• 한국진공학회지
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• 제7권4호
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• pp.285-292
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• 1998

KSTAR 토카막용 진공용기는 토러스형으로써 내부에 사람이 들어가 작업할 수 있 는 큰 종단면을 갖고 있다. 이 용기는 불순물이 적은 깨끗한 플라즈마 발생을 위해 기저압 력이 초고진공이어야 하며 각종 플라즈마 대향부품을 포함해서 용기전체를 $350^{\circ}C$까지 베이 킹하는 것으로 계획되어 있다. 진공용기의 형태가 삼차원적으로 복잡하고 토카막 가동중 용 기에 걸리는 다양한 임을 해소하기 위해 지지구조물이 설치되어 있으며 균일한 온도분포를 만들기 어려워서 베이킹시 큰 열응력이 발생할 것으로 예상된다. 이 논문에서는 진공용기의 불균일한 온도분포를 만들기 어려워서 베이킹시 큰 열응력이 발생할 것으로 예상된다. 이 논문에서는 진공용기의 불균일한 온도분포와 지지구조의 구속조건에 따라 열응력이 어떻게 변하는가를 살펴보고 가능한 해결책을 제시하려고 한다.

• Applied Science and Convergence Technology
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• 제23권2호
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• pp.90-96
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• 2014

Flexible $ZrO_2$ films as dielectric materials for high-energy-density capacitors were deposited on polyethylene terephthalate (PET) substrates by RF magnetron sputtering. The growth behavior, microstructure and electrical properties of the flexible $ZrO_2$ films were dependent on the sputtering pressure and gas ratio. Although $ZrO_2$ films were deposited at room temperature, all films showed a tetragonal crystalline structure regardless of the sputtering variables. The surface of the film became a surface with large white particles upon an increase in the $O_2/Ar$ gas ratio. The RMS roughness and crystallite size of the $ZrO_2$ films increased with an increase in the sputtering pressure. The electrical properties of the $ZrO_2$ films were affected by the microstructure and roughness. The $ZrO_2$ films exhibited a dielectric constant of 21~38 at 1 kHz and a leakage current density of $10^{-6}{\sim}10^{-5}A/cm^2$ at 300 kV/cm.

• 한국진공학회지
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• 제17권3호
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• pp.204-210
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• 2008

산소분압비에 따른 ZnO 박막의 성장특성을 알아보기 위해 RF 스퍼터링 시스템을 이용하여 $0%{\sim}30%$의 산소분압비로 박막을 제작하였다. 위상변조방식의 분광타원계를 이용하여 $1.5{\sim}3.8eV$ 범위에 걸쳐 타원상수를 측정하였고, TL 분산관계식을 이용하여 최적맞춤한 결과 박막과 표면기칠기층의 두께, void 비율을 알 수 있었고, ZnO 알갱이의 크기는 산소분압비의 증가에 따라 그 크기가 작아짐을 알 수 있었다. 산소분압비에 따른 ZnO 박막의 밴드 갭은 산소유입량의 증가에 따라 증가하여 ZnO 박막의 광흡수 특성이 산소분압비에 크게 의존함을 알았고, 산소분압비의 증가는 결정의 불완전성을 증가시키는 것으로 나타났다.

• 한국대기환경학회지
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• 제17권1호
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• pp.75-84
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• 2001

Hot gas filtration method via using ceramic filters is an evolving technology applicable to numerous industrial and air pollution control processes. Alumino silicate, organic and inorganic binders were the major raw materials in manufacturing ceramic filters. In this work, disc type ceramic filters(50$\phi$$\times$10t) were manufactured by vacuum forming processes using ceramic raw materials. The porosity and bulk density of disc type ceramic filers ranged from 86 to 89% and from 0.27 to 0.36 g/㎤, respectively. In this work disc type ceramic medium were tested utilizing coupon experimental apparatus. Disc type filters showed high collection efficiencies over 99.96% with Darchs law coefficients of 4.1$\times$10(sup)10~9.63$\times$10(sup)10/$m^2$ depending on mean pore sizes. In addition, filtration and detachment of ceramic filters turned out to be performed effectively using 10 cm/sec face velocity, 5 minutes filtration cycle, 100msec pulse jet valve opening time and 3 bar pulsing pressure.

• 한국군사과학기술학회지
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• 제7권4호
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• pp.133-137
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• 2004

A simplified test rig to simulate high-altitude environments was designed by analyzing the AEDC (Arnolds Engineering Development Center) report regarding simulated altitude testing. The test rig consists of a vacuum chamber, a supersonic nozzle connected to a cold-gas supplier and a diffuser. The preliminary tests were conducted to validate the AEDC design concepts. The test results showed that sub-atmospheric pressure(1.0psia) environments were realized inside the vacuum chamber and the design concepts were confirmed.

• 한국표면공학회지
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• 제40권1호
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• pp.39-43
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• 2007

The pure CrN powders oxidized to $Cr_2O_3$ noticeably above $850^{\circ}C$ in air. When these powders were sintered into bulk samples at $1500^{\circ}C$ under 40 atm of $N_2$ pressure, the CrN phase partly changed into the $Cr_2N$ phase, owing to the partial loss of nitrogen from CrN. When the bulk sample was heated at $1000-1200^{\circ}C$ for 100 hr under vacuum, the CrN phase also progressively changed into $Cr_2N$. At the same time, a relatively thin $Cr_2O_3$ layer formed on the bulk sample due to the reaction of chromium with residual oxygen in vacuum.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.579-579
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• 2013

We study on Argon metastable and 4p state neutral atom density in magnetized ICP Helicon plasmas by Laser Induced Fluorescence and plasma emission. The results show that metastable density is too low at the center of chamber due to significant neutral depletion. Otherwise, 4p state is high at the center of chamber because electron density is very high. Power and pressure dependence of metastable and 4p state neutral atom have been spatially measured in the radial direction of cylindrical chamber.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.297.2-297.2
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• 2016

Photoacoustic generation of ultrasound is an effective approach for development of high-frequency and high-amplitude ultrasound transmitters. This requires an efficient energy converter from optical input to acoustic output. For such photoacoustic conversion, various light-absorbing materials have been used such as metallic coating, dye-doped polymer composite, and nanostructure composite. These transmitters absorb laser pulses with 5-10 ns widths for generation of tens-of-MHz frequency ultrasound. The short optical pulse leads to rapid heating of the irradiated region and therefore fast thermal expansion before significant heat diffusion occurs to the surrounding. In this purpose, nanocomposite thin films containing gold nanoparticles, carbon nanotubes (CNTs), or carbon nanofibers have been recently proposed for high optical absorption, efficient thermoacosutic transfer, and mechanical robustness. These properties are necessary to produce a high-amplitude ultrasonic output under a low-energy optical input. Here, we investigate carbon nanotube (CNT)-polydimethylsiloxane (PDMS) composite transmitters and their nanostructure-originated characteristics enabling extraordinary energy conversion. We explain a thermoelastic energy conversion mechanism within the nanocomposite and examine nanostructures by using a scanning electron microscopy. Then, we measure laser-induced damage threshold of the transmitters against pulsed laser ablation. Particularly, laser-induced damage threshold has been largely overlooked so far in the development of photoacoustic transmitters. Higher damage threshold means that transmitters can withstand optical irradiation with higher laser energy and produce higher pressure output proportional to such optical input. We discuss an optimal design of CNT-PDMS composite transmitter for high-amplitude pressure generation (e.g. focused ultrasound transmitter) useful for therapeutic applications. It is fabricated using a focal structure (spherically concave substrate) that is coated with a CNT-PDMS composite layer. We also introduce some application examples of the high-amplitude focused transmitter based on the CNT-PDMS composite film.

• 한국기계연구소 소보
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• 통권20호
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• pp.5-11
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• 1990

Most water cannon machines use compressed gas to accelerate a piston which extrudes water through a cumulation nozzle. Very high jet stagnation-pressures can be achieved by using a specially-shaped nozzle which is initially filled with air or vacuum. The objective of this study was to establish the basic technology of water cannon using exponential type nozzle. An experimental water cannon including high pressure components such as exponential nozzle and 300atm air resrvior were designed and tested. Parameters that influence the performance of the system and jet characteristics were examined.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.105-110
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• 2010

Supersonic ejectors are simple mechanical components, which generally perform mixing and recompression of two fluid streams. Ejectors have found many applications in engineering. In aerospace engineering, they are used for high altitude testing (HAT) of a propulsion system by reducing the pressure of a test chamber. It is composed of three major sections: a vacuum test chamber, a propulsive nozzle, and a supersonic exhaust diffuser (SED). This paper aims at the improvement in HAT facility by focusing attention on the vertical firing rocket test stand with shock generators. Shock generators are mounted inside the SED for improving the pressure recovery. The results clearly showed that the performance of the ejector-diffuser system was improved with the addition of shock generators. The improvement comes in the form of reduction of the starting pressure ratio and the vertical height of test stand. It is also shown that shock generators are useful in reducing the total pressure loss in the SED.