نشریه علم و فناوری در مهندسی مکانیک
سال دوم شماره 1 (پیاپی 2، بهار و تابستان 1402)

The limitation of global fossil fuel resources has had a significant impact in recent years. Iran wastes 570 million barrels of oil out of the allocated 1463 million barrels for the residential, industrial, and transportation sectors. The cement industry, as one of the high-energy consumers, accounts for approximately 14% of the country's industrial energy consumption, with about 40% of this energy being lost during production processes. This study aims to recover the waste heat from the cement industry using the Rankine cycle and simulate it using the Engineering Equation Solver (EES) software. Additionally, a thermal oil loop has been employed to prevent corrosion of heat exchangers and control the organic fluid evaporation process. Ethanol has been selected as the suitable working fluid, with a net power production capacity of 6213 kW, a thermal efficiency of 91.22%, and an exergy efficiency of 18.24%, outperforming R123, R1233zd(E), R1234ze(Z), and R600a. Increasing the turbine's inlet pressure by 100 kPa increases thermal and exergy efficiencies by 2.7% and 2.67%, respectively, while decreasing the mass flow rate into the evaporator by 5.6%. Increasing the condenser temperature by one degree results in approximately a 5.6% reduction in thermal efficiency and a 5.5% reduction in exergy efficiency.

In this paper, the phenomenon of liquid drop penetration inside the porous medium is studied by the two-phase fluid volume method. Considering the importance of two-phase and multi-phase flows and achieving the least error in the simulation of this phenomenon, in this research, a model for simulating the two-phase flow of droplet penetration in porous media is proposed, the proposed model has more agreement with experimental results compared with other similar models available in literature, the improvement is the novelty of this paper. The behavior of drop penetration has been predicted by the fluid volume method. The effect of changes in surface tension, viscosity, contact angle, viscosity and permeability and drop spreading level in porous media have been investigated. When the contact angle of the drop is 60 and 20 degrees, the changes of the expansion level are almost the same. The speed of spreading and penetration of water drop without the presence of gravity with surface tension of 0.02 is less than the other two surface tensions of 0.001 and 0.0072, while with the presence of gravity, water droplet with surface tension of 0.001 spreads and penetrates more than the other two cases. The results showed that the fluid volume method used in this research was 9% more accurate than the network Boltzmann method based on the Chan and Shen method with the physics of the same problem compared to the experimental results.

In this study, the problem of falling a non-isothermal non-Newtonian droplet has been investigated numerically. The geometry of the problem is considered in three-dimensional form. The widely used power-law model (n=0.1) has been used to investigate the non-Newtonian behavior of the droplet. COMSOL software has been selected for the numerical simulation of motion and heat transfer of non-Newtonian droplets. The results of this research have been compared with previous similar works and have been successfully validated. The simulations show that considering the surface evaporation compared to the case without considering the surface evaporation can change the temperature of the droplet up to a significant amount of 10°C. Factors affecting surface evaporation, including fluid velocity and droplet temperature, have been investigated in detail. The results show that fluid velocity is the most important factor in changing the amount of surface evaporation of the droplet. By doubling the drop's velocity, its temperature drops by 8°C. Investigating the mechanism of movement and heat transfer of non-Newtonian drops can have significant applications in various processes used in printing, dyeing, and especially pharmaceutical industries.

In this research, after examining the theoretical and experimental work done in the field of turbomolecular pumps, the simulation of the behavior of molecules in the free molecular flow between the stages of the turbomolecular pump, considering the effect of returning molecules from other stages, will be done. This simulation was done in the cylindrical coordinate system, using the test-particle Monte Carlo method and considering the real and three-dimensional geometry of the blade. Then the present work is validated and compared with experimental results and previous works. In the following, to investigate the effect of the blade angle in the middle and final stages of the turbomolecular pump, considering that three angles of 20, 15 and 10 degrees are mainly used in these stages, four different combinations of the aforementioned angles are presented for a five-stage turbomolecular pump. Finally, after examining the four combinations presented, it can be found that, for the middle and final stages of the turbomolecular pump, it should be done from different angles, emphasizing the 15 degree angle compared to the 20 and 10 degree angles and using less than the 10 degree angle in order to achieve the maximum comperation ratio and maximum flow rate.

Improving the performance of satellite attitude control with reaction wheel actuator and considering the sensor noise in this article, robust optimization method has been used to reduce the effect of sensor noise on the performance of the satellite attitude control with reaction wheel actuator. In this regard, the mean absolute pointing error has been chosen as the main performance index. The optimization based on the genetic algorithm and the Monte Carlo method of successive iterations have been used to include the effect of noise and obtain the control coefficients. First-order dynamics have been used to model the reaction wheel, taking into account the practical limit of the maximum production torque. Also, a modified proportional-integral-derivative (PI-D) controller with a observer method has been used to control the satellite. Gaussian white noise is added to angular velocity and angular feedback signals after passing through a first order filter. To compare the results, the control coefficients for the same simulation conditions have been obtained for two approaches: robust optimization and deterministic optimization. The performance in terms of the noise power spectral density function has been investigated for two approaches. The comparative results show that the control system adjusted by the robust optimization method, its performance criterion is more resistant in the face of noise and has less changes, while the performance criterion of the deterministic optimization method has more changes in Exposure to noise. The results indicate the preference of using the robust optimization approach for the control system exposed to noise.

Entropy generation confined flow around a block is studied according to the importance of a solid object’s cooling and heating process. In the current study, numerical simulation of laminar flow and heat transfer of nanofluids with nanoparticles of different shapes is considered—the nanofluids are water mixtures with either Al2O3 nanospheres or carbon nanotubes (CNTs). The incompressible Navier-Stokes and energy equations are solved numerically in a body-fitted coordinate system using a control volume technique. The flow patterns and temperature fields for different values of the particle concentrations are examined in detail. Furthermore, the effects of nanoparticle shape and concentration on heat transfer are studied. Furthermore, the influences of nanofluids on pressure drop and pump power are examined. On the other hand, the entropy generation minimization is considered as the optimization criterion. The results indicate that, in most cases, the nanofluids enhance the heat transfer and pressure drop. Interestingly, nanoparticles’ shape is critical in determining the fundamental mechanism of heat transport in nanofluids. Nanofluids with cylindrical nanoparticles exhibit a more significant heat transfer increase than nanofluids with spherical shape nanoparticles.

Additive manufacturing methods have become very popular in recent years due to their many capabilities, including the optimal use of materials and their use in constructing complex structures. One of the most important methods in these processes is the selective laser melting (SLM) process. In previous research, measuring the residual stress distribution of Inconel 625 samples under the SLM process has not been investigated. Therefore, in this research, the SLM process was carried out on the Inconel 625 sample using the finite element simulation method, and then the residual stress distribution in the sample obtained from the process was investigated in three main directions. Also, the formation of the molten pool, its dimensions, and temperature distribution were investigated. The results showed that tensile residual stresses were formed in the center of the layer and compressive residual stresses were more present at the edges of the sample. Also, the maximum of the residual stresses were formed in the axial direction and their minimum appeared in the layer thickness direction. The results related to the effect of process parameters on the residual stress distribution showed that with increasing laser power, tensile and compressive residual stresses increase in both axial and hoop directions, but decreasing the scanning speed does not give us accurate information about the increase or decrease of these stresses. For validation, the results of the finite element method were compared with the results of other researchers. The obtained difference was 13.97%. Therefore a good agreement existed between them.

In the decade, with the development of technology and the increase in the human factor, we have seen the growth of the use of energy resources in the world. The transportation industry, including land, sea and air, has the highest energy consumption coefficient in the world. the development and of the above-in most regions of the world, problems such as the increase in the temperature of the earth and the nature of climate changes and the increase in environmental pollution have occurred. This phenomenon has drawn attention to the use of sustainable and environmentally friendly energy sources. In the current research, using the method of examining sustainable development criteria, the reliability and comparison of the three fuels diesel, biodiesel and hydrogen for internal combustion engines have been investigated. This method is a useful tool for comparing and improving energy-based systems, which includes three main environmental, social and technological indicators and a total of 30 sub-indices. The score of each index indicates the level of compatibility of the examined process in the scope of that index. So that every element or process that has more reliability gets more points. , points are between 0 and 1. The evaluation indicators of this method include issues such as effectiveness, production costs (extraction, processing, transportation) and environmental pollution of each fuel. The results of this research provide an effective approach to compare the sustainable development capacity of the fuels used in diesel and, as a result, the development of economical and environmentally friendly fuels.

This research investigates the creep phenomenon of a polymeric rotating disk using the generalized Maxwell’s visco-hyperelastic model. After extracting the Lagrangian partial differential equation of equilibrium governing the problem, the rotating disk was analyzed by scripting in FlexPDE. The disk modelling in ANSYS with coding in the APDL environment showed that the radial displacement and Von-Mises stress are in excellent agreement with the FlexPDE results. The advantages of FlexPDE over ANSYS include one-dimensional analysis of axisymmetric plane stress instead of two-dimensional analysis, reduction of computational cost, possibility of defining variable thickness (without additional coding) and need for fewer elements in the radial direction to achieve acceptable accuracy (necessity of using 20 elements in FlexPDE compared to 100 elements in ANSYS). It was shown that with the passage of time and the increase in angular velocity, the radial displacement and Von- Mises stress of the rotating disk due to the creep phenomenon increase. It was shown that by increasing the angular velocity and decreasing the power in the thickness profile n_h, the displacement and Von-Mises stress at a specific time increase, but the change in angular velocity (as the applied load) and the change in parameter n_h (as a geometric characteristic) do not have much effect on the relaxation time of the rotating disk.

In this study, the effect of material imperfection on the free vibration response of perfect and imperfect FG plate is studied. A new hyperbolic shear deformation function is presented in this paper. The new hyperbolic function is chosen in such a way that the degree of the function is reduced as much as possible, despite the sufficient accuracy, so that the calculation speed is greatly reduced. The properties of the FG plate varied along the thickness according to power law. The material composition in production process cannot be completely in accordance with the expected pattern, which leads to the production of imperfect FG material. The governing differential equations are derived using the Hamilton’s principle. The obtained equations were solved using the Navier method with simple boundary conditions. The effects of important geometric and mechanical parameters of perfect model and two types of imperfect model, including length to thickness ratio, length to width ratio, wave number and power-law exponent on natural frequency response of imperfect FG plate are investigated. To verification, the analytical results obtained in this study are compared with the results presented in the literature, and in this comparison, a good agreement was obtained, which shows the correctness theory, deriving and solving equations.

The purpose of this research is thermal analysis of a brushless permanent magnet motor with marine application. The advantages of brushless permanent magnet motors are creating high torque and power in proportion to their weight and size. But this issue leads to a large increase in engine temperature. Therefore, the design of the cooling system is essential for cooling and reducing the temperature of this engine. The engine has been thermal analyzed first without cooling system and then with different cooling systems. For the purpose of thermal analysis, the stator and the shell were first modeled and then simulated. The engine has been thermally analyzed first without cooling system and then with different cooling systems. In order to check the effect of the cooling system and choose an optimal and suitable cooling system for this engine, the maximum temperature in different cooling systems with the number of 4, 8 and 12 holes, the diameter of the holes various 3, 4 and 5 mm diameters and circular and oval cross-sections have been compared with each other and with the state without cooling system. The results showed that the temperature of this engine reaches about 416 ̊c without cooling system. Also, the cooling system with 8 circular 4 mm holes has been introduced as the most suitable cooling system for this engine.

It Is Important to Prevention of Freezing of Water in Fire fighting System in Building on Winter Season. For This Reason Dry Sprinkler Systems Is Used .In This Method Instead of Water, Air or Nitrogen Is Used on System.When Bulb Burst Pressure Drop Occurs on System and Fire Pump Infuse Water to Systems and so According to Standard, Water Should be Reach to Furthest Sprinkler in Specific Time. Nowadays this Time It Is not Satisfied and not Cconsonant with Standards of Fire Fighting Systems. In This Research with Using Fluent Soft Ware and Increasing Air Volume in System and Changing on the Structural of the Sprinkler and Nozzle Angel, with Increasing Air Speed Outlet, Time of Discharge Water to Furthest Consumer Decrease . Results Show with Change of Angel the Converge Angel to 60 and the Diverge Angel to 15 Instead of Standard Tyco manufacturing Speed of Air in Outlet Sprinkler 60 Percentage Increased.

One of the main issues in providing light in office and commercial spaces is the use of natural light. Atriums or voids direct natural light to the interior spaces of buildings. Natural light and its use for lighting are one of the purposes of using windows in buildings. The use of sunlight heat in winter, the use of wind reading and ventilation in atriums are other cases that have taken into consideration the use of atriums for energy saving purposes. Components are important in increasing the efficiency of the use of atriums. The mechanism of the internal walls, the type and form of the atrium roof cover and the general shape of this empty internal space are among the things that should be considered in the optimal design of the spaces.Mechanical optimization methods, which have been used in technological sciences for many years to optimize multi-parameter problems, are seen as a suitable technique for this research. The models created by writing the algorithms in the Grass Hopper plug-in correspondingly deal with energy issues, among which the Honey Bee plug-in is used as an efficient tool to investigate thermal comfort. The mechanism of this variable analysis is towards optimization of energy consumption and thermal comfort, and it has the ability to simultaneously change the configuration of the middle spaces, which makes parametric design possible.

Due to the importance of natural phenomena in human life, investigation and study of these phenomena has always been of interest. The aim of this study is to investigate the stack effect that occurs in all buildings, although it is more noticeable in high-rise buildings. Due to the importance of this phenomenon in the energy consumption of high-rise buildings, in this research, these types of buildings have been studied. Due to the importance of the influence of the cross-section of buildings on the occurrence and behavior of this phenomenon, therefore, elliptical, triangular and rectangular cross-sections with the same surface have been examined and by comparing the results, different cross-sections have been evaluated and compared. The simulation of this phenomenon has been done in Fluent software and the analytical results have been compared, which shows a good match. The results show that the elliptical cross-section, according to its geometry and aerodynamic conditions, has the best performance in terms of the amount of additional pressure required to create positive pressure and energy consumption.