• 한국가시화정보학회지
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• 제14권3호
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• pp.46-50
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• 2016

The objective of the present study is to perform experiments for water filled cavity heated and cooled from the side at $Ra=8.5{\times}108$. This experiment can provide validation database of the standard k-${\varepsilon}$ turbulence model for single-phase turbulent natural convection which has been regarded as one of the important phenomena in nuclear safety. For the natural convection inside a cavity, temperature and velocity were obtained by thermometry and PIV (Particle Image Velocimetry) methods. These results would be used for validation of standard k-${\varepsilon}$ turbulence model.

• 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.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.191-195
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• 2001

The applications of magnetic fluid can be normally made by 1) using changes of a property of matter caused by applied magnetic field; 2) preserving magnetic fluid at a certain position or in a magnetic fluid keeping the body in a floating condition; 3) controlling the flow of magnetic fluid by means of magnetic field. However, these are usually made by using their methods together. In this study, the natural convection flow of a magnetic fluid in annular pipes is experimentally analyzed. High temperature is kept constantly inside of a circular pipe of experimental model, on the other hand, low temperature is kept constantly outside of it. In experiments, several cases are carried out in order to clarify the fluence of direction and intensity of magnetic fields on the natural convection of magnetic fluid. Therefore magnetic fields are applied in various intensity and up and down directions by permanent magnets.

• 대한기계학회논문집B
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• 제23권8호
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• pp.987-996
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• 1999

An algorithm for modeling the filling of metal into a mold and solidification has been developed. This algorithm uses the implicit VOF method for a filling and a general implicit source-based method for solidification. The model for simultaneous filling and solidification is applied to the two-dimensional filling and solidification of a square cavity. The effects of the wall temperature and gate position on the solidification are examined. The mixed natural convection flow and residual flow resulting from the completion of a filling are included in this study to investigate the coupled effects of the filling and natural convection on solidification. Two different filling configurations (assisting flow and opposite flow due to the gate position) are analysed to study the effects of residual flow on solidification. The results clearly show the necessity to carry out a coupled filling and solidification analysis including the effect of natural convection.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.51-56
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• 2000

The Finite Element Solutions Is reported on solid-liquid phase change in porous media with natural convection including freezing. The model is based on volume averaged transport equations, while phase change is assumed to occur over a small temperature range. The FEM (Finite Element Method) algorithm used in this study is 3-step time-splitting method which requires much less execution time and computer storage the velocity-pressure integrated method and the penalty method. And the explicit Lax-Wendroff scheme is applied to nonlinear convective term in the energy equation. For natural convection including melting and solidification the numerical results show reasonable agreement with FDM (Finite Difference Method) results.

• 대한기계학회논문집B
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• 제31권3호
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• pp.273-282
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• 2007

Numerical calculations are carried out for the natural convection induced by temperature difference between a cold outer square cylinder and a hot inner circular cylinder. A two-dimensional solution for unsteady natural convection is obtained, using the immersed boundary method (IBM) to model an inner circular cylinder based on finite volume method, for different Rayleigh numbers varying over the range of $10^4\;to\;10^6$. The study goes further to investigate the effect of an inner cylinder location on the heat transfer and fluid flow. The location of inner circular cylinder is changed vertically along the center-line of square enclosure. The number, size and formation of cell strongly depend on Rayleigh number and the position of inner circular cylinder. The changes in heat transfer quantities have been presented.

• Interaction and multiscale mechanics
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• 제6권2호
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• pp.211-235
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• 2013

An incompressible smoothed particle hydrodynamics (ISPH) method based on the incremental pressure projection method is developed in this study. The Rayleigh-B$\acute{e}$nard convection in a square enclosure is used as a validation case and the results obtained by the proposed ISPH model are compared to the benchmark solutions. The comparison shows that the established ISPH method has a good performance in terms of accuracy. Subsequently, the proposed ISPH method is employed to simulate natural convection from a heated cylinder in a square enclosure. It shows that the predictions obtained by the ISPH method are in good agreements with the results obtained by previous studies using alternative numerical methods. A rotating and heated cylinder is also considered to study the effect of the rotation on the heat transfer process in the enclosure space. The numerical results show that for a square enclosure at, the addition of kinetic energy in the form of rotation does not enhance the heat transfer process. The method is also applied to simulate forced convection from a circular cylinder in an unbounded uniform flow. In terms of results, it turns out that the proposed ISPH model is capable to simulate heat transfer problems with the complex and moving boundaries.

• 설비공학논문집
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• 제7권2호
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• pp.266-275
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• 1995

A numerical investigation on the conduction-natural convection-surface radiation conjugate heat transfer in the enclosure having substrate and chips has been performed. A 2-dimensional simulation model is developed by considering heat transfer by conduction, convection and radiation. The solutions to the equation of radiative transfer are obtained by the discrete ordinates method using S-4 quadrature. The effects of Rayleigh number and the substrate-fluid thermal conductivity ratio on the cooling of chip are analyzed. The result shows that radiation is the dominant heat transfer mode in the enclosure.

• Korean Chemical Engineering Research
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• 제47권2호
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• pp.174-178
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• 2009

이성분 혼합물의 응고중에 수지상 결정으로 이루어진 mush 층이 형성될 수 있다. 본 연구진이 개발한 전파이론으로 mush 층에서 성분적 대류의 발생을 해석하였다. Emms와 Fowler의 모델로부터 유도한 자기유사 안정성 방정식을 사용하여 대류 발생에 대한 임계 Rayleigh 수를 수치방법으로 계산하였다. 과열량이 아주 크거나 mush 층의 성장률이 아주 작은 극한의 경우에 본 연구 결과는 준정적 안정성 해석 결과와 같아진다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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• pp.112-117
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• 2000

A numerical study on natural convection in a vertical square cavity filled with a porous medium is carried out with Brinkman-Forchheimer-extended Darcy flow model, and the validity of local thermodynamic equilibrium assumption is studied. The local thermodynamic equilibrium refers to the state in which a single temperature can be used to describe a heat transfer process in a multiphase system. With this assumption, the analysis is greatly simplified because only one equation is needed to describe the heat transfer process. But prior to using this assumption, it is necessary to know in what conditions the assumption can be used. The numerical results of this study reveal that large temperature difference between fluid phase and solid phase exists near wall region, paticularily when the convection becomes dominant over conduction. And the influence of flow parameters such as fluid Rayleigh number, fluid Prandtl number, dimensionless particle diameter and conductivity ratio are investigated.