Begell House
Journal of Porous Media
Journal of Porous Media
1091-028X
11
7
2008
Numerical Modeling of Turbulent Flow in an Annular Heat Exchanger Partly Filled with a Porous Substrate
Computations are performed for a turbulent flow with the modified k − ε model in a double- pipe heat exchanger with a porous substrate in the annular gap attached to the inner cylinder. A proposal model for approximating the Forchheimer terms in the equations of turbulent kinetic energy and dissipation is developed by time averaging the general macroscopic transport equations. Numerical predictions are obtained using a finite volume method to investigate the turbulent fluid flow and heat transfer characteristics. Parameters such as the Reynolds number, the porous layer thickness, the permeability, and the thermal conductivity ratio are varied to asses their effects. The results show that the permeability has a great influence on turbulence intensity that goes by a maximum value at a certain Darcy number, and the efficiency of the heat exchanger is noticeably improved for a highly conducting porous substrate.
Nadia
Allouache
Faculté de Génie Mécanique et de Génie des Procédés Université des Sciences et de la Technologie Houari Boumedienne, B. P. 32 EL Alia, Bab Ezzouar 16111, Algeria
Salah
Chikh
USTHB, Faculty of Mechanical and Process Engineering, LTPMP, Alger 16111, Algeria
617-632
Superheated Steam Drying of a Spherical Porous Particle
In this article, we present a mathematical model to describe the drying kinetics occurring in a porous particle during superheated steam drying. This model is based on the averaging volume approach. It takes into account the effect of gradients of moisture content, temperature, and pressure. The heat flux by convection is given by the external transfer coefficient between the particle and the surrounding steam. The radiation exchange between the particle and the surrounding during the drying process in superheated steam vapor has been included. For the mass transfer, the natural physical condition at the drying surface is based on the equality of the partial pressure of the vapor and the external pressure of the stream. An iterative method is proposed to process this condition. The system of equations describing heat and mass transfer in a porous particle is solved numerically by the finite volume method with an irregular mesh. The predicted results from the model are compared with experimental data reported in the literature. The validated model is then used to investigate, parametrically the effects of system variables on the drying behavior of a porous particle in steam.
Jalila
Sghaier
Département d'Energétique, Ecole Nationale d'Ingénieurs de Monastir, Avenue Ibn Eljazzar, 5019 Monastir, Tunisie
Wahbi
Jomaa
Laboratoire TREFLE-UMR 8508, Site ENSAM, Esplanade des Arts et Métiers, 33405 Talence Cedex, France
Ali
Belghith
Faculte des Sciences de Tunis, Laboratoire des Transferts de Chaleur et de Masse, Campus Universitaire, 1060 Tunis, Tunisia
633-646
Temperature Distribution in a Microwave Heated Gas Chromatographic Packed Column
To understand how to use microwaves more efficiently to enhance chromatographic separation, we have to understand how the material with which they interact is affected. This is addressed by formulating and solving the energy equation to predict the temperature distribution in the chromatographic column. This issue is addressed in this article by modeling the microwave heated packed column to obtain a temperature difference between the gas and solid pellets. The effect of some parameters on the solid-gas temperature difference in the packed chromatographic column is investigated. Calculated gas velocity and temperature difference reflect their sensitivity to inlet gas velocity, solid particle diameter, and electric field. The used numerical procedure offers an efficient tool to evaluate whether the solid particles can be heated to a higher temperature than the gas in the chromatographic column. Because of the high solid pellet temperature, the separation process will be greatly enhanced in the vicinity of the solid particles.
Abdelaziz
Khlaifat
Department of Chemical Engineering, Mutah University, Mutah 61710, Jordan
647-654
Natural Convection in a Cavity Filled with a Porous Medium with Variable Porosity and Darcy Number
This work presents a numerical analysis of the natural convection in a squared cavity with isothermal vertical walls. The cavity is filled with a saturated porous medium, and the classical equations for natural convection, mass, momentum, and energy balance, together with Brinkman's and Forchheimeir's models, are used to study the phenomenon. The system of equations is numerically solved through the finite volume method. For porous media with constant porosity, the results are compared to those found in the literature, with very good agreement. The influence of the variation of Darcy number in media with variable porosity is investigated. The results indicate that the inclusion of the variation of Darcy number affects significantly the velocity and temperature fields as well as the values of heat transfer rates.
Rejane De C.
Oliveski
Mechanical Engineering Department, UNISINOS, São Leopoldo, Brazil
Ligia D. F.
Marczak
Mechanical Engineering Department, UNISINOS, São Leopoldo, Brazil
655-667
Few Exact Solutions of Non-Newtonian Fluid in Porous Medium with Hall Effect
This article deals with some exact solutions of an incompressible second grade fluid in a porous medium with Hall effects. The solutions are found by considering the vorticity distribution proportional to the stream function perturbed by a uniform stream. The streamlines, velocity distributions, and pressure functions are derived for each case and are compared with the already known results in the literature.
S.
Islam
Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, China
Muhammad Raheel
Mohyuddin
COMSATS Institute of Information Technology, Abbottabad, Pakistan; Department of Physics, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45195, Iran
Chaoying
Zhou
Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, China
669-680
Linear Stability of Solutal Convection in Rotating Solidifying Mushy Layers: Permeable Mush-Melt Interface
The linear stability theory is used to investigate analytically the effect of a permeable mush-melt boundary condition on the stability of solutal convection in a rotating mushy layer of homogenous permeability at the near-eutectic limit. The results clearly show that in contrast to the impermeable mush-melt interface boundary condition, the application of the permeable mush-melt interface boundary condition destabilizes the convection in a rotating mushy layer.
Saneshan
Govender
School of Mechanical Engineering, University of Kwa-Zulu; School of Mechanical Engineering, University of Natal, Durban, South Africa; Eskom Holdings Ltd, Engineering Department (Gas Division), Eskom Enterprises Park, Simba Road, Sunninghill, Johannesburg
683-690
Numerical Study of the Flow of Magnetohydrodynamic Non-Newtonian Fluid Obeying the Eyring-Powell Model through a Non-Darcy Porous Medium with Coupled Heat and Mass Transfer
The numerical solutions of the system of nonlinear partial differential equations that describe the unsteady flow of magnetohydrodynamic non-Newtonian fluid with heat and mass transfer past a porous plate through a non-Darcy porous medium are obtained, taking into account the effect of viscous and Ohmic dissipations. The finite difference method is used for solving the system of equations. The results of the velocity, temperature, concentration distributions, skin friction, rate of heat, and mass transfer are illustrated graphically for different values of physical parameters. Also, the stability condition is studied.
Nabil T. M.
Eldabe
Department of Mathematics, Faculty of Education, Ain Shams University, Heliopolis, Cairo, Egypt
Mokhtar
Ahmed
Department of Mathematics, Faculty of Education, Ain Shams University, Heliopolis, Cairo, Egypt
Ashraf
Fouad
Ain Shams University
Amaney
Sayed
Department of Mathematics, Faculty of Education, Ain Shams University, Heliopolis, Cairo, Egypt
691-700