• Journal of Energy Engineering
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• v.23 no.3
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• pp.27-35
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• 2014

The existing flow regime map on mixed convection in vertical cylinders was investigated through an analysis of original literatures and its re-formation. The original literatures related to the existing map were reviewed. Using the investigated data and heat transfer correlations, the map was redrawn independently, and compared with the existing map. The redrawn map showed that mixed convection regime was not curved lines but straight lines and the transition regime was unable to be reproduced. Unlike the existing map with a little data, there are lots of data in the redrawn map. The reviews revealed that the existing map used the data selectively among the experimental and theoretical results, and a detailed description for lines forming mixed convection and transition regime was not provided. While considerable studies on mixed convection have been performed since that of Metais and Eckert, the existing map has still been used as the best method to distinguish natural, forced and mixed convection regime.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.20 no.4
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• pp.309-332
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• 2016

Finite element method has been applied to solve the fundamental governing equations of natural convective, electrically conducting, incompressible fluid flow past an infinite vertical plate surrounded by porous medium in presence of thermal radiation, viscous dissipation, Soret and Dufour effects. In this research work, the results of coupled partial differential equations are found numerically by applying finite element technique. The sway of significant parameters such as Soret number, Dufour number, Grashof number for heat and mass transfer, Magnetic field parameter, Thermal radiation parameter, Permeability parameter on velocity, temperature and concentration evaluations in the boundary layer region are examined in detail and the results are shown in graphically. Furthermore, the effect of these parameters on local skin friction coefficient, local Nusselt number and Sherwood numbers is also investigated. A very good agreement is noticed between the present results and previous published works in some limiting cases.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.5
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• pp.13-19
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• 2014

Urea-SCR system is the selective catalytic reduction to reduce nitrogen oxides ($NO_x$) emitted from diesel vehicles. The objective of this study is numerical analysis of 3-dimensional unsteady melting problems of frozen urea by using an electric heater. It can be applied to determine capacity of power with respect to time and the location of the urea suction pipe in urea storage tank. The study includes the change of liquid volume fraction, temperature profiles and a influence of natural convection by using the commercial software STAR-CCM+(v7.06). The accuracy of the numerical analysis is estimated by comparisons with experimental data. After validation, a numerical analysis for freezing urea is conducted with four different heating power. From the results, it was found that relation of velocity of phase interface and amount of melting urea by increasing heating power in a container. There is also a difference in trend between velocity of phase interface and amounts of melting urea because of effect of natural convection.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.5
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• pp.731-739
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• 1987

This study has been performed on multiple steady-state natural convection in the upflow region induced by an inclined isothermal plate immersed in pure cold water. The newly found additional steady-state solutions are of considerable practical interest because the heat-transfer rates for a pair of solutions with determining physical parameters and boundary conditions otherwise identical are sometimes vastly different. The results are as follows: First, in the largely upflow region, two solutions exist for 0.15157

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.5
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• pp.983-991
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• 1992

This investigation is carried out numerically for the two dimensional natural convection and surface radiation heat transfer in a square enclosure. The bottom and top walls are isothermal at hot and cold temperatures respectively whereas the left and right side walls are adiabatic except a transparent window on the right side partially. The exchange of radiant energy is obtained by the net radiation method and the shape factor by the crossed string method. The changes in temperature and Nusselt number distributions of the walls due to the surface radiation and insolation are also investigated.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.4
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• pp.333-340
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• 2005

Horizontal air-jet effect has been utilized in some air conditioning systems in order to control the contaminated air indoor. In the present study, the flow and heat transfer of the contaminated air from a range hood system has been investigated with or without horizontal air-jet effect when the hood fan is on or off. For the present numerical experiment, PAT Flow code has been used. From the present numerical simulations, it has been shown that the air jet of a range hood generates coanda effect confining the contaminated air in a certain region. Furthermore, the qualitative relation between the flow rate of the capture air jet and the distribution pattern of the contamination has been discussed.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.2
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• pp.265-279
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• 1986

Ra=$10^{6}$, Pr=5에서 관열전도율과 두께가 변화할 때의 단일수평관에서의 자연대류 열전달에 관하여 유한차분법을 이용하여 해석적으로 연구하였다. .delta.$_{w}$ /d$_{o}$ =0.1에서 관열전도율이 높을수록 높은 온도와 높은 국소 누셀트 수를 나타 내며, .theta.=20。에서의 원주방향속도는 (r-r$_{o}$ )=0.08에서 최대가 되며 반경방향속 도는 (r-r$_{o}$ )=0.14에서 최대가 된다. 관외벽온도는 관 두께가 증가함에 따라 거의 유사하게 감소한다. $K_{w}$ /K$_{f}$ =75에서 각도변위가 증가함게 따라 국소 누셀트수는 현저히 증가하나 관 두께가 증가함에 따라서는 감소한다. .delta.$_{w}$ / d$_{o}$ =0.1에서 평균 누셀트수와 평균 온도는 무차원 열전도율이 증가함에 따라 $K_{w}$ /K$_{f}$ ＞15에서는 평균 누셀트 수는 서서히 증가하고 평균 온도는 거의 같 은 값을 가지며 지수함수로 표시할 수 있었다. $K_{w}$ /K$_{f}$ =75,50에서 평균 누 셀트수와 온도는 무차원 관 두께가 증가함에 따라 거의 직선적으로 감소되며 선형 함 수로 나타낼 수 있었다.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.17 no.4
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• pp.448-455
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• 1988

A study has been conducted experimentally on natural convection heat transfer characteristics of a vertical flat plate with horizontal rectangular fins in air. The effects of fin heights and Rayleigh numbers are mainly investigated. The experimental results are as follows; 1. The mean fin, plate and total Nusselt numbers decrease as dimensionless fin heights H/S increase at $0.50{\leq}H/S{\leq}2.00$. 2. The mean fin surface Nusselt number in case of H/S = 0.50 and $Ra_c=4.33{\times}10^3$ shows its maximum at $X_1$, surface where there is no interference with other fins. 3. Owing to the interference of fins the mean plate Nusselt numbers at H/S=0.50 and 2.00 for $Ra_S=6.57{\times}10^3$ are 35% and 80% respectively less than the mean fin Nusselt numbers. 4. The mean fin, plate and total Nusselt numbers of horizontal rectangular fins show higher values at short fins, but lower values at long fins than those of upward vertical fins.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.699-702
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• 2008

This paper describes the numerical simulations in the cooling of the radiator in a distribution transformer. The aim of this work is the cooling optimization of the transformer by CFD simulations. A clear understanding of the cooling pattern in a radiator which is a main heat remover in the power transformer is essential for optimizing the radiator design increasing the thermal efficiency. In this paper we study the heat transfer and fluid flow in a 3-phase 400kVA transformer. The plate radiators of this transformer become wrinkled (corrugated radiator) and there are filled with transformer oil. The oil is circulated due to the natural convection driven by buoyancy effects through radiators so that the ultimate cooling medium is the surrounding air. In the design of transformers, it is of interest to minimize the cost and size of radiators. The obtained results show the temperature and flow distributions and the possibility to optimize the transformer with 3-dimensional CFD models using FLUENT.

• Journal of the Korean Electrochemical Society
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• v.2 no.2
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• pp.98-105
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• 1999

In the present study, buoyant force and its stabilizing effects in an electrostatic field were examined systematically in order to reduce the effect of natural convection with thermal stratification in a horizontal fluid-saturated porous layer. The correlation of ionic mass transport induced by double-diffusive convection in a horizontal porous layer has been derived theoretically. And the theoretical model was examined by electrochemical experiments. The theoretical correlation for mass transport which is satisfying Forchheimer's flow equation and based on the micro-turbulence model is derived as a function of soltual Darcy-Rayleigh number, thermal Darcy-Rayleigh number and Lewis number. In the experiment, the mass transport of copper ions in $CuSO_4-H_2SO_4$ solution is measured by electrochemical technique. By assembling theoretical correlation and experimental results, the mass transport correlation induced by double-diffusive convection is proposed as $$Sh=\frac{0.03054(Rs_D-LeRa_D)^{1/2}}{1-3.8788(Rs_D-LeRa_D)^{-1/10}}$$ The present correlation looks flirty reasonable with comparing experimental results, and very promising for the applications of its prototype into various systems involving heat transfer as well as mass transfer, in order to control the effects of natural convection effectively.