• 대한기계학회논문집B
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• 제28권2호
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• pp.238-246
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• 2004

This paper reports an experimental study around a module about forced air flow by blower (35${\times}$35${\times}$6㎣) in a portable personal computer model(200${\times}$235${\times}$10㎣). Experimental report is to know three data to investigate thermal resistance, adiabatic wall temperature and visualized fluid flow around the module by combination of the moving number and the arrangement method of blower. The channel inlet flow velocity has been varied between 0.26, 0.52 and 0.78㎧, and input power ( $Q_{p}$) to the module is 4W. To investigate thermal resistance. the heated module is mounted on two boards(110${\times}$110${\times}$1.2㎣, k=20.73, 0.494W/ $m^{\circ}C$) in parallel-plate channel to forced air flow. The temperature distribution were visualized by heated module on acrylic board(k=0.262W/ $m^{\circ}C$) using liquid crystal film. Fluid flow around the module were visualized using particle image velocimetry system.

• 설비공학논문집
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• 제12권7호
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• pp.659-666
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• 2000

Heat transfer characteristics of a heat exchanger for low temperature waste heat recovery using oscillating capillary tube heat pipe were evaluated against the charge ratio variation of working fluid and various working fluids. R-l42b, R-22 and R-290 were used as working fluids. The heat exchanger was composed of heat pipe with capillary tube bundles, having a 2.6mm in outer diameter, 1.4mm in inner diameter with 101m long, and 40 turns. Charge ratio of working fluid was 40% and 50%. Water was used as secondary fluid. Inlet temperature and mass velocity for each secondary fluid were 297 K, 280 K and9~27 kg /$m^2s$,, respectively. From experimental results, it was found that heat transfer performance of R-22 was higher than those of R-l42b and R-290 and it was proportional to Figure of merit for thermosyphons. As a result, it was thought that R-22 was the most suitable working fluid of waste heat recovery for low temperature waste heat recovery.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.19-24
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• 2003

This paper is to research the heat transfer characteristic in copper-water variable conductance heat pipes(VCHP) with a non-condensable gas and gas reservoir. The heat transfer characteristics in the VCHP have not yet been studied much researches. VCHP are used in many applications. These applications range from thermal control of components and systems on satellites, to precise temperature calibration duties, conventional electronics temperature control and thermal diodes. The practical use of VCHP is a simple way to control the temperature of satellites. As the quantity of NCG was increased, there was an increase in the saturation vapor temperatures. As the input heat has loaded from 90 W to 110 W, the difference of the evaporator surface is lower than $10^{\circ}C$.

• 한국정밀공학회지
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• 제27권10호
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• pp.84-92
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• 2010

In this study a numerical analysis has been conducted for the flow characteristics and pumping performance of a piezoelectric-based micropump with electromagnetic resistance exerted on electrically conducting fluid. Here, electromagnetic resistance is alternately applied at the inlet and outlet with alternately applied magnetic fields in association with the reciprocal membrane motion of the piezoelectric-based micropump. A model of Prescribed Deformation is used for the description of the membrane motion. The internal flow characteristics and pumping performance are investigated with the variation of magnetic flux density, tube size, displacement of membrane and the frequency of the membrane. It turns out that the current micropump has a wide range of pumping flow rate compared with diffuser-nozzle based micropumps.

• 한국자동차공학회논문집
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• 제14권2호
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• pp.194-201
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• 2006

Roof-fairing and deflector system have been used on heavy-duty trucks to minimize aerodynamic drag force not only for driving stability of the truck but also for energy saving by reducing the required driving power of the vehicle. In this study, a numerical simulation was carried out to see aerodynamic effect of the drag reducing device on the model vehicle. Drag and lift force generated on the five different models of the drag reducing system were calculated and compared them each other to see which type of device is efficient on the reduction of driving power of the vehicles quantitatively. An experiment has been done to see airflow characteristics on the model vehicles. Airflow patterns around the model vehicles were visualized by smoke generation method to compare the complexity of airflow around drag reducing device. From the results, the deflector systems(Model 5,6) were revealed as a better device for reduction of aerodynamic drag than the roof-fairing systems(Model 2,3,4) on the heavy-duty truck and it can be expected that over 10% of brake power of an engine can be saved on a tractor-trailer by the aerodynamic drag reducing device at normal speed range($80km/h{\sim}$).

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.27-27
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• 2018

알루미늄은 취약한 내식성을 보완하기 위하여 나노다공성의 산화물 피막을 형성하는 양극산화 처리를 주로 활용한다. 이러한 나노다공성 산화물 피막에 소수성 처리와 불용성의 윤활유를 침지하면 표면에 접촉하는 물을 비롯한 다른 유체들의 젖음성을 크게 감소시킬 수 있으며, 이로 인하여 부식성 물질이 다공성 구조물로 침입하는 것을 억제할 수 있다. 따라서 양극산화 피막에 윤활유 침지를 이용하여 알루미늄의 부식에 대한 저항성을 크게 향상시킬 수 있으며, 추가적으로 외부의 물리적인 손상에 대한 치유 능력을 얻을 수 있다. 이러한 성능뿐만 아니라 침지된 윤활유의 내구성은 나노다공성 산화피막의 물리적 형상에 따라 차이가 날 수 있다. 본 연구에서는 나노다공성의 양극산화 피막의 기공 구조를 다양하게 변화시켜 그 형상에 따라서 윤활유를 침지 후 알루미늄 소재의 내식성 및 자기 치유 특성의 차이에 대하여 알아보았다. 기공의 형상은 한쪽 끝이 막혀있는 기둥형, 후처리를 통한 확장된 기둥형 및 침상형의 기공 구조를 제조하였고, 전압제어를 통한 병목 형상의 기공 구조를 구현하여 그 특성 차이를 비교하였다. 기공들이 서로 고립된 형태를 가질수록 윤활유가 안정적으로 산화물에 침지될 수 있으며, 기공의 공간이 클수록 더 많이 윤활유를 포함하여 우수한 자기 치유 특성을 보여주었다. 병목 형상의 가공 구조는 내부의 충분한 크기의 기공 공간과 표면에 작은 기공을 가지고 있기 때문에 우수한 내구성과 자기 치유 특성을 보여준다.

• 지질공학
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• 제11권3호
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• pp.295-301
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• 2001

서울~부산간 경부고속철도 왕림터널 개착구간의 서측 사면에서 발생한 암반사면 사태의 발생원인을 파악하기 위하여 정밀지질조사와 물리탐사를 실시하였다. 지질구조에 대한 물리탐사 및 기하학적 분석결과, 집중강우 시 다량의 지하수가 N60$^{\circ}$ E 방향의 주단열대로 유입되면서 단열공극 내의 유체압력이 상승하여 사면암반의 거동이 유발되었으며, 개착터널의 사면쪽으로 경사하는 편마암의 엽리면을 따라 변위가 진행되어 결과적으로 대규모 사태가 야기되었던 것으로 해석되었다.

• 대한조선학회논문집
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• 제44권3호
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• pp.248-257
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• 2007

Turbulent flows around a sailing yacht hull were calculated using CFD technique. Grid system was generated by using Gridgen package and Fluent package was used to calculate flows around a 30ft-class yacht hull designed by MOERI. The drafts at starboard and port sides of a yacht. when the hull was heeled, were determined by adjusting the same displacement in the generated grid system. Pressure distribution on the sailing yacht hull was obtained and the changes of drag and side force by heel and leeway variation were shown. The flow calculations have been carried out both with and without free surface, and keel and rudder were included for both cases. It was found that the calculated results with free surface gives better agreement with experiments than those without free surface, although there are still a room for the improvement in correct prediction of forces.

• Journal of Advanced Marine Engineering and Technology
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• 제25권4호
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• pp.797-808
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• 2001

Three-dimensional trajectory of fluid particle is simulated by a particle motion, which is able to examine the influences of changes in the several parameters. To calculate the trajectory of a particle, the Runge-Kutta method was utilized. The use of a projectile of particles for the trajectory of liquid jet has been shown to be useful to estimate the influence of different operating parameters such as best particle diameter, density of liquid body, initial take-off velocity, wind velocity, cross wind velocity, take-off angle, and base angle for a released flow from the nozzle. The results give the trajectories of various types of particle of body and at different elevations, base angles, wind velocities and densities of liquid body. The trajectories in a vacuum show that air resistances decreases both the distance and the maximum height of a projectile, and also explain that the termination time is also reduced in air. In addition, the maximum distance in the x direction was obtained with take-off angles from 30 degrees to 45 degrees in still air and the projectile of particles was highly effected by wind and cross wind. Clearly, a particle has to be so positioned as to take the optimum possible advantage of the wind if the maximum distances is requested. The wind astern increased the maximum distances of x direction compared with the wind ahead. Finally, it is possible to optimize the design of pump by using these results.

• Tribology and Lubricants
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• 제25권1호
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• pp.56-60
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• 2009

A journal bearing is used in a hydrodynamic lubrication state, but it becomes a boundary lubrication state that asperity of a contact part touch each other when pressure is too high and an enough oil film is not formed by viscosity change due to lubricating oil temperature. At this time, abrasion due to contact between a journal and a bearing is unavoidable, and scuffing damage that the journal adheres to the bearing occurs if the process is repeated. Damage of the journal bearing is an important problem because it gives huge damage to a machine and can generate large accidents such as economic loss and human life damage. In this study, method for using the pull-up resistor concept was introduced as the monitoring technology. This monitoring system is important to enhance reliability of the engine.