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구획화재에서 환기조건의 변화가 화재특성에 미치는 영향 (Part I: FDS의 성능평가)
황철홍,박충화,고권현,Andrew Lock 한국화재소방학회 2010 한국화재소방학회논문지 Vol.24 No.3
Experimental and numerical studies were conducted to investigate the thermal and chemical characteristics of heptane fires in a full-scale ISO 9705 room. Representative fire conditions were considered for over-ventilated fire (OVF) and under-ventilated fire (UVF). Fuel flow rate and doorway width were changed to create OVF and UVF conditions. Detailed comparisons of temperature and species concentrations between experimental and numerical data were presented in order to validate the predictive performance of FDS (Fire Dynamic Simulator). The OVF and UVF were explicitly characterized with distributions of temperature and product formation measured in the upper layer, as well as combustion efficiency and global equivalence ratio. It was shown that the numerical results provided a quantitatively realistic prediction of the experimental results observed in the OVF conditions. For the UVF, the numerically predicted temperature showed reasonable agreement with the measured temperature. The predicted steady-state volume fractions of O2, CO2, CO and THC also agreed quantitatively with the experimental data. Although there were some limitations to predict accurately the transient behavior in terms of CO production/consumption in the UVF condition, it was concluded that the current FDS was very useful tool to predict the fire characteristics inside the compartment for the OVF and UVF. 실규모 ISO 9705 표준 화재실에서 과환기화재 및 환기부족화재에 대한 열 및 화학적 특성에 관한 실험 및 수치해석 연구가 수행되었다. 과환기화재 및 환기부족화재의 발생을 위하여 연료 유량과 출입구의폭이 변화되었다. FDS(Fire Dynamic Simulator)의 화재현상 예측성능을 검토하기 위하여 실험과 수치해석에서 얻어진 온도 및 화학종의 농도에 대한 상세한 비교가 이루어졌다. 과환기화재 및 환기부족화재의전반적인 특성은 연소효율, 총괄당량비뿐만 아니라 고온 상층부에서 측정된 온도 및 화학종의 농도분포에의해서도 명확하게 구분되었다. 과환기화재에서 FDS는 온도 및 화학종의 농도에 관한 실험결과를 정량적으로 매우 잘 예측하였다. 반면에 환기부족화재의 경우, 시간 증가에 따른 CO2의 감소 및 CO의 증가와같은 비정상적 화학적특성의 예측에는 한계가 있음을 알 수 있었다. 그럼에도 불구하고 정상상태 구간의시간 평균된 온도 및 화학종의 농도는 실험결과를 적절히 잘 예측하였다. 위 결과로 부터 FDS는 과환기화재 및 환기부족화재의 특성을 예측하는데 매우 유용하게 활용될 수 있음을 알 수 있었다.
CH<sub>4</sub>/Air 예혼합화염의 하류영역에서 체류시간 및 열손실에 의한 NOx의 생성특성
황철홍,현승호,탁영조,이창언,Hwang, Cheol-Hong,Hyun, Sung-Ho,Tak, Young-Jo,Lee, Chang-Eon 대한기계학회 2007 大韓機械學會論文集B Vol.31 No.1
In this study, the NOx formation characteristics of one-dimensional $CH_4$/Air premixed flame using detailed-kinetic chemistry are examined numerically. The combustor length and the amount of heat loss are varied to investigate the effect of residence time and heat loss on the NOx formation in a post-flame region. In the flame region, NO is mainly produced by the Prompt NO mechanism including $N_2$O-intermediate NO mechanism over all equivalence ratios. However, thermal NO mechanism is more important than Prompt NO mechanism in the post-flame region. In the case of adiabatic condition, the increase of combustor length causes the remarkable increase of NO emission at the exit due to the increase of residence time. On the other hand, NO reaches the equilibrium state in the vicinity of flame region, considering radiation and conduction heat losses. Furthermore the NO, in the case of $\phi$=1.2, is gradually reduced in the downstream region as the heat loss is increased. From these results, it can be concluded that the controls of residence time and heat loss in a combustor should be recognized as an important NOx reduction technology.
CH<sub>4</sub>공기 제트 확산화염에서 CO<sub>2</sub> 첨가에 따른 단일 와동의 동적거동에 관한 연구
황철홍,오창보,이대엽,이창언,Hwang, Chul-Hong,Oh, Chang-Bo,Lee, Dae-Yup,Lee, Chang-Eon 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.9
The dynamic behaviors of the single vortex interacting with $CH_4-Air$ jet diffusion flame are investigated numerically. The numerical method is based on a predict-corrector scheme for a low Mach number flow. A two-step global reaction mechanism is adopted as a combustion model. Studies are conducted in fixed initial velocities for the three cases according as where $CO_2$ is added; (1) without dilution, (2) dilution in fuel stream and (3) dilution in oxidizer stream. A single vortex is generated by an axisymmetric jet, which is made by an impulse of a cold fuel when a flame is developed entirely in a computational domain. The simulation shows that $CO_2$ dilution in fuel stream results in somewhat larger vortex radius, and greater amount of entrainment of surrounding fluid than in other cases. Thus, the dilution of $CO_2$ in fuel stream enhances the mixing in single vortex and increases the stretching of the flame surface. The budgets of the vorticity transport equation are examined to reveal the mechanism of vortex formation when $CO_2$ is added. It is found that, in the case of $CO_2$ dilution in fuel stream, the vortex destruction due to volumetric expansion and the vortex production due to baroclinic torque are more dominant than in other cases.
STS 316L/A516-70N 클래드 판재의 용접방법에 따른 열영향부 형성과 기계적 물성 특성 평가 및 예측
황철홍,조명우,김선환,한두희,유경훈,김성웅,김영주,이상엽,박준식 대한금속·재료학회 2022 대한금속·재료학회지 Vol.60 No.12
Two welding methods of FCAW (Flux-cored arc welding) + FCAW, and FCAW + GTAW (Gastungsten arc welding) were compared to identify effective routes for STS 316L/A516-70N clad stainless steel. Since the welding speed of the FCAW + GTAW welding method is slower than that of the FCAW + FCAWwelding method, the amount of heat input is large, the size of the heat-affected zone formed is larger, andthe amount of angular deformation is also large. The microstructure and deformation of the weldingspecimens were investigated by computational simulation, and the results were compared with calculatedresults for actual specimens. The results were very similar, thus confirming the high accuracy of thecalculation. After measuring the hardness value of the actual welded specimens, the specimen welded by theFCAW + FCAW welding method was found to have a higher hardness value. The hardness of the weldedportion of the FCAW + GTAW specimen tests tended to remain at nearly the same value throughout thespecimen, indicating that the FCAW + GTAW hardness profile is desirable. In the computer simulation, buttwelding was used to set the optimal heat source conditions for the two welding methods, and the effect of heatformed during welding was confirmed using the thermal analysis results according to the conditions. Basedon the butt welding conditions, the residual stress and strain for the two welding methods are discussed, usingcalculations for the welding of C-seam (circumferential seam) and L-seam (longitudinal seam) used in themanufacture of pressure vessels.
황철홍,정영식,이창언,Hwang, Cheol-Hong,Jeong, Yeong-Sik,Lee, Chang-Eon 대한기계학회 2001 大韓機械學會論文集B Vol.25 No.4
The combustion characteristics of the hybrid catalytic(catalytic+thermal) combustor with a lean methane-air mixture on platinum catalyst were investigated numerically using a 2-D boundary layer model with detailed homogeneous and heterogeneous chemistries. for the more accurate calculations, the actual surface site density of monolith coated with platinum was decided by the comparison with experimental data. It was found that the homogeneous reactions in the monolith had little effect on the change of temperature profile, methane conversion rate and light off location. However, the radicals such as OH and CO were produced rapidly at exit by homogeneous reactions. The effect of operation conditions such as equivalence ratio, temperature, velocity, pressure and diameter of the monolith channel at the entrance were studied. In thermal combustor, the production of N$_2$O was more dominant than that of NO due to the relative importance of the reaction N$_2$+O(+M)→N$_2$O(+M). Finally the productions of CO and NOx by amount of methane addition were studied.
도로터널에서 자연풍에 의한 미세물분무의 화재제어 특성에 관한 수치해석 연구
황철홍,김한수,이창언,장영남,신현준 한국화재소방학회 2008 한국화재소방학회논문지 Vol.22 No.3
In this study, the fire suppression characteristics of a water mist with natural wind in a road tunnel were calculated using the FDS(Fire Dynamic Simulation) code. In addition, the cooling and the chemical kinetic effects of water vapor on fire extinction were investigated in a counterflow non-premixed flame using a detailed chemistry. As a result, the behavior of fire plume and the spray characteristics of water mist are modified remarkably with the increasing of wind velocity. In the case which is not the external natural wind, small droplets are more efficient in fire suppression than large droplets. However, the large droplets show better results on the fire suppression than the small droplets with the increasing of wind velocity. It can be estimated that the natural wind disturb the penetration of water droplets into the flame region and decrease the effect of oxygen dilution. Finally, it can be identified that the fire into the natural wind can be suppressed with smaller amount of H2O by flame stretching effect in the flame region than one in an enclosure, and the chemical kinetic effects of H2O on fire extinction are not affected significantly the velocity of natural wind. 본 연구에서는 FDS 코드를 이용하여 외부 자연풍에 의한 터널 내의 미세물분무 소화특성을 검토하였으며, 상세반응이 고려된 1차원 대향류 비예혼합화염을 이용하여 화염내부에서 미세물분무의 냉각 및 화학반응효과에 의한 소화현상을 규명하였다. 연구결과로서, 외부 자연풍의 유속 증가에 따라 고온 연기층의 분포 및 분무 특성의 큰 변화가 발생됨을 확인하였다. 외부 자연풍이 없는 경우에는 분무입자 직경이 작을수록 소화성능이 좋지만, 풍속이 증가함에 따라 입자직경이 클수록 소화성능이 좋아짐을 알 수 있었다. 자연풍은 입자의 화염면 침투를 방해할 뿐 아니라, 충분한 산소의 공급으로 화제 억제를 방해할 것으로 예측된다. 또한 자연풍이 존재하는 조건의 화염은 화염 신장효과에 의해 밀폐된 공간에서의 화염 보다 작은양의 H2O 침투에 의해서도 소화될 수 있으며, H2O의 화학반응에 의한 소화효과는 외부 자연풍의 유속에 크게 영향을 받지 않음을 확인하였다.