• Journal of the Korean Ceramic Society
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• v.53 no.3
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• pp.301-305
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• 2016

We investigate proton conduction in a nonstoichiometric ${\Sigma}3$ $BaZrO_3$ (210)[001] tilt grain boundary using density functional theory (DFT). We employ the space charge layer (SCL) and structural disorder (SD) models with the introduction of protons and oxygen vacancies into the system. The segregation energies of proton and oxygen vacancy are determined as -0.70 and -0.54 eV, respectively. Based on this data, we obtain a Schottky barrier height of 0.52 V and defect concentrations at 600K, in agreement with the reported experimental values. We calculate the energy barrier for proton migration across the grain boundary core as 0.61 eV, from which we derive proton mobility. We also obtain the proton conductivity from the knowledge of proton concentration and mobility. We find that the calculated conductivity of the nonstoichiometric grain boundary is similar to those of the stoichiometric ones in the literature.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.1
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• pp.22-27
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• 2007

we have been studied on the realization of the boundary layer controlled ozone process and related facilities in order to apply for the photo-resist strip process in the semiconductor and flat panel display manufacturing. By means of developing the technology for the high concentration ozone production, it was possible to realized the boundary layer control ozone process by vapor. As a result of the silicon wafer PR strip test, we obtained the strip rate of about 400nm/min at the ozone concentration of 16wt% and flow rate of 8[liter/min.].

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.10
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• pp.1697-1701
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• 2016

The leakage conduction and critical voltage characteristic of ZnO ceramic were investigated as a function of $Sb_2O_3$ concentration. Leakage conduction in the ohmic region increased with increasing $Sb_2O_3$ concentration and was attributed to the potential barrier height. The nonlinear coefficient increased with an increasing amount of $Sb_2O_3$. It was found that increases in the apparent critical voltages were associated with the lowered donor concentration in the grain boundary of between two ZnO grains. And the decrease of donor concentration on doping with $Sb_2O_3$ additive was attributed to the lowered capacitance in the grain boundary layer.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.648-653
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• 2001

This study represents the numerical analysis of natural convection of a microenvironments with a air permeability in the clothing air-layer. The clothing air layer of shoulder and arm was used for numerical analysis model. As a numerical analysis method, we adopted a finite volume method for two-dimensional laminar flow, and analyzed the flow and thermal characteristics of velocity, temperature and concentration in the air layer between body and clothing. As a temperature boundary conditions, we considered that a body skin has a high temperature with $34^{\circ}C$ the environmental temperatures are $5,\;15\;and\;25^{\circ}C$ for various permeability coefficients. The distributions of concentration, temperature and velocity were showed that two large cells were. formed at horizontal and vertical air layer, respectively. As the temperature difference between body skin and environment decrease, the heat transfer was decreased rapidly.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.12
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• pp.1282-1287
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• 2001

This study presents the numerical analysis of natural convection of a micro- environments with air permeability in the clothing air-layer. As a numerical model the clothing air layer of shoulder and arm were adopted. Finite volume method for two-dimensional laminar flow was used for the analysis of flow and thermal characteristics of velocity, temperature and concentration in the air layer between body and clothing. As temperature boundary conditions, a body skin has a high temperature with $34^{\circ}C$ and the environmental temperatures are 5, 15 and $25^{\circ}C$ for various permeability coefficients. The distributions of concentration, temperature and velocity are shown that two large cells form at horizontal and vertical air layer, respectively. As the temperature difference between body skin and environment decreases, the heat transfer is decreased rapidly.

• Wind and Structures
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• v.27 no.6
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• pp.417-430
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• 2018

The concentration fields in the proximities of a local gas emission source are experimentally analyzed in several combinations of wind incidences and source emissions. These conditions are determined by the plume buoyancy, emission velocity and incident flow wind speed. Concentration measurements are performed by an aspirating probe in a boundary layer wind tunnel. The analysis included the mean concentration values and the intensity of concentration fluctuations in a neutral atmospheric boundary layer flow. Different configurations are tested: an isolated stack in a homogeneous terrain and a stack with a bluff body in close proximity, located windward and leeward from the emission source. The experimental mean concentration values are contrasted with Gaussian profiles and the dilution factor is analyzed with respect to the empirical curves of the minimum dilution. Finally, a study on the plume intermittency is performed in a cross-sectional plane near the emission source. It is possible to highlight the following observations: a) plume vertical asymmetry in the case of an isolated emission source, b) significant differences in the dispersion process related to the relative location of the emission source and bluff body effects, and c) different probabilistic behavior of the concentration fluctuation data in a cross-sectional measurement plane inside the plume.

• Journal of Environmental Science International
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• v.21 no.9
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• pp.1097-1113
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• 2012

Ozone is the secondary photochemical pollutant formed from ozone precursor such as nitrogen dioxide and non-methane volatile organic compounds(VOCs). The ambient concentration of ozone depends on several factors: sunshine intensity, atmospheric convection, the height of the thermal inversion layer, concentrations of nitrogen oxides and VOCs. Busan is located in the southeast coastal area of Korea so the ozone concentration of Busan is mainly affected from the meteorological variables related to the sea such as sea breeze. In this study the ozone concentrations of Busan in 2008~2010 were used to analyse the cause of the regional ozone difference in eastern area of Busan. The average ozone concentration of Youngsuri was highest in Busan however the average ozone concentration of Gijang was equal to the average ozone concentration of Busan in 2008~2010. The two sites are located in eastern area of Busan but the distance of two sites is only 9km. To find the reason for the difference of ozone concentration between Youngsuri and Gijang, the meteorological variables in two sites were analyzed. For the analysis of meteorological variables the atmospheric numerical model WRF(Weather Research and Forecasting) was used at the day of the maximum and minimum difference in the ozone concentration at the two sites. As a result of analysis, when the boundary layer height was lower and the sea breeze was weaker in Youngsuri, the ozone concentration of Youngsuri was high. Furthermore when the sea breeze blew from the south in the eastern area of Busan, the sea breeze at Youngsuri turned into the southeast and the intensity of sea breeze was weaker because of the mountain in the southern region of Youngsuri. In that case, the difference of ozone concentration between Youngsuri and Gijang was considerable.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.7
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• pp.779-784
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• 2005

This paper presents the theory of similarity transformations applied to the momentum and energy equations for laminar, forced, external boundary layer flow over a horizontal flat plate which leads to a set of non-linear, ordinary differential equations of phase change material slurry(PCM Slurry). The momentum and energy equation set numerically to obtain the non-dimensional velocity and temperature profiles in a laminar boundary layer are solved. The heat transfer characteristics of PCM slurry was numerically investigated with similar method. It is clarified that the similar solution method of Newtonian fluid can be used reasonably this type of PCM slurry which has low concentration. The data of local wall heat flux and convective heat transfer coefficient of PCM slurry are higher than those of water more than 150$\~$200$\%$, approximately.

• Applied Chemistry for Engineering
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• v.9 no.5
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• pp.698-703
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• 1998

The pervaporation experiments of aqueous solutions of trichloroethylene (TCE) and chlorobenzene (CB) through the silicone rubber (polydimethylsiloxane, PDMS) membrane were carried out and the effect of concentration polarization on the separation characteristics was investigated. The resistance-in-series model was used to explain the boundary layer resistance. It was clear that the concentration polarization phenomenon had a significant effect on the permeation behavior in the pervaporation separation of the trace organic chlorides from aqueous solutions. With the same membrane thickness, the permeation of TCE, which has a stronger affinity for the PDMS, appeared to be more influenced by the boundary layer resistance than that of CB. The effect of boundary layer resistance was reduced and the membrane resistance became dominant with increasing membrane thickness at a given hydrodynamic condition. The separation factor was increased to approach the intrinsic separation factor of the membrane with its thickness.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.6
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• pp.726-733
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• 2004

The growth of the critical size bubble by diffusion process in viscoelastic medium was treated by an integral method for the concentration boundary layer adjacent to the bubble wall. In this study, we obtained a set of the first order time dependent equations to obtain bubble radius and gas pressure inside the bubble simultaneously. The calculated final cell sizes depending on the initial saturation pressure are in close agreement with the observed ones. The governing equations developed in this study may be used in polymer processing of microcellular foams.