• Journal of the KSME
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• v.23 no.5
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• pp.335-343
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• 1983

새로운 방법에 의한 열역학의 기본법칙의 공식화과정 및 검증, 실제문제의 적용실례로 부터 다 음과 같은 제안을 할 수 있다. (1) 열역학의 기본법칙의 공식화에 있어서 재래방법의 사용도 좋으나 이해와 적용가능성의 측 방법에서 좀더 일반화된 사실에서 출발한 새로운 방법의 도입이 바람직하다. (2) 열역학적 가역에, 비가역성과 관련하여 기본법칙의 공식화과정에서의 시간개념의 도입은 중 요하다. (3) 동력기관의 해석에 있어서 이론적인 최대효율의 관점뿐 아니라 실제적인 최대일의 발생이 병행 취급되어야 하며 생성엔트로피의 개념에 의해 효과적으로 설명될 수 도 있다. (4) 단순한 사이클이 아닌 열역학적 과정에 대한 문제 및 주위조건을 고려한 해석의 경우, 가용 에너지, 엑서지의 보편화가 필요하다. (5) 생성엔트로피개념을 다양한 열역학문제에 적용하여 기존 해석방법에 대한 보완 및 검토가 요구된다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.225-229
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• 1990

As a basic study of optimal design conditions of refrigeration systems, the reversed carnot cycle, including heat transfer processes through the finite temperature differences between heat sources and the working fluids, is analyzed with the capacity of heat exchanger as a design parameter. When the temperatures of heat sources and the input work are fixed as constants, the optimal design condition is obtained as an optimum ratio of capacities of heat exchangers, which is exactly unity when the exergy output and effectiveness are maximum. In addition, the optimum ratio is slightly increased from unity as the irreversibility of the cycle increases.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.1
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• pp.150-156
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• 1986

A Rankine cycle including heat exchange processes in the steam generator has been analyzed by the concept of available energy. The operation condition of the cycle can be expressed with the evaporation temperature, and there exists an optimum power condition at which the thermal efficiency of the cycle is almost the same as that of the Carnot cycle at the maximum power condition. The mass flow rate of the working fluid increases sharply as the evaporation temperature approaches to the critical point, and the regenerative system is needed to operate the cycle at the maximum power condition.

• Journal of the Korean Solar Energy Society
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• v.27 no.4
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• pp.87-95
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• 2007

Thermodynamic analysis of water-to-water heat pump system based on the first and second law of thermodynamics is carried out in this study. This analysis shows the distribution of irreversibilities throughout the system components and informs us of a potential improvements with the temperature condition changes. Source water temperature($T_A$), utilization water temperature($T_D$) and temperature differences (${\Delta}T_{AB}$, ${\Delta}T_{CD}$) are important factors to affect system performances such as component irreversibilities, exergetic efficiency and COPH. Advantages and disadvantages with these factors are discussed. Second law optimization phenomena with $T_A$ and ${\Delta}T_{AB}$ are also indicated.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.2
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• pp.189-199
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• 2000

This paper investigates the thermodynamic performance of latent heat thermal energy storage system using two phase change materials(2-PCM system). The thermodynamic merit of using 2-PCM is clear in terms of exergetic efficiency, which is substantially higher than that of 1-PCM system. Optimum phase change temperature to maximize the exergetic efficiency exists for each case. The heat transfer area ratio of high temperature storage unit, X, becomes another important parameter for 2-PCM system if the phase change temperatures of given materials are different from those of optimum conditions. It is a good approximation for X$_{opt}$ to be 0.5 when optimum phase change temperatures are used. Otherwise X$_{opt}$ is determined differently as a function of given phase change temperatures.res.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.1
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• pp.51-60
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• 2012

Optimization procedures of performance analysis for ORC(Organic Rankine Cycle) system are established to the characteristics of low temperature heat sources such as open-type and closed-type. Effective heat recovery and heat extraction related to maximum power of the cycle as well as heat quality and thermal efficiency must be considered in the case of the open-type low temperature heat source. On the other hand, in the case of the closed-type low temperature heat source, only thermal efficiency is important due to constant heat input. In this study, thermal efficiency and exergy efficiency representing a level of close to Carnot cycle are studied, as useful index for the optimization of the ORC system. To validate the results of cycle analysis, those are compared with appropriate experimental data of ORC system as a thermal efficiency point of view.

• Plant Journal
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• v.12 no.4
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• pp.32-36
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• 2016

In this study, a penalty cost appropriation methodology for CGAM performance acceptance test was suggested. As the result of CGAM performance test, there were 0.31% decreases in electricity output, 0.39% decreases in heat rate on electricity output, 0.31% increases in heat output, and 0.23% increases in heat rate on heat output. As the result of penalty cost appropriation for above performance, the penalty cost was calculated as -$20,837 in electricity output, -$25,930 in heat rate on electricity output, +$10,340 in heat output, and +$7,715 in heat rate on heat output. Each penalty is appropriated as above fore kinds, however the total penalty should be determined as how to combine above fore kinds of penalty. In our calculation, the minimum total penalty was -$18,215 and the maximum total penalty was -$46,767. The methodology of total penalty appropriation should be determined in the contract between ordering organization and construction firm, and we can understand that it is very important.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.4
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• pp.484-496
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• 1996

This paper presents an anlaysis on the thermodynamic performance of ice storage system. The primary interest in this work is the exergetic efficiency of the system. The ice storage system considered here is the capsule type system with the waste plastic bottle being used as a capsule. To examine the characteristics of irreversibility production and exergetic efficiency in detail the ice storage system to be analyzed has been separated from the refrigerator in this analysis. The analysis is based on the lumped model with 3 uniform temperatures. The results indicate that 3 dimensionless parameters can describe the exergetic efficiency of the system, from which the characteristics of irreversibilities and the ranges of these parameters to ensure the reasonable performance of the system can be found. Experiments also have been performed to demonstrate the feasibility of such a system. This analysis only shows the performance of ice storage side, with the refrigeration side excluded. However, the results can be interpreted as a total performance if the refrigerator coupled with the ice storage system operatres reversibly.

• Journal of Hydrogen and New Energy
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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.

• New & Renewable Energy
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• v.20 no.3
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• pp.12-19
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• 2024

This study uses exergy analysis to evaluate the fuel-saving potential of a waste heat recovery unit (WHRU) integrated with an Organic Rankine Cycle (ORC) system for marine applications. Data from the training ship HANBADA of the Korea Maritime University and the general cargo ship BBC CAMPANA, including their operational routes and main engine loads, were used in this study. Simulations indicated that the WHRU system could save approximately 27.5 metric tons of fuel per voyage, equivalent to approximately 2.1% of the total fuel consumption. The WHRU system demonstrated a higher efficiency during long-distance voyages, significantly enhancing fuel savings. In addition, higher engine loads increased the exhaust gas thermal energy, thereby substantially improving the WHRU output. This study emphasizes the importance of evaluating the applicability of the ORC system for marine vessels by closely examining their operational patterns, navigation duration, and main engine load variability.