نشریه مهندسی مکانیک تبدیل انرژی
سال ششم شماره 1 (پیاپی 18، بهار 1398)

The present study aims to identify nanoparticles amenable to the decrease of erosion and corrosion in various working states.  In this regard it is argued that the negative effects on erosion and corrosion imposed due to the presence of nanoparticles are reflected from the nanoparticles shape. In this situation, WS2 featured by possessing an almost round shape is suitable for decreasing the erosion and corrosion which is undergone the present experiment. The presented experiments are in different rotational speeds as well as different working pressures. As a gist, WS2/H-100 nanofluids are suitable to decrease the surface erosion associated with ST420 and ST316 up to about 14% in 5% volumetric fraction, in the working pressures ranging from 2-8 Kg-Force and in the rotational speeds ranging from 19-220rpm. This was whilst, for the above range and with respect to Mo40 the decreasing effect was identified to be about 3%. For the corrosion, the use of nanoparticles with 5% volumetric fraction was suitable to decrease the corrosion effect of the working allows ST420 and ST316 up to 7% compared to the pure base fluid (oil). However, in the same conditions it was recorded a decrease of about 2% with respect to Mo40.

In this research, Gas tungsten arc welding (GTAW) on Hastelloy B-2 Superalloy was used to investigate the effect of current type on microstructure and mechanical properties of welded zone. The welding process was performed using two direct and pulsed current and with Hastelloy X filler metal. Optical Microscope (OM) and Scanning Electron Microscope (SEM) were used to investigate the microstructure and Energy Dispersive X-ray Spectroscopy (EDS) was used to analysis the precipitations. The microscopic observation showed that applying pulsed current led to a significant reduction in the size of the dendrites and microstructure in the weld metal. Hardness results showed that with direct current the hardness of weld metal is 300 Vickers while with pulsed current hardness is 330 Vickers. In the tensile test, all samples were fractured softly from the base metal. Also, the specimen welded with pulsed current has better tensile properties (elongation %50, yield strength 434 MPa and  ultimate tensile strength 660 MPa).

In this study, the exergy analysis of a steam power plant generating electricity with Rankine thermodynamic cycle is studied. Exergy efficiency is a suitable criterion for the analysis of a thermodynamic cycle. To optimize the processes and obtaining higher exergy efficiency, some parameters were considered as decision variables, and by changing these parameters, it was tried to improve the exergy efficiencyOutput temperature and pressure of the boiler, and the output pressures of the four stages of turbine extraction, were selected as six decision variables. In other words, the exergy efficiency function was considered as the objective function, and the six aforementioned variables were considered as decision variables. Optimization algorithm using the behavior of bees, which is one of the relatively new intelligent algorithms for optimization problems, performs the optimization by inspiring from the behavior and action of bees to find food. In this study, firstly, the optimization of exergy efficiency function was done for the steam power plant, and then the results were compared with the results obtained using the genetic and particle swarm optimization algorithms. Results showed that by appropriate changes in decision variables and using bees algorithm, exergy efficiency of the thermal power plant increased from 30.1% to 30.6675%. This increase was equivalent to 0.6675% for the cycle, and compared to the use of genetic and swarm particle optimization algorithms it was 0.0038% and 0.0036% higher, respectively.

Due to the rapid depletion of fossil energy resources and the environmental pollutions caused by consumption of fossil fuels, many countries have started developing renewable energy systems and finding alternative energy resources. One of the best resources of renewable energy is solar energy, which is clean and carbon-free. Solar-based energy systems can be designed in a way to produce hydrogen energy in order to supply the global energy demand, and reducing the environmental effects caused by global warming. In this study, a solar-based integrated hybrid system is considered to generate hydrogen. The system takes advantage of a flat plate collector, an organic Rankine cycle (ORC) and a PEM electrolyzer to convert renewable solar energy into electricity and hydrolyze water to hydrogen gas. To determine the optimum parameters and evaluate their effects on performance of the system, a parametric study is conducted. Outlet temperature of generator, inlet temperature of ORC turbine, irradiation intensity, water mass flow rate of the collector, and collector surface area are considered as the five decision variables. To optimize the design parameters, a multiobjective optimization is performed through the multi-objective particle swarm algorithm. The optimization results indicate that exergy efficiency of the system can increase from 1 to 3.5% meanwhile the total cost of the system can increase from 21 to 28 $/h, at optimum conditions. According to the findings, extending the collector’s surface area can lead to increasing the overall cost of the system, whilst reducing the exergy efficiency. It can also be stated that the collector component contributes to the total cost of the system noticeably.