CH₄/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.

알루미나이드 확산코팅된 스테인레스 합금의 내산화 및 내삭마 특성

황철홍,이효민,오정석,황동현,황유석,이종원,최정묵,박준식,Hwang, Cheol Hong,Lee, Hyo Min,Oh, Jeong Seok,Hwang, Dong Hyeon,Hwang, Yu Seok,Lee, Jong Won,Choi, Jeong Mook,Park, Joon Sik 한국분말재료학회 (*구 분말야금학회) 2021 한국분말재료학회지 (KPMI) Vol.28 No.5

Stainless steel, a type of steel used for high-temperature parts, may cause damage when exposed to high temperatures, requiring additional coatings. In particular, the Cr₂O₃ product layer is unstable at 1000℃ and higher temperatures; therefore, it is necessary to improve the oxidation resistance. In this study, an aluminide (Fe₂Al₅ and FeAl₃) coating layer was formed on the surface of STS 630 specimens through Al diffusion coatings from 500℃ to 700℃ for up to 25 h. Because the coating layers of Fe₂Al₅ and FeAl₃ could not withstand temperatures above 1200℃, an Al₂O₃ coating layer is deposited on the surface through static oxidation treatment at 500℃ for 10 h. To confirm the ablation resistance of the resulting coating layer, dynamic flame exposure tests were conducted at 1350℃ for 5-15 min. Excellent oxidation resistance is observed in the coated base material beneath the aluminide layer. The conditions of the flame tests and coating are discussed in terms of microstructural variations.

반밀폐된 구획에서 발열량 변화에 따른 비정상 화재특성

황철홍 한국화재소방학회 2012 한국화재소방학회논문지 Vol.26 No.2

An experimental study was conducted to investigate the effects of change in heat release rate on unsteady fire characteristics of under-ventilated fire in a semi-closed compartment. A standard doorway width of the full-scale ISO 9705 room was modified to 0.1 m and the flow rate of heptane fuel was increased linearly with time using a spray nozzle located at the center of enclosure. Temperature,heat flux, species concentrations and heat release rate were continuously measured and then global equivalence ratio (GER) concept was adopted to represent the unsteady thermal and chemical characteristics inside the compartment. It was observed that there was a significant difference in unsteady behavior between global and local combustion efficiency, and the GERs predicted by ideal and measured heat release rate were also shown different results in time. The unsteady behaviors of temperature,heat flux and species concentrations were represented well using the GER concept. It was important to note that CO concentration was gradually decreased with the increase in GER after reaching its maximum value in the range of 2.0~3.0 of global equivalence ratio. In addition, the experimental data on unsteady thermal and chemical behaviors obtained in a semi-closed compartment will be usefully used to validate a realistic fire simulation. 반밀폐된 구획에서 발열량 변화에 따른 환기부족화재의 비정상 열 및 화학적특성에 관한 실험적 연구가수행되었다. 이를 위해 실규모 ISO 9705 표준화재실의 출입구 폭이 0.1 m로 축소되었으며, 구획 중앙에설치된 분사노즐을 통해 헵탄 연료의 유량은 선형적으로 증가되었다. 구획 내부의 온도, 열유속, 화학종농도 그리고 발열량의 연속적 측정이 이루어졌으며, 비정상 열 및 화학적특성을 표현하기 위하여 총괄 당량비의 개념이 적용되었다. 주요 결과로서, 총괄 연소효율과 구획 내부의 국부 연소효율은 시간에 따라 매우 다른 결과를 보이며, 이론과 측정된 발열량을 통한 총괄 당량비 역시 큰 차이를 보이게 된다. 온도,열유속 및 화학종 농도의 시간에 따른 변화는 총괄 당량비 개념를 통해 표현될 수 있었다. 구획 내부에서 CO의 농도는 총괄 당량비 2.0~3.0의 범위에서 최대값을 보이며, 보다 과농한 조건에서 점차적으로 감소되는 현상이 발견되었다. 추가로 본 실험을 통해 얻어진 반밀폐된 구획화재의 비정상 열 및 화학적 거동은 향후 현실적인 화재 모델링을 위한 검증 데이터로 활용될 수 있을 것으로 기대된다.

논단(論壇) : 제조물책임법(制造物責任法)의 력안(力案)과 그 대응방안(對應方案) 연구(硏究) -생산물배상책임보험(生産物賠償責任保險)의 활성화방안(活性化方案)을 중심(中心)으로-

황철홍 보험연구원 1990 보험금융연구 Vol.1 No.-

층류 CH₄/Air 예혼합화염의 하류영역에서 NO 농도 예측을 위한 열손실 모델의 검토

황철홍,이창언,금성민,이기만,신명철,김세원,Hwang, Cheol-Hong,Lee, Chang-Eon,Kum, Sung-Min,Lee, Kee-Man,Shin, Myung-Chul,Kim, Se-Won 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.7

One-dimensional modeling of $CH_4$/air premixed flame was conducted to validate the heat loss model and investigate NOx formation characteristics in the postflame region. The predicted temperature and NO concentration were compared to experimental data and previous heat loss model results using a constant gradient of temperature (100 K/cm). The following conclusions were drawn. In the heat loss model using steady-state heat transfer equation, the numerical results using the effective heat loss coefficient ($h_{eff}$) of $1.0\;W/m^2K$ were in very good agreement with the experiments in terms of temperature and NO concentration. On the other hand, the calculated values using the constant gradient of temperature (100 K/cm) were lower than that in the experiments. Although the effects of heat loss suppress NO production near the flame region, a significant difference in NO concentration was not found compared to that under adiabatic conditions. In the postflame region, however, there were considerable differences in NO emission index as well as the contribution of NO formation mechanisms. In particular, in the range of ${\phi}\;{\geq}\;0.8$, the prompt NO mechanism plays an important role in the NO reduction under the adiabatic condition. On the other hand, the mechanism contributes to the NO production under the heat loss conditions.

재일본조선인과학기술협회의 대북한 과학기술협력 경험

황철홍 과학기술정책연구원 2002 과학기술정책 Vol.- No.134

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.

다중구획에서 과환기화재 예측을 위한 CFAST의 성능평가

황철홍,박충화 大田大學校 産業技術硏究所 2013 산업기술연구소 論文集 Vol.24 No.1

For the application and validation of CFAST as a representative fire modeling program, the fire modeling was conducted to simulate the over-ventilated fire in well-confined and mechanically ventilated multi-compartments. The predictive performance of CFAST was evaluated through a comparison among CFAST results, experimental and FDS results. In particular, temperatures in the upper layer, height of smoke layer, major species such as O2, CO2 and CO were compared in details. These fire characteristics values by CFAST was predicted reasonably with in the range of 20% compared to the experimental data. Finally it was reconfirmed that CFAST can be applied as very useful fire modeling tool in terms of the computational cost with allowable numerical accuracy, even though CFAST provided higher numerical errors compared to FDS. 대표적인 화재모델링 프로그램인 CFAST의 활용 및 검증을 위하여, 강제 환기가 적용된 밀폐된 다중구획에서 과환기화재에 대한 화재모델링이 수행되었다. CFAST의 예측성능은 수치결과, 실험결과 및 FDS 수치결과의 비교를 통해 평가되었다. 특히 고온 상층부의 온도, 연층 높이 및 O2, CO2, CO와 같은 주요 화학종의 농도가 상세하게 비교되었다. CFAST는 이들 주요 화재특성 값들을 실험결과의 20% 범위 내에서 비교적 정확히 예측하고 있음을 확인하였다. 비록 FDS에 비해 큰 오차를 제공함에도 불구하고 허용될 수 있는 계산정확도와 계산비용측면에서 유용한 화재모델 툴로서 적용될 수 있음을 재확인하였다.

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.

하이브리드 촉매 연소기의 연소특성에 관한 수치적 연구

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.