• 한국태양에너지학회 논문집
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• 제37권5호
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• pp.65-75
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• 2017

In this study, the change of heat loss due to the degree of deterioration of the XPS insulation in KEPCO's office buildings is analyzed. The acceleration aging test of the XPS insulation was carried out according to the test method A of KS M ISO 11561: 2009. The performance of the insulation was analyzed by applying it to the three - dimensional steady state heat transfer analysis program. The acceleration aging test of the XPS insulation, show that the thermal resistance performance decreased by 1.44% at the A regional headquarters, 0.85% at the B regional headquarters, 6.41% at the C branch office, 7.76% at the D regional headquarters, 8.51% at the E branch office, and by 8.54% at the F branch office respectively. Using simulation, we determined that the thermal resistance value of E branch office decreased by 8.04%, while its heat loss increased by 8.52%. At A regional headquarters, the thermal resistance decreased by 1.38%, and the heat loss increased by 1.51%. At D regional headquarters, these value are 6.82% and 7.17%, respectively.

• 한국전산구조공학회논문집
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• 제25권4호
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• pp.315-321
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• 2012

본 연구에서는 분자동역학 전산모사와 유한요소해석 기반의 균질화 기법을 통해 나노복합재의 열전도 특성을 정확하고 효율적으로 예측할 수 있는 순차적 멀티스케일 균질화 해석기법을 제안하였다. 나노입자의 크기효과가 나노복합재의 유효 열전도 특성에 미치는 영향을 조사하기 위해 크기가 다른 구형 나노입자가 첨가된 나노복합재의 열전도 계수를 분자동역학 전산모사를 통해 예측했고, 그 결과 나노입자의 크기가 작아질수록 계면에서의 Kapitza열저항에 의해 나노복합재의 열전도 계수가 점차 감소하는 것으로 나타났다. 이러한 나노입자의 크기효과를 균질화 해석모델을 통해 정확하게 묘사하기 위해 Kapitza 열저항에 의한 계면에서의 온도 불연속 구간과 고분자 기지가 높은 밀도를 가지며 흡착되는 유효계면을 추가적인 상으로 도입하여 나노복합재를 입자, Kapitza 계면, 유효계면, 기지로 구성된 4상의 연속체 구조로 모델링하였다. 이후 순차적 멀티스케일 균질화 해석기법을 통해 유효계면의 열전도 계수를 나노복합재의 열전도 계수로부터 역으로 예측했으며, 이를 입자의 반경에 대한 함수로 근사하였다. 근사 함수를 토대로 다양한 입자 체적분율과 반경에 대한 나노복합재의 유효 열전도 특성을 예측하였으며, 유효계면에 대한 매개변수 연구를 수행하였다.

• Journal of Welding and Joining
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• 제19권5호
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• pp.499-505
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• 2001

In order to classify the mechanical phenomena of thermal elasto-plastic behavior on the multi-spot welded joints, this study has tried to carry out three-dimensional thermal elasto-plastic analysis on them. However, because the shape of multi-spot welded joints is not taxi-symmetric, unlike the cafe of single-spot welded joint, the solution domain for simulation should be three dimension. Therefore, in this paper, firstly, the three-dimensional thermal elasto-plastic program is developed by an iso-parametric finite element method. Secondly, from the results analyzed by developed program, this has clarified mechanical characteristics and their production mechanism on single and multi-spot waled joints. Moreover, it has been intended to make clear effects of pitch length on welding residual stresses, plastic strain of multi-spot welded joints.

• Design & Manufacturing
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• 제15권3호
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• pp.7-12
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• 2021

Plastic injection molds used for rapid heating and cooling must minimize surface damage due to friction and maintain excellent thermal and low electrical conductivity. Accordingly, various surface treatments are being applied. The properties of Al₂O₃ coating and DLC coating were compared to find the optimal surface treatment method. Al₂O₃ coating was deposited by thermal spray method. DLC films were deposited by sputtering process in room temperature and high temperature PECVD (Plasma enhanced chemical vapor deposition) process in 723 K temperature. For the evaluation of physical properties, the electrical and thermal conductivity including surface hardness, adhesion and wear resistance were analyzed. The electrical resistance of the all coated samples was showed insulation properties of 24 MΩ/sq or more. Especially, the friction coefficient of high temp. DLC coating was the lowest at 0.134.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.721-724
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• 2008

국내 초고층 프로젝트의 증가에 따라 필연적으로 고강도 콘크리트의 사용이 증가되고 있다. 콘크리트의 강도가 증가됨에 따라 화재시 단면결손을 유발하는 폭렬의 경향성이 커지고, 콘크리트부재 내부의 온도를 현저하게 증가시키며 심각한 구조적 손상을 유발할 수 있다는 문제점이 대두되었고, 정부에서도 2008년 7월부터 고강도 콘크리트의 내화성능 관리기준을 시행하고 있다. 이에 국내 각 건설사들은 50MPa 이상의 고강도 콘크리트에 대하여 폭렬방지 대책을 수립 중에 있다. 본 연구소에서는 신축공사 및 리모델링공사에도 적용이 가능한 고강도 콘크리트 폭렬방지 공법인 PFB (Posco E&C Fire Board) 공법을 개발하여 지속적인 공법 개선에 노력하고 있다. 본 연구는 고강도 콘크리트 폭렬방지 대책으로 개발한 PFB 공법을 기존의 습식공법에서 현장적용성 및 경제성이 우수한 건식화 공법개발을 위한 기초 연구로 PF보드의 기초물성 평가, 3시간 내화시험 및 현장 적용위한 실시 상세 설계를 실시하여 당사 초고층 현장에 적용하기 위한 기본 자료로 활용 하고자 하였다.

• 한국의류학회지
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• 제15권2호
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• pp.127-138
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• 1991

The aim of the present stud)r has been to obtain new and additional data allolwing a better design of sports garments as well as a better choice among some materiales, through measure-ment of body surface changes in the upper trunk in movement, measurement on the effects of local heating on other parts of the body and measurement of the thermal resistance of 6 types of materials applied on a manikin. In the first experiment, the upper trunk was divided in 32 Parts, the surface of which was measured by the tape method for two upper limb positions: extension at $90^{\circ}$ and $180^{\circ}$. In the second experiment, skin temperature, local thermal sensations and whole body thermal sensation were measured every 5 minutes during 40 minutes. The four areas of the shoulder, abdomen, hande and feet were heated with the hot pack at $50^{\circ}C$. In the third experiment, the regional thermal resistance of the various materials selected, in two different cases of clothing ease, have been measured by using a thermal manikin. Resultes of experiments were: 1. Extensions cause the upper front part of the trunk surface to lengthen vertically while the back tends to stretch in width. 2. Skin temperatures of the upper limbs are influenced by the abdomen and shoulder boatings. The correlation between the whole body thermal sensation and the upper trunk thermal sensation is significantly asserted. 3. Ceramic and aluminium coated materiales offer the most effective thermal resistance; ease in clothing increases the thermal resistance at the breast and the abdomen as well as the clo value of the materials.

• Advances in materials Research
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• 제8권4호
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• pp.275-293
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• 2019

The engine parts material used in gas turbines (GTs) should be resistant to high-temperature variations. Thermal barrier coatings (TBCs) for gas turbine blades are found to have a significant effect on prolonging the life cycle of turbine blades by providing additional heat resistance. This work is to study the performance of TBCs on the high-temperature environment of the turbine blades. It is understood that this coating will increase the lifecycles of blade parts and decrease maintainence and repair costs. Experiments were performed on the gas turbine blade to see the effect of TBCs in different combinations of materials through the air plasma method. Three-layered coatings using materials INCONEL 718 as base coating, NiCoCrAIY as middle coating, and La₂Ce₂O₇ as the top coating was applied. Finite element analysis was performed using a two-dimensional method to optimize the suitable formulation of coatings on the blade. Temperature distributions for different combinations of coatings layers with different materials and thickness were studied. Additionally, three-dimensional thermal stress analysis was performed on the blade with a commercial code. Results on the effect of TBCs shows a significant improvement in thermal resistance compared to the uncoated gas turbine blade.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.1092-1095
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• 2001

Steady state thermal analysis has been done by a finite element method in a diode of 12kV blocking voltage. The diode was fabricated by soldering ten pieces of 1200V diodes in series, capping a dummy wafer at the far end of diode series, and finally wire bonded for building anode and cathode terminal. In order to achieve high voltage and reliability, the edge of each diode was beveled and passivated by resin with a thickness of 25${\mu}$m. It was assumed that the generated heat which is mainly by the on-state voltage drop, 9V for 12kV diode, is dissipated by way of the conduction through diodes layers to bonding wire and of the convection at the surface of passivating resin. It was predicted by the thermal analysis that the temperature rise of a pn junction of the 12kV diode can reach at the range of 16∼34$^{\circ}C$ under the given boundary conditions. The thickness and thermal conductivity(0.3∼3W/m-K) of the passivating resin did little effect to lower thermal resistance of the diode. As the length of the bonding wire increased, which means the distance of heat conduction path became longer, the thermal resistance increased considerably. The thermal analysis results imply that the generated heat of the diode is dissipated mainly by the conduction through the route of diode-dummy wafer-bonding wire, which suggests to minimize the length of the wire for the lowest thermal resistance.

• 소성∙가공
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• 제27권3호
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• pp.145-153
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• 2018

Magnesium material could be widely used in the automotive industry because of its high strength to weight ratio, but the electric resistance spot welding process of magnesium sheets is difficult because of its low electric resistance and high thermal conduction and thermal expansion. For this reason, an electric resistance surface friction spot welding process using rotating dies is suggested for the spot welding of magnesium metal sheets. This welding method can be characterized by three heating methods: (1) electric resistance heating on contacted surface, (2) surface friction heating by rotating dies, and (3) thermal conduction heating from heated steel electrodes, for the fusion of metal at the interfacial zone between the two magnesium sheets. This welding process also has variables to explore, such as welding currents, diameters of the steel electrode, and rotating dies. It was found that the welding strength could reach industrial requirements by applying a welding current of 11.0kA, with steel electrodes of 12mm diameter, with rotating dies of 4.4 mm diameter, under the condition of a revolution speed of 1200rpm of rotating dies, for the surface friction spot welding process of AZ31 magnesium alloy sheets of 1.4mm thickness.

• 한국의류학회지
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• 제16권2호
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• pp.237-244
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• 1992

The purpose of this study was to comparatively evaluate thermal and water transmission properties of several vapor permeable water repellent (VPWR) fabrics and synthetic battings that became available in recent years. Five VPWR fabrics evaluated were Hipora in three coating variants, $Gore-Tex^{\circledR}$ and $Aitace^{\circledR}$. Battings evaluated were $Viwarma^{\circledR}$, $Uniwarmr^{\circledR}$, $Thinsulate^{\circledR}$, and $Airseal^{\circledR}$ Thermal resistance and water vapor transmission were measured for each fabric and batting and in all combinations. Thermal resistance at zero and 37 cm/sec air velocity was determined by the Thermo Labo II technique for simultaneously measuring conduction and radiation heat transfer. Water vapor transmission over 24 hours was measured by a modified weight-gain method in a compact humid chamber at conditions simulating the clothing climate under heavy exercise ($40{\pm}1^{\circ}C$, $90{\pm}2\%$ R.H., and 0.5 m/sec air velocity). Fabric porosity was calculated from fiber density and fabric weight, thickness, and area. Thermal resistance results for the fabrics showed the effectiveness of coatings in inhibiting heat transfer. Measurements taken in wind were: $31.1\~37.6\%$ for $Hipora^{\circledR}$ variants; $31.0\%$ for $Gore-Tex^{\circledR}$; and $18.4\%$ for $Aitaca^{\circledR}$ Measurements without wind were higher but in the same order. Water vapor transmission results were in reverse order: $Aitac^{\circledR}$, $8.8 kg/m^{2};\;Gore-Tex^{\circledR}$, 6.4 kg/$m^{2}$; and $Hipora^{\circledR},\;4.4\~6.0\;kg/m^{2}$. In general thermal resistance increased with porosity. For battings, the thermal resistance with wind results were: $Viwarmu^{\circledR}$, $65.0\%;\; Thinsulate^{\circledR}$, $62.0\%$; $Uniwarm^{\circledR}$, $61.0\%$; and $Airseala^{\circledR},\;53.1\%$. Thermal resistance was proportional to thickness. Thermal resistance of fabric-batting combinations were $20\%$ higher than those of the battings only. Water vapor transmission for combinations was mainly affected by that for the VPWR fabric used.