• 한국연소학회:학술대회논문집
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• 한국연소학회 2005년도 제31회 KOSCO SYMPOSIUM 논문집
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• pp.85-92
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• 2005

Oil-fired power plants usually use several burners and the combustion air is supplied to each burner through the complicated duct which is called windbox. A windbox should be designed to supply combustion air to each burner evenly but, due to the complicated duct shape, flow distribution in the windbox is unbalanced and uneven supplies of combustion air to each burner are induced by these unbalanced flow distribution in the windbox. These flow patterns tend to make flame unstable, increase the formation of pollutants and lower the overall combustion efficiency. To prevent these disadvantages, flow patterns in the windbox should be investigated for the uniform flow distribution. In this study, computational simulation method was used to investigate the flow distribution in the windbox and measured the velocities at the exit of burners in the real windbox to compare with CFD results. The results show two significant flow patterns. One is that the flow rates of each burner are different from each other and this means that all burners operate in different conditions of air to fuel ratio. The other is that the flow distribution at the exit of each burner is not axi-symmetric although the burner shape is axi-symmetric and this increases the pollutant products like CO.

• 대한기계학회논문집A
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• 제39권9호
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• pp.947-954
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• 2015

염료감응형 태양전지용 플렉시블 필름에 도포된 코팅물질의 균질한 코팅은 제품의 성능과 내구성과 매우 밀접한 관계가 있고, 균질한 코팅은 열풍건조로 노즐에서의 균일한 온도분포와 질량유량에 의해 얻어질 수 있다. 본 연구에서 열풍건조로의 성능향상에 영향을 주는 다양한 인자들에 대한 수치해석을 수행함으로써 열풍건조로 출구의 균일한 온도분포와 질량유량을 얻고자 하였다. 수치해석 모델은 유동방정식과 에너지방정식으로 구성되었고, 수치해석을 모델의 검증을 위해 수치해석 결과값과 실험결과를 비교하였다. 연구결과로서 열풍건조로의 타공판이 균일한 온도분포 및 질량유량에 큰 영향을 미친다는 것을 알 수 있었다.

• 한국유체기계학회 논문집
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• 제15권5호
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• pp.11-19
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• 2012

The main function of fuel cell manifold is to render reactants distribution as uniform as possible into a fuel cell stack. The purpose of this study is to numerically investigate the effects of stack manifold design on reactants distribution within a fuel cell stack. Four manifold designs with different manifold entrance shapes (expansion or diffuser) and different values of the extra width between the cell outer channel and manifold side wall are considered and applied to the fuel cell stack consisting of 50 cells. Since the fuel cell stack geometry involves several millions of grid points for numerical calculations, a parallel computing methodology is employed to substantially reduce the computational time and overcome the memory requirement. The numerical simulations are carried out and calculated results clearly demonstrate that both the manifold entrance shape and extra width have a substantial influence on manifold performance, controlling the degree of flow separation and entrance length for fully developed flow in the manifold channel. Finally, we suggest the optimum design of fuel cell manifold based on the simulation results.

• 설비공학논문집
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• 제25권6호
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• pp.324-330
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• 2013

The main objective of this work is to experimentally investigate the effect of inlet geometries on the distribution of two-phase annular flow at header-channel junctions simulating the corresponding parts of compact heat exchangers. The cross-section of the header and the channels were fixed to $16mm{\times}16mm$ and $12mm{\times}1.8mm$, respectively. Experiments were performed for the mass flux and the mass quality ranges of $30{\sim}140kg/m^2s$ and 0.3~0.7, respectively. Air and water were used as the test fluids. Three different inlet geometries of the header were tested:no restriction (case A), a single 8 mm hole at the center (case B), and nine 2 mm holes around the center (case C) at the inlet, respectively. The tendencies of the two-phase flow distribution were different, in each case. For cases B and C (flow resistance exists), more uniform flow distribution results were seen, compared with case A(no flow resistance), due to the flow pattern change to mist flow from annular flow at the inlet, and the flow recirculation near the end plate of the header.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.567-570
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• 2010

With continuously increasing flat panel display size, uniformity of thin film deposition has been drawing more attentions and associated fabrication methodologies are being actively investigated. Since the convective flow field of mixture gas plays a significant role for deposition characteristics of thin film in an APCVD system, it is greatly important to maintain uniform distribution and consistent concentration of mixture gas species. In this paper, computational study has been performed for the improvement of flow uniformity of mixture gas in an APCVD reactor during thin film deposition process. A diffuser slit has bee designed to spread the locally concentrated gas flow exiting from the flow distributor. A uniform flow distributor has been developed which has less dependency on operating conditions for global flow uniformity

• Nuclear Engineering and Technology
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• 제53권1호
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• pp.93-102
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• 2021

The analysis of the fluid flow characteristics in reactor pressure vessel is an important part of the hydraulic design of nuclear power plant, which is related to the structure design of reactor internals, the flow distribution at core inlet and the safety of nuclear power plant. The flow distribution and mixing characteristics in the pressurized reactor vessel for the 1000MWe advanced pressurized water reactor is analyzed by using Computational Fluid Dynamics (CFD) method in this study. The geometry model of the full-scaled reactor vessel is built, which includes the cold and hot legs, downcomer, lower plenum, core, upper plenum, top plenum, and is verified with some parameters in DCD. Under normal condition, it is found that the flow skirt, core plate holes and outlet pipe cause pressure loss. The maximum and minimum flow coefficient is 1.028 and 0.961 respectively, and the standard deviation is 0.019. Compared with other reactor type, it shows relatively uniform of the flow distribution at the core inlet. The coolant mixing coefficient is investigated with adding additional variables, showing that mass transfer of coolant occurs near the interface. The coolant mainly distributes in the 90° area of the corresponding core inlet, and mixes at the interface with the coolant from the adjacent cold leg. 0.1% of corresponding coolant is still distributed at the inlet of the outer-ring components, indicating wide range of mixing coefficient distribution.

• 한국습지학회지
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• 제19권2호
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• pp.202-210
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• 2017

전단응력은 여러 분야에서 사용하는 매우 중요한 역학 인자 중 하나이며, 인공수로의 설계를 위해서 중요하다. 현재 전단응력은 과거에 정해진 계산법을 사용하고 있지만, 사용되는 식에서 바닥전단응력과 에너지경사와 같이 실제로 측정하거나 계산하기 어려운 요소들이 존재한다. 특히, 에너지경사는 산정하기 매우 어려운 인자이며, 전단응력분포를 구하기위해서는 에너지경사가 있어야만 산정할 수 있지만, 경계층의 유속기울기와 유속을 측정하는 것은 현실적으로 어려운 부분이다. 또한 전단응력분포 중 바닥전단응력은 직접 측정하기 매우 어렵고, 유속에 비해 연구가 다소 더딘 실정이다. 전단응력분포를 정확하게 산정할 수 있다면, 바닥전단응력과 에너지경사를 손쉽게 산정할 수 있다. 본 연구에서는 에너지경사를 반영하지 않고 엔트로피 M을 이용하여 평균유속과 전단응력분포를 간단히 산정하는 연구를 진행하였고, 적용한 식의 효용성을 증명하기 위해 기존의 실험실 실측 자료를 사용하였다. 이는 그래프를 통해 응력분포를 나타내어 비교분석을 하였으며, 등류와 부등류에서 각각 결정계수는 0.930-0.998까지로 거의 일치하였다.

• 수산해양교육연구
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• 제9권1호
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• pp.40-48
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• 1997

In this study, uniform pressure distribution with small hole on the surface of symmetric object were given to reduce the viscous frictional force. The results were as follows : 1. The velocity on upper stream were accelerated by uniform pressure distribution on symmetric objects for reducing the viscous frictional resistances. 2. The effects of the distributed small holes were reduced the viscous frictional resistances in down stream region more than upper stream due to the increasing pressure in reverse flow region. 3. The viscous skin friction on surface of symmetric objects with and without distributed small holes are effect in region of upper stream and much decreased in down stream region due to increasing of boundary layer thickness.

• 소성∙가공
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• 제7권6호
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• pp.610-619
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• 1998

The superplastic blow forming technology has advantages of cost reduction and low material consumption. compared to the conventional sheet metal forming technology due to the capability of precisely forming with high elongation and low flow stress. however it has a disadvantage that its partial thickness distribution is non-uniform. A processing technology like diaphragm forming has been developed even though it is difficult to prepare materials for superplastic blow forming. in this study a hemisphere forming of sheet before superplastic forming. It was found that the rotary forming material was less in quantity of cavitation at pole than that of hemisphere part that was superplastic formed without rotary forming treatment. Also discussed are the critical strain which is closely related to cavity shape and size.

• Journal of Advanced Marine Engineering and Technology
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• 제34권3호
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• pp.360-368
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• 2010

A SCR catalytic filter system is used for reducing $NO_x$ and soot emissions simultaneously from diesel combustors. The amount of ammonia (as a reducing agent) must be controlled with the amount of $NO_x$ to obtain an optimal $NO_x$ conversion. Hence, gas mixing between ammonia and exhaust gases is vital to ensure that the SCR catalyst is optimally used. If ammonia mass distribution is not uniform, slip potential will occur in rich concentration areas. At lean areas, on the other hand, the catalyst is not fully active. The better mixing is indicated by the higher uniformity of ammonia mass distribution which is necessary to be considered in SCR catalytic filter system. The ammonia mass distributions are depended on the flow field of fluids. In this study, the velocity field of gaseous flow is investigated to characterize the transport of ammonia in SCR catalytic filter system. The influence of different injection placements on the ammonia mass distribution is also discussed. The results show that the ammonia mass distribution is more uniform for the injector directed radially perpendicular to the main flow of inlet at the gravitational direction than that at the side wall for both laminar (Re = 640) and turbulent flows (Re = 4255). It is also found that the mixing index decreases as increasing the heating temperature in the case of ammonia injected at the side wall.