Mechanical Engineering

A numerical investigation of the vortex shedding past a circular cylinder in a two- dimensional channel of varying height is presented in the term of Strouhal number by solving continuity and momentum equations using FLUENT 6.3. The computational grid structure is generated by using Gambit. In this work, the result is carried out with blockage ratio b=0.83, 0.85, 0.88.

Explosion welding (EXW) is a solid state (solid-phase) process where welding is accomplished by accelerating one of the components at extremely high velocity through the use of chemical explosives. This process is most commonly utilized to clad carbon steel plate with a thin layer of corrosion resistant material (stainless steel, nickel alloy, titanium, or zirconium). Due to the nature of this process, producible geometries are very limited. They must be simple. Typical geometries produced include plates, tubing and tube sheets. Explosion welding or bonding is a solid-state welding process that is used for the metallurgical joining of dissimilar metals. The process uses the forces of controlled detonations to accelerate one metal plate into another creating an atomic bond. Explosion bonding can introduce thin, diffusion inhibiting interlayer such as tantalum and titanium, which allow conventional weld-up installation. In addition, explosive welding is considered a cold-welding process, which allows metals to be joined without losing their pre-bonded properties.

Post weld heat treatment and subsequent aging (PWHTA) effect on dissimilar friction stir welding (DFSW) (AA2024-T6 to AA6351-T6) were investigated in the present study. The micro structural measurement techniques (Optical, SEM- EDS) have been employed to understand the precipitate distribution and the elements distribution in the Stirred zone (SZ). PWHTA on dissimilar FSWs shows better mechanical properties and pitting corrosion than as welded specimens. A post weld solution treatment at 5200 C for 1 hr and subsequent ageing at 1800 C for 12 hrs and 8 hrs aging time resulted in better mechanical and corrosion properties respectively than other conditions.

The wave propagation in an infinite, homogeneous transversely isotropic solid cylinder of elliptic inner and outer cross-section immersed in a fluid is studied using the Fourier expansion collocation method, within the framework of the linearized, three-dimensional theory of elasticity. The equation of motion of solid and fluid are respectively formulated using the constitutive equations of a transversely isotropic cylinder and the constitutive equation of an inviscid fluid. Three displacement potentional functions are introduced to uncouple the equation of motion. The frequency equations of longitudinal and flexural (symmetric and antisymmetric) modes are analyzed numerically for an elliptic cross-sectional transversely isotropic solid cylinder of elliptic inner and outer cross-section immersed in a fluid. To compare the model with the existing literature, the results of a fluid-loaded transversely isotropic cylinder are obtained and they are compared with the results of Berlinear and Solecki (1996). It shows very good degree of agreement. The computed non-dimensional wave numbers are presented in the form of dispersion curves for the material zinc.

In this paper design special frame vertical axis wind turbine and test in the wind tunnel. This design is presented as vertical locations of the three movable vanes that create scoop shape when closed. Scoop shape of frame increases the drag factor and increase the torque, in the other side of impeller movable vanes are opened under action of wind and the air pass freely to reduce the negative torque. Fabricate two models of impeller with movable vanes and with fixed vanes model and test it in wind tunnel. The maximum power coefficient for three frames movable vanes is 0.32 and higher than the same dimensions of model with fixed vanes about 11%.

The effects of alkalinity/acidity, addition of copper and zinc, and seeding material on biogas generation using freshly voided cow dung as feedstock were investigated. Experimental set-up for seven digesters, labeled A to F, were carried out in the laboratory with varying measurements of slurry in the digesters, varying pH values for three digesters, some with seeding materials while others with addition of metals –copper and zinc separately. The study was carried out for an hydraulic retention time of 32 days during which volumes of gas generated from all digesters range from 1022cm3 to 1723cm3 with the highest gas produced from digester with the rice husk and banana peels. The results showed best yields with cow dung seeded with rice husk and banana peels, while addition of metals and an alkaline slurry solution of pH = 7 had an improving effect on biogas production.

Heat Exchangers are widely used in many industries, such as chemical, food, air-conditioning system, petrochemical, oil, and thermal power plant. In the air-to-air and air-to-liquid heat exchangers for air-side heat transfer applications, special surfaces are often employed to obtain high rates of heat transfer. One geometry that can be used to enhances heat exchanger performance is a sinusoidally curved wavy passage. Wavy channels are easy to fabricate, and can provide significant heat transfer enhancement in the appropriate Reynolds number regime. This article offers a new method for calculating total heat transfer area in a plate-fin heat exchanger with waviness surfaces. Kays and London presented some experimental data to determine heat transfer area in wavy surfaces, based on the ratio of total heat transfer area / total volume. One of the important weakness of the method presented by Kays and London is calculating total heat transfer area is a chain process and depends on the other thermal properties of the heat exchanger. So, existence of a direct method can be helpful and , of course, a strong tool in optimization process.

This study focuses on a manufacturing process modification that can be carried out during the process of casting Aluminium-Silicon alloy in order to obtain desired properties and characteristics of a material for a particular usage. The effect of cooling rate was studied using sand and die moulds. Three types of mould were used namely dry sand mould, green sand mould and die mould .The result shows that the rate of cooling is faster in the die mould and the specimen obtained has the highest value of yield strength, ultimate tensile strength and hardness value but a low impact strength. The microstructure reveals that specimen A(dry sand mould) has a coarse microstructure, specimen B(green sand mould)exhibits a fairly wide spread distribution of silicon deposits while specimen C(die mould) exhibits fine and even distribution pf silicon deposits.

In this work the combined effect of injector orientation and nozzle hole geometry on performance, emissions and combustion were analyzed. Experiments were carried out on a single cylinder DI diesel engine for different orientation of injector located nearer to intake and exhaust valve in the combustion chamber. Effects of increase in injector opening pressure and injection timing advance were also analyzed. Experiments were carried out by plugging one of the two injector mounting holes. It was observed that for the injector located nearer to the exhaust valve, the combination of static injection timing 26o BTDC and injector opening pressure of 230 bar was found effective in reducing NOx levels with no significant drop in performance. Advancing the injection timing to 29° BTDC with 230 bar injector opening pressure resulted in marginal increase in performance and reduction in Smoke levels by 0.4 Bosch Smoke Unit Number (BSN). NOx emissions were slightly higher than that of baseline. Drop in brake thermal efficiency and increase in smoke emission levels observed for the injector located nearer to intake valve. Performance and smoke levels are inferior to that of conventional baseline reading even after the injection timing advance. Increase of smoke by 1.6 Bosch Smoke Number (BSN) is observed at full load for the injection timing of 29° BTDC. Significant increase in Hydrocarbon and Carbon Monoxide emissions were also observed. In general it is observed that the injector location nearer to the exhaust valve has a very good potential for reducing Oxides of Nitrogen emissions without affecting the performance.

In this paper, the laser beam welding is studied and Aluminium temperature field is gained in this process. The thermal effect of laser beam that specially depends on the laser type and temperature field of it in workpiece, is the main key of analysis and optimization of this process, from which the main goal of this paper has been defined. Utilizing laser as a method to join plastic components is growing in popularity. There are two laser welding mechanisms, keyhole mode and conduction mode. Keyhole welding is widely used because it produces welds with high aspect ratios and narrow heat affected zones. However keyhole welding can be unstable, as the keyhole oscillates and closes intermittently. This intermittent closure causes porosity due to gas entrapment. Conduction welding, on the other hand, is more stable since vaporisation is minimal and hence there is no further absorption below the surface of the material. Conduction welds are usually produced using low-power focused laser beams. This results in shallow welds with a low aspect ratio. In this work, high-power CO2 and YAG lasers have been used to produce laser conduction welds on 2mm and 3mm gauge AA5083 respectively by means of defocused beams. Full penetration butt-welds of and 3mm gauge AA508 using this process have been produced. It has been observed that in this regime the penetration depth increases initially up to a maximum and then decreases with increasing spot size.