• 한국연소학회:학술대회논문집
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• 1999.10a
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• pp.11-20
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• 1999

Acoustic pressure response and NO formation of hydrogen-air diffusion flames at various pressures are numerically studied by employing counterflow diffusion flame as a model flame let in turbulent flames in combustion chambers. The numerical results show that extinction strain rate increases linearly with pressure and then decreases, and increases again at high pressures. Thus, flames are classified into three pressure regimes. Such non-monotonic behavior is caused by the change in chemical kinetic behavior as pressure rises. Acoustic pressure response in each regime is investigated based on the Rayleigh criterion. At low pressures, pressure-rise causes the increase in flame temperature and chain branching/recombination reaction rates, resulting in increased heat release. Therefore, amplification in pressure oscillation is predicted. Similar phenomena are predicted at high pressures. At moderate pressures, weak amplification is predicted. Emission index of NO shows similar behaviors as to the peak-temperature variation with pressure.

• Progress in Superconductivity and Cryogenics
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• v.9 no.3
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• pp.72-82
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• 2007

This paper relates to reducing the temperature of a cryogenic liquid by contacting it with gas bubbles, which can be characterized by diffusion-driven evaporative cooling, The characteristic of diffusion-driven evaporative cooling is thoroughly examined by theoretical. analytical and experimental methods specifically for the case of helium injection into liquid oxygen. The results reveal that if the gaseous oxygen partial pressure in helium bubbles is lower than the liquid oxygen vapor pressure, cooling occurs autonomously due to diffusion mass transfer. The method of lowering the injected helium temperature turns out to be very effective for cooling purpose.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1133-1138
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• 2003

The pressure tubes, which contain high temperature heavy water and fuel, are within the core of a CANDU nuclear reactor, and are thus subjected to high stresses, temperature gradient, and neutron flux. Further, it is well known that pressure tubes of cold-worked Zr-2.5Nb materials result in hydrogen diffusion, which create fully-hydrided regions (frequently called Blister). Thus a proper investigation of hydrogen diffusion within zirconium-alloy nuclear components, such as CANDU pressure tube and fuel channels is essential to predict the structural integrity of these components. In this respect, this paper presents numerical investigation of hydrogen diffusion to quantify the hydrogen concentration for blister growth of CANDU pressure tube. For this purpose, coupled temperature-hydrogen diffusion analyses are performed by means of two-dimensional finite element analysis. Comparison of predicted temperature field and blister with published test data shows good agreement.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.2
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• pp.189-195
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• 2004

The pressure tubes, which contain high temperature heavy water and fuel, are within the core of a CANDU nuclear reactor, and are thus subjected to high stresses, temperature gradient, and neutron flux. Further, it is well known that pressure tubes of cold-worked Zr-2.5Nb materials result in hydrogen diffusion, which create fully-hydrided regions (frequently called Blister). Thus a proper investigation of hydrogen diffusion within zirconium-alloy nuclear components, such as CANDU pressure tube and fuel channels is essential to predict the structural integrity of these components. In this respect, this paper presents numerical investigation of hydrogen diffusion to quantify the hydrogen concentration fur blister growth of CANDU pressure tube. For this purpose, coupled temperature-hydrogen diffusion analyses are performed by means of two-dimensional finite element analysis. Comparison of predicted temperature field and blister with published test data shows good agreement.

• Membrane Journal
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• v.12 no.2
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• pp.90-96
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• 2002

A novel methodology on the calculations of osmotic pressure and gradient diffusion coefficient has been provided ill the present study, by applying a succinct numerical analysis on the experimental results. Although both the osmotic pressure and the gradient diffusion coefficient represent a fundamental characteristic in related membrane filtrations such as microfiltration and ultrafiltration, neither theoretical analysis nor experiments can readily determine them. The osmotic pressure of colloidal suspension has been successfully determined from a relationship between the data of the time-dependent permeate flux, their numerical accumulations, and their numerical derivatives. It is obvious that the osmotic pressure is gradually increased, as the particle concentration increases. The thermodynamic coefficient was calculated from the numerical differentiation of the correlation equation of osmotic pressure, and the hydrodynamic coefficient was evaluated from the previously developed relation for an ordered system. Finally, the estimated gradient diffusion coefficient, which entirely depends on the particle concentration, was compared to the previous results obtained from the statistical mechanical simulations.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.11
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• pp.1527-1537
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• 1997

Extinction characteristics and acoustic response of hydrogen-air diffusion flames at various pressures are numerically studied by employing counterflow diffusion flame as a model flamelet in turbulent flames in combustion chambers. The numerical results show that extinction strain rate increases linearly with pressure and then decreases, and increases again at high pressures. Thus, flames are classified into three pressure regimes. Such nonmonotonic behavior is caused by the change in chemical kinetic behavior as pressure rises. The investigation of acoustic-pressure response in each regime, for better understanding of combustion instability, shows different characteristics depending on pressure. At low pressures, pressure-rise causes the increase in flame temperature and chain branching/recombination reaction rates, resulting in increased heat release. Therefore, amplification in pressure oscillation is predicted. Similar phenomena are predicted at high pressures. At moderate pressures, weak amplification is predicted since flame temperature and chain branching reaction rate decreases as pressure rises. This acoustic response can be predicted properly only with detailed chemistry or proper reduced chemistry.

• Nuclear Engineering and Technology
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• v.33 no.2
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• pp.192-200
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• 2001

Hydride blisters were formed on the outer surface of Zr-2.5Nb pressure tube by a non- uniform steady thermal diffusion process. A thermal gradient was applied to the pressure tube with a heat bath kept at a temperature of 415$^{\circ}C$ and an aluminum cold finger cooled with flowing water of 15$^{\circ}C$. Optical microscopy and tree-dimensional laser profilometry were used to characterize the hydride blisters with different hydrogen concentrations and thermal diffusion time. Hydride blisters were expected to start at a hydrogen concentration of 30 - 70 ppm and a thermal diffusion time of 4 - 6$\times$10$^{5}$ sec. The hydride blister size increases with higher hydrogen concentrations and longer thermal diffusion time . Some of the samples revealed cracks on the hydride blisters. The ratio of hydride blister depth to height was estimated as approximately 8: 1.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.9
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• pp.1174-1184
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• 1997

Extinction characteristics of pure hydrogen-oxygen diffusion flames, at high pressures in the neighborhood of the critical pressure of oxygen, is numerically studied by employing counterflow diffusion flame as a model flame let in turbulent flames in rocket engines. The numerical results show that extinction strain rate increases almost linearly with pressure up to 100 atm, which can be explained by comparison of the chain-branching-reaction rate with the recombination-reaction rate. Since contributions of the chain-branching reactions, two-body reactions, are found to be much greater than those of the recombination reactions, three-body reactions, extinction is controlled by two-body reactions, thereby resulting in the linearity of extinction strain rate to pressure. Therefore, it is found that the chemical kinetic behaviors don't change up to 100 atm. Consideration of the pressure fall-off reactions shows a slight increase in extinction strain rate, but does not modify its linearity to pressure. The reduced kinetic mechanisms, which were verified at low pressures, are found to be still valid at high pressures and show good qualitative agreement in prediction of extinction strain rates. Effect of real gas is negligible on chemical kinetic behaviors of the flames.

• Applied Science and Convergence Technology
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• v.27 no.4
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• pp.65-69
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• 2018

We studied the critical pressure characteristics of an anode type ion beam source driven by both charge repulsion and diffusion mechanism. The critical pressure $P_{crit}$ of the diffusion type ion beam source was linearly decreased from 2.5 mTorr to 0.5 mTorr when the gas injection was varied in 3~10 sccm, while the $P_{crit}$ of the charge repulsion ion beam source was remained at 3.5 mTorr. At the gas injection of 10 sccm, the range of having normal beam shape in the charge repulsion ion beam source was about 6.4 times wider than that in the diffusion type ion beam source. An impurity of Fe 2p (KE = 776.68 eV) of 12.88 at. % was observed from the glass surface treated with the abnormal beam of the charge repulsion type ion beam source. The body temperature of the diffusion type ion beam source was observed to increase rapidly at the rate of $1.9^{\circ}C/min$ for 30 minutes and to vary slowly at the rate of $0.1^{\circ}C/min$ for 200 minutes for an abnormal beam and normal beam, respectively.

• Journal of the Korea Society of Computer and Information
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• v.15 no.9
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• pp.155-164
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• 2010

Until now, most of studies on Electronic Data Interchange(EDI) have been focused on the introduction of EDI and the performance of EDI. But recently, there have been increasing researches on diffusion of Electronic Data Interchange. The aims of this study are twofold. First, to find the impacts of various factors on EDI diffusion, second, to examine the relationship between EDI diffusion factors and EDI diffusion degree. To accomplish those aims of study, two kinds of methodologies are adopted in the studies, First, model building by wide investigation on previous papers, Second, empirical research for finding the determinants of diffusion of EDI. The results of testing the hypotheses of this research are summarized as follows. First, The important EDI diffusion variables influencing internal diffusion of EDI consist of top management support, scope for EDI, IS sophistication, compatibility, complexity, relative advantages, competition intensity and external pressure. Second, Top management support, scope for EDI, IS sophistication, compatibility, relative advantages, competition intensity and external pressure are associated with external diffusion of EDI. We are aware of the important fact that top management support, scope for EDI, IS sophistication, compatibility, relative advantage, competition intensity and external pressure were simultaneously associated with internal and external diffusion of EDI.