• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2334-2339
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• 2008

This paper proposes an improved mathematical model for predicting the frosting behavior on a two-dimensional fin considering the heat conduction of heat exchanger fins under frosting conditions. The model consists of laminar flow equation in airflow, diffusion equation of water vapor for frost layer, and heat conduction equation in fin, and these are coupled together. In this model, the change in three-dimensional airside airflow caused by frost growth is accounted for. The fin surface temperature increased toward the fin tip due to the fin heat conduction. On the contrary, the temperature gradient in the airflow direction(x-dir.) is small throughout the entire fin. The frost thickness in the direction perpendicular to airflow, i.e. z-dir., decreases exponentially toward the fin tip due to non-uniform temperature distribution. The rate of decrease of heat transfer in the airflow direction is high compared to that in the z-direction due to more decrease in the sensible and latent heat rate in x-direction.

• Coupled systems mechanics
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• v.8 no.2
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• pp.129-146
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• 2019

The main goal of this work is to develop a numerical simulator to study an isothermal single-phase two-component flow in a naturally fractured oil reservoir, taking into account advection and diffusion effects. We use the Peng-Robinson equation of state with a volume translation to evaluate the properties of the components, and the discretization of the governing partial differential equations is carried out using the Finite Difference Method, along with implicit and first-order upwind schemes. This process leads to a coupled non-linear algebraic system for the unknowns pressure and molar fractions. After a linearization and the use of an operator splitting, the Conjugate Gradient and Bi-conjugated Gradient Stabilized methods are then used to solve two algebraic subsystems, one for the pressure and another for the molar fraction. We studied the effects of fractures in both the flow field and mass transport, as well as in computing time, and the results show that the fractures affect, as expected, the flow creating a thin preferential path for the mass transport.

• Journal of Korean Society for Atmospheric Environment
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• v.8 no.3
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• pp.162-168
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• 1992

Numerical solutions to the advection equations used for long-range transport air pollution models are calculated using three numerical methods; Antidiffusion correction method(Smolarkiewicz, 1983), Positive definite advecton scheme obtained by nonlinear renormalization of the advective fluxes(Bott, 1989), and Positive definite pseudospectral method(Bartnicki, 1989). Accuracy, numerical diffusion and computational time requirement are compared for two-dimensional transport calculations in a uniform rotational flow field. The solutions from three methods are positive definite. Bartnicki(1989)'s method is most conservative but requires approximately 10 times as much computational time as Smolarkiewicz(1983)'s method of which numerical diffusion is the largest. All three methods are more conservative for a cone shape initial condition than for a rectangular block initial condition with a steep gradient.

• Communications of the Korean Mathematical Society
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• v.34 no.4
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• pp.1365-1388
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• 2019

In this paper we consider a class of nonlinear nonlocal parabolic equations involving p-Laplacian operator where the nonlocal quantity is present in the diffusion coefficient which depends on $L^p$-norm of the gradient and the nonlinear term is of polynomial type. We first prove the existence and uniqueness of weak solutions by combining the compactness method and the monotonicity method. Then we study the existence of global attractors in various spaces for the continuous semigroup generated by the problem. Finally, we investigate the existence and exponential stability of weak stationary solutions to the problem.

• Korean Journal of Optics and Photonics
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• v.12 no.5
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• pp.394-400
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• 2001

We studied thermal diffusion properties diffusion properties of multi-layered Ge-Sb-Te alloy thin films for optical recording media by solving the thermal equation. Based on the numerical analysis of optical energy distribution and absorption inside multi-layered films including temperature gradient and heat transfer simultaneously, we proposed the optimum parameters of the input laser power and the multi-layer structure as follow. i) Input laser power is 18 mW, ii) laser exposure time is 60 ns, iii) the thicknesses of the lower and the upper ZnS-SiO$_2$are 140 nm and 20~30 nm respectively, and iv) thickness of Ge-Sb-Te recording film is 20 nm.

• The Korean Journal of Ceramics
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• v.6 no.2
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• pp.177-182
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• 2000

At the porous $La_{0.6}Ca_{0.4}MnO_{3-{\delta}}$(LCM)/YSZ electrodes of solid oxide fuel cells (SOFC), the electrochemical redox reaction of oxygen proceeds via the triple boundary (TPB) of gas/LCM/YSZ. The surface diffusion of adsorbed oxygen on LCM has been proposed as the rate determining process, assuming the gradient of oxygen chemical potential from the outer surface of porous layer to TPB. Along with the formation of this gradient, oxygen nonstoichiometry in the bulk of LCM may varies. In this paper, an electrochemical technique was described precisely to determine the variation of oxygen content in LCM of porous LCM/YSZ under polarization. It was shown that the oxygen potential in LCM layer under large cathodic polarization is much lower than that in the gas phase, being determined from the electrode potential and Nernst equation.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.2
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• pp.18-27
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• 2022

In this study, the time-dependent chloride ingress behavior in GGBFS concrete was evaluated considering marine exposure conditions and the properties of concrete mixtures. The concrete mixture for this study had 3 levels of water to binder ratio and the substitution rate of GGBFS, and outdoor exposure tests were performed considering submerged area, tidal area, and splash area. According to the evaluation results of diffusion coefficient considering properties of concrete mixtures, as the substitution rate of GGBFS increased, the decreasing rate of the diffusion coefficient decreased based on exposure periods of 730 days(2 years). As the evaluation result of the diffusion behavior according to the marine exposure conditions, the diffusion coefficient was evaluated in the order of submerged area, tidal area, and splash area. In tidal area, a relatively high diffusion coefficient was evaluated due to the repetition of wet and dry seawater. In this study, the effects of GGBFS substitution rate on the decreasing behavior of apparent chloride diffusion coefficient was analyzed in consideration of exposure conditions and periods. Linear regression analysis was performed with apparent chloride diffusion coefficient as output value and GGBFS substitution rate as input value. After 730 days of exposure, the effect of GGBFS on diffusion coefficient was significantly reduced. Even for OPC concrete, after 730 days, the diffusion coefficient was as low as that of GGBFS concrete, so the gradient of the regression equation decreased significantly. It is thought that improved durability performance for chloride ingress can be secured before 730 days through the use of GGBFS.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.90.2-90.2
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• 2012

Geosynchronous electron flux dropouts are most likely due to fast drift loss of the particles to the magnetopause (or equivalently, the "magnetopause shadowing effect"). A possible effect related to the drift loss is the radial diffusion of PSD due to gradient of PSD set by the drift loss effect at an outer L region. This possibly implies that the drift loss can affect the flux levels even inside the trapping boundary. We recently investigated the details of such diffusion process by solving the diffusion equation with a set of initial and boundary conditions set by the drift loss. Motivated by the simulation work, we have examined observationally the energy spectrum and pitch angle distribution near trapping boundary during the geosynchronous flux dropouts. For this work, we have first identified a list of geosynchronous flux dropout events for 2007-2010 from GOES satellite electron measurements and solar wind pressures observed by ACE satellite. We have then used the electron data from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft measurements to investigate the particle fluxes. The five THEMIS spacecraft sufficiently cover the inner magnetospheric regions near the equatorial plane and thus provide us with data of much higher spatial resolution. In this paper, we report the results of our investigations on the energy spectrum and pitch angle distribution near trapping boundary during the geosynchronous flux dropout events and discuss implications on the effects of the drift loss on the flux levels at inner L regions.

• Applied Chemistry for Engineering
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• v.5 no.1
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• pp.127-138
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• 1994

In the process of pervaporation separation for aqueous ethanol solution through cellulose tai-acetate(CTA) membrane, the modelling on the solution-diffusion permeation mechanism was built up on the basis of sorption and permeation experimental results. Also its function type and parameter were examined. The composition of sorption equilibrium in three component system(Ethanol/Water/CTA) were compared with the calculated value by Flory-Huggins' equation using the pure component sorption data. In order to apply the thermodynamic equilibrium relationship between the membrane free composition in the membrane and the equilibrium composition in the liquid phase, the apparent activity this system, however, the results were not satisfied. Diffusion equations were expressed with the concentration gradient considering permeate alone, and a concentration-dependent diffusion coefficient which includes a parameter was used. And this model was fitted with the measured permeation rates. If the permeation rate and the amount of sorption of one component were much larger than those of the other, the bulk flow term could not be negligible. The flux and selectivity were increased with increasing temperature, and with decreasing downstream pressure.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.122-122
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• 2012

Geosynchronous electron flux dropouts are most likely due to fast drift loss of the particles to the magnetopause (or equivalently, the "magnetopause shadowing effect"). A possible effect related to the drift loss is the radial diffusion of PSD due to gradient of PSD set by the drift loss effect at an outer L region. This possibly implies that the drift loss can affect the flux levels even inside the trapping boundary. We recently investigated the details of such diffusion process by solving the diffusion equation with a set of initial and boundary conditions set by the drift loss. Motivated by the simulation work, we have examined observationally the energy spectrum and pitch angle distribution near trapping boundary during the geosynchronous flux dropouts. For this work, we have first identified a list of geosynchronous flux dropout events for 2007-2010 from GOES satellite electron measurements and solar wind pressures observed by ACE satellite. We have then used the electron data from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft measurements to investigate the particle fluxes. The five THEMIS spacecraft sufficiently cover the inner magnetospheric regions near the equatorial plane and thus provide us with data of much higher spatial resolution. In this paper, we report some case studies showing energy dependence during magnetopause shadowing effect.