• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.71-74
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• 2008

This paper aims at studying the key design elements for the optimal ventilation system design, developing the design models and suggesting the design guidelines. The key elements include the basic exhaust emission rate, wall friction coefficient, vehicle drag coefficient and slip streaming effect, jet fan operating efficiency, natural ventilation force and installation scheme for jet fans and ventilation monitors in tunnel. The design models developed in this study are one-dimensional ventilation simulator to analyze the air flow, pressure profile and pollutant dispersion inside and outside tunnel, expert model to choose the optimal ventilation method, and the ventilation characteristic chart to evaluate the preliminary ventilation system. The study results are reflected in the design guideline for road tunnel ventilation system.

• Journal of Powder Materials
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• v.7 no.3
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• pp.154-160
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• 2000

In order to enhance sinterability of W-Cu composites used for heat sink materials, mechanical alloying process where both homogeneous mixing of component powders and fine dispersion of minor phase can be easily attained was employed. Nanostructured W-Cu powders prepared by mechanical alloying showed W grain size ranged of 20-50 nm and were able to be efficiently sintered owing to the fine particle size as well as uniform distribution of Cu phase. The thermal properties such as electrical resistivity, coefficient of thermal expansion and thermal conductivity were evaluated as functions of temperature and Cu content. It was found that the coefficient of thermal expansion could be controlled by changing Cu content. The measured electrical resistivities and thermal diffusivities were also varied with Cu content. The thermal conductivities calculated from the values of resistivities and diffusivities showed similar tendency as a function of temperatures. However, this is in contradiction with thermal conductivities of pure W and Cu which decrease with increasing temperature.

• Journal of Wetlands Research
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• v.13 no.3
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• pp.385-394
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• 2011

In this study, optimal parameters of diffusion-analogy GIUH were calculated by separating channel and hillslope from drainage structures in the basin. Parameters of the model were composed of channel and hillslope, each velocity($u_c$, $u_h$) and diffusion coefficient($D_c$, $D_h$). Tanbu subwatershed in Bocheong river basin as a target basin was classified as 4th rivers by Strahler's ordering scheme. The optimization technique was applied to the SCE-UA, the estimated optimal parameters are as follows. $u_c$ : 0.589 m/s, $u_h$ : 0.021 m/s, $D_c$ : $34.469m^2/s$, $D_h$ : $0.1333m^2/s$. As a verification for the estimated parameters, the error of average peak flow was about 11 % and the error of peaktime was 0.3 hr. By examining the variability of parameters, the channel diffusion coefficient didn't have significant effect on hydrological response function. by considering these results, the model is expected to be simplified in the future.

• KSBB Journal
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• v.7 no.1
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• pp.59-65
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• 1992

Hydrodynamics and mixing characteristics such as circulation time, mixing time, circulation velocity and axial dispersion coefficient were investigated using highly viscous pseudoplastic solutions of carboxymethyl cellulose(CMC) in an external circulation loop air-lift reactor with 13$\ell$ working volume. The superficial gas velocity was changed from 1.9 to 6.2cm/s and CMC concentration from 0 to 1.0wt%. The theoretical model based on the pressure balance is developed mathematically to predict liquid circulation velocity. Gas hold-up, circulation velocity and axial dispersion coefficient of liquid phase increased with increasing gas velocity and decreased slightly with increasing liquid viscosity. Mixing time and circulation time decreased with increasing gas velocity and increased with increasing liquid viscosity. Experimental data on liquid circulation velocity were in good agreement with the predicted values.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.9
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• pp.1267-1275
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• 2002

An experimental study was performed to investigate adiabatic wall temperature and heat transfer coefficient around a module cooled by forced air flow. The flow angle of attack to the module were 0$^{\circ}$and 45$^{\circ}$. In the first method, inlet air flow(1~7m/s) and input power.(3, 5, 7W) were varied after a heated module was placed on an adiabatic floor(320$\times$550$\times$1㎣). An adiabatic wall temperature was determinated to use liquid crystal film. In the second method to determinate heat transfer coefficient, inlet air flow(1~7m/s) and the heat flux of rubber heater(0.031~0.062W/$m^2$) were varied after an adiabatic module was placed on rubber heater covering up an adiabatic floor. Additional information is visualized by an oil-film method of the surface flow on the floor and the module. Plots of $T_{ad}$ and $h_{ad}$ show marked effects of flow development from the module and dispersion of thermal wake near the module. Certain key features of the data set obtained by this investigation may serve as a benchmark for thermal-design codes based on CFD.

• Journal of Industrial Technology
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• v.6
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• pp.19-31
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• 1986

The residence time distribution of liquid flow in a 4.0cm diameter column packed with porous $Al_2O_3$ spheres of 0.37cm diameter were measured with pulse injections of a tracer under cocurrent trickling flow conditions. The mean residence time of liquid flow and liquid hold-up calculated by the transient curve of tracer were unaffected by gas flow rates under experimental ranges of liquid flow rates from 2.4 to $4.5(kg/m^2\;sec)$ and gas flow rates from 0 to $0.13(kg/m^2\;sec)$. The axial dispersion coefficient of liquid stream and apparent diffusivity of tracer in a micropore of solid particle were estimated from the response curve of tracer. The calculated Peclet No. were increased in ranges of 68-to 82 with a increasing of liquid mass velocity, and the external effective contacting efficiency between liquid and solid which can be expressed. by $(D_i)_{app}/D_i$ varied in ranges of 0.54 to 0.68 depending on the liquid flow rates. The gas to liquid(water) volumetric mass transfer coefficient were determined from desorption experiments with oxygen at $25^{\circ}C$ and 1 atm. The measured mass transfer coefficients were increased with liquid flow rates and the effect of gas flow rates on the mass transfer coefficient was insignificant.

• Magazine of the Korea Concrete Institute
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• v.8 no.5
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• pp.135-143
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• 1996

Diffusion of water in hardened cement concrete and mortar influences on the dry shrinkage. creep. modulus of' elasticity, etc. In general, water loss through drying process in polymer-modified concrete and mortar is small compared with that of unmodified concrete and mortar due to the films formed by polymer as cement modifieder. The purpose of this study is to investigate the diffusion process of water in the polymer-modified mortars. The polymer-modified mortars using three polymer dispersions and epoxy resin are prepared with various polymer-cement ratios, and water diffusion coefficient of polymer-modified mortars according to inside water content is calculated. From the test results, the water diffusion coefficient of polymer modified mortars i s smaller than that of unmodified mortars and decreases with increasing polymer cement ratio.

• Journal of Soil and Groundwater Environment
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• v.13 no.4
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• pp.1-7
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• 2008

This study analyzed for hydrodynamic dispersion characteristics of multi-soil layer (Silt and clay, Find sand, Coarse sand), data of a field tracer test on the multi-soil layer and data of laboratory column experiments on the samples on each soil layers. Through the analysis of permeability and flow, MS (Silt and clay) and FS (Fine sand), which were low effective porosity, were higher average linear velocity while CS (Coarse sand), which was high effective porosity, was higher hydraulic conductivity. Hydraulic conductivity function based on average soil particle diameter was assumed Y=$3.49{\times}10^{-8}e^{15320x}$ and coefficient of determination was 0.90. Average linear velocity function based on average soil particle diameter was assumed Y=$1.88{\times}10^{-7}e^{11459x}$ and coefficient of determination was 0.81. Longitudinal dispersivity function based on average soil particle diameter was Y = 0.00256$e^{5971x}$ and coefficient of determination was 0.98. According to the linear regression analysis of average linear velocity and longitudinal dispersivity, assumed function was Y = 21.7527x + 0.0063, and coefficient of determination was 0.9979. The ratio of field scale/laboratory scale was 54.09, it exhibited scale-dependent effect of hydrodynamic dispersion. Field longitudinal dispersivity (1.39m) was 7.47 times as higher than longitudinal dispersivity estimated by the methods of Xu and Eckstein (1995). Hydrodynamic dispersion on CS layer was occurred mainly by diffusion flow in the test aquifer.

• Journal of the Korean Society of Groundwater Environment
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• v.6 no.2
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• pp.95-100
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• 1999

Hydrocarbon compounds in vadose zone soils caused by adsorption onto the surfaces of solid particles are generally considered to show retardation effect. In this study, we investigated the retardation effect on the transport of Benzene in a sandy soil by conducting batch and column tests. The batch test was conducted by equilibrating dry soil mass with Benzene solutions of various initial concentrations. and by analyzing the concentrations of Benzene in initial and equilibrated solutions using HPLC. The column test consisted of monitoring the concentrations of effluent versus time known as a breakthrough curve (BTC). We used KCl and Benzene solutions with the concentration of 10 g/L and 0.88 g/L as a tracer, and injected them into the inlet boundary of the soil sample as a square pulse type respectively, and monitored the effluent concentrations at the exit boundary under a steady state condition using an EC-meter and HPLC. From the batch test, we obtained a distribution coefficient assuming that a linear adsorption isotherm exists and calculated the retardation factor based on the bulk density and porosity of the column sample. We also predicted the column BTC curve using the retardation factor obtained from the distribution coefficient and compared with the measured BTC of Benzene. The results of the column test showed that i) the peak concentration of Benzene was much smaller than that of KCl and ⅱ) the travel times of peak concentrations for the two tracers were more or less identical. These results indicate that adsorption of Benzene onto the sand panicles occurred during the pulse propagation but the retardation of Benzene caused by adsorption was not present in the studied soil. Comparison of the predicted with the measured BTC of Benzene resulted in a poor agreement due to the absence of the retardation phenomenon. The only way to describe the absolute decrease of Benzene concentration in the column leaching experiment was to introduce a decay or sink coefficient in the convection-dispersion equation (CDE) model to account for an irreversible sorption of Benzene in the aqueous phase.

• Nuclear Engineering and Technology
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• v.52 no.4
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• pp.819-826
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• 2020

The method of the Laplace transform has been used to obtain an analytical solution of the three-dimensional steady state advection diffusion equation for the airborne radionuclide release from any nuclear installation such as the power reactor in an area source. The present treatment takes into account the removal of the pollutants through the nuclear reaction. We assume that the pollutants are emitted as a constant rate from the area source. This physical consideration is achieved by assuming that the vertical eddy diffusivity coefficient should be a constant. The prevailing wind speed is a constant in 𝑥- direction and a linear function of the vertical height z. The present model calculations are compared with the other models and the available data of the atmospheric dispersion experiments that were carried out in the nuclear power plant of Angra dos Reis (Brazil). The results show that the present treatment performs well as the analytical dispersion model and there is a good agreement between the values computed by our model and the observed data.