• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2002년도 춘계 학술대회논문집
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• pp.79-87
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• 2002

The present work analyzed the effect of mixing vane shape on the flow structure and heat transfer downstream of mixing vane in a subchannel of fuel assembly, by obtaining velocity and pressure fields, turbulent intensity, flow-mixing factors, heat transfer coefficient and friction factor using three-dimensional RANS analysis. NJl5, NJ25, NJ35, NJ45, which were designed by the authors, were tested to evaluate the performances in enhancing the heat transfer. Standard $\kappa-\epsilon$ model is used as a turbulence closure model, and, periodic and symmetry conditions are set as boundary conditions. The flow blockage ratio is kept constant, but the twist angle of mixing vane is changed. The results with three turbulence models( $\kappa-\epsilon$, $\kappa-\omega$, RSM) were compared with experimental data.

• 한국물환경학회지
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• 제28권1호
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• pp.26-37
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• 2012

Multi-dimensional hydrodynamic and water quality models are widely used to simulate the physical and biogeochemical processes in the surface water systems such as reservoirs and estuaries. Most of the models have adopted the Eulerian grid modeling framework, mainly because it can reasonably simulate physical dynamics and chemical species concentrations throughout the entire model domain. Determining the optimum grid cell size is important when using the Eulerian grid-based three-dimensional water quality models because the characteristics of species are assumed uniform in each of the grid cells and chemical species are represented by concentration (mass per volume). The objective of this study was to examine the effect of grid-size of a three dimensional hydrodynamic and water quality model (EFDC) on hydrodynamics and mass transport in the Saemangeum Reservoir. Three grid resolutions, respectively representing coarse (CG), medium (MG), and fine (FG) grid cell sizes, were used for a sensitivity analysis. The simulation results of numerical tracer showed that the grid resolution affects on the flow path, mass transport, and mixing zone of upstream inflow, and results in a bias of temporal and spatial distribution of the tracer. With the CG, in particular, the model overestimates diffusion in the mixing zone, and fails to identify the gradient of concentrations between the inflow and the ambient water.

• 태양에너지
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• 제19권4호
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• pp.21-31
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• 1999

This paper presents a quasi-three-dimensional calculation method considered a spanwise mixing effect in a diagonal flow impeller. The effect of this spanwise mixing caused by spanwise distribution of blade loading is evaluated by a secondary flow theory. In order to verify the validity of this method, it is applied to the analysis of a diagonal flow fan designed under a vortex type of constant circumferential velocity and that of a free vortex. The comparison of the calculated result with experimental data shows a good agreement except the regions near the casing where the flow field is affected by the tip leakage flow.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2460-2464
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• 2008

The present paper suggests new method to know the effects of molecular diffusion and the helicity of microchannel flows on mixing in passive micromixers, which are essential components of a microfluidic chip. In this study, 'Helix Index' is newly defined as the magnitude of chaotic advection. Relationship between Helix Index and Mixing Index is analyzed numerically such as the wide range of Peclet and Reynolds numbers in three dimensional serpentine microchannel when using soluble solutions (water/glycerol). As a result, a simple algebraic equation is derived by this relationship based on a regression analysis. The algebraic equation is found to be able to accurately predict the mixing performance without solving the coupled, complex momentum and mass transfer equations.

• 한국해양환경ㆍ에너지학회지
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• 제11권3호
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• pp.164-174
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• 2008

섬진강 하구역을 중심으로 광양만과 여수해만에서의 동시 관측한 염분의 현장관측자료의 분석과 기상, 조석, 하천유출수 및 온배수를 고려한 3차원 수치모델(EFDC) 결과를 이용하여 섬진강 하구역의 3차원 혼합특성을 파악하였다. 수치모델에 고려된 입력조건은 수심, 기상, 하천유출수 및 온배수 등이며, 개방경계에서는 염분 및 조석을 고려하여 수치모의하였다. 수치모델 검증은 조위 2개 정점과 조류 2개 정점의 조화분석을 통한조화상수 비교를 통하며 모델결과가 관측결과와 잘 일치하고 있음을 확인하였고, 조시별 유동장을 잘 재현하고 있음을 확인하였다. 동계 및 하계시 월평균 하천유출수를 고려하여 수치모의한 결과, 동계에는 32.0 psu의 등염분선이 섬진강 하구에 국한되어지나, 하계에는 30.0psu의 등염분선이 하천유출량의 영향으로 섬진강 하구역으로 확장되어짐을 확인할 수 있었다. 한편, 섬진강 하구역의 3차원 혼합특성은 전반적으로 섬진강 유출량의 변동, 해수유동구조 및 온배수 등에 의해 복잡한 형태를 보이는 것을 확인할 수 있었다.

• 대한기계학회논문집A
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• 제29권10호
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• pp.1289-1297
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• 2005

The flow in a microchannel is usually characterized as a low Reynolds number (Re) so that good mixing is quite difficult to be achieved. In this regard, we developed a novel chaotic micromixer, named Serpentine Laminating Micromixer (SLM) in the present study, Part 1. In the SLM, the higher level of chaotic mixing can be achieved by combining two general chaotic mixing mechanisms: splitting/recombination and chaotic advection. The splitting and recombination (in other term, lamination) mechanism is obtained by the successive arrangement of 'F'-shape mixing units in two layers. The chaotic advection is induced by the overall three-dimensional serpentine path of the microchannel. Chaotic mixing performance of the SLM was fully characterized numerically. To compare the mixing performance, a T-type micromixer which has the same width, height and length of the SLM was also designed. The three-dimensional numerical mixing simulations show the superiority of the SLM over the T-type micromixer. From the cross-sectional simulation results of mixing patterns, the chaotic advection effect from the serpentine channel path design acts favorably to realize the ideal lamination of fluid flow as Re increases. Chaotic mixing mechanism, proposed in this study, could be easily integrated in Micro-Total-Analysis-System, Lab-on-a-Chip and so on.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 12th Asian Congress of Fluid Mechanics
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• pp.36.1-36.1
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• 2008

• Journal of the Korean Wood Science and Technology
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• 제34권5호
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• pp.52-58
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• 2006

Coffee chaff for manufacturing of the 6 mm thick cement-bonded boards was obtained from a coffee processing industry at Omuo-Ekiti, in Ekiti State, Nigeria. Boards were produced with three levels of cement to coffee chaff ratio of 1.5:1, 2.5:1 and 3.5:1; and at three levels of mixing curing reagent of 2.0%, 2.5% and 3.0%. Three dimensional properties of thickness swelling (TS), water absorption (WA) and linear expansion (LE) were investigated after 48 hours immersion in water. The mean values obtained for TS, WA and LE ranged from 0.46% to 1.47%, from 11.52% to 24.00%, from 0.19% to 0.35%, respectively. The most dimensionally stable boards were produced at the highest mixing levels of curing reagent and cement to coffee chaff ratio of 3.0% and 3.5:1, respectively. The coffee chaff is suitable as raw material for the manufacture of cement-bonded composites and it would be able to stimulate and activate the use of other agro-byproducts for the manufacture of value-added panels.

• 대한기계학회논문집B
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• 제31권8호
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• pp.711-717
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• 2007

Shape optimization of a staggered herringbone groove micromixer using three-dimensional Navier-Stokes analysis has been carried using Kriging model. The analysis of the degree of mixing is performed by the calculation of spatial data statistics. The calculation of the variance of the mass fraction at various nodes on a plane in the channel is used to quantify mixing. A numerical optimization technique with Kriging model is applied to optimize the shape of the grooves on a single wall of the channel. Three design variables, namely, the ratio of groove width to groove pitch, the ratio of the groove depth to channel height ratio and the angle of the groove, are selected for optimization. A mixing index is used as the objective function. The results of the optimization show that the mixing is very sensitive to the shape of the groove which can be used in controlling mixing in microdevices.

• 한국유체기계학회 논문집
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• 제10권4호
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• pp.9-14
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• 2007

The purpose of present work is to analyze the convective heat transfer downstream of mixing vane in subchannel of nuclear reactor with three-dimensional Navier-Stokes equations. SST model is selected as a turbulence closure by comparing the performances of two different turbulent closures. Three different shapes of mixing vane are tested. And, thermal-hydraulic performances of these vanes are discussed. The results show that twist of the vane improves the heat transfer performance far downstream of the vane.