• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.7
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• pp.1720-1730
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• 1995

Finite-difference analysis was conducted to study the natural convection of a stably stratified salt-water solution in an annulus due to lateral heating. The main purpose of this study is to examine in detail the multi-layered flow structure. Calculation was thus made for R $a_{\eta}$=2*10$^{5}$ and 6.5*10$^{5}$ . Formation of layered flow structure, merging process of layers, the corresponding temperature and concentration distributions, Nusselt number variations with time are examined. Numerical results show that in each layer, the temperature profile looks 'S`-shaped and the concentration profile is uniform due to the convective mixing. The formation of the roll and the layer is governed by natural convection due to the temperature gradient and the merging process of the layer by diffusion of the concentration.ation.

• Journal of The Korean Society of Agricultural Engineers
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• v.48 no.5
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• pp.51-60
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• 2006

In order to examine the heat transfer characteristic of a soil warming system and effects of soil warming on the greenhouse heating load, control experiments were performed in two greenhouses covered with double polyethylene film. One treated the soil warming with an electric heat wire and the other treated a control. Inside and outside air temperature, soil temperature and heat flux, and heating energy consumption were measured under the set point of heating temperature of $5,\;10,\;15,\;and\;20^{\circ}C$, respectively. Soil temperatures in a soil warming treatment were observed $4.1\;to\;4.9^{\circ}C$ higher than a control. Heating energy consumptions decreased by 14.6 to 30.8% in a soil warming treatment. As the set point of heating temperature became lower, the rate of decrease in the heating energy consumptions increased. The percentage of soil heat flux in total heating load was -49.4 to 24.4% and as the set point of heating temperature became higher, the percentage increased. When the set point of heating temperature was low in a soil warming treatment, the soil heat flux load was minus value and it had an effect on reducing the heating load. Soil heat flux loads showed in proportion to the air temperature difference between the inside and outside of greenhouse but they showed big difference according to the soil warming treatment. So new model for estimation of the soil heat flux load should be introduced. Convective heat transfer coefficients were in proportion to the 1/3 power of temperature difference between the soil surface and the inside air. They were $3.41\;to\;12.42\;W/m^{2}^{\circ}C$ in their temperature difference of $0\;to\;10^{\circ}C$. Radiative heat loss from soil surface in greenhouse was about 66 to 130% of total heating load. To cut the radiation loss by the use of thermal curtains must be able to contribute for the energy saving in greenhouse.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1554-1559
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• 2003

The objective of the present study is to reveal thermal characteristic of microcapsulated lauric acid slurry, which have high latent heat during phase change from solid to liquid, in circular pipe. Test were performed with microcapsulated lauric acid slurry in a heating test section with a constant heat flux boundary condition. Local Nusselt number and the effective thermal capacity were measured. As the size of microcapsulated lauric acid were increased, Local Nusselt number of microcapsulated lauric acid slurry were increased. The effective thermal capacity of microcapsulated lauric acid slurry was 0.5 times than it of water

• Journal of Mechanical Science and Technology
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• v.15 no.2
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• pp.239-247
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• 2001

Measured radiative heat fluxes on the furnace exit plane of a heavy duty power boiler of steam output 1650 T/h are discussed. A high-ash pulverized bituminous coal was used. Such measurements are necessary to improve heat fluxes inside a steam boiler furnace was manufactured. An extra small heat radiation sensor was placed in the water cooled head of the probe. The sensor had no direct contact with furnace gases and measured only the radiant energy. There was no exposure to convective heat transfer. With the radiometric probe, one can obtain a spherical indicatrix of radiation intensity as well as hemispherical radiative heat flux incident on any surface passing through a measuring point inside the furnace. Thus, the quantity of radiation energy, passing through the furnace exit plane, to the convective heating surfaces and the quantity of radiation energy going in the opposite direction were measured. A formula for relative radiative heat flux on the furnace exit plane has been proposed.

• Journal of Welding and Joining
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• v.15 no.6
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• pp.105-115
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• 1997

A numerical study is performed to predict the thermal response of a detailed card assembly during infrared reflow soldering. The card assembly is exposed to discontinuous infrared panel heater temperature distributions and high radiative/convective heating and cooling rates at the inlet and exit of the oven. The convective, radiative and conduction heat transfer within the reflow oven as well as within the card assembly are simulated and the predictions illustrate the detailed thermal responses. The predictions show that mixed convection plays an important role with relatively high frequency effects attributed to buoyancy forces, however the thermal response of the card assembly is dominated by radiation. The predictions of the detailed card assembly thermal response can be used to select the oven operating conditions to ensure proper solder melting and minimization of thermally induced card assembly tresses and warpage.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.11
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• pp.1006-1012
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• 2004

The objective of the present study is to reveal thermal characteristic of micro-capsulated lauric acid slurry, which has high latent heat during phase change from solid to liquid, in circular pipe. Tests were performed with the microcapsulated lauric acid slurry in the heating test section with a constant heat flux boundary condition. Local Nusselt number and the effective thermal capacity were measured. As the sizes of microcapsulated lauric acids were increased, local Nusselt numbers of microcapsulated lauric acid slurries were increased. The effective thermal capacity of microcapsulated lauric acid slurry was 1.43 times larger than that of water.

• Solar Energy
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• v.18 no.4
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• pp.39-47
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• 1998

The natural convection heat transfer in a vertical plate with discrete heat sources was studied experimentally. The particular interest was the thermal interaction of the heat sources. In this study, the radiative and conductive heat transfer were considered as heat loss, Thus, the net convective heat transfer rate was presented as adiabatic temperature and thermal wake function. As a results, for non-uniform heating condition, heat input ratio(q1/q2) was most dominant parameter for the thermal wake function. The convective heat transfer rate is decreased with the increasing of channel ratio. For the range of $7.50{\times}10^5<Rac<8.66{\times}10^6$, a useful correlation was proposed as a function of channel Rayleigh number.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.3
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• pp.277-283
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• 2000

The heat transfer characteristics for air jet vertically impinging on a flat plate which had a set of hybrid rod were investigated experimentally. The rod had a cross section made with a half of circular cross section and that of rectangular and was installed in front of the plate. The heating surface was given constant heat flux value of 1020 W/$m^2^{\circ]C$ and the problem parameters investigated were jet Reynolds number, nozzle-to-plate spacing and the rod size. The local and local average Nusselt number characteristics were found to be dependent on the rod size because the flow was disturbed by installing the rod. Higher convective heat transfer rate occurred in the whole plate as well as in the stagnation region.

• Solar Energy
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• v.7 no.1
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• pp.23-29
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• 1987

TAP system, a kind of natural convective space heating collector, has a good heat loss by night. The aim of this paper is to induce and to study an hourly heat flow theory by response factors analysis with TAP in inside and outside insulated construction, to compare and evaluate on thermal performance an hourly natural temperature, heated room temperature and heating load in aboved-mention constructions with computer simulation. The results of the study can be summarized as follows. According that there is no TAP and with TAP, it is inside insulated construction and outside insulated construction, daily natural range of temperature each shows $12.5^{\circ}C$ and $16.7^{\circ}C$, $2.7^{\circ}C$ and $3.7^{\circ}C$, daily heated range of temperature with noramal control heating system each shows $6.6^{\circ}C$ and $12.1^{\circ}C$, $1.7^{\circ}C$ and $3.1^{\circ}C$, heating hours each show 10 hr and 7 hr, 9 hr and 4 hr and heating energy saving percentage in january 123% and 79%, 100% and 40%. Therefore, energy saving percentage shows that outside insulated construction saves about 54% in comparision with inside insulated construction.

• Atmosphere
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• v.28 no.1
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• pp.53-67
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• 2018

This study examined the lake effect of the Yellow Sea which was induced by the Siberian High pressure system moving over the open waters. The development mechanism of the convective cells over the ocean was studied in detail using the Weather Research and Forecasting model. Numerical experiments consist of the control experiment (CTL) and an experiment changing the yellow sea to dry land (EXP). The CTL simulation result showed distinct high area of relative vorticity, convergence and low-level atmospheric instability than that of the EXP. The result indicates that large surface vorticity and convergence induced vertical motion and low level instability over the ocean when the arctic Siberian air mass moved south over the Yellow Sea. The sensible heat flux at the sea surface gradually decreased while latent heat flux gradually increased. At the beginning stage of air mass modification, sensible heat was the main energy source for convective cell generation. However, in the later stage, latent heat became the main energy source for the development of convective cells. In conclusion, the mechanism of the west coast heavy snowfall caused by modification of the Siberian air mass over the Yellow Sea can be explained by air-sea interaction instability in the following order: (a) cyclonic vorticity caused by diabatic heating induce Ekman pumping and convergence at the surface, (b) sensible heat at the sea surface produce convection, and (c) this leads to latent heat release, and the development of convective cells. The overall process is a manifestation of air-sea interaction and enhancement of convection from positive feedback mechanism.