• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 추계학술대회 초록집
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• pp.86.1-86.1
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• 2011

To improve the safety, the fuel cell operate inside a pressurized enclosure which contains inert gas so called protective gas. The protective gas not only prevents the mixture of hydrogen and oxygen, but also removes the water in the vessel with the condenser. This study presents the details of the flow optimization in order to reduce the humidity in the fuel cell housing. The protective gas flow in the fuel cell container is studied by Computational Fluid Dynamics(CFD) simulations. This study focuses on optimizing the geometry of an protective gas circulation system in fuel cell module to reduce the humidity in the vessel. CFD analysis was carried out for an existing model to understand the flow behavior through the fuel cell system. Based on existing model CFD results, geometrical changes like inlet placement, optimization of outlet size, modification of fuel cell module system are carried out, to improve the flow characteristics. The CFD analysis of the optimized model is again carried out and the results show good improvement in protective gas flow behavior.

• 한국수자원학회논문집
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• 제53권9호
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• pp.637-646
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• 2020

산지 사면에서 발생하는 토석류는 지형변화에 큰 영향을 미치는 대표적인 자연재해 중 하나이다. 특히, 도심지역에서 발생된 토석류는 유동 및 퇴적과정에서 막대한 재산피해와 인명피해를 야기할 수 있으며 이러한 토석류로 인한 피해를 줄이기 위해서는 토석류의 유동과 피해규모를 예측하기 위한 해석모형들이 필수적이다. 하지만 아직 토석류 모형들의 매개변수에 대한 분석은 충분하지 않으며, 특히 토석류의 유동과정 및 피해 규모에 큰 영향을 미치는 연행작용에 대한 연구는 미비한 실정이다. 본 연구에서는 국내에서 개발된 토석류 유동해석 모형인 Deb2D 모형을 통하여 토석류의 매개변수 변화에 따른 흐름, 피해지역에 미치는 영향 그리고 침식과정에 대하여 분석하였다. 2011년 우면산에서 발생한 산사태에 적용하였으며, 수치모형의 객관적인 정확성 판단을 위해 현장 조사를 통해 얻어진 토석류의 피해 범위, 총 퇴적량, 특정 지점에서 관측된 최대 퇴적 높이, 토석류의 첨두 유속를 검토하였다. 또한 매개변수 변화가 연행작용에 미치는 영향에 대하여 침식 형상 및 깊이를 통해 분석하였다. 연행작용을 고려한 래미안 아파트와 신동아 아파트 유역의 모의는 성공적으로 수행되었다. 매개변수 변화에 따른 두 유역에서의 민감도 분석을 통해 각 매개변수의 영향성을 판단할 수 있었다.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2012년도 전기공동학술대회 논문집
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• pp.276-278
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• 2012

This study was performed to investigate wake flow and unsteady flow characteristics using a model for actual shape of a wind breaker and visualization of flow through the particle image velocity. three control angle of flap were selected and instantaneous velocity distributions and flow characteristics were experimently investigated. It is found that as the control angle increase, the flows are characterized by the appearance of the growth of recirculation region.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2006년도 제33회 KOSCO SYMPOSIUM 논문집
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• pp.242-250
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• 2006

The impacts of equivalence ratio on the flow structure and flame dynamics in a model gas turbine combustor are investigated using large eddy simulation(LES). Dynamic k-equation model and G-equation flamelet model are employed as LES subgrid model for flow and combustion, respectively. As a result of mean flow field for each equivalence ratio, the increase of equivalence ratio brings about the decrease of swirl intensity through the modification of thermal effect and viscosity, although the same swirl intensity is imposed at inlet. The changes of vortical structure and turbulent intensity etc. near flame surface are occurred consequently. That is, the decrease of equivalence ratio can leads to the increase of heat release fluctuation by the more increased turbulent intensity and fluctuation of recirculation flow. In addition, the effect of inner vortex generated from vortex breakdown on the heat release fluctuation is increased gradually with the decrease of equivalence ratio. Finally, it can be identified that the variations of vortical structure play an important role in combustion instability, even though the small change of equivalence ratio is occurred.

• 대한기계학회논문집A
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• 제21권3호
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• pp.369-377
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• 1997

The torque converter, a major part of automatic transmissions, has many difficulties in analysis due to the factors such as power transmission through fluid flow, complex internal geometry, and various operating conditions. Because of such difficulties, the dynamic analysis and design of a torque converter are generally carried out by using equivalent performance model which is based on the concept of mean flow path. Since the design procedures of a torque converter are essential technology of automotive industry, the details of the procedures are rarely published. In this study, the basic design procedures of a torque converter are systemized and coded based on the equivalent performance model. The mathematical methods to deal with mean flow path determination and the core-shape are developed. And by using this model, the method of determination of performance parameters satisfying the requested performance is proposed. Finally, to embody the three-dimensional shape, the intermediate blade angles which maximize the tractive performance are determined and laid out.

• 한국대기환경학회지
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• 제17권4호
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• pp.347-354
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• 2001

SCR (Selective Catalytic Reduction) process is presently considered as one of the most effective techniques for removing nitric oxides from exhaust gases. In this study, based on the conceptually designed SCR reactor of 500 MW coal fired power plant. a reduced scale (1/20) SCR reactor model was made to analyze the flow pattern in front of catalyst layer according to the guide vane's design factors such as the number, interval, and angle of vanes. The results of the test were compared to those numerical simulation in order to assure the reliability of two methods. On the basis of our study. the critical Reynolds number (2.0$\times$ 10$^{5}$ ) was proposed for ensuring the similarity between the reduced scale model and the prototype of SCR reactor. Optimum design parameters of guide vanes were determined as follows, 4 vanes, the first vane angle of 93$^{\circ}$, and the vane intervals of 0.85 S/n, 1.05 S/n, 1.1 S/n, 1.0S/n, 1.0S/n (S: the distance of duct, n: the number of guide vanes). The excellent agreement between the results of the numerical simulation and the reduced scale model provides the validation of two methods for prediction of flow through SCR reactor.

• 한국수자원학회논문집
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• 제30권1호
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• pp.63-73
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• 1997

본 연구는 지하심부에 유류를 저장할 때 널리 이용되는 수막시설의 설치에 따른 공동주변의 흐름해석을 모의하기 위한 유한요소모형의 확립에 관한 것이다. 최종 행렬방정식의 대칭형 전체전도행렬을 풀기위해 벡터저장방식의 Choleski법을 이용하였으며, 전기상사법의 결과와 비교하여 모형을 검증하였다. 모형을 실제 비축기지에 적용하였으며, 대표적인 횡단면에 대해 요소망을 구성하여 공동내부의 압력과 수평수막설치에 따른 포텐션과 유속의 변화 등을 비교하고, 종단면에 대한 분석을 통해 연직수막설치에 따른 포텐셜의 변화와 인접공동간의 영향을 비교 분석한 결과 본 연구에서 확립된 모형은 공동주변 흐름해석에 유용하게 이용될 수 있는 것으로 확인되었다.

• Nuclear Engineering and Technology
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• 제41권6호
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• pp.841-848
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• 2009

A simple model to analyze non-linear density-wave instability in a sodium-cooled helically coiled steam generator is developed. The model is formulated with three regions with moving boundaries. The homogeneous equilibrium flow model is used for the two-phase region and the shell-side energy conservation is also considered for the heat flux variation in each region. The proposed model is applied to the analysis of two-phase instability in a JAEA (Japan Atomic Energy Agency) 50MWt No.2 steam generator. The steady state results show that the proposed model accurately predicts the six cases of operating temperatures on the primary and secondary sides. The sizes of three regions, the secondary side pressure drop according to the flow rate, and the temperature variation in the vertical direction are also predicted well. The temporal variations of the inlet flow rate according to the throttling coefficient, the boiling and superheating boundaries and the pressure drop in the two-phase and superheating regions are obtained from the unsteady analysis.

• Nuclear Engineering and Technology
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• 제55권12호
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• pp.4561-4569
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• 2023

A correct understanding of vibration-based degradation is crucial from the standpoint of maintenance for Steam Generators (SG) as crucial mechanical equipment in nuclear power plants. This study has established a novel approach to developing a model for investigating tube bundle degradation according to crack growth caused by two-phase Flow-Induced Vibration (FIV). An important step in the approach is to calculate the two-phase flow field parameters between the SG tube bundles in various zones using the porous media model to determine the velocity and vapor volume fraction. Afterward, to determine the vibration properties of the tube bundles, the Fluid-Solid Interaction (FSI) analysis is performed in eighteen thermal-hydraulic zones. Tube bundle degradation based on crack growth using the sixteen most probable initial cracks and within each SG thermal-hydraulic zone is performed to calculate useful lifetime. Large Eddy Simulation (LES) model, Paris law, and Wiener process model are considered to model the turbulent crossflow around the tube bundles, simulation of elliptical crack growth due to the vibration characteristics, and estimation of SG tube bundles degradation, respectively. The analysis shows that the tube deforms most noticeably in the zone with the highest velocity. As a result, cracks propagate more quickly in the tube with a higher height. In all simulations based on different initial crack sizes, it was observed that zone 16 experiences the greatest deformation and, subsequently, the fastest degradation, with a velocity and vapor volume fraction of 0.5 m/s and 0.4, respectively.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2791-2796
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• 2007

In their long journey through the cardiovascular circuit, erythrocytes are coerced to shape transform and assume different shapes on account of varying flow conditions in different blood vessels. The present work was aimed to visualize these erythrocyte shape transformations by an invitro microcirculatory model, and assess multi-shape erythrocyte deformability. The model uses an in-house fabricated, inexpensive disposable micro flow channel to mimic certain invivo conditions and a fast frame video microscopic system for imaging the shape changes in erythrocytes. Results show the multi-shape transformation of erythrocyte christened as discoidal shape, the asymmetrically deformed 'hat' and 'bullet-like' shapes, and the axially deformed 'slipper' and 'spindle-like' shapes. Specific erythrocyte showed the shape transition and transformation while passing through the observed window. The obtained erythrocyte shapes very analyzed for deformability index using image processing techniques that varied significantly (p <0.001) for different shapes as compared with the resting shape.