Sharif Digital Repository

A mathematical model is presented to simulate the multiple heterogeneous reactions with complex set of physicochemical and thermal phenomena in a moving bed of porous pellets. This model is based on both heat and mass transfer phenomena of gaseous species in a porous medium including chemical reactions at interfaces whose areas vary during the conversion. This model accounts for both the exothermic and endothermic reactions which can be equimolar or nonequimolar. Furthermore it considers simultaneously the reactions in the nonisothermal transient condition. A powerful technique based upon finite volume fully implicit approach has been implemented to solve the complicated governing equations... 

A mathematical model is developed to investigate the reduction process of hematite in the reduction zone of the Midrex shaft furnace as a moving bed reactor. It is described as a counter-current moving bed cylindrical reactor in which hematite pellets are reduced by a gaseous mixture of hydrogen, water vapour, carbon dioxide and carbon monoxide, namely Syngas. It is laterally injected into the bed at the lower part close to the bottom. Governing equations, including continuity, momentum, energy and mass equations, are derived based on the conceptual model for both gas and solid phases in the cylindrical coordinate system. A three interface unreacted shrinking core model (USCM) is applied to... 

A mathematical model has been developed to simulate heterogeneous reactions with a complex set of physicochemical and thermal phenomena in a packed bed. These include the chemical reaction itself, the transport of gaseous species in the pores, the generation or consumption of heat by the reactions, and the transport of heat in the porous domain. Solution of complicated sets of governing equations is based upon the concept of a finite volume fully implicit approach. The model has then been applied to analyze the reduction of a hematite pellet in a moving packed bed reactor. © 2005 Elsevier Ltd  

Small Permanent Magnet Synchronous Generators (PMSG's) are widely used in low power wind turbines. In order to inject the electrical power, generated by PMSG, to the grid, a back-To-back AC/AC power electronic converter is required. In this paper, a novel low cost efficient AC/DC converter is proposed for rectifier stage to obtain the maximum power per ampere of PMSG by using Power Factor Correction method. The new structure is based on DCM SEPIC converter. Reducing the number of semi-conductor switches has decreased converter cost. Additionally, other advantages of this Converter are employing easy control method to obtain the maximum power per ampere and using Synchronous inductance of... 

Recent developments in improving lighting efficiency and cost reduction of LEDs have made them suitable alternatives to the current lighting systems. In this paper, a novel offline structure is proposed to drive LEDs. The proposed circuit has a high-input power factor, high efficiency, a long lifetime, and it produces no flicker. To increase the lifetime of the converter, the proposed circuit does not include any electrolytic capacitors in the power stage. The proposed circuit consists of a transition mode flyback converter in order to improve power factor. Additionally, a buck converter is added to the third winding of the flyback transformer in order to create two parallel paths for the... 

Recent developments in improving lighting efficiency and cost reduction of LED's have caused them to be a suitable alternative for the current lighting systems. In this paper a novel off-line structure is proposed to drive LED's. The proposed circuit has a high power factor and high efficiency and a long lifetime. To increase the life time of the converter, the proposed circuit doesn't use any electrolytic capacitors in the power stage. The proposed circuit consists of a transition mode (TM) Flyback converter in order to have power factor correction (PFC). A Buck converter is added to the third winding of the Flyback transformer in order to create two paths for the electrical power. DC power... 

A mathematical time-dependent and isothermal model based on the grain model has been developed to simulate the kinetic and thermal behaviors of a porous iron oxide pellet undergoing chemical reactions with a mixture of hydrogen, carbon monoxide, carbon dioxide and water vapor. Its novelty consists in fact that it can deal with a multi-species reducing gas and oxide pellet. In spite of previous models in which the pure reductant was applied as reducing gas, this model can indicate an actual view of pellet reduction including the effects of reducing gas utility and reducing gas ratio. A finite volume fully implicit technique was applied for solving the governing equations. The model has been... 

12-tungstophosphoric acid, polyoxometalate with Keggin structure, and γ-Al2O3 were synthesized. Loading of 12-tungstophosphoric acid (HPW) on γ-Al2O3 was performed by the post-impregnation method. The catalysts were characterized by XRD, SEM, FTIR, BET, and DRS techniques. According to the pertinent observation, using the post-impregnation method promises the stability of polyoxometalate Keggin structure after loading on γ-Al2O3 support. The stability of 20 %HPW/Al2O3 was also confirmed by a leaching test. Textural characterization demonstrates that HPW on the γ-Al2O3 had a much larger surface area as compared with the pure HPW. The 20 %HPW/Al2O3 exhibited roughly high activity toward an... 

Proton affinity (PAs) and molecular basicities (GBs) of the CaO cluster and CaO modified with protic and aprotic ionic liquids in the gas phase have been calculated at the DFT/B3LYP level with a 6-311++G (d, p) basis set. The investigations of PAs and GBs in the solution phase have been studied by means of SCRF solvent effect computations using PCM solvation model for water solvent. The influence of the ILs cations and anions on the PA and GB in the gas phase and solution at the same level of theory has been investigated. We also studied the effect of [bmTr][NO3] ionic liquid on the basicity of CaO. The calculations display that this energetic ionic liquid has a high ability to improve the... 

Abstract: The magnetite (Fe3O4) nanoparticles were synthesized and supported on the reduced graphene oxide. The characterization of the catalyst was performed by FT-IR, VSM, SEM, XRD, and BET techniques. The obtained results indicated that the in situ synthesis of Fe3O4 using coprecipitation method caused the homogenous formation of magnetite nanoparticles on the surface of reduced graphene oxide (average particle size ~ 71.032 nm) with high stability and catalytic activity toward electro-Fenton removal of Reactive Red 195. The effect of various factors (current intensity, initial pollutant concentration, catalyst weight, and pH) was evaluated by response surface methodology using central... 

The nanocomposite of zero-valent iron and delafossite CuFeO2 supported on reduced graphene oxide was synthesized for the first time to evaluate its performance as the heterogeneous catalyst toward electro-Fenton (EF) removal of catechol. X-ray diffraction, Fourier transform-infrared, scanning electron microscopy and Brunauer–Emmett–Teller (BET) were used to characterize the nanocomposite. It was found that the rhombohedral structure of CuFeO2 remained stable during the nanocomposite preparation. The BET surface area of the nanocomposite increased about 102 times in comparison with bare CuFeO2. The influence of the operating parameters was investigated. The optimum operating conditions were... 

The new model for the Morita–Baylis–Hillman reaction based on the proton transfer were inquired by MP2 and DFT methods with 6-311G++(d, p) basis set combined with IEF-PCM solvent model. We focused on the reaction between acrylonitrile and benzaldehyde, catalyzed by CaO cluster and CaO modified with [Pyr][HSO4] ionic liquid. Our results indicate that in the presence of ionic liquid, the ionic liquid acts as a shuttle for the proton transfer between species in a lower energy pathway. The proton transfer step from enolate to catalyst is predicted to be the rate-limiting step for the whole process. In order to investigate the catalyst basicity, the pKa values of acrylonitrile and methyl acrylate... 

One of the most significant parameters that the electronic designers are trying to increase, is the reliability or the effective lifetime of the circuit. For example the designers are always trying to achieve higher efficiency. One of the most important influence of the greater efficiency is the reduction of the thermal stress on the components, that leads to increase of the reliability. In this paper the reliability of two different industry-based structures as an AC/DC converter, have been compared. These circuits are from two different generations of power supplies in a particular industry, which the first introduced structure has greater efficiency due to soft switching. FIDES method has...