• 대한기계학회논문집B
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• 제23권8호
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• pp.1040-1047
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• 1999

The characteristics of flame propagation in inert particle-laden $H_2$/Air premixed gas are numerically investigated on this study. The 2nd order TVD scheme is applied to numerical analysis of governing equations and multi-step chemical reaction model and detailed transport properties are sued to solve chemical reaction terms. Radiation heat transfer is computed by applying the finite volume method to a radiative transfer equation. The burning velocities against the mole fractions of hydrogen agree well with results performed by different workers. The inert particles play significant roles in the flame propagation on account of momentum and heat transfer between gas and particles. Gas temperature, pressure and flame propagation speed are decreased as the loading ratio of particle is increased. Also the products behind flame zone contain lots of water vapor whose absorption coefficient is much larger than that of unburned gas. Thus, the radiation effect of gas and particles must be considered simultaneously for the flame propagation in a mixture of $H_2$/Air and inert particles. As a result, it is founded that because the water vapor emits much radiation and this emitted radiation is released at boundaries as radiant heat loss as well as reabsorbed by gas and particles, flame propagation speed and flame structure are altered with radiation effect.

• 전기학회논문지
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• 제63권11호
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• pp.1575-1581
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• 2014

In this paper, eddy current loss, iron loss and heat transfer of PMSG with 2,000kW capacities were analyzed for wind turbine. The PMSG with 3 split magnet was analyzed using ansoft maxwell commercial program and, generator was tested by Back to Back converter with no load condition at laboratory. Rotor surface temperature was measured by Pt100 sensors for investigating heat transfer from rotor to atmosphere. The simulation results shows 27.4kW eddy current loss in no load condition and 50.2kW eddy current loss in rated load condition with 3 split magnet, and also shows 4.3kW iron loss in no load condition and 7.3kW iron loss rated load condition. The heat transfer coefficient of convection between rotor surface and atmosphere was investigated by $9.6W/m^2{\cdot}K$. Therefore the heat transfer from rotor to atmosphere was about 17kW(54%) and from rotor to air-gap was about 14.6kW(46%) in no load condition. It is identified that the cooling system for stator have to include the 46% of iron loss, and heat dissipation structure of rotor surface have to be suggested and designed for efficiency improvement of generator.

• 대한기계학회논문집
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• 제13권2호
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• pp.265-270
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• 1989

본 연구에서는 복사강도를 반구에 대하여 적분하여 비정상 미분방정식의 형태로 로 얻어지는 2-유속 회매질복사모델을 사용하여 복사전달방정식을 구성하고, 전술한 Yoshizawa 등의 가정을 배제하면서, 다공매질의 물리적 길이, 흡수계수 및 혼합기체의 당량비(equivalenceratio) 등을 변화시킴으로써 매질 내의 열적 구조를 분석하여 그들의 의 연구를 확장, 해석한다.

• Nuclear Engineering and Technology
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• 제51권7호
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• pp.1749-1757
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• 2019

Predicting lower flammability limits (LFL) of hydrogen has become an ever-important task for safety of nuclear industry. While numerous experimental studies have been conducted, LFL results applicable for the harsh environment are still lack of information. Our aim is to develop a calculated non-adiabatic flame temperature (CNAFT) model to better predict LFL of hydrogen mixtures in nuclear power plant. The developed model is unique for incorporating radiative heat loss during flame propagation using the CNAFT coefficient derived through previous studies of flame propagation. Our new model is more consistent with the experimental results for various mixtures compared to the previous model, which relied on calculated adiabatic flame temperature (CAFT) to predict the LFL without any consideration of heat loss. Limitation of the previous model could be explained clearly based on the CNAFT coefficient magnitude. The prediction accuracy for hydrogen mixtures at elevated initial temperatures and high helium content was improved substantially. The model reliability was confirmed for $H_2-air$ mixtures up to $300^{\circ}C$ and $H_2-air-He$ mixtures up to 50 vol % helium concentration. Therefore, the CNAFT model developed based on radiation heat loss is expected as the practical method for predicting LFL in hydrogen risk analysis.

• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2008년도 춘계학술발표대회 논문집
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• pp.227-232
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• 2008

Stirling engine for solar thermal power is an essential part of Dish-Stirling system which generates electricity by using direct normal irradiation and will go into commercialization in near future. For the Stirling engine used in this study is Solo 161 model the capacity of which is 10 kWe and was already used for the Dish-Stirling system of KIER in Jinhae. The receiver of Stirling engine absorbes concentrated solar radiation and transfer it to working fluid of Hydrogen. The working condition of striling engine is high temperature and high pressure to make high efficiency. Therefore the receiver should stand against high temperature of above 800 $^{\circ}C$ and high pressure of max. 150 bar with good performance of heat transfer. The receiver is composed of 78 Inconel tubes of 1/8" with thickness of 0.71 mm and two reserviors which is connected with two cylinders. In order to know the charaterristics of heat transfer of Stirling engine receiver, simulation on the heat transfer of the receiver of Solo 161 is conducted by using CFD code of Fluent. The heat flux on the receiver surface has a shape of Gaussian distribution so, it is necessary to simulate a whole receiver. However, It is difficult and time consuming to simulate the whole receiver that one tube with different heat flux conditions are considered in this study. From the simulation results, heat transfer charateristics of receiver are observed and tube wall and fluid temperature and heat transfer coefficient are obtained and compared with the calculated results from Dittus-Boelter's correlation.

• 한국산업융합학회 논문집
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• 제6권1호
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• pp.65-71
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• 2003

Infrared heating has been traditionally used in industrial applications for processes such as dehydration of food industrial. This heating method involves the application of radiation in the wavelength range of 5~50 micrometers. In this work, simultaneous heat balance equations were developed to simulate the infrared radiation heating of red peppers. The equations assume that moisture diffuses to the outer boundaries of the material in liquid form and evaporation occurs at the surface of the red peppers. Energy for moisture evaporation is supplied by the infrared radiant energy. The equations were validated with experimental data on surface temperature and average moisture content of red peppers. Average deviations of predicted surface red peppers temperature and average red peppers moisture from experimental data were 323~353K and 50~80%, respectively. The spectral extinction coefficients in the wavelength range $1.5<{\lambda}<27$ micrometer at 293K for Red Peppers were determined from results of reflection measurements and the four flux radiative heat transfer calculation. The radiation extinction coefficients were obtained from effective drying factor the temperature 373K.

• 항공우주기술
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• 제8권1호
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• pp.17-25
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• 2009

복사전달식에서 흡수 계수의 정확한 계산은 액체 엔진 저부의 단열재 설계의 입력 값으로 사용되는 플룸의 복사 열전달을 예측하는데 매우 중요하다. 이를 위해서 가스 흡수 계수를 직접 모델링 할 수 있는 WNB 모델을 중요 인자의 선정을 위주로 설명하였고, 그 결과를 비교적 정확한 기준 값을 제공하는 SNB의 결과와 비교하였다. 비교 인자들은 총 방사율, 좁은밴드 복사강도 및 총 복사강도이며, 결과적으로 방사율의 경우 주어진 조건에서 3.1% 이내, 총 복사 강도역시 5%이내의 계산결과를 보여 이 모델의 타당성을 확인할 수 있었다. 추가적으로, 액체 엔진의 연소가스들의 성분비를 예측하고 이 조건에 대한 가스모델링 인자를 계산하여 데이터베이스를 구축하였다.

• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2008년도 추계학술발표대회 논문집
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• pp.190-195
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• 2008

The objective of this research is to determine overall heat transfer coefficients (K-value) of exterior wall, floor, and roof of Nakseonjae, a Korean traditional residence via field measurement of transient heat flow and temperature difference across each envelope component. Heat flow sensors and T-type thermocouple were attached on the internal and the external surface of each building component, and real-time measurement data were collected for the three consecutive summer days. The K-values determined in this research showed good agreement with other results from open literature. Peak and annual thermal loads of the traditional residence estimated by a commercial energy simulation program were compared with those for a current apartment house. The traditional house showed lower annual cooling load than that of the current building. It may caused by the fact that the traditional building has less air-tight envelopes and no fenestration passing direct solar radiation into the space.

• 대한기계학회논문집
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• 제19권9호
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• pp.2353-2364
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• 1995

The ignition phenomena of a solid fuel plate of polymethyl-methacrylate(PMMA), which is vertically positioned and exposed to a thermal radiation source, is numerically studied here. A two-dimensional transient model includes such various aspects as thermal decomposition of PMMA, gas phase radiation absorption, gas phase chemical reaction and air entrainment by natural convection. Whereas the previous studies considers the problem approximately in a one-dimensional form by neglecting the natural convection, the present model takes account of the two-dimensional effect of radiation and air entrainment. The inert heating of the solid fuel is also taken into consideration. Radiative heat transfer is incorporated by th Discrete Ordinates Method(DOM) with the absorption coefficient evaluated using gas species concentration. The thermal history of the solid fuel plate shows a good agreement compared with experimental results. Despite of induced natural convective flow that induces heat loss from the fuel surface, the locally absorbed radiant energy, which is converted to the internal energy, is found to play an important role in the onset of gas phase ignition. The ignition is considered to occur when the rate of variation of gas phase reaction rate reaches its maximum value. Once the ignition takes place, the flame propagates downward.

• 한국강구조학회 논문집
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• 제9권3호통권32호
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• pp.431-440
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• 1997

본 논문에서는 교량 단면 내의 시간 종속적 온도 분포를 결정하기 위해, 기존의 열 전달 이론 및 태양 에너지 전달에 대한 이론을 바탕으로 기상관측소 및 현장에서 측정한 기상 자료로부터 교량 온도의 예측에 관한 이론적 모델에 대해 기술하였다. 특히 이 모텔에서는 주간에 교량의 온도 상승에 지배적인 영향을 미치는 태양일사(solar radiation)에 대해 태양 에너지 관련 분야의 여러 실험적 연구 결과를 바탕으로 태양일사량의 계산에 대해 기존에 연구되어 있는 식들 중에서 가장 적합한 식을 제시하였다. 이 해석 모델의 타당성은 사당 고가차도의 장기 계측된 온도 측정 결과와 비교 검토되었다. 또한 장기간 측정된 온도 결과로부터 교량 온도 예측에 대한 해석적 기준(analytical criteria)을 제시하기 위해, 교량의 축 방향 신축의 원인이 되는 단면평균온도, 그리고 곡률 변형을 유발하는 단면온도차 등 교량 단면의 온도 분포와 관련된 변수들과 대기온도, 일사량 등 기상 자료와 관련된 변수들 간의 선형 상관관계(linear correlation)에 대해 기술하였다.