galerkin finite element methods for variably saturated groundwater flow have several deficiencies. For instance, local oscillations can appear around sharp infiltration fronts without the use of mass-lumping, and velocity fields obtained from differentiation of pressure fields are discontinuous at element boundaries. Here, we consider conforming finite element discretizations based on a multiscale formulation along with recently developed, local postprocessing schemes. The resulting approach maintains the basic flexibility and appeal of traditional finite element methods, while controlling nonphysical oscillations and producing element-wise mass-conservative velocity fields. Accuracy and efficiency of the proposed schemes are evaluated through a series of steady-state and transient variably saturated groundwater flow problems in homogeneous as well as heterogeneous domains. The schemes are formulated for a generic nonlinear advection–diffusion equation and are thus applicable to many other flow models.

Impact of flow rate, water content, and capillary forces on in situ colloid mobilization during infiltration in unsaturated sediments

We studied in situ colloid mobilization under transient flow conditions using columns repacked with Hanford sediments. Rainfall infiltration was experimentally simulated using different flow rates and initial moisture conditions. Five series of column experiments were performed with initial infiltration rates of 0.018, 0.036, 0.072, 0.144, and 0.288 cm/min, and the columns reached water saturations in the range of 53 to 81%. The infiltration of water into the columns provided unfavorable conditions for colloid attachment to the sediments. Colloids were eluted by the infiltrating water with the peak colloid concentrations in the outflow coinciding with the arrival of the infiltration front. A larger flow rate led to a greater amount of colloids released from the column. The cumulative amount of colloids released was proportional to the column water content established after steady state flow rates were achieved. We used the advection‐dispersion equation with a first‐order colloid release reaction to analyze the experimental data. The colloid release rate coefficient increased with the increase of water content. We calculated forces exerted on colloids, and found that electrostatic and van der Waals interactions, calculated based on the DLVO (Derjaguin‐Landau‐Verwey‐Overbeek) theory, and hydrodynamic forces, were all less important than capillary forces in controlling colloid release. In one experiment, the ionic strength of the infiltration solution was increased, such that colloid attachment was favorable. Nonetheless, colloids were mobilized and eluted with the infiltration front, implying that non‐DLVO forces, such as capillary forces, played a prominent role in colloid mobilization.

Upward Infiltration into Porous Media as Affected by Wettability and Anionic Surfactants

The influence of surfactants on water infiltration in soil is not fully understood. The objective of this study was to propose a model for evaluating effects of an anionic surfactant on upward infiltration under saturated conditions in porous materials with highly contrasting wettability. The simplified equation for upward infiltration based on Darcy's law is equivalent to the widely used Washburn equation. We experimentally determined upward infiltration of sodium dodecyl sulfate (SDS) solution (0–700 mol m−3) into 60‐cm‐long, 2‐cm‐diameter columns filled with air‐dry materials (glass beads, sand, leaf mold, peat moss, or polyethylene particles). In hydrophilic glass beads and sand, the infiltration rate decreased as the SDS concentration increased due to a decrease in solution surface tension (from 72 to 38 mN m−1). The proposed model could describe the infiltration in all materials and at all concentrations when fitting to the initial parts of the curve of infiltration front vs. time. Contact angles were obtained by fitting the model to the measured height of the infiltration front in the saturated range as a function of time. In columns filled with hydrophobic materials, the infiltration rate increased with SDS concentration, corresponding with a decrease in contact angles from >125 to 69° for polyethylene particles and from 102 to 43° for peat moss. In leaf mold, the infiltration rate decreased as the SDS concentration increased, probably due to swelling. The proposed equation was found useful for calculating saturated hydraulic conductivity and contact angles but limited in the case of swelling porous material.

Two-scale modeling of unsaturated water flow in a double-porosity medium under axisymmetric conditions

In this paper the development and experimental validation of a numerical model of two-dimensional unsaturated flow in a double-porosity medium is presented. The model is based on the coupled formulation for flow in macro- and micropores obtained by homogenization. It was applied to simulate the axisymmetrical tension disk infiltration experiments that were carried out in a double-porosity medium. The physical model was a three-dimensional periodic structure, composed of porous spheres made of sintered clay and embedded in Hostun fine sand HN38. The hydraulic parameters of both porous materials were determined by inverse analysis of independent infiltration experiments performed on sand and sintered clay. The effective parameters of the double-porosity medium were calculated from the solution of the local boundary value problem, obtained from the homogenization procedure. The cumulative infiltration curve and the global dimensions of the humidified zone obtained from the numerical solution are in good agreement with the observations. Moreover, numerical simulations showed the existence of a narrow zone of local nonequilibrium that moves with the infiltration front. Upstream of this zone, the infiltration bulb is in the local equilibrium conditions.

Solidification and remelting of aluminum though alumina preform under a centrifugal force field

Solidification and remelting of aluminum though alumina preform under a centrifugal force field were modeled numerically. Transient solidification and remelting phenomena appear on the infiltration front in three distinct regions: the remelting region, the solid–liquid congruent melting region and the uninfiltrated region. The regional extent of solidified metal and its solid volume fraction increase with the moving of the infiltration front. The speeds of the infiltration and remelting fronts decrease with decreasing porosity and rotational frequency.

Reducing Threshold Pressure for Infiltration of Al-12Si Alloys into Carbon Particle Compacts by Placing a Thin Layer of Sn at the Infiltration Front

The oxide layer that usually covers the surface of liquid aluminum and its alloys, is one of the main factors that hinders infiltration of these alloys into graphite particle compacts. The oxide film increases the threshold pressure for infiltration and the porosity of the resulting composites is large because the wetting at the metal/carbon interface is reduced. Infiltrating graphite compacts with tin requires, however, a much lower pressure, less than half of that required to infiltrate the eutectic Al-12Si alloy. As the surface tension of tin is half that of the Al-12Si alloy, this result indicates that wetting at the Sn/C interface is slightly better. As a result, porosity in the infiltrated samples is reduced. In order to reduce the threshold pressure and improve the properties of Al-Si/graphite composites, a novel method has been used in this work that consists in placing a thin film of tin at the compact end through which infiltration takes place. During the infiltration process the graphite particles are firstly infiltrated by tin, which is pushed by the aluminum alloy, thus avoiding the oxidation of the latter. The method proved to be very effective in reducing the threshold pressure, while keeping almost constant the infiltration rate.

Streaming current generation in two‐phase flow conditions

Self‐potential (SP) signals that are generated under two‐phase flow conditions could be used to study vadose zone dynamics and to monitor petroleum production. These streaming‐potentials may also act as an error source in SP monitoring of vulcanological activity and in magnetotelluric studies. We propose a two‐phase flow SP theory that predicts streaming currents as a function of the pore water velocity, the excess of charge in the pore water, and the porosity. The source currents that create the SP signals are given by the divergence of the streaming currents, and contributions are likely to be located at infiltration fronts, at the water table, or at geological boundaries. Our theory was implemented in a hydrogeological modeling code to calculate the SP distribution during primary drainage. Forward and inverse modeling of a well‐calibrated 1D drainage experiment suggest that our theory can predict streaming potentials in the vadose zone.

Numerical Simulation of Heat and Mass Transfer of the Infiltration in Liquid Infiltration Extrusion Process

The pressure infiltration process of porous preforms by molten metals was investigated numerically in this paper. The finite element model of heat and mass transfer of the infiltration in liquid infiltration extrusion process was founded by the introduction of a new continuum model of fluid in porous medium and a distribution resistance concept. The proposed model can describe the transient flow behavior of semisolid materials qualitatively. Numerical simulations were developed in particular for non-isothermal infiltrations which take into account the thermal aspects (the mould, the fibres and the metal are initially preheated at different temperatures). The temperature distribution, infiltration front and infiltration depth in the infiltration area were gained by the simulation of ANSYS／FLOTRAN code. It is shown that the fiber volume fraction and initial temperature have a strong effect on the infiltration process. The simulation results of axisymmetric infiltration have a good agreement with their experimental ones. In addition, the infiltration time was predicted to get the effective infiltration depth based on the simulation results.

Assessment of adaptive and heuristic time stepping for variably saturated flow

AbstractThe performance of improved initial estimates and ‘heuristic’ and ‘adaptive’ techniques for time step control in the iterative solution of Richards equation is evaluated. The so‐called heuristic technique uses the convergence behaviour of the iterative scheme to estimate the next time step whereas the adaptive technique regulates the time step on the basis of an approximation of the local time truncation error. The sample problems used to assess these various schemes are characterized by nonuniform (in time) boundary conditions, sharp gradients in the infiltration fronts, and discontinuous derivatives in the soil hydraulic properties. It is found that higher order initial solution estimates improve the convergence of the iterative scheme for both the heuristic and adaptive techniques, with greater overall performance gains for the heuristic scheme, as could be expected. It is also found that the heuristic technique outperforms the adaptive method under strongly nonlinear conditions. Previously reported observations suggesting that adaptive techniques perform best when accuracy requirements on the numerical solution are very stringent are confirmed. Overall both heuristic and adaptive techniques have their limitations, and a more general or mixed time stepping strategy combining truncation error and convergence criteria is recommended for complex problems. Copyright © 2006 John Wiley & Sons, Ltd.

Modeling of Liquid Metal Infiltration of Porous Fiber Preform During Squeeze Casting

The present work adopts a new approach to the analytical modeling of infiltration of porous fiber preforms by liquid metal in the squeeze casting of metal matrix composites, with the assumption that the process is adiabatic and that the flow is unidirectional. Fluid dynamics is described on the basis of Darcy's law, while separate equations are derived to explain the thermal behavior of the liquid metal and the fiber, assuming that the thermal interactions between the two are interfacial. Unlike earlier models, this approach does not consider the thermal behavior of a “composite,” but instead studies the behavior of the liquid metal and the fiber preform separately. In addition to the conventional application of heat balance techniques and development of partial differential equations involving temperatures, this work introduces supplementary conditions for temperature calculations, specifically at the entry and front points during infiltration. Differential equations are solved by a method of finite differences, and the problem of additional unknowns (preform temperature) at the infiltration front position is overcome using the “virtual point” concept. Simple expressions are derived for the calculation of process parameters like total time for complete infiltration and time for solidification, on the basis of which the occurrence of complete infiltration is predicted. A novel attempt in generating the profiles of the preform and liquid temperatures at specific instants during infiltration has also been made. The relative influence of the liquid superheat temperature, the preform preheat temperature, and the squeeze pressure on the infiltration mechanism is analyzed by studying the infiltration characteristics for various squeeze conditions.

Synthesis of an Al 2O 3/Al co-continuous composite by reactive melt infiltration

The route for the fabrication of an Al 2O 3/Al co-continuous composite by reactive melt infiltration was investigated using scanning electron microscopy, energy dispersive X-ray microanalysis and X-ray diffraction analysis. It was found that in the process of molten aluminium infiltration into the SiO 2 preform, the chemical reaction of 3SiO 2 + 4Al → 2Al 2O 3 + 3Si occurred at the infiltration front, and generated a transition zone containing a new type of continuous porosity about 100 μm in width. The reaction continued with further infiltration of molten aluminium alloy into this porosity which reacted with the residual SiO 2 until all the SiO 2 was transformed into Al 2O 3. A comparison was made between this route and that by direct infiltration of molten aluminium alloy into the open porosity of an Al 2O 3 preform. As a result of the increased wetting ability of the molten aluminium alloy by the chemical reaction, reactive melt infiltration took place at a higher rate for the SiO 2 preform than that for the direct infiltration of the Al 2O 3 preform. A fracture surface examination demonstrated a toughening effect provided by the continuous aluminium alloy in the composite.

Review of state of the art methods for measuring water in landfills

In recent years several types of sensors and measurement techniques have been developed for measuring the moisture content, water saturation, or the volumetric water content of landfilled wastes. In this work, we review several of the most promising techniques. The basic principles behind each technique are discussed and field applications of the techniques are presented, including cost estimates. For several sensors, previously unpublished data are given. Neutron probes, electrical resistivity (impedance) sensors, time domain reflectometry (TDR) sensors, and the partitioning gas tracer technique (PGTT) were field tested with results compared to gravimetric measurements or estimates of the volumetric water content or moisture content. Neutron probes were not able to accurately measure the volumetric water content, but could track changes in moisture conditions. Electrical resistivity and TDR sensors tended to provide biased estimates, with instrument-determined moisture contents larger than independent estimates. While the PGTT resulted in relatively accurate measurements, electrical resistivity and TDR sensors provide more rapid results and are better suited for tracking infiltration fronts. Fiber optic sensors and electrical resistivity tomography hold promise for measuring water distributions in situ, particularly during infiltration events, but have not been tested with independent measurements to quantify their accuracy. Additional work is recommended to advance the development of some of these instruments and to acquire an improved understanding of liquid movement in landfills by application of the most promising techniques in the field.

Quantitative network model predictions of saturation behind infiltration fronts and comparison with experiments

Infiltrations with certain boundary and initial conditions show an anomalous behavior where the water saturation and pressure profile are inverted in the vertical direction. This occurs when the water at the infiltration front oversaturates the porous medium, causing drainage behind the front, and is most likely due to the front being sharp at the pore scale. Here we attempt to quantitatively model water flow at infiltration fronts by using a physically based network model that includes viscous effects. The network model includes pore and throat elements of different shapes and sizes, and a connection topology based on geologic media. Viscous effects are added quasi‐statically through calculating the water pressure in each element for a particular applied flux. For media with a small initial saturation, the infiltration flux range for which saturation overshoot occurs is predicted by the network model. For initially dry media, the model predictions scale correctly with media size but require an independent parameter to predict the absolute transition flux. The predicted magnitude of the overshoot does not match particularly well with the measured magnitude for coarse media, although this may be the result of certain simplified assumptions in the model. The results suggest that pore‐scale modeling can make certain quantitative predictions of saturation overshoot.

The role of the chemical reaction in the infiltration of porous carbon by NiSi alloys

Abstract The infiltration of porous carbon by NiSi alloys is studied using the sessile drop technique in high vacuum. The role of the NiSi-carbon reaction in infiltration is determined and discussed. The experimental infiltration results are used to determine which process—viscous flow or the reaction at the infiltration front—limits the infiltration rate.

Comparison of Equivalent Conductivities for Numerical Simulation of One‐Dimensional Unsaturated Flow

Water flow in unsaturated porous media is usually simulated using the Richards equation in combination with some numerical method for spatial and temporal discretization. In this study we implement a mixed hybrid finite element solution with different formulations for the equivalent hydraulic conductivity in an attempt to more accurately simulate variably saturated flow. The advantages of a quadrature rule are demonstrated for simulations of sharp infiltration fronts. Results show the importance of selecting an appropriate equivalent conductivity. Geometric, weighted and integrated formulations produced better solutions than a traditional scheme using a mean conductivity calculated with a mean pressure head. Two illustrative test cases are considered for infiltration in initially dry homogeneous and heterogeneous soils subject to both Dirichlet and variable Neumann boundary conditions. The accuracy and computational efficiency of the proposed algorithm with the different conductivity formulations is demonstrated by means of comparisons with a finite difference approach using various interblock conductivity averages.

A stochastic model for 3-dimensional flow patterns in infiltration experiments

Modelling the 3-dimensional water flux at field scale is important for the design and the analysis of dye tracer experiments. Furthermore, it enables the estimation of the risk to groundwater by pollutants, and the visualisation and classification of flux patterns. A stochastic model is presented that allows for the modelling of a wide range of flow patterns in soils as they appear in dye tracer experiments. The leading idea is that infiltrating water runs along paths, not necessarily preferential ones, and water spreads into the soil uniformly from the paths into the matrix. The model is essentially based on a Poisson point process and three independent random fields. The point process defines the starting points of the paths at the surface. The values of two random fields determine the course of the paths. The third random field governs the depth of the infiltration front. As an extension of the model, we present two simulated examples for stratified soils.

Mass-conservative finite volume methods on 2-D unstructured grids for the Richards’ equation

The solution to the 2-D time-dependent unsaturated flow equation is numerically approximated by a second-order accurate cell-centered finite-volume discretization on unstructured grids. The approximation method is based on a vertex-centered Least Squares linear reconstruction of the solution gradients at mesh edges. A Taylor series development in time of the water content dependent variable in a finite-difference framework guarantees that the proposed finite volume method is mass conservative. A Picard iterative scheme solves at each time step the resulting non-linear algebraic problem. The performance of the method is assessed on five different test cases and implementing four distinct soil constitutive relationships. The first test case deals with a column infiltration problem. It shows the capability of providing a mass-conservative behavior. The second test case verifies the numerical approximation by comparison with an analytical mixed saturated–unsaturated solution. In this case, the water drains from a fully saturated portion of a 1-D column. The third and fourth test cases illustrate the performance of the approximation scheme on sharp soil heterogeneities on 1-D and 2-D multi-layered infiltration problems. The 2-D case shows the passage of an abrupt infiltration front across a curved interface between two layers. Finally, the fifth test case compares the numerical results with an analytical solution that is developed for a 2-D heterogeneous soil with a source term representing plant roots. This last test case illustrates the formal second-order accuracy of the method in the numerical approximation of the pressure head.