• Journal of the Korea Safety Management & Science
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• v.4 no.3
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• pp.35-43
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• 2002

For the unconfined vapor cloud explosion accident by the continuous release of gas-liquid flow of various saturated liquids in a vessel at ground level, overpressures were estimated and analyzed with various release conditions and materials by TNT equivalency model with vapor dispersion. We found that at same release conditions, overpressure showed n-heptane > xylene > n-hexane > toluene > n-heptane > benzene, respectively and that overpressure was increased with increasing the hole diameter and the storage pressure, but it was increased with decreasing the wind speed, the interested distance, and the vessel thickness.

• Water for future
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• v.22 no.3
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• pp.289-298
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• 1989

A review is made of transient phenomena ralation to flow in the vadose zone. Reviewed topics include rapid water table response to rainfall, pulsating flow due to pressure perturbations in the vasoes zone, and the wave-like propagation of increased soil moisture caused by intermittent rainfall. As a basis of interpreting these phenomena, zoning of the vadose zone into a residual water zone, an unsaturated capillaty zone, and a saturated capillary zone are proposed. Possible implications with respect to hydrological processes relating to these phenomena are discussed.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.5
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• pp.299-308
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• 2022

This study was conducted to predict the tendency for heat exchange and boil-off gas (BOG) in a liquefied hydrogen tank under sloshing excitation. First, athe fluid domain excited by sloshing was modeled using a multiphase-thermal flow domain in which liquid hydrogen and hydrogen gas are in the saturated state. Both the the volume of fluid (VOF) and Eulerian-based multi-phase flow methods were applied to validate the accuracy of the pressure prediction. Second, it was indirectly shown that the fluid velocity prediction could be accurate by comparing the free surface and impact pressure from the computational fluid dynamics with those from the experimental results. Thereafter, the heat ingress from the external convective heat flux was reflected on the outer surfaces of the hydrogen tank. Eulerian-based multiphase-heat flow analysis was performed for a two-dimensional Type-C cylindrical hydrogen tank under rotational sloshing motion, and an inflation technique was applied to transform the fluid domain into a computational grid model. The heat exchange and heat flux in the hydrogen liquid-gas mixture were calculated throughout the analysis,, whereas the mass transfer and vaporization models were excluded to account for the pure heat exchange between the liquid and gas in the saturated state. In addition, forced convective heat transfer by sloshing on the inner wall of the tank was not reflected so that the heat exchange in the multiphase flow of liquid and gas could only be considered. Finally, the effect of sloshing on the amount of heat exchange between liquid and gas hydrogen was discussed. Considering the heat ingress into liquid hydrogen according to the presence/absence of a sloshing excitation, the amount of heat flux and BOG were discussed for each filling ratio.

• Proceedings of the Korean Reliability Society Conference
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• 2001.06a
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• pp.455-462
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• 2001

We propose a new method to evaluate the network reliability which greatly reduces the intermediate steps toward calculations of maximum capacity flow by excluding unnecessary simple paths contained in the set of failure simple paths. By using signed simple paths and signed flow, we show that our method is more efficient than that of Lee and Park (2001a) in the number of generated composite paths and in the procedure for obtaining minimal success composite paths. Numerical examples are given to illustrate the use and the efficiency of the method.

• Advances in environmental research
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• v.5 no.4
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• pp.263-282
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• 2016

Contaminant transport in groundwater induces major threat and harmful effect on the environment; hence, the fate of the contaminant migration in groundwater is seeking a lot of attention. In this paper a two dimensional numerical flow and transport model through saturated layered soil is developed. Groundwater flow and solute transport has been simulated numerically using proposed model. The model implements the finite volume time splitting method to discretize the main equations. The performance, accuracy and efficiency of the out coming numerical models have been successfully examined by two test cases. The verification test cases consist of two-dimensional, groundwater flow and solute transport. The final purpose of this paper is to discuss and compare the shape of contaminant plume in homogeneous and heterogeneous media with different soil properties and control of solute transport using a zone for minimizing the potential of groundwater contamination; furthermore, this model leads to select the effective and optimum remedial strategies for cleaning the contaminated aquifers.

• Magazine of the Korean Society of Agricultural Engineers
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• v.42 no.2
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• pp.71-77
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• 2000

A multi-region model for solute transport through saturated soils has been developed to describe preferential flow. The model consists of numerous discrete pore groups, which are characterized by a discrete dispersion coefficient, flow velocity, and porosity . The hydraulic properties for each pore group are derived from a soil's hydraluic conductivity and soil water characteristic functions . Flow in pore group is described by the classical advection-disersion equation (ADE). An implict finite difference scheme was applied to the governing equation that results in a block-tridiagonal system of equations that is very efficient and allows the soil to be divided into any number of pore groups. The numerical technique is derived from methods used to solve coupled equations in fluid dynamics problems and can also be applied to the transport of interacting solutes. The results of the model are compared to the experimental data from published papers. This paper contributes on the characteristics of the method when applied to the parallel porosity model to describe preferential flow of solutes in soil.

• Journal of the Korean GEO-environmental Society
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• v.11 no.5
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• pp.35-43
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• 2010

Partially saturated permeability should be defined by the function of suction (or degree of saturation) and porosity. However, commercial software and most researchers' model often describe as the function of suction. The stability of a soil slope can be affected by both hydraulic and shear strength properties of partially saturated soils. For both studies, we generally use an uncoupled seepage analysis program Seep/W(Geo-Slope, 2007) and a series stress-deformation analysis program Sigma/W, or slope stability analysis program Slope/W. Seep/W is performed for simulations of partially saturated flow problems in non-deformable soil media. However, under real situations, the water flow processes in a deformable soil are influenced by soil skeleton movement and the pore water pressure changed due to seepage will lead to changes in stresses and to deformation of a soil. Many researchers are currently developing their models for solving coupled hydro-mechanical problems to simulate slope stability during a rainstorm. For a proper implementation in the field, the developed model should be still needed in order to achieve appropriate accuracy of the solution for coupled hydro-mechanical problems in soil slope stability. Thus, the paper presents the comparison of slope stability between uncoupled and coupled analyses of seepage and stress deformation problems.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.5 s.236
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• pp.643-652
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• 2005

Saturated nucleate pool boiling experiments for binary mixtures, which are consisted of refrigerant R11 and R113, were performed with constant wall temperature condition. Results for binary mixtures were also compared with pure fluids. A microscale heater array and Wheatstone bridge circuits were used to maintain the constant temperature of the heating surface and to obtain heat flow rate measurements with high temporal and spatial resolutions. Bubble growth images were captured using a high speed CCD camera synchronized with the heat flow rate measurements. The departure time for binary mixtures was longer than that for pure fluids, and binary mixtures had a higher onset of nucleate boiling (ONB) temperature than pure fluids. In the asymptotic growth region, the bubble growth rate was proportional to a value between $t^{\frac{1}{6}}$ and $t^{\frac{1}{4}}$. The bubble growth behavior was analyzed to permit comparisons with binary mixtures and pure fluids at the same scale using dimensionless parameters. There was no discernable difference in the bubble growth behavior between binary mixtures and pure fluids for a given ONB temperature. And the departure radius and time were well predicted within a ${\pm}30{\%}$ error. The minimum heat transfer coefficient of binary mixtures occurred near the maximum ${\mid}y-x{\mid}$ value, and the average required heat flux during bubble growth did not depend on the mass fraction of R11 as more volatile component in binary mixtures. Finally, the results showed that for binary mixtures, a higher ONB temperature had the greatest effect on reducing the heat transfer coefficient.

• Journal of Advanced Marine Engineering and Technology
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• v.19 no.2
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• pp.1-9
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• 1995

The processing paper has devoted to the theory of the flow equations, the basic derivative procedure, the meaning of a valve flow coefficient $C_v$, the valve Reynolds R$R_{ev}$ and its application for liquid control valves, which applicable under the condition of a non-critical flow and the case of piping geometry factor $F_p$=1.0. However there is no information on the effects of fittings, a critical flow and the flow resistance coefficient of a valve equivalent to that of pipe which is conveniently used in the piping design. Since the piping systems of plants or ships generally contain various fittings such as expanders and reducers due to different size between pipes and valves and there may occur a critical flow, that a mass flowrate is maintained to be constant, due to the pressure drop in a piping when a liquid is initially maintainder ar a saturated temperature or at nearby corresponding to upstream pressure, system designer should have a knowledge of the effect to flow due to fittings and the critical flow phenomenon of a liquid. This study is performed to inform system designers with the critical flow phenomenon of a liquid, a valve resistance coefficient, a valve geometry factor and their applications.

• Transactions on Electrical and Electronic Materials
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• v.8 no.2
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• pp.73-78
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• 2007

The crystallization temperature in GeTe solid electrolyte films was improved by in situ-nitrogen doping by rf magnetron co-sputtering technique at room temperature. The crystallization temperature of $250\;^{\circ}C$ in electrolyte films without nitrogen doping increased by approximately $300\;^{\circ}C$, $350\;^{\circ}C$, and above $400\;^{\circ}C$ in films deposited with nitrogen/argon flow ratios of 10, 20, and 30 %, respectively. A PMC memory device with $Ge_{45}Te_{55}$ solid electrolytes deposited with nitrogen/argon flow ratios of 20 % shows reproducible memory switching characteristics based on resistive switching at threshold voltage of 1.2 V with high $R_{off}/R_{on}$ ratios. Nitrogen doping into the silver saturated GeTe electrolyte films improves the crystallization temperature of electrolyte films and does not appear to have a negative impact on the switching characteristics of PMC memory devices.