نشریه مهندسی مکانیک و ارتعاشات
سال نهم شماره 1 (پیاپی 30، بهار 1397)

Increasing development of industry And keep pace with the rising cost of energy around the world Has meant that engineers are always looking for items The ability have to transfer large amounts of heat in the area of long and low, with a drop in temperature as well as lower power consumption than traditional equipment . Thermosyphon heat pipe type have attracted much attention. The main purpose of this project Evaluate the performance of a particular type of thermosyphon heat pipe with variable conductivity. The heat input to changes in load or temperature evaporation temperature of the evaporator can be fixed. We did this by using the metal balls in the evaporator tube thermosyphon . According to the current situation and said Laboratory equipment was required by the With to provide for measuring The rate of fluid filling tube , We study on heat pipe with variable coefficients The loss and the overall heat transfer coefficient. The results showed that Performance of the heat pipe is different in the thermal load 30, 60, 90, 120 watts per square meter due to changes in the size of the evaporator . The best performance of themosyphon was by comparing the data on the maximum amount of heat load of 120 watts at least during the inactive part of the evaporator between 0 to 1.5 cm.

In this study, the thermal efficiency of a double-pipe heat exchanger with Fe3O4-water nanofluid in Reynolds numbers between 2000-21000 and volume fractions between (0.1-0.4% v / v) using artificial neural networks and correlation with experimental data has been evaluated and predicted. Iron oxide nanoparticles were about 20 nm in size. SEM photography of nanoparticles is provided to show the stability and homogeneity of suspension. Different Reynolds numbers and volume fractions of iron oxide nanofluid are used as the training data for ANN. A two-layer feed-forward neural network with back-propagation Levenberg-Marquardt learning algorithm (BP-LM) was used for heat transfer pre-parameters. Moreover, 70% of data were used in training set and 15% of data were used in evaluation set and remaining data were used as test data to prevent preprocess of network and to study the final efficacy of the network. In addition, based on the experimental data and the use of artificial neural network, data predicted by the neural network are in good agreement with experimental data measured by the double-pipe heat exchanger. The overall verification by the mean squared error (MSE) and correlation coefficient (R2) for the thermal efficiency of a double-pipe heat exchanger is 0.0001 and 0.996, respectively, indicating that prediction is successful.

Percolation is one of the most common phenomena in nature. For example water goes to ground or transport salt in reverse osmose. Many natural events or influence in the heat transfer, mass transfer issues have also been analyzed. With the advance of knowledge and enter into new areas, new issues emerge in the face of science. In this paper, the three main types of penetration, diffusion, mass diffusion and diffusion in the fluid will be discuses. The influence of molecular diffusion topics in molecular size and low displacements are often based on the concentration is investigated. The mass that occurs on a larger scale is usually different factors such as physical and environmental factors

In this research, the effect of porous layer on the efficiency of a single slope solar still is studied, experimentally. Accordingly, two single slope solar stills with same sizes containing conventional and modified by using porous layer are fabricated and tested, simultaneously. Black sponge rubber with low heat capacity and wick characteristic is selected as porous material. All experiments were performed in Semnan with geographical coordinates of 35° 33' N, 53° 23' E, Iran. Results showed that daily total water productions enhance by using sponge in solar still. Daily total water productions are 3263 and 3829 cc/m2 for conventional and modified stills, respectively. Accordingly, modified still produces 17.35% more distilled water in comparison with conventional one during one day. There is a direct relationship between trends of daily efficiencies of stills and trends of surrounding temperature or solar radiation intensity.

In today's world, the national security of most countries has depended on secure energy access, and therefore the optimum use of it has been the focus of attention of many statesmen and researchers. Expansion of consumption in the household sector and waste of energy in the urban community are among the obvious reasons for the rapid growth of energy consumption in the national economy. For this reason, energy consumption in the building sector needs to be considered. In this paper, after simulating an office building in Garmsar City with Design-Builder Software and validating it, the effect of the roof insulation and double wall parameters on the energy consumption has been investigated. The results show that the roof insulation and the use of a double wall can have a significant impact on building energy consumption.

Gallium arsenide is a compound of the elements gallium and arsenic. It is a III-V direct band gap semiconductor with a zinc blende crystal structure. GaAs is used in the manufacture of devices such as microwave frequency integrated circuits, monolithic microwave integrated circuits, infrared light-emitting diodes, laser diodes, solar cells and optical windows. From this view point, study of the electronic properties of GaAs single crystals is of prime importance. In this experimental work, electrical conductivity of two kinds of p-type GaAs samples each doped with Cr and Fe have been studied in the wide temperature range (100-400) K. Apart from temperature dependency of mobility of charge carriers also different predominant scattering mechanisms occurring in these crystals have been given.

The aim of this study, is study on the effects of flash gutter geometry on the material flow, predict of defect formation and forging process parameters in cold forging. For this purpose, effects of three flash geometry with trapezoidal, oval and square shapes were investigated on the simple frustum part. The effect of flash gutter geometry simulated using ABAQUS finite element software and then form with the optimized flash gutter was manufactured and forging process to verify the simulation results on a piece of AA3003aluminum alloy, was carried out. The results showed that trapezoidal flash gutter had more appropriate conditions for material flow than other cases. According to the simulation results, the maximum plastic strain was formed around the flash area and its value was maximum in the die with trapezoidal flash gutter, which was due to the greater flow of the material in the trapezoidal flash gutter geometry. According to the simulation results prediction, the distribution and exerted applied pressure to produce the final part on die with square flash gutter was more than others. The maximum applied pressure was on the flash area of die, which was the largest for the square flash gutter, and had the smallest amount of trapezoidal flash gutter geometry.