• 한국연소학회:학술대회논문집
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• 2000.12a
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• pp.113-122
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• 2000

Dynamic structures of unsteady $CH_4$/Air jet diffusion flames with flame-vortex interaction were numerically investigated. A time-dependent, axisymmetric computational model was adopted for this calculation. Two step global reaction mechanism which considers 6 species, was used to calculate the reaction rates. The predicted results including gravitational effect show that the large outer vortices and the small inner vortex street can be well simulated without any additional disturbances in the downstream of nozzle tip. It was found that the temperature and species concentrations had various values for the same mixture fraction in flame-vortex interaction region. This unsteady jet flame configuration accompanying flame-vortex interaction is expected to give good implications for the structure of turbulent flames.

• Journal of the Korean Mathematical Society
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• v.53 no.1
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• pp.27-43
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• 2016

This paper deals with a degenerate parabolic system with coupled nonlinear localized sources subject to weighted nonlocal Dirichlet boundary conditions. We obtain the conditions for global and blow-up solutions. It is interesting to observe that the weight functions for the nonlocal Dirichlet boundary conditions play substantial roles in determining not only whether the solutions are global or blow-up, but also whether the blowing up occurs for any positive initial data or just for large ones. Moreover, we establish the precise blow-up rate.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.4
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• pp.160-165
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• 2001

The effects of various metals on Field Aided Lateral Crystallization (FALC) behaviors of amorphous silicon (a-Si) were investigated. Under an influence of electric field, metals such s Cu, Ni and Co were found to fasten the lateral crystallization toward a metal-free region, exhibiting a typical FALC behavior while the lateral crystallization of a-Si was not obvious for Pd. However, Au, Al and Cr did not induce the lateral crystallization of a-Si in metal-free region. Such phenomenological differences in various metals were studied in terms of dominant diffusing species (DDS) in the reaction between metal and Si. It was judged that the applied electric field enhanced the crystallization velocity by accelerating the diffusion of metal atoms since the occurrence of lateral crystallization would be strongly dependent on the diffusion of metal atoms than that of Si atoms. Therefore, it was concluded that he only metal-dominant diffusing species in the reaction between metal and Si results in the crystallization of a-Si in metal-free region.

• Carbon letters
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• v.9 no.2
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• pp.121-126
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• 2008

High modulus pitch based carbon fibers (HM) were exposed to isothermal oxidation using tube furnace in carbon dioxide gas to study the oxidation kinetics under the temperature of $800-1100^{\circ}C$. The kinetic equation $f=1-{\exp}(-at^b)$ was introduced and the constant b was obtained in the range of 1.02~1.42. The oxidation kinetics were evaluated by the reaction-controlling regime (RCR) depending upon the apparent activation energies with the conversion increasing from 0.2 to 0.8. The activation energies decrease from 24.7 to 21.0 kcal/mole with the conversion increasing from 0.2 to 0.8, respectively. According to the RCR, the reaction was limited by more diffusion controlling regime for the HM fibers with the conversion increasing. Therefore, it seems that the oxidation which is under the diffusion controlling regime takes place continuously from the skin to the core of the fiber.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.73-78
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• 2003

The InP thin films grown by metalorganic chemical vapor deposition (MOCVD) are widely used to optoelectronic devices such as laser diodes, wave-guides and optical modulators. Effects of various parameters controlling film growth rate such as gas-phase reaction rate constant, surface reaction rate constant and mass diffusivity are numerically investigated. Results show that at the upstream region where film growth rate increases with the flow direction, diffusion including thermal diffusion plays an important role. At the downstream region where the growth rate decreases with flow direction, film deposition mechanism is revealed as a mass-transport limited. Mass transport characteristics are also studied using systematic analyses.

• The KSFM Journal of Fluid Machinery
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• v.15 no.1
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• pp.64-69
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• 2012

Currently axial flow compressor is used primarily in a large power generation gas turbine. In this paper,the main factors to be considered when designing a axial flow compressor were compared to those of a small power generation gas turbine(DGT-5). The main design parameters was examined in the aspect ratio, solidity, as well as reaction, diffusion factor, incidence angle, etc. The results in case of a small compressor are showed a regular pattern but there were not found any specific design patterns for a large class compressor.

• KSBB Journal
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• v.5 no.4
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• pp.397-402
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• 1990

Hydrolysis of inulin was investigated employing various commercially available resin catalysts for the production of high grade fructose syrup. The particle size and porosity of the resin significantly affected the distribution of the products, indicating that the intraparticle diffusion of reactants controls thc selectivity as well as the reaction rate. To confirm the effect of the intraparticle diffusion, two different types of resin catalysts were prepared: the one having sulfonic acid group distributed uniformly throughout genular microparticles (A-type) and the other having sulfonic acid group located mainly at the exterior surface of genular microparticles (E-type). The results were found that the reaction rate and the selectivity of the E-type catalyst were higher than those of the A-type catalyst.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1130-1131
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• 2006

We found that the """interface reaction between Ni-based alloy bond, diamond, and steel core is very critical in bond strength of diamond tool. None element from metal bond diffuses into the steel core but the Fe element of steel core was easily diffused into the bond. This diffusion depth of Fe has a great effect on the bonding strength. The Cr in steel core accelerated the Fe diffusion and improved the bond strength, on the other hand, carbon decreased the strength. Ni-based alloy bond including Cr was chemically bonded with diamond by forming Cr carbide. However, the Cr and Fe in STS304 were largely interdiffused, the strength was very low. The Cr passivity layer formed at surface of STS304 made worse strength at commissure in brazing process.

• Journal of Environmental Health Sciences
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• v.19 no.1
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• pp.51-56
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• 1993

This study was performed to find the ability of bituminous coal fly ash to remove fluoride from water and wastewater at different fluoride concentration, reaction temperature, reaction time and pH. The removal of fluoride is favorable at low concentration, high temperature and acidic pH. With the increase in the initial fluoride concentration, the amount adsorbed increased. Adsorption process was exothermic at pH 2.0. Physisorption process was predominant over pH 2.3, while Chemisorption was under pH 2.3. Fluoride uptake by fly ash was conducted the adherence of fluoride on the active surface sites of adsorbent and its intraparticle diffusion within adsorbent. The values of rate constants of adsorption were 3.028X 10$^{-3}$, 4.715X 10$^{-3}$, 2.88X 10$^{-3}$ (min) and intraparticle diffusion were 1.434X10$^{-3}$, 3.012X10$^{-3}$, 5.635X10$^{-3}$ at each temperatures.

• KCI Concrete Journal
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• v.11 no.3
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• pp.175-180
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• 1999

In order to predict the onset of the corrosion of steel bars in concrete, a mathematical model was presented to observe the diffusion of chloride ion in aqueous phase, the adsorption and desorption of chloride ions to and from the surface of solid phase of concrete, and the chemical reaction or chloride ions with solid phase. The finite element method was employed to carry out the numerical analysis. The chlorides enetrating through the wall of the concrete structure from the external environment and the chlorides contained in the concrete admixture were confirmed to be two important factors to determine the onset of the corrosion of steel bars.