• Title/Summary/Keyword: 미소중력

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The Solidification Phenomena of Materials under Microgravity-Review (미소중력하에서의 재료의 응고현상-연구동향과 분석)

  • Kim, Sin-U
    • Korean Journal of Materials Research
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    • v.6 no.7
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    • pp.752-758
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    • 1996
  • 지상에서 금속제품의 제조시 필수적으로 일어나는 응고과정은 중력에 기인한 액상분리, 부력, 침전 및 대류등으로 균일하지 못한 응고조직을 보여준다. 그래서 최근의 우주비행선의 비행으로 가능하게 된 긴 시간의 미소중력 환경을 이용하여 균일하고 향상된 재료를 만들기 위하여 수행된 많은 실험들 중에서 공정, 수지상, 편정합금들의 응고와 관련된 미소중력하의 결과들을 분석하였다. 또한 지상에서 중력에 기인한 대류를 극소화시켜 균일한 응고조직을 보여준 새로운 응고방법을 조사하고 향후 미소중력하의 실험의 방향을 제시하였다.

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Survey on a Research for Fire Safety in Space with the Understanding of Combustion Characteristics in Microgravity based on NASA's Space Research Program (NASA의 우주 연구 프로그램에 따른 미소 중력하에서의 연소 특성 및 화재 안전 연구 개괄)

  • Sohn, Chae-Hoon;Son, Young-Jin
    • Journal of the Korean Society of Propulsion Engineers
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    • v.11 no.3
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    • pp.65-72
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    • 2007
  • Fire is one of important checkpoints in crewed exploration systems, where men inhabit in space. In space, astronaut can't escape from fire out of a spacecraft and not expect any help of fire fighters, either. Accordingly, the best way to stand against fire is to prevent it. But, when fire occurs in space, flame behaviors are quite different from those observed on earth because of micro- or zero-gravity in space. The present paper introduces major research results on flame behaviors under microgravity and fire prevention, detection, and suppression in crewed exploration spacecrafts and international space station based on NASA's FPDS research program.

Flow Patterns of Gas-Liquid Two-phase Flow under Microgravity (미소중력하의 기액이상류의 유동양식)

  • 최부홍
    • Journal of Advanced Marine Engineering and Technology
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    • v.27 no.3
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    • pp.460-465
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    • 2003
  • Microgravity experiments were conducted to determine the effect of liquid and gas superficial velocities on flow behaviors. Flow behaviors observed under microgravity conditions can be classified into five flow patterns: bubble. Taylor bubble, slug, semi-annular and annular flows. Transition boundary between four flow patterns could be determined by drift-flux model. It was also found that the effect of gravity and pipe inclination on flow pattern transition was not significant in the inertia dominant region.

Microgravity Combustion Characteristics of Polystyrene Spheres with Various Ambient Gases (분위기 가스 변화에 의한 폴리스틸렌 구의 미소중력 연소특성)

  • Choe, Byeong-Cheol
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.11
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    • pp.1509-1517
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    • 2001
  • An experimental and numerical analysis were conducted to investigate the transient temperature distribution and flame propagation characteristics over an inline polystyrene spheres under microgravity. From the experimental, a self-ignition temperature of polystyrene bead was 872 K under gravity. Flame spread rates were 4.7-5.1 mm/s with ambient gas N$_2$and 2.3-2.5 mm/s with ambient gas CO$_2$, respectively. Flame radius diameters were 17 mm with ambient gas N$_2$and 9.6 mm with ambient gas CO$_2$, respectively. These results suggest that the flame propagation speed could be affected in the Diesel engine and the boiler combustor by EGR. In terms of the flame spread rate and the transient temperature profile, numerical results have the qualitative agreement with the experiment.

Numerical Analysis for Impurity Effects on Diffusive-convection Flow Fields by Physical Vapor Transport under Terrestrial and Microgravity Conditions: Applications to Mercurous Chloride (지상 및 미소중력 환경에서 물리적 승화법 공정에 미치는 불순물의 영향 분석: 염화제일수은에 대한 응용성)

  • Kim, Geug Tae;Kwon, Moo Hyun
    • Applied Chemistry for Engineering
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    • v.27 no.3
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    • pp.335-341
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    • 2016
  • In this study, impurity effects on diffusive-convection flow fields by physical vapor transport under terrestrial and microgravity conditions were numerically analyzed for the mixture of $Hg_2Cl_2-I_2$ system. The numerical analysis provides the essence of diffusive-convection flow as well as heat and mass transfer in the vapor phase during the physical vapor transport through velocity vector flow fields, streamlines, temperature, and concentration profiles. The total molar fluxes at the crystal regions were found to be much more sensitive to both the gravitational acceleration and the partial pressure of component $I_2$ as an impurity. Our results showed that the solutal effect tended to stabilize the diffusive-convection flow with increasing the partial pressure of component $I_2$. Under microgravity conditions below $10^{-3}g_0$, the flow fields showed a one-dimensional parabolic flow structure indicating a diffusion-dominant mode. In other words, at the gravitational levels less than $10^{-3}g_0$, the effects of convection would be negligible.

Numerical Simulation on Characteristics of Laminar Diffusion Flame Placed Near Wall in Microgravity Environment (미소중력 환경내의 벽면 근방 확산 화염 특성에 관한 수치 해석)

  • Choi Jae-Hyuk;Fujita Osamu
    • Journal of Advanced Marine Engineering and Technology
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    • v.30 no.1
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    • pp.140-149
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    • 2006
  • Characteristics of a laminar diffusion flame placed near wall in microgravity have been numerically analyzed in a two-dimension. The fuel for the flame is $C_2H_4$. The flame is initiated by imposing a high temperature ignition source. The flow field, temperature field, and flame shape in microgravity diffusion flame are detailed. Especially, effects of surrounding air velocity and fuel injection velocity on the microgravity diffusion flame have been discussed accounting for standoff distance. And, the effect of curvature rate has been also studied. The results showed that velocities in a diffusion flame were overshoot because of volumetric expansion and distribution of temperature showed regularity by free-buoyancy This means that the diffusion flame in microgravity is very stable, while the flame in normal gravity is not regular and unstable due to buoyancy. Standoff distance decreases with increase in surrounding air velocity and with decrease in fuel injection velocity. With increasing curvature rate, the position of reaction rate moves away the wall.

Changes of Antioxidant Enzymes in Stevia Plants under Clinorotation, Shaking, and Low Temperature Stresses (스테비아(Stevia rebaudiana Bertoni)에 있어서 유사미소중력, 진동 및 저온처리에 의한 항산화 활성 변화)

  • Choi, Yong-Sang;Jung, Mun-Yhung;Soh, Woong-Young;Han, Kyeong-Sik;Yeo, Up-Dong
    • Korean Journal of Plant Resources
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    • v.24 no.4
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    • pp.343-350
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    • 2011
  • A medicinal herb, Stevia rebaudiana Bertoni which is grown under physical stresses such as simulated microgravity, shaking, and low temperature for 4 days, showed fresh weight decrease of 3.6%, 21% and 8.7% compared with the respective control. On control plants, the radical scavenging value of DPPH represented 86% and 55%, respectively in the leaves and stems extracts. Relatively weak antioxidant activities of 22% and 27% were measured respectively in AA (ascorbic acid) and BHA (beta-hydroxyacetic acid) known as synthetic antioxidants. The radical scavenging effect of DPPH (2,2-diphenyl-1-picryl hydazal) in stevia plants under a simulated microgravity was observed to be consistently higher relative to the control, whereas those effects of shaking and low temperature treatments rapidly increased and then reduced after 6 hours in case of shaking process and 24 hours in case of low temperature treatment, which results had similar levels of scavenging effects to the control. The plants under simulated microgravity showed the highest level of activity with the value of 147% and the shaking and low temperature treatments showed the increases of SOD activity by 121% and 125%, respectively. From the above results, it is clarified that the simulated microgravity is more effective to the antioxidant activity than those of other abiotic stresses.

In-situ Observation of Soot Deposition Behavior in a Diffusion Flame along Solid Wall by using Microgravity Environment (미소중력환경을 이용한 벽면근방 확산화염내 매연부착거동의 원위치 관찰)

  • Choi Jac-Hyuk;Fujita Osamu
    • Journal of Advanced Marine Engineering and Technology
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    • v.29 no.8
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    • pp.907-914
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    • 2005
  • Experiments at the Japan Microgravity Center (JAMIC) have investigated the interaction between diffusion flames and solid surfaces Placed neat flames The fuel for the flames was $C_{2} H_{4}$ The surrounding oxygen concentration was 35$\%$ with surrounding air temperatures of $T_{a}$ : 300K. Especially, the effect of wall temperature on soot deposition from a diffusion flame Placed near the wall has been studied by utilizing microgravity environment, which can attain very stable flame along the wall. Cylindrical burner with fuel injection was adopted to obtain two dimensional soot distributions by laser extinction method. In the experiment two different wall temperatures. $T_{w}$=300, 800 K, were selected as test conditions The results showed that the soot distribution between flame and burner wall was strong1y affected by the wall temperature and soot deposition increases with decrease in wall temperature. The comparison among the values lot two different wall temperatures suggests that the change in thermophoretic effect is the most dominant factor to give the change in soot deposition characteristics.

Soot Deposition Process in a Diffusion Flame to the Wall under Microgravity (미소중력환경하에서의 확산화염내 매연입자의 벽면부착 관찰)

  • Choi, Jae-Hyuk;Fujita, Osamu;Yoon, Suck-Hun
    • Proceedings of the Korean Society of Marine Engineers Conference
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    • 2005.06a
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    • pp.87-92
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    • 2005
  • Experiments at the Japan Microgravity Center(JAMIC) have investigated the interaction between diffusion flames and solid surfaces placed near flames. The fuel for the flames was $C_2H_4$. The surrounding oxygen concentration was 35% with temperatures of $T_a$=300. Especially, the effect of wall temperature on soot deposition from a diffusion flame placed near the wall has been studied by utilizing microgravity environment, which can attain very stable flame along the wall. Cylindrical burner with fuel injection was adopted to obtain two dimensional soot distributions by laser extinction method. In the experiment two different wall temperatures, $T_w$=300,800K, were selected as test conditions. The results showed that the soot distribution between flame and burner wall was strongly affected by the wall temperature and soot deposition increases with decrease in wall temperature. The comparison among the values for two different wall temperatures suggested that the change in thermophoretic effect is the most dominant factor to give the change in soot deposition characteristics.

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