• Elastomers and Composites
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• 제36권3호
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• pp.153-161
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• 2001

궤도차량의 고무패드는 상당한 크기의 진폭과 주파수를 가지고 반복되는 동적 변형을 받고 있으므로, 이로 인하여 열발생과 더불어 상당한 내부온도의 상승을 초래한다. 이러한 열발생은 고무 재료의 점탄성 특성에 기인한 것으로, 점성효과에 의하여 변형시의 기계적 에너지의 일부가 히스테리시스 루프의 면적에 해당되는 열에너지로 변환되기 때문이다. 발생한 열은 발산조건이 충분하지 못할 경우 내부온도의 상승을 초래하며, 온도가 과다할 경우에는 고무제품의 성능이나 수명에 중대한 장애요인으로 작용하게 된다. 본 연구에서는 전차 궤도고무에 작용하는 동적 하중에 근거하여 각 부품별 열발생률을 실험을 통하여 측정하고, 이를 입력자료로 하여 궤도패드에 발생하는 온도분포를 유한요소법으로 해석하였다.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2019년도 춘계 학술논문 발표대회
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• pp.34-35
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• 2019

In recent years, the construction industry has also applied the dry method that can be assembled in the field by industrialization and factory production, which is free from climatic effects and can reduce the cost due to mass production and simplify the work in the field. Among the building materials used in this dry method, ALC products are made by mixing calcium oxide, gypsum, cement, and water in silica and putting them in an autoclave to create voids in the interior through steam curing at high temperature and pressure. But it requires curing cycle conditions of warming, isothermal, and temperature curing. It depends on the performance of the product depending on the curing conditions, the economical efficiency due to high oil prices, the emission of greenhouse gases by the use of fossil fuels. Experiments were conducted to select an appropriate animal protein foam for lightweight foamed concrete block which was cured by applying a prefilling method to replace existing ALC products. As a result of investigating the characteristics of lightweight foamed concrete by type of animal protein foam, it is considered that FP3 is most suitable for manufacturing lightweight foamed concrete block.

• 대한기계학회논문집B
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• 제31권12호
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• pp.1002-1008
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• 2007

Natural convection flows in a doubly-inclined cubical air-filled cavity are numerically simulated by a solution code(PowerCFD) using unstructured cell-centered method. For a physical realizability, the cavity has one pair of opposing isothermal faces at different temperatures, $T_h\;and\;T_c$, respectively, the remaining four faces having a linear variation from $T_c\;to\;T_h$. The paper redefines a new doubly-inclined orientation for the cubical-cavity benchmark problem. Special attention is paid to three-dimensional thermal characteristics in natural convection according to the new orientation at $Ra=4\times10^4$. Comparisons of the average Nusselt number at the cold face are made with benchmark solutions and experimental results found in the literature. It is found that the average Nusselt number at the cold face has a maximum value at the doubly-inclined angle ranging from $40^{\circ}\;to\; 45^{\circ}$ We also report the effect of new orientation on the type of temperature structure in a doubly-inclined cubical-cavity.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2053-2058
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• 2008

It was investigated thermal performances on two array types of a serial circulation and a two-way parallel circulation for six water-cooled cold plates covered with non-metallic material (polycarbonate, PC) to reduce weight of the cooling devices for humanoid robot cooling. Six cold plates attached on $10{\times}10\;mm^2$ copper base : $0.5{\times}0.5\;mm^2$ pin-finned surfaces of 1.5 mm high with 0.5 mm array spacing, was mounted on six copper heating blocks with isothermal conditions of $50{\sim}90^{\circ}C$, respectively. In order to compare thermal characteristics according to two circulation types, the surface temperatures of heating blocks and the cooling water temperatures at inlets and outlets of cold plates were measured. From the results, it was found that a two-way parallel circulation was better performance than a serial circulation in terms of total thermal resistance, total heat transfer rate, and surface temperature rises from $1^{st}$ heating block to last one for six multiple cold plates.

• 설비공학논문집
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• 제22권9호
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• pp.614-619
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• 2010

Recently, a problem related to the thermal management in portable electronic and telecommunication devices is becoming issued. That is due to the trend of a slimness of the devices, so it is not easy to find the optimal thermal management solution for the devices. From now on, a pressed circular type cooling device has been mainly used, however the cooling device with thin thickness is becoming needed by the inner space constraint of the applications. In the present study, the silicon flat plate type cooling device with the separated vapor and liquid flow path was designed and fabricated. The normal isothermal characteristics created by vapor-liquid phase change was confirmed through the experimental study. The cooling device with 70 mm of total length showed 6.8 W of the heat transfer rate within the range of $4{\sim}5^{\circ}C/W$ of thermal resistance. In the future, it will be possible to develop the commercialized cooling device by revising the fabrication process and enhancing the thermal performance of the silicon and glass cooling device.

• 대한기계학회논문집
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• 제12권6호
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• pp.1381-1389
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• 1988

본 연구에서는 앞서의 여러 경우에서 단순하게 취급 되었던 화염면과 연료표 면의 경계조건을 무한히 길고, 평행한 확산, 회색 평판(gray, diffuse plates)으로 보 고, 이 두 평판 사이에 흡수(absorbing), 방사(emitting), 산란(scattering)을 하는 회색매질(gray medium)이 차여져 있다고 생각한다. 이런 가정하 에서, 여러 매개변 수들을 변화시켜가며 전도, 대류, 복사열전달들의 상호작용과 온도 분포를 수치적으로 해석하였다. 특히 화염면과 연료표면간의 열교환에 있어서의 분출에 의한 효과와 복 사열전달의 영향에 관심을 기울였다.

• Transactions on Electrical and Electronic Materials
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• 제1권2호
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• pp.7-11
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• 2000

a-Si:H and poly-Si TFT(thin film transistor) characteristics were investigated using an inverted staggered type TFT. The TFT an as-grown a-Si:H exhibited a low field effect mobility, transconductance, and high gate threshold voltage. The poly-Si films were achieved by using an isothermal and RTA treatment for glow discharge deposited a-Si:H films. The a-Si:H films were cystallized at the various temperature from 600$^{\circ}C$ to 1000$^{\circ}C$. As anneal temperature was elevated, the TFT exhibited increased g$\sub$m/ and reduced V$\sub$ds/. V$\sub$T/. The poly-Si grain boundary passivation with grain boundary trap types and activation energies as a function of anneal temperature. The poly-si TFT showed an improved I$\sub$nm//I$\sub$off/ ratio of 10$\^$6/, reduced gate threshold voltage, and increased field effect mobility by three orders.

• 한국자동차공학회논문집
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• 제21권2호
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• pp.87-97
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• 2013

Recently the use of gas spring in the combat and commercial vehicle's suspension is increasing. Because of its nonlinear characteristics, the gas spring can support wide range of dynamic loads and gives good ride quality. In design of gas spring, isothermal and adiabatic processes are applied generally, but those processes could not produce heat transfer effect in the simulation. So in this study, heat transfer differential equation and BWR/Ideal state equation are used to calculate the pressure of gas spring which is changing with time. The numerical analysis showed that the pressure of gas spring forms a hysteresis loop in the both of the state equations. But the peak pressure value of BWR equation over 0.1Hz frequency are higher than that of adiabatic process. And the test results showed that the differences between test results and ideal gas equation are smaller than those of BWR equation, so the ideal equation is more accurate than BWR equation in this case.

• 한국주조공학회지
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• 제28권3호
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• pp.129-135
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• 2008

The reheating stage of electromagnetically stirred Al billet is a critical factor in the thixoforming process. When reheated to the solid-liquid state, the microstructure evolves to a more globular and more homogeneous structure by a coarsening mechanism, the kinetics depending on the initial microstructure. Microstructural evolution has been characterized by conventional parameters (mean size of particle and shape factor) as a function of holding time in the solid-liquid state. The aim of this study is to report experimental results concerning microstructural evolution in the solid-liquid state of electromagnetically stirred Al billet. The material was elaborated in the form of continuously cast bars solidified with electromagnetic stirring to degenerate the dendritic structure. The choice of the reheating conditions is determined by a dendritic ripening and coalescence mechanism, involving variations of both the shape and size of the particles. The reheating time has to be long enough to allow a minimum degree of spheroidizing, but has to be limited as much as possible in order to avoid excessive ripening. The optimum microstructure was obtained at the reheating temperature of near $584^{\circ}C$ and the holding time of 5 min. The only means of combining high productivity with good casting quality was to use feedstock billets whose microstructure showed rapid transformation characteristics.

• 동력기계공학회지
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• 제17권4호
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• pp.109-114
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• 2013

In this study, the microstructure, mechanical properties and high temperature oxidation characteristics of HiSiMo and HiSiMoM ductile iron for exhaust manifold were investigated. The HiSiMoM ductile iron was developed by optimization of alloying element addition and casting design. The exhaust manifold prototype was fabricated using the HiSiMoM iron and this resulted in the weight saving of 0.73kg. The microstructures of the HiSiMo and HiSiMoM irons were similar each other and graphite nodularity was 89% and 93% respectively. Tensile strengths of them were 663.5 and 674.4 MPa and Brinell hardness were 235.3 and 243.9 respectively. Both irons showed parabolic weight gain behavior in high temperature oxidation atmosphere. Oxidation layer was divided into external and internal layers. The weight gain of the HiSiMoM iron was lower than that of the HiSiMo iron after isothermal oxidation test at $900^{\circ}C$. This should be rationalized by higher Si enrichment at the interface of the matrix and internal layer of the HiSiMoM iron.