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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.
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.
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.
Study of Steam Ejector in Experimental and Numerical
S. Wibowo(위보워),M. Sq. Rahman(라흐만),G. H. Lee(이경환),H. M. Jeong(정효민),H. S. Chung(정한식) 한국동력기계공학회 2009 한국동력기계공학회 학술대회 논문집 Vol.2009 No.6
Steam jet ejectors are essential part in many industrial applications such as refrigeration and air conditioning, desalination, chemical industries, and so on. In this study, experiment and numerical of jet ejector model were investigated to reveal the complication of the flow and the mixing process in a steam ejector. Air was used as primary and secondary fluids in experiment. In the experiment, the influence of nozzle exit positions was investigated. The result shows the static pressure distribution along the ejector wall is influenced by nozzle exit position. We also carried out CFD simulation in this study. Realizable k-epsilon turbulence model was tested in CFD. The CFD results were validated with available experimental data.
Experimental study on Vacuum evaporation by ejector of fresh water generator system
S. Wibowo(위보워),ZhenHua Zin(김진화),J.S. Woo(우주식),H. M. Jeong(정효민),H. S. Chung(정한식) 한국동력기계공학회 2009 한국동력기계공학회 학술대회 논문집 Vol.2009 No.11
담수와 시스템은 염수를 음용수로 만들기 위해 해수에 열을 가하는 형태로 설계된다. 본 논문에서는 진공 튜브 증발을 하는 한 가지 형태의 청수제조장치의 진공튜브내의 특성을 알아보았다. 담수에 필요한 열에너지는 증류법을 이용하여 비등점을 내릴 수 있다. 이 실험에서는 증발기로 보내는 물의 온도는 60~90로 제어하여 실험하였다. 이는 버려지는 저압의 스팀과 같은 에너지를 이용하여 담수화 시스템을 구성할 수 있다.
Numerical and Experimental Study on the Steam Ejector
S. Wibowo(위보워),M. Sq. Rahman(라흐만),J. S. Woo(우주식),H. M. Jeong(정효민),H. S. Chung(정한식) 한국마린엔지니어링학회 2009 한국마린엔지니어링학회 학술대회 논문집 Vol.2009 No.-
Ejectors are simple pieces of equipment. They are employed in the industry such as in refrigeration and air conditioning, desalination, petrochemical and chemical industry. The purpose of this paper is to reveal the complication of the flow and the mixing process in a steam ejector. Air was used as primary and secondary fluids here. In this experiment, the influence of nozzle exit positions was investigated. The result shows the static pressure distribution along the ejector wall is influenced by nozzle exit position. In this study CFD simulation were also undertaken. Standard k-epsilon, RNG k-epsilon, and Realizable k-epsilon were tested in CFD. The CFD results were validated with available experimental data. In this case the result shows that realizable k-epsilon model closer with experimental result than another models.