• 대한기계학회논문집B
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• 제23권2호
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• pp.226-233
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• 1999

An experimental study has been performed on natural convection heat transfer with a rapid crust formation in the molten metal pool of a low Prandtl number fluid. Two types of steady state tests, a low and high geometric aspect ratio cases in the molten metal pool, were performed. The crust thickness by solidification was measured 88 a function of boundary surface temperatures. The experimental results on the relationship between the Nusselt number and Rayleigh number In the molten metal pool with a crust formation were compared with existing correlations. The experimental study has shown that the bottom surface temperature of the molten metal layer, in all experiments. is the major influential parameter in the crust formation, duo to the natural convection flow. The Nusselt number of the case without a crust formation in the molten metal pool is greater than that of the case with the crust formation at the same Rayleigh number. The present experimental results on the relationship between the Nusselt number and Rayleigh number In the molten metal pool match well with Globe and Dropkin's correlation. From the experimental results, a now correlation between the Nusslet number and Rayleigh number in the molten metal pool with the crust formation was developed as $Nu=0.0923(Ra)^{0.302}$ ($2{\times}10^4< Ra<2{\times}10^7$).

• 설비공학논문집
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• 제4권2호
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• pp.106-115
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• 1992

Numerical analysis of the laminar natural convection in an enclosure of the 20KVA oil-immeresed transformer is presented. The core in the transformer is modelled as a rectangular cylinder and calculation is carried out for $Ra=10^3-10^6$. The correlating equation between the inner cylinder mean Nusselt numbers and Rayleigh numbers can be obtained. The conduction and convection regimes for the variation of Rayleigh numbers are well represented in the temperature distributions along the side wall of the inner cylinder. For high Rayleigh numbers, it is found that the recirculating flow in the enclosure above the inner cylinder is divided into two recirculation regions.

• 동력기계공학회지
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• 제13권5호
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• pp.11-17
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• 2009

A numerical study of unsteady mixed convection in a cavity with high viscous fluid is presented. Finite volume method was employed for the discretization and PISO algorithm was used for calculating pressure term. The parameters governing the problem are the Rayleigh number ($10^3\;{\leq}\;Ra\;{\leq}\;10^5$), the Reynolds number (0 < Re $\leq$ 1), and the aspect ratio (0.5 $\leq$ AR $\leq$ 2). The fluid used is silicon oil, a high prandtl number fluid, Pr = 909.1. The results show velocity vectors and temperature distributions. It is found that the periodic flows in a cavity are observed at very low Reynolds numbers, and the period of periodic flow decreases with increasing Reynolds and Rayleigh numbers, and increases with increasing aspect ratio. Also, the Reynolds number range of periodic flow increases with increasing Rayleigh numbers and aspect ratio.

• 한국전산유체공학회지
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• 제18권2호
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• pp.35-40
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• 2013

Natural convection of air with Pr=0.7 between two horizontal plates with small magnitude non-uniform temperature distribution[${\in}{\Delta}Tsin({\kappa}X/H)$, H : gap width, X : horizontal coordinate] in the lower plate is numerically(${\in}=0.01$) investigated. In the conduction-dominated regime with $Ra{\leq}1700$, two upright cells are formed over one wave length($2{\pi}/{\kappa}$). For small wave number, the flow becomes unstable with increase of Rayleigh number, and multicellular convection occurs above a critical Rayleigh number. The flow patterns are classified by the number of eddies over one wave length. When ${\kappa}=1$, a transition of $2{\rightarrow}4{\rightarrow}6$ eddy flow occurs with increase of Rayleigh number, and no hysteresis phenomenon is observed. Dual and triple solutions are found for ${\kappa}=1$, and transitions of $10{\rightarrow}8$, $8{\rightarrow}6$, $6{\rightarrow}4{\rightarrow}2$ eddy flow occur with decrease of Rayleigh number.

• Korean Chemical Engineering Research
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• 제53권6호
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• pp.814-817
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• 2015

A new ionic mass transfer correlation is derived for the fluid-saturated, horizontal porous layer. Darcy-Forchheimer model is used to explain characteristics of fluid motion. Based on the microscales of turbulence a backbone mass transfer relation is derived as a function of the Darcy-Rayleigh number, $Ra_D$ and the porous medium Schmidt number, $Sc_p$. For the Darcy's limit of $Sc_p{\gg}Ra_D$, the Sherwood number, Sh is a function of $Ra_D$ only. However, for the region of high $Ra_D$, Sh can be related with $Ra_DSc_p$. Based on the present backbone equation and the electrochemical mass transfer experiments which are electro plating or electroless plating, the new ionic mass transfer correlation is suggested in the porous media.

• 대한기계학회논문집B
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• 제31권3호
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• pp.273-282
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• 2007

Numerical calculations are carried out for the natural convection induced by temperature difference between a cold outer square cylinder and a hot inner circular cylinder. A two-dimensional solution for unsteady natural convection is obtained, using the immersed boundary method (IBM) to model an inner circular cylinder based on finite volume method, for different Rayleigh numbers varying over the range of $10^4\;to\;10^6$. The study goes further to investigate the effect of an inner cylinder location on the heat transfer and fluid flow. The location of inner circular cylinder is changed vertically along the center-line of square enclosure. The number, size and formation of cell strongly depend on Rayleigh number and the position of inner circular cylinder. The changes in heat transfer quantities have been presented.

• 한국전산유체공학회지
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• 제21권3호
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• pp.1-7
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• 2016

In the present study, the homogeneous model is used to simulate the natural convection heat transfer of the CuO-water nanofluid in a concentric annular enclosure. Simulations have been carried while the Rayleigh number ranges from $10^3$ to $10^6$, solid volume fraction ranges from 0.01 to 0.04 and the radius ratio varies between 0.1 and 0.7. Results are presented in the form of streamlines, isotherm patterns and averaged Nusselt numbers for different values of solid volume fraction, radius ratio of the annulus and Rayleigh numbers. The results show that by decreasing the radius ratio and/or increasing the Rayleigh number, the averaged Nusselt number increases. Also the heat transfer rate increases as increased solid volume fractions.

• 대한기계학회논문집
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• 제12권1호
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• pp.28-35
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• 1988

본 연구는 이중벽용기에서 볼 수 있는 환상공간에 관한 자연대류 연구로서 용기속에 들어있는 유체의 열차폐를 위한 최적의 가스두께를 측정하기 위하여 필요한 지식을 얻기위한 열전달 연구이다.

• 대한기계학회논문집B
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• 제34권8호
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• pp.739-747
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• 2010

고온의 내부 원형 실린더가 존재하는 저온의 사각 밀폐계 사이의 온도차이에 의해 발생하는 자연대류에 관해 수치해석을 수행하였다. 본 연구는 내부의 원형 실린더를 표현하기 위해 유한 체적법에 기초한 가상 경계법을 사용하여 Ra = $10^7$ 에서 2 차원 비정상상태의 자연대류 현상에 대한 해를 얻었다. 더욱이 밀폐계의 수직 중심선에 따른 내부 원형 실린더의 위치 변화에 의한 열전달과 유동에 관한 영향을 연구하였다. 내부원형 실린더의 위치 변화에 따라 자연대류 현상은 비정상상태에서 정상상태로 변화 되었다. 연구 결과 두가지의 임계 위치를 얻을 수 있었다. 하부 경계는 0.05 인 지점이고 상부경계는 0.18 인 지점이다. 하부 경계와 상부 경계의 사이의 위치에서는 열 및 유동장이 정상상태임을 알 수 있었다.

• 동력기계공학회지
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• 제11권4호
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• pp.56-64
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• 2007

A numerical simulation is carried out mixed convection in horizontal channel with a heat source from below of rectangular cavity. Finite volume method was employed for the discretization and PISO algorithm was used for calculating pressure term. The parameters governing the problem are the Reynolds number ($10^{-2}{\leq}Re{\leq}50$), the Rayleigh number ($10^3{\leq}Ra{\leq}2.06{\times}10^5$), the Prandtl number ($0.72{\leq}Pr{\leq}909$), the aspect ratio ($0.5{\leq}AR=W/H{\leq}2$) and the angle of inclination ($0^{\circ}{\theta}60^{\circ}$). Mean Nusselt number distributions were obtained and effect of Reynolds number, Rayleigh number and Prandtl number on mixed convection in the horizontal channel with rectangular cavity were investigated.