Begell House
Journal of Porous Media
Journal of Porous Media
1091-028X
16
11
2013
MIXED CONVECTION ON A PERMEABLE STRETCHING CYLINDER WITH PRESCRIBED SURFACE HEAT FLUX IN POROUS MEDIUM WITH HEAT GENERATION OR ABSORPTION
The steady mixed convection boundary layer flow due to a permeable stretching cylinder with prescribed heat flux in
porous medium with heat generation/absorption is investigated numerically. The governing system of partial differential equations is converted into a system of ordinary differential equations using similarity transformation, which is then solved numerically by the fourth-order Runge-Kutta method with shooting technique. The influence of the governing parameters, namely the permeability, heat generation/absorption, suction/injection, Prandtl number, and Reynolds
number on the flow and heat transfer characteristics are analyzed and discussed. It is found that the skin-friction coefficient and the Nusselt number at the surface increase as the Prandtl number increases. The same behavior is observed for the wall permeability parameter while the opposite behavior is observed for the heat generation parameter and Reynolds number of the cylinder. On the other hand, in the case of opposing flow with an increase in the mixed convection parameter velocity decreases whereas the temperature increases but the opposite behavior is observed in the case of assisting flow.
Sadegh
Khalili
Binghamton University
Arezoo
Khalili
Department of Mechanical Engineering, Saveh Branch, Islamic Azad University, Saveh, Iran
Sara
Kafashian
Department of Energy System Engineering, Faculty of Mechanical Engineering, K. N. Toosi University of Technology, Tehran, Iran
Abbas
Abbassi
Mechanical Engineering Department, Amirkabir University of Technology 424 Hafez Avenue, P.O. Box 15875-4413, Tehran, Iran
967-977
CONJUGATED NATURAL CONVECTION IN HORIZONTAL ANNULI PARTIALLY FILLED WITH METALLIC FOAMS BY USING TWO-EQUATION MODEL
The current study presents the natural convection in a horizontally positioned concentric annulus partially filled with highly conductive metallic foams by using a two-equation model for non-equilibrium heat transfer. Annuli with a porous layer sintered on the inner wall (mode I) and on the outer wall (mode II) are compared with each other via numerical simulation. In the metal-foam region, the momentum transfer is described using the Forchheimer and Brinkman-extended Darcy flow model, whereas the energy conservation is described using the local thermal non-equilibrium model. Some numerical treatments are adopted for the conjugated flow and heat transfer in the two regions besides the foam-fluid
interface. The effects of some key parameters on heat transfer are discussed. These key parameters include the Rayleigh number (Ra), dimensionless foam thickness, thermal conductivity ratio, porosity, and pore density. The conductiondominated, transition, and convection-dominated regimes are found with increasing Ra. The dimensionless interfacelocation scope for the thermal performance being superior to empty annulus is provided for the two modes. Under the same foam thickness, the Nusselt number of mode I is slightly higher than that of mode II.
Zhiguo
Qu
Key Laboratory of Thermo-Fluid Science and Engineering Ministry of Education
School of Power and Energy Engineering
Xi'an Jiaotong University, Xi'an, 710049, China
H. J.
Xu
MOE Key Laboratory of Thermo-Fluid Science and Engineering, Energy and Power Engineering School, Xi'an Jiaotong University, Xi'an 710049, China
Wen-Quan
Tao
Key Laboratory of Thermo-Fluid Engineering and Science of MOE, School of Energy and Power
Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi, 710049, China
979-995
THREE-DIMENSIONAL NUMERICAL SIMULATION OF A THREE-LAYERED RADIANT POROUS HEAT EXCHANGER WITH VARIABLE GAS PROPERTIES
This paper deals with the thermal analysis of a new type of porous heat exchanger (PHE). This system operates based on energy conversion between gas enthalpy and thermal radiation. The proposed PHE has one high temperature (HT) and two heat recovery (HR1 and HR2) sections. In the HT section, the enthalpy of flowing high temperature gas that is converted to thermal radiation emitted towards the two heat recovery sections where the reverse energy conversion from thermal radiation to gas enthalpy occurs. In each section, a 3D cubic porous layer which is assumed to be absorbing, emitting and scattering is presented. For theoretical analysis of the PHE, the gas and solid phases are considered in nonlocal thermal equilibrium and separate energy equations are used for these two phases. For thermal analysis of the proposed PHE, the coupled energy equations for the gas and porous layer at each section are numerically solved using the
finite difference method. The radiative transfer equation is solved by the discrete ordinates method (DOM) to compute the distribution of radiative heat flux in the porous layer. The numerical results consist of the gas and porous temperature distributions. The variations of radiative heat flux and gas property are also presented. Furthermore, the effects of scattering albedo, optical thickness and inlet gas temperature on the efficiency of the proposed PHE are investigated. It is shown that this type of porous heat exchanger has a very high efficiency especially when the porous layers have high optical thickness. The present results are compared with those reported theoretically by other researchers and good
agreement is found.
Mohammad
Sajedi
Mechanical Engineering Department, Shahid Bahonar University, Kerman, Iran
S. A. Gandjalikhan
Nassab
Mechanical Engineering Department, School of Engineering, Shahid Bahonar University of
Kerman, Kerman, Iran
E. Jahanshahi
Javaran
Mechanical Engineering Department, Shahid Bahonar University, Kerman, Iran
997-1010
ON A LINEARIZATION METHOD FOR MHD FLOW PAST A ROTATING DISK IN POROUS MEDIUM WITH CROSS-DIFFUSION AND HALL EFFECTS
We investigate the effects of thermo-diffusion (Soret number) and diffusion-thermo (Dufour number) on hydromagnetic steady flow past a rotating disk in a porous medium with Hall current. The governing equations are transformed into a system of ordinary differential equations and solved using the successive linearization method (SLM). The effects of the magnetic interaction parameter, Soret number, Dufour number, Schmidt number, Prandtl number, and suction or injection parameter on the fluid velocity, temperature, and concentration distributions in the regime are depicted graphically and are analyzed in detail. The skin-friction coefficients for some parameters are also calculated and displayed
in tables showing the effects of various parameters.
Ahmed A.
Khidir
School of Mathematics, Statistics and Computer Science, University of KwaZulu-Natal Private Bag X01 Scottsville 3209, Pietermaritzburg, South Africa; Faculty of Technology of Mathematical Sciences and Statistics, Alneelain University, Algamhoria Street
Precious
Sibanda
University of KwaZulu-Natal
1011-1024
DETERMINATION OF UNSATURATED HYDRAULIC PROPERTIES USING DRAINAGE GRAVITY TEST AND PARTICLE SWARM OPTIMIZATION ALGORITHM
There are different tests to estimate the hydraulic parameters of the van Genuchten−Mualem model needed to simulate the flow in unsaturated porous media. In this paper it is shown that it is possible to identify all the hydraulic parameters of sand by using a unique column test, which is a gravity drainage test where only the flow-rate temporal evolution is measured. To do so, we use several tensiometers installed in different positions along the column to measure the pressure head inside the soil sample. Inverse analysis is performed thanks to the particle swarm optimization (PSO) algorithm and the finite element modeling of the column test. This optimization algorithm is easy to implement and is efficient for this strongly nonlinear problem. The identification is validated by using conventional tests such as the multi-step outflow test and the constant-head permeameter test.
Tarek
Lazrag
Universite de Lyon, Ecole Nationale d'Ingenieurs de Saint-Etienne, Laboratoire de Tribologie et Dynamique des Systemes UMR 5.65 rue Jean Parrot, Saint Etienne 42100, France; Ecole Nationale d'Ingenieurs de Monastir, Unite de Recherche de Thermique
M.
Kacem
Universite de Lyon, Ecole Nationale d'Ingenieurs de Saint-Etienne, Laboratoire de Tribologie et Dynamique des Systemes UMR 5.65 rue Jean Parrot, Saint Etienne 42100, France
Ph.
Dubujet
Universite de Lyon, Ecole Nationale d'Ingenieurs de Saint-Etienne, Laboratoire de Tribologie et Dynamique des Systemes UMR 5.65 rue Jean Parrot, Saint Etienne 42100, France
Jalila
Sghaier
Département d'Energétique, Ecole Nationale d'Ingénieurs de Monastir, Avenue Ibn Eljazzar, 5019 Monastir, Tunisie
Ahmed
Bellagi
U. R. Thermique & Thermodynamique des Procédés Industriels, National Engineering School at Monastir E.N.I.M, Av. Ibn Jazzar, 5060 Monastir, Tunisia
1025-1034
SOME BASIC RESULTS IN NONLINEAR THEORY OF DIPOLAR POROUS MATERIALS
In our study we extend some results due to Langenbach in order to cover the nonlinear theory of dipolar porous bodies. In this context, we obtain some results regarding the existence and uniqueness of the solution of boundary-value problems.
Marin
Marin
Department of Mathematics, University of Brasov, Romania
Gabriel
Stan
Department of Mathematics, University of Brasov, Romania
1035-1042
GRAIN SIZE EFFECTS ON EFFECTIVE THERMAL CONDUCTIVITY OF POROUS MATERIALS WITH INTERNAL THERMAL CONTACT RESISTANCE
We study the effective thermal conductivity of granular porous materials with or without consideration of the thermal contact resistance. A negligible thermal contact resistance means the particles connect well with each other. Otherwise we assume thermal contact resistance layers between the particles forming a network frame in the system We calculate the effective thermal conductivity by a high-efficiency lattice Boltzmann method and examine its dependence on the grain size of porous materials. The results show that the effective thermal conductivity decreases slightly with the averaged grain size for negligible thermal contact resistance, consistent with existing observations in engineering materials studies. When the thermal contact resistance is significant, the effective thermal conductivity decreases sharply as the grain size gets smaller, which agrees with the experimental measurements on nanoporous materials where the particles are not able to contact well with each other and the resistance dominates the thermal transport.
Moran
Wang
Department of Engineering Mechanics and CNMM, Tsinghua University, Beijing 100084, China
Xinmiao
Wang
Department of Engineering Mechanics and CNMM, Tsinghua University, Beijing 100084, China
Jinku
Wang
National Institute of Metrology, Beijing 100013, China
Ning
Pan
Biological and Agricultural Engineering and NEAT, University of California, Davis, California 95616, USA
1043-1048
MODELING OF LAMINAR FORCED CONVECTION HEAT TRANSFER IN PACKED BEDS WITH PEBBLES OF ARBITRARY GEOMETRY
Porous media are excessively well-known because of their frequent presence in nature and their special characteristics which make them appropriate for many scientific and technological purposes. High convection heat transfer coefficient is one of the inherent worthwhile properties that has been investigated extensively. Porosity and pebble geometry have significant effects on convection heat transfer in packed beds due to the fact that they are two important parameters which form the flow pattern and local flow conditions. Three different pebble geometries, namely sphere, cylinder, and cone, have been considered for studying the role of pebble geometry in the current work. Here, a general familiar model of convection heat transfer from isothermal bodies, next to some reliable experimental data from previous experiments, have been used as a basis to develop some comprehensive and more accurate correlations. On the other hand, previous works have not dealt with geometry thoroughly; additionally they do not typically cover the entire range of porosity and do not likewise preserve their accuracy over a wide range of Reynolds and Prandtl numbers. Thus, the present study includes different correlations for packed beds with spherical, cylindrical, and conical pebbles. Furthermore, general correlations for evaluation of forced convection heat transfer from isothermal beds with arbitrary pebble geometry and aspect ratio are also developed. In the end, results have been corroborated by comparison with previous works showing very good agreement for laminar flows over all porosities and Prandtl numbers.
Yaser
Hadad
School of Mechanical Engineering, Shiraz University, Shiraz, Iran, 71348-51154
Khosrow
Jafarpur
School of Mechanical Engineering, Shiraz University, Shiraz, Iran
1049-1061