Energy Equipment and Systems
Volume:10 Issue: 2, Spring 2022

The axial turbine is one of the most important components of gas turbines in industrial and aerospace applications. As time passing the increasing of the roughness of the axial turbine blades is unavoidable. The aim of this paper is numerical investigation of the blades roughness effects on the flow field and performance of a two-stage axial gas turbine. In this research, the axial turbine is simulated three-dimensionally and the results are validated with experimental data. Then, the effects of blade roughness on flow field and performance of the turbine are investigated in five different pressure ratios. Also, in order to determine the role of stators and rotors roughness in decreasing the turbine efficiency, in a specific roughness, the first and second stators and then the corresponding rotors have been simulated separately. Numerical results show that the efficiency drop in the turbine stage is approximately equal to summation of efficiency drops when the roughness effect on the stator and rotor blades is applied, separately.

It is important to study real thermodynamic systems and evaluate the inefficiency of thermodynamic components in power plants in order to improve their performance. In this work, exergy analysis and investigation of the gas turbine segment of the Kerman combined cycle, are examined. The results reveal that the most exergy efficiency defect is related to the combustion chamber and compressor and finally to the gas turbine, respectively, and also in the combustion chamber the irreversibilities are mainly due to chemical nonequilibrium, thermal nonequilibrium, and mechanical nonequilibrium caused by combustion; 22.835% of exergy is lost during the combustion process. Therefore, this work introduces and defines ecological - cost or ecologicost as a new criterion. Ecologicost indicates that dissipated energy is more than production power; In other words, the system is defective and needs to be repaired or replaced. Ecologicost has the potential to replace traditionally criteria. Moreover, the ecological function and ecologicost value of the gas turbine are -20.418 MW and -0.05701, respectively. This Negative number indicates that system goes to destruction and needs repair or replacement or improvement. The optimization results show that the maximum power, maximum energy efficiency, maximum exergy efficiency, maximum ecological, and maximum ecologicost are 136.437 MW, 38%, 48.39%, 6.069 MW, and 0.01695, respectively.

In this study, the analysis of experimental results is used to investigate heat transfer and pressure drop characteristics of Titanium Oxide nanoparticles in an Alternating Flattened Tube. The impact of nanoparticles has not been studied before on Alternating Flattened tubes heat transfer characteristics. Experiments were conducted on 3 different AF tubes with heat transfer oil as base fluid with TiO2 nanoparticles volumetric concentrations of 1% and 2% in 400 to1800 Re range. Our experiments show increasing in flattening leads to a heat transfer increase in AF tubes by a factor of 1.58, 2.08, and 2.21 compared to circular pipes. Pressure drop also increases by 1.08, 1.19 and 1.25 times. The addition of TiO2 nanoparticles enhances heat transfer and pressure drop as well. We also found higher nanoparticle concentration provides more improvement. The most flattened tube with 2% particle concentration shows 2.85 and 1.32 times increase in heat transfer and pressure drop compared to the circular tube respectively. An efficiency parameter is used to study heat transfer and pressure drop simultaneously. Our analysis shows that the efficiency of the alternating flattened tube is higher than the circular tube and increases with the increase in flattening and nanoparticles concentration.  The efficiency of alternating flattened tubes reads 1.26, 1.62 and 1.76 times that of a circular tube. The efficiency of nanofluid with a volume concentration of 2% in alternating flattened tubes is 1.76, 2.01 and 2.15 times the base fluid in a circular tube. This experiment concludes the presence of nanoparticles improves overall heat exchange performance at the alternating flattened tubes.

In the present article, performance of a glazed photovoltaic thermal system integrated with phase change materials (GPVT/PCM) is numerically examined based on both energy and exergy viewpoints. The effect of PCM volumetric fraction and environmental temperature on thermal and electrical characteristics of the system is evaluated. A three-dimensional model of the system is simulated transiently in the ANSYS Fluent 18.2 using pressure-based finite volume method and SIMPLE algorithm selected for coupling pressure and velocity components. Validity of the numerical results is confirmed based on available data. The results indicate that PCM melting is more likely far from the riser tube and absorption of thermal energy be the PCM is mostly effective for filling the PCM container by around 2/3 of the volume. Increase of the PCM volumetric fraction reduces the module temperature and enhances the electrical performance of the system in terms of both energy and exergy efficiencies, while it decreases the thermal efficiency. An opposite trend is experienced by increase of the environmental temperature in which the thermal efficiency enhances and the electrical efficiency declines.

The irreversible Brayton cycle is usually used in gas turbine-based power plants. In this study, energy and exergy analysis has been performed for an irreversible Brayton cycle with a regenerator, reheater, and intercooler for the first time. The influence of different parameters such as the efficiency of the cycle's components is examined based on the first and the second laws of thermodynamics. The lost exergy in different components and the total exergy loss of the irreversible Brayton cycle are calculated for various conditions. The optimum pressure of the intercooler and the reheater is obtained for different cases. An irreversible Brayton cycle with regenerator, reheater, and intercooler is simulated in engineering equation solver software and the optimum pressure in each simulation is determined based on the first and the second laws of thermodynamics. Furthermore, the obtained optimum pressures are compared with the geometric mean of the low and the high pressure of the cycle in each simulation.

This paper presents an experimental study of a 10 kW grid-connected photovoltaic (PV) system installed on the roof of a government building located in Ilam, Iran. The purpose of this study is threefold: firstly, to assess the quality of the electrical power generated by the system; secondly, to analyze the CO2 mitigation potential of the system; and thirdly, to investigate the economic viability of the system. The economic analysis of the system is performed considering three different scenarios. In the first and the second scenarios, it is assumed that the PV system is installed for complete self-consumption, while in the third scenario, it is supposed that the PV power plant is built to sell its generated electricity. Besides, the first and the second scenarios are based on the average retail electricity price of 5.79 cents of US dollars per kWh and 8.22 cents of US dollars per kWh, respectively, while the third scenario assumed that the government purchases the electricity generated by the power plant at a fixed rate of 21.33 cents of US dollar per kWh. Each scenario is assessed in two modes, with and without including greenhouse gas (GHG) emissions reductions credit.

Nowadays, steel hardening has received much attention from researchers due to its frequent use in industries, especially is widely used in energy equipment, aerospace, and petrochemical industries. Low capability in chip removal of hardened steel has always been a significant machining issue. Mounted point grinding is a machining method to improve surface finish and remove burrs on the workpiece walls and hard-to-reach areas. This process is usually used without preparing the grinding wheel before and during the grinding operation, which reduces the proper performance of the process. Environmental contamination, surface integrity, coolant-lubricant-related diseases that affect workers' health, and machining costs heavily depend on the appropriate dressing and proper coolant-lubricant usage. In this study, the effect of dressing conditions (depth of dressing and dressing feed) and the workpiece feed rate during the mounted point grinding of a Mo40 hardened steel in two traditional wet and Minimum Quantity Lubrication (MQL) environments has been investigated. Surface roughness and wheel loading are two significant outputs in every grinding operation. The experimental result of this study reveals an improvement in enhancing the surface roughness in a soft dressing condition. Moreover, this study aimed to achieve proper surface roughness by implementing MQL technique to significantly reduce total cutting fluid usage compared to traditional wet machining. This study observed a higher wheel loading in MQL technique than in the conventional wet grinding.