• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2011.11a
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• pp.298-301
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• 2011

본 연구에서는 지하 방호공간에서 화재가 발생한 경우 워터커튼 시스템에 의한 연기의 차단효과와 화재제어 특성을 분석하였다. 이를 위해서 분사각도 $180^{\circ}$, 오리피스 직경 8.2 mm의 노즐과 지하방호 공간용 실화재 실험 장치를 제작하였으며, 화재강도 1.5 MW 기준 A급 1단위 화재 실험으로부터 온도분포와 가시도를 측정하여 연기의 차단효과를 확인하였다. 화재제어 특성을 분석하기 위해서 NIST(National Institute of Standards and Technology)의 해석프로그램인 FDS(Fire Dynamic Simulator)를 사용하여 동일한 실험조건에서 온도분포를 비교하였으며 노즐의 설치개수 변화에 대한 화재해석 및 실험결과로부터 워터커튼 시스템은 노즐의 설치위치와 개수, 화원으로부터의 거리, 제연 등의 설비 조건과 분사 노즐의 특성, 공급 유량 등이 중요한 상관관계를 갖고 있음을 확인하였다.

• Journal of ILASS-Korea
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• v.22 no.4
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• pp.159-168
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• 2017

Numerical studies on the spray characteristics of closed-type and open-type swirl injectors were conducted using ANSYS Fluent. By changing injection pressures, discharge coefficient and spray angle were calculated using the Reynolds stress BSL turbulent model. The numerical results were compared with previous experimental data to examine their accuracy. For a closed-type swirl injector, spray angles matched well with experimental results and discharge coefficients showed approximately 8% differences. On the contrary, discharge coefficients of an open-type swirl injector were similar with experimental result but its spray angles presented around 15% differences. Though the numerical results were not perfectly consistent with experimental data, it is thought that they could be sufficiently used for analyzing spray characteristics, specially which is hard to be measured from experiments. Numerical simulation with different turbulent models was also performed to examine their effects on the numerical results.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05a
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• pp.571-576
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• 1998

고온의 증기가 과냉각 상태의 물과 직접접촉에 의해 발생하는 응축현상(DCC Direct Contact Condensation)을 실험적으로 고찰하였다. 본 연구는 두단계로 나누어 수행하였다. 1단계 연구에서는 간단한 원형관 형태의 수평 노즐을 통하여 증기제트가 대기압 상태의 과냉각수로 분출될 때 증기제트 및 주위의 거동을 측정·분석하였다. 수조의 온도와 증기유량의 변화에 따른 증기제트의 축방향과 반경방향 온도분포와 수조 벽면에서의 동압을 측정하였으며, 고속 비디오 카메라를 사용하여 각각의 경우에 대하여 증기제트의 분출이미지를 촬영하였다. 벽면에서의 동압은 노즐의 분출구직경과 응축수의 온도에 비례하여 증가하였다. 2단계 연구에서는 몇가지 형태의 증기분사기 축소 모형에 대한 응축성능을 비교하였다. 이때에는 수조의 온도상승으로 인해 수조가 가압되는 정도를 알아보기 위해 수조를 밀봉한 상태로 실험을 수행하였다. 실험시 수조의 압력은 시간의 경과에 따라 계속적으로 증가하였으나, 이는 방출된 증기의 불완전한 응축에 의한 것은 아니고 증기의 분출과 응축으로 인한 응축수의 부피팽창과 수조 온도의 상승으로 인한 증기압의 상승 때문인 것으로 판단된다.

• Journal of ILASS-Korea
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• v.23 no.2
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• pp.49-57
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• 2018

Numerical study under single-injection on bi-swirl coaxial injectors with different recess lengths was performed using ANSYS Fluent. The bi-swirl coaxial injectors which consisted of inner closed-type and outer open-type swirl injectors, had three different recess lengths. By changing mass flow rates, numerical simulation was repeated using the Reynolds stress BSL turbulent model. The numerical results such as discharge coefficient and spray angle were compared with previous experimental data and were found to be approximately matched well with them, irrespective of recess length. Quantitative data which was hard to be measured from experiments, were successfully obtained through the present numerical study.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.2
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• pp.61-66
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• 2011

The purpose of this paper is to design a hydraulic actuator to operate under high pressure conditions. The flow characteristics under design conditions of hydraulic actuator were numerically conducted by commercial fluid dynamic code(ANSYS CFX V11). The numerical analysis was performed by transient technique according to the variation of stroke times, which was changed from 0 to 1 second by interval of 0.01. Turbulence model, $k-\omega$ SST was selected to secure more accurate prediction of hydraulic oil flow. The ICEM-CFD 11 and CFXMesher, reliable grid generation software was also adapted to secure high quality grid necessary for the reliable analysis. According to the simulation results, the flow rate which was supplied to the hydraulic actuator was 30.4l/min. These results are in good agreement with design results within 3.5% error.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1998.04a
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• pp.27-27
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• 1998

연구소기내에서 원활한 연소를 위하여 액체의 균일하고 완전한 미소분열 문제는 매우 중요한 연구분야라 할 수 있으며, 특히 항공기용 가스터빈 연소기에 사용되는 분사 시스템의 설계시에는 단순한 미소분열 문제뿐 아니라 시동성 향상, 화염의 안정화, 공해물질의 저감 등은 물론 압력 차가 작고 유량범위가 넓으며 공기를 이용한 미립화(Atomization)의 효율이 낮은 영역, 즉, 시동(Start-up) 및 플레임 아웃(Flame-out)근처의 영역에서도 효율적인 미립화가 이루어지도록 고려되어져야 한다.

• Journal of ILASS-Korea
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• v.24 no.1
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• pp.27-34
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• 2019

An experimental study on the spray characteristics of aerated-liquid jets discharged from effervescent injectors to a subsonic crossflow was conducted to investigate effects of a gas to liquid mass ratio (GLR) and a ratio of the orifice length to the diameter (L/d). The present effervescent injectors consist of a plain orifice injector and an aerator. To analyze breakup length and spray trajectory, instantaneous spray images were taken by a high speed camera. As the GLR increased, the spray penetration became higher under the same liquid mass flow rate and the breakup length became shorter due to the bubble expansion or the annular liquid film breakup. To predict the spray trajectory of two-phase flow jets into the crossflow, the homogeneous and the separated flow models were compared.

• Journal of ILASS-Korea
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• v.27 no.3
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• pp.144-154
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• 2022

Gas injection is a technique applied to improve throttling in liquid rocket engines and atomization in effervescent injectors. When a gas is injected into a liquid, it creates a two-phase flow inside the injector. The changes (bubbly flow, slug flow, annular flow, etc.) in the two-phase flow affect the injector's spray characteristics. In this study, cold-flow tests were performed by using three injectors with different orifice diameters and four aerators with different gas injection hole diameters. The experiments were done by changing the thrust ratio (liquid mass flow rate ratio) and gas-liquid mass flow rate ratio. Two-phase flow transition, breakup length, and discharge coefficient according to the injector/aerator design and flow conditions were investigated in detail.

• Journal of the Korean Society of Propulsion Engineers
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• v.2 no.2
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• pp.24-29
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• 1998

An experimental study was carried out to investigate the characteristics of spray pattern such as discharge coefficient, spray angle, and mass distribution for two-fluid airblast swirl injector, within the range of fluid supply pressure 0~13kg/$\textrm{cm}^2$. In general atomization is promoted with increasing total gas mass flow and performance of the splay pattern was more stable when radial mass flow was greater than axial mass flow, radial swirler was better than Axial swirler for atomization. Equivalent spray angle did not change with water mass flow except for the condition of 3kg/$\textrm{cm}^2$ and showed the same for the gas mass flow. Mass distribution from the patternator shows that maximum value of the distribution were lowered but distributed larger area when gas flow rate increased. Center of mass position did not change with increasing water mass flow.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.1
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• pp.22-27
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• 2017

$TiO_2$ films, thickness of $1{\sim}30{\mu}m$ were deposited on glass substrate at room temperature by room temperature granule spray in vacuum. The starting powder was calcinated at $600^{\circ}C$ for 4 h using $Al_2O_3$ crucible in the furnace. The particle size of the $TiO_2$, $1.5{\mu}m$ was measured by a particle size analyzer. The effect of different process parameters such as number of pass, gas flow rate and feeder voltage was studied. As the number of passes increased, the film thickness increased proportionally due to adequate kinetic energy conserved. The effect of three different flow rates (i.e. 15, 25, and 35 LPM) on deposited film was investigated. As gas flow rate increased, the film thickness increased up to 25 LPM and then decreased. Higher feeder voltage with low flow rate of 15 LPM resulted in unsufficient coating thickness due to insufficient kinetic energy. Microstructure of $TiO_2$ films was investigated by scanning electron microscope and high resolution tramission electron microscope.