Begell House
Journal of Porous Media
Journal of Porous Media
1091-028X
4
3
2001
Experimental Study of a Staged Methane/Air Burner Based on Combustion in a Porous Inert Medium
Further decreases in NOx emissions from burner systems, in particular domestic heating systems, Stirling engines, gas and steam turbines, and so forth, are of enormous interest at present. Staged combustion in inert porous media offers a high potential to meet the operational and environmental requirements for those applications. A special experimental facility was built to study the behavior of staged combustion in porous inert media. The construction allows investigations of the effects of staging with pure methane or air by measuring the temperatures in the combustion region. In addition, the emissions of NOx, CO, and CH4 were measured in the flue gases to establish how the thermal heat load, the staged quantity, and the air ratio affect them. For certain staged quantities and overall air ratios, the pollutant emissions lie in an optimal range. The results show that the NOx emissions can be decreased by approximately 30—40% for the same overall air ratio in comparison with the case without staging. Two different porous media used—an alumina fabric lamella structure and an SiC foam—show that the characteristics of the pollutant emissions are only slightly dependent on the porous medium. Another result is that in the staged mode, the combustion can be kept stable at higher primary air ratios.
O.
Pickenacker
Institute of Fluid Mechanics, University of Erlangen-Nuremberg, Cauerstr. 4, D-91058 Erlangen, Germany
Dimosthenis
Trimis
Institute of Thermal Engineering, Technische Universitat Bergakademie Freiberg, Gustav-Zeuner-Strasse 7, D-09596 Freiberg, Germany; Engler-Bunte-Institute Division of Combustion Technology, Karlsruhe Institute of Technology, Engler-Bunte-Ring 1, D-76131
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Flow and Heat Transfer Within Segregated Beds of Solid Particles
A model for the transient fluid flow and heat transfer within an axially symmetrical circular cylindrical packed bed of solids containing two different layers of porous matrices is described. The system relates to a cylindrical packed bed fitted with an axial core of a porous matrix that is different from the surrounding cylindrical shell. The influence of permeability ratio (0.0625−16) and Reynolds number (1000 and 2000) on the thermal wave propagation is described. A hot stream of dry air is forced to flow axially at the inlet to the bed. The numerically predicted results are validated against experimental data obtained in a small laboratory test rig 63 mm in diameter and 120 mm in length that is packed with uniform diameter spherical glass beads (3−12 mm in diameter). An analytical model was also developed to estimate the velocity in the bed and compared with the value obtained from the numerical solution of the volume-averaged Navier-Stokes equation. The results are presented for Reynolds numbers of 1000 and 2000. It is found that for a highly fractured core, the heat diffuses radially, while for a low permeability core the heat transfer takes place by advection and diffusion. In the latter case, the Reynolds number has a significant effect on the rate of heat transfer.
Abdulmajeed A.
Mohamad
Department of Mechanical and Manufacturing Engineering, Schulich School of Engineering, CEERE, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4
G. A.
Karim
Deptartment of Mechanical and Manufacturing Engineering, University of Calgary, Calgary, Alberta, Canada T2N 1N4
10
Effect of a Traveling Thermal Wave on Weakly Nonlinear Convection in a Porous Layer Heated from Below
The stability of weakly nonlinear convection in a porous layer heated from below is considered. Much is known about those cases where the boundary temperatures are uniform, or display steady small-amplitude variations about a uniform mean. In this study we consider the effects of small-amplitude traveling thermal waves on the ensuing weakly nonlinear convection. At sufficiently low Rayleigh numbers the induced flow follows the motion of the thermal wave. But at higher Rayleigh numbers this form of convection breaks down and there follows a regime where the flow travels more slowly on average and does not retain the forcing periodicity. It appears that the flow passes through all. multiples of the forcing periodicity as the Rayleigh number increases. At much higher Rayleigh. numbers within the weakly nonlinear regime two very distinct time scales appear in the numerical simulations, and these are described analytically using the method of multiple scales; comparisons with numerical simulations are excellent. A similar scenario exists for large wavespeeds but moderate values of the Rayleigh number.
Nurzahan
Banu
Department of Computer Science, North South University 12 Kemal Ataturk Avenue, Banani, Dhaka-1213, Bangladesh
D. Andrew S.
Rees
Department of Mechanical Engineering, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom
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Analysis of Melt Infiltration into a Moving Bundle of Fibers Relevant to Processing of Metal Matrix Composite Wires
An analysis is made for radial melt infiltration into a moving, axially oriented bundle of fibers in the presence of a gas counterflow (i.e., the fiber motion in the z-direction and the gas flow in the — z-direction) under an isothermal condition. Governing equations consist of continuity of the melt and the gas phase, Darcy's equation for the melt and the gas phase taking into account the differences in permeability in the axial and the radial direction, and the ideal gas equation of state. With the melt infiltration starting at z = 0 and ending at a location, z = L, where the gas pressure considering the effect of the melt—gas interfacial pressure differential is specified, a solution yields a growth profile of the melt-infiltrated layer and the pressure drop over the axial distance L.
Uichiro
Narusawa
Department of Mechanical, Industrial & Manufacturing Engineering, Northeastern University, Boston, MA 02115, USA
J. T.
Blucher
Department of Mechanical, Industrial & Manufacturing Engineering, Northeastern University, Boston, MA 02115, USA
D.
Goldthwaite
Department of Mechanical, Industrial & Manufacturing Engineering, Northeastern University, Boston, MA 02115, USA
10
A Novel Porous Membrane Reactor for a Controllable Butene Oxidative Reaction
A novel membrane reactor, composed of a specially prepared porous γ-alumina ceramic membrane tube and a stainless steel shell, has been designed, and a butene oxidative dehydrogenation reaction has been carried out in it overferrite catalyst. By introducing butene and air into two sides of the porous membrane tube and adjusting the pressure difference across the tube, air permeation into the reaction region can be controlled and butene counterpermeation to the air region can be eliminated. Thus, the oxidative reaction of butene can be carried out at a high butene concentration and a suitable oxygen content, leading to much higher reactive selectivity and yield compared with the conventional fixed bed reactor. A method for preparing a nonuniform membrane is given. The effects of some operation parameters, such as the permeation and its axial distribution across the membrane, temperature, composition of the feed, and space velocity on the reaction performance have been studied and discussed. It is shown from the study that this kind of reactor can be used for most oxidation reactions if the oxygen reaction order of the main reaction is lower than that of the side reaction.
Lianjun
Wang
Department of Chemical Engineering, Dalian University of Technology, Dalian.l 16012, P.R. China
Shanhai
Ge
Department of Chemical Engineering, Dalian University of Technology, Dalian.l 16012, P.R. China
Changhou
Liu
School of Chemical Eng., Dalian University of Technology, Dalian, 116012, P.R. China
Zhihua
Li
Department of Chemical Engineering, Dalian University of Technology, Dalian.l 16012, P.R. China
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A Combined Use of Direct Search Algorithms and Exterior Penalty Function Method for Groundwater Pollution Management
An optimization based numerical management model has been developed to address groundwater pollution problems cropping up at different scales. The management model consists of objective function for water supply and imposed restrictions on decision variables such as physical, operational, and managerial constraints. To simulate groundwater flow and pollutant transport processes, coupled set of discretized forms of governing partial differential equations describing two-dimensional flow through porous media and two-dimensional movement of dissolved contaminant within the porous medium with appropriate initial and boundary conditions are conflated within a single framework of the optimization model. A combined use of the Exterior Penalty Function Method (EPFM) and two direct search methods; the Hooks-Jeeves (HJ) method and the Powell's Conjugate Direction (PCD) method are employed to solve the multivariable constrained nonlinear optimization model. The optimal solutions are obtained for a number of management scenarios, each representing different porous media environment and operating situations for aquifers. The optimal solutions are also compared to investigate the relative performance of the proposed two methodologies (EPFM&HJ and EPFM&PCD) in terms of its robustness, versatility, accuracy, efficiency, ease in implementation, and computational feasibility. These methodologies avoid the repetitive use of physical system simulators and enable to handle fully embedded optimization model, although it increases the dimension. Limitations of these two methodologies are also discussed in terms of its applicability, suitability, and global optimality of solutions.
Ashok K.
Keshari
Department of Civil Engineering, Indian Institute of Technology, Delhi, Hauz Khas, New Delhi 110016, India
Bithin
Datta
Department of Civil Engineering, Indian Institute of Technology, Kanpur, Kanpur 208016, India
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Radiation and Flow Through a Porous Medium
Flow through a porous medium in the presence of heat transfer has been analyzed. Special studies can be found in Nield and Bejan (1998). Recently Raptis (1998) studied the steady flow of a viscous fluid through a porous medium bounded by an infinite plate in the presence of thermal radiation in the fluid when the porosity of the porous is very high. The aim of the present article is to investigate the steady flow of a viscous fluid through a porous medium bounded, by a horizontal semi-infinite plate in the presence thermal radiation in the fluid.
A.
Raptis
Department of Mathematics, University of Ioannina, Ioannina 451 10, Greece
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