International Journal of Engineering
Volume:25 Issue: 2, Jun 2012

In this research, formation of nanocrystalline Ni3Al intermetallic from Ni and Al elemental powders by mechanical alloying (MA) process and its characterization was investigated. Therefore, the evolutions in microstructure such as phase transformation, oxidation in air and introduction of Fe impurity from milling media after MA were evaluated using XRD, Rietveld refinement, TEM, SEM, EDS and ICP analyses. Milling after 4 h resulted in formation of Ni3Al/Al2O3 composite in air while continuing milling time up to 8 h resulted in obtaining Ni3Al product. TEM observations along with XRD combined Rietveld’s refinement analysis confirmed the existence of a disorder structure and nanocrystals of Ni3Al embedded in an amorphous matrix after 16 hours of milling. Moreover, the lattice parameter of Ni3Al product and Fe contamination of powder were increased by increasing milling time.

(Mo1-x-Crx)Si2 composite powders were successfully synthesized by ball milling of Mo, Cr and Si elemental powders. Effects of the Cr content, milling time and annealing temperature were investigated. X-ray diffraction (XRD) was used to characterize the milled and annealed powders. The morphological and microstructural evolutions were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results showed that this composite formed after 20 h of milling. Increasing Cr content from 0.1 to 0.25 or 0.4 at.% changed the polymorph of synthesized MoSi2 from to as well as the formation reaction mechanism from mechanically induced self sustaining reaction (MSR) to gradual. Annealing of the milled powders led to the formation of -MoSi2 in all Cr contents. An average grain size of less than 40 nm was obtained for all Cr contents at the end of milling. In spite of grain growth and strain release during annealing, these nanocomposites remained in their nanocrystalline nature.

In this paper, a new method for gray-scale image and color zooming algorithm based on their local information is offered. In the proposed method, the unknown values of the new pixels on the image are computed by Moving Least Square (MLS) approximation based on both the quadratic spline and Gaussian-type weight functions. The numerical results showed that this method is more preferable to bilinear interpolation in term of quality (for the quadratic spline weight function), and is comparable to bicubic interpolation (for the Gaussian-type weight function).

The annular foam breaker is one which uses the vacuum and shear force generated by the Coanda effect to break foam. The pressure distribution directly affects its performance. So an investigation on the flow characteristics inside the annular foam breaker is important to optimize its structure. In this paper, the computational fluid dynamics (CFD) code, FLUENT, is employed to simulate the flow phenomena. The effect of various geometric parameters on the pressure distribution inside the annular foam breaker has been evaluated, including the width of the annular slot, the Coanda surface radius and the diffuser dimensions, etc. The numerical results show that the optimum value of the annular slot d = 0.5mm, the Coanda surface radius r = 20mm, the diffuser angle θ=6°, and the ratio of the diffuser length to radius is more than 14. Based on these analyses, an optimum structure of the annular foam breaker was designed and tested in the well bore flow simulation loop laboratory equipment. Compared with the old ones, the foam-breaking efficiency of the optimized annular foam breaker is improved from 71.16% to 86.58%, which increases by some 22.61%.

In this study effect of Stearamide as a corrosion inhibitor for mild steel in hydrochloric acid media was investigated employing various electrochemical techniques include potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and liner polarization resistance (LPR). In view of the fact that Stearamide is an insoluble compound in water, its inhibitive effect was examined by dissolving 10000ppm of it into an organic solvent followed by immersing of steel surface into the solution for 7, 15, 30 and 60 minutes. As a result of the immersion of steel into the solution, the Stearamide was allowed to be adsorbed on the surface and its corrosion inhibition was investigated by moving the sample into a 0.1M HCl solution and employing several electrochemical techniques. Such a method of inhibitor adsorption is regularly used during corrosion inhibitor injection into the gas well tubing. The results of investigation show that Stearamide acts as adsorptive inhibitor, reduces anodic dissolution and also retards the hydrogen evolution reaction via blocking the active reaction sites on the metal surface. Additionally, it was illustrated that Isopropyl alcohol is a more beneficial solvent for Stearamide as compared to demethyl sulfoxide (DMSO). Isopropyl alcohol acts as inhibitor itself and its mixture with Stearamide has synergistic effect on corrosion inhibition. The optimal condition of immersing steel into the solution was 15min immersion of mild steel in both solutions, and the inhibition efficiency was approximately 90% when Isopropyl alcohol was used as the solvent. EIS investigation demonstrates that the thickness of protective layer formed on metal surface by Isopropyl alcohol solution is almost 5 times higher than that formed by DMSO.

Corrosion resistance of iron can be drastically improved by addition of passivating alloying elements. A supersaturated solid solution of Fe-25at%Sn was produced by mechanical alloying of commercially pure iron and tin powders for 24 hours using a planetary ball mill. Electrochemical measurements were performed on cold compacted unsintered specimens.. XRD investigation on produced alloy showed the characteristics of a supersaturated solid solution. Corrosion behavior of the solid solution alloy was investigated in 0.1M H3PO4 employing potentiodynamic and potentiostatic polarization techniques. The anodic behavior of mechanically alloyed specimens was compared with specimens prepared from individually compacted iron, tin and appropriate admixture of tin/iron powders. Potentiodynamic polarization of supersaturated specimen featured a gradual decrease in anodic current density, indicating a feature of quasi passivation which was attributed to the tin surface enrichment as a result of preferential iron dissolution. Anodic current density from the result of potentiostatic polarization of the prepared alloy also showed a gradual decrease with time following i¥t-0.45 relationships indicating a characterization of passivity. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) examination of the specimen surface after potentiostatic anodic polarization test confirmed the presence of high tin content on the surface.

One of the important problems in reducing of pollutant emission from DI and IDI diesel engines is trade-off between soot and NOx. Split injection is one of the most powerful tools that makes the chance to shift the trade-off curve closer to origin. At the present work, the effect of split injection on the combustion process and emissions of a cylinder IDI diesel engine under the specifications of 5.9 kW maximum engine power and engine speed of 730 rpm has been investigated. The studies of injection timing and split injection parameters, including the delay dwell and the fuel quantity injected between injection pulses are carried out. Three different split injection schemes, in which 10, 20 and 25% of total fuel injected in the second pulse, have been considered. The numerical results show that 25% of total fuel injected in the second pulse which is accompanied with the 20ºCA delay dwell between injections, reduces the total soot and NOx emissions effectively in IDI diesel engines. The predicted values of combustion process and emissions by the model at baseline engine show a good agreement with the corresponding experimental data. This agreement makes the model a reliable tool that can use for exploring new engine concepts.

Characteristics of ground motions close to the earthquake source can be considerably different from those of far-field motions which should be considered in design process of structures. The current study aimed to present new design response spectra for Iranian seismic design code taking into account the near-fault effects. For this purpose, a new attenuation relation based on the ground motion records obtained from fault-normal orientation of near-fault earthquakes at different parts of the world including Iran, has been derived. Subsequently, near-fault modification factors for short and long periods were extracted to present the modified design response spectra for the Iranian design code. The proposed factors are relatively comparable with those of UBC97, Chinese and Taiwanese seismic design codes. Analyses also showed that the distance criterion that defines near-fault region consistence with design spectra of Iranian seismic code can be taken as 18 km.

Probabilistic seismic hazard analysis is a technique for estimating the annual rate of exceedance of a specified ground motion at a site due to the known and suspected earthquake sources. A Monte-Carlo approach is utilized to estimate the seismic hazard at a site. This method uses numerous resampling of an earthquake catalog to construct synthetic catalogs to evaluate the ground motion hazard and its uncertainties. The method has been tested for peak ground acceleration and spectral response accelerations of 0.2 and 1.0 sec for sites in Tehran and the surrounding area. The disaggregation technique of seismic hazard provides relative contribution to hazards from sources of different magnitudes, M, distance, R and a measure of the deviation of the ground motion from its median value, ε, as predicted by an attenuation relationship. In different sites in Tehran, the major contribution comes from moderate and large magnitudes, at close distances.

This study presents an optimization problem for shape design of a 2-D radiant enclosure with transparent medium and gray-diffuse surfaces. The aim of the design problem is to find the optimum geometry of a radiant enclosure from the knowledge of temperature and heat flux over some parts of boundary surface, namely the design surface. The solution of radiative heat transfer is based on the net radiation method where the configuration factors are obtained by the Hottel’s crossed-string approach by treating blockage and convex surfaces. The conjugate gradient method is used for minimization of an objective function, which is expressed as the sum of square residuals between estimated and desired heat fluxes over the design surface, and the sensitivity coefficients are calculated by the finite difference method. A regularization approach is proposed to numerically regularize the ill-ordered grids, which are commonly found during the iterative optimization process. Some example problems are presented to show the performance and accuracy of the method. The results show that the optimization procedure can successfully generate the optimum geometry of radiant enclosure.