Sharif Digital Repository

In this article, the problem of simultaneous heat, mass, and momentum transfer in the developing region of tubular reactors with homogeneous chemical reaction and laminar power-law fluid flow under unsteady-state conditions has been solved. In this regard, the general governing equations were solved using finite-difference method and analyzed carefully. Moreover, the influences of various parameters and dimensionless numbers such as power-law index, heat of reaction, reaction order, and Damköhler number value on the numerical results were investigated. In addition, the numerical results obtained for the fully-developed velocity distribution of Newtonian fluid flow and Sherwood number value... 

Bubble splitting in 2D gas-solid freely bubbling fluidized beds is experimentally investigated using digital image analysis. The quantitative results can be applied for the development of a new breakage model for bubbly fluidized beds, especially discrete bubble models. The variation of splitting frequency with bubble diameter, new resulting bubble volumes, positions, and also the assumptions of mass and momentum conservation for bubbles after breakage are studied in detail. Small bubbles are found to be more stable than large ones and nearly all mother bubbles split into two almost equally sized daughter bubbles. The momentum of gas bubbles in the vertical direction remains approximately... 

In the present study, first, Fe3O4nanoparticles were functionalized using glutaric acid and then composited with CQDs. Doxorubicin (DOX) drug was loaded to evaluate the performance of the nanocomposite for targeted drug delivery applications. The XRD pattern confirmed the presence of characteristic peaks of CQDs and Fe3O4. In the FTIR spectrum, the presence of carboxyl functional groups on Fe3O4/CQDs was observed; DOX (positive charge) is loaded onto Fe3O4/CQDs (negative charge) by electrostatic absorption. FESEM and AFM images showed that the particle sizes of Fe3O4and CQDs were 23-75 and 1-3 nm, respectively. The hysteresis curves showed superparamagnetic properties for Fe3O4and Fe3O4/CQDs... 

In this article, adsorption of p-xylene, m-xylene, o-xylene, and ethylbenzene on Na-BETA type zeolite in liquid phase at 15, 25, and 35 °C has been studied and the single adsorption isotherms have been obtained and reported. The Langmuir isotherm model was used to describe the experimental adsorption isotherm data. It was found that p-xylene is more strongly adsorbed component followed by ethylbenzene, m-xylene and o-xylene. This means that this adsorbent is selective for p-xylene. Using Langmuir isotherm model, the saturation adsorption capacities of the adsorbent were obtained as follows 143 mg/g for p-xylene, 105 mg/g for ethylbenzene, 83 mg/g for m-xylene, and 68 mg/g for o-xylene at 25... 

Heterogeneous solid catalysts comprising CaO and ZrO 2 mixed oxides with various Ca-to-Zr molar ratios were synthesized by means of coprecipitation method. These synthesized mixed oxide catalysts were used for the transesterification of waste cooking oil (WCO) as feedstock with methanol to produce biodiesel fuel (BDF) at 65 °C and 1 atm. The influences of Ca-to-Zr molar ratio, catalyst loading, methanol-to-oil molar ratio, and the reaction time on the BDF yield were carefully investigated. In addition, the stability of prepared solid catalysts was studied. These catalysts were characterized by using techniques of X-ray diffraction, X-ray florescence, X-ray photoelectron spectroscopy, surface... 

Dual-phase (DP) steels with different martensite contents were produced by subjecting a low carbon steel to various heat treatment cycles. In order to investigate the effect of dynamic strain aging (DSA) on mechanical properties, tensile specimens were deformed 3% at 300 °C. Room temperature tensile tests of specimens which deformed at 300 °C showed that both yield and ultimate tensile strengths increased, while total elongation decreased. The fatigue limit increased after pre-strain in the DSA temperature range. The effects of martensite volume fraction on mechanical properties were discussed  

A numerical study was conducted on the transient behavior of a hydrodynamically fully developed, laminar flow of power-law fluids in the thermally developing entrance region of circular ducts with taking into account the effects of viscous dissipation, axial conduction, and variations of viscosity with temperature. In this regard, the unsteady-state thermal energy and momentum equations were solved numerically using a finite-difference method, whereas the steady-state thermal energy equation with constant wall heat flux as the boundary condition was solved analytically as the initial condition of the former. The numerical procedure used in the present work was validated with an analytical... 

Dual phase (DP) steels with network and fibrous martensite were produced by intercritical annealing heat treatment cycles. Some of these steels were deformed at dynamic strain aging temperatures. Room temperature tensile tests of specimens deformed at 300 °C showed that both yield and ultimate tensile strengths for both morphologies increased, while total elongation decreased. Fatigue test results before and after high temperature deformation showed that dynamic strain aging has a stronger effect on fatigue properties of dual phase steels with fibrous martensite. Cracks in DP steels with fibrous martensite propagate in a tortuous path in soft ferrite phase, while they pass of both hard and... 

The kinetics and equilibrium of isomerization reaction of D-glucose to D-fructose have been investigated using a commercial immobilized glucose isomer ase (IGI), Sweetzyme type IT®, in a batch stirred-tank reactor. The batch experimental data were used to model the reaction kinetics using the well-known Michaelis-Menten rate expression. The kinetic model was utilized in a dynamic-mathematical model for a packed-bed reactor to predict the concentration profiles of D-glucose and D-fructose within the reactor. The experimental results for the fractional conversion of D-glucose in the packed-bed reactor of IGI catalyst indicated that the model prediction of the transient and steady-state... 

The oxidative desulfurization of a real refinery feedstock (i.e., non-hydrotreated kerosene with total sulfur mass content of 0.16%) with a mixture of hydrogen peroxide and acetic acid was studied. The influences of various operating parameters including reaction temperature (T), acid to sulfur molar ratio (nacid/nS), and oxidant to sulfur molar ratio (nO/nS) on the sulfur removal of kerosene were investigated. The results revealed that an increase in the reaction temperature (T) and nacid/nS enhances the sulfur removal. Moreover, there is an optimum nO/nS related to the reaction temperature and the best sulfur removal could be obtained at nO/nS8 and 23 for the reaction temperatures of 25... 

A deterministic model based on the discrete population balance equation (PBE) is used to examine the precipitation of barium sulfate nanoparticles in nonionic inverse microemulsion systems. It is shown that coagulation can have a significant effect at low initial reactants concentration. The simulation results show that a bimodal particle size distribution (PSD) observed in experimental analysis reported in the literature cannot be predicted by neglecting the coagulation effect. A coagulation kernel is proposed that takes into account the effect of interparticle forces through the Fuchs' stability ratio. The effect of electrolyte concentration on the surfactant headgroup area is also... 

TiO2 nanorod layers are synthesized by simple chemical oxidation of Ti substrates. Diffuse reflectance spectroscopy measurements show effective light scattering properties originating from nanorods with length scales on the order of one micron. The films are sensitized with CdSe quantum dots (QDs) by successive ionic layer adsorption and reaction (SILAR) and integrated as a photoanode in quantum dot sensitized solar cells (QDSCs). Incorporating nanorods in photoanode structures provided 4- to 8-fold enhancement in light scattering, which leads to a high power conversion efficiency, 3.03% (Voc = 497 mV, Jsc = 11.32 mA/cm2, FF = 0.54), in optimized structures. High efficiency can be obtained... 

A novel phenomenological discrete bubble model was developed and tested for prediction of the hydrodynamic behavior of the dense phase of a 3D gas-solid cylindrical fluidized bed. The mirror image technique was applied to take into account the effects of the bed wall. The simulation results were validated against experimental data reported in the literature that were obtained by positron emission particle tracking. The time-averaged velocity profiles of particles predicted by the developed model were found to agree well with experimental data. The initial bubble diameter had no significant influence on the time-averaged circulating pattern of solids in the bed. The model predictions clearly... 

In this article, a comprehensive 2D mathematical model has been developed to simulate process intensification of carbon dioxide absorption in the presence of nanoparticles in hollow fiber membrane contactors (HFMCs). The influences of nanoparticle were taken into account considering Brownian motion and Grazing effect as dominant phenomena of mass-transfer enhancement in nanofluids. The obtained simulation results were validated against experimental data reported in the literature and excellent agreement was obtained. It was found that by adding 0.05 wt % silica nanoparticles, the absorption rate could be enhanced by 16%, while the corresponding value is 32% for CNT nanoparticles. High... 

In this paper, we study the role of inlet gas temperature and jet to bed cross-section ratio on hydrodynamics and circulation patterns of particles in a spout-fluid bed. The system is modeled using CFD-TFM approach based on Eulerian-Eulerian method. Simulation results are validated by experimental data measured by (Link 2008. "PEPT and Discrete Particle Simulation Study of Spout-fluid Bed Regimes." Aiche Journal 54 (5): 1189-202). First, the sensitivity analysis of simulation results versus the most significant parameters are conducted to find the optimum values for each parameter. Subsequently, the role of inlet gas temperature and cross-section ratios are studied in detail. The simulation... 

Due to considerable use of electric drives in industrial applications, reliability assessment of drive-motor systems both in design and operating phases is of considerable importance. Reliability assessment of drive-motor systems is presented in this paper. Using the basic component of a drivemotor system, a suitable reliability block diagram is first developed. The system availability and reliability is then determined using developed block diagram. The impacts on system reliability of various parameters such as failure rate and repair rate of system components are investigated. The proposed technique is then applied to a practical drive-motor system and the results are presented. © 2006... 

Choosing the appropriate ion exchange membrane in vanadium redox flow batteries plays an important role in achieving optimal system performance. In this article, the implementation of commercial cation exchange membranes (Nafion 115, Nafion 117, and Nafion 212), anion exchange membranes (FAP 450 and QA-PFE), and the combination of them are investigated. In this regard, the effects of membrane type, thickness, electrical conductivity, and the transfer of vanadium species at different current densities are examined carefully. In addition, the influences of the flow rate and the concentration of electrolytes are investigated using a comprehensive developed model. The model predictions are... 

Simple synthesis of silver doped TiO2 nanostructured layers by micro arc oxidation process is reported for the first time. The layers consisted of anatase and rutile phases whose characteristic XRD-peaks shifted toward lower diffraction angles when compared to the pure micro arc oxidized TiO 2 layers. Silver-doping was confirmed by XPS technique. The anatase phase crystalline size was determined as 27.6 and 21.8 nm for the layers grown under the voltages of 350 and 500 V. Employing a UV-Vis spectrophotometer, a red shift in the absorption edge of the layers was observed when silver was incorporated into the titania lattice  

TiO2 nanotubes were synthesized using a modified autoclave-free thermal method from as-prepared initial powders. The size of initial powders (IP) was found to be critical in determining the morphology and crystal structure of the final product. Oleylamine (OA) was used as the polymer agent in the preparation of initial powders with different mol ratios of OA/Ti: 1, 5, and 10. X-ray diffraction analysis depicted that the increase of mole ratio up to 10 resulted in smaller nanoparticles with the sizes of about 8 nm. It was also deliberated that low temperature thermally treated IP showed the characteristic diffraction pattern of titanate phase of nanotubes. Scanning electron...