• Transactions of the Korean hydrogen and new energy society
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• v.28 no.5
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• pp.570-576
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• 2017

Gas turbine system with steam injection has shown outstanding advantages such as high specific power and NOx reduction. In the present work, a comparative exergetic analysis was carried out for Steam Injected Gas Turbine (STIG), Regenerative Steam Injected Gas Turbine (RSTIG), and Regenerative After Fogging Gas Turbine (RAF). Effects of pressure ratio, steam injection ratio and steam injection method on the system performance was theoretically investigated. The results showed that the order of the highest exergy efficiency is RSTIG, RAF, and STIG for low pressure ratios but STIG, RSTIG, and RAF for high pressure ratios. In each arrangement, the combustion chamber has the highest exergy destruction and the compressor has the second one.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.6
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• pp.550-560
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• 2000

In order to minimize compression power and analyze the cause of exergy loss for a dry ice production cycle with 3-stage compression, the variation of compression power was investigated and the exergy analysis was peformed for the cycle. In this cycle, $CO_2$, is used both as a refrigerant and as a raw material for dry ice. The behavior of compression power and irreversibility in the cycle were examined as a function of intermediate pressure. From this result, the conditions for the minimum compression power were obtained in terms of the first stage or the third stage pressure. In addition, the irreversibilities for the cycle were investigated with respect to the efficiency of compressor. Result shows that the optimum pressure is not consistent with the conventional pressure obtained from the equal-pressure-ratio assumption. This is mainly due to the change in mass flow rate of the intermediate stage compressor by the flash gas evaporation from the flash drums. Most important is that the present exergy analysis enabled us to find bad performance components for the cycle and informed us of methods to improve the cycle performance.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.1
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• pp.91-97
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• 2013

Recently a novel cycle named organic flash cycle (OFC) has been proposed which has improved potential for power generation from low-temperature heat sources. This study carries out thermodynamic performance analysis of OFC using various working fluids for recovery of low-grade heat sources in the form of sensible energy. Special attention is focused on the optimum flash temperature at which the exergy efficiency has the maximum value. Under the optimal conditions with respect to the flash temperature, the thermodynamic performances of important system variables including mass flow ratio, separation ratio, heat addition, specific volume flow rate at turbine exit, and exergy efficiency are thoroughly investigated. Results show that the exergy efficiency has a peak value with respect to the flash temperature and the optimum working fluid which shows the best exergy efficiency varies with the operating conditions.

• Transactions of the Korean hydrogen and new energy society
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• v.32 no.5
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• pp.356-364
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• 2021

During the hydrogen fueling process, hydrogen temperature inside the compressed tank were limited below 85℃ due to the allowable pressure of tank material. The chiller system to cool compressed hydrogen used R407C, greenhouse gas with a high global warming potential (GWP), as a refrigerant. To reduce greehouse gas emission, it should be replaced by refrigerant with a low GWP. This study proposes a chiller system for fueling hydrogen with R290, consisted in propane, by applying the C3 pre-cooled system use d in the LNG liquefaction process. The proposed system consisted of hydrogen compression and cooling sections and optimized the operating pressure through exergy analysis. It was also compared to the exergy efficiency with the existing system at the optimal operating pressure. The result showed that the optimal operating pressure is 700 kPa in 2-stage, 840 kPa/490 kPa in 3-stage, and the exergy efficiency increased by 17%.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.871-878
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• 2000

Exergetic and thermoeconomic analysis were performed for a 500-MW combined cycle plant and a 137-MW steam power plant without decomposition of exergy stream of matter into thermal and mechanical exergies. The calculated costs of electricity are almost same within 0.5% as those obtained by the thermoeconomic method with decomposition of exergy into thermal and mechanical exergies of the combined cycle plant. However for the gas-turbine cogeneration plant having different kinds of products. the difference in the unit costs of products, obtained from the two methodologies is about 2%. Such outcome indicates that the level at which the cost balances are formulated does not affect the result of thermoeconomic analysis, that is somewhat contradictory to that concluded previously.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.1 no.3
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• pp.235-243
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• 1989

The purpose of this paper is to obtain enthalpy balance and exergy analysis for the energy losses in a steam power plant. The enthalpy and exergy analysis of the steam power plant were carried out on the various output of steam turbine. While enthalpy analysis shows that circulating loss in the condenser is maximum, exergy evaluation of the power plant shows that the losses of the boiler and turbine are considerably larger than those of condenser and feed water heater. Most irreversible losses of the power plant occur at the boiler. For improving the performance, the precise study about the irreversible losses of the boiler is necessary.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.24 no.5
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• pp.571-585
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• 1995

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.8
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• pp.1036-1042
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• 2012

This paper describes an analysis on exergy efficiency of R744 OTEC power system to optimize the design for the operating parameters of this system. The operating parameters considered in this study include subcooling and superheating degree, evaporation and condensation temperature, and turbine and pump efficiency, respectively. The main results are summarized as follows : As the evaporation temperature, superheating degree, and turbine and pump efficiency of R744 OTEC power system increases, the exergy efficiency of this system increases, respectively. But condensation temperature and subcooling degree of R744 OTEC power system increases, the exergy efficiency of this system decreases, respectively. The effect of evaporation temperature and pump efficiency on R744 OTEC power system is the largest and the lowest among operation parameters, respectively. Therefore, the refrigerant temperature in the evaporator must be closely to the surface seawater temperature to enhance the exergy efficiency of R744 OTEC power system.

• 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.