Begell House Inc.
Journal of Porous Media
JPM
1091-028X
12
12
2009
Simulation and Characterization of High-Porosity Media for Aerosol Particle Processing: A Numerical Study
1129-1137
Ana
Serrenho
Geophysics Centre of Évora, Rua Romão Ramalho, 59, 7000-671 Évora, Portugal; and Department of Civil Engineering, Nationa lUniversity of Ireland, Galway, Ireland
Antonio Ferreira
Miguel
Department of Physics, School of Sciences and
Technology, University of Evora, Institute of Earth Sciences (ICT) Pole of Evora,
Portugal
Processes involving suspensions flow occur in many natural, biological, and industrial systems. Examples also include the production of many advanced materials, such as semiconductors, and new product formulations with importance in pharmaceutical and medical applications. In certain tasks microchannels and porous media are used to promote a rapid mixing of aerosol streams to produce more uniform dispersions and coatings. A major concern for industrial use is caused by the fact that the aerosol particles deposit onto the solid structure of channels and this must be controlled to avoid clogging. We report a study of the application of high-porosity media for the generation of uniform flow suspensions. Two key quantities were used to characterize the process: particle losses (deposition) within the porous medium and residence time distribution of the particles. This study clearly demonstrates that the geometric characteristics of the porous media, the fluid velocity, fluid viscosity, and particle size should be controlled in order to get more uniform dispersions and prevent the unwanted particle loss.
Analytical and Numerical Solution for One-Dimensional Two-Phase Flow in Homogeneous Porous Medium
1139-1152
Michal
Benes
Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Trojanova 13, 120 00 Prague, Czech Republic
Radek
Fucik
Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Trojanova 13, 120 00 Prague, Czech Republic
Jiri
Mikyska
Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Trojanova 13, 120 00 Prague, Czech Republic
Tissa H.
Illangasekare
Center for Experimental Study of Subsurface Environmental Processes, Colorado School of Mines, USA
The article presents a comparison of a semianalytical and a numerical approach to a one-dimensional flow-function model of two-phase flow through a homogeneous porous medium which is used for validation of more complex numerical models of two-phase flow. The flow-function model equation can be treated analytically to obtain an implicit formula for the saturation, which is resolved iteratively. This approach, originally derived by McWhorter and Sunada (1990; 1992), is used in its improved version so that we are able to readily obtain the wetting-phase saturation for all parameter values. To enlarge the class of admissible boundary and initial conditions, we propose another approach which relies on a numerical algorithm which solves the flow-function model equation, based on the finite-difference method in space and time, yielding values of the solution at given time moments and on a spatial grid of positions. Our approach is demonstrated in a series of one-dimensional computations showing the accuracy, efficiency, and generality of the proposed algorithms.
Nonlinear Instability of Two Superposed Electrified Bounded Fluids Streaming Through Porous Medium in (2 + 1) Dimensions
1153-1179
Mohamed F.
El-Sayed
Department of Mathematics, Faculty of Education, Ain Shams University, Heliopolis (Roxy), Cairo, Egypt; Department of Mathematics, College of Science, Qassim University, P. O. Box 6644, Buraidah 51452, Saudi Arabia
G. M.
Moatimid
Department of Mathematics, Faculty of Education, Ain Shams University, Heliopolis, Roxy, Cairo, Egypt
T. M. N.
Metwaly
Department of Mathematics, Faculty of Education, Ain Shams University, Heliopolis, Roxy, Cairo, Egypt
Nonlinear electrohydrodynamic stability of two superposed dielectric bounded fluids streaming through porous media in the presence of a horizontal electric field is investigated in three dimensions. The method of multiple scales is used to obtain a dispersion relation for the linear problem and a Ginzburg-Landau equation for the nonlinear one, describing the behavior of the system. The stability of the system is discussed both analytically and numerically, and the stability conditions are obtained. It is found, in the linear case, that the stability criterion is independent of the permeability of the medium and that the fluid viscosities, velocities, depths, and the dimension have destabilizing effects, while the porosity of porous medium, electric field, and surface tension have stabilizing influences on the system. In the nonlinear case, using the obtained stability conditions, the effects of all physical parameters included in the analysis on the stability of the system are discussed in detail for both two- and three-dimensional disturbances cases, respectively. The system has been found to be usually unstable if the fluids are pure for both cases. It is found also that the dimension has a dual role (stabilizing as well as destabilizing) on the considered porous system, whereas it has a destabilizing effect if the medium is nonporous.
Two-Dimensional Modeling of Transport Phenomena by the CVFE Method in the Porous Cathode of a PEM Fuel Cell
1181-1193
Faycel
Khemili
Laboratoire d'Etudes des Systèmes Thermiques et Energétiques, Cité Riadh, Zirig 6072 Gabès, Tunisia
Mustapha
Najjari
Laboratoire d'Etudes des Systemes Thermiques et Energetiques, Cite Riadh, Zirig 6072 Gabes, Tunisia
Nidhal Ben
Khadher
Laboratoire d' Etudes des Systemes Thermiques et Energetiques, Ecole Nationale d'lngenieurs de Monastir, Avenue Ibn El Jazzar 5019, Monastir, Tunisia
Sassi Ben
Nasrallah
Laboratoire d'Études des Systèmes Thermiques et Énergétiques, Ecole Nationale d'Ingénieurs
de Monastir, Monastir 5019 Tunisie
In this work, we study the two-phase flow and mass transport in the porous cathode of a proton exchange membrane fuel cell (PEMFC). A model based on the method of the separate phase flow is used to solve the conservation equations. For the discretization of the equation system, we used the control volume finite element (CVFE) method. This model is used to test the effect of the presence of liquid water on the mechanisms of transport in the porous cathode and its influence on the performances of the fuel cell.
Characterization of Sewage Sludge Water Vapor Diffusivity in Low-Temperature Conductive Drying
1195-1210
Rayan
Slim
Ecole des Mines de Paris, Center for Energy and Process Studies, 60 Boulevard Saint-Michel - F - 75272 Paris Cedex 06, France
Assaad
Zoughaib
Ecole des Mines de Paris, Center for Energy and Process Studies, 60 Boulevard Saint-Michel - F - 75272 Paris Cedex 06, France
Denis
Clodic
Ecole des Mines de Paris, Center for Energy and Process Studies, 60 Boulevard Saint-Michel - F - 75272 Paris Cedex 06, France
In order to study the low-temperature conductive drying of urban sewage sludge and evaluate its essential characteristics, a laboratory-scale drying device was set up. Sludge is modelled as a coarse aggregated, porous medium, and experiments are conducted to study its rheological behavior throughout a drying cycle and aggregation effects on diffusion. Investigations are based on a macroscopic model of sludge aggregates where only external porosity is accounted for. This paper presents a method to evaluate water vapor diffusivity within urban sludge based on an analytical solution of a Fickian diffusive model which enables diffusivity determination by simple exponential regression over experimental data. Experiments are carried out with three levels of heating fluxes, 300, 525 and 700 W/m2, without any remarkable effect of flux density on water vapor diffusivity over the tested range. Further experiments are conducted to underline the effect of mixing frequency. Predictive correlations for water vapor diffusivity as a function of sludge dry solid content and mixing frequency are reported in this work.
Darcian Flow with Heat and Mass Transfer through Lung Tissues under High-Frequency Ventilation
1213-1223
Assma F.
El-Sayed
Department of Mathematics, Faculty of Education, Ain Shams University, Heliopolis, Cairo, Egypt
A Darcian mathematical model for heat and mass transfer through lung tissues under high-frequency ventilation has been studied. High-frequency ventilation is an effective treatment that helps premature infants and patients with severe respiratory distress. A lung-ventilator system under high frequency is described by Navier-Stokes and viscoelastic tissue deformation equations, while the transient convection-diffusion through this system is based on bioheat transfer and concentration equations. The mathematical functions distributions are discussed and shown graphically for different values of biomechanical properties of the lung such as the Young's modulus for the solid E and permeability K.
Unsteady Natural Convection Flow over a Heated Cylinder Buried in a Fluid Saturated Porous Medium
1225-1235
Girishwar
Nath
Professor S. K. Sinha, KNIT Campus, IV/17, KNIT, Sultanpur 228118, India
Mahesh
Kumari
Department of Mathematics, Indian Institute of Science, Bangalore 560 012, India
Transient natural convection flow on a heated cylinder buried in a semi-infinite liquid-saturated porous medium has been studied. The unsteadiness in the problem arises due to the cylinder, which is heated (cooled) suddenly and then maintained at that temperature. The coupled partial differential equations governing the flow and heat transfer are cast into stream function-temperature formulation, and the solutions are obtained from the initial time to the time when steady state is reached. The heat transfer is found to change significantly with increasing time in a small time interval immediately after the start of the impulsive change, and steady state is reached after some time. The average Nusselt number is found to increase with Rayleigh number. When the surface of the cylinder is suddenly cooled, there is a change in the direction of the heat transfer in a small time interval immediately after the start of the impulsive change in the surface temperature; however, when the surface temperature is suddenly increased, no such phenomenon is observed.
Numerical Study of a Desiccant Cooling Installation in Variable Climates
1237-1246
Issam
Mtimet
Ecole Nationale d'Ingenieurs de Monastir, 5000 Monastir, Tunisia
Leila
Zili-Ghedira
Energy and Thermal Systems Laboratory, National Engineering School of Monastir, University of Monastir, Avenue Ibn El Jazzar, 5019 Monastir, Tunisia
Desiccant materials open new possibilities in air-conditioning technology. In desiccant cooling installations, air is dehumidified via a desiccator and its temperature consequently increases. Air temperature is then deceased by heat exchanger and evaporator while its humidity increases. Desiccant cooling installations require a relatively moderate heat source for regeneration. Solar energy is an interesting source. This technology is profitable for the Tunisian climate because moisture is important especially in certain coastal zones. This study compares two desiccators directly in series and using an exchanger between them for different climates and examines the possibility of using a desiccator instead of a desiccant wheel and a second desiccator at the desorption phase in place of the evaporator.