نشریه مهندسی مکانیک و ارتعاشات
سال دوازدهم شماره 3 (پیاپی 44، پاییز 1400)

Extensive research has been done to improve the quality and reduce the propulsion weight of aircraft, which has led to the invention of new technologies and the construction of new engines. In all these studies, the study of temperature distribution and heat transfer in the body of the combustion engine in order to evaluate the characteristics and performance of the engine is considered important and necessary. One of the most innovative designs is the vane rotary motor design, which is considered to be a revolution in the motor industry. In this article, initial design of the seals of this engine is discussed based on thermal analysis. The method of increasing the air temperature in the combustion chamber has been investigated and the temperature distribution has been calculated by two methods of engineering estimation and numerical analysis. In engineering estimation, the basic relations of heat transfer, radiative, conduction, and energy balance equation are used, and the energy survival equations are satisfied, and the combustion process is modeled as a diesel cycle. Combustion is considered as a heat source and heat transfer coefficients are calculated in the form of computer code. The results of numerical analysis of this issue are compared and validated with the results of the estimation program and the appropriate cover and material for the components of the combustion chamber as well as the appropriate material and location of the seals are selected according to the temperature distribution

Due to the growing need of industries to improve heat transfer methods, the nucleate boiling region is of special interest to researchers because fluid boiling makes it possible to achieve higher heat fluxes than processes that are based only on non-boiling convection heat transfer. In addition, the change of working fluid in boiling heat transfer systems from pure fluid to nanofluid improves the heat transfer characteristics and thus allows the transfer of higher heat flux at lower temperatures. At the critical heat flux point, where the heat flux is maximum, it is important to secure the boiling surface and protect it from overheating. The purpose of this study is to numerically simulate the pool boiling of a water-based hybrid nanofluid containing 30% multi-walled carbon nanotubes and 70% titanium oxide with a volumetric concentration of 0.5% on a polished copper circular surface and to investigate the heat transfer characteristics, especially the critical heat flux point. For this purpose, the boiling process of pure deionized water was first simulated by ANSYS-Fluent software and the results were compared with experimental data. According to the observed acceptable agreement, the mentioned water-based hybrid nanofluid, as boiling working fluid is numerically simulated by changing the density of nucleation sites and its heat transfer and heat flux characteristics are obtained. The results show that the critical heat flux for pure deionized water was occurred at 24.4 °C and is about 1.1 MW per square meter, while the critical heat flux for the hybrid nanofluid was occurred at 13 °C and is about 1 MW per square meter.

Fly ash is a by-product of the combustion process and consists of tiny components that are emitted by combustion gases. Fly ash has been widely used in the manufacture of concrete. The purpose of this paper is to determine the performance of fly ash as a filler in hot mix asphalt. In this study, fly ash additive with different amounts (FA-0, FA-2, FA-4, FA-6) according to the weight of stone materials, was used as a filler. Modified asphalt mixtures were tested for stability, flow, stiffness, moisture sensitivity and material loss (Cantabro loss). The results showed that the stability of asphalt mixtures containing fly ash is higher than conventional mixtures. In addition, the compounds contained in fly ash improved moisture resistance and durability. According to the results of the experiments, it can be concluded that the use of fly ash as a filler can have a favorable effect on the hot asphalt mixture.

The main cause of failure and significant reduction in battery performance is a rise in temperature, so battery thermal control systems (BTMS) are built to monitor and optimize the thermal status of batteries. In this paper, two series and parallel arrangements for placing battery packs in electric vehicles with the same number of 17,280, 18650 battery cells are proposed and compared to select the best position for placing the battery packs. With the help of the Comsol program, the temperature change of the battery pack in the laminar fluid flow regime and the heat flux changes in the first 700 seconds of discharging the battery cells from the full charge mode and selecting the best design of the battery pack placement are compared. The maximum closed surface temperature of batteries is measured from the initial temperature of 27 degrees in series and parallel arrangement, respectively. The maximum temperature difference in the series of batteries is 10% different from the parallel arrangement. Also, by comparing the total heat flux, the better performance of the parallel arrangement compared to the arrangement of the battery series, makes this type of design a practical and more cost-effective priority than other designs.

Steam power plants are an advanced and complex design of the Rankin steam-liquid cycle. Therefore, understanding the concepts of effective parameters in increasing energy and exergy efficiency and also exergoeconomic are very important. The purpose of this study is to investigate the three basic scenarios of steam power plants, till the required changes in design and its effects on power plant efficiency to be determined. The third scenario has a preheater, a deaerator and two turbine extraction. The second scenario has a turbine extraction and preheater. In third scenario, energy and exergy efficiency are 20.74% and 26.91%, respectively. it’s increases of energy and exergy efficiency relative to second scenario are equal to 19.13% and 9.48%, respectively. Exergoeconomic analysis has shown that boiler and turbine have the highest total cost of investment, maintenance and exergy destruction, hence special attention should be paid to this equipment. The high relative cost factor of the boiler (r) indicates that the boiler efficiency can provide an overall improvement in the cost of this equipment. This can be done by reducing the exergy destruction by preheating and reducing losses and use of excess air. The Exergoeconomic coefficient of fk turbine is high. This means that to reduce the cost of the turbine, the possibility of reducing parameters such as inlet steam temperature, turbine pressure and it’s efficiency should be given more attention.

In this article, the effect of the work piece geometry and microstructure grain size on the heat treatment of 1050 steel has been investigated. For this purpose, two samples of work pieces with round (cylindrical) and square (flat) sections were considered for simulation with AC3 software. The effect of each of them was investigated on the growth of grain size in different cooling environments. Also, the hardness at the surface and depth was evaluated for both conditions. The results of the simulation show that the used software has a suitable ability to predict surface and depth hardness, grain size and the behavior of CCT parameters and cooling curves in the heat treatment of 1050 steel and this method can be used on a workshop scale and to be used in industrial applications.