• Journal of Advanced Marine Engineering and Technology
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• 제38권1호
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• pp.8-14
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• 2014

본 연구에서는 R-245fa를 작동유체로 하는 250kW급의 선박폐열회수 발전 시스템을 설계하고 과열기의 구성에 따른 사이클 특성을 연구 하였다. 과열기와 증발기의 직렬연결과 병렬연결의 2가지 조건을 시뮬레이션 하였다. 과열기와 증발기의 직렬연결 시뮬레이션에서는 작동유체 과열에 따른 엔탈피 증가로 4.7%의 출력상승을 얻을 수 있었고, 목표출력을 250kW로 정하였을 경우에는 사이클유량을 4.1% 감소시킬 수 있었다. 과열기와 증발기의 병렬연결 시뮬레이션에서는 사이클의 목표출력을 250kW로 정하였을 경우에 과열기로 가는 열원유체의 유량이 증가함에 따라 사이클 유량이 감소하여 작동유체펌프의 소요동력이 최대 7.9% 감소 하였으며, 유량비율에 따른 사이클효율과 정미효율은 큰 변화가 없었다.

• Journal of Advanced Marine Engineering and Technology
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• 제37권6호
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• pp.575-581
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• 2013

본 논문은 R744-R404A 캐스케이드 냉동시스템의 최적 냉매 충전을 위해 과냉도, 과열도, 내부열교환기 효율 등에 대한 영향을 분석한 것이다. 연구에 사용된 캐스케이드 냉동시스템의 고온 사이클에는 R404A, 저온 사이클에는 R744를 적용하였다. 그 주요 결과는 다음과 같다 : 고온 사이클의 과냉도, 과열도, 내부열교환기 효율과 저온 사이클의 증발온도와 압축효율은 크게 할수록 질량유량비가 작게 나타났다. 그리고 캐스케이드 온도차와 고온 사이클의 증발온도, 응축온도와 저온 사이클의 과냉도, 과열도, 내부열교환기 효율은 작을수록 질량유량비가 작게 나타났음을 확인하였다.

• Journal of Welding and Joining
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• 제13권4호
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• pp.55-64
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• 1995

A study was made to examine the effects of postweld heat treatment(PWHT) on the toughness and microstructures in the weld heat affected zone(HAZ) of Cu-bearing HSLA-100 steel. The Gleeble thermal/mechanical simulator was used to simulate the weld HAZ. The details between toughness and PWHT of HAZ were studied by impact test, optical microscopy(O.M.), scanning electron microscopy (SEM), transmission electron microscopy(TEM) and differential scanning calorimetry(DSC). The decrease of HAZ toughness in single thermal cycle comparing to base plate is ascribed to the coarsed-grain formed by heating to 1350.deg.C. The increase of HAZ toughness in double thermal cycle comparine to single thermal cycle is due to the fine ferrite(.alpha.) grain transformed from austenite(.gamma.)formed by heating to .alpha./.gamma. two phase region. Cu precipitated during aging for increasing the strength of base metal is dissolved during single thermal cycle to 1350.deg.C and is precipitated little on cooling and heating during subsequent weld thermal cycle. It precipitates by introducing PWHT. Thus, the decrease of toughness in triple thermal cycle of $T_{p1}$ = 1350.deg.C, $T_{p2}$ = 800.deg.C and $T_{p3}$ = 500.deg.C does not occur owing to the precipitation of Cu. The behaviors of Cu=precipitates in HAZ is similar to that in base plate. PWHT at 550.deg.C shows highest hardness and lowest toughness, whereas PWHT at 650.deg.C shows reasonable toughness, which improves the toughness of as-welded state.state.

• 한국유체기계학회 논문집
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• 제20권1호
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• pp.41-47
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• 2017

This study aimed to analyze organic Rankine cycle(ORC) which recovers discarded heat from a gas turbine based combined cycle cogeneration(CC-cogen) plant in terms of both performance and economics. The nominal electric power of the CC-cogen plant is around $120MW_e$, and heat for district heating is $153MW_{th}$. The major purpose of this study is to compare various options in selecting heat source of the ORC. Three heat sources were compared. Case 1 uses the exhaust gas from the HRSG, which is purely wasted to environment in normal plant operation without ORC. Case 2 also uses the exhaust gas from the HRSG. On the other hand, in this case, the DH economizer, which is located at the end of the HRSG, does not operate. Case 3 generates power using some of the district heating water which is supplied to consumers. The estimated ORC power generation ranges between 0.3 to 2.3% of the power generation capacity of the CC-cogen plant. Overall, Case 3 is evaluated to be better than other two options in terms of system design flexibility and power generation capacity.

• 대한금속재료학회지
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• 제48권1호
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• pp.28-38
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• 2010

High temperature high cycle and low cycle fatigue deformation behavior of automotive heat resistant aluminum alloys (A356 and A319 based) were investigated in this study. The microstructures of both alloys were composed of primary Al-Si dendrite and eutectic Si phase. However, the size and distribution for eutectic Si phase varied: a coarse and inhomogeneous distributed was observed in alloy B (A319 based). A brittle intermethallic phase of ${\alpha}-Fe\;Al_{12}(Fe,Mn)_3Si_2$ was detected only in B alloy. Alloy B exhibited high fatigue life only under a high stress amplitued condition in the high cycle fatigue results, whereas alloy A showed high fatigue life when stress was lowered. With regard to the low-cycle fatigue result ($250^{\circ}C$) showing higher fatigue life as ductility increased, alloy A demonstrated higher fatigue life under all of the strain amplitude conditions. Fractographic observations showed that large porosities and pores near the outside surface could be the main factor in the formation of fatigue cracks. In alloy B. micro-cracks were formed in both the brittle intermetallic and coarse Si phasese. These micro-cracks then coalesced together and provided a path for fatigue crack propagation. From the observation of the differences in microstructure and fractography of these two automotive alloys, the authors attempt to explain the high-temperature fatigue deformation behavior of heat resistant aluminum alloys.

• Journal of Advanced Marine Engineering and Technology
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• 제26권4호
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• pp.457-463
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• 2002

The closed cycle diesel engine is used in a closed circuit system which has no air breathing. The working fluid as intake mixture are consisted of oxygen, argon and recirculated exhaust gas in order to obtain underwater or underground power sources. In the present study, the high pressure diesel engine which can be operated by the closed cycle system with high intake pressure for increasing the net power rate is designed. It has been carried out to investigate the combustion characteristics of high pressure diesel engine according to the power rate. The maximum cylinder pressure and heat release rate were investigated. Also, major experimental data such as specific fuel consumption rate, oxygen concentrations, fuel conversion efficiency, polytropic exponent, and IMEP were compared with low pressure diesel engine experimental data.

• 한국수소및신에너지학회논문집
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• 제31권3호
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• pp.302-306
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• 2020

In this study, computer simulation works using PRO/II with PROVISION V10.2 have been performed for a cascade refrigeration cycle using methane, ethylene and propane as refrigerants. LNG cold heat was also utilized in order to save the compression powers for the ethylene and propane refrigeration cycles. It was concluded that about 77% of compression power can be saved by using LNG cold heat through the exchanging heat with refrigerants. We could also know that the cold heat price contained in 1 ton of LNG is 16,155 won.

• 한국기계가공학회지
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• 제7권1호
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• pp.9-16
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• 2008

It is important not only to reduce the casting defects of piston but also to improvement in the mechanical properties(hardness) of piston for the air compressor. The blow hole is typical casting defects in the conventional cast of aluminium alloy(AC8A-T6) piston. Because of the heat treatment method, mechanical properties of the aluminium alloy for piston was decided on the heat treatment method and cycle. Therefore, we tested on the development of mechanical properties and on the casting defects of piston for the air compressor in accordance with the heat treatment and casting condition. After the heat treatment and casting was carried out as several times, and was compared with the imported piston. As a result of several investigations; microstructure, hardness and casting defects of piston was changed under the influence of the heat treatment and casting method. When the cooling rate was controlled and the uni-cast method used, it bas the same mechanical properties and microstructure.

• 대한기계학회논문집
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• 제13권4호
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• pp.734-738
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• 1989

본 연구에서는 한 걸음 더 나아가 작동유체의 온도 뿐만 아니라 열기기의 규모를 결정하는 열교환기의 용량도 변수로 하여 출력과 효율의 변화를 조사하고, 최대출력을 얻기 위한 운전 조건 뿐만 아니라 설계조건에 대해서도 살펴 보았다.

• 설비공학논문집
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• 제23권5호
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• pp.313-320
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• 2011

For a steam Rankine cycle to recover waste heat from the exhaust gas of an Internal combustion engine, a swash plate type of expander as a power conversion unit has been designed. Numerical simulation has been carried out to estimate the performance of the designed expander. With the steam pressure and temperature of 35 bar and $300^{\circ}C$ at the expander inlet, respectively, the expander was estimated to produce the shaft power output of about 2.67 kW from the exhaust gas waste heat of 25.2 kW. The expander output increased almost linearly with the amount of exhaust gas waste heat in the range of from 5~40 kW, and the expander and Rankine cycle efficiencies showed gradual decreases in the ranges of 72.2%~69.5% and 10.8%~10.4%, respectively.