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Calibration of the plate thermometer for measuring heat flux using a conical heater
한호식,윤홍석,황철홍 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.7
An experimental study was conducted on the calibration method and measurement error for a plate thermometer (PT) that can replace the heat flux gauge (HFG), which is generally used to measure heat flux. A conical heater included in the cone calorimeter (ISO 5660-1) was used. It is well known that this device can easily control heat flux and has excellent measurement reproducibility. Heat flux values between 10 and 50 kW/m 2 were considered and the heat flux calculated by PT was compared with the measurement result obtained using HFG. The major finding is that the gas temperature (T g ) required for the calculation of heat flux using the PT must be measured at the bottom of the sample and not in the vicinity of PT’s surface. This resulted in a significantly reduced relative error of approximately 5.3 % based on HFG. It was also confirmed that the conduction correction factor ( cond K ), which has the largest uncertainty in the calculation of the heat flux based on PT, was 8.6 W/m 2 ·K on average and the final relative error was significantly reduced to 1.4 % based on HFG. It is expected that the measurement error of the PT can be further improved by utilizing more specific heat flux range settings in the calibration process of the PT using a conical heater included in the cone calorimeter (ISO 5660-1).
화재시뮬레이션에서 입력변수 및 모델 불확실도가 고려된 허용피난시간(ASET)에 관한 연구
한호식,황철홍 한국화재소방학회 2019 한국화재소방학회논문지 Vol.33 No.3
To improve the reliability of a safety assessment using a fire simulation in domestic PBD, the evaluation method ofASET considering the uncertainties of the input parameters and numerical model of fire simulation was carried out. To thisend, a cinema and officetel were selected as the representative fire spaces. The main results were as follows. Consideringthe uncertainty of the heat release rate, which has the greatest effect on the major physical quantities presented in the lifesafety standard, significant changes in temperature, CO, and visibility occurred. In addition, when the bias factors reflectingthe uncertainty of the numerical model were applied, there were no significant changes in temperature and COconcentration. On the other hand, the visibility was increased considerably due to the low prediction performance of smokeconcentration in FDS. Finally, the reason why the physical quantity determining the ASET in domestic PBD is mainlyvisibility was discussed, and the application of uncertainty of the input parameters and numerical model in a fire simulationwas suggested for an accurate ASET evaluation. 국내 PBD에서 화재시뮬레이션을 이용한 안전성 평가의 신뢰성을 개선시키기 위하여, 화재시뮬레이션의 입력변수및 수치모델의 불확실도가 고려된 ASET의 평가방법에 대한 검토가 수행되었다. 이를 위해 영화관 및 오피스텔이검토 대상으로 선정되었다. 주요 결과는 다음과 같다. 인명안전기준에 제시된 주요 물리량에 가장 큰 영향을 미치는열발생률의 불확실도를 고려할 때, 온도, CO 및 가시도의 상당한 변화가 발생됨을 확인하였다. 또한 수치모델의 불확실도를 반영한 편향인자를 고려할 때, 온도 및 CO는 큰 변화가 없으나 FDS의 낮은 연기농도 예측성능으로 인하여가시도는 크게 증가됨을 알 수 있었다. 마지막으로 국내 PBD에서 ASET이 대부분 가시도에 의해 결정되는 원인이논의되었으며, 정확한 ASET 평가를 위해 화재시뮬레이션의 입력변수 및 수치모델의 불확실도 적용 방안이 제안되었다.
한호식,황철홍,오창보,최동원,이상규 한국화재소방학회 2018 한국화재소방학회논문지 Vol.32 No.3
Large Eddy Simulation (LES) 기반의 Fire Dynamics Simulator (FDS) Version(5와 6)에 따른 아격자 난류 및 연소모델의 변화가 헵탄 풀화재의 평균 화염높이에 미치는 영향이 검토되었다. 화재시뮬레이션을 위한 열발생률은 동일한조건에서 수행된 실험을 통해 제공되었으며, FDS Version에 따른 평균 화염높이의 예측성능은 기존 상관식과의 비교를 통해 평가되었다. FDS 5와 6에 각각 적용된 Smagorinsky 및 Deardorff 난류 모델은 평균 유동장, 화염형상 및 화염높이에 큰 영향을 주지 않는다. 그러나 평균 화염높이를 포함한 풀화재 특성 차이는 주로 FDS 5와 6에 각각 적용된혼합분율 및 Eddy Dissipation Concept (EDC) 연소모델 차이로 인하여 발생됨을 확인하였다. 마지막으로 FDS 6에 비해 FDS 5는 상당히 긴 화염높이의 예측결과를 제공하며, 기존 상관식과 보다 일치하는 평균 화염높이 예측이 가능함을 확인하였다. The effect of sub-grid turbulence and combustion models on the mean flame height in a heptane pool fire according tothe Fire Dynamics Simulator (FDS) version (5 and 6) based on Large Eddy Simulation (LES) was examined. The heat releaserate for the fire simulation was provided through experiments performed under identical conditions and the predictiveperformance of the mean flame height according to FDS version was evaluated by a comparison with the existing correlation. As a result, the Smagorinsky and Deardorff turbulence models applied to FDS 5 and 6, respectively, had no significant effectson the mean flow field, flame shape and flame height. On the other hand, the difference in pool fire characteristics includingthe mean flame height was due mainly to the difference in the mixture fraction and Eddy Dissipation Concept (EDC)combustion models applied to FDS 5 and 6, respectively. Finally, compared to FDS 6, FDS 5 provided the predictive resultof a significantly longer flame height and more consistent mean flame height than the existing correlation.