• 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.

• 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.

• 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.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.4
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• pp.111-117
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• 2004

An analytical study was carried out to evaluate the regenerative cooling characteristics in the liquid rocket engine of a 10tf-thrust level using kerosene as a fuel. As a supplementary cooling method, a radiative cooling was applied to the nozzle extension. It was found out from this work that the cooling system with the regenerative and radiation cooling only is not adaptable for the liquid rocket engine of a 10tf-thrust level using kerosene as a fuel for the $2^{nd}$ stage of the space launch vehicle, with the viewpoint of the thermal and thermo-structural instability and the excessive pressure drop in the cooling channel.

• Journal of Embryo Transfer
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• v.21 no.4
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• pp.323-330
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• 2006

본 연구의 목적은 3주 동안 장기간 냉각상태로 보관된 개 정자의 기능적 특성을 알아보고자 두 종류의 정자 희석액, Glucose-BSA(G-BSA), Dimitropoulos-II(BIMI)가 정자의 기능적 특성에 미치는 영향을 알아보고자 한다. 개 정액을 수지법에 의해 채취하여 원심분리한 후 정장은 제거하였다. 정자를 G-BSA나 DIMI으로 희석하여 최종 농도를 $100\times10^6$ sperm/ml로 하였다. 희석된 정자를 정자 운송 시스템을 이용하여 루지애나 주립 대학에서 뉴올리언즈 실험실까지 운송하였다. 정자 운송 시스템은 $20^{\circ}C$에서 $9^{\circ}C$까지 분당 $0.08^{\circ}C$ 냉각율로 설정하였다. 희석된 정자는 $4^{\circ}C$에서 3주간 보관하였다. 보관 1일부터, 매주 단위로 정자의 활력, 정자 원형질막 고유성(생존성), 정자 첨체의 고유성을 검사하였다. 또한 체외조건하에서의 정자 번식 능력을 평가하기 위해 zona binding assay를 실시하였다. 실험 결과 냉각 상태로 3주 동안 보관된 개 정자는 여전히 정자의 기능적 특성을 나타냈다. 냉각기간이 길어질수록 정자의 활력 및 생존성은 감소하였으며(P<0.01), 첨체의 고유성은 냉각기간에 따라 감소하였으나 유의성은 없었다. 정자의 특성 중 활력이 다른 특성에 비해 냉각처리에 민감한 반응을 보였다. G-BSA배지에 보관된 정자의 활력 및 생존성이 DIMI에 비해 높게 나타났으며, 1 주 동안 보관된 정자의 생존성의 비교시 유의성이 높게 나타났다(P<0.05). 그러나 첨체의 고유성은 1일 동안 DIMI에 보관된 정자에서 높게 나타났다(P<0.05). 3주 동안 냉각상태로 보관된 개 정자는 여전히 난자의 투명대에 결합하는 능력을 보였으며, G-BSA에 보관된 정자의 경우 난자에 부착되는 평균 정자 수가 보관일수에 따라 유의적으로 감소하였다(P<0.05). 그러나 희석액 종류에 따른 난자에 부착되는 평균 정자 수의 유의적 차이는 없었다. 정자의 활력 및 생존성과 난자의 투명대에 결합하는 정자 수와의 상관관계를 본 결과, 활력 및 생존성이 높은 정자일수록 난자의 투명대에 많이 결합하여 정자의 잠재적 번식력이 증가함을 보였다. 결론적으로 G-BSA나 DIMI의 희석액으로 희석된 후 $4^{\circ}C$에서 냉각 보관된 정자는 3주 동안 정자의 기능적 특성을 유지하였으며 냉각 보관 2주까지 좋은 성적의 정자 특성을 나타냈다. 개 정자 냉각 보존에 대안적인 희석액으로 G-BSA도 사용 가능한 것으로 사료된다.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.81-81
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• 2011

Sol-gel spin-coating법을 이용하여 ZnO 박막을 증착하였다. Sol 전구체 용액을 Si(100) 기판에 증착하고 전열처리(pre-heat treatment)하여 gel 상태의 ZnO 박막을 형성시킨 후 다른 속도로 냉각시켰다. Atomic force microscopy (AFM), X-ray diffraction (XRD), Raman, photoluminescence (PL)을 이용하여 냉각속도가 ZnO 박막의 구조적 및 광학적 특성에 미치는 영향을 분석하였다. 느린 속도($5^{\circ}C$/min)로 냉각시킨 ZnO 박막은 나노섬유질구조(nano-fibrous structure)를 나타내었고, 상온에서 바로 냉각시킨 ZnO 박막은 매우 매끄러운 표면(mirror-like surface)을 나타내었다. ZnO (100), ZnO (002), ZnO (101) 방향을 나타내는 회절피크가 관찰되었고, 냉각속도에 따른 ZnO 박막의 배향성을 알아보기 위하여 texture coefficient (TC)를 계산해 보았다. 상온에서 바로 냉각시킨 ZnO 박막(TC(002)=76.3%)이 느린 속도로 냉각시킨 박막(TC(002)=45.2%)보다 (002) 방향으로의 배향성이 우세하게 나타났으며, 잔류응력도 작았다. 뿐만 아니라 PL을 이용한 광학적 특성평가에서도 상온에서 바로 냉각시킨 ZnO 박막에서 더 강한 강도와 좁은 반치폭(full-width at halt-maximum)을 갖는 near-band-edge emission (NBE) 피크가 관찰되었다. 후열처리에 따른 구조적 및 광학적 특성 변화 또한 연구하였다.

• Journal of the Korean GEO-environmental Society
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• v.23 no.4
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• pp.11-20
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• 2022

In order to acquire hydraulic characteristics for unsaturated layers, water retention tests were performed and compared by using the evaporation method, volumetric pressure plate extractor (VPPE) and chilled-mirror dew point method. The evaporation and chilled-mirror method are currently developed experimental technology and measure the water retention curve of unsaturated soils quickly and accurately. In the evaporation and VPPE method, the water retention has been measured and compared until 100kPa matric suction and consequently the result of the evaporation method could be verified. In the chilled-mirror method, the water retention has been measured until high level of matric suction and the overall shape of water retention curves could be obtained. As a result of water retention tests, the representative water retention curves were obtained and the applicability of each test method was discussed. Using both the evaporation and chilled-mirror methods, the soil water retention curve can be acquired reasonably for the whole range of matric suction.