• 전기화학회지
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• 제8권2호
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• pp.106-114
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• 2005

This article covers the theoretical ac-impedance models for the analysis of oxygen reduction on the porous cathode electrode f3r solid oxide fuel cell (SOFC). Firstly, ac-impedance models were explained on the basis of the mechanism of oxygen reduction, which were classified into the rate-determining steps; (i) adsorption of oxygen atom on the electrode surface, (ii) diffusion of adsorbed oxygen atom along the electrode surface towards the three-phase (electrode/electrolyte/gas) boundaries, (iii) surface diffusion of adsorbed oxygen atom m ixed with the adsorption reaction of oxygen atom on the electrode surface and (iv) diffusion of oxygen vacancy through the electrode coupled with the charge transfer reaction at the electrode/gas interface. In each section for ac-impedance model, the representative impedance plots and the interpretation of important parameters attributed to the oxygen reduction reaction were explained. Finally, we discussed in detail the applications of the proposed theoretical ac-impedance models to the real electrode of SOFC system.

• 한국안전학회지
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• 제25권3호
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• pp.22-27
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• 2010

A prediction performance of Fire Dynamics Simulator(FDS) developed by NIST for the diffusion flame structure was validated with experimental results of a laminar slot jet diffusion flame. Two mixture fraction combustion models and two finite chemistry combustion models were used in the FDS simulation for the validation of the jet diffusion flame structure. In order to enhance the prediction performance of flame structure, DNS and radiation model was applied to the simulation. The reaction rates of the finite chemistry combustion models were appropriately adjusted to the diffusion flame. The mixture fraction combustion model predicted the diffusion flame structure reasonably. A 1-step finite chemistry combustion model cannot predict the flame structure well, but the simulation results of a 2-step model were in good agreement with those of experiment except $CO_2$ concentration. It was identified that the 2-step model can be used in the investigation of flame suppression limit with further adjustment of reaction rates

• 한국수소및신에너지학회논문집
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• 제18권3호
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• pp.265-274
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• 2007

A study has been conducted to clarify NO emission behavior through preferential diffusion effects of $H_2$ and H in methane-hydrogen diffusion flames. A comparison is made by employing three species diffusion models. Special concerns are focused on what is the deterministic role of the preferential diffusion effects in flame structure and NO emission. The behavior of maximum flame temperatures with three species diffusion models is not explained by scalar dissipation rate but the nature of chemical kinetics. The preferential diffusion of H into reaction zone suppresses the populations of the chain carrier radicals and then flame temperature while that of $H_2$ produces the increase of flame temperature. These preferential diffusion effects of $H_2$ and H are also discussed about NO emissions through the three species diffusion models.

• 반도체디스플레이기술학회지
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• 제23권2호
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• pp.60-64
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• 2024

The threshold voltage shift in thin-film transistors (TFTs) is modeled using stretched-exponential (SE) and stretched-hyperbola (SH) functions. These models are derived by introducing empirical parameters into reaction rate equations that describe defect generation or charge trapping caused by hydrogen diffusion in the dielectric or interface. Separately, the dielectric relaxation phenomena are also described by the same reaction rate equations based on defect diffusion. Dielectric relaxation was initially modeled using the SE model, and various models have been proposed using fractional calculus. In this study, the characteristics of the threshold voltage shift and the dielectric relaxation phenomena are compared and analyzed to explore the applicability of analytical models used in the field of dielectric relaxation, in addition to the conventional SE and SH models.

• 대한기계학회논문집B
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• 제31권12호
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• pp.1009-1016
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• 2007

Numerical study on preferential diffusion effects in flame structure in $CH_4-H_2$ diffusion flames is conducted with detailed chemistry. Comparison of flame structures with mixture-averaged species diffusion and suppression of the diffusivities of $H_2$ and H was made. Discernible differences in flame structures are displayed with three species diffusion models. The behaviors of maximum flame temperatures with those species diffusion models are not explained by scalar dissipation rate but by the nature of chemical kinetics. It is seen that the modifcation of flame structure is mainly due to the preferential diffusion of H2 and thereby the nature of chemical kinetics. It is also found that the behaviors of major species with the three species diffusion models are addressed to the nature of chemical kinetics, and this is evident by examining importantly contributing reaction steps to the production and destruction of those chemical species.

• International Journal of Concrete Structures and Materials
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• 제6권3호
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• pp.155-163
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• 2012

In order to predict the neutralization of concrete which is the reaction of carbonation dioxide from the outside and cement hydration product, such as calcium hydroxide and C-S-H, it was studied the numerical analysis method considering change of the pore structure and relative humidity during the neutralization reaction. Diffusion-reaction neutralization model was developed to predict the neutralization depth of concrete with coating finishing material. In order to build numerical analysis models considering outdoor environment and finishing materials, the adaption of proposed model was shown the results of existing outdoor exposure test results and accelerated carbonation test.

• Nuclear Engineering and Technology
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• 제53권3호
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• pp.833-841
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• 2021

During the postulated severe accident of nuclear reactor, eutectic reaction leads to low-temperature melting of fuel cladding and early failure of core structure. In order to model eutectic melting with the moving particle semi-implicit (MPS) method, the eutectic reaction model is developed to simulate the eutectic reaction phenomenon. The coupling of mass diffusion and phase diagram is applied to calculate the eutectic reaction with the uniform temperature. A heat transfer formula is proposed based on the phase diagram to handle the heat release or absorption during the process of eutectic reaction, and it can combine with mass diffusion and phase diagram to describe the eutectic reaction with temperature variation. The heat transfer formula is verified by the one-dimensional melting simulations and the predicted interface position agrees well with the theoretical solution. In order to verify the eutectic reaction models, the eutectic reaction of uranium and iron in two semi-infinite domains is simulated, and the profile of solid thickness decrease over time follows the parabolic law. The modified MPS method is applied to calculate Transient Reactor Test Facility (TREAT) experiment, the penetration rate in the simulations are agreeable with the experiment results. In addition, a hypothetical case based on the TREAT experiment is also conducted to validate the eutectic reaction with temperature variation, the results present continuity with the simulations of TREAT experiment. Thus the improved method is proved to be capable of simulating the eutectic reaction in the severe accident.

• Journal of Welding and Joining
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• 제32권5호
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• pp.13-20
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• 2014

A brief overview is given of the corrosion and hydrogen diffusion behaviors of high strength pipe steel in sour environment. Firstly, hydrogen adsorption and diffusion mechanism of the pipe steel is introduced. Secondly, the effect of iron sulfide film precipitated as a result of the corrosion reaction on the steel surface on hydrogen reduction reaction and subsequent hydrogen permeation through the steel is discussed. Moreover, the hydrogen diffusion behavior of the pipe steel under tensile stress in both elastic and plastic ranges is reviewed based on a number of experimental permeation data and theoretical models describing the hydrogen diffusion and trapping phenomena in the steel. It is hoped that this paper will result in significant academic contributions in the field of corrosion and hydrogen related problems of the pipe steel used in sour environment.

• Bulletin of the Korean Chemical Society
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• 제33권3호
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• pp.1020-1028
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• 2012

This work compares various models for geminate reversible diffusion influenced reactions. The commonly utilized contact reactivity model (an extension of the Collins-Kimball radiation boundary condition) is augmented here by a volume reactivity model, which extends the celebrated Feynman-Kac equation for irreversible depletion within a reaction sphere. We obtain the exact analytic solution in Laplace space for an initially bound pair, which can dissociate, diffuse or undergo "sticky" recombination. We show that the same expression for the binding probability holds also for "mixed" reaction products. Two different derivations are pursued, yielding seemingly different expressions, which nevertheless coincide numerically. These binding probabilities and their Laplace transforms are compared graphically with those from the contact reactivity model and a previously suggested coarse grained approximation. Mathematically, all these Laplace transforms conform to a single generic equation, in which different reactionless Green's functions, g(s), are incorporated. In most of parameter space the sensitivity to g(s) is not large, so that the binding probabilities for the volume and contact reactivity models are rather similar.

• Journal of Advanced Marine Engineering and Technology
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• 제32권5호
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• pp.737-746
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• 2008

Numerical study is conducted to grasp preferential diffusion effects on flame characteristics in $H_2/CO$ syn-gas diffusion flames diluted with $CO_2$. The models of Sun et al. and David et al., which have been well known to be best-fitted for $H_2/CO$ synthetic mixture flames. are evaluated for $H_2/CO$ synthetic mixture flames diluted with $CO_2$. Comparison of flame structures with mixture-averaged species diffusion and suppression of the diffusivities of $H_2$ and H was made. The behaviors of maximum flame temperatures with those species diffusion models are not explained by scalar dissipation rate but by the nature of chemical kinetics. Importantly-contributing reaction steps to heat release rate are also compared for the three species diffusion models in $H_2/CO/CO_2$ flames with and without $CO_2$ dilution.