نشریه مهندسی مکانیک تبدیل انرژی
پیاپی 2 (پاییز 1389)

Solar energy is one of the most promising renewable energy sources. The values of the global solar radiation (GSR) are the most important parameter for the solar energy applications. The main objective of the present study is to apply Genetic Algorithm (GA) to estimate Global Solar Radiation over central arid deserts of Iran. To achieve this, the measured weather data for six stations, spread over the study area, were used to develop comprehensive models to estimate GSR. Monthly maximum, minimum, and mean air temperature, mean relative humidity, total sunshine hours, maximum possible sunshine duration and extra-terrestrial solar radiation were used as inputs variables and the measured global solar radiation (GSR) was used as output. The obtained results confirm the ability of the developed models to predict solar radiation values precisely.

Gas turbines are one of the most important machines for producing power. According to the important place of these turbines and their expanded application in powerhouses, has been done a lot of efforts for increasing work cycle efficiency of gas turbines. According to increased air temprature in hot months of year, so was decreased air density and after that, external power of gas turbine. One of the most important guideline is increasing the efficiency of  gas turbines by cooling entrance air to compressor. One of the most basic methods for cooling entrance air to compressor is using of fogging system. In this article, was discussed about thermodynamical modeling in fogging coolig by using of drop model. At first, for accounting drops evaporation being a model by using of steam density different in drop level and the air of internal canal environment to compressor, then for accounting operational parameters of gas turbine, was provided a computer code and  after comparing their results with experimental data, has been obtained results for gas powerhouse called shahid Modhaj of Ahwaz.

Designing synchronic recovery cycle was very complex due to existence two different recovery cycle power which was related to retrievers boiler. And any changes in designing directly were eclipsed power, efficiency, and costs, and many other variables.Researchers always was tied to indicating a way for optimizing properties and different sections (parts) of synchronic recovery cycles, but complete reviewing cycle was less considered due to unique complexities.In this article, we are considered to complete modeling synchronic recovery cycle, indicating the results of energy analysis, exergy of defining appropriate fitness function and then optimizing the model which was indicated by powerful instruments of genetic algorithm.Also, the accuracy of calculated results was proved by comparing with practical cycle results of biklent university. It was necessary to say that in this research, for the first time, has been optimized complete cycle synchronic recovery by genetic algorithm.

In this paper, energy and exergy analysis of fuel cell systems has been considered in simple and CHP modes. System model consists of following components: fuel cell stacks, burner, reformer, heat exchanger, battery and water heater. Thermodynamic analysis of system has been investigated with consideration of variations of energy efficiency, exergy efficiency and entropy generation versus internal air temperature to the fuel cell for different air stoichiometries. Results show that by increasing of internal air temperature to the fuel cell, entropy generation and exergy efficiency increase in both simple and CHP modes. Also, in simple mode, not in CHP mode, increasing of intenal air temperature leads to decreasing of energy efficiency.

In this paper, a free heat movement model in a room affected by Trombe wall three-dimensionally for laminar and turbulent flows was simulated by Fluent numerically model and the optimized air channel geometry for optimal temperature was obtained. In order to predict effects resulting from direct radiation, solar ray tracing algorithm, modeled by using solar positioning vector and radiation parameters and  the results were compared with those of experimental models to select the appropriate model. Using this model, the optimized geometry of Trombe wall was selected to transmit maximum heat in a range of Rayleigh values from 107 to1010 with the help of Nusselt values. The result indicate that the low Reynolds shear stress model was a superior model as a turbulence model. Also, they indicated that the geometrical parameters including heat wall distance from glass, wall thickness and upper and lower channels area decrease by Rayleigh number.

In this paper, the effects of velocity parameter on pressure drop and particle diameter on cyclone efficiency with 1300000 elements were investigated. In order to form the coupling between continuity and momentum equations simple algorithm was used. Velocity profiles were calculated in Y and Z directions at two cyclone sections using turbulence models of RNG k-ε, Standard k-ε and Realizable k-ε and finally they are compared with the experimental results. The results indicated that as the inflow velocity increases, the cyclone pressure loss is higher due to the increase of turbulence and formation of strong rotating flows. The results were compared with those of experimental models showing that second order RNG k-ε model reduce more accurate predictions in comparison to other k-ε models.

The aim of this work is to analysis parameters variation effect on PEM static model output voltage .Fuel cells designing parameters play an important role in their operation improvement .This paper has been shown the effects of several numerically simulated parameters such as temperature, pressure, cross section and Membrane thickness on PEM fuel cell operation. In this study we have been abbreviated anode and cathode pressures by fuel cell pressure. Simulation has been done under following conditions: temperature cell 298-353 , pressure 1.2-10 atm, cross section 0.016-0.05 m2 . Voltage current curves have been shown in different cases of parameters variation. MATLAB software has been applied for PEM static model simulation.