• 한국산학기술학회논문지
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• 제10권5호
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• pp.955-961
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• 2009

현재 소형 휴대용 배터리의 용량 증가에 따라 배터리 부피가 커지는 문제를 가지고 있다. 이러한 문제를 해결하기 위해 직접 메탄올 연료전지가 대안으로 떠오르고 있다. 본 논문에서는 직접 메탄올 연료전지를 상온 상태에서 자연 대류 방식으로 공기를 공급하고, 메탄올의 농도와 유량의 변화에 대한 특성을 분석하였다. 분석 결과 저 농도의 메탄올에서는 수소 이온의 확산 속도 지연에 따른 분극현상이 발생하였고, 메탄올의 공급량이 높을수록 전지 Cell의 냉각 효과가 발생하여 출력이 감소한다.

• 설비공학논문집
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• 제17권1호
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• pp.56-61
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• 2005

Indoor air quality becomes of a concern recently in view of human health. This study investigates the air diffusion performance and the air change efficiency of a classroom, when outdoor air is introduced in addition to the heating/cooling operation of a ceiling-mounted heat pump. A CFD analysis has been performed to investigate the effect of the discharge angle of the air jets from the heat pump for both parallel and series types of outdoor air system. It is observed that the series type creates more uniform indoor environment compared to the parallel type in general. It can be concluded the discharge angle should not be larger than 40o for the parallel type, in order not to generate thermal stratification in the room.

• 환경위생공학
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• 제1권1호
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• pp.47-58
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• 1986

The underground living spaces have become one of the major environment of this decade in urban area. This study was carried out to examine contamination level for purpose of preservation of the pleasant underground environment. Three subway stations and three underground shopping centers in Seoul and two underground shopping centers in Busan were selected and surveyed by measuring gaseous pollutants $(SO_2,\; NO_2,\;CO,\;HC,\; HCHO,\;CO_2)$, dust, airborne microbes, and the other air condtions (temperature, humidity, air pressure, air flow, kata cooling power). These examined data were compared with four kinds of standard (building sanitation management, room air quality standards, occupational safety and health standards, ventilation equipment) as environmental hygiene.

• 한국태양에너지학회 논문집
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• 제25권3호
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• pp.69-75
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• 2005

The PV-Solarwall system has been introduced as a promising alternative to harness solar energy for both heating applications and electricity generation simultaneously. The system comprises a PV solar panel(for electricity generation). In addition, the solarwall incorporates a fan strategically located behind the PV panel to bring the warm and fresh air from the solarwall into the room. Because of its location and convective cooling principle, the fan also serves to reduce the operating temperature of the PV panel thereby increasing its efficiency. So this PV-Solarwall system holds much promise for saving heating and electricity costs compared with a PV system without solarwall. In particular, by controlling the tilt angle of the entire PV-Solarwall system between $0^{\circ}$(horizontal) and $90^{\circ}$(vertical), the performance of the system can be further evaluated. It is expected that the range of tilt angle PV-Solarwall between $40^{\circ}$ and $50^{\circ}$ will improve the output of the system.

• 설비공학논문집
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• 제19권10호
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• pp.703-709
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• 2007

Much energy is used in occupying stage of the Building Life Cycle. Electric charge is one of the various factors that influence on energy use of residents. This study focused on electric charge and searched that whether electric charge affects residents' behavior of operating air conditioner and their controlled indoor climate. We surveyed three groups for field study ; A group is residents who live in a studio apartment, B group is residents who live in a university dormitory and C group is residents who live in a apartment with their family. The A and C groups are charged for electric as energy consumption they used. And the B group is students who live in a university dormitory and they are not charged for their energy consumption. We measured the time to use the air conditioner for cooling, on/off temperature of air conditioner, and room air temperature for these three groups. The result shows that consideration for electric charge affects to the residents' behavior of operating air conditioner and their acceptable thermal range.

• KIEE International Transactions on Power Engineering
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• 제3A권4호
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• pp.222-230
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• 2003

This paper presents reference designs for vapor-cooled HTS/Copper leads rated at 25 kA and 40 kA and that satisfy a protection criterion. Each HTS section is cooled by the effluent helium vapor boiling from a 4.2-K bath. Each HTS section is based on a design concept in which a short portion of its warm end (77.3 K) operates in the current-sharing mode; such operation results in a considerable saving for HTS materials required in the HTS section. Two designs of "fully superconducting" vapor-cooled HTS sections, one rated at 25 kA and the other at 40 kA are also presented as comparison bases for the new HTS sections. Each warm end of HTS sections is coupled to an optimal vapor-cooled copper lead rated at the same current as that for the HTS section. The extra coolant required at 77.3 K at the coupling station, an optimal length of the copper section will be shorter than that optimized for helium-vapor cooling between 4.2 K and room temperature.mperature.

• 한국주조공학회지
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• 제40권1호
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• pp.1-6
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• 2020

Many studies involving a thermal stress analysis using computational methods have been conducted, though there have been relatively few experimental attempts to investigate thermal stress phenomena. Casting products undergo thermal stress variations during the casting process as the temperature drops from the melting temperature to room temperature, with gradient cooling also occurring from the surface to the core. It is difficult to examine thermal stress states continuously during the casting process. Therefore, only the final states of thermal stress and deformations can be detemined. In this study, specimens sensitive to thermal stress, were made by a casting process. After which the residual stress levels in the specimens were measured by a hole drilling method with Electron Speckle-Interferometry technique. Subsequently, we examined the thermal stresses in terms of deformation during the casting process by means of a numerical analysis. Finally, we compared the experimental and numerical analysis results. It was found that the numerical thermal stress analysis is an effective means of understanding the stress generation mechanism in casting products during the casting process.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2009년도 춘계학술대회 논문집
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• pp.633-638
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• 2009

This paper presents an optimal design of a magnetorheological(MR) fan clutch based on finite element analysis and also presents torque control of engine cooling fan using a sliding mode control. The MR fan clutch is constrained in a specific volume and the optimization problem identifies the geometric dimension of the fan clutch that minimizes an objective function. The objective function for the optimization problem is determined based on the solution of the magnetic circuit of the initially designed clutch. Under consideration of spatial limitation, design parameters are optimally determined using finite element analysis. After describing the configuration of the MR fan clutch, the viscous torque and controllable torque are obtained on the basis of the Bingham model of MR fluid. Then, a sliding mode controller is designed to control the torque of the fan clutch according to engine room temperature and control performance is evaluated through computer simulation.

• 대한기계학회논문집A
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• 제21권10호
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• pp.1571-1579
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• 1997

The development of a new material which should be continuously use under severe environment of very high temperature has been urgently requested. For the development of such super-heat resistant materials, the main problem is not only to make the superior thermal barrier properties but also to actively release thermal stress. So, a new concept of functionally graded material(FGM) has been proposed to overcome this problem. A composition and microstructure of FGM are varied continuously from place to place in ways designed to provide it with the maximum function of mitigating the induced thermal stress. So, FGM can be applied in the aerospace, the electronic and the medical field, etc.. In this study, thermal stress analysis of sintering PSZ/NiCrAlY graded material was conducted theoretically using a finite-element program. The temperature condition was sintering temperature assuming a cooling-down process up to room temperature. Fracture damage mechanism was anlayzed by the parameters of residual stress. It could be known that FGM provided with the function of mitigating the induced thermal stress.

• 한국정밀공학회지
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• 제21권10호
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• pp.162-169
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• 2004

High temperature uniaxial compression tests in the alpha single phase region were carried out on the Ti -43mo1%Al intermetallic compound, in order to obtain oriented lamellar microstructure. The compression deformation temperatures and strain rates are from 1573k to 1623k and 1.0x10$^{-4}$ s to 5.0x10$^{-3}$ s, respectively. Fully lamellar microstructure was observed after the uniaxial compression deformation in a single phase region followed by cooling to room temperature. Lamellar colony diameter depended on strain rates and test temperatures. The diameter varied between 8601m and 300fm. Stress-strain curve showed a work softening and the size of lamellar colony diameter varied depending on peak stresses. This shows the occurrence of dynamic recrystallization. Texture measurements after the uniaxial compression deformation, showed the development of fiber during dynamic recrystallization. It is seen that the area for the maximum pole density existed in 35 degrees away from the compression plane. The texture sharpens with a decrease in strain rate