• 대한기계학회논문집B
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• 제27권4호
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• pp.476-483
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• 2003

A mathematical model is presented to predict the two-phase flow and heat transfer phenomena of the evaporating extended meniscus region in a micro-channel. The pressure difference at the liquid-vapor interface can be obtained by the augmented Laplace-Young equation. The correlative equations for film thickness, pressure, and velocity in the meniscus region are derived by applying the mass, momentum, and energy equations into the control volume. The results show that increasing the heat flux and the liquid inlet velocity cause the length and liquid film thickness of the extended meniscus region to decrease. The variation, however, of the heat flux and liquid inlet velocity has no effect on the profile of film thickness. The majority of heat is transferred through the thin film region that is a very small region in the extended meniscus region. It is also found that the vapor velocity increases gradually in the meniscus region. However, it increases sharply at the junction of the meniscus and thin film regions.

• 대한기계학회논문집
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• 제19권5호
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• pp.1269-1279
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• 1995

An experimental study is carried out on turbulent diffusion flames stabilized by a circular cylinder in a divergent duct flow. A commercial grade gaseous propane is injected from two slits on the rod as fuel. Flame stability limits, as well as size and temperrature of recirculation zone, are measured by direct and schlieren photographs to clarify the characteristics and structure of diffusion flames and to assess the effect of various divergent angle of duct. The results of the present study are as follows. Temperature in the recirculation zone decreases with increasing divergent angle. The blow-off velocity in parallel duct is higher than that in divergent duct. Critical blow-off velocity is expected to be about 8-12 degree through blow-off velocity pattern. Regardless of divergent angles, the length of recirculation zone is nearly constant, and this length becomes longer with rod diameter. Pressure gradient has an effect on the eddy structure in shear layer behind the rod. With the increase of divergent angle, large scale eddies by dissipated energy in shear layer are split into small scale eddies, and the flame becomes a typical distributedreacting flame.

• 에너지공학
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• 제7권1호
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• pp.44-56
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• 1998

분리형 히트파이프식 열교환기는 증발기와 응축기를 폐열원과 열풍이 필요한 곳에 분리설치하고 증기 및 액체의 연락관으로 두 열교환기를 연결하여 하나의 폐루프를 구성하고 증발기와 응축기의 설치 높이차에 의해 작동이 이루어지는 것이다. 따라서 고온 및 저온유체의 병류 및 향류의 혼합배치가 용이하다는 장점이 있으나, 고온유체의 온도가 높을 경우에는 포화증기의 압력이 높아져 파이프가 견딜 수 있는 사용한계를 초과하게 될 수 있다. 또한 너무 낮으면 증기의 비체적증가와 함께 유속의 증가로 압력손실이 커져 설치높이차를 크게 하던지 증기연락관의 직경을 크게 하여야 하는 문제가 발생할 수 있다. 따라서 설계과정에서 고온유체 및 저온유체의 온도, 유량 등이 정하여진 상태에서 병류 및 향류로 배치하는 경우에 분리형 히트파이프식 열교환기를 Lmtd방법으로 설계하고, 고온 및 저온유체의 온도 및 유량이 실제 운전과정에서 변화가능한 범위에 대해 Ntu 방법으로 열교환량,포화증기압력 및 압력손실에 따른 증발기와 응축기의 설치높이차 등에 대한 가동특성을 고찰하였다.

• Progress in Superconductivity
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• 제7권1호
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• pp.17-21
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• 2005

We report the oscillation of the Josephson vortex-flow resistance in the rectangular stacks of $Bi_{2}Sr_{2}CaCu_{2}O_{8+x}$(Bi-2212) intrinsic Josephson junctions (IJJs). Apiece of Bi-2212 single crystal containing a few tens of IJJs was sandwiched between two gold electrodes and fabricated into a rectangular shape with the typical lateral size of about $1.5{\times}10\;{\mu}m^2$, using e-beam lithography and focused ion-beam etching techniques. In a tesla-range magnetic field applied in parallel with the junction planes, the oscillation of the Josephson vortex flow resistance was observed at temperatures near 60 K. The oscillation results from the interplay between the triangular Josephson vortex lattice and the potential barrier at the boundary of a single crystal. The oscillatory magnetoresistance for different bias currents, external magnetic fields, and the tilt-angles provides useful information on the dynamics of the coupled Josephson-vortex lattice system.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.1
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• pp.546-549
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• 2003

The principle of the superconducting vortex flow transistor (SVFT) is based on control of the Abrikosov vortex flowing along a channel. The induced voltage is controlled by a bias current and a control current, instead of external magnetic field. The device is composed of parallel weak links with a nearby current control line. We explained the process to get an I-V characteristic equation and described the method to induce the external and internal magnetic field by the Biot-Savarts law in this paper. The equation can be used to predict the I-V curves for fabricated device. From the equation we demonstrated that the current-voltage characteristics were changed with input parameters. I-V characteristics were simulated to analyze a SVFT with multi-channel by a Matlab program.

• 한국자동차공학회논문집
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• 제17권3호
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• pp.45-53
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• 2009

Die casting process of Mg alloys for high temperature applications was studied to produce an engine oil pan. The aim of this paper is to evaluate die casting processes of the Aluminium oil pan and in parallel to apply new Mg alloy for die casting the oil pan. Temperature distributions of the die and flow pattern of the alloys in cavity were simulated to diecast a new Mg alloy by the flow simulation software. Dies have to be modified according to material characteristics because melting temperature and heat capacity are different. We changed the shape and position of runner, gate, vent hole and overflow by the simulation results. After several trial and error, oil pans of AE44 and MRI153M Mg alloys are produced successfully without defect. Sleeve filling ratio, cavity filling time and shot speed of die casting machine are important parameter to minimize the defect for die casting Magnesium alloy.

• 한국자동차공학회논문집
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• 제8권5호
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• pp.20-27
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• 2000

Characteristics of two favorite injection tools for gasoline direct injection application were compared. An air-assisted fuel injector (AAFI) and a high-pressure swirl injector (HPSI) were designed and fabricated for prototype development, and the characterization strategies and processes for both injection tool have been arranged in parallel. Characterization works were carried out mainly through measurements, and in some cases, computational fluid dynamic analysis was utilized. In this paper, overall characteristics defined as flow rate, spray pattern, penetration, internal spray structure and drop size distribution, was discussed. The AAFI was found to be advantageous in flexibility of fuel flow rate, and the HPSI in stability and precision. Spray shape factor was introduced to describe the development of intermittent sprays from both injectors. Axial penetration appeared to be almost linear in the case of the AAFI while its speed continuously decreased with time in the HPSI.

• International Journal of Air-Conditioning and Refrigeration
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• 제6권
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• pp.148-157
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• 1998

This study presents test results of a residential window air-conditioner using R22 and two potential alternative refrigerants, R407C and R410B. A series of performance tests has been carried out for the basic and liquid-suction heat exchange cycles in a psychometric calorimeter test facility. For R407C, the same rotary compressor was used as in the R22 system. However, compressor for the R410B system was modified to provide the similar cooling capacity. The evaporator circuit was changed to get a counter-cross flow heat exchanger to take advantage of zeotropic mixture's temperature glide, and liquid-suction heat exchange cycle was also considered to improve the system performance. Test results were compared with those for the basic R22 system. The modified system with a liquid-suction heat exchanger increased cooling capacity and energy efficiency by up to 5%.

• 한국콘텐츠학회논문지
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• 제18권6호
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• pp.27-37
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• 2018

스트림라인 생성은 유동해석 데이터에서 유동의 흐름을 해석하기 위한 대표적인 가시화 기법이다. 그러나 효과적인 스트림라인 배치를 위한 씨드 포인트의 위치를 결정하는 것은 매우 어려운 문제이다. 한편, 대용량의 유동해석 데이터에서 씨드 포인트 결정과 스트림라인 생성 계산은 매우 오랜 시간을 필요로 한다. 본 논문에서는 효과적인 스트림라인 배치를 위해 유동해석 데이터의 중요도를 기반으로 한 씨드 포인트 결정 방법과 분산병렬 가시화 시스템 환경에서의 병렬 처리 기법을 제안한다. 또한, GLOVE 가시화 시스템에서 실제 유동해석 데이터를 이용한 구현 결과를 소개하고 이를 통해 본 논문의 제안 방법을 검증하고자 한다.

• 한국유체기계학회 논문집
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• 제15권5호
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• pp.11-19
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• 2012

The main function of fuel cell manifold is to render reactants distribution as uniform as possible into a fuel cell stack. The purpose of this study is to numerically investigate the effects of stack manifold design on reactants distribution within a fuel cell stack. Four manifold designs with different manifold entrance shapes (expansion or diffuser) and different values of the extra width between the cell outer channel and manifold side wall are considered and applied to the fuel cell stack consisting of 50 cells. Since the fuel cell stack geometry involves several millions of grid points for numerical calculations, a parallel computing methodology is employed to substantially reduce the computational time and overcome the memory requirement. The numerical simulations are carried out and calculated results clearly demonstrate that both the manifold entrance shape and extra width have a substantial influence on manifold performance, controlling the degree of flow separation and entrance length for fully developed flow in the manifold channel. Finally, we suggest the optimum design of fuel cell manifold based on the simulation results.