• 한국유체기계학회 논문집
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• 제15권5호
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• pp.11-19
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• 2012

The main function of fuel cell manifold is to render reactants distribution as uniform as possible into a fuel cell stack. The purpose of this study is to numerically investigate the effects of stack manifold design on reactants distribution within a fuel cell stack. Four manifold designs with different manifold entrance shapes (expansion or diffuser) and different values of the extra width between the cell outer channel and manifold side wall are considered and applied to the fuel cell stack consisting of 50 cells. Since the fuel cell stack geometry involves several millions of grid points for numerical calculations, a parallel computing methodology is employed to substantially reduce the computational time and overcome the memory requirement. The numerical simulations are carried out and calculated results clearly demonstrate that both the manifold entrance shape and extra width have a substantial influence on manifold performance, controlling the degree of flow separation and entrance length for fully developed flow in the manifold channel. Finally, we suggest the optimum design of fuel cell manifold based on the simulation results.

• 한국분무공학회지
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• 제22권1호
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• pp.13-21
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• 2017

The fog screen is a device projecting the media to the aerosol flow field. As major parameters to generate dense and steady fog screen, shear stress, optical blockage ratio and SMD were obtained result through experiment. The micro droplet was generated by the piezo oscillation element, and the aerosol flow mixed with an air flow was sprayed into the vertical direction from the top of the fog screen through the 280 mm slot. For produce a dense, uniform fog screen, the shear effect, optical blockage ratio and SMD between aerosol and air curtain were measured. The minimum and maximum shear stress conditions were selected and it was confirmed that the optical transmission deviation of the aerosol flow field was small when the aerosol and air curtain flow rates were changed. When the aerosol and air curtain flow power were 18 V (1.51 m/s) and 24 V (2.55 m/s), respectively, under the condition of the minimum shear stress and laminar flow, the optical blockage ratios with the spray length were small, and it produced a most stable and high density uniform fog screen by injecting a constant of $10{\mu}m$ or less.

• 한국추진공학회지
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• 제9권1호
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• pp.9-16
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• 2005

제트베인은 로켓추진기관의 발사초기 자세제어와 조정 안정성의 확보를 위해 로켓노즐 출구부에 장착되어지며, 발사 수초 후까지 연소가스와의 접촉으로 인해 구동부를 가열시키고, 그 자체도 화학적 혹은 기계적으로 삭마된다. 본 연구는 제트베인의 열해석을 위한 기초연구로서 균일 초음속 유동장내에 위치한 단일 제트베인으로의 열전달 특성 해석을 수행하여 보았다. 경계층 적분법과 유한차분법의 연립해석이 이루어 졌으며, 벽근방에서 도출된 경계조건을 바탕으로 베인 내부의 비정상 열전도 해석도 수행되었다.

• 한국진공학회지
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• 제2권3호
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• pp.368-373
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• 1993

LCVD법에 의한 박막성장장치를 제작하였다. 제작한 CO2 레이저는 CO2 : N2 : He이 1 : 1 : 8로 혼합된 가스를 사용하였으며 최대 출력은 60W였고 혼합가스의 유량이 20l/min, 방전전류 40mAdlfEo 50W의 비교적 안정된 출력을 얻을 수 있었다. 반응실의 기초 진공은 1$\times$10-6torr였으며 레이저를 기판에 수직 혹은 수평으로 조사할 수 있도록 설계하였다. 제작된 장치로 SiH4 및 NH3를 재료로 하여 실리콘 및 quartz 기판위에 silicon nitride 박막을 증착하였다. 박막 생장시 가스를 흘리는 방식보다 가스를 채워놓고 하는 방식이 낮은 레이저 출력하에서 균일한 박막을 얻는데 효율적이라는 것을 발견하였다. 출력 55W의 레이저를 실리콘 기판에 5분간 조사하였을 때 최대 두께1.5$mu extrm{m}$의 박막을 얻었으며 quartz 기판위에는 출력 4W, 조사시간 6분에서 두께가 약 1$\mu\textrm{m}$인 비교적 균질의 박막을 얻을 수 있었다. FT-IR 및 XPS 분석 결과 SiH4와 NH3의 혼합비가 1 : 12일 때 비교적 nitride화가 잘 된 박막이 얻어졌음을 알았다.

• 설비공학논문집
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• 제27권9호
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• pp.491-496
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• 2015

Generally, the phase of the refrigerants that circulate in air-conditioning systems is repeatedly changed from liquid to gas and from gas to liquid. In vapor-compression refrigeration, the refrigerant at the inlet of the evaporator is in a gas-liquid two-phase state; therefore, to enhance the heat-transfer performance of the evaporator, the even distribution of the refrigerant across multiple passages of the evaporator is essential. Unlike the distribution of a single-phase refrigerant, multi-phase distribution requires further considerations. It is known that the multi-phase distribution at the outlet of the distributor is affected by factors such as the operating condition, the distributor's shape, and the insertion depth of the outlet pipes; here, the insertion depth of the outlet pipes is especially significant. In this study, for a cylindrical distributor with a 90-degree bend entrance and three outlet pipes, the flow uniformity at the outlet pipes was numerically tested in relation to variations of the insertion depth of the outlet pipes.

• 설비공학논문집
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• 제10권3호
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• pp.282-291
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• 1998

Heat transfer performance are studied for the turbulent flow of water in 3 smooth tube coils having ratios of coil to tube diameter of 16, 21 and 27, and a corrugated-coiled tube having a ratio of coil to tube diameter of 29, for Reynolds numbers from 8000 to 60000 and is also compared with the limited results available to data. The experiments are carried out for the fully developed turbulent flow of water in tube coils under the condition of uniform heat flux. This work is limited 0 tube coils of R/a between 10 and 30. The tube having a ratio of coil to tube diameter of 27 among the 3 smooth tube coils shows the best heat transfer performance. The performance of coiled tube best transfer performance. The performance of coiled tube with a similar curvature ratio is better for a corrugated-coiled tube(R/a=17) than for a smooth coiled tube(R/a=16). An empirical relation which correlates most of the data within $\pm$25% was also developed. Test result shows that the Nusselt number is found to be affected by a secondary flow due to curvature.

• 한국식품과학회지
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• 제10권1호
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• pp.16-26
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• 1978

UVSL-25 mineralight를 조사(照射)한 경우에 발생하는 식품자체(食品自體)의 형광(螢光)을 이용하여 Adulteration이나 변질(變質)에 의한 불량식품(不良食品)을 감별(鑑別)할 수 있는 방법확립(方法確立)을 시도(試圖)해 보았다. 형광(螢光)의 육안관찰(肉眼觀察) 및 표면발광(表面發光)의 스펙트럽분석(分析)은 본 실험조건(實驗條件)하에서는 식품감별방법(食品鑑別方法)으로 부적당하게 보였다. 유동(流動)파라핀에 현탁(懸濁)된 분말물질(粉末物質), 또는 액체(液體) 시료(試料)의 흡수(吸收) 및 발광(發光)스펙트럼은 식품(食品)의 종류에 따라 특징적인 패턴을 나타냈다. 재현성(再現性)있는 실험결과(實驗結果)를 얻기위해서는 시료(試料)의 균일성(均一性)이 가장 중요한 요인으로 보였다.

• 한국수소및신에너지학회논문집
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• 제30권6호
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• pp.585-592
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• 2019

In this study, a flashing boiling phenomenon of pressurized water jet was numerically studied and validated against an experimental data in the literatures. The volume of fluid (VOF) technique was used to consider two-phase behavior of water, while the homogeneous relaxation model (HRM) model was used to provide the velocity of phase change. During the flashing boiling through a nozzle, a mach disk was observed near nozzle exit because of pressure drop resulting from two-phase under-expansion. The flashing jet structure, local distributions of temperature/vapor volume fraction/velocity, and position of the mach disk were examined as nozzle inlet temperature changed.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제36회 춘계학술대회논문집
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• pp.253-257
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• 2011

고체로켓에서 발생하는 vortex shedding 현상 중 인히비터로 인해 발생하는 연소실내 와류(vortex)의 특성을 조사하기 위해 Large Eddy Simulation을 수행하였다. 해석의 결과는 기존 연구자들의 결과와 잘 일치하며 정략적 및 정성적 분석을 수행하였다. 인히비터 후방에서 발생하는 vortex는 Flow-acoustic coupling 에 의해 주기적으로 반복되며 생성, 소멸이 이루어지는 것을 확인 할 수 있었으며, 발생 주기는 연소실내 mode 2의 주파수와 일치하는 것을 확인하였다. 3차원 해석결과 인히비터 후방에서 Roll 발생은 비균일한 노즐 유동을 발생시킨다.

• 설비공학논문집
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• 제20권6호
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• pp.416-426
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• 2008

The boiler tube failure often experienced in the superheater of a utility boiler can seriously affect the economic and safe operation of the power plant. It has been known that this failure is mainly caused by the thermal load deviation in the superheater tube system, and deeply intensified by the non-uniform distribution of steam flow rates. The nonuniform steam flow is distinctively prominent at low power load rather than at full power load. In this paper, we analyze the steam flow distribution in the superheater tube system by using one dimensional flow network model. At 30% power load, the deviation of steam flow rate is predicted to be within 0.8% of the averaged flow rate. This deviation can be reduced to 0.1% and 0.07% by assuming two cases, that is, the removal of 13th tube at each tube rows and the installation of intermediate header, respectively. The assumed two cases would be effective for the uniform steam flow distribution across 85 superheater tube rows.