• Proceedings of the KSME Conference
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• 2001.06d
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• pp.751-758
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• 2001

Exergy concept is applied to the analysis of part-load performance of gas turbine engine. Exergy is a useful tool to find the source of irreversibility in thermal system. In this study, details of the performance characteristics of a heavy-duty gas turbine, l50MW-class GE 7FA model, are described by theoretical investigations with exergy analysis. Result shows that exergy destruction rate of gas turbine increases with decreased load, which means increase of irreversibility. Also, it is found that variations of IGV angle and amount of cooling air for turbine blades are closely related to the inefficiencies of compressor and turbine, respectively.

• The Journal of Korean Institute for Practical Engineering Education
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• v.3 no.1
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• pp.9-14
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• 2011

The expansion work that is wasted through the irreversible expansion through the PC valve of decompression process of the natural gas governor station can be recovered by replacing the process by an isentropic expansion. The energy and exergy analyses for the two decompression process models of power producing and current decompression process model are presented. Analysis results showed that the exergy by gas supply is 56.29%, the exergy by producing power is 32.12 % in case of preheating system and 22.52% in case of non-preheating system. The dead exergy at the PCV is generated much more network. As these results, the usefulness of exergy analysis is verified.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.8
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• pp.829-835
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• 2013

This paper describes an analysis on exergy efficiency of proposed high-efficiency R717 OTEC power system to optimize the design for the operating parameters of this system. The operating parameters considered in this study include outlet pressure in an evaporator and high turbine, inlet pressure condenser and vapor quality at cooler outlet, respectively. The main results are summarized as follows : As the outlet pressure in an evaporator and vapor quality at cooler outlet of R717 OTEC power system increases, the exergy efficiency of this system increases, respectively. But outlet pressure in the high turbine, inlet pressure in the condenser of R717 OTEC power system increases, the exergy efficiency of this system decreases, respectively. And, incase of exergy efficiency of this OTEC system, the effect of inlet pressure in an evaporator and outlet pressure in the high turbine on R717 OTEC power system is the largest and the lowest among operation parameters, respectively.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.5
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• pp.413-421
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• 2014

Desiccant cooling system is an air conditioning system that uses evaporative cooler to cool air and it can perform cooling by using heat energy only without electrically charged cooler. Thus, it can solve many problems of present cooling system including the destruction of ozone layer due to the use of CFC[chloro fluoro carbon] affiliated refrigerants and increase of peak power during summer season. In this study, cooling performance and exergy analysis was conducted in order to increase efficiency of desiccant cooling system. Especially, using exergy analysis based on the second law of thermodynamics can resolve the issue related to system efficiency in a more fundamental way by analyzing the cause of exergy destruction both in whole system and each component. The purpose of this study is to evaluate COP[coefficient of performance], cooling capacity and exergy performance of desiccant cooling system incorporating a regenerative evaporative cooler in various regeneration temperature and outdoor air conditions.

• The KSFM Journal of Fluid Machinery
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• v.18 no.6
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• pp.19-26
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• 2015

The present paper presented and applied an exergy analysis method to evaluate the magnitudes and the locations of exergy losses in the conventional desuperheating and depressurizing process of high pressure and temperature steam delivery system. In addition, for the reduction of exergy losses occurred in conventional process, the present study proposed new alternative processes in which the pressure reducing valve and the desuperheater of conventional process are substituted with steam turbine and heat exchanger, and their effects on exergy loss reduction and exergy efficiency improvement are theoretically investigated and compared. From the present analysis results, the total exergy loss caused in conventional desuperheating and depressurizing process accounted for 66.5% of exergy input and 85% of the total exergy loss was due to the mixing between steam and cold water(e.g desuperheating). However, it was shown from the present analysis results that the present alternative processes can additionally reduce exergy loss by maximum 92.7% of the total exergy loss in conventional process, and can also produce additional and useful energy, the electricity of 220.6 kWh and the heat of 54.3 MJ/hr.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.6
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• pp.483-491
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• 2014

In this study, a thermodynamic analysis was carried out for a combined power generation system using a low-temperature heat source in the form of sensitive energy and liquefied natural gas cold energy. An ammonia-water mixture, which is a zeotropic mixture, was used as the working fluid, and systems with and without a regenerator were comparatively analyzed. The effects of the mass fraction of ammonia and the condensation temperature of the working fluid on the system variables, including the net work production, exergy destruction, and thermal and exergy efficiencies, are analyzed and discussed. The results show that the performance characteristics of the system varied sensitively with the ammonia concentration or condensation temperature of the working fluid. The system without regeneration was found to be better in relation to the net work per unit mass of the source fluid, whereas the system with regeneration was better in relation to the thermal or exergy efficiency.

• Journal of the Korean Institute of Gas
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• v.27 no.3
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• pp.27-34
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• 2023

Using ammonia as fuel for solid oxide fuel (SOFC) cells has become an attractive topic nowadays due to its high efficiency, environmental friendliness, and ease of storage and transportation. Several configurations of ammonia-fed SOFC systems have been proposed and investigated, demonstrating high electrical efficiency. However, to further enhance efficiency, it is crucial to understand the inefficient components of the system. The exergy concept is well-suited for this purpose, making exergetic analysis essential for ammonia-fed SOFC systems. This study conducts an exergetic analysis for three selected systems: a simple fuel cell system (FC), an anode off-gas recirculation system (RC-FC), and a recirculation system with water removal (RC-WR-FC). The results reveal that the exergetic efficiencies of the FC, RC-FC, and RC-WR-FC are 48.7%, 51.6%, and 58.4%, respectively. In all three systems, the SOFC stack is the main source of exergy destruction. However, other components with relatively low exergetic efficiency, such as the burner, air heat exchanger, and cooler/condenser, offer greater opportunities for improvement.

• Journal of the Korean Institute of Gas
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• v.23 no.1
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• pp.27-35
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• 2019

In order to solve the global warming and reduce greenhouse gas emissions, $CO_2$ capture technology was developed by applying oxy-fuel combustion. But there has been such a problem that its economic efficiency is low due to the high price of oxygen gases. ASU is known to be most suitable method to produce large quantity of oxygen, to reduce the oxygen production cost, the efficiency of ASU need to be improved. To improve the efficiency of ASU, exergy analysis can be used. The exergy analysis provides the information of used energy in the process, the location and size of exergy destruction. In this study, the exergy analysis was used for process developing and optimization of large scale ASU. The process simulation of ASU was conducted, the results were used to calculate the exergy. As a result, to reduce the exergy loss in the cold box of ASU, a lower operating pressure process was suggested. It was confirmed the importance of heat leak and heat loss reduction of cold box. Also, the unit process of ASU which requires thermal integration was confirmed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.12
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• pp.1137-1145
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• 2013

In this study, exergy analysis of a thermally activated refrigeration cycle, a combined organic Rankine cycle (ORC), and a vapor compression cycle (VCC) were conducted. It is considered that a system uses a low-temperature heat source in the form of sensible heat, such as various renewable energy sources or waste heat from industries, and one of eight working fluids: R143a, R22, R134a, propane, isobutane, butane, R245fa, or R123. The effects of turbine inlet pressure and the working fluid selected on the exergy destructions (anergies) at various system components as well as the COP and exergy efficiency of the system were analyzed and discussed. The results show that the component of the greatest exergy destruction in the system varies sensitively with the turbine inlet pressure and/or working fluid.

• Journal of the Korean Society for Marine Environment & Energy
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• v.15 no.2
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• pp.126-132
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• 2012

In recent years, serious environmental problems occur in coastal area due to high pollution loads from human activity in land. Marine biomass utilization system therefore has been proposed to prompt material circulation between land and sea. Comprehensive assessment is necessary to determine that the proposed system is suitable and sustainable. This study introduces thermodynamic concept exergy, which expresses energy quality, to describe material and energy flowing in the material circulation system. This study presents material, energy and exergy flows in the material circulation system at Sakai city located in the middle of Osaka in Japan. It is found that exergy helps a better understanding of what is a key role is in exergy-efficient material circulation system.