• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2303-2308
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• 2007

Experiments were performed to determine the thermal (or turbulent) diffusion coefficient (TDC) and to investigate the critical heat flux (CHF) performance in the 5${\times}$5 rod bundle with 5 unheated rods which are supported by Hybrid Mixing Vane. In this study, HFC-134a fluid was used as working fluid and the fluid temperature were measured in the important subchannels. To determine the TDC value, the measured fluid temperatures were compared with the predicted values obtained from the MATRA code. The best optimized value of ${\beta}$ was found to be 0.02 by considering prediction statistics, i.e., average and standard deviations of the differences between the experimental results and code calculations. Using the best optimized value of ${\beta}$ as 0.02, the MATRA code predicts the test results of the fluid temperature within ${\pm}$1.0 % of error. According to the experimental results on CHF of 5 non-heating guide tubes, the case with non-heating guide tube showed a little good performance in terms of CHF.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.1
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• pp.56-61
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• 2005

Indoor air quality becomes of a concern recently in view of human health. This study investigates the air diffusion performance and the air change efficiency of a classroom, when outdoor air is introduced in addition to the heating/cooling operation of a ceiling-mounted heat pump. A CFD analysis has been performed to investigate the effect of the discharge angle of the air jets from the heat pump for both parallel and series types of outdoor air system. It is observed that the series type creates more uniform indoor environment compared to the parallel type in general. It can be concluded the discharge angle should not be larger than 40o for the parallel type, in order not to generate thermal stratification in the room.

• Journal of the Korean Vacuum Society
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• v.18 no.3
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• pp.203-207
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• 2009

Copper is known as a replacement for aluminum wire which is used for semiconductor. Because specific resistance of Cu ($1.67{\mu}{\Omega}$-cm) is lower than that of Al ($2.66{\mu}{\Omega}$-cm), Cu reduce RC delay time. Although melting point of Cu($1085^{\circ}C$) is higher than melting point of Al, Cu have characteristic to easily react with Silicon(Si) in low temperature, and it isn't good at adhesive strength with Si. For above these reason, research of diffusion barrier to prevent reaction between Cu and Si and to raise adhesive strength is steadily advanced. Our study group have researched on W-C-N (tungsten-carbon-nitrogen) Diffusion barrier for preventing diffusion of Cu through semiconductor. By recent studies, It's reported that W-C-N diffusion barrier can even precent Cu and Si diffusing effectively at high temperature. In this treatise, we vaporized different proportion of N into diffusion barrier to research Cu's Electromigration based on the results and studied surface hardness in the heat process using nano scale indentation system. We gain that diffusion barrier containing nitrogen is more stable for Cu's electromigration and has stronger surface hardness in heat treatment process.

• Journal of Radiation Protection and Research
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• v.16 no.2
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• pp.27-39
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• 1991

The diffusion of Sr-85, Cs-137, Co-60 and Am-241 in compacted domestic bentonite was studied, using a diffusion cell unit in which diffusion took place axially from the center of cylindrical bentonite sample body. The effects of compaction density and heat-treated bentonite on diffusion were analysed. And the diffusion mechanism of radionuclide was also analysed by evaluating the measured diffusivity of anion Cl-36. The apparent diffusivities obtained for Sr-85, Cs-137, Co-60 and Am-241 were $l.07{\times}10^{-11},\;6.705{\times}10^{-13},\;l.226{\times}10^{-13}\;and\; l.310{\times}10^{-14}m^2/sec$, respectively. When the as-pressed density of bentonite increased from $1.8\;to\;2.0g/cm^3$, the apparent diffusivity of Cs-137 decreased by quarter. In the case of bentonite heat-treated to $150^{\circ}C$, no significant change in diffusivity was observed, which showed the possibility that the domestic bentonite could be used as a chemical barrier to retard the radionuclide migration at below $150^{\circ}C$. From the calculated pore and surface diffusivity, the surface diffusion due to the concentration gradient of radionuclide sorbed on the solid phase was found to dominate greatly in total transport process.

• Journal of Environmental Science International
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• v.17 no.6
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• pp.689-698
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• 2008

Numerical study is conducted to predict effects of radiative heat loss and fuel composition in synthetic gas diffusion flame diluted with $CO_2$. The existing reaction models in synthetic gas flames diluted with $CO_2$ are evaluated. Numerical simulations with and without gas radiation, based on an optical thin model, are also performed to concrete impacts on effects of radiative heat loss in flame characteristics. Importantly contributing reaction steps to heat release rate are compared for synthetic gas flames with and without $CO_2$ dilution. It is also addressed that the composition of synthetic gas mixtures and their radiative heat losses through the addition of $CO_2$ modify the reaction pathways of oxidation diluted with $CO_2$.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.11
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• pp.965-973
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• 2005

This paper proposes a mathematical model for predicting the frosting performance on a fin-tube heat exchanger. The model consists of empirical correlations of average heat transfer coefficients for the plate and tube surfaces and a diffusion equation inside the frost layer. The numerical results are compared with experimental data for the frost thickness, the frosting rate and the heat transfer rate to validate the proposed model. The results are in good agreement with the experimental data, and show that this model can be applied to predict frosting performance of common fin-tube heat exchanger.

• Bulletin of the Korean Chemical Society
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• v.24 no.2
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• pp.178-182
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• 2003

The stress and the heat-flux auto-correlation functions in the Green-Kubo formulas for shear viscosity and thermal conductivity have non-decaying long-time tails. This problem can be overcome by improving the statistical accuracy by N (number of particles) times, considering the stress and the heat-flux of the system as properties of each particle. The mean square stress and the heat-flux displacements in the Einstein formulas for shear viscosity and thermal conductivity are non linear functions of time since the quantities in the mean square stress and the heat-flux displacements are not continuous under periodic boundary conditions. An alternative to these quantities is to integrate the stress and the heat-flux with respect to time, but the resulting mean square stress and heat-flux displacements are still not linear versus time. This problem can be also overcome by improving the statistical accuracy. The results for transport coefficients of liquid argon obtained are discussed.

• Journal of the Korean Society of Visualization
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• v.14 no.2
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• pp.25-30
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• 2016

The wafer temperature and its uniformity inside the LPCVD chamber were analyzed. The temperature uniformity at the end of the wafer load depends on the heat-insulating cap. The finite difference method was used to investigate the radiation and conduction heat transfer mechanisms, and the temperature field and heat diffusion in the LPCVD chamber was visualized. It was found that the temperature uniformity of the wafers could be controlled by the size and distance of the heat-insulating cap.

• Journal of the Korea Furniture Society
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• v.20 no.5
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• pp.490-503
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• 2009

The objective of this work was to investigate the mechanism of heat transfer in hot-pressing process for MDF manufacturing by reference study. Firstly, general heat transfer theory was studied. The numerical analysis of heat transfer in hot-pressing process was studied on temperature profile, moisture profile, physical properties between moisture and board. The mechanism of heat and moisture transfer inside of board was analyzed by conduction, convection, radiation and diffusion of bound water in wood cell walls. Especially, the change of core temperature as hot press time was important factor to setup hot-pressing schedule in MDF manufacturing.

• Fire Science and Engineering
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• v.10 no.2
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• pp.28-39
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• 1996

A recently developed electro-thermal simulation methodology is used to analyze the behavior of a PWM(Pulse-Width-Modulated) voltage source inverter which uses IGBT(Insulated Gate Bipolar Transistor) as the switching devices. In the electro-thermal network simulation methdology, the simulator solves for the temperature distribution within the power semiconductor devices(IGBT electro-thermal model), control logic circuitry, the IGBT gate drivers, the thermal network component models for the power silicon chips, package, and heat sinks as well as the current and voltage within the electrical network. The thermal network describes the flow of heat form the chip surface through the package and heat sink and thus determines the evolution of the chip surface temperature used by the power semiconductor device models. The thermal component model for the device silicon chip, packages, and heat sink are developed by discretizing the nonlinear heat diffusion equation and are represented in component from so that the thermal component models for various package and heat sink can be readily connected to on another to form the thermal network.