• 대한기계학회논문집B
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• 제34권1호
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• pp.1-8
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• 2010

수직 원형관내 자연대류에 의한 열전달량을 $Gr_H$ 수 2.1x$10^6{\sim}2x10^9$의 범위에 대해 측정하였다. 유사성 원리를 이용하여 열전달계를 물질전달계로 대체하였다. 본 연구에서 채택된 물질전달계는 황산-황산구리 수용액의 전기도금계였다. 본 실험의 결과를 층류 및 난류에 대한 수직평판에 대하여 개발된 자연대류 열전달상관식과 비교한 결과, 일치함을 확인하였다. 다만 $Gr_H$ 수 $10^9$이상의 난류 영역에서는 수직관내에서 경계층간 간섭의 영향으로 인하여 수직관에서의 실험결과가 수직평판보다 높게 나타났다. 이러한 일치는 유사성 실험의 유용성을 증명한다. 3가지 다른 형태의 양극과 6가지 다른 기하구조를 사용하여, 양극의 면적과 위치가 미치는 영향을 실험적으로 평가하였다. 예상된 바와 같이 양극의 면적과 위치는 대부분의 경우 한계전류에 영향을 주지 않았다. 이러한 결과는 보다 복잡한 실험에 있어서 양극의 크기와 위치를 지정하는 이론적 근거로 활용될 것이다.

• 한국결정성장학회지
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• 제15권4호
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• pp.129-134
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• 2005

초크랄스키 단결정장치내 실리콘 유동의 자기장효과에 대한 수치해석을 하였다. 8" 단결정 성장과정에서 난류 모형을 사용하여 수송현상을 계산하였다. 도가니 회전수가 작으면 자연대류가 지배적이었다. 도가니 회전수가 증가할수록 강제대류가 증가되며 온도 분포는 더 넓어진다. cusp 자기장을 인가하면 도가니근처의 유동이 크게 감소하며 온도분포는 전도의 경우와 비슷해진다.

• 설비공학논문집
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• 제10권2호
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• pp.217-226
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• 1998

A numerical study has been carried out for two- and three-dimensional buoyant turbulent flow in a stairwell model. The Reynolds-averaged Navier-Stokes and energy equations are solved with the authors'own computer program. Two models by the Boussinesq approximation and the density-gradient form are used for buoyancy terms in the governing equations. Two- and three-dimensional predictions of the velocity and temperature fields are presented and the results are compared with experimental data. Comparisons have also been made in detail with two-dimensional predictions. Two-dimensional and three-dimensional simulations have predicted the overall features of the flow satisfactorily. A better agreement with experiment is achieved with three-dimensional simulations.

• 설비공학논문집
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• 제11권1호
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• pp.73-80
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• 1999

This paper describes a numerical study of three-dimensional buoyant turbulent flow in a stairwell model with three convective differencing schemes, which include the upwind differencing scheme, the hybrid scheme and QUICK scheme. The Reynolds-averaged Navier-Stokes and energy equations are solved with a two-equation turbulence model. The Boussinesq approximation is used to model buoyancy terms in the governing equations. Three-dimensional predictions of the velocity and temperature fields are presented and are compared with experimental data. Three-dimensional simulations with each scheme have predicted the overall features of the flow fairly satisfactorily. A better agreement with experimental is achieved with QUICK scheme.

• 한국전산유체공학회지
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• 제21권4호
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• pp.102-111
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• 2016

In this paper a computation of turbulent natural convection in enclosures with the elliptic-blending based differential and algebraic flux models is presented. The primary emphasis of the study is placed on an investigation of accuracy of the treatment of turbulent heat fluxes with the elliptic-blending second-moment closure for the turbulent natural convection flows. The turbulent heat fluxes in this study are treated by the elliptic-blending based algebraic and differential flux models. The previous turbulence model constants are adjusted to produce accurate solutions. The proposed models are applied to the prediction of turbulent natural convections in a 1:5 rectangular cavity and in a square cavity with conducting top and bottom walls, which are commonly used for validation of the turbulence models. The relative performance between the algebraic and differential flux model is examined through comparing with experimental data. It is shown that both the elliptic-blending based models predict well the mean velocity and temperature, thereby the wall shear stress and Nusselt number. It is also shown that the elliptic-blending based algebraic flux model produces solutions which are as accurate as those by the differential flux model.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 추계 학술대회논문집
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• pp.77-82
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• 2006

Evaluation of the elliptic blending turbulence model (EBM) together with the two-layer model, shear stress transport (SST) model and elliptic relaxation model (V2-F) is performed for a better prediction of natural convection and thermal stratification. For a natural convection problem the models are applied to the prediction of a natural convection in a rectangular cavity and the computed results are compared with the experimental data. It is shown that the elliptic blending model predicts as good as or better than the existing second moment differential stress and flux model for the mean velocity and turbulent quantities. For thermal stratification problem the models are applied to the thermal stratification in the upper plenum of liquid metal reactor. In this analysis there exist much differences between the turbulence models in predicting the temporal variation of temperature. The V2-F model and EBM better predict the steep gradient of temperature at the interface of thermal stratification, and the V2-F model and EBM predict properly the oscillation of temperature. The two-layer model and SST model fail to predict the temporal oscillation of temperature.

• 대한기계학회논문집
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• 제18권10호
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• pp.2738-2750
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• 1994

The Effects of radiative heat transfer on turbulent flow in a partitioned enclosure is studied numerically. The enclosure is partially divided by a thin, poorly conducting vertical divider projecting from the ceiling of the enclosure. The low Reynolds number $k-{\epsilon}$ model is adopted to calculate the turbulent flow field. The solutions to the radiative transfer equations are obtained by the discrete ordinates method(DOM). This method is based on control volume method and is compatible with the SIMPLER algorithm used to solve the momentum and energy equations. The effects of optical thickness and Planck number on the flow, temperature fields and heat transfer rates are investigated for a moderate Rayleigh number($=10^9$). The changes in buoyant flow fields and temperature distributions due to the variation of baffle length are also analyzed. From the predictions, radiant heat exchange between the baffle and the sidewalls strongly influences the temperature distribution in the baffle and its vicinity and total heat transfer increases as the optical thickness and the baffle length decrease. It is possible to neglect the radiative heat transfer effect when Planck number is over one.

• 전기화학회지
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• 제2권2호
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• pp.98-105
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• 1999

본 연구에서는 전기장에 의하여 유발되는 자연대류의 영향을 줄이기 위하여 수평 다공성 유체층에 열적 성충화를 유지하여 부력과 유체층의 안정화 효과를 체계적으로 조사하였다. 이를 위하여 수평 다공성 유체층에서 이중확산대류에 의한 물질전달 상관식을 이론적으로 유도하고, 전기화학 실험을 통하여 이론에 의한 모델을 보완하였다. 물질전달 상관식은 다공성 매질층에 대한 유동 방정식으로 Forchheimer모델을 사용하고 미세 난류 모델을 적용하여, 용질 및 열 Darcy-Rayleigh수와 Lewis 수로 유도하였다. 실험에서는 다공성매질에 포화된 황산구리황산용액내의 구리이온을 전기 화학적 방법을 통하여 확산 또는 자연대류에 의한 물질전달 실험을 수행하였다. 이론 및 실험적 해석 결과를 종합하면 다공성 매질 내에서 구리이온의 이중확산대류에 의한 물질전달 상관식은 다음과 같다. $$Sh=\frac{0.03054(Rs_D-LeRa_D)^{1/2}}{1-3.8788(Rs_D-LeRa_D)^{-1/10}}$$ 본 연구의 결과는 실험치와 잘 부합되었으며, 모델식의 원형은 열 및 물질전달계에서 자연대류의 영향을 효과적으로 제어할 수 있는 방안으로 활용될 수 있을 것이다.

• 한국전산유체공학회지
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• 제21권4호
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• pp.1-10
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• 2016

The analysis of characteristics of turbulent flow and thermal boundary layer for natural convection caused by fire along vertical wall is performed. The 4m-high vertical copper plate is heated and kept at a uniform surface temperature of $60^{\circ}C$ and the surrounding fluid (air) is kept at $16.5^{\circ}C$. The flow and temperature is solved by large eddy simulation(LES) of FDS code(Ver.6), in which the viscous-sublayer flow is calculated by Werner-Wengle wall function. The whole analyzed domain is assumed as turbulent region to apply wall function even through the laminar flow is transient to the turbulent flow between $10^9$<$Gr_z$<$10^{10}$ in experiments. The various grids from $7{\times}7{\times}128$ to $18{\times}18{\times}128$ are applied to investigate the sensitivity of wall function to $x^+$ value in LES simulation. The mean velocity and temperature profiles in the turbulent boundary layer are compared with experimental data by Tsuji & Nagano and the results from other LES simulation in which the viscous-sublayer flow is directly solved with many grids. The relationship between heat transfer rate($Nu_z$) and $Gr_zPr$ is investigated and calculated heat transfer rates are compared with theoretical equation and experimental data.

• 한국가스학회지
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• 제2권1호
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• pp.28-39
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• 1998

본 연구에서는 $20\%$ 천장개구부가 있는 정사각형 밀폐공간내의 순수자연대류와 자연대류 -복사가 고려된 복합열전달을 순차해석과 실험을 통하여 비교 분석하였다. 수치해석은 순수자연대류에 대하여 SIMPLE 알고리즘을 사용하였고, 복사열전달에 대해서는 S-N 구분 종좌표법을 이용하였으며 난류유동의 경계조건은 벽함수를 적용하였다. 실험은 수치해석의 결과와 비교하기 위하여 동일한 조건에 대하여 수행되었다. 그 결과 순수자연대류와 복합열전달의 유동장, 온도장의 형상은 유사한 유선함수를 보이고 있으며, 유동가시화를 통한 실험결과와 잘 일치하고 있음을 보여준다. 수치해석과 실험의 온도분포를 비교한 결과 평균 $8.5\%$의 오차를 보였다.