نشریه علم و فناوری در مهندسی مکانیک
پیاپی 1 (پاییز و زمستان 1401)

Nanoparticles are materials which have at least one of their dimensions (length, width, height) at the nano scale (among 1 and 100 nm). Nanofluids are obtained from the distribution of particles with nano dimensions in normal fluids. Common fluids such as water, oils and ethylene glycol, which are usually used in heat transfer, have limited ability in terms of thermal properties. The interesting properties of nanofluids (such as high heat transfer coefficient) and the great potential they show for increasing heat transfer have caused this group of fluids to be in the focus of researchers' attention in recent years. One of the key factors in optimizing the properties of these fluids is their stability. The gathering of particles and their agglomeration increases the possibility of sedimentation, reduces the stability of the suspension, and causes the loss of the properties of the suspension, such as thermal conductivity, viscosity, and increase in heat capacity. In this research, methods of increasing stability and inspection tools were investigated. The results showed that the simultaneous use of ultrasonic vibration and surface activating substances (surfactant) has a significant effect on the stability of nanofluid. And two methods of using DLS light scattering and ultraviolet-visible absorption spectrometry have been used by many researchers in their research in order to check stability.

Heart attack and stroke are the leading causes of death in the world. Often the main reason for this phenomenon is the clogging of arteries. This project aims is analyzing the flow in the artery-clogging effects. In the present study unsteady flow and flow also developed before is completely eroded. After parsing several different models, the Careau model for the simulation of non-Newtonian fluid in the blood is considered. The following research vessels of different sizes Eclipse model is analyzed. In the case where the output is narrowing the vessels have been strongly accelerating and up to 12% faster dilemma can be seen. However, the software cannot simulate tear, but the power of the threshold of bearing pressure on the wall tissue suggests that up to 50 percent of the eclipse diameter is tolerable. Pressure values in the vessels by flooded 80 percent of the inner diameter with Eclipse reflects the diversity of pressure and speed with high intensity within the veins that causes in areas near Eclipse values of shear stress to considerably increase the flow, vessel wall under pressure.

Here, Discrete Element Method (DEM) has been used to study effects of vibration, created by a vibrator, on the outflow of silos. To ensure the simulations accuracy, sensitivity analysis was performed on the numerical solution factors. For validation, comparisons with the results available in the open literature have been made. Realistic conditions show that when the opening of the silo is not large enough, the silo becomes blocked. Here, by performing a number of simulations, the opening size threshold at which the silo becomes blocked was determined and named as the critical size. Numerical studies have been done for different values of the outlet size, vibration frequency and amplitude. Moreover, to find out effects of the vibrator location, relevant stimulations were conducted, and based on the obtained results, when its location was within 20% of the bottom height of the discharge funnel, it had the greatest effect. Furthermore, it was found that by increasing the vibration frequency, the impact of the vibrator increases however, the difference in the effects of different frequencies decreases with the increase of the vibration amplitude. In addition to the theoretical explanation, physical interpretation and reasoning has also been discussed.

In this article, the mechanical behavior of triangular origami DNA, which has a special appearance and functional characteristics, has been investigated. Triangular origami DNA can be introduced as a nanodevice with several degrees of freedom. To investigate this issue, molecular dynamics modeling and simulation have been done and then its performance is analyzed. The first step in knowing a nanodevice is its structural analysis. In this report, the structural changes of the nanodevice due to the change in temperature have been investigated. The results show that the amount of structural changes has reached its lowest level in approximately 800 picoseconds. After this period of time, it can be said that the triangular origami DNA has relatively reached structural stability. Is. The mechanical behavior of Origami DNA will be such that it is suitable for taking different volumes of cargo. In other words, it can be used to carry nano drugs with various dimensions. In fact, the most interesting parameter in this nanodevice is the flexibility of its arms. This flexibility can be properly used to carry different types of cargo.

The camshafts are responsible for controlling the timing of the intake and exhaust valves at the right time in internal combustion engines. In this study, failure analysis was performed on two camshafts in a six-cylinder car made of gray cast iron. One camshaft failure occurred after about 177,000 kilometers and the other after about 208,000 kilometers between cam 1 and 2. In order to investigate the cause of cam failure, first, a series of tests including determination of chemical composition, microstructure, hardness measurement, and fractography were performed. The morphology of the fracture surface showed that the growth of intergranular crack was from the zone of stress concentration and accompanied by ratchet marks. The hardness measurement results of the camshaft cross-section measured a maximum of 155 HB, while the average surface hardness values of the heat-treated surfaces are suggested to be at least 480 HB. The results of the investigation showed that the phenomenon of crack initiation and eventual failure of the cam can be caused by factors such as excessive load, low hardness, and the presence of impurities in the stress concentration zone of the camshaft.

Aluminum alloys have good anti-corrosion properties and strength to weight ratio. In this paper, a statistical method based on finite element simulation was used to obtain the highest percentage of mold filling and the minimum percentage of thinning in the forming area. First, the finite element model is prepared and the accuracy is compared with the results of the experimental part. Effective factors including, temperature, pressure, pressure rate, axial feed and punch speed were evaluated by the response surface method in order to extract the model and find the maximum effect. Design Expert software was used to model the response surface methodology and Abacus finite element software was used to simulate it. According to the obtained results, the optimal points obtained for both characteristics are: temperature 552°C, pressure 6.5 bar, bar rate 0.02 bar/s, axial feed 7 mm and feed rate 0.05 mm /s with filling percentage 91.2 and a thinning percentage of 10.37 were obtained. The proposed model for predicting the values of variables had very close results with the experimental findings.

In this paper, the Carbon nanotube was stabilized in a water-based fluid by sodium dodecyl sulfate as a surfactant. Then, hot fluid (water) was in contact with the nanofluids (carbon nanotube -weight percentage of 0. 01) on both sides of the heat exchanger plate that has 13 plates. In order to investigate the functional groups and morphology of nanoparticles, obtained by FTIR, EDX, Raman analysis, Transmission, and Scanning electron microscopes images were used. The effect of the flow rate of hot fluid and nanofluid on the heat transfer coefficient and pressure drop was analyzed experimentally. The results in the range of laminar flow showed that the heat transfer coefficient increased by the flow rate of hot fluid and nanofluid rising (53.47% and 43.4%, respectively) and decreases the pressure drop of nanofluid, which are both positive effects. Determining the effect of nanofluid on the efficiency of the heat exchanger compared to the state without nanofluid (water-water), it was found that the increase in the flow rate of hot fluid and cold fluid causes an increase of 22.9% and 17.3%, respectively. It indicates the benefit of using carbon nanotubes in high stated flow rates.

The present study investigates the structure of a nuclear fusion reactor and the importance of magnetic hydrodynamic fluid. In reactors, the fluid is separated from the main body of the blanket by a separating layer. The separating structure is important in two ways. This structure primarily acts as a thermal insulator. The second priority is used for the separator to adjust the pressure and reduce it. The topics selected in this study are: the effect of magnetic field strength, profiles and dimensions of a blanket, wall thickness, flow velocity and pressure drop, as well as the profile of flow velocity changes due to magnetic field strength. The results show that the maximum velocity in blanket with rectangular cross section in 1T field is 11% and in 4T field is 9% faster than blanket with square cross section. Also, increasing the magnitude of the magnetic field from 1T to 4T causes a 9-fold increase in pressure drop in the blanket with a square cross-section and an 11-fold increase in the pressure drop in the blanket with a rectangular cross-section.

Today, various cooling systems such as evaporative cooler, split, air conditioner etc., are used to cool the building, which have a number of advantages and disadvantages. One of the most important disadvantages that can be mentioned for many cooling systems is the non-uniform temperature distribution in the building zones. The most important part of the building's heat loss is through the windows. Accordingly, in this research, a new cooling system based on compression refrigeration cycle is proposed and examined numerically and experimentally. Experimental evaluation of this system was performed in the air conditioning workshop and its numerical evaluation was performed in Design Builder software. In addition this system was compared with split cooling system. Among the most important results obtained from this research, we can point out the uniform distribution of the indoor air temperature and the reduction of energy consumption compared to the convectional cooling systems. When using a window coil system, the difference between the maximum and minimum temperature in a large part of the room was less than 1 degree Celsius. In the split system, however, the temperature has changed by about 2 degrees Celsius by moving from the ceiling of the room to the floor. Moreover, energy consumption of the system was 6.7% lower than that of split cooling system.

In recent decades, due to the significant increase in the elderly in the age pyramid of most of the country, wearable orthoses have received more attention with regard to rehabilitation. Sudden falls are one of the most important factors leading to death in the elderly. In this article, the impact of an orthosis on human balance while standing and walking has been investigated. The effect of this simple orthosis in reducing body metabolism while walking has been studied. In this article, the experimental effect of this orthosis on people's balance has been investigated. For this purpose, the desired orthosis was designed and manufactured. Then a data bank was created by the results of the experiments. To compile this data, the results of the experiments conducted by 10 volunteer students were used. In these tests, ear fluid and vision indicators were analyzed on the performance of people when using this orthosis. The findings of the studies are related to the study between people. According to the results of the tests, the use of the above orthosis improves the performance of people in the dynamic body, while the results of this research on static performance do not show any effect.