جستجوی مقالات مرتبط با کلیدواژه « exergy losses » در نشریات گروه « مکانیک »

The main objective of this article is to present a novel method for comprehensive and accurate exergy analysis of waste-to-energy power plants. In all previous studies conducted in this field, the average numerical value of waste analysis over a specific time period has been used. However, using this value leads to errors in exergy analysis data. In this study, an inverse solution method is initially employed to calculate the chemical composition, mass flow rate of fuel, and air. The measurement of the fuel flow rate is also averaged over the calculation time period, introducing errors into the calculations. By calculating the waste mass flow rate using the inverse method, the possibility of introducing such errors into the calculations is eliminated. After calculating the waste composition, waste and fresh air mass flow rates, a precise and reliable exergy analysis is provided for the entire controlled volume of the waste-to-energy power plant. The method includes 8 degradation terms and 10 loss terms. The inefficiency factors presented in this article represent the most comprehensive inefficiency factors in waste-to-energy power plants. The applied method is implemented for the Aradkuh power plant, and the results demonstrate that the gasifier is the main exergy destruction factor with the highest exergy losses. The calculated exergy efficiency for the power plant is determined to be 1.13%.

The present study aimed to introduce two novel power-refrigeration combined cycles into optimal usage of LNG cryogenic energy and reducing exergy losses due to high-temperature difference in the heat transfer process. The combined cycles include a compression-ejector refrigeration cycle and two low and high-pressure Rankine cycles in which the power required to operate the compression-ejector refrigeration cycle’s compressor is provided by the power generated by the two-cycle Rankin turbines. Increasing the cooling energy compared to direct LNG evaporation is considered as the benefits of the novel combined cycles. A thermodynamic analysis, along with optimizing both novel combined power-refrigeration cycles, was performed through the first and second thermodynamics laws and the fixed surface model assumption for the ejector. Analyzing the design parameters demonstrated that the maximum thermal and exergy efficiency and maximum refrigeration increasing ratio in both novel combined power-refrigeration cycles increase as the pump discharge pressure increases and the output pressure of Rankine cycle turbine reduces. The maximum thermal and exergy efficiency in cycle (І) were 77.31% and 23.69%, and 87.49% and 23.95% in cycle (ІІ), respectively through performing optimization in the boundaries set for the design parameters. Finally, the highest refrigeration increasing ratio to direct evaporation of LNG for cycle І and ІІ was 63.37% and 73.9%, respectively.

In this research, the performance of the J85-GE21 turbojet engine by exergy analysis of engine components was evaluated. The performance of the engine and its components for different power loads, at S.L. and 11000 meters and several different speeds, was investigated by the equilibrium exergy and energy equations. The highest exergy efficiency at sea level was related to the compressor by 96.72%, and then the nozzle and turbine by 93.70% and 92.31%, respectively. By reducing the inlet air speed to the engine at any altitude, the efficiency of all engine components and overall efficiency decreased. The lowest exergy efficiency at sea level related to afterburner was 54.81%, and then the combustion chamber was 80.42%. Increasing the altitude reduces the exergy destruction of the engine by 70%. It was found that the overall efficiency of the turbojet engine was reduced by 0.45% due to increasing one air inlet engine temperature rise by assuming that the air pressure was constant.