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2개의 축방향핀을 가진 전도관과 원통사이의 자연대류 열전달
정한식,이상훈,김찬원,권순석,Chung, H.S.,Lee, S.H.,Kim, C.W.,Kwon, S.S. 대한설비공학회 1989 설비공학 논문집 Vol.1 No.3
A numerical study has been performed on the natural convection heat transfer from a conducting tube with two axial fins to a surrounding cylinder. As increasing dimensionless fin length ($L_F$), the center of flow moves to the bottom of annulus and the recirculating flow rate is decreased. The maximum local Nusselt number of conducting tube appears at ${\theta}=180^{\circ}$ for $L_F=0.0$, but at ${\theta}=130^{\circ}$ for $L_F{\geq}0.3$ and that of outer cylinder appears at ${\theta}=13^{\circ}$ for $L_F{\leq}0.6$ but at ${\theta}=33^{\circ}$ for $L_F=1.0$. The fin temperature is decreased by increasing radial distance and the temperature distribution of the downward fin is generally less than that of the upward fin. By increasing fin length, the local Nusselt number of the upward fin appears negative values for $L_F=1.0$, but appears positive values for $L_F<0.8$, and that of the downward fin appears positive values.
나인(Md. J. Nine),이경환(G. H. Lee),정효민(H. M. Jeong),정한식(H. S. Chung) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
The article represents an experimental investigation on pressure drop and friction loss behaviors of free airflow through a rectangular duct fitted with semicircular ribs of uniform height on one principle wall. The aspect ratio of the rectangular duct is AR= 5, duct height was of H= 30 ㎜ and uniform rib heights (e = 3.5 ㎜m) were used for three different rib pitches of 30 mm, 35 ㎜ and 42 ㎜. For this cases, the rib height to hydraulic diameter ratio were e/D = 0.07 and rib height to channel height ratio were e/H = 0.11. The experimental results show some significant effects of static pressure near the wall and at various configurations and different numbers of rib arrangements within test section. Each result is compared with another among different configurations of rib arrangement over the 90 ㎝ X 15 ㎝ copper plate test section. The Reynolds number in the inlet of calculation domain was in a range of 10000 to 30000. Digital micro manometer and pressure transducer were used for taking static pressure of this experiment. Darcy friction factor was used and isothermal pressure drop had been considered in data evaluation. These experiment will be the preliminary investigation for turbulence analysis as heat transfer enhancement using periodic semicircular ribs.
2개(個)의 수직(垂直) 평판(平板)핀을 가진 전도관(傳導管)으로 부터의 자연대류(自然對流) 열전달(熱傳達)
정한식,이철재,권순석,Chung, H.S.,Lee, C.J.,Kwon, S.S. 대한설비공학회 1991 설비공학 논문집 Vol.3 No.4
Conjugate heat transfer by steady laminar natural convection from a conducting tube with two vertical axial fins has been studied by a finite difference numerical procedure under basic conditions; $Ra=10_6$, Pr = 5 and $L_F=0.15$. The maximum local tube Nusselt number appears at ${\theta}=140^{\circ}$ for $L_F=0.06$, at ${\theta}=130^{\circ}$ for $L_F=0.30$ and at ${\theta}=120^{\circ}$ for $L_F=0.30$, $L_F=0.06$, respectively. The maximum mean Nusselt number shows at $L_F=0.18$ for the downward fin and at $L_F=0.12$ for the upward fin. Therefore the optimized fin length is $L_F{\approx}0.15$ under these conditions. At $L_F=0.15$, the mean Nusselt number by increasing Rayleigh number is remarkably increased for downward fin and then is slowly increased except for downward fin, it by increasing Prandtl number is apparently increased at $Pr{\leq}2$, and slightly increased at Pr>2.