• 설비공학논문집
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• 제26권11호
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• pp.497-503
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• 2014

The performances of refrigeration truck systems using R404A and R134a were investigated by experimental testing, and compared. The optimal COPs of the R404A and R134a systems were 2.96 and 3.42, when the refrigerant charge amount was 1.3 kg and 1.4 kg, respectively. When the indoor side air temperature increased from $5^{\circ}C$ to $9^{\circ}C$, the total exergy destruction rate of the R404A system was on average 39.1% higher than that of the R134a system. In addition, the exergy efficiency of the R404A system was 12.9% higher than that of R134a system, for various indoor air temperatures. When the outdoor side air temperature increased from $25^{\circ}C$ to $35^{\circ}C$, the total exergy destruction rate of the R404A and R134a systems decreased by 18.9% and 19.5%, respectively. In addition, the exergy efficiency of the R404A and R134a systems increased by 25.2% and 30.7%, respectively. As the compressor rotating speed increased, the COP of the R404A and R134a systems decreased by 23.6% and 18.4%. The total exergy destruction rate and exergy efficiency of the R404A system were 27.2% and 15.7% higher than those of R134a system, respectively. Compared to the R404A system, the R134a system showed a higher COP and a lower exergy destruction rate; thus it can be concluded that the R134a system has the better performance.

• 한국수소및신에너지학회논문집
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• 제24권1호
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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.

• Journal of Advanced Marine Engineering and Technology
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• 제36권8호
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• pp.1036-1042
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• 2012

본 논문은 R744용 해양온도차 발전 시스템의 운전변수에 대한 최적의 설계를 위해서 엑서지효율을 이론적으로 분석하였다. 본 연구에서 고려된 작동변수로는 과열도와 과냉각도, 증발온도와 응축온도, 터빈과 펌프 효율 등이다. 분석한 결과를 요약하면 다음과 같다. R744용 해양온도차 발전 사이클의 증발온도, 과열도, 터빈효율, 펌프효율이 증가할수록 엑서지 효율은 증가한다. 그러나 응축온도와 과냉각도는 증가할수록 엑서지 효율이 감소한다. 이 중에서 증발온도의 변화가 R744용 해양온도차 발전 사이클의 엑서지 효율에 가장 크게 영향을 미치고, 펌프효율이 가장 적게 영향을 미친다. 따라서 R744용 해양온도차 발전 사이클의 엑서지 효율을 증가시키기 위해서는 증발온도를 표층수 온도에 가장 근접하게 증가시키는 것이 유리하다.

• 설비공학논문집
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• 제12권4호
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• pp.363-370
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• 2000

Experiments have been peformed, using pure refrigerant R134a and a zeotropic refrigerant mixture R290/R600a(60%/40%) and their performances have been analyzed by the first and second laws(exergy method) of thermodynamics. From the experimental results, variations of compressor speed and air temperature have a great effect on the performance of the system. The sum of exergy losses in compressor and evaporator is about 60% of total exergy loss, using refrigerant R134a, so it is necessary to improve the performance of compressor and evaporator. According to the experimental results using refrigerant mixture of R290/R600a(60%/40%), the exergy losses in heat exchange processes are decreased but the exergy loss in throttling process is increased. The performance of the system has been improved by 20∼30% compared with that of R134a and exergy losses have been also reduced.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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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.

• 한국해양공학회지
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• 제2권1호
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• pp.176-182
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• 1988

The exergy analysis on the heat storage performance of the senible heat storage unit which consists of the heat storage material in the concentric annulus and the hot fluid flowing through the inner tube is performed. Heat transfer characteristics which are necessary for the performance of the exergy analysis is obtained from the energy balance equations and the second law of thermodynamics. As the index of heat storage performance, the exergy lossnumber $N_{s}$, and exergy storage ratio from the concepts of the second law of thermodynamics are defined. Results are ovtained for the grometry of the storage unit, the Biot number Bi, ambient temperature $T_{o}$ as parameters. From these results the exergy storage ratio can be considered as the efficiency of the hat storage unit and is introduced as a guide to design.

• 플랜트 저널
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• 제9권3호
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• pp.43-47
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• 2013

발전 플랜트의 발전량 최적화 및 발전효율 최적화는 에너지공학을 전공한 전문가일지라도 이해하기 힘든 개념이다. 본 연구에서는 엑서지 및 엑서지율이라는 열역학적 상태값을 적용하여 에너지 공학을 전공하지 않은 일반인일지라도 발전량 및 발전효율 최적화 개념을 쉽게 이해할 수 있는 차트가 개발되었다. 발전소의 성능을 파악할 수 있는 대표적인 물성치는 주증기의 온도 및 압력이다. 개발된 차트에서는 주증기의 온도 및 압력에 따른 최대 발전량 곡선과 최대 효율 곡선이 도시되어 있으므로, 해석하고자 하는 발전소의 온도 및 압력을 차트에 적용하여 그 발전소가 얼마만큼 최대 발전량과 최대 효율에 접근해 있는지를 쉽게 파악할 수 있다.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 1999년도 제1회 학술대회논문집(KIASC 1st conference 99)
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• pp.169-172
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• 1999

The exergy method is used for analysis and evaluation of the cryogenic nitrogen production process which is operated by expansion turbene and liquid nitrogen. The exergy loss and thermodynamic effeciency are calculated for the each process. Also the operating efficiency and the exergy distribution are examined for each unit of proces. The optimal conditions to minimize the exergy loss of nitrogen column are found that nitrogen recovery ratio is maximum and operating pressure is 5.0 kg/cm2g. The exergy method can be used to design a plant and to evaluate its process.

• 에너지공학
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• 제12권3호
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• pp.165-176
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• 2003

본 연구에서는 발전 시스템에서 이미 알려진 성능에 대한 엑서지 분석을 실시하고, 이전에 우리가 알고 있던 각 기기의 효율과 비교하여 최적의 시스템 운영이 가능하도록 제안을 하였다. 본 연구에 사용된 대상시스템은 500MW 석탄 화력발전소이다. 엑서지 분석결과 보일러의 효율은 67%로 가장 낮았고, 복수기의 효율은 99%로 가장 양호하게 나타났다. 100% 부하에서 보일러의 엑서지 손실은 32.95%, 고압터빈과 저압터빈의 손실은 8.31%, 8.12%로 나타났다. 본 연구를 통해 증명된 발전시스템의 저 효율 성능개선 대상에 대한 구체적 연구와 함께 현재 운전되고 있는 발전 시스템의 기기 운전조건에 대한 상세한 엑서지 분석이 지속된다면 노후 되거나 잘못 설치된 비효율적 부분을 줄이는데 도움이 되리라 예상한다.

• 한국수소및신에너지학회논문집
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• 제31권6호
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• pp.637-645
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• 2020

In this paper, entransy analysis is carried out for combined heat and power (CHP) generation system driven by low-grade heat source compared with energy and exergy analyses. The system consists of a regenerative organic rankine cycle (ORC) and an additional process heater in a series circuit. Special attention is paid to the effects of the turbine inlet pressure, source temperature, and the working fluid on the thermodynamic performance of the system. Results showed that the work efficiency of entransy is higher than that of energy but lower than that of exergy, wheress the process heat efficiency of entransy is lower than that of energy but higher than that of exergy. Entrance analysis showed the potential to complement the exergy analysis in the optimal design of the energy system.