• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.11
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• pp.1014-1021
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• 2005

Flow channels with non-circular cross-sections are encountered in a wide variety of heat exchangers. Accurate friction factor and Colburn j factor data are essential for the design and viable applications of such heat exchangers. In this study, an analysis is con ducted on heat transfer and pressure drop characteristics for tube-bundle heat exchanger with various arrangements of tubes, of which their geometry could easily be modified from a circular one in a harsh environment. The parameters investigated are aspect ratio, pitch, and inclined angle of tubes. The results obtained are: (1) Aspect ratio has larger influence on the j and f factor than pitch; (2) As aspect ratio increases, both j and f factors decrease; (3) The high performance is achieved when the pitch and aspect ratio are in the range of 1.5${\~}$2.5 and 1.25${\~}$2.0, respectively; and (4) the inclined arrangements of tubes show unfavorable results for both heat transfer and pressure drop characteristics in spite of the positive possibility of condensate removals in a latent heat recovery system.

• Transactions of Materials Processing
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• v.16 no.1 s.91
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• pp.48-53
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• 2007

LCD-BLU(Liquid Crystal Display - Back Light Unit) consists of several optical sheets: LGP(Light Guiding Plate), light source and mold frame. The LGP of LCD-BLU is usually manufactured by etching process and forming numerous dots with $50{\mu}m$ in diameter on the surface. But the surface roughness of LGP with etched dots is very high, so there is much loss of light. In order to overcome the limit of current etched dot patterned LGP, optical pattern design with microlens of $50{\mu}m$ diameter was applied in the present study. The microlens pattern fabricated by modified LiGA with thermal reflow process was applied to the optical design of LGP and optical simulation was carried out to know tendency of microlens patterned LGP simultaneously. The attention was paid to the effects of different aspect ratio(i.e. $0.2\sim0.5$) of optical pattern conditions to the brightness distribution of BLU with microlens patterned LGP. Finally, high aspect ratio microlens patterned LGP showed superior results to the one made by low aspect ratio in average luminance.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.10a
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• pp.671-672
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• 2009

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.233-236
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• 2002

The high-pressurized spray nozzle is used f3r special washing and cutting with strong impact force. The performance of this nozzle, which focused on spray penetration and radial dispersion, was mainly investigated to maximize the momentum and minimize the flow loss. Hence, our experimental research was conducted by changing the aspect ratio ranging from 0 to 3 with nozzle outlet of 1.1. The spray trajectory far high-pressurized water was experimentally investigated using PDPA diagnostics, which was available at spray downstream region. As the spray at upstream near the nozzle exit did not show the improved disintegration. The results showed empirical correlation with regard to non-dimensional axial velocity distribution, spray penetration, and radial spreading rate with photographic visualization.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.85-90
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• 2000

The fracture toughness and crack propagation behaviors of short nylon66 fiber reinforced Chloroprene rubber nave been Investigated as functions of fiber aspect ratio, fiber content and interphase conditions. The J for crack initiation and rupture were determined for short-fiber reinforced rubber. The values of $J_c$ for most reinforced rubbers were low compared that of matrix. But, $J_r$ at rupture showed a higher value than that of matrix. The crack propagation behaviors were analyzed into 3 patterns with increasing fiber aspect ratio and fiber content. The tearing mechanisms of matrix and fiber reinforced rubber were observed by CCD camera focused on the tip of crack and load-displacement graph. Both cases showed a completely different behaviors

• Journal of computational fluids engineering
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• v.18 no.4
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• pp.35-40
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• 2013

A series of numerical simulation has been carried out to study thermo-hydraulic characteristics of a primary surface type heat exchanger, which is designed for the evaporator and condenser of a geothermal ORC. Working fluid is geothermal water at hot side and R-245fa, which is a refrigerant designed for ORC, at cold side. Aspect ratio of the channel and Reynolds number are considered as design parameters. Nusselt number is presented for the Reynolds number ranging from 50 to 150 and compared to existing correlations. The result shows that higher aspect ratio channel gives better heat transfer performance within the range of investigation.

• 한국전산유체공학회:학술대회논문집
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• 2002.10a
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• pp.95-102
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• 2002

Studies of the numerical characteristics of implicit upwind schemes, such as upwind ADI, Line Gauss-Seidel(LGS) and Point Gauss-Seidel(LU) algorithms, for preconditioned Navier-Stokes equations ate performed. All the algorithms are expressed in approximate factorization form and Von Neumann stability analysis and convergence studies are made. Preconditioning is applied for efficient convergence at low Mach numbers and low Reynolds numbers. For high aspect ratio computations, the ADI and LGS algorithms show efficient and uniform convergence up to moderate aspect ratio if we adopt viscous preconditioning based on min- CFL/max- VNN time-step definition. The LU algorithm, on the other hand, shows serious deterioration in convergence rate as the grid aspect ratio increases. Computations for practical applications also verify these results.

• Proceedings of the Korean Information Science Society Conference
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• 2006.06c
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• pp.226-228
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• 2006

관심사 분리는 소프트웨어 공학에서 핵심 문제로 다루어왔다. 기존의 OOD나 CBD등은 관심사를 분리하여 모듈화함으로써 프로그램 개발 및 유지보수를 용이하도록 발전해왔다. 하지만, 에러 처리나 로깅과 같이 여러 모듈에 산재되어 실행되는 횡단 관심사는 기존의 방법으로 해결하기 어려웠다. AOP는 이와 같은 횡단 관심사를 처리하려는 데 목적을 두고 제안된 방법으로 기존의 OOD나 CBD의 단점을 보완하면서 병행적으로 발전해왔다[1]. AOP가 나타난 가장 큰 특징은 기존의 개발 방법론을 기반으로 핵심 관심사를 개발하고 해결하기 어려운 횡단 관심사는 AOP로 개발하려는데 초기 목적을 두고 있다. 하지만, 대부분의 연구가 초기 요구사항 분석 단계에서 관심사를 명시하는데 초점을 두고 있을 뿐 구현 단계에서 효율적인 접근 방법은 아직 부족한 편이다. 본 논문에서는 Java와 AspectJ를 이용하여 구현한 간단한 사례 연구를 적용한 AOP 개발 프레임워크를 제안한다. AOP 개발 프레임워크에서는 관심사 분리, 구현, 평가의 세 단계를 기술한다. 이 중 구현단계에서는 핵심 관심사와 횡단 관심사 구현에 초점을 두고 AOP 기법에 쉽게 접근할 수 있는 방법을 기술하고 있다. 프레임워크는 프로그램 개발을 보다 용이하게 하고 확장 및 유지보수시 많은 시간을 단축시키려는데 있다.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.9
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• pp.52-57
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• 2010

The analysis of a crack in a bone-like material is performed numerically. The bone-like material is hierarchically structured and each hierarchy is structured by mineral platelets and protein matrix through staggered arrangement. Mechanical behavior of the composite can be analyzed using tension shear chain model. The Dugdale model is adopted to evaluate the fracture energy of Bone-like material. The fracture energy dissipation is assumed to concentrate within a strip near the crack tip along the prospective crack path. Fracture criterion of the bone-like material is estimated by using J integral. Effects of hierarchical level, ratio of elastic modulus of mineral to protein, aspect ratio of mineral platelet and volume fraction on J integral are investigated. It is found that the J integral decreases as elastic modulus ratio and hierarchy level increase. It is also shown that the J integral increases as the volume fraction and aspect ratio decrease.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.269-276
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• 2009

The local preconditioning method has both robust convergence and accurate solutions by using local flow properties for parameters in the preconditioning matrix. Preconditioning methods have been very effective to low speed inviscid flows. In the viscous and turbulent flows, deterioration of convergence should be overcame on the high aspect ratio grids to get better convergence and accuracy. In the present study, the local time stepping and min-CFL/max-VNN definitions are applied to compare the results and we propose the method that switches between two methods. The min-CFL definition is applied for inviscid flow problems and the min-CFL/max-VNN definition is implemented to viscous and turbulent flow problems.