• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.705-712
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• 2000

The fluid generally flows through fractures in crystalline rocks where most of underground storage facilities are constructed because of their low hydraulic conductivities. The fractured rock is better to be conceptualized with a discrete fracture concept, rather continuum approach. In the aspect of fluid flow in underground, the simultaneous flow of groundwater and gas should be considered in the cases of generation and leakage of gas in nuclear waste disposal facilities, air sparging process and soil vapor extraction for eliminating contaminants in soil or rock pore, and pneumatic fracturing for the improvement of permeability of rock mass. For the purpose of appropriate analysis of groundwater-gas flow, this study presents an unsteady-state multi-phase FEM fracture network simulator. Numerical simulation has been also conducted to investigate the hydraulic head distribution and air tightness around Ulsan LPG storage cavern. The recorded hydraulic head at the observation well Y was -5 to -10 m. From the results obtained by the developed model, it shows that the discrete fracture model yielded hydraulic head of -10 m, whereas great discrepancy with the field data was observed in the case of equivalent continuum modeling. The air tightness of individual fractures around cavern was examined according to two different operating pressures and as a result, only several numbers of fractures neighboring the cavern did not satisfy the criteria of air tightness at 882 kPa of cavern pressure. In the meantime, when operating pressure is 710.5 kPa, the most areas did not satisfy air tightness criteria. Finally, in the case of gas leaking from cavern to the surrounding rocks, the resulted hydraulic head and flowing pattern was changed and, therefore, gas was leaked out from the cavern ceiling and groundwater was flowed into the cavern through the walls.

• Journal of computational fluids engineering
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• v.16 no.2
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• pp.66-74
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• 2011

The SCR catalyst in coal-fired power plant is eroded by the collision of fly ash on the catalyst surface. However the erosion of SCR catalyst by the collision of fly ash has not been fully studied, especially in terms of fluid dynamics. Hence, in the present study, we focus on the gas and solid flows inside the SCR catalyst duct and their consequent effect on the erosion characteristics. For this purpose, computational fluid dynamics is applied to investigate the two-phase flows and to evaluate the erosion rate for different flow and particle injection conditions. Also, the erosion rate and pressure drop of commonly used square shape are compared with equilateral triangle and hexagon shapes. The pressure drop of SCR catalyst is increased when SCR catalyst surface area per unit volume increases. The erosion rate of SCR catalyst is enhanced when the particle velocity, mass flow rate of particle, particle diameter and cell density of SCR catalyst are increased. From the results, the pressure drop and erosion rate at the catalyst surface can be minimized by reducing cell density of SCR catalyst to decrease particle velocity and number of particle impacts.

• Journal of Mechanical Science and Technology
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• v.14 no.10
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• pp.1159-1167
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• 2000

Particles in liquid-solid suspension flow might enhance or suppress the rate of heat transfer and turbulence depending on their size and concentration. The heat transfer characteristics of liquid-solid suspension in turbulent flow are not well understood due to the complexibility of interaction between solid particles and turbulence of the carrier fluid. In this study, the heat transfer coefficients of liquid-solid mixtures are investigated using a double pipe heat exchanger with suspension flows in the inner pipe. Experiments are carried out using spherical fly ash particles with mass median diameter ranging from 4 to $78{\mu}m$. The volume concentration of solids in the slurry ranged from 0 to 50% and Reynolds number ranged from 4,000 to 11,000. The heat transfer coefficient of liquid-solid suspension to water flow is found to increase with decreasing particle diameter. The heat transfer coefficient increases with particle volume concentration exhibiting the highest heat transfer enhancement at the 3% solid volume concentration and then gradually decreases. A correlation for heat transfer to liquid-solid flows in a horizontal pipe is presented.

• Journal of the Korean Society of Visualization
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• v.18 no.2
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• pp.18-27
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• 2020

Air lift pump operated by buoyancy is mainly used for the continuous circulation and the purification of fluids. In this study, the computational flow analysis has been performed with the geometric and operating conditions of the air lift pump. The numerical data from the analysis have been verified by comparing with the previous experimental data. The following results are obtained which advance the efficiency of the air lift pump. As the submergence length of pipe increases and the pipe length over the water surface decreases, the non-dimensional mass flow ratio increases in both cases. When the position of the air injection hole is within the pipe, the circulation range of the surrounding fluid becomes widened with the distance between the air injection hole and the pipe inlet relatively becoming narrower. It is more efficient both when the air injection velocity is at 10 m/s and at 15 m/s, and when the diameter of the pipe with holes is doubled near the water surface. It is expected that these results can be provided as fundamental data for operating the air lift pump.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.3
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• pp.279-285
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• 2012

It is necessary to install the inert gas system(IGS) for preventing fire and explosion in LNGC main diesel engine crankcase besides oil mist detector(OMD) unit with $CO_2$ gas injector. Therefore, to design the liquid nitrogen IGS, analytical work is conducted for predicting the heat input load of liquid nitrogen heater with two-phase stratified flow model. This paper also presents the effects of changes in pipe diameter, saturated pressure, and inclination angle by ship's movement on cryogenic two-phase stratified flows. It is found that the stratified model gives reasonable predictions, and the model is effective to predict the heat input load of liquid nitrogen IGS.

• Transactions of the Korean hydrogen and new energy society
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• v.30 no.6
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• pp.585-592
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• 2019

In this study, a flashing boiling phenomenon of pressurized water jet was numerically studied and validated against an experimental data in the literatures. The volume of fluid (VOF) technique was used to consider two-phase behavior of water, while the homogeneous relaxation model (HRM) model was used to provide the velocity of phase change. During the flashing boiling through a nozzle, a mach disk was observed near nozzle exit because of pressure drop resulting from two-phase under-expansion. The flashing jet structure, local distributions of temperature/vapor volume fraction/velocity, and position of the mach disk were examined as nozzle inlet temperature changed.

• Journal of the Society of Naval Architects of Korea
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• v.56 no.4
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• pp.361-372
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• 2019

The flow pattern of air layers and skin-friction drag reduction by air injection are investigated to find the suitable multiphase flow model using unstructured finite-volume CFD solver for the Reynolds-averaged Navier-Stokes equations. In the present computations, two different multiphase flow modeling approaches, such as the Volume of Fluid (VOF) and the Eulerian Multi-Phase (EMP), are adopted to investigate their performances in resolving the two-phase flow pattern and in estimating the frictional drag reduction. First of all, the formation pattern of air layers generated by air injection through a circular opening on the bottom of a flat plate are investigated. These results are then compared with those of MMkiharju's experimental results. Subsequently, the quantitative ratios of skin-friction drag reduction including the behavior of air layers, within turbulent boundary layers in large scale and at high Reynolds number conditions, are investigated under the same conditions as the model test that has been conducted in the US Navy's William B. Morgan Large Cavitation Channel (LCC). From these results, it is found that both VOF and EMP models have similar capability and accuracy in capturing the topology of ventilated air cavities so called'air pockets and branches'. However, EMP model is more favorable in predicting quantitatively the percentage of frictional drag reduction by air injection.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.1
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• pp.142-155
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• 1992

Numerical analysis is performed for the unsteady axisymmetric two dimensional phase change problem of freezing of water around a vertical tube. Heat conduction in the tube wall and solid phase, natural convection in liquid phase and volume expansion caused by density difference between solid and liquid phases are included in the numerical analysis. Existing correlation is used for estimating density-temperature relation of water, and the effect of volume expansion is reflected as fluid velocity at the interface and the free surface. As pure water has maximum density at 4.deg. C, it is found that there exists an initial temperature at which the flow direction reverses near the interface and by this effect the slope of interface becomes reversed depending on the initial temperature of water. By considering natural convection and solid-liquid density difference in the calculation, their effects on phase change process are studied and the effects of various parameters are also studied quantitatively.

• Journal of Energy Engineering
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• v.14 no.1
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• pp.11-17
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• 2005

The purpose of this research is to develop the model of pressure drop per unit pipe length due to the turbulence modulations in particle-laden flows which can be applied to various fluid conditions. The wake behind a particle, particle size, loading ratio and density difference between two phases of particle-laden flow was considered. The frictional pressure drop was modeled with the force balance in control volume. The numerical results show good agreements with available experimental data and the model success-fully predicted the mechanism of the pressure drop in particle-laden flows.

• Aerospace Engineering and Technology
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• v.12 no.1
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• pp.163-172
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• 2013

In this study, the cooling of rocket exhaust plume by sprayed water inside plume were investigated as varying of sprayed water mass, location, and method using computational fluid analysis. For Analyze rocket exhaust plume, a single species unreacted analysis model based on the chemically frozen analysis was used and the discrete particle model which was a kind of Euler-Lagrangian analysis model was used for simulate sprayed water inside plume. It was confirmed that the temperature of plume was reduced without cooling when water mass was two times of plume mass through analysis results.