Modares Mechanical Engineering
Year:2021 | Volume:21 | Issue:7|Papers Count:6

In the present study, the effect of putting a porous medium in natural-gas pressure regulators, on the operation and reducing the sound intensity, is studied. First, it was studied experimentally. Experiments were applied on a system with porous medium 20 ppi, a system with porous medium 10 ppi, and a system without a porous medium. To check the validity of the results, experiments were evaluated in four pressure difference levels 20, 10, 5, and 2. 5 MPa, and in the critical pressure ratio condition. Afterward, for evaluation the flow parameters on the performance of regulators and the sound intensity level, numerical simulation of fluid flow was performed. The results show that implementing porous media with 10 ppi and 20 ppi porosity, decreases flow coefficient, respectively 7% and 15% and sound intensity level, respectively 25 and 30 dB. The amount of porosity does not have much effect on the sound intensity. On the other hand, the results of the fluid flow simulation show that placing the porous medium in the flow direction reducing the turbulent intensity and regulating the flow. As well as, it decreases the sound intensity by decreasing the maximum velocity and the vortex power.

The Heller towers are the most common types of power plants cooling towers، where their efficiency is very sensitive to wind. According to the general approach of cooling systems designer، Direct dry cooling (ACC) systems are more popular today in power plants located in arid areas. In Heller towers due to the empty space inside them, in this study, instead of proposing the replacement of ACC towers, the hybrid model is proposed, where steam is Directly passed into the ACC radiators without fan installed inside the Heller Tower, and condenses with a natural suction mechanism. The flow around the proposed model is investigated in three dimensions in two cases of no wind and at 8 different wind speeds with the assumption of incompressibility flow by the continuity, momentum, energy, and turbulence equations. The hybrid tower performance has been compared with the Fars power plant cooling system and it has been shown that the proposed cooling tower has performed 25% better than the Fars cooling system in no wind condition. It has also performed better in wind conditions at different speeds except for speeds above 12. 5 m/s at a parallel and vertical array with the wind of ACCs. A vertical array of ACCs performance has been better than the parallel array. Therefore, the hybrid model with a vertical array of ACCs can be efficient to replace the cooling system of the Fars power plant.

Deep drawing is one of the sheet forming processes, in which a metal sheet with mechanical operation, reaches the desired shape. One of the most important issues in deep drawing is the optimal design of the initial blank. In this paper, the main purpose is to design the optimal initial blank (with minimum circumference and minimum defects), for deep drawing of parts with a rectangular shape. To this end, in this study, a program in Visual Basic has been written in SolidWorks software, in which the press velocity variables and tensile depth are inputs, designs the optimal blank for rectangular shapes. Also in this program, blanks with rectangular, circular, octagonal, and rhombus contours have been obtained; So that they are tangent to the initial contour. A separate program has also been written to display contour blanks at different times. The blank design program obtained in this study has this unique feature that for any type of rectangular sheet and with any desired dimensions, according to the dimensions of the sheet and the depth of tension, it will be possible to design the optimal blank. To ensure the accuracy of the program written in Visual Basic language, the results of the program have been compared and validated by performing experimental work. Experimental results prove that the blanks obtained by the program have acceptable accuracy. During experimentation, defects such as earring and shrinkage have also been observed in parts produced with optimal blanks.

Cold work hardening and nonlinear strain path, cause the failure strain change. Therefore, it is necessary to consider the created cold-work hardening and its distribution for predicting and simulating the behavior of products. The composite rupture disc cold-work hardened during manufacturing and burst and release pressure in a pressure commensurate with this hardening. In this case, the sheet metal undergoes a nonlinear strain path during forming and after slotting during the burst test. In this paper, the burst pressure of a composite rupture disc is estimated by using finite element simulation in Abaqus-implicit and explicit and by considering the strain hardening during bulge forming before the slotting process. The burst pressure is estimated according to the maximum plastic failure strain that changes due to nonlinear strain path and work hardening. The burst pressure predictions were compared and validated by experimental tests. In this paper, the effect of slotting pattern is investigated by using FEM simulations and experiments. In the prepared samples for this paper, by slotting after bulge forming, the burst pressure reduced more than 80%. The simulation with this method predicted this pressure reduction with an error of about 3%.

In this research, the geometric parameters of a preheated furnace burner in the press line of Esfarayen Industrial Complex have been studied, experimentally and numerically. To improve the combustion process in the burner, three different diameters (10, 20, and 30 mm) are provided for the nozzle diameter and three different lengths (225, 250, and 300 mm) for the mixing length of the burner. Ansys-Fluent software and RNG k-ε turbulence model have been used for the simulation and the modeling results show that the applied method has good accuracy and with a maximum error of 23% higher than the experimental values for temperature. This temperature difference is due to the lack of accurate measurement of inlet airflow and also point measurement of temperature in the burner. In the study of the effect of nozzle diameter, it was observed that by increasing the nozzle diameter from 10 to 30 mm, the maximum temperature inside the burner increased by 6%, which against a slight increase in nitrogen oxides (Nox) pollutants inside the burner, the 30 mm diameter for optimum design is selected among the tested diameters. Also, the results of the study for the effect of mixing length on burner performance have shown that by increasing the length, the amount of heat produced decreases slightly, which due to more favorable stability of NOx pollutants due to more space and complete reaction, length of 300 mm has been chosen for the optimal design of the burner.

The flow forming process is widely used in the production of axisymmetric industrial parts. The advantages of the flow forming process over other manufacturing methods are the use of simple tooling, reduced forming loads due to localized deformation, and enhanced mechanical properties and surface quality of finished parts. In this research, the warm flow forming process of AA6061-O aluminum alloy has been investigated for the first time. For this purpose, laboratory equipment and samples were designed and fabricated. In this study, the effect of temperature, thickness reduction, and number of passes (number of forming steps) on dimensional accuracy (thickness variation) and mechanical properties of warm flow formed AA6061-O alloy pipes have been experimentally investigated. The experimental results show that flow forming increases the strength and decreases the ductility of the formed pipe at all process levels compared to the initial non-flow forming pipe. However, the ductility of the pipe increases and its strength and microhardness decrease by increasing the forming temperature from 20 to 300 ° C. While increasing the percentage of thickness reduction from 20% to 60% at a constant forming temperature, the strength and microhardness of the warm flow-formed pipe increases, and its ductility decreases.