AUT Journal of Mechanical Engineering
https://ajme.aut.ac.ir/
AUT Journal of Mechanical Engineeringendaily1Thu, 01 Jun 2023 00:00:00 +0430Thu, 01 Jun 2023 00:00:00 +0430A modified biogas-driven combined cooling and power system based on open and close Brayton cycles
https://ajme.aut.ac.ir/article_5179.html
A novel method of a biogas-driven cogeneration system for electricity and cooling with recovering liquefied natural gas heat sink is introduced in this study. The proposed system consists of an open loop Brayton cycle or gas turbine cycle fed by biogas, a close loop Brayton cycle, a liquefied natural gas open power generation cycle, and a dual-stage combined cooling and power unit composed of an organic Rankine cycle integrated with an ejector refrigeration cycle. The superiority of the system over previous models is demonstrated from the thermodynamic and economic points of view. In addition, a multi-criteria optimization of the proposed set-up is conducted regarding crucial decision variables, energy and exergy metrics, and unit overall product cost as objective functions. It is deduced that gas turbine 1 inlet temperature is the most influential decision variable affecting the objective functions. From the optimization, it is discovered that the developed unit can generate cooling and net electricity of 424.1 kW and 1,864 kW, correspondingly, resulting in energetic efficiency of 80.4%, exergetic efficiency of 41.24%, and unit cost of 10.07 $/GJ. The performance of the biogas-fueled combined system can be improved by 71.17% in the form of energy efficiency at the optimum scenario. Among all elements available in the developed cogeneration system, the combustion chamber has the highest contribution to the overall exergy destruction rate, followed by the condenser.Finite element modeling of heat transfer in pulsed laser welding of similar and dissimilar carbon and stainless steels
https://ajme.aut.ac.ir/article_5185.html
Laser welding is one of the most prominent manufacturing methods in various industries due to its speed and high quality. The laser beam welding process has two modes of conduction and keyhole. The keyhole mode is more attractive due to its greater penetration depth and smaller heat-affected zone. &nbsp;To achieve the keyhole mode, it is necessary to adjust the welding process variables, which requires many experiments. Hence, simulation can be used as a powerful tool to reduce the cost. In this study, similar and dissimilar lap joints of low-carbon steel and stainless steel using pulsed laser welding were simulated by finite element software ANSYS. The effects of pulse energy and frequency were examined and the values for obtaining the keyhole mode were determined. Simulated weld pool dimensions were compared to experimental results and the good agreement between them showed that the model is appropriate for simulating pulsed laser welding. Numerical results showed that the keyhole mode is created in dissimilar joints of low-carbon steel and stainless steel, similar joints of stainless steel, and similar joints of low-carbon steel at pulse energies of 17.1, 11.8, and 13.9 J, respectively.&nbsp; A pulse frequency of 14 Hz was found to be the optimal condition for the formation of the keyhole.Ferrofluid Injection and Applied Magnetic Field Influences on the Characteristics of Flow Over a Cylinder
https://ajme.aut.ac.ir/article_5241.html
The present article presents an innovative method to reduce drag in flow over a cylinder by using Kelvin force. In contrast to the previous works, there is no need to move or additional geometry parts. For this purpose, &nbsp;nanofluid is injected from gaps embedded over the circular cylinder surface. Moreover, the heat transfer rate has been evaluated over the rigidly fixed cylinder surface. In this study, flow and heat transfer characteristics are investigated by the open-source code of Openfoam, under the effect of the induced magnetic field of a single electric current carrier wire. The modified model of Buongiorno that contains the magnetophoresis term is utilized for the two-phase modeling of ferrofluid flow. For discretization of the governing unsteady equations including conservation laws of mass, volume fraction transport, and momentum equations that contain the ferro-hydrodynamics force as a source term, the Finite volume method, and PISO algorithm are considered. The drag coefficient, entropy generation, Nusselt number, streamlines, and temperature contours are computed for three Reynolds numbers of 120,150, and 180. It is obtained that, the presence of the magnetic field at various volume fractions has significant effects on these parameters. For instance, by increasing the magnetic intensity (B) from 0 to 0.002 T, the pressure drag coefficient, the total entropy generation, and the Nusselt number are reduced by about 153%, 11.76%, and 17.24%, respectively.Large Eddy Simulation and Proper Orthogonal Decomposition Analysis of Two-phase Turbulent Thermomagnetic Convection of a Ferrofluid in a Cubic Cavity
https://ajme.aut.ac.ir/article_5242.html
This paper presents the Large-Eddy-Simulation (LES) of two-phase turbulent thermo-magnetic convection of ferrofluid (water-Fe3O4) within a cubic cavity. The current two-phase model considers Brownian, thermophoresis, magnetophoresis, and eddy diffusions in the dispersion of ferromagnetic particles. Two parallel electrical wires influence ferrofluid flow. The numerical computations are performed by utilizing the finite volume method for three different magnetic numbers (i.e. Mnf=0, 1.4&times;1010 and 1.4&times;1010). For all numerical calculations, particle volume fraction and Rayleigh are held constant at 0.04 and 108, respectively. Based on the heat transfer analysis, a magnetic field with a strength of 5.6&times;1010 enhances the Nusselt number by 16.67%. Observed increases in heat transfer can probably be attributed to the Kelvin force induced by the magnetic field, which affects the coherent structures of the flow. Using the Proper Orthogonal Decomposition (POD) method, coherent structures are extracted from velocity and pressure fluctuations. Further, the time coefficients of the first three modes are extracted for the pressure fluctuation. According to the results, the applied magnetic field reduces the cumulative energy of modes and increases the number of modes required to reconstruct a given amount of flow. The coherent structures also change from plane to spanwise roll structures with increasing magnetic number. The energy content of the first three modes decreases from 98.7% to 73% as the magnetic field increases from Mnf=0 to 1.4&times;1010.Perforation study of steel sheet under high velocity impact using Peridynamic theory
https://ajme.aut.ac.ir/article_5240.html
Peridynamic theory is a new method to model material behavior under impact loading. The simplest type of this method is called bond-based peridynamics. The present study is concerned with the modification of the bond-based peridynamic theory to account for inelastic behavior and the modified theory is used to study the dynamic fracture of plates, made of ductile materials, due to impact. &nbsp;This theory assumes that the bonds between two points can bear stretches more than the yield stretch. In this regard, The modified bond-based theory is used to study the effect of penetration, resulting from the impact of a projectile into a rectangular steel sheet. The results are validated against experimental results, and the crack growth and its propagation paths are studied for different geometric shapes and impact velocities of the projectiles. The results show that with this modification, the bond-based peridynamics could be employed more inclusively to simulate the behavior of materials.Numerical Investigation Of The Best Wind Turbine Shroud Flange Curvature For Maximum Wind Power Extraction
https://ajme.aut.ac.ir/article_5259.html
In today's world, net zero energy buildings are growing and developing. These buildings generally supply their energy needs from renewable sources such as wind. Unfortunately, in urban areas, the quality of the passing wind is low and it is not able to create the necessary force for the proper rotation of turbines. To overcome this problem, it is necessary to use a tool that can speed up the flow like a shroud. In the present work, a vertical straight flange is considered at the end of the shroud. The points in the middle of the flange height move to the end of the shroud with a very small interval and create different curves. By using this procedure, a flange with an optimal curve that is able to create the highest mean velocity of air passing through the shroud will be obtained. The results show a significant increase in mean velocity, which has been confirmed by studies of turbulent kinetic energy behind the turbine shroud. Based on the results of a three-dimensional simulation, it is concluded that in the turbine section, a mean velocity increase of 20% can be achieved, which is the first time that using an aerodynamic cross-section for the flange of the shroud and optimizing it has achieved such a great increase in air mean velocity along wind turbine shroud.Experimental and Numerical Study of a Supercritical Wing Performance at Low Reynolds Numbers Equipped with Different Winglet Planforms
https://ajme.aut.ac.ir/article_5273.html
In the era of rapid technological developments, the green aircraft and winglets of an airplane play a crucial role in reducing fuel consumption and its ensuing pollution. In this regard, the novelty of this paper is to focus on investigating the effect of the different geometrical parameters of winglets planforms on improving the aerodynamic performance of a wing with a supercritical airfoil (NACA 641412) at lower Reynolds numbers (take-off and landing phase). These investigations were conducted experimentally in a wind tunnel by force measurements through an external force balance. The aerodynamic coefficients of CL and CL/CD were obtained for the clean wing and nine various winglet planforms at a wide range of angles of attack from -4&deg; to 20&deg; and Reynolds numbers from Re=0.99&times;105 to Re=1.98&times;105. Furthermore, to get better insight into the physics of the flow, the numerical simulation of specific cases was carried out. According to the force measurement and vorticity magnitude results, among single winglets of W1, W2, W3, and W4, the W1 winglet with vertical height and linear side showed a better performance in all Reynolds numbers with a maximum lift increment of 26%; also, the W7 winglet planform represented the best performance as in double winglets with a maximum lift-to-drag ratio increment of 40%.