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수직평행채널의 벽면에 부착된 단일모듈로부터의 3차원 자연대류 열전달
유갑종(K.J.Riu),이진호(J.H.Lee),김현우(H.W.Kim) 한국태양에너지학회 1999 한국태양에너지학회 논문집 Vol.19 No.3
본 연구에서는 돌출된 단일 모듈이 부착된 수직 채널내의 3차원 자연대류 특성을 실험적으로 조사하였으며, 특히 모듈로부터 대류에 의한 열에너지 제거에 초점을 두었다. 채널내의 유동장은 smoke-method를 이용하여 가시화 하였다. 또한 채널내부, 수직벽면 및 모듈표면의 국소온도를 열전대와 열플럭스 센서를 이용하여 측정하여 복사와 전도에 의한 열손실량을 계산하였다. 실험결과 대류열전달은 모듈 하부의 모서리 부근에서 가장 활발히 일어나고, 모듈 상부에서의 재순환영역은 열전달을 감소시킴을 알 수 있으며 임계 채널간격비를 예측할 수 있는 상관식을 레일리히수의 함수로 구하였다. 또한 8.28*10³<Ra^*_c<3.48*10^6의 범위에서 수정 채널 레일리히수의 함수로써 평균 누셀트수와의 상관식을 구하였다. Three-dimensional natural convective heat transfer in a vertical channel with a protruding single module was investigated experimentally. The particular interest was in the removal of thermal energy from the module by convective heat transfer. Hence radiative and conductive heat losses were estimated by using thermocouples and heat flux sensor respectively. The flow fields in the channel were visualized by means of a smoke-method. Also, local temperatures were measured by thermocouples inside the channel, along the vertical wall and module surface. It is found that convective heat transfer was promoted at the lower comer of the module and was decreased at the upper comer due to a recirculation zone. A general correlation of the critical channel ratios was found as a function of Rayleigh number. For the range of 8.28*10³<Ra^*_c<3.48*10^6, a useful correlation for the mean Nusselt number was proposed as a function of modified channel Rayleigh number.
최대밀도점 부근의 물 속에 잠겨있는 수직 등온 강선에 의한 자연대류
엄용균,유갑종,Eom, Y.K.,Riu, K.J. 대한설비공학회 1996 설비공학 논문집 Vol.8 No.3
A numerical analysis is carried out to study the two-dimensional steady state natural convection from vertical wires immersed in cold pure water. The surface of the wire is $0^{\circ}C$ unifrom temperature. Results of the analysis are presented for free stream temperature from $0^{\circ}C$ to $25^{\circ}C$ and the aspect ratio N from $5.26{\times}10^{-3}$ to $1.0{\times}10^{-3}$. The effects of the density extremum and aspect ratio on the flow pattern and the heat transfer characteristics are discussed As the aspect ratio N becomes larger, in the range of $1.0^{\circ}C{\leq}T_{\infty}{\leq}4.4^{\circ}C$ and $6{^{\circ}C}{\leq}T_{\infty}{\leq}17^{\circ}C$, the effect of Pr number on the heat transfer is shown to be more significant than the aspect ratio. Investigating into the effect of the density extremum on the heat transfer from wires, the new heat transfer correlations are suggested with the relation of average Nu mumber vs. modified Ra number. Here, the coefficient values C of correlations are presented as the function of density extremum parameter $R^*$. The effects of the density extremum parameter are also discussed.
공기공급 시스템에 적용되는 Vortex Tubes 의 에너지 분리특성에 관한 연구(2) : 표면의 단열효과에 따른 영향 the effect of surface insulation
추홍록,유갑종,방창훈 한국산업안전학회 1999 한국안전학회지 Vol.14 No.1
The vortex tube is a simple device which splits a compressed gas stream into a cold stream and a hot stream without any chemical reactions. Recently, vortex tube is widely used to 1ocal cooler of industrial equipments and air supply system. In this study, the insulation effect of surface on the efficiency of vortex tube was performed experimentally. The experiment is carried out for nozzle area ratio of 0.194, diameter ratio of cold end orifice of 0.6 and input pressure ranging from 0.2Mpa to 0.5Mpa. The purpose of this study is focused on the effect of surface insulation of vortex tube with the variation of cold air mass flow ratio. The results indicate that the temperature difference of cold and hot air are higher about 12% and 30% than that of not insulated vortex tube respectively. Furthermore, for the insulated vortex tube, the similarity relation for the prediction of cold end temperature as the function of cold air mass flow ratio and input pressure is obtained.