• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.71-78
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• 2008

For analyses of multi-phase flows in a water-cooled nuclear power plant, a three-dimensional SIMPLE-algorithm based hydrodynamic solver CUPID-S has been developed. As governing equations, it adopts a two-fluid three-field model for the two-phase flows. The three fields represent a continuous liquid, a dispersed droplets, and a vapour field. The governing equations are discretized by a finite volume method on an unstructured grid to handle the geometrical complexity of the nuclear reactors. The phasic momentum equations are coupled and solved with a sparse block Gauss-Seidel matrix solver to increase a numerical stability. The pressure correction equation derived by summing the phasic volume fraction equations is applied on the unstructured mesh in the context of a cell-centered co-located scheme. This paper presents the numerical method and the preliminary results of the calculations.

• 한국전산유체공학회:학술대회논문집
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• 2005.04a
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• pp.219-222
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• 2005

A compressible two-fluid two-phase flow computation model using the stiffened-gas equation of state is formulated. Since the conservation equation system is of mixed type, it gives complex eigenvalues. The sonic speeds obtained from the individual single phase have been simply used in the literature for the fastest wave speeds necessary in the HLL scheme. This method has worked fine but proved to be quite diffusive according to our test. To improve the accuracy, we here propose to utilize the analytic eigenvalues evaluated from an approximate Jacobian matrix lot the fastest wave speeds. The interfacial transfer terms were dropped in constituting the Jacobian matrix for this purpose. The present scheme proved efficient, robust and accurate in comparison with other existing methods. We solved the cavitating flow problem using the present scheme. The result shows more detailed wave structure in the cavitating process caused by the strong expansion waves.

• Journal of Power System Engineering
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• v.5 no.1
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• pp.27-34
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• 2001

관 외벽에 낮은 핀을 가진 수직 및 경사 열사이폰의 열전달 성능에 관한 실험적인 연구를 하였다. 관 외벽에 낮은 핀을 가진 이상밀폐 열사이폰의 열전달 성능을 비교 분석하기 위하여 동일한 규격의 평관에서도 실험적인 연구를 하였다. 작동유체는 증류수와 CFC-30을 사용하였다. 열사이폰의 경사각과 자동온도를 변화시키면서 실험한 결과 경사각의 변화에 따라 열사이폰의 열전달 성능은 큰 변화를 나타내었다. 그리고 평관으로 제작한 열사이폰보다 관 외벽에 낮은 핀관을 가진 동관으로 제작한 열사이폰의 열전달 성능이 높게 나타났다. 그리고 열사이폰의 경사각이 $20{\sim}50^{\circ}$ 범위에서 열전달 성능이 높게 나타났다.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.65-69
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• 2015

하천에서 유사이동은 하천환경과 하천형상을 결정하는 주요 요소이므로 이를 해석하는 것은 매우 중요하다. 그러나 유사이동은 일반적으로 이상흐름 (two-phase flow)이며 난류를 동반하기에 이를 해석하기에는 쉽지 않다. 이상흐름을 해석하는 방법으로는 유사를 연속상인 유사구름(sediment cloud)으로 표현하여 해석하는 Euler-Euler 모형이 있으며 입자를 직접 추적하여 해석하는 Euler-Lagrange 모형이 있다. 본 연구에서는 유사이동 해석을 위하여 Euler-Lagrange 모형을 사용하였으며 흐름의 진동성분을 고려하기 위하여 EIM (Eddy Interaction Model)을 사용하였다. 유체의 유속은 Dou (1987)가 제시한 경험식을 사용하였고 난류운동에너지와 소산률은 Nezu and Nakagawa (1993)가 제시한 식을 사용하였다. EIM에서 입자에 발생하는 와의 영향시간(eddy interaction time)을 계산하기 위해 Gosman and Ioannides (1983)가 제시한 eddy lifetime과 eddy crossing time을 사용하였다. 유사입자는 입자의 운동량방정식을 풀어 그 거동을 추적하였으며 일정 시간 후 입자의 수를 이용하여 농도를 계산하였다. 유체에 발생하는 유속의 진동성분에 의해 입자가 부상하고 중력에 의해 흐름에 따른 일정한 농도분포 형태를 가지는 것을 확인하였다. 유사의 입자크기와 흐름에 따른 농도분포를 계산하였으며, 이를 측정치와 비교하여 EIM의 적용성을 확인하였다.

• Solar Energy
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• v.15 no.2
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• pp.39-46
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• 1995

Reported is a visual and quantitative experimental study on the two-phase flow and heat transfer characteristics of miniature two-phase closed thermosyphons with wire inserts. The visual study clearly demonstrated the two-phase flow involved in such thermosyphons. In the quantitative study, the effects on the heat transfer rate of the insert wire diameter, the ratio of heated-length to cooled length and the applied heat flux were investigated.

• Journal of Navigation and Port Research
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• v.31 no.8
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• pp.683-687
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• 2007

Hydroelastic deformation of pontoon type floating structure in waves is critical in structural design. Therefore, it is necessary to develop additional technology that make to dissipate the wave energy as the submerged horizontal plate. In this study, we investigate the characteristics of hydrodynamic interaction effect by the submerged plate affecting to the radiation forces on a pontoon type floating structure using numerical analysis. We have developed the numerical method based on the composite grid system that consists of moving and fixed grid to compute the radiation forces due to the heaving motion of pontoon type floating structure and submerged plate. The numerical simulations based on the finite difference method are carried out to solve the fully nonlinear free surface involving the breaking waves and compared with the experimental data to confirm the reliability of the numerical method. Then, we discuss the interaction effects on the hydrodynamic forces that could influence on the hydroelastic response of floating structure.

• Journal of the Korean Institute of Gas
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• v.26 no.2
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• pp.1-8
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• 2022

The purpose of this study is to prepare GPTMS((3-Glycidoxypropyl) trimethoxysilane)-SiO₂ nanofluid and analyze the effect of nanofluid injection on carbonate reservoirs. Structural analysis of silica nanoparticles modified by GPTMS was investigated by FTIR(Fourier transform infrared spectroscopy). C-H stretching vibrations at 2,950 cm^-1 indicating the silica surface modification with GPTMS were observed when the silane feed was over 0.5 mmol/g. Also, the coreflooding test by nanofluid injection on the aged limestone and dolomite plug samples was carried out with different particle concentration and flow rate. The incremental oil recovery was up to 18.9%, and contact angle and permeability of carbonate samples were changed by the effect of nanoparticle adsorption on pore which caused wettability alteration and pore size change. Therefore, the prepared nanofluid will be utilized as an injection fluid for enhancing oil recovery and modifying fluid flow properties such as change of rock wettability and permeability in carbonate reservoirs.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2023.05a
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• pp.151-151
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• 2023

An accurate prediction of the hydrodynamic maneuvering darivatives is essential to desing a robust control system of a UUV(unmanned underwater vehicle). Typically, these derivatives were estimated by either the towing tank experiment or semi-empirical methods. With the enhancement of high performance computing capacity, a numerical analysis using computational fluid dynamics has reach the level of experiment. Therefore, the aims of the present research are to numerically develop a computational model for the vertical planar motion mechanism of a UUV and to estimate the hydrodynamics loads in 6-DOF. The target structure of the present study was manta type UUV (12meter length). The numerical model was developed in 1/ 6 model scale. Numerical results were compared with the results of the towing tank experiment for validation. In the present study, a commercial RANS-based viscous solver STARCCM+ (ver 17.06) was used.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.1 no.1
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• pp.15-22
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• 2000

There are lots of industrial machines of which functions are achieved by operation of multi-phase fluids. Some of them take advantage of the characteristics of counter-current two-phase flow The maximum flow rates of gas and liquid phases which flow in opposite-directions (counter-current flow) are limited by a phenomenon known as a Counter-Current Flow Limitation (CCFL or Flooding) The mass and momentum conservation equations for each Phase were established to build a first-order hyperbolic partial derivative equations system. A new CCFL model is developed based on the characteristic equation of the hyperbolic PDE system. The present model has its applicationto the case in which a non-uniform flow is developed around a square or sharp-edged entrance of liquid phase. The model is able to he used to Predict the operating-limit of components in which mass and heat transfer are taking place between liquid and gas phases.

• 순환기질환의공학회:학술대회논문집
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• 2005.12a
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• pp.65-66
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• 2005