Transport In Porous Materials Research Articles

Determination of Capillary Motion of Water in Bricks Using Neutron Radiography

Vertical migration of water in several porous materials has been directly observed and recorded with the recently installed neutron and gamma radiography facility at the MARIA reactor of Institute of Atomic Energy, Swierk. The density profiles of water in samples were obtained from the optical density of digitised images. A simple model (representing the porous material as the collection of capillary tubes of various radii) has been introduced to describe the liquid transport in porous materials in terms of capillary motion. The equation for viscous movement of water in porous material in presence of the gravitation is proposed. A good agreement of the calculated density profiles for vertical water migration with the data collected for siliceous bricks suggests that the thinnest capillary tubes determine the upper edge of the water density profile.

ChemInform Abstract: Modeling the Influence of Chemical Reactions on the Mechanisms of Ionic Transport in Porous Materials. An Overview

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Modeling the influence of chemical reactions on the mechanisms of ionic transport in porous materials: An overview

This paper attempts to critically review various approaches developed to model the effects of chemical reactions on the mechanisms of ionic transport in porous media. A comprehensive overview of the various types of chemical reactions that can occur in reactive porous solids is first presented. Methods to model each of these chemical reactions are then described and analyzed. The ability of each of the proposed algorithms to predict the behavior of hydrated cement systems is discussed. The implementation of these algorithms in an ionic transport numerical model is also discussed.

A nuclear magnetic resonance microscopy study of mass transport in porous materials

The1H nuclear magnetic resonance (NMR) microimaging is employed to study the mass transport processes in porous materials, including individual catalyst support pellets and beds comprised of porous grains. Drying and adsorption are investigated by detecting the temporal evolution of the one-dimensional spatial profiles or two-dimensional maps of liquid content without interrupting the process under study. The characteristic features of these processes, such as the main mechanisms and the limiting stages of mass transport, and some factors which can alter the efficiency of mass transport are considered. The problems associated with the relaxation weighting of the NMR signals, often unavoidable for liquids permeating mesoporous solids, and the possibilities to overcome these problems are discussed.

Laws of capillary transport in porous materials prepared from titanium alloy VT6 fibers

A study was made of the kinetics of capillary absorption of ethanol in highly porous (70–75%) materials prepared from discrete fibers of titanium alloy VT6 (specimen dimensions 330×20×(0.4–1.3) mm). The fibers, 3 mm in length and 20–140 μm in diameter, were obtained by rapid solidification from the melt. Capillary transport against the force of gravity up to the equilibrium height of capillary rise was investigated in an atmosphere of saturated ethanol vapor. Experimental data on the rate of absorption were analyzed with reference to the properties of the pore space structure—effective pore size, tortuosity of the pore channels, and free surface area. The laws of capillary transport of ethanol in porous materials composed of titanium alloy VT6 fibers, discrete copper fibers, and grade VTEM-2 titanium powder were compared. It was shown that, with regard to the speed of absorption, the advantage of fiber materials over those made from powder is attributable to the less convoluted pore channels in the former.

The influence of sorption isotherms on the drying of porous materials

A model is presented for the simultaneous vapour and liquid transport in porous materials. The model describes the evaporation inside a porous material with a mass transfer coefficient and a specific evaporating surface. The model also includes the effect of sorption isotherms. Predictions of the model are compared with experimental results found in the literature.

Fluid Transport in Porous Materials Characterised by NMR.

Fluid Transport in Porous Materials Characterised by NMR.

Transverse component of the electrical conductivity of porous silicon — I

The study of transport in porous materials is a very challenging problem. In particular, the understanding of electric transport in porous silicon is fundamental for its promising technological impact. In a previous work we obtained an analytical expression for the axial effective electrical conductivity of a model simulating porous silicon (PS). We used the averaging volume method that has proven to be successful in treating fluid transport in porous media. The PS model was based on experimental information about this new material's structure and experimental data for crystalline Si and hydrogenated a-Si thin films. With this method we can calculate the bulk and the surface contribution to the tensorial effective conductivity. Here we present the transverse effective conductivity results where percolation effects can be observed, using the same method and model. However, in the XY plane the calculation is more complicated and it can only be solved numerically. We find that there is a range at low porosities where the effective electrical conductivity can be enhanced due to the surface contribution.

Multiphase Radon Generation and Transport in Porous Materials

Radon generation and transport in porous materials involve solid, liquid, and gas phases in the processes of emanation, diffusion, advection, absorption, and adsorption. Oversimplifications, such as representing moist soil systems by air-phase emanation and transport models, cause theoretical inconsistencies and biases in resulting calculations. Detailed Rn rate balance equations for solid, liquid, and gas phases were analyzed and combined using phase equilibrium constants to derive a single diffusive-advective rate balance equation in the traditional form. The emanation, diffusion, and permeability coefficients in the new equation have expanded definitions and interpretations to include Rn phase transfer. Radon adsorption was characterized by an exponential moisture dependence, and diffusion and permeability constants utilized previous moisture relationships. Correct boundary and interface conditions were defined, and the unified theoretical approach was applied to field data from a diffusion-dominated system and to laboratory data from an advection-dominated system. Measured 222Rn fluxes and concentrations validated the modeled values within the measurement variability in both applications.

Relation between macroscopic conductance and microscopic structural parameters of stochastic networks with application to fluid transport in porous materials

The effective medium approximation is used to relate explicitly the conductance of a macroscopic model stochastic network to the structural characteristics of its constituent microscopic elements. The expressions obtained are relevant to the description of thermal, electrical or fluid transport properties of microscopically non-homogeneous or composite solid materials. Here, they are applied to two regimes of fluid transport in porous media where conductance depends on the radius or on the cube of the radius representing diffusion in slit-like pores and dilute gas flow in cylindrical pores, respectively. The network permeability is obtained in the form of expansions with readily evaluated terms describing the effect of the breadth and shape of the pore radius distribution and of the connectivity of the network. The validity of these expansions is tested by comparison with results obtained from direct numerical solutions and is shown to be acceptable for most applications over a wide range of parameter values. As a result of this work, a deeper insight into the role of various microscopic structural features on macroscopic permeability is gained, and the task of predicting network permeability in specific cases is greatly simplified.

Mass transport in porous materials under combined gradients of composition and pressure

AbstractAn expression is derived for the analysis of gas‐phase mass transport in porous media in the presence of gradients in pressure and mole fraction. The behavior of porous media is contrasted with that of capillary tubes. A continuous‐flow diffusion and permeation apparatus was employed for studies of mass transport in a fritted glass diaphragm. Measurements were obtained at varying levels of pressure and cover both isobaric binary diffusion and the permeation of pure gases and gas mixtures. These experimental results and previous data obtained by Hewitt and Sharratt and by Mason, et al. bear out the form of the equation and successfully provide independent checks of the three constants necessary to characterize a given porous medium.