Begell House
Journal of Porous Media
Journal of Porous Media
1091-028X
7
2
2004
Compositional Variation Considering Diffusion and Convection for a Binary Mixture in a Porous Medium
In this article we study the compositional variation in a porous cavity having different aspect ratios, accounting for natural convection and for thermal, pressure, and molecular diffusion for a binary mixture. The momentum equation is represented by Darcy's law and is solved numerically together with the energy equation and the species conservation equation using the control-volume scheme. The binary mixture's density and viscosity, as well as molecular, thermal, and pressure diffusion coefficients, vary with temperature, composition, and, pressure. Various thermal boundary conditions are investigated. In the lateral heating case the Soret effect is found to be weak, whereas in the bottom heating condition the Soret effect is more pronounced. Such findings are also evident when both bottom and lateral heating are combined, as in the third case studied in this article. In the presence of pressure diffusion, the competing effect of the thermal and pressure diffusions affects the compositional variation in the cavity. Darcy number variation also plays an important role in the mixture variation in the cavity, because of the formation of convective cells. It is important to note that the Soret effect is dominant when bottom heating is present and therefore should not be neglected.
D.
Faruque
Department of Mechanical Engineering, Ryerson University, Toronto, Ontario, Canada
M. Ziad
Saghir
Department of Mechanical and Industrial Engineering, Ryerson University, Toronto, Canada
M.
Chacha
Department of Mechanical Engineering, Ryerson University, Toronto, Ontario, Canada
K.
Ghorayeb
Abingdon Technology Center, Schlumberger, Abingdon, UK
20
A Numerical Investigation of Catalytic Oxidation of Very Lean Methane-Air Mixtures within a Packed-Bed Reactor
A model for the combustion of methane-air mixtures in the presence of a catalyst in a packed-bed reactor has been developed. The one-dimensional model accounts for both gas-phase (homogeneous) and catalytic surface (heterogeneous) reactions. These reactions are modeled as single-step reactions of the Arrhenius type. Heat transfer by conduction, convection, and radiation has also been included. The governing equations, which are solved numerically, are the unstead-state equations of conservation of mass, chemical species, and energy for both solid and gas phases, which are assumed not to be in local thermal equilibrium. The results of a numerical investigation conducted with methane as a fuel and platinum as a catalyst are presented for a range of operational conditions, such as inlet temperatures (700−1,300 K), approach velocities (1−3 m/s), and equivalence ratios (0.15−0.50). The calculated values of methane conversion within the packed-bed reactor showed good agreement with some corresponding experimental data obtained for similar conditions. The preliminary results of the numerical investigation showed that the oxidation of methane in such a reactor can be modeled adequately.
L. B.
Younis
SNC-Lavalin Inc, Calgary, Alberta, T2P 3H5, Canada
I.
Wierzba
Department of Mechanical and Manufacturing Engineering, University of Calgary 2500 University Drive N.W., Calgary, Alberta, Canada T2N 1N4
8
Seepage-Induced Consolidation in Permeability Measurements for Fibroporous Media — A Finite-Element Investigation
This article reports a finite-element investigation of seepage-induced consolidation in permeability measurements for a fibroporous material, prepared sugar cane. The constituents of fibroporous prepared sugar cane allow macroscopic representation of the material using coupled solid-liquid finite-element formulations, where the intrinsic permeability of the solid matrix is defined as a function of void ratio. Simulation of experimental flow cell permeability measurements predicts significant seepage-induced consolidation and nonuniform void ratio distribution in the cell, particularly at low compression ratios. Permeability values derived from flow cell experiments at low compression ratios may be up to four times lower than the actual permeability response.
Clayton J.
Adam
School of Mechanical, Manufacturing and Medical Engineering, Queensland University of Technology, GPO Box 2434, 2 George St., Brisbane, Queensland, 4001 Australia
Jeffrey G.
Lounghran
School of Engineering, James Cook University
18
On the Prediction of Darcy Permeability in Nonisotropic Periodic Two-Dimensional Porous Media
Numerical computations of Stokes flow through a representative range of arrays of squares and rectangles are carried out. In each case, the unit-cell aspect ratio is the same as the particle aspect ratio. A deterministic analytical pore-scale model, based on a Poiseuille approximation to the actual flow field, provides a simple expression characterizing the trends of the numerical results. This model incorporates dependence on porosity and on a particle shape factor, and discriminates between regular and staggered arrays. The analytic expression derived is shown to agree remarkably well with the numerical results, especially at low porosities.
Mouaouia
Firdaouss
LIMSI-CNRS (UPR 3251), BP 133, 91405 Orsay Cedex, France, and UFR 923, Universite Pierre et Marie Curie, Paris 6, France
J. Prieur
Duplessis
Department of Applied Mathematics, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa
14
Water Vapor Transfer through Textile under a Temperature and Humidity Gradient
Moisture movement in a porous medium is a process that occurs in many engineering applications. These include moisture movement in soils, nutrient uptake by plants, drying of food, and petroleum extraction. This process is also of special interest to the textile industry. The mechanisms of water vapor transmission through textile fabrics are not well known. The rate at which they are able to transmit water vapor is most often measured under standard textile testing conditions of 20° C and 65% relative humidity. The experiments described in this article are designed to measure the effect of the temperature and the humidity gradients on water vapor resistance of these fabrics. Experiments involve relative humidities of 40%, 50%, and 70% with the temperature held at a constant 30°C throughout and temperatures of 25, 30, and 35°C with the relative humidity held at a constant 50% throughout.
Nada
Nefzi
Laboratoire d'Etudes des Systemes Thermiques et Energetiques, Ecole Nationale d'Ingenieurs de Monastir, TUNISIA
Moez
Jouini
Laboratoire d'Etudes des Systemes Thermiques et Energetiques, Ecole Nationale d'Ingenieurs de Monastir, TUNISIA
Sassi Ben
Nasrallah
Laboratoire d'Études des Systèmes Thermiques et Énergétiques, Ecole Nationale d'Ingénieurs
de Monastir, Monastir 5019 Tunisie
10
Heat and Mass Dispersion in Flows through Porous Media
The description of transport phenomena associated with flows of fluids in porous media requires the use of phenomenological coefficients with a complicated dependence on the fluid velocity. Directional dependence of conductivities is present even if the porous media structure is isotropic. The fluid velocity field provides a director with respect to which the orientation of all thermodynamic forces is compared. Transport in the transverse direction differs from transport in the velocity direction. Furthermore, linear dependence on the thermodynamic forces is insufficient once it has been experimentally observed that transport is faster in the flow direction than in opposition. Experimental data supporting this statement exist for the special case where fluid and porous media are at local thermal equilibrium at a single temperature.
Affonso Silva
Telles
Curso de Pos-Graduagao em Tecnologia de Processos Quimicos e Bioquimicos (TPQB), Departamento de Engenharia Quimica, Escola de Quimica, Centre de Tecnologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
Jose Teixeira
Freire
Departmento Engenharia Quimica, Universidade Federal de Sao Carlos, Sao Carlos, Brazil
11