• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 추계학술대회 논문집 전기물성,응용부문
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• pp.19-21
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• 2002

Recently, it has become more competitive to take larger market share among domestic companies manufacturing high-power apparatus. Unfortunately, the size of total market in this field is being smaller than before because the business of transmission and distribution of electric power is being shifted from government control to private management. To save this situation, we are trying to develop new high-voltage Gas Insulated Switchgear for export such as 245kV GIS and 300kV GIS. It is very important to make GIS compact size to have international competitiveness against European companies. By reducing GIS's dimensions same as 170kV class, we expect to launch abroad successfully. Many factors should be considered to achieve good performance during short-circuit making-breaking. Analysis on cold gas flow is one method widely used to evaluate small-current interruption. Through this analysis, we can examine the dielectric characteristics at the weak points in the circuit-breaker. In this paper, we describe the results of cold-gas flow analyses on 245kV and 300kV circuit-breakers.

• 자원리싸이클링
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• 제11권3호
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• pp.17-24
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• 2002

There has been an increasing demand over the years for steels with lower[s] content. For the purpose of improving the efficiency of desulphrization in the powder injection process of ladle, experimental studies were carried out by using cold model to optimize the lance configuration, gas flow rate, immersion depth of lance nozzle, position of lance nozzle relative to the ladle and the effect with slag, etc. As the results of this study, it was made clear that 2-hole nozzle lance (C, E type) placed in an asymmetric position gives the shortest mixing times.

• 한국항공우주학회지
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• 제33권5호
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• pp.72-78
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• 2005

대기압 하에서 노즐목 직경이 1.0, 0.5, 0.25 mm인 마이크로노즐을 이용하여 성능시험을 하였다. 냉가스 추진제로는 질소를 사용하였다. 성능평가를 위하여 챔버내 전압력을 2~20 bar까지 변화시키면서 추력과 질유량을 측정하였다. 실험결과 압력이 낮아질수록 점성에 의한 손실이 크다는 것을 비추력을 비교해 봄으로써 알 수 있었다. 그리고 오리피스와 노즐의 추력 비교를 통해 노즐의 효율의 더 좋다는 것을 확인할 수 있었다.

• 한국산학기술학회논문지
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• 제11권1호
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• pp.55-60
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• 2010

고압의 가스를 이용하여 고온 가스와 저온 가스를 분리하거나 입자상 물질의 분리에 사용 할 수 있는 장치인 볼텍스 튜브의 에너지 분리 특성을 적용하여 자동차의 EGR Cooler 대체장치의 기본 설계 자료를 구축하기 위하여 실험을 수행하였다. 설계를 위한 기초 자료를 확보하기 위하여, 볼텍스 튜브의 입구 압력, 저온출구 및 고온출구압력 변화에 따른 에너지 분리 특성을 분석하였다. 공급압력이 상승할수록 에너지 분리 효과가 상승하였으며, 최고온도는 저온유량비가 약 0.85 에서, 최저온도는 저온유량비가 약 0.35 에서 발생하였다. 볼텍스 튜브의 고온측 출구온도는 고온측 및 저온측 출구압력에 영향을 받으며, 저온측 출구온도는 출구압력 변화에 독립적인 온도변화 특성을 나타내었다. 본 연구의 결과는 자동차의 EGR Cooler 대체장치의 기본 설계 자료로 응용될 수 있을 것이다.

• 한국가스학회지
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• 제12권4호
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• pp.21-28
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• 2008

삼지화염과 포와젤(Poiseuille) 및 균일분포 연료출구 속도에 따른 부상화염의 부상거동 그리고 화염면 부근에서의 연소 유동 특성에 대하여 수치적 해석을 수행하였다. 부상화염에 대한 수치해석으로 기존 연구 결과를 검정하고 화염대 부근에서 구조적 특성을 살펴보며 포와젤 및 균일분포 연료출구속도 조건에서 운동량 유속으로 부상높이를 일반화하여 비교하였다. 또한 화염면 부근에서 속도, 압력, 온도, 화학반응속도 등으로 연소 유동 특성을 분석하고 규명하였다. 특히 중심선을 따른 속도 변화의 경우 노즐에서 화염대 부근까지는 전형적인 비반응제트 유동에 따른 속도 분포를 형성하지만 화염대 직전에서 속도가 급격히 감소하다가 화염대를 지나면서 급격히 증가한 후에 다시 감소하는 현상을 규명하였다. 화염대 전의 유동영역에서는 화염대가 장애물역할을 하다가 화염대를 지나고 나면 유동을 가속시켜주는 역할을 하고 있기 때문이다. 이러한 현상은 기존의 비반응 제트 유동으로 규명하지 못하였던 것이다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1436-1441
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• 2004

The internal cooling passage of a gas turbine blade can be modeled as a ribbed channel. Most studies have considered square ribs. However, the ribs can be rounded due to improper manufacturing or wear during the operation. Hence, we have studied two different rib geometries in this study, i.e. square and semicircle ribs. We have performed large eddy simulations (LES) and experiments to validate the results from the simulations. LES predicts the detailed flow and thermal features, which have not been captured by simulations using turbulence models. By investigating the instantaneous flow and thermal fields, we propose the mechanisms for the local heat transfer distribution between ribs. For both the geometries, heat transfer is enhanced by the entrainment of the cold fluid by the vortical motions and impingement of the entrained cold fluid on the ribs.

• 한국군사과학기술학회지
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• 제14권6호
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• pp.1067-1072
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• 2011

If the flow of booster gas which is exhausted to the rear part of a canister is properly restricted in the canister of a hot-launch system, the resultant pressure built up in the canister provides additional force to accelerate the missile to a required launch velocity. These thrust augmentation performances can be controlled through the configuration design of baseplate orifices. In this paper, the simple technique to analyze the thrust augmentation performances of baseplate orifices is suggested and the thrust augmentation characteristics by its various configurations are compared. According to the initial displacement of a missile, the inner pressure of a canister is measured from scaled cold flow tests, and the discharge coefficient of baseplate orifices is calculated. Then the thrust augmentation in a canister is simulated by applying these discharge characteristics to the AMESIM software for launch dynamics.

• 한국해양공학회지
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• 제28권6호
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• pp.517-526
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• 2014

The leakage of cryogenic LNG through cracks in the insulation membrane of an LNG carrier causes the hull structure to experience a cold spot as a result of the heat transfer from the LNG. The hull structure will become brittle at this cold spot and the evaporated natural gas may potentially lead to a hazard because of its flammability. This paper presents a computational model for the LNG flow and heat diffusion in an LNG insulation panel subject to leakage. The temperature distribution in the insulation panel and the speed of gas diffusion through it are simulated to assess the safety level of an LNG carrier subject that experiences a leak. The behavior of the leaked LNG is modeled using a multiphase flow that considers the mixture of liquid and gas. The simulation model considers the phase change of the LNG, gas-liquid multiphase interactions in the porous media, and accompanying rates of heat transfer. It is assumed that the NO96-GW membrane storage is composed of glass wool and plywood for the numerical simulation. In the numerical simulation, the seepage, heat diffusion, and evaporation of the LNG are investigated. It is found that the diffusion speed of the leakage is very high to accelerate the evaporation of the LNG.

• Journal of Mechanical Science and Technology
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• 제20권12호
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• pp.2284-2291
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• 2006

The present study investigates gas residence time and mixing characteristics for various swirl numbers generated by injection of secondary air into a lab-scale cylindrical combustor. Fine dust particles and butane gas were injected into the test chamber to study the gas residence time and mixing characteristics, respectively. The mixing characteristics were evaluated by standard deviation value of trace gas concentration at different measurement points. The measurement points were located 25 mm above the secondary air injection position. The trace gas concentration was detected by a gas analyzer. The gas residence time was estimated by measuring the temporal pressure difference across a filter media where the particles were captured. The swirl number of 20 for secondary air injection angle of 5$^{\circ}$ gave the best condition: long gas residence time and good mixing performance. Numerical calculations were also carried out to study the physical meanings of the experimental results, which showed good agreement with numerical results.

• Corrosion Science and Technology
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• 제8권6호
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• pp.217-222
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• 2009

The production of advanced high strength steels requires the improvement of cooling technology. The use of high cooling rates allows relatively low levels of expensive alloying additions to ensure sufficient hardenability. In classical annealing and hot-dip galvanizing lines a mixing station is used to provide atmosphere gas containing 3-5% hydrogen and 97-95% nitrogen in the various sections of the furnace, including the rapid cooling section. Heat exchange enhancement in this cooling section can be insured by the increased hydrogen concentration. Drever International developed a patented improvement of cooling technology based on the following features: pure hydrogen gas is injected only in the rapid cooling section whereas the different sections of the furnace are supplied with pure nitrogen gas; the control of flows through atmosphere gas management allows to get high hydrogen concentration in cooling section and low hydrogen content in the other furnace zones. This cooling technology development insures higher cooling rates without additional expensive hydrogen gas consumption and without the use of complex sealing equipments between zones. In addition reduction in electrical energy consumption is obtained. This atmosphere control development can be combined with geometrical design improvements in order to get optimised cooling technology providing high cooling rates as well as reduced strip vibration amplitudes. Extensive validation of theoretical research has been conducted on industrial lines. New lines as well as existing lines, with limited modifications, can be equipped with this new development. Up to now this technology has successfully been implemented on 6 existing and 7 new lines in Europe and Asia.