• Journal of the Korean Solar Energy Society
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• v.31 no.6
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• pp.49-56
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• 2011

In this study a novel cogeneration system driven by low-temperature sources at a temperature level below $190^{\circ}C$ is investigated by first and second laws of thermodynamics. The system consists of Organic Rankine Cycle(ORC) and an additional heat generation as a parallel circuit. Seven working fluids of R143a, R22, R134a, R152a, $iC_4H_{10}$(isobutane), $C_4H_{10}$(butane), and R123a are considered in this work. Maximum mass flow rate of a working fluid relative to that of the source fluid and optimum turbine inlet pressure are considered to extract maximum power from the source. Results show that due to a combined heat and power generation, both the efficiencies by first and second laws can be significantly increased in comparison to a power generation, however, the second law efficiency is more resonable in the investigation of cogeneration systems. Results also show that the working fluid for the maximum system efficiency depends on the source temperature.

• Journal of Power System Engineering
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• v.13 no.6
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• pp.22-28
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• 2009

열역학 제 2법칙의 관점의 열역학적 가용에너지인 엑서지 해석법을 적용하여 가솔린, 메탄올, M90 연료를 사용한 전기점화 기관의 성능해석을 수행하였다. 열역학적 사이클 해석을 위하여 사이클을 구성하는 각 과정은 열역학적 모델로 단순화하였고, 크랭크 각도에 따른 실린더의 압력과 작동유체를 구성하는 연료, 공기 및 연소생성물의 열역학적 물성 값들을 이용하여 각 과정에서의 엑서지와 손실 일을 계산하였다. 실험데이터는 단기통 전기점화기관을 가솔린, 메탄올과 M90(메탄을 90%+부탄 10%의 혼합연료)을 연료로 WOT(Wide Open Throttle), MBT(Minimum advanced spark timing for Best Torque), 2500rpm 조건으로 운전하여 측정하였다. 계산에 이용한 자료는 실험으로 측정한 크랭크 각도에 따른 연소실의 압력, 흡입공기와 연료유량, 흡입공기 온도, 냉각수 온도와 배출가스 온도 등이다. 이를 이용하여 각 과정에서의 엑서지와 손실 일을 계산하였으며 각 과정에서의 손실 일은 연소과정에서 가장 크며 팽창과정, 배출과정, 압축과정 및 흡입과정 순으로 크게 나타났다.

• Journal of Mechanical Science and Technology
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• v.17 no.1
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• pp.122-128
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• 2003

This paper presents a thermodynamic analysis of heat pump system using water as a heat source and heat sink. The primary object in this study is the optimization of exergetic efficiency. Two different systems, 2-stream and 1-stream system, are analyzed in detail. Mass flow ratio (the ratio of mass flow rate of water through evaporator to that through condenser) is identified as the most important parameter to be optimized. It is shown that there exists an optimum mass flow ratio to maximize exergetic efficiency. The variation of optimum exergetic efficiency of 2-stream system is quite small and the value lies between 0.2∼0.23 for the range of investigation in this study. However, far better performance can be obtained from 1-stream system. This means considerable irreversibilities are generated through condenser of the 2-stream system. The effects of adiabatic efficiency of compressor-motor unit on the overall system performance are also examined in the analysis.

• Advances in Energy Research
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• v.8 no.3
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• pp.125-136
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• 2022

Entropy generation along with exergetic analysis is carried out using turbulent nanofluid flow in the heat exchanger. To obtain the optimized percentage constituent of nanofluid, the nanofluid volume concentrations is varied for the given input conditions. For different Reynolds number of the fluid and heat capacity rate ratio between the streams, the heat transfer improvements are studied in terms of nano particles diameter. Parametric analysis is carried out for a counterflow heat exchanger using turbulent nanofluid flow with exergetic efficiency along with entropy generation number as performance parameters. The exergetic efficiency provides realistic approach in the design of nanofluid applications in heat exchanger leading to conservation of energy.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.1
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• pp.97-104
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• 1987

An analysis on the thermodynamic optimum use of thermal water has been accomplished. The systems investigated are power generation and space heating. The space heating systems considered in this study are direct heating, heat pumps and heat pump assisted heating. The object of this study is to find the optimum selection and operation of the system under the given resources. The measure of such optimum conditions is the EFFECTIVENESS, the concept of efficiency based upon the Second Law of Thermodynamics. The temperature of water to waste is identified as the most important parameter to be optimized. The analysis indicates that for high temperature resources (higher than about 425K) power generation yields the best performance and is therefore recommended. The heat pumps are recommended for the resource temperature less than about 327K. The heat pump assisted heating system shows its superiority for the very narrow temperature range (320K-330K) and thus the use of this system should be considered when the flow rate is very limited. thus the direct heating is appropriate for the temperature range of 330K-425K. The analysis also shows the optimum capacity of thermal water, which may be useful for the initial estimation of heating or power generation potentials of given resources.

• Journal of the Korean Chemical Society
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• v.31 no.5
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• pp.395-399
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• 1987

The two dissociation constants of leucine were measured in the temperature range from 15 to 40$^{\circ}$C and pressure up to 2,500 bar by conductometric method. Both constants were increased as the temperature increased but pressure effect was not same as temperature effect. The first constants were increased as pressure increase but the second constants were decreased as pressure increase in the law temperature range but increased in some higher temperature range. These phenomena were discussed from the thermodynamic properties of the dissociation reactions.

• Journal of the Korean Society of Combustion
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• v.15 no.2
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• pp.1-11
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• 2010

Power generation systems based on the oxy-coal combustion with carbon dioxide capture and storage (CCS) capability are being proposed and discussed lately. Although a large number of lab scale studies for oxy-coal power plant have been made, studies of pilot scale or commercial scale power plant are not enough. Only a few demonstration projects for oxy-coal power plant are publicized recently. The proposed systems are evolving and various alternatives are to be comparatively evaluated. This paper presents a proposed approach for performance evaluation of a commercial 100 MWe class power plant, which is currently being considered for 'retrofitting' for the demonstration of the concept. The system is configurated based on design and operating conditions with proper assumptions. System components to be included in the discussion are listed. Evaluation criteria in terms of performance are summarized based on the system heat and mass balance and simple performance parameters, such as the fuel to power efficiency and brief introduction of the second law analysis. Also, gas composition is identified for additional analysis to impurities in the system including the purity of oxygen and unwanted gaseous components of nitrogen, argon and oxygen in air separation unit and $CO_2$ processing unit.

• Korean System Dynamics Review
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• v.14 no.4
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• pp.63-89
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• 2013

The purpose of this paper is to explain the entropic measures could cause the organization to increase the entropy. The organization as an open system has a tendency to input new energy to adapt itself to the change in its surroundings. This intention of inputting energy into organization is based on the second law of thermodynamics, the laws of entropy.Entropy is a measure of disorder, or a measure of progressing towards thermodynamic equilibrium. The entropy of an isolated system increases. Organizations have to open to their environment, have to do something to reduce their entropy. But, this attempt to reduce entropy entails another entropy. This study shows the side effects by giving examples of illegal receipt of worker's compensation insurance. The implications through the cases of illegal receipt of workers' compensation are as follows. Firstly, organizational policy is that inaction in itself may be the best policy, unless we always think the action best. Secondly, public organization should be careful in substituting business management in the private sector such as customer satisfaction(CS) for the value in public sector. Thirdly, the setting the expiration date of organizational policy could be the way to slow down the degree of entropy.

• Magazine of the Korea Concrete Institute
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• v.7 no.5
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• pp.172-178
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• 1995

Concrete contains numerous microcracks at initially poured. The growth and propagation of nicrockacsk are believed tc finally incur the faiure of concrete. These processings are understood as a damage. Damage IS represented as a second-order tensor and crack is treated as a con tinuum phenomenon. In this paper, damage is characterized through the effective stress concept together with the hypothesis of elastic energy equivalence, and damage evolution law and constitutive equation of a damage model are derived by using the Helmholtz frte eriergy and the dissipation potential by means of the thermodynamic principles. The constitutive equation of the model includes the effects of elasticity, anisotropic damage and plasticity of concrete. There are two effective tangent stiffness tensors in this model : one is for elastic-darnage and the other for plastic damage. For the verification of the model, finite element analysis was performed for the analysis of concrete subjec:t to uniaxial and biaxial loading and the results obtained were compared with test results.

• Korean Journal of Agricultural and Forest Meteorology
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• v.22 no.1
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• pp.26-46
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• 2020

An irrigated-maize agroecosystem is viewed as an open thermodynamic system upon which solar radiation impresses a large gradient that moves the system away from equilibrium. Following the imperative of the second law of thermodynamics, such agroecosystem resists and reduces the externally applied gradient by using all means of this nature-human coupled system acting together as a nonequilibrium dissipative process. The ultimate purpose of our study is to test this hypothesis by examining the energetics of agroecosystem growth and development. As a first step toward this test, we employed the eddy covariance flux data from 2003 to 2014 at the AmeriFlux NE1 irrigated-maize site at Mead, Nebraska, USA, and analyzed the energetics of this agroecosystem by scrutinizing its radiation, energy and entropy exchange. Our results showed: (1) more energy capture during growing season than non-growing season, and increasing energy capture through growing season until senescence; (2) more energy flow activity within and through the system, providing greater potential for degradation; (3) higher efficiency in terms of carbon uptake and water use through growing season until senescence; and (4) the resulting energy degradation occurred at the expense of increasing net entropy accumulation within the system as well as net entropy transfer out to the surrounding environment. Under the drought conditions in 2012, the increased entropy production within the system was accompanied by the enhanced entropy transfer out of the system, resulting in insignificant net entropy change. Drought mitigation with more frequent irrigation shifted the main route of entropy transfer from sensible to latent heat fluxes, yielding the production and carbon uptake exceeding the 12-year mean values at the cost of less efficient use of water and light.