• 해양환경안전학회지
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• 제23권1호
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• pp.104-111
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• 2017

본 연구는 원심펌프 내부 유동장 특성에 대한 시뮬레이션 및 시각화에 중점을 둔다. 3D 수치해석은 Reynolds Average Navier-stock 코드를 k-${\varepsilon}$ 표준 2차방정식 난류 모델로 처리하여 수행하였다. 시뮬레이션은 흡입측, 임펠러, 토출측 영역에서 조도로 인한 마찰 손실과 임펠러 웨어링에서 체적 손실을 포함한다. 해석과 실험사이의 성능곡선 비교결과 최대 5 %의 작은 차이를 보이며 동일한 추세를 나타냈다. 최고 효율점에서 속도 벡터는 고르게 나타났지만 비 설계점에서는 현저한 변화가 나타났고, 텅 부근의 임펠러 유로토출부에서 강력한 재순환 영역이 나타났다. 비교적 일정한 압력분포가 텅 부근임에도 불구하고 임펠러 주위에 관찰되었다. 볼류트 내에서 기하학적으로 인해 형성된 나선형 와류가 이 영역에서 유동장이 상대적으로 난류이고 불안정하다는 것을 증명하였다.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 동계학술발표대회 논문집
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• pp.469-474
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• 2008

The objective of this study is to propose basic design guidelines for more effective air ventilation system in apartments. It is well known that ventilation depends on whether the room doors are open or closed as well as people's living patterns. This study considers 84 ㎡-sized apartment which has extended living room without balcony. Ventilation of bathroom and kitchen is not considered. The height of the building, external air pressure and air infiltration through the windows are also neglected. The regulation on indoor air quality made it mandatory that the air change per hour be more than 0.7. Four models are suggested to study the effect of open and closed doors. Models 1 and 3 are open door types and models 2 and 4 are closed door types. The open types have 50 mm hole near the top of the door to substitute exhaust outlet. The ventilation effectiveness was evaluated by 3-dimensional numerical simulation using finite volume method by a commercial software. This work compares air flow, temperature of air, age of air and the efficiency of ventilation of apartments with wooden doors of bedroom 1 and 2, which are open or closed.

• 한국태양에너지학회 논문집
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• 제39권6호
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• pp.83-91
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• 2019

Photovoltaic thermal (PVT) collectors are devices that simultaneously produce electricity and heat. Research on conventional air-type PVT collector focuses on installing baffles to enhance the collector's thermal performance. However, the baffles have pressure drop inside the collector which degrades the thermal performance. Thus, it is necessary to design baffles to smoothen the flow inside the air-type PVT collector. Alternatively, installing perforated baffles in air-type PVT collectors can reduce the collector weight, but parameters such as the diameter of the perforated holes and the height of the perforated plates should be considered. Therefore, the main aim of this study was to analyze thermal characteristics of each variable of perforated baffles installed inside air-type PVT collector. For this purpose, the uniformity of air flow in the collector was compared through NX program, and the resultant heat gain and thermal efficiency of the air-type PVT collector were compared and analyzed. Therefore, the main aim of this study was to analyze thermal characteristics of each variable (Baffle angle, length, height, pitch, perforated ratio) of perforated baffles installed inside air-type PVT collector. For this purpose, the uniformity of air flow in the collector was compared through CFD program, and the resultant heat gain and thermal efficiency of the air-type PVT collector were compared and analyzed. As a result, the maximum outlet temperature was increased by 1.45 times and the heat gain was increased by 193.8 Wth, depending on the perforated baffle plate, compared to the collector without the baffle. The heat transfer performance showed that the maximum internal velocity was 1.61 times higher and the Reynolds number was 1.06 times higher depending on the parameters of the baffle plate.

• 한국수소및신에너지학회논문집
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• 제31권2호
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• pp.210-222
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• 2020

Hydrogen is evaluated as one of new energy sources that can overcome the limitations and pollution problems of conventional fossil fuels. Although hydrogen is free from CO₂, attention is required in NOx emission and flame stability in order to use hydrogen in existing gas fuel system. This study investigates the differences in operating characteristics and its problems to be modified when the hydrogen is used as fuel for existing domestic boilers and new heat recover boilers with water spray. When the hydrogen is used in domestic boilers, the efficiency is about 6-7% lower than methane due to higher partial vapor pressure in the exhaust gas at usual operating conditions above 60℃ in combustion chamber outlet temperature. On the other hand, the heat recovery boiler with water spray (HR-B/WS-X) is expected to achieve up to 95% efficiency, which is 12% more efficient than conventional boilers. It can also significantly reduce NOx emission by lowering the flame temperature.

• Journal of Biosystems Engineering
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• 제26권5호
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• pp.449-460
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• 2001

This study was carried out to develop a simulation model with EES(Engineering equation solver) for analyzing the performance of a grain cooler. In order to validate the developed simulation model, several main factors which have affected on the performance of the gain cooler were investigated through experiments. A simulation model was developed in the standard vapor compression cycle, and then this model was modified considering irreversibe factors so that the developed alternate model could predict the actual cycle of a grain cooler. The compressor efficiency in vapor compression cycle considering irreversibility much affected on the coefficient of performance(COP). The COP in the standard vapor compression cycle model was greatly as high as about 6.50, but the COP in an alternative model considering irreversibility was as low as about 3.27. As a result of comparison between the actual cycle and the vapor compression cycle considering irreversibility, the difference of pressure at compressor outlet(inlet) was a little by about 48kPa (8.8kPa), the temperatures of refrigerant at main parts of the grain cooler were similar. and the temperature of chilled air was about 8$\^{C}$ in both. The model considering irreversibility could predict performance of the grain cooler. The theoretical period required to chill grain of 1,383kg from the initial temperature 24$\^{C}$ to below 11$\^{C}$ was about 55 hours 30 minutes, and the actual period required in a grain bin was about 58 hours. The difference between the predicted and an actual period was about 2 hours 30 minutes. The cooling performance predicted by the developed model could well estimate the cooling period required to chill the grain.

• Journal of Chest Surgery
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• 제23권3호
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• pp.474-481
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• 1990

We have experienced 44 cases of coarctation of aorta in the age of infancy and children from April 1986 to September 1989 at Seoul National University Children`s hospital. Patients were thirty males and fourteen females, and their age ranged from one month to ten years[mean 23.84 $\pm$33.06 months] with thirty-two infant cases. In the infantile age, congestive heart failure was the most common chief complaint[18/32], and above that age, frequent upper respiratory infection was most common[8/12]. We experienced thirteen cases of isolated COA, twenty-two cases of COA with VSD, eight cases of COA with VSD, eight cases of COA with intracardiac complex anomalies and one case of COA with atrial septal defect. The associated intracardiac complex anomalies were three Taussig-Bing type double outlet right ventricle, one single ventricle, one transposition of great arteries, one atrioventricular septal defect, one hypoplastic aortic arch with left heart hypoplasia, and one Tetralogy of Fallot. Operative techniques of COA were twenty-three subclavian flap arterioplasty, 12 resection and end to end anastomosis, eight onlay patch angioplasty, and I direct angioplasty after resection of web. Among the cases with other cardiac anomalies, staged operation was done in twenty-nine patients, and single stage total correction was performed only in three patients. There were seven operative mortality[15.9%], all being in infantile age group, and among fourteen cases associated with large VSD[Qp/Qs>2.0, mean pulmonary arterial pressure>50mmHg], four patients were died, but there was no mortality in patients with small VSD. With above results, we are intended to discuss about the interval between staged operation, the fate of VSD after coarctoplasty in case of COA with VSD, causes of death, complications etc.

• 한국진공학회지
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• 제7권2호
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• pp.82-87
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• 1998

$O_2$기체에 $NH_3/O_2$기체를 첨가하여 실리콘 표면에 산화막을 형성하는 $NH_3/O_2$산화법 에 의한 산화공정시 반응석영관 외부에 방출하는 기체는 $N_2,O_2$및 $H_2O$이며 극소량의 $CO_2$, NO 및 $NO_2$가 검출되었다. 두 종류의 산화제($O_2$ 및 $H_2O$)가 산화에 기여하며 성장률은 $NH_3$및 $O_2$ 의 부분압과 온도에 의해 결정되며, 그 기울기는 건식 및 습식 산화법의 중간에 평행 하게 위치함을 확인하였다. Auger Electron Spectroscopy(AES) 측정결과 $NH_3/O_2$ 산화막은 정확한 $SiO_2$의 화학량론을 가지며 $SiO_2/Si$계면에 발생하는 결합을 억제하며 고정전하의 발 생을 최소화함을 알 수 있었다. $NH_3/O_2$ 산화막(470$\AA$)의 항복전압을 57.5Volt이며, C-V특성 곡선을 축정한 결과 플랫밴드 전압은 0.29Volt이며 곡선의 형태는 이상곡선과 일치하였다.

• 대한기계학회논문집
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• 제12권5호
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• pp.1158-1174
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• 1988

본 연구에서는 계단형 벽면조건을 없게 하기 위해서 비직교 좌표계(non-orth- ogonal coordinate system)를 사용하여 수치해석하였다. 비직교 좌표계를 이용한 수 치해석의 예는 Thompson등이 Laplace방정식 혹은 Poisson방정식을 해석함으로써 비직 교 격자망을 구성한 바 있고, Fahgri와 Asako는 대수적 비직교 좌표변환으로 유한차분 방정식을 유도하여 비정규경계면을 갖는 관로에서의 유동특성을 해석하였으며 이재헌 과 이상렬은 Fahgri와 Asako의 방법을 비정규경계면을 갖는 밀폐공간내에서의 자연대 류의 수치해석에 적용한 바 있다. 본 해석에서도 Fahgri와 Asako의 변환법으로 유한 차분방정식을 유도하였는데, 이 방법을 사용할 경우 확대관의 경사벽면을 계단형으로 만들지 않고 유한차분방정식을 유도할 수 있어서 계단형 벽면으로 인한 해의 오차를 제거할 수 있다. Fig.2는 본 해석에서 사용한 비직교 격자망을 나타낸다.

• 대한조선학회 특별논문집
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• 대한조선학회 2015년도 특별논문집
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• pp.50-55
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• 2015

Application of newly conceptualized Anti-Splash Devices designed for COT vent pipes were studied on a P/V valve located on the upper deck of an oil carrier vessel. Anti-Splash devices are used in the shipbuilding industry in order to avoid oil overflow and spray accidents caused by excess pressure and vacuum condition in the cargo oil tanks. These conditions are caused by the transverse and longitudinal sloshing forces that arise from ship motion during sea voyages. The main issue with existing Anti-Splash device model is flux at the outlet of the Anti-Splash Device, and so, new conceptual models for the Anti-Splash device were developed and compared to existing Anti-Splash device model using CFD analysis. Transient analysis was used to capture the flow and velocity of each model and a comparative analysis was performed between old and new-concept models. This data was used to determine the optimal design parameters in order to develop an optimized Anti-Splash Device. A Factory acceptance test was performed on the new-concept models in order to verify the performance and efficiency against their design requirements and other criterion. The final step performed was to apply the optimized Anti-Splash Device models for COT vent pipes to an actual vessel and verify performance through a seawater cargo operation during a sea voyage as per the ship owner's request. The patent for the aforementioned device was obtained by the Korean Intellectual property Office dated Dec. 18th,2014.

• 한국추진공학회지
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• 제22권6호
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• pp.64-71
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• 2018

가스터빈엔진의 탈설계점 운전 성능해석을 수행하기 위해서는 구성품의 성능 특성을 파악하는 것이 필수적이다. 본 연구에서는 가스터빈의 성능특성을 이해하기 위하여 마이크로 가스터빈엔진 성능시험 장치를 구축하였다. 구축된 마이크로 가스터빈 시험 장치를 이용하여 엔진의 회전수에 따른 유동장내의 온도와 압력 데이터를 수집하였으며, 수집된 실험 데이터를 이용하여 압축기 성능선도를 구성하였다. 터빈 출구부에서 배기가스를 포집하여 연소효율을 계산하였다. 구성된 압축기 성능선도와 연소효율을 GasTurb 성능해석 소프트웨어에 적용하여 지상 정지시의 탈설계점 성능해석을 수행하였고, 측정된 엔진성능데이터와 비교분석을 수행하였다.