• 폴리머
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• 제36권6호
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• pp.685-692
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• 2012

사출성형공정은 충전, 보압, 냉각, 이형 및 취출 순서로 이루어진다. 이러한 공정 중 보압단계에서 캐비티 내에 가장 큰 압력이 주어진다. 따라서 캐비티 내압은 보압전환 시점과 보압의 크기에 가장 크게 영향을 받는다. 캐비티의 큰 내압은 금형에 큰 응력을 집중시켜 금형을 손상시킬 우려가 있으므로 캐비티 내압을 관찰하고 조절하는 것은 매우 중요하다. 본 연구에서는 이론해석과 실험을 통하여 보압전환 시점과 보압의 크기에 따라 캐비티 내압을 분석하였다. 보압전환 시점이 늦어짐에 따라서 내압이 증가하였다. 또한 보압전환이 늦어지면서 충전시간이 길게 되어 전체적으로 압력을 받는 시간이 길어져 보압 이후 냉각이 끝난 후에도 잔여압력이 존재하였다. 캐비티 내의 압력은 보압크기가 커질수록 비례적으로 증가하는 경향을 보였다. 역시 보압의 크기가 클수록 냉각 후 잔여압력이 증가하였다. 결과적으로 보압전환 시점이 늦고 보압크기가 크면 캐비티 내에 높은 압력이 형성되고 냉각이 끝난 후에도 잔여압력이 존재함을 알 수 있었다. 실험과 해석을 비교해 보았을 때 전체적인 경향은 매우 유사하였으나 해석에서는 잔여압력을 예측하지 못하였다. 캐비티 내압 조절을 위해서는 보압조건의 설정이 중요하며 CAE 해석을 통하여 최적 조건 설정이 가능함을 알 수 있었다.

• 항공우주시스템공학회지
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• 제6권4호
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• pp.24-28
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• 2012

In this paper, 2-D experiment and steady-state computational fluid analysis were conducted for measuring the hear transfer coefficient of pintle type controllable thruster in high pressure and temperature. In case of 2-D experiment, transient liquid crystal technique was used for measuring heat transfer coefficient for the 2-D pintle model. The experimental result was used to validate the CFD result. The CFD results well predicted the heat transfer coefficient on the pintle surface except the nozzle downstream region, where the results by CFD was higher than experimental results. The CFD results were also compared with the result by Bartz equation and the it was shown that the Bartz equation overestimated the heat transfer coefficient on the nozzle throat as much as 80%.

• 대한기계학회논문집B
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• 제22권6호
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• pp.803-812
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• 1998

In this study, testing equipment with which several kinds of valves can be tested was composed. Two kinds of tilting check valves and a swing check valve were tested to analyze their dynamic characteristics. The results of the experiment showed that the tilting check valves protected the pump but that the swing check valve could not protect the pump when the reverse flow rate was high. Also the dynamic equation of the tilting check valve was formulated and simulated using system characteristic constant t$_{c}$ and one method of predicting t$_{c}$ by comparing the results of the simulation with the results of the experiment was proposed.sed.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2000년도 춘계학술대회논문집
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• pp.83-87
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• 2000

The die for cold forging gets a ver high axial load and radial pressure during processing and hence deforms considerably in the radial direction. This radial deformation of die becomes a important factor influencing the dimensional accuracy of a product. In order to obtain a product with highly accurate dimension therefore it is essential to acquire some information on elastic deformation of the die and the product. The study has been performed for the relation of the deformation between a die and a product in backward extrusion. The strain of the die has been given by the simple experiment using the strain gauges attached to the outer surface of the die. Also the history of the deformation of the die and the product has been given by the experiment and Lames' formula. The results has been compared with the previous another method. The study has given useful results for the deformation history of the die and the product through the experiment and Lame's formula in backward extrusion which can be applied in the die design for the product with accurate dimension

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.250.2-250.2
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• 2014

Currently, teeth whitening method which is applicable to dental surgery is that physician expertises give medical treatment to teeth directly dealed with a high concentration of hydrogen peroxide and carbamide peroxide. If hydrogen peroxide concentration is too high for treatment of maximized teeth whitening effect [1], it is harmful to the human body [2]. To the maximum effective and no harmful teeth whitening effect in a short period of time at home, we have observed the whitening effect using carbamide peroxide (15%) and a low-temperature atmospheric pressure plasma jet which is regulated by the Food and Drug Administration. The gas supplied conditions of the non-thermal atmospheric pressure plasma jet was with the humidified (0.6%) gas in nitrogen or air at gas flow rate of 1000 sccm. Also, the measurement of chemical species from the jet was carried out using the optical emission spectroscopy (OES), the evidence of increased reactive oxygen species compared to non-humidified plasma jet. We have found that the whitening effect of the plasma is very excellent through this experiment, when bovine teeth are treated in carbamide peroxide (15%) and water vapor (0.2 to 1%). The brightness of whitening teeth was increased up to 2 times longer in the CIE chromaticity coordinates. The colorimetric spectrometer (CM-3500d) can measure color degree of whitening effect.

• 생명과학회지
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• 제19권4호
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• pp.492-501
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• 2009

일반계 비만고교생 60명을 4그룹으로 구분, 웨이트트레이닝을 1일 60${\sim}$70분, 주 3회, 8주간 강도별(A group: control group, B group: $40{\sim}55%RM$, C group: $60{\sim}75%RM$, D group: $80{\sim}90%RM$)로 실시하여 대사증후군 5가지 인자(waist size, fasting glucose, TG, HDL-C, blood pressure) 개선을 위한 가장 효과적인 WT 강도를 알아보았다. Waist size의 감소는 운동군 모두 효과적이었으나 $40{\sim}55%RM$과 $60{\sim}75%RM$ 실시 그룹이 더욱 효과적이었고, TG의 감소도 운동군 모두 효과적이었으나 $40{\sim}55%RM$ RM 실시 그룹이 더욱 효과적이었다. Fasting glucose는 차이가 없었으며, HDL-C는 대조군보다 $80{\sim}90%RM$ 실시 그룹이 유의하게 증가하였고, blood pressure는 diastolic blood pressure는 차이가 없었고, systolic blood pressure는 다른 그룹보다 $40{\sim}55%RM$ 실시 그룹이 유의하게 감소하였다. 이러한 결과는 중 고강도보다는 오히려 저강도가 대사증후군 인자 개선에 효과적이라는 것을 시사하며, 웨이트트레이닝이 비만고교생의 대사증후군 위험 인자를 개선해준다는 사실을 확인하였다. 따라서, 비만고교생은 대사증후군 인자의 개선을 위해 $40{\sim}55%\;RM$의 웨이트트레이닝을 실시하는 것이 효과적이라 생각된다.

• Journal of Advanced Marine Engineering and Technology
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• 제33권2호
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• pp.244-251
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• 2009

Porous media have especially large surface area per volume, which contain complex fluid passage. If porous media can be applied to cool a CPU or an electronic device with large heat dissipation, it could result in heat transfer enhancement due to the enlargement of the heat transfer area and the flow disturbance. This study is aimed to identify the heat transfer and pressure drop characteristics of high-porosity metal foams in a horizontal channel. Experiment is performed with the various heat flux, velocity and pore density conditions. Permeabilities, which is deduced from Non-Darcy flow model, become lower with increasing pore density. Nusselt number also decreases with higher pore density. High pore density with same porosity case shows higher pressure loss due to the increase of surface area per unit volume. The fiction factor decreases rapidly with increase of Reynolds number in Darcy flow region. However, it converges to a constant value of the Ergun coefficient in Non-Darcy flow region.

• 대한기계학회논문집B
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• 제33권7호
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• pp.520-526
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• 2009

The objectives of this paper are to measure the heat transfer and pressure drop of the plate heat exchangers for absorption system applications. Three types of plate heat exchangers with different chevron angles are tested in the present experiment. Heat transfer and pressure drop performance of plate heat exchangers are measured in various operating conditions, and compared each other. The results show that the heat transfer rate of high theta ($120^{\circ}$) and mixed theta plate heat exchanger increases about 118% and 98% at the solution flow rate 350 kg/h compared to that of low theta ($60^{\circ}$), respectively. The effectiveness of high theta was evaluated about $0.53{\sim}0.85$ in this experimental range. The experimental correlations of the Nu and f were developed with error bands of ${\pm}7%$ and ${\pm}12%$.

• 설비공학논문집
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• 제18권6호
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• pp.459-467
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• 2006

Rapid development of electronic technology requires small size, high density packaging and high power in the electronic devices, which results in more heat generation. Suitable heat dissipation is required to ensure the guaranteed performance and reliable operation of the current state-of-the-art electronic equipment. The aim of the present study is to find out the forced-convective thermal-hydraulic characteristics of a pin-fin heat exchanger as a candidate for cooling system of the electronic devices through the analysis and experiment. Various configuration of the pin-fin array is selected in order to find out the effect of spacing and diameter of the pin-fin on the heat transfer and pressure drop characteristics. Experimental results are compared with the analyses and correlations of several researchers. Finally, the design guide are provided for the required pressure drop and/or the heat transfer characteristics of the heat exchanger.

• 소성∙가공
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• 제18권8호
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• pp.633-639
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• 2009

Remarkable progress had been made in both technology and production of optical elements including aspheric lens. In the past, precision optical glass lenses were produced through multiple processes such as grinding and polishing, but mass production of aspheric lenses requiring high accuracy and having complex profile was rather difficult. Against such a background, the high-precision optical GMP process was developed with an eye on mass production of precision optical glass pasts by molding press. This GMP process can produce with precision and good repeatability special form lenses such as for cameras, video cameras, aspheric lenses for optical items. In this study, Design Of Experiment(Taguchi method) was adopted to find a tendency of molding conditions that influence formability. Three main factors for molding conditions were selected based on pressure at pressing stage and temperature, pressure at cooling stage. Also, the DOE was carried out and the interference patterns were measured to evaluate the formability of GMP process. From the results, it was found that the cooling pressure is the most sensitive parameter for progressive GMP process.