Begell House
Journal of Porous Media
Journal of Porous Media
1091-028X
9
3
2006
Coking of a Porous Catalyst and Its Inhibiting by Siliconiting Modification
In order to inhibit the coke deposition on the surface of ZSM-5, used as the catalyst for oxidation of benzene to phenol (BTOP) by nitrous oxide, the method of chemical surface deposition of silicon is chosen to modify the surface of ZSM-5. In this paper, the effect of modification condition on the micropore structure and catalyst activity was studied. The porous catalyst was characterized by XRF, EPMA, TEM, XRD, N2 adsorption at −196° C, and pyridine adsorption-infrared techniques. The results show that the uniform SiO2 membrane can be formed on an external surface of the ZSM-5 crystal under moderate modification conditions. The SiO2 membrane covers the acid centers on ZSM-5 external surface, so ZSM-5 external surface coking is inhibited and the pore blockage is avoided or decreased. At the same time, the SiO2 membrane does not change the acid centers located in pores so that the catalyst activity and stability can be improved efficiently. The optimal siliconiting conditions were determined by experiments. Compared with the samples without siliconiting treatment, the samples treated under the optimal conditions can increase the productivity of phenol by 14% for 3 h reaction time and by 41% for 6 h reaction time, respectively.
Pimu
Zhai
School of Chemical Eng., Dalian University of Technology, Dalian, 116012, P.R. China
Liqiu
Wang
School of Chemical Eng., Dalian University of Technology, Dalian, 116012, P.R. China
Changhou
Liu
School of Chemical Eng., Dalian University of Technology, Dalian, 116012, P.R. China
Shouchen
Zhang
School of Chemical Eng., Dalian University of Technology, Dalian, 116012, P.R. China
185-193
Stokes Problem for an Oscillating Plate in a Porous Medium with Hall Effects
An exact solution of the flow of a viscous fluid on a porous plate by using the Laplace transform is obtained in the presence of a strong magnetic field by introducing the Hall currents. The fluid half-space is considered to be porous. Large time solution, displacement thickness, energy aspects, and effects of a porous medium are discussed. Finally, some special cases with graphs are presented.
Muhammad Raheel
Mohyuddin
COMSATS Institute of Information Technology, Abbottabad, Pakistan; Department of Physics, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45195, Iran
195-205
Free Convection in a Wavy Cavity Filled with Heat-Generating Porous Media
A numerical investigation of steady free convection inside a cavity made of two horizontal straight walls and two vertical wavy walls filled with a heat-generating porous medium is carried out. Wavy walls are assumed to follow the profile of a cosine curve. Horizontal straight walls are kept adiabatic, while the bent walls are isothermal and kept at the same temperature. The governing Darcy and energy equations were discretized using the Galerkin finite element method. The results provide detailed information on the influences of the governing parameters, which describe this problem. Simulations are carried out for a range of wave ratio λ = 0 to 0.6, aspect ratio A = 1 to 5, and Rayleigh number Ra = 10 to 1000. Results are presented in the form of streamlines, isotherms, and local and average Nusselt numbers. Comparison with known results from the open literature for natural convection in a porous cavity with plane vertical walls (λ = 0) is in excellent agreement. In all the results presented, steady state has been attained.
Aydin
Misirlioglu
Istanbul Technical University, Faculty of Aeronautics and Astronautics, 34469 Maslak-Istanbul, Turkey
A. Cihat
Baytas
Istanbul Technical University, Faculty of Aeronautics and Astronautics, 34469 Maslak Istanbul, Turkey
Ioan
Pop
Department of Mathematics, Babes-Bolyai University, 400084 Cluj-Napoca, Romania
207-222
Natural Convective Mass Transfer from Embedded Cylinders in Saturated Porous Media
Natural convective mass transfer coefficients from vertical cylinders of varying aspect ratio, embedded in saturated porous media, were measured using the limiting diffusion current technique. A copper ion reduction from an acidified cupric sulphate solution was used as the electrolyte. Randomly packed identical glass spheres of different size formed the porous media that were saturated with electrolyte solution The obtained data are correlated in terms of modified Sherwood number (ShL* ), modified Rayleigh number (RAL* ), and Darcy numbers (DaL). The correlation is expected to work in the range 6 × 104 < RaL* < 6.1 × 106 and 1.40 × 10−6 < DaL < 1.02 × 10−3.
S. U.
Rahman
Electrochemical Research Group, Chemical Engineering Department, King Fahd University of Petroleum & Minerals, Dhahran-31261, Kingdom of Saudi Arabia
M.
Al-Khater
Electrochemical Research Group, Chemical Engineering Department, King Fahd University of Petroleum & Minerals, Dhahran-31261, Kingdom of Saudi Arabia
N. A.
Al-Baghli
Electrochemical Research Group, Chemical Engineering Department, King Fahd University of Petroleum & Minerals, Dhahran-31261, Kingdom of Saudi Arabia
M. A.
Abul-Hamayel
Electrochemical Research Group, Chemical Engineering Department, King Fahd University of Petroleum & Minerals, Dhahran-31261, Kingdom of Saudi Arabia
223-234
Numerical Analysis of Natural Convection in Porous Media: The Influence of Non-Darcian Terms and Thermal Dispersion
Two-dimensional steady natural convection in a porous cavity, bounded both by isothermal vertical walls at different temperatures and adiabatic horizontal ones, has been numerically studied. A generalized model for the momentum equations was employed. Non-Darcian effects were taken into account in the momentum equations, the thermal dispersion effect and the variable stagnant thermal conductivity were included in the energy equation, and the wall effect on porosity variation was approximated by an exponential function. The governing equations in terms of the primitive variables were numerically solved by the finite-volume method using a staggered variable arrangement, and the pressure-velocity coupling was treated by the PRIME algorithm. The influence of the inertial, Brinkman's, and Forchheimer's terms was compared to the experimental and numerical Nusselt numbers available in the literature. The numerical results indicate that the generalized model with thermal dispersion reduces the discrepancy in the experimental results for Prandtl numbers ranging from 7.1 to 480 for a high modified Rayleigh number; while for a low modified Rayleigh number, the thermal dispersion term is not appropriate. Two correlations were also proposed in order to evaluate the average Nusselt number, considering the thermal dispersion: one for a tall cavity and another for a shallow cavity.
Jesus Marlinaldo
De Medeiros
Federal Center of Technological Education of Sergipe, 49400-000 Lagarto, Brazil
Jose Mauricio
Gurgel
Mechanical Technology Department, Federal University of Paraíba, P.O. Box 5115, 58051-970 João Pessoa, Brazil
Francisco
Marcondes
Departamento de Engenharia Metalúrgica e Ciencias dos Materiais, Universidade Federal do Ceará
235-250
Radiation Effects on Mixed Convection over a Nonisothermal Cylinder and Sphere in a Porous Media
In this paper, numerical solutions for the effect of thermal radiation on mixed convection of optically dense viscous fluids about a nonisothermal cylinder and sphere is presented. The governing equations are transformed by using a set of nonsimilarity variables and solved by using the Keller box method. Numerical results for the dimensionless velocity and temperature profiles and local Nusselt number for the mixed convection parameter ζ, the power index of temperature variation λ, the radiation-conduction parameter Rd, and the surface temperature parameter H are presented. Comparison with previous works shows complete agreement. It is found that when the radiation effect becomes significant for both cases of large values of Rd and H, the local Nusselt numbers are also greatly increased; this is due to the important role played by the radiation mechanism in transferring heat between gray fluid layers.
Hamzeh M.
Duwairi
Mechanical Engineering Department, Faculty of Engineering and Technology, The University of Jordan, 11942, Amman, Jordan
251-259
Simulation of Ordinary Gas Transfer in Porous Solid with Tubular Inclined Pores
Ideal pure gas transfer at constant temperature through a porous solid and under a pressure gradient is studied. This study is based on a diffusional formalism in the ordinary regime of gas transfer. In this regime, gas transfer is controlled by the successive collisions that occur between the gas particles. The final equation resulting from theoretical consideration expresses the transported gas fraction. This is the ratio of the gas flux to the difference between the rate of particle collisions with the unit area of the two ends of the solid. These collisions are the ones that occur from the gas sources beside the two ends. The realized formulation is evaluated by computer simulation for different porous media consisting of cylindrical tubes as the pores. From simulation results, the transported gas fraction and the tortuosity factor of an inclined tube are determined and discussed. This determination provides the possibility to replace the real porous solid with an equivalent porous model containing the tubular inclined pores. Discussions will be realized on the tortuosity factor of such models.
Mohammad-Hasan
Abbasi
Department of Materials Engineering, Isfahan University of Technology, 84156 Isfahan, Iran
261-273
General Announcement: Second International Conference on Porous Media and its Applications in Science, Engineering and Industry, June 17-22, 2007 Kauai, Hawaii
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