• Nuclear Engineering and Technology
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• v.44 no.3
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• pp.283-296
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• 2012

The natural convection in a horizontal enclosure heated from the bottom wall, cooled at the top wall, and having a square adiabatic body in the center is studied. Three different Prandtl numbers (0.01, 0.7 and 7) are considered for the investigation of the effect of the Prandtl number on natural convection. Adiabatic boundary conditions are employed for the side walls. A two-dimensional solution for unsteady natural convection is obtained, using an accurate and efficient Chebyshev spectral methodology for different Rayleigh numbers varying over the range of $10_3$ to $10_6$. It had been experimentally reported that the heat transfer mode becomes oscillatory when Pr is out of a specific Pr band beyond the critical Ra. In this study, we reproduced this phenomenon numerically. It was found that when Ra=$10_6$, only the case for intermediate Pr (=0.7) reached a non-changing steady state and the low and high Pr number cases (Pr=0.01 and 7) showed a periodically oscillatory fashion hydrodynamically and thermally. The variation of time- and surface-averaged Nusselt numbers on the hot and cold walls for different Rayleigh numbers and Prandtl numbers are presented to show the overall heat transfer characteristics in the system. Further, the isotherms and streamline distributions are presented in detail to compare the physics related to their thermal behavior.

• Journal of computational fluids engineering
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• v.16 no.3
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• pp.29-36
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• 2011

The natural convection in a horizontal enclosure heated from the bottom wall, cooled at the top wall, and having a square adiabatic body at its centered area was studied. Three different Prandtl numbers (0.01, 0.7 and 7) were considered for an effect of the Prandtl number on natural convection. A two-dimensional solution for unsteady natural convection was obtained, using Chebyshev spectral methodology for different Rayleigh numbers varying over the range of $10^4$ to $10^6$. It had been experimentally and numerically reported [1,2] that the heat transfer mode becomes oscillatory when Pr is out of a specific Pr band beyond the critical Ra. In this study, we reproduced this phenomenon numerically. The variation of time- and surface-averaged Nusselt numbers on the hot and cold walls for different Rayleigh numbers and Prandtl numbers was presented to show the overall heat transfer characteristics in the system. And also, the isotherms and streamline distributions were presented in detail to compare the physics related to their thermal behavior.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.7
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• pp.833-841
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• 2007

The aim of this paper is to analyze the conjugate problems of heat conduction in solid walls coupled with laminar free convection flow adjacent to a vertical flat plate under boundary layer approximation. Using the similarity transformations the governing boundary layer equations for momentum and energy are reduced to a system of partial differential equations and then solved numerically using Finite Difference Method(FDM) known as the Keller-box scheme. Computed solutions to the governing equations are obtained for a wide range of non-dimensional parameters that are present in this problem, namely the coupling parameter P. the Prandtl number Pr and the heat generation parameter Q. The variations of the local heat transfer rate as well as the interface temperature and the friction along the plate and typical velocity and temperature profiles in the boundary layer are shown graphically. Numerical solutions have been consider for the Prandtl number Pr=0.70

• Journal of applied mathematics & informatics
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• v.12 no.1_2
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• pp.281-289
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• 2003

The convection of water is investigated in the vicinity of its density maximum temperature (277 K) in an inclined square cavity in the presence of heat sources. Numerical investigations are carried out by maintaining one of the vertical walls uniformly at 273 K and varying the other wall between temperatures 275 K and 285 K at different inclinations angles. The isotherms, streamlines and velocity profiles reveal the possible existence of multicellular fluid motions, and bidirectional velocity distributions. These fluid flow and heat transfer characteristics are significantly modified by the cavity inclination in the presence of heat sources.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.402-407
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• 2001

This paper reports a result of numerical heat transfer analysis for heat spreader with various ribs. Four different ribs are compared in this study. In general, the heat transfer on a vertical plate is enhanced when a rib is attached as the surface area increases, and the growth of the boundary layer is interrupted. However, for a low flow less than 0.1m/s, it is observed that the heat transfer is sensitive to the height of a rib: it decreases as the height increases. Among the four ribs, the H-shaped rib showed better performance than other ribs.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.28 no.8
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• pp.305-310
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• 2016

A thermal storage systems was designed to correspond to the temporal or quantitative variation in the thermal energy demand, and most of its heat is stored using the latent and sensible heat of the heat storage material. The heat storage method using latent heat has a very complex phenomenon for heat transfer and thermal behavior because it is accompanied by a phase change in the course of heating/cooling of the heat storage material. Therefore, many studies have been conducted to produce an experimentally accessible as well as numerical approach to confirm the heat transfer and thermal behavior of phase change materials. The purpose of this study was to investigate the problems encountered during the actual heat transfer from an internal storage tank through simulation of the process of storing and utilizing thermal energy from the thermal storage tank containing charged PCM. This study used analysis methods to investigate the heat transfer characteristics of the PCM with simultaneous heating/cooling conditions in the rectangular space simulating the thermal storage tank. A numerical analysis was carried out in a state considering natural convection using the ANSYS FLUENT(R) program. The result indicates that the slope of the liquid-solid interface in the analysis field changed according to the temperature difference between the heating surface and cooling surface.

• Journal of Energy Engineering
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• v.1 no.1
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• pp.66-75
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• 1992

The performance of heat transfer through double pane window has been investigated using experimental and numerical methods. The range of the gap distance between glasses are 0.5-10 cm. The convection heat transfer plays the dominant role for the case of the wide gap distance together with the large Rayleigh number and thereby, reduces the enhanced thermal resistance due to the increased air gap, while the conduction heat transfer does the major role for the case of small gap distance. In order to enhance the thermal insulation of the double pane window, the heat transfer of triple pane window, which is constructed to put one more glass at the middle of the double pane, is investigated to check the reduction of the convection heat transfer together with the effect of the radiation shield due to the presence of the additional glass. Further, a spacer is installed at the middle height of the double pane, and the effect of which on the suppression of the convective heat transfer is analyzed carefully, using experimental and numerical methods. For the case of the spacer-installation, the amount of energy saving is considered about 10%, but the energy saving increases a lot to 30-50% for the case of triple pane window, due to the substantial radiation shield effect of the presence of the additional glass.

• Korean Chemical Engineering Research
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• v.53 no.1
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• pp.91-102
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• 2015

Analytical solutions for the forced convection heat transfer of viscoelastic fluids obeying the Giesekus model are obtained in a concentric annulus under laminar flow for both thermal and hydrodynamic fully developed conditions. Boundary conditions are assumed to be (a) constant fluxes at the walls and (b) constant temperature at the walls. Temperature profiles and Nusselt numbers are derived from dimensionless energy equation. Subsequently, effects of elasticity, mobility parameter and viscous dissipation are discussed. Results show that by increasing elasticity, Nusselt number increases. However, this trend is reversed for constant wall temperature when viscous dissipation is weak. By increasing viscous dissipation, the Nusselt number decreases for the constant flux and increases for the constant wall temperature. For the wall cooling case, when the viscous dissipation exceeds a critical value, the generated heat overcomes the heat which is removed at the walls, and fluid heats up longitudinally.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.55 no.4
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• pp.196-202
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• 2006

This paper presents a new magneto-thermal finite element analysis for predicting the temperature rise of the EHV GIS busbar. Joule's heat due to current flowing in the main conductor and the heat due to the induced eddy current in the tank are calculated by the magnetic field analysis. And these heats are used as the input data to predict the temperature rise for the thermal analysis. However, it is not easy to apply the heat-transfer coefficients on the boundaries for the thermal analysis. In this paper, the heat-transfer coefficients on the boundaries are analytically calculated by applying the Nusselt number considering material constant and model geometry for the natural convection. The temperature distribution in the busbar by coupled magneto-thermal finite element analysis shows good agreement with the experimental data.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.652-652
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• 2013

The conventional thermal chemical vapor deposition (CVD) setup for the graphene synthesis has mainly used convective heat transfer in order to heat a catalyst (e.g. Cu) up to $1,000^{\circ}C$. Although the conventional CVD has been so far widely accepted as the most appropriate candidate enabling mass-production of high-quality graphene, this method has stillremained under the standard for the commercialization largely due to the poor productivity arisen out of the required long processing time. Here, we introduced a fast and efficient synthetic route toward CVD-graphene. Unlike the conventional CVD using convection heat transfer, we adopted a CVD setup utilizing conduction heat transfer between Cu catalyst and rapid heating source. The high thermal conductive nature of Cu and the employed rapid heating source led to the remarkable reduction in processing timeas compared to the conventional convection based CVD (Fig. 1A), moreover, the synthesized graphene was turned out to have comparable quality to that synthesized by the conventional CVD (Fig. 1B). For the optimization of the conduction based CVD process, the parametric studies were thoroughly performed using through Raman spectroscopy and electrical sheet resistance measurement. Our approach is thought to be worth considerable in order to enhance productivity of the CVD graphene in the industry.