نشریه مهندسی مکانیک مدرس
سال بیست و یکم شماره 7 (تیر 1400)

In the present study, the effect of the porous medium in natural-gas pressure regulators, on the operation and reduce the intensity of the sound produced, is studied. First, it was studied experimentally. Experiments apply for the porous medium 20 ppi (pores per inch) and 10 ppi and non-porous system. To check the validity of the results, experiments were evaluated in four different pressure upstream 20, 10, 5, and 2.5 MPa on the critical pressure ratio. Afterward, for evaluation of the flow parameters on the performance of regulators and the sound intensity level, numerical simulation of fluid flow was performed. The results show that the use of porous media for 10 ppi and 20 ppi, flow coefficient decrease, respectively 7% and 15%, and sound intensity level decrease, 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, it decreases the sound intensity by decreasing the maximum velocity and the vortex power.

The Heller towers are the most common types Power plants cooling towers، where its efficiency is  is very sensitive to wind. according to the general approach of  designer of cooling systems، 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 gonig into the ACC radiators without fan installed inside the Heller Tower، and condenses with a natural suction mechanism. The flow around the proposed model are investigated in three dimensions in two cases of no wind and no wind 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 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 in different speeds except speeds above 12.5 m / s at a horizontal array of ACCs..A vertical array of ACCs performance has been better than the horizontal array.Therefore, the hybrid model with vertical array of ACCs can be efficient to replace the cooling system of 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 cross section. To this end, in this study, a program in Visual Basic has been written in SolidWorks software, in which a rectangular piece and press velocity variables take the tensile depth as input and design the optimal blank. 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 piece and with any desired dimensions, according to the dimensions of the piece 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 are of acceptable accuracy. In experimental parts, 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 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 changed due to nonlinear strain path and work hardening. The burst pressure predictions were compared and validated by experimental tests. In this paper, the effect slotting pattern, investigated by using FEM simulations and experiments. In the prepared samples for this paper, by slotting after bulge forming, the burst pressure reduces more than 80%. The simulation with this method predicts 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 air flow 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 optimal design of burner.

The flow forming process is widely used in the production of axisymmetric industrial parts. The advantage of the flow forming process over other manufacturing methods is 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 alloys 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 with increasing the percentage of thickness reduction from 20% to 60% at a constant forming temperature, the strength and micro-hardness of the warm flow-formed pipe increases and its ductility decreases.