• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.8
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• pp.1566-1574
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• 1992

Local heat transfer characteristics for a round air jet impinging normally on a heated flat plate were experimentally investigated. The problem parameters investigated were jet Reynolds number, Re=4000,10000, and 20000, and nozzle-to-plate spacing(L/D) of 2,6, and 10. The temperature variations on the flat uniform heat flux surface were mapped using a thermo-sensitive liquid crytal sheet. The isochromatic images corresponding to the characteristic temperature of liquid crystal were analyzed with the help of a digital image processing system. The local Nusselt number, Nu decreased rapidly in the impingement region and exhibited a similar profiles in the wall jet region independent of the nozzle-to-plate spacing L/D. In the case of large Reynolds number, heat transfer rate (Nu) was proportional to 0.5 power of the Reynolds number. For L/D=2, a secondary peak in the heat transfer rate was seen in the region of X/D=1.5~3 due to the transition from laminar to turbulent boundary layer.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.8
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• pp.12-19
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• 2004

Low-speed gas flows around a micro-scale flat plate are investigated using a kinetic theory analysis. The Boltzmann equation simplified by a collision model is solved by means of a finite difference approximation with the Discrete Ordinate method. Calculations are made for flows around a 5% flat plate with a finite length of 20 microns. The results are compared with those from the Information Preservation method and a continuum approach with slip boundary conditions. It is shown that three different approaches predict a similar basic flow patterns, while the results from the present method are more accurate than those from the other two methods in details.

• Electrical & Electronic Materials
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• v.15 no.12
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• pp.11-18
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• 2002

전계 방출 디스플레이(Field Emission Display : FED)는 금속 또는 반도체로 만들어진 극미세 구조의 전계 에미터(field emitter)에 전기장을 인가하여 진공 속으로 방출되는 전자를 형광체에 충돌시켜 화상을 표시하는 디스플레이 소자로서, 원리적으로 브라운관(CRT)의 우수한 표시 특성을 그대로 가지면서 경량 박형화가 가능하기 때문에 'Thin CRT'라고 불리기도 한다 FED는 원리적으로 고휘도, 저소비전력, 빠른 응답속도, 광시야각, 고해상도, 우수한 칼라 표시. 넓은 사용온도 범위 등 CRT 및 평판 디스플레이의 장점을 모두 갖추고 있는 이상적인 디스플레이 소자로 평가되어 1990년대 초반부터 세계 유수의 연구 기관들이 본격 적 인 연구 개발을 추진하여 왔지만, 아직까지 평판 디스플레이 시장에 진입 할 만큼 기술 개발이 이루어지지 못하고 있다. 본 고에서는 FED의 근간이 되는 전계방출 소자의 원리 및 종류, FED의 핵심요소 기술, 최근 연구 개발 동향, FED의 응용 분야 및 상용화 가능성 등에 대하여 살펴보기로 한다.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.1
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• pp.189-196
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• 2004

A modified generalized particle algorithm, MGPA, was suggested to improve the calculation efficiency of standard SPH Method in numerical analysis of high speed impact behavior. MGPA had a new weight function to reduce computation time. The efficiency of this method was proven through calculation for the sample problems of one dimensional rod impact problem and two dimensional plate impact problem. The MGPA method reduced the calculation error and stress oscillation near the boundaries. The validity of this approach was shown by the comparison with ABAQUS results in two dimensional plate impact problem.

• Fire Science and Engineering
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• v.15 no.1
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• pp.41-46
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• 2001

The flow induced by a vertically impinging circular jet under a horizontal plate is investigated by visualization technique, using kerosene smoke in nitrogen gas to visualize the vortex flow and impinging flow. The light source was the sheet beam of Ar-Ion laser. The vertical and horizontal images scattering of kerosene smoke were recorded by the high speed CCD camera and the video camera. The instantaneous velocity of the vortex and the mean velocity of the smoke front were measured from the acquisited images.

• Journal of KSNVE
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• v.10 no.6
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• pp.1035-1040
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• 2000

The Impingement of a weak shock wave discharged from the open end of a shock tube upon a flat plate was investigated using shock tube experiments and numerical simulations. Harten-Yee Total Variation Diminishing method was used to solve axisymmetric, unsteady, compressible flow governing equations. Computations predicted the experimented results with a good accuracy. The peak pressure on the flat plate was not strongly dependent of the shock wave Mach number in the present range of Mach Number from 1.05 to 1.20. The distance between the plate and shock tube was changed to investigate the effect on the peak pressure. From both the results of experiments and computations we obtained a good empirical equation to predict the peak pressure on the flat plate.

• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.103-108
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• 2009

The droplet impact and merging process on a flat substrate with contact angle hysteresis is numerically studied. The droplet deformation is determined by an improved level-set method employing a sharp-interface technique for the stress condition at the liquid-gas interface and the contact angle condition at the liquid-gas-solid interline. Based on the computations, the droplet impact and merging pattern is investigated to find the optimal condition in manufacturing a micro-line. The effects of dynamic contact angles and droplet spacing on droplet motion are quantified.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.129-134
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• 2011

In this paper, the confined single slot jet impingement is investigated numerically. Although the geometry of the jet impingement is simple, the flow pattern of the jet impingement is complex and the numerical results of the jet impingement is affected much by numerical methods. The first goal of this study is to analyze the effects of Reynolds models and numerical spatial discretization schemes on the results of heat transfer performance and the flaw characteristics and to select the best method. Various versions of the low Reynolds number k-epsilon turbulence models are compared. Using the selected numerical method, the flow field and heat transfer characteristics of confined single slot jet impingement on a moving plate are analyzed.

• 한국연소학회:학술대회논문집
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• 2003.12a
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• pp.167-173
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• 2003

An experimental study on the behavior of droplets impinging on a solid flat surface was carried out in the present study. Breakup of a liquid droplet impinging on a solid surface has been investigated experimentally for various fuels with different properties. The fuel temperature and incident angle were chosen as major parameters. And fuel temperature and incident angle varied in the range from $-20^{\circ}C$ to $30^{\circ}C$ and from $30^{\circ}$ to $60^{\circ}$, respectively, were investigated. It was found that the variation of fuel temperature influences upon droplet mean diameter which were bounced out from the solid surface. As the increases of incident angle, the break-out mass flow rate increases. This causes the decrease of liquid film flow rate. The larger incident angle gives less liquid film flow rate.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.3 no.1
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• pp.61-68
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• 1991

The purpose of this study is to investigate the heat transfer characteristics and the flow structure in the case of rectangular air jet impinging vertically on the flat heating surface. The maximum value of Nusselt number at stagnation point is observed at H/B=10. It is found that this trend has been caused by the effect of stretching of large scale vortex in the stagnation region. For potential core region the Nusselt number distribution in the downstream of the stagnation point decreases gradually and begins to increase at about X/B=3. From the flow visualization it could be seen that small eddy produced from the nozzle edge grows in large scale and that large scale eddy disturbed the thermal boundary layer on the heating plate. The local average Nusselt number becomes maximum at X/B=0.5 regardless of H/B variation.