نشریه مهندسی مکانیک و ارتعاشات
سال هشتم شماره 4 (پیاپی 29، زمستان 1396)

Thermal conductivity is one of the most important property of any type of materials. It’s shown that how much thermal energy can be cross inside the body. Solid material have the most rate of thermal conductivity. After solid material, fluid and gases have thermal conductivity rate. Measuring this property is step 1 to understand where and how material can be use. In this study several ways to measure thermal conductivity is shown. Also for non-solid material like fluid and component material introduce some new experimental test to measure thermal conductivity

The main cause of the energy dissipation in buildings in the country, in addition to design style of employment in the town of Bad materials in different parts of the building. It can be simple solutions to the implementation of some of the loss of a significant amount of renewable energy. In this study , optimize energy consumption in an administrative building in Semnan province climate in a bid to replace the window glass - with the designated low dispatch in foreign wall instead of single - walled window with the situation by simulator design builder software was investigated. Results of energy - saving by 12 percent annually in the coolant load, 2 percent in heating load and 11 percent of the total sample building in loads.

Drinking water scarcity has become one of the main challenges of human societies in recent years. Most of the water resources are stored as the non-drinkable saline water or are frozen in the poles. Therefore, they cannot be used directly for drinking. This issue indicates the importance of using appropriate techniques for water purification. One of these techniques is the usage of solar stills that can be used in remote tropical areas. The simple structure, low cost of manufacturing, and the usage of solar energy as a clean source is some benefits of this kind of equipment. The main problem of solar stills is their low efficiency. The researchers in this field used many active and passive methods to increase the efficiency of this device. In this research, two passive techniques used for enhancing the efficiency of solar stills containing usage of porous materials and nanoparticles are reviewed. The results of the research in these fields are briefly presented. Finally, based on the literature review, some suggestions for future works are provided.

Nowadays, there are some worries about the increasing temperature of earth and the pollution of fossil burning, hence using of new techniques in increasing power plant efficiency are very important. In this paper three structure layouts of turbine and power plant elements have been presented and The energy and the exergy losses for each component, energy and exergy efficiency of overall plant and irreversibility have also been determined using mass, energy and exergy balance equations. The energy and exergy analysis have been calculated in traditional and sub-system techniques namely boiler subsystem, steam cycle or thermal cycle subsystem and cooling tower subsystem. Results of exergy analysis in different steam power plants show that the major source of exergy destruction is the boiler. Suitable power plant design and its energy and exergy efficiency will be presented to client, till to support project and have capital investment on it. In this paper, in addition to suggested proportional power plant designs, the technical suggestions have been also presented to increase the power plant efficiencies.

Bending is one of the most usable metal forming processes. Due to the limited elasticity coefficient of the material, followed by plastic deformation, after removing the load, there is always an elastic recovery. Reducing the amount of spring back and process optimization are important in bending process. In this article, the effects of temperature and time on spring back of stainless steel and aluminum tubes bending have investigated. For this purpose, bending process has stimulated by finite element method using Abacus software. This method has investigated for different temperatures and times. Finally, to validating simulation results, a series of practical examinations have done for tube bending. The results of both methods are in a good agreement with each other so that with increasing of temperature, spring back effect has decreased and also with increasing time after bending, spring back amount percent has decreased.

This paper investigates the sophisticated analysis of a novel switching strategy for a matrix converter (MC) based direct torque control (DTC) of an induction motor (IM) drive. The proposed switching paradigm utilizes twelve 30° sectors for both flux and voltage vectors. Analytical expression of change rates of torque and flux for IM as a function of MC’s voltage vectors are derived. The influence of MC’s voltage vectors on the stator flux and electromagnetic torque variation is scrutinized and  an advanced switching scheme independent of any load and speed variation is developed. To decrease the switching losses of MC, the optimum switching state is selected by means of discretization and averaging on the flux variations. The performance of the proposed switching strategy is corroborated under rated conditions, and is also compared to the conventional hexagonal boundary switching scheme. The proposed method is characterized by low torque ripples, no need for rotational coordinate transformation and minimized switching frequency. The results verify that the degree of freedom to select proper voltage increases, and the torque ripple is hence significantly reduced up to 40%.

In this day and age, the ultra-fine materials due to their unique properties have found a special place in various industries. By reducing the grain size, the share of atoms at the grain boundaries has been increased and the increase of grain boundaries prevents the movement of dislocations and increases the strength. One method of producing ultra-fine materials is imposing severe plastic deformation. In order to apply Plastic deformation, disparate methods can be used that parallel angled channels are used in this study. ABAQUS finite element software is used to analyze the process numerically and to optimize the results, neural network and genetic algorithm methods have been used. In this study, the effects of die parameters including channel angle, tube length, increase of diameter difference and the friction coefficient are checked out. The results depicted that the coefficient of friction and pipe length which are tested, played a pivotal role in the homogenization of strain distribution separately; that by increasing the supposed friction coefficient and reducing the length of the tube, the strain distribution will be homogeneous. The difference between the increase in the diameter of pipe and the angle of die’s channel will have little impact on the improved uniformity of strain distribution. On the other hand, increasing the coefficient of friction, pipe length and diameter of pipe ends with an increase in the force of process while increasing the angle of die’s channel culminated in reducing the formation force. Additionally, considering the results obtained from optimization of parameters,