• Nuclear Engineering and Technology
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• 제53권10호
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• pp.3196-3206
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• 2021

For the Korean design of the PCCS (passive containment cooling system) in an innovative PWR, the overall thermal resistance around a condenser tube is dominated by the heat transfer coefficient of steam condensation on the exterior surface. It has been reported, however, that the calculated heat transfer coefficients by thermal-hydraulic system codes were much lower than measured data in separate effect tests. In this study, a new empirical model of steam condensation in the presence of a noncondensable gas was implemented into the MARS-KS 1.4 code to replace the conventional Colburn-Hougen model. The selected correlation had been developed from condensation test data obtained at the JERICHO (JNU Experimental Rig for Investigation of Condensation Heat transfer On tube) facility, and considered the effect of the Grashof number for naturally circulating gas mixture and the curvature of the condenser tube. The modified MARS-KS code was applied to simulate the transient response of the containment equipped with the PCCS to the large-break loss-of-coolant accident. The heat removal performances of the PCCS and corresponding evolution of the containment pressure were compared to those calculated via the original model. Various thermal-hydraulic parameters associated with the natural circulation operation through the heat transport circuit were also investigated.

• International Journal of Automotive Technology
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• 제8권4호
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• pp.421-428
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• 2007

This paper investigates the combustion and emission characteristics of a compression ignition engine fueled with neat and blended Shell's gas-to-liquid (GTL) fuel, which was derived from natural gas through the Fischer-Tropsch process. The experiments were conducted in a 6-cylinder DI diesel engine with pump timing settings of $6^{\circ},\;9^{\circ}\;and\;12^{\circ}$crank angle before TDC over ECE R49 and US 13-mode cycles separately and compared to a conventional diesel fuel. The results show that GTL exhibited almost the same power and torque output, improved fuel economy and effective thermal efficiency. It was found that GTL displayed lower peak in-cylinder combustion pressure and maximum heat release rate (HRR), the timings of the peak pressure and the maximum HRR were generally delayed, and the combustion durations were almost equivalent for diesel and GTL under the same speed-load condition. The results also indicate that, compared to diesel fuel, GTL blends showed a trend forward decreasing four regulated emissions simultaneously and a higher GTL fraction in blends contributing to further reductions in the emissions. In particular and on average, neat GTL significantly reduced HC, CO, NOx and PM by 16.4%, 17.8%, 18.3% and 32.4%, respectively, for all cases.

• Journal of Microbiology and Biotechnology
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• 제9권6호
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• pp.737-743
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• 1999

A conventional thermophilic anaerobic digester was converted into a thermophilic high-rate hybrid anaerobic reactor (THAR) for treating distillery wastewater. The THAR has been operating successfully since May 1995 at a loading rate of 5.45 to $11.52{\;}kg/\textrm{m}^3/d$ (maximum of 15.02). The THAR has demonstrated a soluble Chemical Oxygen Demand (sCOD) removal efficiency of 85 to 91% and a total COD (tCOD) removal efficiency of as much as 72 to 84%. Product gas had a methane content of 59 to 68%. The tCOD removal rates were 4.31 to 5.43, 6.26 to 6.89, and 9.03 to $9.78kg{\;}tCOD/\textrm{m}^3/d$ for tapioca, com, and naked-barley wastewater, respectively. The sCOD removal rates ranged from 3.75 to 4.79,3.28 to 4.89, and 5.57 to 6.21kg $sCOD/\textrm{m}^3/d$ for tapioca, com, and naked-barley wastewater, respectively. There were unknown substances in a naked-barley distillery wastewater that were identified as being toxic for microorganisms. However, the THAR treated naked-barley wastewater continuously for 26 days, operating at an average tCOD loading of $11.08{\;}kg/\textrm{m}^3/d$without any signs of deterioration in either COD removal efficiency or gas production rate. During this period, the average removal efficiencies of tCOD and sCOD were 84% and 91%, respectively, and the gas production rate averaged 6.61 to $7.57{\;}\textrm{m}^3/\textrm{m}^3$ reactor/d which produced 0.57 to $0.69{\;}\textrm{m}^3{\;}biogas/kg{\;}tCOD_{rem}$. From tapioca and com wastewater, the reactor showed an average gas production rate of 3.18 to 3.46 and 4.91 to $5.22{\;}\textrm{m}^3/\textrm{m}^3$ reactor/d which produced 0.53 to 0.69 and 0.62 to $0.71{\;}\textrm{m}^3/kg{\;}tCOD_{rem}$, respectively.

• 설비공학논문집
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• 제17권4호
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• pp.285-296
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• 2005

In order to reduce the compression power and to use the overall energy contained in LNG effectively, a combined cycle is devised and simulated. The combined cycle is composed of two cycles; one is an open cycle of liquid/solid carbon dioxide production cycle utilizing LNG cold energy in $CO_2$ condenser and the other is a closed cycle gas turbine which supplies power to the $CO_2$ cycle, utilizes LNG cold energy for lowering the compressor inlet temperature, and uses the heating value of LNG at the burner. The power consumed for the $CO_2$ cycle is investigated in terms of a production ratio of solid $CO_2$. The present study shows that much reduction in both $CO_2$ compression power (only $35\%$ of power used in conventional dry ice production cycle) and $CO_2$ condenser pressure could be achieved by utilizing LNG cold energy and that high cycle efficiency ($55.3\%$ at maximum power condition) in the gas turbine could be accomplished with the adoption of compressor inlet cooling and regenerator. Exergy analysis shows that irreversibility in the combined cycle increases linearly as a production ratio of solid $CO_2$ increases and most of the irreversibility occurs in the condenser and the heat exchanger for compressor inlet cooling. Hence, incoming LNG cold energy to the above components should be used more effectively.

• 한국수소및신에너지학회논문집
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• 제12권4호
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• pp.239-246
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• 2001

Fossil fuel such as oil and natural gas has been used and will be no longer supplied enough to demand in the beginning of thisg century. The use of the fuel makes a lot of environmental pollution to threaten human being's health especially in big cities and produces a lot of $CO_{2}$ to make green house effect of the earth. It is the time to use clean fuel such as hydrogen to prevent the expected energy crisis and the pollution. A new engine such as fuel cell can be used instead of the conventional internal combustion engine with 2 to 3 times higher efficiency of the conventional engine. The fuel cell uses hydrogen and oxygen and produces electric energy and pure water, which is a calm engine without air pollution. In big cities the city buses and the taxies powered by hydrogen fuel cells are suggested to be operated for clean environment. The energy and cost analysis performed for hydrogen and electricity production from wind power and solar cell.

• Structural Engineering and Mechanics
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• 제31권1호
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• pp.11-24
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• 2009

In China, the oil and natural gas resources of Bohai Bay are mainly marginal oil fields. It is necessary to build both ice-resistant and economical offshore platforms. However, risk is involved in the design, construction, utilization, maintenance of offshore platforms as uncertain events may occur within the life-cycle of a platform under the extreme ice load. In this study, the optimum design model of the expected life-cycle cost for ice-resistant platforms based on cost-effectiveness criterion is proposed. Multiple performance demands of the structure, facilities and crew members, associated with the failure assessment criteria and evaluation functions of costs of construction, consequences of structural failure modes including damage, revenue loss, death and injury as well as discounting cost over time are considered. An efficient approximate method of the global reliability analysis for the offshore platforms is provided, which converts the implicit nonlinear performance function in the conventional reliability analysis to linear explicit one. The proposed life-cycle optimum design formula are applied to a typical ice-resistant platform in Bohai Bay, and the results demonstrate that the life-cycle cost-effective optimum design model is more rational compared to the conventional design.

• 에너지공학
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• 제5권1호
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• pp.42-49
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• 1996

천연가스는 기존 내연기관의 구조를 크게 변경시키지 않고도 사용이 가능하며, 저공해성, 안전성, 내구성 등에 있어서 우수한 특성을 가지고 있고, 매장량이 풍부하다는 점에서 자동차용 대체연료로서 유망시 되고 있다. 본 연구에서는 기존 가솔린 기관을 CNG 전용기관으로 개조한 후, 공연비, 점화시기 등과 같은 기관 운전조건들을 최적화한 CNG전용기관을 기존 가솔린차량에 탑재하여, 샤시동력계상에서 연료소비량 및 배기배출물 농도를 측정·비교하였다. 또한, 실도로상에서 가속성, 운전성 등의 차량 주행특성에 대해서도 평가하였다. 그 결과, 시작 CNG차량의 경우에는 가솔린 차량에 비하여 연비는 향상되었고 배기배출물은 저감되었으나 출력은 약간 감소되었다.

• 한국수소및신에너지학회논문집
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• 제9권1호
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• pp.38-45
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• 1998

An energy crisis is expected in near future. Fossil fuel such as oil and natural gas has been used and will be no longer supplied enough to demand in the beginning of coming century. The use of the fuel makes a lot of environmental pollution to threaten human being's health especially in big cities and produces a lot of $CO_2$ to make green house effect of the earth. It is the time to use clean fuel such as hydrogen to prevent the expected energy crisis and the pollution. A new engine such as fuel cell can be used instead of the conventional internal combustion engine with 2 to 3 times higher efficiency of the conventional engine. The fuel cell uses hydrogen and oxygen and produces electric energy and pure water, which is a calm engine without air pollution. In big cities the city buses and the taxies powered by hydrogen fuel cells are suggested to be operated for clean environment. A model of the total energy system for production, transportation and utilization of hydrogen is calculated.

• 한국가스학회지
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• 제18권5호
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• pp.6-11
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• 2014

차량용 LNG 연료 용기의 내진동 단열 지지구조 최적화 설계 개발을 위하여 종래의 해외특허구조 설계를 기본으로 한 특성요인도 분석으로 용기의 내조 및 외조 지지부 구조설계의 주요 설계 인자를 도출하였다. 도출된 설계인자 중에서 우선적으로 지지 봉재의 직경과 단열 격판 연결부 곡률을 대상으로 하여 최적화를 수행하였다. 차량용 LNG 연료 용기 설계안에 대한 평가를 위해 설계안을 MSC/MARC 상용유한 요소해석 패키지를 활용하여 유한요소 모델링하여 진동모드해석과 열전달 및 열응력해석을 수행하였다. 최적화 설계 결과를 통하여 도출된 설계안은 고유진동해석을 통한 1차 모드 고유진동수(1st Mode Natural Frequency), 열전달해석을 통한 초저온 용기 내조 외조간 지지부를 통한 총전열량 및 열응력해석을 통한 최대 Von-Mises 응력이 모두 설계 목표치를 만족하였으며, 개발된 설계안에 따라 차량용 LNG 연료 용기의 제작하여 3차원 진동 시험과 단열성능 시험을 통해 설계를 검증하였다.

• Wind and Structures
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• 제21권6호
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• pp.625-639
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• 2015

Monopiles have been most widely used for supporting offshore wind turbines (OWTs) in shallow water areas. However, multi-member lattice-type structures such as jackets and tripods are also considered good alternatives to monopile foundations for relatively deep water areas with depth ranging from 25-50 m owing to their technical and economic feasibility. Moreover, jacket structures have been popular in the oil and gas industry for a long time. However, several unsolved technical issues still persist in the utilization of multi-member lattice-type supporting structures for OWTs; these problems include pile-soil-interaction (PSI) effects, realization of dynamically stable designs to avoid resonances, and quick and safe installation in remote areas. In this study, the effects of PSI on the dynamic properties of bottom-fixed OWTs, including monopile-, tripod- and jacket-supported OWTs, were investigated intensively. The tower and substructure were modeled using conventional beam elements with added mass, and pile foundations were modeled with beam and nonlinear spring elements. The effects of PSI on the dynamic properties of the structure were evaluated using Monte Carlo simulation considering the load amplitude, scouring depth, and the uncertainties in soil properties.