Begell House
Journal of Porous Media
Journal of Porous Media
1091-028X
3
3
2000
Measurement of Velocity and Temperature Distributions in a Highly Porous Medium
In the present article, the experimental results on the velocity and temperature distributions in a highly porous medium are reported. The highly porous medium used in the present study is made of aluminum oxide ceramic and has a porosity of about 87.5%. The velocities at the downstream end of the highly porous medium were measured using a laser Doppler velocimetry. Temperature within the highly porous medium was measured using a matrix of chromel-alumel thermocouples of 100 μm diameter. The following conclusions were drawn from the results obtained in the present study. Higher velocities were measured in the pore regions, whereas lower velocities were measured in the frame region. From the microscopic aspect, the highly porous medium has an ability to change the velocity distribution with its mesh frame. The velocity distributions at the upstream side of the highly porous medium were almost parabolic in the area average. However, the area averaged velocity distributions at the downstream end of the highly porous medium were homogeneous. From the macroscopic aspect, it can be concluded that the highly porous medium has an ability to make the flow velocity distribution homogeneous. The high temperature region was established in the highly porous medium. The stored energy in the highly porous medium was about 100 times larger than that for a medium that was not highly porous medium. It is presumed that the heat energy in the highly porous medium was maintained not only in the flow channel but also in the highly porous medium itself by convection in the complex flow path, as the heat capacity of the highly porous medium is about 180 times larger than the heat capacity of air. It can be said that the highly porous medium can retain much thermal energy by the complex three-dimensional slim mesh frames and the fact that it has a higher heat capacity than air. The facts obtained in the present study therefore suggest that the highly porous medium can be used in high-performance energy-conversion devices.
Masaaki
Okuyama
Department of Mechanical Systems Engineering, Yamagata University, Yonezawa, Yamagata, 992-8510 Japan
Yutaka
Abe
University of Tsukuba, Graduate School of System and Information Engineering, 1-1-1, Tennoudai, Tsukuba, Ibaraki, 305-8573, Japan
14
Thermal Instability in an Inclined Isotropic Porous Medium
Convective instability in afluid-saturated isotropic porous layer between infinite parallel plates inclined arbitrarily with respect to gravity is investigated for both Darcy and Brinkman models. When the heat flux at the boundaries is fixed, it is shown that if the temperature gradient parallel to the plates is adverse, the critical Rayleigh number is zero.
Sherin M.
Alex
Department of Mathematics, Anna University, Chennai (Madras), India
Prabhamani R.
Patil
Department of Mathematics, Anna University, Chennai (Madras), India
10
Cross-Flow Microfiltration of an Oily Emulsion Using Alumina Membranes
Separation of oil-in-water emulsions has been experimentally investigated by cross-flow microfiltration using alumina membranes. Microfiltration α-Al2O3 membranes with pore sizes of 0.46 μm, 0.67 μm, and 0.89 μm were tested. The oil-in-water emulsions comprised 1000 ppm ofdodecane in distilled water. Effects of operation parameters such as transmembrane pressure, cross-flow velocity, and feed concentration were examined on oil rejection as well as permeate flux. To recover the permeateflux, backflushing and chemical cleaning were applied. Typically, a membrane with pore size of 0.46 μm had rejection higher than 99% under 2.10 m/s cross-flow velocity and 0.10 MPa transmembrane pressure.
Weidong
Zhu
Department of Materials Science & Engineering, University of Science & Technology of China, 230026, Hefei, China
Changrong
Xia
Department of Materials Science & Engineering, University of Science & Technology of China, 230026, Hefei, China
Shuqin
Lin
Department of Materials Science & Engineering, University of Science & Technology of China, 230026, Hefei, China
Guangyao
Meng
Department of Materials Science & Engineering, University of Science & Technology of China, 230026, Hefei, China
9
Free Convection from a Horizontal Surface in a Porous Medium with Newtonian Heating
A very effective solution method is proposed to solve the steady free convection boundary-layer flow on a horizontal surface embedded in a porous medium in which the flow is generated by Newtonian heating. Asymptotic solutions, which are valid for small and large values of x, the coordinate along the plate, as well as a very accurate numerical solution of the full governing equations that matches the asymptotic solutions have been obtained It is found that for small values of x the first-order flow is driven by a constant heat flux from the surface, and the higher order terms are then perturbations of the standard uniform heat flux solution, which is the same behavior seen in the corresponding conjugate problem. However, there is an essential difference between the present situation and the conjugate problem when the solution far downstream is considered. For the conjugate problem, the flow far downstream approaches the standard isothermal wall solution, whereas in the present situation, the flow far downstream at large values of x gives rise to a new similarity solution in which the wall fluid velocity and temperature are almost linear and quadratic functions of x, respectively.
Daniel
Lesnic
Department of Applied Mathematics, University of Leeds, Leeds LS2 9JT, UK
Derek B.
Ingham
Centre for CFD, Department of Applied Mathematical Studies, The University of Leeds, Leeds, LS2 9JT, UK; Energy-2050, Faculty of Engineering, University of Sheffield, Sheffield, S10 2TN, UK
Ioan
Pop
Department of Applied Mathematics, Babes-Bolyai University, 400084 Cluj-Napoca, Romania
9
Effective Conductivity for Porous Media: A Maxwellian Approach
In the present work, our objective is the development of an expression for the effective conductivity of transport processes that obey Laplace equation at the steady state, such as mass diffusivity, coefficient for diffusive mass transport, or thermal diffusivity for molecular heat transport. The Laplace equation for the electrical potential was solved for a cylindrical domain that contains a concentric nonconductive obstruction. As the central obstruction radius approaches zero, an equation for electrical potential in an homogeneous domain is obtained, leading to an expression for the effective conductivity.
Rogerio E.
Martinez-Gomez
Universidad Autonoma Metropolitana—Iztapalapa, Av. Michoacan y La Purisima, Col.Vicentina, 09340 Mexico D.F.
Alberto
Soria
Universidad Autonoma Metropolitana—Iztapalapa, Av. Michoacan y La Purisima, Col.Vicentina, 09340 Mexico D.F.
7
Forced Convection in a Couette Flow in a Composite Duct: An Analysis of Thermal Dispersion and Non-Darcian Effects
In this article an analysis of fluid flow and heat transfer in a fully developed Couette flow through a composite channel that is partly filled with a clear fluid and partly with a fluid-saturated porous medium is presented. The porous medium is attached to a fixed plate and uniform heat fluxes of different intensities are imposed on both plates. The momentum transport is described by the Brinkman−Forchheimer−Darcy equation and the effect of transverse thermal dispersion is accounted for in the energy equation for the porous region. An analytical solution for the fluid flow is obtained utilizing the boundary layer technique. The temperature field and the Nusselt numbers at the upper and lower plates are obtained by direct numerical integration. The dependence of the Nusselt numbers on the thickness of the porous region, the ratio of heat fluxes on both plates, and the Darcy number is investigated.
Ming
Xiong
Department of Mechanical and Aerospace Engineering, North Carolina State University, Campus Box 7910, Rayleigh, North Carolina 27695-7910, USA
11
Hydromagnetic Coupled Heat and Mass Transfer by Natural Convection from a Permeable Constant Heat Flux Surface in Porous Media
Ali J.
Chamkha
Mechanical Engineering Department, Prince Mohammad Bin Fahd University, Al-Khobar 31952,
Kingdom of Saudi Arabia; Prince Sultan Endowment for Energy and Environment, Prince Mohammad Bin Fahd University, Al-Khobar 31952, Saudi Arabia; RAK Research and Innovation Center, American University of Ras Al Khaimah, P.O. Box
10021, Ras Al Khaimah, United Arab Emirates
A.-R.A.
Khaled
King Abdulaziz University
8
Radiative and Thermal Dispersion Effects on Non-Darcy Natural Convection
M. A.
Mansour
Department of Mathematics, Assuit University, Faculty of Science, Assuit, Egypt
Rama Subba Reddy
Gorla
Department of Mechanical Engineering, Cleveland State University, Cleveland, OH, 44115 USA; Department of Mechanical Engineering, University of Akron, Akron, Ohio 44325, USA; Department of Mechanical & Civil Engineering, Purdue University Northwest, Westville, IN 46391, USA
6
Book Review: Transport Phenomena in Porous Media, edited by Ingham, D. B. and & Pop, I.
Marcelo
de Lemos
Instituto Tecnologico de Aeronautica - ITA
3