• International Journal of Air-Conditioning and Refrigeration
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• 제16권1호
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• pp.30-36
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• 2008

Modern world takes advantages of gas-turbines for various purposes. Most of gas-turbines incorporate various heat exchangers in order to achieve specific functions and enhance thermal efficiency as well. This paper reviews heat exchangers that had been used, currently being used, and under development for the future application in various kinds of gas turbines. The heat exchanger matrix configurations and manufacturing methods depend on where they are applied. This review work shows that the recent advancement in heat exchanger technologies makes it possible to develop intercoolers and recuperators for large gas turbines as well as micro gas turbines.

• Journal of Welding and Joining
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• 제34권3호
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• pp.52-60
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• 2016

Recently nickel based superalloys are extensively being regarded as the materials for the steam turbine parts for hyper super critical (HSC) power plants working at the temperature over $700^{\circ}C$, since the materials have excellent strength and corrosion resistance in high temperature. In this paper, alloy 617 of solution strengthened material and alloy 263 of ${\gamma}^{\prime}$-precipitation strengthened material were prepared as the testing materials for HSC plants each other. Post weld heat treatment (PWHT) was conducted with the gas tungsten arc (GTA) welded specimens. The microstructure of the base metals and weld metals were investigated with Electron Probe Micro-Analysis (EPMA) and Scanning Transmission Electron Microscope (STEM). The experimental results revealed that Ti-Mo carbides were formed in both of the base metals and segregation of Co and Mo in both of the weld metals before PWHT and PWHT leaded to precipitation of various carbides such as Mo carbides in the specimens. Furthermore, fine ${\gamma}^{\prime}$ particles, that were not precipitated in the specimens before PWHT, were observed in base metal as well as in the weld metal of alloy 263 after PWHT.

• KIEE International Transactions on Power Engineering
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• 제3A권1호
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• pp.27-34
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• 2003

In this paper, the power conditioner composed of the stand-alone single-phase squirrel cage rotor type self-excited induction generator (SEIG) driven by prime movers such as a wind turbine and a micro gas turbine (MGT) is presented by using the steady-state circuit analysis based on the two nodal admittance approaches using the per-unit frequency in addition to a new state variable defined by the per-unit slip frequency along with its performance evaluations for the stand-alone energy utilizations. The stande-alone single-phase SEIG operating performances in unregulated voltage control loop are then evaluated on line under the conditions of the speed change transients of the prime mover and the stand-alone electrical passive load power variations with the simple theoretical analysis and the efficient computation processing procedures described in the part I of this paper. In addition, a feasuible PI controlled feedback closed-loop voltage regulation scheme of the stande-alone single-phase SEIG is designed on the basis of the static VAR compensate. (SVC) and discussed in experiment for the promising stand-alone power conditioner. The experimental operating performance results are illustrated and give good agreements with the simulation ones. The simulation and experimental results of the stand-alone single-phase SEIG with the simple SVC controller for its stabilized voltage regulation prove the practical effectiveness of the additional SVC control loop scheme including the PI controller with fast response characteristics and steady-sate performance improvements.

• 대한기계학회논문집A
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• 제34권4호
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• pp.475-480
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• 2010

가스터빈 블레이드는 터빈 가동 시 발생하는 고온화염으로부터 블레이드를 보호하고, 구조물의 표면 온도를 안전한 수준으로 낮추기 위하여 블레이드 표면에 열차폐 코팅(TBC; Thermal barrier coating)을 하여 사용하고 있다. 본 논문에서는 가스터빈 1단 블레이드에 적용되는 코팅 방식을 이용하여 코인형 시험편을 제작하였고 열화 온도 및 유지 시간의 변화에 따른 코팅 계면 산화물의 성장 거동을 분석하였다. 코팅 단면에 대하여 코팅 계면 산화물의 두께와 마이크로 비커스 경도를 측정하여 열화 특성을 평가 하였다. 또한 성분분석을 통하여 미세조직의 변화를 관찰함으로써 열차폐 코팅의 열적 열화특성을 평가하였다.

• 한국추진공학회지
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• 제11권3호
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• pp.20-28
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• 2007

압축기의 써지 현상을 관찰하는 가장 쉬운 방법의 하나로는 부분품의 성능특성도상에 정적 그리고 동적 운용 특성을 나타내는 것이 될 수 있다. 이 경우 엔진의 작동범위가 써지 범위에 의하여 제한될 것이고 따라서 엔진은 엔진의 정적 또는 과도 성능의 전 과정에 걸쳐 일정한 써지 한계를 갖도록 요구되고 있다. 로터의 극관성 모멘트, 닥트 내 공기/가스의 용적 그리고 열전달 효과 등은 엔진의 작동이 정적 특성으로부터 일탈하게 되는 주요 요소들이다. 시스템 내에서 열교환기가 존재하는 경우처럼 큰 용적의 경우 그것은 동적 작동 특성에 상당한 영향을 주게 될 것인데 본 논문에서는 보조동력기관으로 사용되는 마이크로터빈의 예를 들어 엔진의 과도성능 특성에 압축기의 출구에서 추출되는 냉각공기가 미치는 영향을 조사코자 하였다. 질량 및 일 그리고 회전수 일치 법칙에 근거하여 터빈을 흐르는 가스 유량, 압력비, 회전 속도, 동력 그리고 모멘트가 계산되었다. 본 연구의 결과는 제어시스템 설계를 위한 기초 자료로 활용될 수 있을 것이다. 이러한 과도 성능을 계산하기 위한 프로그램을 개발을 위해서 상업용 MathCAD 소프트웨어를 사용하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.204-209
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• 2004

SiC materials have been extensively studied for high temperature components in advanced energy system and advanced gas turbine. However, the brittle characteristics of SiC such as low fracture toughness and low strain-to fracture still impose a severe limitation on practical applications of SiC materials. For these reasons, $SiC_f/SiC$ composites can be considered as a promising for various structural materials, because of their good fracture toughness compared with monolithic SiC ceramics. But, high temperature and pressure lead to the degradation of the reinforcing fiber during the hot pressing. Therefore, reduction of sintering temperature and pressure is key requirements for the fabrication of $SiC_f/SiC$ composites by hot pressing method. In the present work, Monolithic LPS-SiC was fabricated by hot pressing method in Ar atmosphere at 1760 $^{\circ}C$, 1780 $^{\circ}C$, 1800 $^{\circ}C$ and 1820 $^{\circ}C$ under 20 MPa using $Al_2O_3-Y_2O_3$ system as sintering additives in order to low sintering temperature. The starting powder was high purity ${\beta}-SiC$ nano-powder with an average particle size of 30 nm. Monolithic LPS-SiC was evaluated in terms of sintering density, micro-structure, flexural strength, elastic modulus and so on. Sintered density, flexural strength and elastic modulus of fabricated LPS-SiC increased with increasing the sintering temperature. In the micro-structure of this specimen, it was found that grain of sintered body was grown from 30 nm to 200 nm.

• 대한조선학회지
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• 제9권2호
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• pp.43-48
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• 1972

Inertia friction welding, a relatively recent innovation in the art of joining materials, is a forge-welding process that releases kinetic energy stored in the flywheel as frictional heat when two parts are rubbed together under the right conditions. In a comparatively short time, the process has become a reliable method for joining ferrous, and dissimilar metals. The process is based on thrusting one part, attached to a flywheel and rotating at a relatively high speed, against a stationary part. The contacting surfaces, heated to plastic temperatures, are forged together to produce a reliable, high-strength weld. Welds are made with little or no workpiece preparation and without filler metal or fluxes. However, In order to obtain a good weld, the determination of the optimum weld parameters is an important problem. Especially, because the amount of the flywheel mass will be determined according to the initial rotating velocity values at the constant thrust load, the initial rotating velocity is an important factor to affect a weld character of the inertia-welded IN713C-SAE8630, which is used for the wheel-shafts of turbine rotors or turbochargers, exhausting valves, etc. In this paper, the effects of initial rotational velocity on a weld character of inertia-welded IN713C-SAE8630 was studied through considerations of weld parameters determination, micro-structural observations and tensile tests. The results are as the following: 1) As initial rotating velocity was reduced to 267 FPM, cracks and carbide stringers were completely eliminated in the micro-structure of welded zone. 2) As initial rotating velocity was reduced and flywheel mass was increased correspondingly, the maximum welding temperatures were decreased and the plastic working in the weld zone was increased. 3) As initial rotating velocity was progressively decreased and carbides were decreased, the tensile strengths were increased. 4) And also the fracture location moved out of the weld zone and the tensile tests produced, the failures only in the cast superalloy IN713C which do not extend into the weld area. 5) The proper initial rotating velocity could be determined as about 250 thru 350 FPM for the better weld character.

• 전기학회논문지
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• 제65권2호
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• pp.239-246
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• 2016

In recent years, the power demand has been increasing steadily and the occurrence of maximum power demand has been moving from the summer season to the winter season in Korea. And since the control of electric power supply and demand is more important under those situations, a micro-grid system began to emerge as a keyword for the sTable operation of electric power system. A micro-gird power system is composed of various kinds of distributed generators(DG) such as small diesel generator, wind turbine, photo-voltaic generator and energy storage system(ESS). This paper introduces a method to determine the optimal capacities of the distributed generators which are installed in a stand-alone type of microgrid power system based on the fundamental proportion of diesel generator. At first, the fundamental proportion of diesel generator will be determined by changing from 0 to 50 percent. And then we will optimize the capacities of renewable energy resources and ESS according to load patterns. Lastly, after recalculating the capacity of ESS with consideration for SOC constraints, the optimal capacities of distributed generators will be decided.

• 한국유체기계학회 논문집
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• 제11권5호
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• pp.22-29
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• 2008

This study is performed to understand the effect of the variation in the passage area of a two-dimensional impeller on its performance characteristics. We observe the results with changing the area ratio of inlet to outlet about $1{\sim}2.8$. A comparison between the experimental and numerical results was performed for the same configuration in order to verify the reliability of the CFD code. Overall characteristics in the passages of impeller were analyzed in detail including streamline, Mach number, pressure and polytropic efficiency distribution. When the passage area ratio exceeds 2, the pressure ratio is high. An area ratio of 2.3 showed the highest efficiency. The results will be used as useful reference data to establish the design concept of two-dimensional impeller and to improve its performance.

• Applied Microscopy
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• 제47권3호
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• pp.208-213
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• 2017

The microstructural changes in Co nanoparticles and an Au-10at.%Pd thin film have been investigated using an in situ heating holder with a micro-electro-mechanical system (MEMS). In Co nanoparticles, two phases (face-centered cubic and hexagonal close-packed crystal structures) were found to coexist at room temperature and microstructures at temperatures, higher than $1,000^{\circ}C$, were observed with a quick response time and significant stability. The actual temperature of each specimen was directly estimated from the changes in the lattice spacing (Bragg-peak separation). For the Au-10at.%Pd thin film, at a set temperature of $680^{\circ}C$, the actual temperature of the sample was estimated to be $1,020^{\circ}C{\pm}123^{\circ}C$. Note that the specimen temperature should be carefully evaluated because of the undesired effects, i.e., the temperature non-uniformity due to the sample design of the MEMS chip, and distortion due to thermal expansion.