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김태진(Taejin Kim),서성현(Seonghyeon Seo) 한국추진공학회 2015 한국추진공학회 학술대회논문집 Vol.2015 No.5
고체 로켓 모터에서 발생하는 연소 불안정 현상을 억제하는 방법에는 많은 방법들이 존재한다. 이중 추진제 조성시 금속 입자를 첨가함으로써 연소 메커니즘을 변화시켜 고주파 연소 불안정을 효과적으로 억제한다. 주로 첨가되는 금속 입자는 알루미늄(Al) 입자가 사용된다. 알루미늄 입자는 연소과정을 통해 알루미나(Al₂O₃)가 된다. 알루미나 입자들은 연소가스보다 밀도가 높기 때문에 연소가스가 진동하는 동안 가스의 움직임에 즉각적으로 반응하지 못하고 음향 감쇠가 발생한다. 본 논문에서는 비연소 실험을 통해 입자에 의한 감쇠 효과를 확인하였다. There are many ways of suppressing combustion instability generated in the solid rocket motor. Changing the combustion mechanisms by adding the metal particles in the propellant effectively suppresses the high-frequency combustion instability. The metal particles are mostly added of aluminum(Al) particles in propellant. Aluminum particles are changed to alumina(Al₂O₃) through the combustion process. Acoustic attenuation occurs by the alumina particles. Because the density of alumina particles is more than denser the combustion gas. Particles does not react immediately to the movement of gas during the oscillation. In this paper, carry out the acoustic attenuation by the particles over a cold-flow experiment.
입자 크기에 따른 물/에틸렌글리콜 기반 알루미나 나노유체의 열전도도
최태종(Tae Jong Choi),김수빈(Soo Bin Kim),장석필(Seok Pil Jang),정대수(Dae Soo Jung),임형미(Hyung Mi Lim) 대한기계학회 2018 大韓機械學會論文集B Vol.42 No.3
본 논문에서는 입자 크기에 따른 물/에틸렌글리콜 기반 알루미나 나노유체의 열전도도 특성을 실험적으로 연구하였다. 이를 위해 물/에틸렌글리콜 기반 알루미나 나노유체를 Modified two-step method를 이용하여 제작하였다. 나노유체 속에 분산된 입자의 크기는 Particle Size Analyzer(PSA)로 분석하였으며, 나노유체의 열전도도는 비정상열선법(Transient Hot Wire Method)을 이용하여 측정하였다. 나노입자의 크기는 RCF×h가 증가할수록 감소하는 것을 확인하였으며, 입자의 크기가 감소할수록 온도에 따라 열전도도가 상승하는 온도 의존성이 나타나는 것을 확인하였다. 또한, 단위부피당 열전도도 측정 결과, 입자의 크기가 작을수록 열전도도 향상 폭이 더 높은 것을 실험적으로 확인하였다. This paper experimentally reports the effect of particle size on the thermal conductivity of water/ethylene glycol-based alumina nanofluids. For this study, the water/ethylene glycol-based alumina nanofluids was manufactured using the modified two-step method. The particle size dispersed in nanofluids was measured by the particle size analyzer, and thermal conductivity of nanofluids was measured by the transient hot wire method. The particle size decreased with total RCF and the temperature dependence of nanofluids was observed as the particle size decreased. Moreover, it was experimentally confirmed that the nanofluids exhibit higher thermal conductivity as the particle size decreased.
다양한 조건에 따른 주철 소재의 마찰/마모 특성에 관한 연구
주지훈(Ji-Hoon Joo),김창래(Chang-Lae Kim),나르게스 네마티(Narguess Nemati),오정택(Jeong-Taek Oh),김대은(Dae-Eun Kim) 대한기계학회 2015 大韓機械學會論文集A Vol.39 No.8
주철은 산업현장에서 중장비나 철도차량 등과 같은 다양한 기계장치의 주재료로 널리 사용된다. 이러한 기계장치의 운전 성능은 접촉 특성에 따라 크게 좌우되며 이를 개선시키기 위한 연구들이 진행되고 있다. 본 연구에서는 모래와 알루미나 입자가 주철의 마찰/마모 특성에 미치는 영향에 대해 다양한 조건에서의 미끄럼 실험을 통해 규명하였다. 입자의 크기 및 시편 온도 등을 변수로 하여 스틸 볼이 pin 으로 장착된 pin-on-reciprocator 방식의 트라이보테스터를 사용하여 실험을 진행하였다. 주사전자현미경(Scanning Electron Microscope), confocal microscope 와 3d profiler 를 이용해서 주철 시편과 스틸 볼의 마모표면을 관찰하고 마모량을 정량적으로 측정하여 마모 특성을 파악하였다. 실험 결과 주철의 마찰/마모 특성은 입자 주입에 의해 크게 달라짐을 알 수 있었다. 또한, 주철 시편에 가해준 온도에 따라 마찰/마모 특성이 크게 달라지는 것을 확인하였다. 이 연구의 결과는 산업에서 주철 재료의 트라이볼로지 특성을 이해하는데 도움이 될 것이다. Cast iron is widely used in fields such as the transport and heavy industries. For parts where contact damage is expected to occur, it is necessary to understand the friction and wear characteristics of cast iron. In this study, we use cast iron plates as the specimens to investigate their friction and wear characteristics. We perform various experiments using a reciprocating type tribotester. We assess the frictional characteristics by analyzing the friction coefficient values that were obtained during the sliding tests. We observe the wear surfaces of cast iron and steel balls using a scanning electron microscope, confocal microscope, and 3d profiler. We investigate the friction and wear characteristics of cast iron by injecting sand and alumina particles having various sizes. Furthermore, we estimate the effect of temperature on the friction and wear characteristics. The results obtained are expected to aid in the understanding of the tribological characteristics of cast iron in industry.
형상 계수를 이용한 알루미나 입자구름의 열복사 예측 기법 연구
고주용(Ju-Yong Ko),김인선(In sun Kim) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
In order to predict the thermal radiation induced from alumina particle cloud in the plume of solid propellant motor, view factor method is applied to space shuttle SRB and the result is compared with that of monte carlo method. For this purpose, radiative characteristics, such as particle cloud temperature distribution, effective emissivity or emissive power of particle cloud are studied. In the case of effective emissivity, inverse wavelength method is applied and plume reduction characteristic length is used for emissive power distribution. As a result, thermal radiation using view factor method gives more conservative results than that using monte carlo method. So it can be used for preliminary design of thermal protection system.
자동차 섀시 시스템에 유입되는 먼지입자에 의한 고무-씨일 부품의 마멸특성
정순오(Soon-Oh Chung),원태영(Tae-Yeong Won),김기훈(Gi-Hoon Kim),김대성(Dae-Sung Kim),이영제(Young-Ze Lee) 한국트라이볼로지학회 2009 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.25 No.4
Environmental factors affect parts of the automobile. When dust particles are embedded, specially, friction and wear of the rubber-seal in automobile chassis system are increased. Increase in friction and wear leads to weakness of component and reduction of mechanical life. In this study, the wear characteristics of rubber-seal for inflow of dust particles are investigated. Silica(SiO₂) and alumina(Al₂O₃) particles are used as a dust particle because these particles are main elements of dust particles. The sliding wear tester are used for investigate the wear characteristics of rubber-seal. If the single dust particle(SiO₂) is embedded in the rubber-seal component, the influence of dust particle size is more than that of inflow rate on the wear characteristics of rubber-seal. If the mixed dust particles are embedded in the rubber-seal component, the wear rate is increased as the rate of alumina that has a bigger hardness is increased. If the mixed dust particles that have different hardness are embedded in the rubber-seal component, the influence of particle size is more than that of particle hardness.
α-Al₂O₃가 코팅된 폴리프로필렌 분리막에서 무기물 입자 크기에 따른 물성 변화 및 전기화학적 특성
심형석(Hyeong-seok Shim),신혜주(Hyu-ju Shin),오상준(Sang-jun Oh),최신호(Sinho Choi),김태희(Tae-Hee Kim) 한국전지학회 2021 한국전지학회지 Vol.1 No.2
본 연구에서는 리튬 이온 이차전지의 핵심 소재인 분리막에 다양한 입자 사이즈(150 nm, 200 nm, 300 nm)의 Commercial Al₂O₃(CM- Al₂O₃)를 사용해서 세라믹 코팅 분리막을 제작하였다. 제조된 코팅분리막의 물성을 평가하고, 이를 코인 하프셀에 적용하여 전기화학적 특성 변화를 관찰하였다. In this study, ceramic-coated separators were fabricated using α-Al₂O₃ of various particle sizes (150 nm, 200 nm, 300 nm). The physical properties of ceramic-coated separators were analyzed, and a coin half-cell including the ceramic-coated separator was assembled to observe electrochemical properties.
카본 나노튜브 및 알루미나 첨가제가 윤활 및 마모특성에 미치는 영향에 대한 연구
윤창석(Chang-Seok Yun),오대산(Dae-San Oh),김현준(Hyun-Joon Kim) 한국트라이볼로지학회 2017 한국윤활학회지(윤활학회지) Vol.33 No.5
In this work, carbon nanotube and nano-size alumina particle are exploited as additive for lubrication experiment. We used pin-on-disk type tribometer to investigate the tribological characteristics of lubricants with respect to additives and rotational speed. We conducted more than 15 trials of tribotests for two hours for each specimen to obtain stable and accurate frictional force and to create measurable wear track on the substrate. We conducted tests at the boundary/mixed lubrication regime to evaluate the influence of additives on the tribological characteristics. We found that the friction coefficient decreased as the rotational speed increased and as additives were added. In particular, the reduction of friction by adding additives was more significant at low rotational speed than at high rotational speed. We speculate that the additives helped to separate and protect the two contacting surfaces at low speed, while the influence of additives was not significant at high speed since sufficiently thick lubricant film was formed. The wear of the substrate was also reduced by adding additives to the lubricant. However, in contrast to friction, the amount of wear at high rotational speed was less when alumina particles were added to the lubricant than the amount of wear at low speed. We speculate that the increased wear at low rotational speed is as a result of the intermittent abrasive wear caused by alumina particles with uneven shape, while the reduced wear at high speed is as a result of sufficient film thickness which prevented the abrasive wear.