• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.8
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• pp.69-76
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• 2003

For stable combustion and safety of a structure of the propulsion system, a cooling system to the liquid rocket engine should be incorporated. In this study, Eulerian-Lagrangian scheme for two phase combustion, nongray radiation and soot formation effect, and film-wall interaction have been introduced to study the effect of film cooling. After briefly introducing the governing equation, combustion characteristics with change of wall temperature has been investigated by varying such parameters as fuel mass fraction for film cooling, diameter of the fuel droplet, overall mixture fraction of oxygen to fuel. Also, radiative heat flux is compared with the conductive one at the combustor wall.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.12
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• pp.1635-1640
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• 2011

The objective of this study is to design of a cooling system of the over-molding mold for a socket component of an automobile wiper by performing numerical analyses. Hot spots in which the temperature distributions are higher than those of other region, were estimated by an initial over-molding analysis for the initial design of the mold. On the basis of the initial over-molding analysis, two types of cooling system designs with a linear cooling channel and a volumetric heat sink, were considered to improve the cooling characteristics of hot spots. To obtain an appropriate cooling system design, the effects of the diameter and the position of the linear cooling channels on the cooling characteristics and the product qualities were quantitatively examined. In addition, the effects of the design of the volumetric heat sink on the cooling characteristics and deformation distributions in the molded product were investigated. The results of the over-molding analysis of the two types of cooling systems showed that the multi-sliced over-molding mold with a volumetric heat sink can improve both the product quality and the cooling characteristics of the mold.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.6
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• pp.1150-1155
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• 1992

The cooling characteristics of a hot steel plate by a laminar impinging water bar were investigated experimentally. The dynamic parameters investigated were nozzle height L between nozzle and the hot plate, flow rate Q, and initial cooling temperature. Because the boiling phenomena on a hot steel plate are unsteady and change discontinuously, it is difficult to analyze the cooling characteristics directly. In this study the cooling efficiency was estimated by using the temperature decay rates and expansion speed of the water cooling zone. Temperature in the water cooling zone decreased rapidly and the radius of the water cooling zone expanded nearly in proportion to square root of the cooling time. With increasing initial temperature of a hot steel plate, the cooling efficiency became descendent. The cooling curve in the case of L/D = 30 showed the largest temperature decay rate and excellent cooling performance.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.5 no.2
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• pp.29-38
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• 1994

The denser and higher speed telecommunication systems get, the more electromagnetic waves and more heat they throw off. With power predictions lastly for the upcoming systems, they need the enforced method to optimize the technologies between shielding effectiveness and cooling characteristics. In the present study, the shielding effectiveness and cooling characteristics for en- closures with multiapertures considered as fundamental solution in telecommunication systems are performed both of experimentally and unmerically. The shielding effectiveness measured from ex- perimental work is compared with both of the analytical data for flat plates with multi-apertures and the cooling characteristics by the numerical solution. As results, the most significant influence on the shielding effectiveness of enclosures is determined by the porosities of apertures, and it is found that shielding effectiveness and cooling capabilities are significant varied, reciprocally,at which porosity is more than 80%.

• Korean Journal of Materials Research
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• v.7 no.10
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• pp.891-897
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• 1997

본 논문은 용액법으로 성장시킨 저밀도 폴리에틸렌 박막의 냉각 조건에 따른 결정화도의 관계와 냉각 조건에 따른 전기전도현상, 유전특성 및 절연파괴에 관하 연구로서 박막은 140[$^{\circ}C$]에서 2시간 유지후 냉각 조건을 달리하여 제작하였다. 결정화도는 XRD를 이용하여 측정하였으며 냉각 속도가 빠를수록 결정화도가 감소함을 볼 수 있었다. 전기전도현상은 냉각 조건에 무관하게 저전계에서는 이온전도특성이 나타나고 고전계에서는 공간전하제한전류이론이 지배적이다. 절연파괴전계는 냉각속도가 증가할수록 증가하고 self-healing절연파괴 방법에서는 시험회수가 증가할수록 증가하였다.

• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.1
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• pp.34-41
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• 2001

A study has been conducted to observe the slot film cooling effect on a convergent nozzle wall. The slot film cooling is used to protect the nozzle wall from the hot combusted gas by the coolant injected from the slot around the inner wall of the nozzle. The film cooling effectiveness and the heat transfer to the nozzle wall are influenced significantly by the blowing ratio of the coolant to the main flow and those are also influenced by the shape of the slot and the flow acceleration in the nozzle. In the present study, the heat transfer for the various blowing ratios has been performed by the experimental method and the results are compared with the results computed by the empirical formula. The numerical method has been conducted to compare the film cooling effectiveness of the convergent nozzle with that of the cylinder. For the relatively low blowing ratio, the cooling effectiveness increases sharply as the blowing ratio increases, and the increasing rate slows down for the high blowing ratio.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.4
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• pp.342-348
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• 2017

In this paper, film cooling characteristics at supersonic free stream conditions were examined experimentally by applying an IR-thermography. Film cooling experiments were carried out in a free-jet facility at Mach number of 3.0 and with unit Reynolds number of $42.53{\times}10^6$ and $69.35{\times}10^6$ using wedge shaped film cooling model which has a converging film cooling nozzle. Film cooling efficiency was calculated by measuring the surface temperature of PEEK(Polyether Ether Ketone) and the effects of angle of attack and blowing ratios on the film cooling efficiency were examined. The measured wall temperature was significantly reduced by the film cooling flow compared with the results without the film cooling flow. The usefulness of film cooling was also confirmed by the surface heat flux calculated using the surface temperature history of PEEK. As the blowing ratio increases the protected area of PEEK was also expanded along the direction of free stream and film cooling flow.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.1
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• pp.47-57
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• 2020

The present study investigates to improve the film cooling performance on the vane endwall. Numerical simulation was conducted to analyze film cooling characteristics on the vane endwall. Six different hole arrangements were designed considering flow characteristics on the endwall. The results showed that the film cooling effectiveness was low on the pressure side and nozzle throat in the base case, because coolant was deflected from the pressure side to the suction side. On the other hand, when the holes were installed near the pressure side, the film cooling effectiveness was enhanced on the pressure side and nozzle throat, because the coolant was less affected by cross flow. Therefore, the film cooling effectiveness increases about 16% compared to the base hole arrangement.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.148-151
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• 2007

We made two injectors that were equal to all design except for existence or nonexistence of swirl chamber of fuel part, because we want to find cooling characteristics at the injector face according to existence or non existence of swirl chamber of fuel part. And we set regenerative cooling channel in injector face for protecting injector face for prolonged combustion time. Two injectors were performed hot firing test, and then we compared cooling characteristics of two injectors. Also we compared O/F ratio effects on cooling characteristics and combustion characteristics.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.46-46
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• 2008

스텔스 기능을 가진 군사용 항공기는 레이다 망의 추적을 피하기 위해 일반 냉각수 대신에 절연유를 냉각매체로 사용한다. 그러나 절연유는 물에 비하여 열전달특성이 매우 낮기 때문에 항공기 전기전자 기기/부품 발열부를 효과적으로 냉각시키지 못하는 한계성을 가지고 있다. 따라서 본 연구에서는 나노유체(Nanofluid) 개념을 이용하여 절연유에 알루미나 및 질화알루미늄 나노분말을 미랑 분산시킨 나노절연유를 제조하고 이것의 열전달특성을 순수 절연유의 그것과 비교 평가함으로써, 냉각특성이 크게 개선된 새로운 냉매로서의 적용 가능성을 확인하고자 하였다. 다만 나노절연유를 제조함에 있어서 가장 큰 장애물은 오일에 대한 분산성 확보에 있기 때문에, 비드밀 및 초음파를 이용한 나노분말 응집체의 습식분산 및 분산제를 이용한 친유성 표면개질을 동시에 수행함으로써 장시간 안정된 분산성을 확보하도록 노력하였다. 나노유체의 열전도도 및 대류열전달계수는 비정상열선법을 이용하여 측정하였으며, 유체 속의 분말 분산 상태는 원심력을 이용한 분산안정성 평가장치 및 cryo FE-SEM을 이용하여 확인하였다. 또한 분말 형상이 대류열전달에 미치는 영향을 조사하기 위하여 알루미나 나노분말은 구상과 침상의 분말을 모두 사용하였고, 질화알루미늄 외에 다이아몬드 나노절연유도 함께 제조, 평가함으로써 냉각 및 절연특성, 그리고 물리화학적 안정성이 우수하고 실적용 가능성이 가장 높은 재료를 도출하고자 하였다.