JOURNAL OF FACULTY OF ENGINEERING (UNIVERSITY OF TABRIZ)
Year:2002 | Volume:28 | Issue:2 (29) Mechanics|Papers Count:8

We consider the Isothermal flow of superfluid Helium through small hole (d<=10-6 m). It is known that below certain velocity, so called critical velocity U s.c, there is no dissipation in energy and pressure of the fluid. But as soon as Us exceeds U s.c, dissipation arises due to the Magnus force acting on the quantum vortices which may be generated in different kinds such as, line vortex, Ring vortex and Pinned vortex. In this paper we study specifically, the effect of three-Dimensional Magnus force acting on the vortex Ring, and find a relation for energy of dissipation, Equating this relation with the energy of Pressure head (Delta Z), we show that the velocity required for generation and growing a Ring vortex with hole"s radius is proportional to (Delta Z) 1/2.

Turbine inlet temperature strongly affects gas turbine performance. Today blade cooling technologies facilitate the use of higher inlet temperatures. Of course blade cooling causes some thermodynamic penalties that destroys to some extent the positive effect of higher inlet temperatures. This research aims to model and evaluate the performance of gas turbine cycle with air cooled turbine. In this study internal and transpiration cooling methods has been investigated and the penalties as the result of gas flow friction, cooling air throttling, mixing of cooling air flow with hot gas flow, and irreversible heat transfer have been considered. In addition, it is attempted to consider any factor influencing actual conditions of system in the analysis. It is concluded that penalties due to blade cooling decrease as permissible temperature of the blade surface increases. Also it is observed that transpiration method leads to better performance of gas turbine comparing to internal cooling method.

Channel erosion or sedimentation will occur, if balance between water and sediment flows, is affected by any natural events or human activities. This will happen if the geometry of channel (area, shape or slope) or the rate of sediment transport change. Therefore, accurate evaluation of erosion and bed-load transport will be very important in river engineering. In this paper an unsteady one dimensional model with moving bed is presented. The Saint-Venant Equations and the continuity equation of sediment were solved by finite difference method, using McCormak algorithm. The results also compared with experimental information to evaluate the mode. Reasonable agreement was found between the model and experimental results.

Chromium plating with different concentrations of CrO3, can be done for surface hardening and decorative purposes. In hard chromium plating the aim is to get an adhesive surface, resistant to wear. and corrosion. However the best coating from the view of physical and mechanical points is the brightness of layer. The cathodic efficiency in standard chromium bath is about 10 to 12%. Many studies have shown that by changing the kind of catalyst in the bath, it is possible to increase the cathodic efficiency. In this study the region of brightness in baths with strontium sulfate catalyst and also in standard bath of hard chromium were determined, and then the effect of strontium sulfate as a catalyst on the efficiency of hath was studied. The results show that for producing a bright coating, the current e11iciency and also the region or current density and temperature in a bath with a catalyst of strontium sulfate increase in comparison with standard bath or hard chromium.

The effect of titanium content from 3 to 10 Wt. % on the microstructure of Fe/TiC metal matrix composites was studied. The in-situ melting of Fe - 4 Wt. % C and Fe - 72 Wt.% Ti caused reaction between carbon and titanium which produced titanium carbide particles within the melt. The amount of TiC particles and the type of phases present in the matrix were related to primary chemical composition of the melt. Type and amount of matrix phases, shape, size, and distribution of the secondary phase were identified by an optical microscope equipped with micro hardness tester, image analyzer, and X-ray diffractometer. It was found that an increase in titanium content increases the amount of titanium carbide particles and pearlite and decreases eutectical cementite in the matrix.

In this paper, the rate of reactions of Gas-Solid (Nonporous) such as metals and alloys are simulated. The offered kinetics models of these reactions by scientists and mathematician are divided into two parts: "Shrinking - core model" and "Nonshrinking - core model". Kinetics model of Mazet, which is designed on the basis of "Shrinking - core model", has been recognized as a more suitable model in order to simulate the equation of reaction rate of the Gas - Solid (Nonporous). In this work, the "GSR.EXE" in "CLIPPER" language was designed and written in order to solve the equation of Mazet Model by method of the "least square". Then, the equation of the rate of the number of reaction was simulated by software and was compared with the exiting informations in the papers.

Vehicles are one of the major source of the environment pollution, particularly the air. The safety of the human being and all other creatures would be in serious danger if the amount of pollutants in air are not controlled. Exhaust gas recirculation is one of the common methods of reducing nitrogen oxides pollutants. In this experimental research work. in order to reduce the amount of NO pollutant further, and for reducing its negative effects on engine performance, cold EGR was investigated in a 1725cc spark ignited automotive engine of Iran khodro. The engine equipped with the EGR circuit went under comprehensive test of performance and pollutant evaluation. The results of the experiments showed that the power and torque losses for the experiments in which cold EGR was used were less than that of hot EGR. Moreover the amount of NO pollutant were reduced further for the cold EGR experiments. The optimum amount and temperature of EGR under test condition were 8% and 430K respectively.