• Title/Summary/Keyword: 순환영역

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Internal Flow Analysis of Seawater Cooling Pump using CFD (CFD를 이용한 해수냉각펌프의 내부유동 분석)

  • Bao, Ngoc Tran;Yang, Chang-jo;Kim, Bu-gi;Kim, Jun-ho
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.23 no.1
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    • pp.104-111
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    • 2017
  • This research focuses on simulation and visualization of flow field characteristics inside a centrifugal pump. The 3D numerical analysis was carried out by using a numerical CFD tool, addressing a Reynolds Average Navier-Stock code with a standard k-${\varepsilon}$ two-equation turbulence model. The simulation accounts for friction head loss due to rough walls at suction, impeller, discharge areas and volumetric head loss at impeller wear ring. A comparison of performance curves between simulation and experimentation is included, and it reveals a same trend of those results with a small difference of maximum 5 %. At best efficiency point, velocity vectors are smooth but it changes significantly under off-design point, a strong recirculation appears at the outlet of impeller passages near tongue area. A relatively uniform preassure distribution was observed around the impeller in despite of the tongue. Within the volute, because of its geometry, spiral vortexes formed, proving that the flow field in this region was relatively turbulent and unsteady.

Atherogenic Risk Stratification According to Changes in the Geometrical Shape of the Coronary Artery (관상동맥의 기하학적 형상변화에 따른 동맥경화 위험도)

  • Suh, Sang-Ho;Park, Jun-Gil;Roh, Hyung-Woon;Lee, Byung-Kwon;Kwon, Hyuck-Moon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.34 no.10
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    • pp.893-899
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    • 2010
  • A previous study showed that hemodynamics is correlated with stenosis in the coronary artery. The flow characteristics and the distributions of the hemodynamic wall parameters in the coronary artery are investigated under physiological flow condition. The present study also aims to establish the mechanism of the generation of atherosclerosis by analyzing the hemodynamic variables in the coronary artery where atherosclerosis frequently occurs. The stenosis phenomena due to atherosclerosis are related to not only the biochemical reaction between blood and blood vessels but also the hemodynamic factors sush as flow separation and oscillatory wall shear stress. As the bifurcated angle increases, the size of the recirculation area that appears in the cross section increases and disturbed flow is observed in this area. We speculate that this area is the starting point of atherosclerosis in the coronary artery.

Synthesis of ultrafine calcium carbonate powders from high concentrated calcium hydroxide solution (고농도 수산화칼슘 수용액으로부터 초미립 경질 탄산칼슘 분말의 합성)

  • Ahn, Ji-Whan;Park, Charn-Hoon;Kim, Jeong-Heo;Lee, Jong-Kook;Kim, Hwan
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.6 no.4
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    • pp.509-520
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    • 1996
  • Ultrafine calcim carbonate powders with the size of $0.05~0.1\;{\mu}m$ and the calcite phase were synthesized by the nozzle spouting method, which could be only obtained when high calcium ion concentration within slurry was maintained at the beginning of the reaction. But, in the regions of low ${Ca(OH)}_2$ concentration (0.5~1.0 wt%) or high ${Ca(OH)}_2$ concentration (<3.0 wt%), synthesized calcium carbonate powder was shown the large particle size with agglomeration. To obtain ultrafine calcium carbonate powder in this region, the methods of slurry circuation and $CO_{2}$ gas supply were changed during reaction. Resultly, it was possible to synthesize ultrafine particles (${\approx}0.05{\mu}\textrm{m}$)in the regions of low ${Ca(OH)}_2$ concentration (${\approx}0.5wt%$) and high ${Ca(OH)}_2$ concentration (${\approx}0.5wt%$), which can not be obtained the fine calcium carbonate powder still now.

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Characteristic Study on Effect of the Vent Mixer to Supersonic Fuel-Air Mixing with Stereoscopic-PIV Method (3차원 PIV 기법을 사용한 벤트혼합기가 초음속 연료-공기 혼합에 미치는 특성 연구)

  • Kim, Chae-Hyoung;Jeung, In-Seuck;Choi, Byung-Il;Kouchi, Toshinori;Masuya, Goro
    • Journal of the Korean Society of Propulsion Engineers
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    • v.16 no.4
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    • pp.50-56
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    • 2012
  • Vent mixer can provide main flow directly into a recirculation region downstream of the mixer to enhance fuel-air mixing efficiency. Based on experimental results of three-dimensional velocity, vorticity and turbulent kinetic energy obtained by a stereoscopic PIV method, the performance of the vent mixer was compared with that of the step mixer which was used as a basic model. Thick shear layers of the vent mixer induced the increase of the penetration height. The turbulent kinetic energy mainly distributed along a boundary layer between the main flow and the jet plume. This turbulent field activates mass transfer in a mixing region, leading to the mixing enhancement.

Analysis of Surface Flow around a sequence of Spur Dikes Using Surface Image Velocimetry (표면영상유속계를 활용한 연속된 수제 주변의 흐름특성 분석)

  • Yong Jun Kwon;Hyung Suk Kim
    • Proceedings of the Korea Water Resources Association Conference
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    • 2023.05a
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    • pp.324-324
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    • 2023
  • 수제는 비용 대비 높은 효율을 가지는 수공 구조물로 하천과 해안에 많이 이용된다. 수제는 하천에서 식생물의 서식처, 유량 확보, 하천시설 보호 등의 목적으로 설치되며 해안에서는 해안선보호, 수심 확보 등의 다양한 목적으로 설치된다. 수제는 일반적으로 넓은 영역을 제어할 수 있도록 여러개의 군수제 형태로 설치한다. 수제설치 시 기존 하도나 수로의 흐름에 교란이 일어나는데 본류부에서는 하폭이 좁아져 수제선단부에 의한 영향으로 높은 유속이 발생되며 수제역내에서는 재순환흐름과 함께 다양한 형태의 유속분포가 형성된다. 이러한 수제에 의한 흐름은 수제 선단부의 영향으로 발생하는 흐름분리선(Separation Layer)을 기준으로 흐름중심선(Talweg Line)과 흐름분리영역(Separation area)을 만들어내며 수제역내의 재순환영역에서 완화된 유속은 제방을 침식으로부터 보호하며 식생물의 서식처를 제공한다. 기존의 연구는 대부분 단일수제에 대한 연구가 수행되었으며 연속된 군수제에 대한 연구는 다소 제한된 조건에서 수행되었다. 이에 본 연구에서는 연속된 수제가 설치된 경우 수리실험을 통해 수제주변의 흐름 변화 특성을 분석하였다. 수리실험은 30.0m(L')×1.52m(B')×1.10m(H')의 직선 개수로에 050m(l)×0.10m(b)×0.25m(h)의 수제를 수로측면을 따라 연속적으로 배열하여 설치하였다. 실험은 수심, 유량, 수제설치간격을 변화시키면서 수행했으며 마그네틱유속계를 사용해서 수제의 영향을 받지 않으며 벽면의 영향이 가장 적은 수로상류의 중앙지점에서 접근유속을 측정했다. 표면유속을 취득하기 위해 일반디지털카메라로 FHD(1920×1080) 해상도를 가진 영상을 각각의 조건마다 10~20분 촬영했다. 촬영된 영상을 연속된 정지영상으로 변환하고 영상해석 프로그램을 이용하여 표면유속을 도출했다. 표면영상유속계를 활용하여 도출한 결과로 각각 조건에 따라 발생하는 최대유속과 최대역방향유속, 와도(vorticity), 흐름중심선과 단면유속분포의 변화와 발생 위치를 분석했다.

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A Study on the Evaluation of Greening Level of Domestic Public Libraries (국내 공공도서관의 녹색화 수준 평가 연구)

  • Noh, Younghee
    • Journal of the Korean BIBLIA Society for library and Information Science
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    • v.28 no.2
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    • pp.5-34
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    • 2017
  • This study measured greening level on the 978 public libraries nationwide, making and distributing questionnaires based on green library evaluation indicators developed to measure the greening level of public libraries. As a result of analyzing the averages by evaluation area, among the green library evaluation areas, the whole average of the library resources was the highest by 1.93, and followed by land use and traffic 1.81, indoor environment 1.30, management of water circulation 1.20, etc. The greening evaluation area which shows the best strength in the surveyed public libraries, was the area of the library resource, and it turned out that it use spaces effectively like effective use of the entire area, effectiveness of conservation of books, use and management of eco-friendly products etc., or use the equipments in eco-friendly way which are purchased or used frequently in the libraries, and, as for the land use and traffic area, most of the libraries had bicycle racks, and chose the location of the libraries, considering accessibility to public transportation and a distance between central urban area and libraries. Also, it turns out that, in the area of materials and resources, most of the libraries were equipped with hand dryers and rolling towels and maintained the eco-friendly view.

Effects of Combustion Characteristics of the Burners for Non-Oxidizing Direct Fired Furnaces on the Oxidization of the Surface of Steel Plate (무산화 직화로 버너의 연소특성이 강재표면의 산화에 미치는 영향)

  • Park, Heung Soo;Riu, Kap Jong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.23 no.3
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    • pp.330-341
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    • 1999
  • An experimental study for the two types of burners used in the non-oxidizing direct fired furnaces of the heat treatment process for the cold rolled plate has been carried out to investigate the combustion characteristics and the oxidization of the surface of steel plate. A steep temperature gradient and entrainment of residual oxygen were found near the heating surface in the flame of the nozzle mixing burner which has strong swirl velocity component. It was concluded that the elimination of the residual oxygen and the increase of the temperature of combustion gas on the heating surface are needed to enhance the performance of the burners for application to the non-oxidizing direct fired furnaces.

Numerical Analysis for the Flow Field past a Two-Staged Conical Orifice (이단 원추형 오리피스를 지니는 유동장에 대한 수치해석)

  • Kim, Yeon-Soo;Kim, You-Gon
    • Proceedings of the KSME Conference
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    • 2001.06e
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    • pp.499-505
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    • 2001
  • The objective of the paper was to measure the pressure drop and to investigate the recirculation region of the conical orifices used in Kwang-yang Iron & Steel Company. The flow field with water used as a working fluid was the turbulent flow for Reynolds number of $2{\times}10^4$. The effective parameters for the pressure drop and the recirculation region were the conical orifice's inclined angle (${\theta}$) against the wall, the interval(L) between orifices, the relative angle of rotation(${\alpha}$) of the orifices, the shape of the orifice's hole(circle, rectangle, triangle) having the same area. It was found that the shape of the orifice's hole affected the pressure drop and the flow field a lot, But the other parameters did not make much differences to the pressure drop. The PISO algorithm with FLUENT code was employed.

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Spray Characteristics of a Pilot Nozzle in a Counter-Swirl Type Gas Turbine Combustor (가스터빈 연소기용 대향류 선회기의 분무 특성)

  • Ko, Y.S.;Kim, M.H.;Kim, D.J.;Min, D.K.;Chung, S.H.
    • Journal of ILASS-Korea
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    • v.1 no.2
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    • pp.42-49
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    • 1996
  • The structure of sprays from a simplex type pilot nozzle atomizer is studied experimentally by measuring velocities, Sauter mean diameter, and number density. Interaction of the spray with gas-phase flow field generated from a 1 MW range industrial gas turbine combustor adopt ing a counter-swirler is investigated. Various spray behaviors are reported. Especially interest ing characteristics are the tangential motion of the spray and of the spray with swirl interaction. It shows a Rankine combined vortex type of velocity characteristics, having linear velocity profile inside the inner core whole small particles exist and rapidly decreasing velocity profiles outside. Interacting spray has relatively uniform number density profiles compared to the nozzle spray itself.

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Study on Two-Phase Flow generated by Two Jets with Height Difference (높이차가 존재하는 두 분류의 2상유동에 관한 연구)

  • 박상규;양희천;이용호
    • Journal of Advanced Marine Engineering and Technology
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    • v.24 no.1
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    • pp.88-93
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    • 2000
  • In this study, the mixing process of two-phase flow generated by two jets with height difference is analyzed. The primary jet is jetted on the condition of the state mixed pulverized solid particles with air. The height difference between the main jet and the secondary jet is changed into three kinds(0, 32.5, 47.5mm). The velocity vector field, concentration field and turbulent properties of solid particles are measured by using 3-Dimensional Particles Dynamics Analyzer. As the height difference of two jets through the two nozzles increases, the solid particle recirculation zone and the dense zone in the combustion chamber become large. The solid particle concentration at the center of the combustion chamber gets dense because the particle velocity remains slow due to the existence of the solid particle recirculation zone. The particle concentration in the combustion chamber can also be influenced by the hight difference of two jets.

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