Diffusion in Solids and Liquids VI

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Authors: Mohammad Ebrahim Zeynali, Feridoon Mohammadi
Abstract: The effective diffusion coefficients for a single catalyst pellet were determined by numerical integration of the Johnson-Stewart equation for bimodal and unimodal pore size distributions assuming a transitional diffusion regime. The effectiveness factors of a spherical catalyst pellet were determined at various pore size distribution probability density functions. Using effectiveness factors the production rates were determined. The results showed that the effectiveness factor and production rate are sensitive to catalyst pore size distribution and diffusion coefficient.
Authors: Mohammad Ebrahim Zeynali
Abstract: The diffusion coefficients of DEB and EVB into a synthesized and a commercial catalyst pellet were determined by numerical integration of the Stewart-Johanson equation at the reaction condition. The continuity equation was solved by the orthogonal collocation method. DVB was prepared by a commercial catalyst. The production rate and effectiveness factor were determined experimentally and compared with the predicted value. It was seen that the diffusion into the catalyst pellet is strongly limiting the process of DVB production.
Authors: Iulia Mirela Britchi, Mircea Olteanu, Niculae Ene, Petru Nita
Abstract: Pack cementation procedure implies the use of a powder mixture containing the diffusive elements, which in our case are either Ti or Ti+Al, Al2O3 and NHCl as activator. In the case of titanizing the powder mixture contained 77% in weight Ti, while for alumino-titanizing Al/Ti = 1/5 ratio was employed. NH4Cl content was 3% in weight in all cases. Aluminium additions to the powder mixtures led to a decrease of the process temperature. Activation energy for the aluminizing of austenitic 316L steel is 73.87 KJ/mol, much smaller than for the titanizing, 257.86 KJ/mol. Activation energy for alumino-titanizing, in the same conditions, is 146.01 KJ/mol. All diffusion coatings, in the Ti – 316L and Ti+Al – 316L couples are formed of two layers having different structures and compositions. All couples were investigated by optical microscopy, electron microscopy (SEM and EDX), X-ray diffraction and microhardness trials.
Authors: Zahra Fakhroueian, Pouriya Esmaeilzadeh, N. Afroukhteh Langroudi, H. Varmazyar, M. Ahmadirad, Pouyan Esmaeil Zadeh, M. Yousefi, M. Karami, A. Shafiekhani, S. Sepehriseresht
Abstract: The synthesis of nanostructures are very various, and the most of scientists always fabricate them by the coprecipitation method at pH = 10.5-11. If we prepare these nanocatalysts for partial oxidation of methane (POM), processes to transforme methane gas into hydrogen or synthesis gas (H2 + CO) for obtaining exact green fuel H2 gas at different pH, what will be occurring?, and what is the influence of pH on nanoemulsion, nanofluids, nanostructures, and finally the application in syngas process? In this study we prepared many different nanoparticles containing % x (w/w) Co, Ni, Ru and La oxides over the various supports e.g. Ce-ZrO2, MgO-CeO2, AlCeO2, SiO2, SiAl2O3, SiMgO, SiO2Al-MCM-41 nano mixed oxides sized (1-2 nm) at various pH (7, 8, 9, 11) by new coprecipitation and combine with nanofluids method using different direct agent surfactant, stabilizer, binder, alcohol solvent, dispersant and variable chemical pH controllers. The prepared nanostructures were characterized by common techniques such as SEM, TEM, XRD, Raman, FTIR, BET and TPR analysis at various pH. Also many marvellous and new mixture of nanotubes-nanoclay and nanotubes-nanocomposites with high % H2 selectivity and methane conversion were fabricated by CuOx and NiOx sputtering test followed coprecipitation method at pH 9, for POM reactions used in petrochemical industry for the first time.
Authors: R. Leticia Corral Bustamante, Aarón Raúl Rodríguez-Corral, T.J Amador-Parra, E.A. Vázquez-Tapia
Abstract: Cosmic censorship!: black hole wrapped up by its entropy and hidden by its event horizon. In this paper, we postulate a metric to solve the Einstein equations of general relativity, which predicts the thermodynamic behavior of a gigantic mass that collapses to a black hole; taking into account the third law of thermodynamics that states that neither physical process can produce a naked singularity. However, under certain conditions, the model allows to evident violation to the cosmic censorship, exposing the hole nakedness. During the collapse of the hole, quantum effects appear: the area decrease and radiation produced has a high entropy, so that increases total entropy and expose the presence of the hole, while the appearance of the event horizon hide the singularity of the exterior gazes. It is verified that in certain circumstances, the model predicts that the hole mass is bigger than its angular momentum; and in all circumstances, this predicts an hole with enormous superficial graveness that satisfy a relationship of the three parameters that describe the hole (mass, charge and angular momentum); factors all indicative that the singularity is not naked. Then, there are no apparent horizons in accord with cosmic censorship conjecture. Even though the surface gravity of the hole prevents destroying its horizon wrapping singularity, there exists evidence of this singularity by the results of the spin-mass relationship and the escape velocity obtained. The lost information and the slow rate of rotation of the semi-major axis of the mass (dragging space and time around itself as it rotates), agree with Einstein's prediction, show the transport of energy through heat and mass transfer, which were measured by entropy of the hole by means of coordinated semi-spherical that include the different types of intrinsic energy to the process of radiation of the hole event horizon.
Authors: M. Abkar, P. Forooghi, A. Abbassi
Abstract: In this paper, forced convection in a channel lined with a porous layer is investigated. The main goal is to assess the effect of local thermal non-equilibrium condition on overall heat transfer in the channel. The effects of thermal conductivity of solid and thickness of porous layer are also studied. Flow assumed to be laminar and fully developed. The Brinkman-Forchheimer model for flow as well as the two equation energy model is used. The results showed that when the problem tends to local thermal equilibrium condition, heat transfer is enhanced due to heat conduction through solid phase. Another factor, which can facilitate the heat transfer, is the increase of the thermal conductivity of solid material. This trend is sensitive to the thickness of porous layer and modified Biot number, which is a measure (criterion) of local fluid to solid heat transfer. As thickness and modified Biot number increase, the Nusselt number becomes more sensitive to the thermal conductivity ratio.
Authors: Naser Ghafooriadl, Sohrab Asadzadeh Olghi, Ali Moghani
Abstract: Recently, the dominant classes and integer-valued characters of un-matured full non-rigid group of tert-butyl alcohol has been found by the third author (see, J. Nano Res. 11, 7-11, 2010). In this paper, the unit subdued cycle index table introduced by S. Fujita for the above molecule is successfully derived for the first time.
Authors: M.A.G. Figueiredo, G.V. Estrela, W.C. Souza, S.S.X. Chiaro
Abstract: The use of adsorbents in the final steps during petroleum fuels refining is still the usual practice in Brazilian refineries. The production of kerosene via the Bender process still demands that the fuel goes through a bed of clay to remove nitrogen contaminants. Thus, several studies are being developed based on adsorption over clays for the removal of nitrogen and sulfur compounds. However, the major problem is the sharp decrease in the adsorbents durability. The procedure currently employed by the refineries is the one recommended by the annex 1 from ASTM D2007 methodology. By this method, the evaluation of the adsorbent capacity is done without any pretreatment for water removal. This study aimed to establish a comparison between the results obtained by ASTM D2007 with the results obtained by a procedure developed on a bench unit which comprises a pretreating stage to remove water from the adsorbents before feeding the column. The results show that the water content strongly influences the adsorption capacity of the clays, and may even spoil high-capacity adsorbents if they are not pretreated for water removal.
Authors: A. Shokohfar, S. M. Abbasi, Ali Yazdani, Behnam Rabiee
Abstract: In this study, cold rolling and annealing are used to refine the austenite grains of 301 austenitic stainless steel. The 301 austenitic stainless steel was cold rolled for 70 and 90% strain and then annealed. Effects of cold rolling factors and temperatures and annealing times on microstructure, hardness and tensile properties have been studied.

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