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최대밀도점 부근의 물 속에 잠겨있는 등온 수직 긴원기둥에 의한 자연대류의 실험적 연구
엄용균,권승혜 安東大學校 工業技術硏究所 1996 공업기술연구논문집 Vol.3 No.1
An experimental study of the free convection due to a isothermal vertical long cylinder immersed in water near its density extremum has been carried out. The surface temperature of the cylinder is 0℃, the aspect ratio is 4.8×10^(-2). Time-exposure photographs of the buoyancy-driven flow adjacent to a vertical cylinder in pure water are presented for adjacent water temperatures between 2.0 and 10℃. These conditions are of special interest since between 2.0 and 10℃ the buoyancy force distribution id locally bi-directional across the thermal transport region, Oweing to the density extremum at about 4℃. Resurts of the visualization show three distinct flow regions: upware flow for 2.0℃≤T_(∞)≤4.3℃, downward flow for 5.8℃≤T_(∞), dual flow for 5.6℃<T_(∞)<5.8℃ and unsteady atate flow for 4.3℃<T_(∞)≤5.6℃. The temperature range which the upward flow regions appeared is the same with those of short cylinder, but the temperature which the dualflow region and the downflow region occur is lower than those of short cylinder. Mean Nusselt numbers were smaller at unsteady state region than at the other regions. In the downward flow region, mean Nusselt number increase with increasing the surrounding temperature. In the upward flow region, mean Nusselt number increase and decrese with increasing the surrounding temperature, so there are maxmum Nusselt number at T_(∞)=3.0℃. Comparion of mean Nusselt number with past theoretical study shows good agreement