• Journal of Convergence for Information Technology
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• v.9 no.12
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• pp.147-156
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• 2019

Numerical study was performed to investigate the convective heat transfer of Al₂O₃/water nanofluid flowing through the concentric double pipe counterflow heat exchangers. Hot fluid flowing through the inner pipe transfers its heat to cooling fluid flowing in the outer pipe. Effects of important parameters such as hot and cold volume flow rates, fluid type in the outer and inner pipes, and nanoparticles concentration on the heat transfer and flow characteristics are investigated. The results indicated that the heat transfer performance increases with increasing the hot and cold volume flow rates, as well as the particle concentrations. When both outer and inner pipes are nanofluids with 8% nanoparticle volume concentration, nanofluids showed up to 17% better heat transfer rate than basic fluids. Also, the average heat transfer coefficient of the base fluid for annulus-side improved by 31%. Approximately 20% enhancement in the heat exchanger effectiveness can be achieved with the addition of 8% alumina particles in base fluid. But, addition of nanoparticles to the base fluid enhanced friction factor by about 196%.

• Journal of computational fluids engineering
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• v.3 no.1
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• pp.1-10
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• 1998

서로 섞이지 않는 두 비압축성 유체의 유동을 해석하기 위하여 VOF 방법에 기초한 수치 기법을 개발하였다. 유체간의 계면형상의 거동은 유동장내의 유체의 점유체적비의 변화에 의해 묘사되는데 이를 지배하는 이동방정식을 풀기 위한 새로운 대류항 계산법을 고안하였다. 대류항은 유체계면의 방향에 따라 풍상법과 역풍상법의 적절한 조합을 취하여 계산하는데 여기에 대각방향의 상류효과를 포함시켜 시간에 대한 2차 정확도를 갖도록 하였다. 또한 이 방법을 유량보정수송(FCT)법과 결합시켜 해의 단조성을 보장하였다. 몇 가지 단순 문제에 대한 시험 결과 이 기법이 수치오차에 의한 계면형상의 변형과 파손을 감소시킴을 확인하였다.

• The Journal of Engineering Geology
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• v.15 no.3
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• pp.349-363
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• 2005

Many Quaternary faults are recognized as thin gouge and narrow cataclastic zone juxtaposing the Bulguksa granite and Quaternary deposit bed in the eastern block of the Using Fault, Korea: Gaegok 1, Caegok 2, Singye, Madong Wonwonsa and Jinhyeon faults. This study was performed to calculate chemical change, volume change, silica loss and fluid-rock ratio taken place in gouge zones of these Quaternary faults using XRF, XRD, EPMA. The chemical compositions of fault rocks reveal that the fault gouges are depleted in $SiO_2,\;Na_2\;O,and\;K_2O$ and enriched in $Al_2O_3,\;Fe_2O_3,\;P_2O_5,\;MgO,\;MnO,\;CaO,\;and\;LOI(H_2O+CO_2)$ relative to protoliths. The fact that there is enrichment of relatively immobile elements and depletion of the more soluble elements in the fault gouges relative to protoliths can be explained by fluid-assisted volume loss of $56\%$ for Caegok 1 fault, $22\%$ for Caegok 2 fault,$34\%$, for Singye fault, $8\%$ for Madong fault, $2\%$ for the Wonwonsa fault and $53\%$ for the linhyeon fault. Madong fault and Wonwonsa fault where ratios of the volume change, silica loss and fluid-rock are low might have acted as a closed system for fluid activity, whereas Caegok 1 fault and Jinhyeon fault with high ratios in those factors be an open system. The volumetric fluid-rock ratios range $10^2\sim10^4$ for all faults, being highest in Caegok 1 fault and Jinhyeon fault whose fluid activity was most significant.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.132-133
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• 2007

자성유체의 전자기력에 의한 거동 파악을 위해 전자기 체적력에 의한 접근법을 제안한다. 정유체역학식에 수정 된 Kelvin 가진력식이 도입되며, 유체표면에서의 압력이 일정하여야 한다는 원리에서 유체 표면의 형상을 얻어낼 수 있다.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1459-1460
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• 2011

자성유체에 60Hz의 교류자기장을 인가할 때 발생되는 냉각효과를 해석하기 위해 유한요소법을 결합하였다. 열원으로는 전류가 코일에 흐를 때 생성되는 줄열과 닐운동과 브라운운동으로 야기되는 전력손실에 의한 발열이 있다. 교류자기장은 주파수가 낮기 때문에 줄열이 주요한 열원이 된다. 그러므로 코일에서 자성유체로 일어나는 열전달과 자연대류현상은 코일의 표면에서 일어난다. 자연대류현상을 해석하기 위해서는 자성유체의 부력밀도를 고려해야 한다. 부가적으로 자계의 세기와 온도에 관한 함수인 자화와 자기체적력밀도로 인해 자기대류현상과 같은 강제대류가 일어난다. 이러한 두 가지 대류현상으로 인해 교류자기장을 인가한 자성유체에서 냉각효과가 일어난다. 자기체적력밀도는 유한요소법으로 보간된 가상공극개념을 이용하여 켈빈전자기력밀도를 이끌어 낸 후 이를 수치적으로 이용하여 구하였다. 랑제방함수는 켈빈전자기력밀도와 전력손실을 계산하는데 필요한 비선형 자화율을 고려하기 위해 사용하였다.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.114-119
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• 1996

증기방출계통은 원자력 발전소의 안전을 위한 계통인데 이 계통의 작동 초기에 복잡한 열유체적 현상과 더불어 큰 유체적 진동하중이 구조물에 발생하게 됨으로 이 계통의 설계 개발을 위하여는 이러한 초기현상에 대한 정성적 및 정량적인 이해가 요구된다. 이를 위하여 본 연구에서는 이러한 초기 현상을 해석할 수 있는 방법론을 개발하고 이를 이용하여 이 현상의 특성을 분석하였으며 종합적으로 유체적 진동 하중으로부터 구조물의 기계적 건전성을 확보하기 위한 이 계통의 설계 방향을 제시하였다.

• Journal of Convergence for Information Technology
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• v.9 no.8
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• pp.155-163
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• 2019

Laminar mixed convection of a nanofluid consists of water and $Al_2O_3$ in a horizontal circular tube has been studied numerically. Two-phase mixture model has been used to investigate hydrodynamic and thermal behaviors of the nanofluid with variables physical properties. Three dimensional Navier-Stokes, energy and volume fraction equations have been discretized using the finite volume method. The Brownian motions of nanoparticles have been considered to determine the thermal conductivity and dynamic viscosity of $Al_2O_3$-Water nanofluid, which depend on temperature. The calculated results show good agreement with the previous numerical data. Results show that in a given Reynolds number (Re), increasing solid nanoparticles volume fraction and Richardson number (Ri) increases the convective heat transfer coefficient and wall shear stress.

• Proceedings of the Korean Society of Rheology Conference
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• 2002.11a
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• pp.63-66
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• 2002

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.5
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• pp.541-548
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• 2017

A theoretical study on gas-liquid two-phase flow flushing systemnitrogen gas to the oil used for existing flushing equipment was conducted on the basis of ISO code so as to improve performance of existing high-temperature oil flushing equipment used in ocean plant facility drying field. For study, we analyzed process simulation results mixed fluid mixing ratio, temperature, Reynolds number and liquid hold up affectcleaning performance after designing oil-nitrogen gas mixture flushing system process. As a result, as the volume flow rate of mixed fluid increases with the tube diameter the volume fraction of the gas phase constant, the liquid fraction difference value at the inlet and outlet of horizontal hydraulic piping increases. It was found that the phase distribution between oil and nitrogen gas bubbles varies depending on the position the pipe lengthdirection. This change in phase distribution is expected to have a significant impact on the clean performance of an oil-nitrogen gas mixture flushing system.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.6
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• pp.351-356
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• 2022

In this paper, we present the regression analysis and design optimization for improving the permeability of 3D woven materials based on numerical analysis data. First, the parametric analysis model is generated with variables that define the gap sizes between each directional wire of the woven material. Then, material properties such as bulk modulus, thermal conductivity coefficient, and permeability are calculated using numerical analysis, and these material data are used in the polynomial-based regression analysis. The Pareto optimal solution is obtained between bulk modulus and permeability by using multi-objective optimization and shows their trade-off relation. In addition, gradient-based design optimization is applied to maximize the fluid permeability for 3D woven materials, and the optimal designs are obtained according to the various minimum bulk modulus constraints. Finally, the optimal solutions from regression equations are verified to demonstrate the accuracy of the proposed method.