• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.2
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• pp.382-390
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• 1992

The problem of natural convection from a vertical fin is solved by coupling the thermal diffusion equation in the fin to the constitutive equations of the ambient medium involving the radiation of the medium. The analysis is accomplished by employing an integral method. The governing equations for the problem are solved by shooting method based on the Runge-Kutta Scheme at Pr= 0.7. For the range of values of the fin parameter and the radiation-conduction parameter in the analysis, the numerical results show that the radiation effects play an important role in the heat transfer and enhance the heat transfer.

• Journal of computational fluids engineering
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• v.18 no.4
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• pp.25-34
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• 2013

A numerical study of a laminar natural convection of the CuO-water nanofluid in a square cavity using the Buongiorno's nonhomogeneous model is presented. All the governing equations including the volume fraction equation are discretized on a cell-centered, non-uniform grid employing the finite-volume method with a primitive variable formulation. Calculations are performed over a range of Rayleigh numbers and volume fractions of the nanopartile. From the computed results, it is shown that both the homogeneous and nonhomogeneous models predict the deterioration of the natural convection heat transfer well with an increase of the volume fraction of nanoparticle at the same Rayleigh number, which was observed in the previous experimental studies. It is also shown that the differences in the computed results of the average Nusselt number at the wall between the homogeneous and nonhomogeneous models are very small, and this indicates that the slip mechanism of the Brown diffusion and thermophoresis effects are negligible in the laminar natural convection of the nanofluid. The degradation of the heat transfer with an increase of the volume fraction of the nanoparticle in the natural convection of nanofluid is due to the increase of the viscosity and the decrease of the thermal expansion coefficient and the specific heat. It is clarified in the present study that the previous controversies between the numerical and experimental studies are owing to the different definitions of the Nusselt number.

• Journal of computational fluids engineering
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• v.12 no.4
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• pp.7-13
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• 2007

Numerical analysis is carried out for combined heat transfer in an indirected NIR(Near Infrared Ray) heating chamber. Reynolds number and shapes of absorbed cylinder are known as important parameters on the combined heat transfer effects. Reynolds number based on the outer diameter of the cylinder is varied from $10^3$ to $3{\times}10^5$. Four difference heat transfer regimes are observed: forced convection and radiative heat transfer on the outer surface of the cylinder, pure conduction in the cylinder body, pure natural convection and radiation between lamp surface and inner surface of the cylinder, and radiation from the lamp. Flow and temperature characteristics are presented with iso-contour lines for the absorbed circular and elliptic cylinders to compare their differences. The convective and radiative heat transfer fluxes are also compared with different Reynolds numbers. As usual, Reynolds number is an important factor to estimate increasing convective heat transfer as it increases. The shape of absorbed cylinder results overall heat transfer rates remain unchanged.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.6
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• pp.512-518
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• 2002

The real chip and similarity model were used to investigate the thermal behavior and velocity distribution of air from the heat source with the location and the amount of heat experimentally and numerically, and compared. The heat generated in the block is not cooled by convection and show the high temperature by the stagnation of heat flow. After maintaining the high temperature of block by the natural convection, the sudden drop of temperature with the air flow was shown in the channel but the decreasing rate was small with the time. The inward block was effected by infinitesimal air flow generated between block and channel and outward block was effected by the entry condition.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.4
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• pp.771-779
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• 1989

Numerical analysis by SIMPLE algorithm has been performed to predict the characteristics of flow and heat transfer in channels between the printed circuit boards of an electronic cabinet. It is assumed that the electronic parts release uniform heat flux per unit axial length to the cooling air. The air flow between channels is assumed fully developed laminar, incompressible, and mixed convective. In this study, the electronic parts are mounted on both sides of the prinked circuit boards by two kinds of configuration such as the zig-zag and the symmetric one. The Rayleigh numbers ranging from 0 to 10$^{6}$ are considered to predict the characteristics of the main flow and the secondary flow occurred by natural convection, the temperature distribution in channel, the heat transfer rate from heated electronic parts and the increase of friction factor by natural convection. As the results of numerical calculation, several conclusions are drawn as follows. The influence of natural convection on the flow characteristics appears strong when the Rayleigh number is above 10$^{4}$. The main axial flow rate decreases by a half or more at the Rayleigh number of 10$^{6}$ . Although the friction factor increases as Rayleigh number increases, the increasing rate of heat transfer is higher than that of the friction factor. The cooling efficiency of the zig-zig-configuration is superior to that of the symmetric configuration at same Rayleigh number.

• Solar Energy
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• v.12 no.2
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• pp.28-42
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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 wall is a constant heat flux at hot temperature and also top wall is isothermal at cold temperature 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 change in temperature and Nusselt number distributions of the walls due to the effect of the wall emissivity for various emissivities and for various dimensionless insolation energies are investigated. The dimensionless local convective heat flux and local radiative heat flux distributions in the wall except an adiabatic wall are also compared.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.571-575
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• 2006

To improve economic of solar power generation, stirling engine is required continuous operation and the receiver has to be provided with an additional combustion system. The hybrid receiver with a specially adapted combustion system is possible to 24 hr/day operation by solar and gas-fired. The inner cavity and external wall serve as absorber surfaces using collected irradiation and heat transfer surfaces for the gas heat flow, respectively. The hybrid receiver was designed and fabricated for the dish/stirling system. The analytical method for pridicting natural convective heat loss from receiver is used. The Koenig and Marvin model is used to estimate convection heat loss and heat transfer coefficiency.

• Journal of the Semiconductor & Display Technology
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• v.16 no.4
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• pp.5-10
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• 2017

This paper analyzed the heat transfer characteristics on the outer surface of the ambient air vaporizer which received the heat from the air through natural convection by using numerical and experimental methods. The working fluid was a liquid nitrogen. The experimental variables were the length (2,000 mm, 1,800 mm, 1,600 mm) and width of the vaporizer fin and the fluid flow ($6.7m^3/h$, $7.1m^3/h$, $7.5m^3/h$). Based on the temperature data from the experiments, the heat transfer coefficient was calculated. Numerical analyses were also conducted in order to find the heat transfer coefficient for the range of Nusselt number which was difficult to get the data from experiments. The correlation equation between Nusselt number and Rayleigh number were suggested using both the experimental and numerical data.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1080-1085
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• 2004

The physical model considered here is a horizontal layer of fluid heated below and cold above with heat-generating conducting body placed at the center of the layer. The dimensionless thermal conductivities of body considered in the present study are 0.01, 1 and 150. The dimensionless temperature difference ratios considered are 0.25, 2.5 and 25. Two-dimensional solution for unsteady natural convection is obtained using an accurate and efficient Chebyshev spectral methodology for variety of Rayleigh number from $10^{3}$ to $10^{6}$. Multi-domain technique is used to handle square-shaped heat-generating conducting body. The results for the case of conducting body with heat generation are also compared to those without heat generation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.6
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• pp.1609-1620
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• 1993

A Study on the trombe wall system, a kind of passive solar systems, has been performed numerically. The system is treated as a two-dimensional steady turbulent natural convection including constant heat source per unit area. The numerical code, "PHOENICS, " was employed to analyze this conduction-convection conjugated heat transfer. The general mode of the flow field was examined, and the exchange of mass between two recirculating flows is found to be the major mechanism of the heat transfer. It is shown that the performance is affected by the changes in the geometrical factors-the thickness of the wall, the width between the windowand the wall, and size of the vents. Further analysis has been performed to show the optimal geometry with regard to the last two factors.o factors.