Begell House
Journal of Porous Media
Journal of Porous Media
1091-028X
15
6
2012
THE INTERACTION BETWEEN DIESEL SPRAYS AND POROUS MEDIA: EFFECT OF MEDIUM PORE DENSITY AND INJECTION PRESSURE
The unique properties of porous structures have been utilized in different applications, such as gaseous and liquid fuel burners, to enhance the rate of fuel-air mixing and to increase the thermal efficiency. There have been attempts to utilize these unique features of porous structures to improve the combustion process in direct injection diesel engines as well. In this article, the characteristics of high-pressure diesel sprays directly impinging on the surfaces of porous media (PM) of different pore densities mounted in a constant-volume steel chamber are experimentally investigated. A high-speed imaging technique, designed to capture impingement and egress events at the highest possible frame rates to ensure adequate temporal and spatial resolution for the captured images, is used throughout. The results show that injection pressure and medium pore density have strong influence on the spray patterns above and below the porous medium, streamwise and spanwise spray penetrations, and spray-projected area. The increased projected spray area coupled with multijet splitting following egress from the porous medium is an indication of increased air entrainment and improved degree of air-fuel mixture homogenization.
Navid
Shahangian
Laboratory for Turbulence Research in Aerospace and Combustion, Department of Mechanical and Aerospace Engineering, Monash University, VIC 3800, Australia
Jamil
Ghojel
Laboratory for Turbulence Research in Aerospace and Combustion, Department of Mechanical and Aerospace Engineering, Monash University, VIC 3800, Australia
501-516
A POROUS MODEL FOR THE INTERPRETATION OF MERCURY POROSIMETRY TESTS
Recently, the pore size distribution obtained from mercury intrusion porosimetry tests has been used by different researchers to describe some properties of soils. For example, porosimetry results have been used to obtain the soil-water characteristic curve and the hydraulic conductivity for different soils. One of the main assumptions of the mercury intrusion porosimetry test is to consider that the pores of soil can be represented by a bundle of capillary tubes, each of a different diameter, which saturate or dry independently from the others. However, this assumption is unrealistic. This article presents a more realistic porous model based on three different types of pores that allow for the simulation of the hysteresis of the soil-water characteristic curve as for the collapse of pores during drying. This model is a computational type, which means that the different elements are accommodated in two- or three-dimensional regular networks and the filling or drying of pores is followed step by step. The model is used to simulate a mercury intrusion porosimetry test in a material where the pore size distribution has also been obtained from image analysis of scanning electron micrographs. This simulation shows that the current interpretation for mercury intrusion porosimetry test results in pore sizes much smaller than the real values.
Eduardo
Rojas
Faculty of Engineering, Universidad Autonoma de Queretaro, Centro Universitario, Cerro de las Campanas, 76160, Queretaro, Qro., Mexico
Maria de la Luz
Perez-Rea
Faculty of Engineering, Universidad Autonoma de Queretaro, Centro Universitario, Cerro de las Campanas, 76160, Queretaro, Qro., Mexico
Gustavo
Gallegos
Faculty of Engineering, Universidad Autonoma de Queretaro, Centro Universitario, Cerro de las Campanas, 76160, Queretaro, Qro., Mexico
Julio
Leal
Faculty of Engineering, Universidad Autonoma de Queretaro, Centro Universitario, Cerro de las Campanas, 76160, Queretaro, Qro., Mexico
517-530
NUMERICAL AND EXPERIMENTAL STUDY OF CONVECTIVE HEAT TRANSFER IN A VERTICAL POROUS CHANNEL USING A NON-EQUILIBRIUM MODEL
Convective heat transfer in a vertical porous channel heated by the wall and isolated on the other face was simulated numerically and experimentally. The porous medium is formed by a solid matrix of spherical beads. The considered fluid is air that saturates the solid matrix. The two-temperature model and the Darcy-Brinkman-Forchheimer equation are adopted to represent this system, and the porosity is considered as variable in the domain. The numerical model was used to analyze the effect of several operating parameters on heat transfer enhancement. Heat transfer decreases with the increase of the form factor. When Biot number increases, heat transfer between the heated wall and the porous domain is increased. Heat transfer increases with Reynolds number and with the thermal conductivity of the solid matrix. The influence of the thermal conductivity of the particles on heat transfer in the porous medium decreases with an increase of the thermal conductivity of the metallic beads, principally when the diameter of the beads increases. An increase of the bead diameter induces a decrease of heat transfer. Nusselt numbers based on the particle diameter have been correlated with respect to Reynolds number and the particle diameter. Furthermore, simulation results have been validated by experiments.
W.
Foudhil
Faculte des Sciences de Tunis, Laboratoire des Transferts de Chaleur et de Masse, Campus Universitaire, 1060 Tunis, Tunisia
B.
Dhifaoui
Faculte des Sciences de Tunis, Laboratoire des Transferts de Chaleur et de Masse, Campus Universitaire, 1060 Tunis, Tunisia
S. Ben
Jabrallah
Faculte des Sciences de Tunis, Laboratoire des Transferts de Chaleur et de Masse, Campus Universitaire, 1060 Tunis, Tunisia ; Faculte des Sciences de Bizerte, 7021 Bizerte, Tunisia
Ali
Belghith
Faculte des Sciences de Tunis, Laboratoire des Transferts de Chaleur et de Masse, Campus Universitaire, 1060 Tunis, Tunisia
J. P.
Corriou
Laboratoire Reactions et Genie des Procedes, CNRS-ENSIC-INPL, Nancy Universite, 1 rue Grandville, BP 20451, F-54001 Nancy CEDEX, France
531-547
A STUDY OF HIGH REYNOLDS NUMBER PIPE FLOWS WITH POROUS INSERTS
This article reports experiments and calculations for the flow at the inlet and exit of a ceramic foam located in a straight pipe and in a pipe with a 1:4 sudden expansion. For the latter, the foam, with thickness to diameter ratio between 0.15 and 0.60, was located at different distances from the sudden expansion wall. Three different pore sizes (10, 20, and 60 ppi) were investigated for pore Reynolds numbers in the range 20 ≤ Rep ≤ 400. LDA measurements include velocity profiles at the foam exit as a function of the Reynolds number, foam thickness, and inlet conditions and confirm that the outlet multijet flow structure induced by the nonregular configuration of the porous matrix results in a strongly three-dimensional velocity field that dissipates as the fluid flows downstream. Numerical calculations were performed to assess the suitability of available models for turbulent flow within porous media. Two different turbulence models and a laminar model for flow within the porous medium were considered. The numerical and physical models used could not reproduce completely the foam influence on the separated turbulent flow region formed between the sudden pipe expansion and the foam inlet.
Jose C. F.
Pereira
Mechanical Engineering Department Instituto Superior Tecnico Av. Rovisco Pais, 1049-001 Lisboa Portugal
Isabel
Malico
Department of Physics, University of Évora, R, Romão Ramalho, 59, 7000-671, Évora, Portugal ; IDMEC/IST, Department of Mechanical Engineering, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
T. C.
Hayashi
Department of Chemical Engineering, Universidade Federal da Bahia,R. Aristides Novis, 2, Federação, 40210-630, Salvador, BA, Brazil
Jorge M. F.
Raposo
IDMEC/IST, Department of Mechanical Engineering, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
549-563
NATURAL CONVECTION HEAT TRANSFER IN A HORIZONTAL CONCENTRIC ELLIPTIC ANNULUS CONTAINING SATURATED POROUS MEDIA
Natural convection heat transfer in a horizontal elliptic annulus filled with saturated porous media is investigated experimentally and numerically. The inner horizontal elliptic tube is heated under constant heat flux conditions and is located concentrically in a larger isothermally cooled horizontal cylinder. Both ends of the water-saturated porous annulus are closed. The heated elliptic tube was made of copper material and has an axis ratio (AR = a/b) of 3.0. The porous media used in the experiments were made of sandstone and glass materials with different solid thermal conductivities and particle diameters. The elliptic tube orientation angle is varied from 0° to 90°, and the hydraulic radius ratio, HRR = Ro/Ri, is 6.85. The numerical solution scheme is based on a two-dimensional model, which is governed by Darcy-Boussinseq equations. The inner elliptic cylinder is heated isothermally, while the outer circular cylinder is also cooled isothermally. Discretization of the governing equations is achieved using a finite element scheme based on Galerkin method of weighted residuals. The effect of pertinent parameters such as modified Rayleigh number, Ra (Rayleigh-Darcy), orientation angle of the elliptic cylinder, δ, and the axis ratio of the elliptic cylinder, AR, is investigated. The numerical results obtained from the present model are compared with the available published results and with the present experimental results, and good agreement is found. The variation of the average Nusselt number with the investigated parameters is presented. It is concluded that the effect of modified Rayleigh number, which includes the effect of fluid properties, porous medium properties, and operating conditions on the average Nusselt number, is more significant than the effect of the geometric parameters such as the elliptic cylinder orientation angle and the elliptic cylinder axis ratio. The results showed that the average Nusselt number increases with the increase of the modified Rayleigh number. Also, the flow and heat transfer characteristics are illustrated via stream function and isotherms contours. Moreover, an empirical correlation for the average Nusselt number is obtained as a function of Rayleigh number, elliptic cylinder orientation angle, and elliptic cylinder axis ratio.
Ramadan Y.
Sakr
Department of Mechanical Engineering, Faculty of Engineering, Benha University, 108 Shoubra Street, 11689, Cairo, Egypt
Nabil S.
Berbish
Department of Mechanical Engineering, Faculty of Engineering, Benha University, 108 Shoubra Street, 11689, Cairo, Egypt
567-584
NATURAL CONVECTION BOUNDARY LAYER FLOW PAST A FLAT PLATE OF FINITE DIMENSIONS
Natural convection boundary layer flow from a flat plate of arbitrary inclination embedded in a porous medium of a rotating environment with finite dimensions has been studied. The growth of a boundary layer thickness except the point of separation is assumed to be constant to exhibits of similarity solution. To examine the velocity of the boundary layer flow, the angle of attack plays an important role in preventing back flow. The influence of a Darcy number exhibits the behavior of primary and secondary flows. The bulk temperature of a porous medium flow has become of physical significance to a moving boundary layer flow.
M.
Jana
Department of Applied Mathematics, Vidyasagar University, Midnapore 721 102, India
S.
Das
Department of Applied Mathematics with Oceanology and Computer Programming, Vidyasagar University, Midnapore 721 102, West Bengal, India
S. L.
Maji
Department of Applied Mathematics, Vidyasagar University, Paschim Medinipur, West Bengal-721102, India
Rabindra N.
Jana
Department of Applied Mathematics, Vidyasagar University, Midnapore-721 102, West Bengal, India
S. K.
Ghosh
Department of Mathematics, Narajole Raj College, Narajole, District - Midnapore (West)-721211, West Bengal, India
585-593
EFFECT OF ANISOTROPY ON NATURAL CONVECTIVE FLOW THROUGH A RECTANGULAR POROUS SLAB
The natural convective flow and heat transfer, within the framework of Boussinesq approximation, in an anisotropic fluid-filled porous rectangular slab subjected to end-to-end temperature difference have been investigated using a Brinkman extended non-Darcy flow model. The studies involve simultaneous consideration of hydrodynamic and thermal anisotropy, when the principal axes may or may not coincide with the coordinate axes. The flow and temperature fields in general are governed by Ra, the Rayleigh number, AR, the aspect ratio of the slab, K*, the permeability ratio, k*, the thermal conductivity ratio, the angles φ1 and φ2, the principal axes made with the coordinate axes, and Da, Darcy number. Numerical solutions employing the successive accelerated replacement (SAR) scheme have been obtained for Ra = 500, AR = 1, 0.5 ≤ K* ≤ 5, 0.5 ≤ k* ≤ 5,0° φ1 ≤ 90°, 0° ≤ φ2 ≤ 90°, and 0 ≤ Da ≤ 0.1. The results obtained and the conclusions drawn describe the composite effect of non-Darcy flow when the principal axes describing anisotropy in permeability and thermal conductivity do not coincide with the coordinate axes.
Prakash
Chandra
Thermal Engineering Group, Central Mechanical Engineering Research Institute, Durgapur 713209, India
V. V.
Satyamurty
Department of Mechanical Engineering, Indian Institute of Technology, Kharagpur-721302 , India
595-605