• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.276-279
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• 2008

Heat/smoke detectors are installed in most subway platforms in Korea to detect fire. Subway platform is divided by smoke-control zones for efficient smoke-control. Once the detectors detect heat or smoke, the smoke-control ventilation system in the platform and concourse is activated according to the smoke-control ventilation mode. Smoke-control mode during fires in Korean subway platforms is that the smoke zones operate by exhausting smoke while other zones in the platform and in the concourse which is the upper floor of the platform operate by supplying air or stopping any ventilation. This study is conducted to evaluate performance of passengers' evacuation for various smoke control modes in the subway station. Distribution of smoke and heat due to fire on the platform is analyzed by using Fire Dynamics Simulator(FDS V 4.06) of NIST. Various smoke-control ventilation modes and locations of fire are considered. Evacuation and movement of passengers within the platform is simulated by buildingEXODUS V 4.0.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.12
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• pp.1102-1106
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• 2008

Microfluidics deals with the behavior, precise control and manipulation of fluids at a micro scale. It has become increasingly prevalent in various applications such as biomedical applications (diagnostics, therapeutics, and cell/tissue engineering), inkjet head, and fuel cells etc. The issue of inspection and characterization of microfluidics has emerged as a major consideration in design, fabrication, and detection of microfluidic devices. In this paper, we characterize a diffusion based mixing in Y-microchannel using a fluorescent optical scanner based on a DVD pick-up module, which is widely used in optical storages. Using fluorescent dye, we measure the fluorescent intensity that represents the mixing patterns in Y-microchannel. We also compare these experimental results with computational fluid dynamics (CFD) simulation ones. It is shown that the proposed optical scanner can be used as an alternative measurement system with high performance and cost-effectiveness, compared to conventional optical tools such as epifluorescent microscopes using high resolution CCD camera and confocal microscopes with photomultiplier (PMT) detectors.

• Fire Science and Engineering
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• v.16 no.4
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• pp.7-14
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• 2002

The diffusion characteristics of the smoke by effect of an ascending air movement in a local part of the room where heat generated was studied. How the smoke move in the limited parts of the room at which heat generated was studied through 3 cases altering locations of inlet and outlet of ventilated air and heat generated by CFD(Computational Fluids Dynamics) method. It was found that 1. Similar distribution of air velocity, air temperature and smoke concentration appeared in the case of upper left inlet and lower right outlet and the case of lower inlet and upper right outlet. 2. Distribution of temperature and smoke concentration was 0∼0.3, 0.06∼0.14 in the case of lower left inlet and upper right outlet. 3. the location of heat generation did not influence on the temperature distribution, but influence on the distribution of smoke concentration.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.267-274
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• 2004

The optimum condition is defined as one that best suits the purpose of flocculation; the number of small particles should decrease, while that of large particles should increase. The object of this research was to develop a new impeller and substitute for conventional flocculators. The flow characteristics of turbines and hydrofoil type flocculators in turbulent fluids were observed using a standard k-$\epsilon$ Model and a computational fluid dynamics (CFD) simulation program- FLUENT The experiments were performed to compare PBT(Pitched Blade Turbine) flocculator with twisted hydrofoil type flocculators for velocity distribution, and floc formation at conventional water treatment plants in Korea. As a result of the CFD solution, twisted hydrofoil types are similar to hydrofoil flocculators for flow characteristics without regard to the twisted angle, On the other hand, it was established that turbine flocculators are greater than hydrofoil flocculators with flow unevenness and dead zone formation. Twisted hydrofoil type- II (Angle $15{\~}20^{\circ}$) is the most proper impeller for water flocculation from this point of view with a decreasing the dead zone, maintaining of the equivalent energy distribution and a drawing up of the sedimentation substance from the bottom of the flocculation basin.

• The KSFM Journal of Fluid Machinery
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• v.19 no.4
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• pp.19-28
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• 2016

Objective of this study is to compare the inherent characteristics of natural convection flow inside the canister of spent fuel dry storage system with different backfill gases by utilizing computational fluid dynamics (CFD) code. Four working fluids were selected for comparison study. Helium currently used backfill gas for canister, air, nitrogen, and argon are frequently used as coolant in many heat transfer applications. The results indicate that helium has very distinct conductive behavior and show very weak natural convective flow compared to the others. Argon showed the strongest natural convective flow but also the worst coolability. Air and nitrogen showed similar characteristics to each other. However, due to difference in Prandtl number, nitrogen showed more effective natural convective flow. These results suggest that experimental validation for the nitrogen is needed to investigate the potential coolability other than currently commercially used helium.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.10
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• pp.99-103
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• 2019

Recently, as the high-precision machinery industry has developed rapidly, peripheral equipment has been developed to improve machining efficiency. Peripheral equipment for machining includes cooling units, housings, oil separators, and much more. Oil, such as cleaning and cutting fluids, is used for machining. When waste oil is reused, the contamination of the workpieces and reduction in machining accuracy are generated by the waste oil, including sludge. Therefore, the development of an oil separator is necessary for efficiently separating oil, water, and sludge. The purpose of this study is to analyze the oil separation efficiency and flow characteristics of a high-speed centrifugal separator according to the rotation velocity and diffusion plate. The oil separation efficiency and flow characteristics were analyzed using hydrodynamic theory and computational fluid dynamics (CFD). The results of this study will be used as basic data for the development of a high-speed centrifugal separator.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.5
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• pp.84-90
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• 2022

Hydraulic coupling systems play an important role in easily connecting or disconnecting pipes or hoses that transmit high-pressure fluids without hydraulic oil leakage in hydraulic power transmission equipment. A flat-face hydraulic quick coupler is a recently developed product that can reduce environmental pollution by minimizing hydraulic oil leakage during connection and disconnection. In this study, the influence of the shape of the inner ring of a 3/8" flat-face hydraulic quick coupler on its internal flow characteristics was analyzed and evaluated by numerical analysis based on computational fluid dynamics. The flow velocity distribution, temperature distribution, and optimal shape design of the inner ring were obtained by comparing the results of the flow characteristics, such as the pressure drop.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.7
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• pp.1173-1182
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• 2000

The rapid mixing process has been considered as an important step in water treatment. Since the coagulant dispersion into raw water by rapid mixer can influence on the flocculation and filtration efficiency, many researchers have developed various devices and mixing methodologies. Until now, they focused attention on only coagulant dose, pH. rotating velocity and G value but overlooked the real turbulent flow and mixer geometry in rapid mixer. Therefore this paper questions the significance of turbulent flows in rapid mixer and focuses on the analysis of turbulent fluid in various mixer geometry with CFD(Computational Fluid Dynamics). The results of the jar-tests using various geometries indicate that the turbidity removal rate in a circular jar without baffle is higher than that of a circular with baffle. And the turbidity removal rate in Hudson jar is also founded to be higher than in the circular jar with baffle. The CFD simulation of velocity fields in jar demonstrates that the differences of removal rates among the various geometries are largely due to the formation of the different turbulent fluids fields with different geometries.

• Korean Journal of Mineralogy and Petrology
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• v.33 no.3
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• pp.143-152
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• 2020

Birnessite is a layered manganese oxide mineral with ~7 Å of d-spacing. Because of its high cation exchange capacity, birnessite greatly impacts the chemical compositions of ground water and fluids in sediment pores. Understanding the cation exchange mechanisms requires atomistic investigations of the crystal structures and coordination environments of hydrated cations in the interlayer. In this study, we conducted classical molecular dynamics (MD) simulations, an atomistic simulation method of computational mineralogy, for triclinic Na-birnessite and K-birnessite whose chemical formula are from previous experiments. We report our MD simulation results of the crystal structures, coordination environments of Na⁺ and K⁺, and the polytypes of birnessite and compare them with available experimental results. The simulation results well reproduced experimental lattice parameters and provided atomic level information for the interlayer cation and water molecule sites that are difficult to distinguish in X-ray experiments. We also report that the polytype of the Mn octahedral sheets is identical between Na- and K-birnessite, but the cation positions differ from each other, demonstrating a correlation between the coordination environment of the interlayer cations and the crystal lattice parameters. This study shows that MD simulations are very promising in elucidating ion exchange reactions of birnessite.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.190.2-190.2
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• 2016

메탄은 변환을 통해 아세틸렌 및 수소와 같은 에너지 생산에 보다 유용한 기체를 얻을 수 있다. 메탄의 열분해 온도는 약 1,200 K로 알려져 있으며, 그 이상의 고온 환경 및 첨가물을 제공한 경우 효과적인 변환을 기대할 수 있다. 이러한 고온 환경 및 화학반응을 제공할 수 있는 시스템으로 열플라즈마 반응로가 있다. 일반적인 열플라즈마는 아크 방전이나 고주파 유도결합 방전으로 플라즈마 발생기에서 발생시킨 이온화된 열유체로 10,000 K 이상의 초고온과 최대 수천 m/s의 특성을 가지고 있다. 본 연구에서는 효율적인 메탄 변환을 위한 저전력 아크 플라즈마 발생기 및 반응로 내부의 온도 및 속도장을 전산모사하여 열유동 특성을 분석하였다. 아크 플라즈마 토치 영역의 전산해석은 전자기적 현상과 고온 열유동의 유체역학적 현상이 함께 작용하므로 기존에 사용되고 있는 전산유체 역학적인 방법론에 전자기적 현상에 대한 보존 방정식이 결합된 자기유체역학(Magnetohydrodynamic, MHD)방법을 이용하였고, 반응기 내부의 복잡한 열유동은 안정적인 계산이 가능한 상용 전산 유체역학(Computational Fluids Dynamics, CFD) 코드를 MHD 코드를 이용한 전산해석 결과 및 고온 물성치와 결합하여 해석하였다. 전산해석에 사용된 운전 변수로는 방전기체인 아르곤과 수소의 전체 유량을 45 L/min 으로 고정하고 수소의 비율을 0%, 6%, 12.5%, 20%로 하였으며, 각 유량 조건에서 입력 전력을 0.7 ~ 2.5 KW로 변화시켜 전체 15종의 운전조건에 따른 전산해석을 수행하여 각각의 운전변수에 따라 입력전력 기준 오차 1 ~ 28%에 해당하는 결과를 도출하였다. 본 연구를 통해 개발된 전산해석 방법을 이용하여 다양한 조건에서 아크 플라즈마 반응로 내부의 온도 및 속도장에 대한 전산해석 결과를 제시하였고, 효율적인 메탄 변환 공정을 개발하기 위한 아크 플라즈마 반응로의 설계조건 및 운전 조건을 제시할 수 있는 기반을 확보하였다.