Sharif Digital Repository

In this study, mathematical modeling of fixed-bed plasma reactor operated under isothermal condition was investigated. In this process, methane and acetylene were the inputted feed and ethane, ethylene, propylene, propane, i-butane, and n-butane were the output products. The amount of methane conversion obtained was 12.7% for the former feed, however, if pure methane was inputted this conversion rose to 13.8%. Furthermore, the plasma process enhanced the conversion as well as the selectivity toward the desired product and yield. In the present study, when methane and acetylene were fed at a molar ratio of CH4/C2H2 = 10 to the reactor, the selectivity of C2, C3, and C4 hydrocarbons was... 

In this research, data on liquid-liquid extraction of platinum from commercial spent catalysts by trioctylphosphine oxide (TOPO) in toluene were experimentally obtained. Alkaline metal salts were used to optimize the separation process. Best Salting-out effect was obtained by KCl which extracted up to 90% of platinum utilizing TOPO. Furthermore, extraction percentages of Pt and Al depending upon different factors were investigated. It was observed that the extraction process was kinetically fast and achieving the equilibrium time took less than 30 seconds. Optimized points obtained utilizing response surface methodology (RSM) by the "Design Expert" software in order to minimize the... 

In the present work, a multi sensing grasper has been developed for minimally invasive surgery with embedded ZnO piezoelectric and Fiber Bragg Grating sensors. In this model, a sensing patch equipped with three FBG sensors to sense the temperature in rage of 800 n.m and two separated FBG in range of 1550 m.m to detect the displacement in x and y directions. ZnO piezoelectric is highly sensitive to time and provides a good resistance to temperature. Therefore, this sensor is used for measuring the rate of strain and creep coefficient. A finite element approach based on the viscous material theory and plane displacement theory of anisotropic materials has been utilized to obtain the compliance... 

Etheno-damaged DNA adducts such as 3,N4- ethenocytosine, N 2,3-ethenoguanine, and 1,N2-ethenoguanine are associated with carcinogenesis and cell death. These inevitable damages are counteracted by glycosylase enzymes, which cleave damaged nucleobases from DNA. Escherichia coli alkyl purine DNA glycosylase is the enzyme responsible for excising damaged etheno adducts from DNA in humans. In an effort to understand the intrinsic properties of these molecules, we examined gasphase acidity values and proton affinities (PA) of multiple sites of these molecules as well as equilibrium tautomerization and base pairing properties by quantum mechanical calculations. We also used calculations to compare... 

The present investigation considers the thermally developing electroosmotic flow of power-law fluids through a parallel plate microchannel. Both the viscous dissipation and Joule heating effects are taken into account and a step change in wall temperature is considered to represent physically conceivable thermal entrance conditions. Expressions for the dimensionless temperature and Nusselt number in the form of infinite series are presented. In general, the resultant eigenvalue problem is solved numerically; nevertheless, an analytical solution is presented for the regions close to the entrance. A parametric study reveals that increasing amounts of the Peclet number result in higher wall... 

Dye sensitizers loaded on TiO2 decrease the electron excitation energy, thereby improving the photocatalytic performance by causing an increase in sensitivity under visible light irradiation. Three dye sensitizer precursors, Mordant Orange 1, N3 (red dye) and Cobalt (II) Phthalocyanine Tetrasulfonate (CoPcTs), were utilized to load the photocatalyst. The rate of the electron trapping process on platinum is clearly compatible with the migration rate of boundary electrons. Consequently, the migration of boundary electrons from the conduction band towards electron acceptors is increased by loading platinum onto the titanium dioxide. In this research, TiO2 was synthesized from a titanium... 

A mathematical model for a fixed bed radial flow catalytic reactor was developed for dehydrogenation of heavy paraffins over Pt-Sn/Al2O3 catalyst. The model included appropriate kinetic rate expressions for the main dehydrogenation reaction as well as side reactions and catalyst deactivation. The reactor model consisted of a set of partial and ordinary as well as algebraic equations that were solved numerically to determine the concentration of various species along the radius of the bed as a function of time. The Nelder-Mead optimization method was used to obtain the optimum kinetic parameters. The validity of the model was demonstrated by comparing the predicted paraffin conversion and... 

In the present study, a procedure was developed to determine the optimum reaction rate constants in generalized Arrhenius form and optimized through the Nelder-Mead method. For this purpose, a comprehensive mathematical model of a fixed bed reactor for dehydrogenation of heavy paraffins over Pt-Sn/Al 2O 3 catalyst was developed. Utilizing appropriate kinetic rate expressions for the main dehydrogenation reaction as well as side reactions and catalyst deactivation, a detailed model for the radial flow reactor was obtained. The reactor model composed of a set of partial differential equations (PDE), ordinary differential equations (ODE) as well as algebraic equations all of which were solved... 

The FT reaction involves the conversion of syngas which is derived from natural gas or coal to different kinds of products according to the operating conditions and the type of the catalyst. In other words, it is a practical way to convert solid fuel (coal) and natural gas to various hydrocarbons (C1-C60) and oxygenates such as alkanes, alkenes etc. The main products of the reaction are naphtha and gasoline. This paper deals with developing a proper product distribution model for FT process using the appropriate kinetic model, optimizing the respective rate constants while applying them in product distribution equations. The results revealed only 8.09% deviations from the olefin experimental... 

In the present work, accumulative roll bonding (ARB) was used as an effective method for manufacturing nanoparticle/Al composite filler metals of tungsten inert gas (TIG) welding. After welding, the distribution of ceramic nanoparticles and mechanical properties of welds were investigated. By applying ARB, ceramic nanoparticles were uniformly dispersed in the composite filler metals. Consequently, the welds produced by these filler metals had a uniform dispersion of ceramic nanoparticles in their compositions. The test results showed that the yield strength of welds was greatly increased when using the nanoparticle/Al composite filler metals. The improvement in the yield strength was... 

In this study, mathematical modelling of oxidative coupling of methane (OCM) to C 2 hydrocarbons (C 2H 6 and C 2H 4) over La 2O 3/CaO catalyst in a fixed-bed reactor operated under isothermal and non-isothermal conditions was investigated using the MATLAB program. In this process, methane and acetylene were the inputted feed and ethane, ethylene, propylene, propane, i-butane and n-butane were the output products. The amount of methane conversion obtained was 12.7% for the former feed however; if pure methane was inputted this conversion rose to 13.8%. Furthermore, the plasma process would enhance the conversion, selectivity towards desired product and process yield. A comparison between the... 

The effects of selected metal ions on the gas-phase acidity of weak organic acids have been explored using the DFT and Moller-Plesset Perturbation Theory (MP2) calculations. The three organic acids selected for this study were acetic acid (aliphatic), benzoic acid (aromatic), and glycine (amino acid). The acidities of these compounds are compared with the acidity of their Li +-, Na+-, and K+ -complexed species. The results indicate that upon complexation with Li+, Na+, and K+ at 298K, the gas-phase acidity of acetic acid, for example, varies from 345.3 to 218.8, 230.2, and 240.1 kcal/mol, respectively (i.e., its dissociation becomes much less endothermic). These values indicate that a weak...