Papers by Keyword: Microgravity

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Authors: Bin Zhou, Ludo Froyen
Abstract: A special type of divorced eutectic growth mode (symbiotic growth) in a ternary Al-Mn-Si alloy, triggered by addition of titanium boride (TiB2) has been studied under both ground and microgravity conditions. During directional solidification, α (AlMnSi) particles nucleate ahead of the planar solidification front and are pushed and later engulfed by the interface forming a banded particle layer structure. The presence of fine titanium boride particles (clusters) in front of the growing α (AlMnSi) particles makes the interaction between the intermetallic α (AlMnSi) particles and solidification front much more complex than most proposed models for particle/interface interactions. Microgravity experiments can eliminate the gravity related effects and thus provide an opportunity to better understand the formation mechanism of symbiotic growth. In this study, hypoeutectic Al-1Mn-3Si alloys with addition of 0.33 wt% TiB2 were directionally solidified in ESA Solidification and Quenching Furnace (SQF) on board of the International Space Station (ISS). The ground experiment was conducted in a replica of this furnace prior to the microgravity experiments. Non-destructive X-ray tomography and its 3D reconstruction software was used to characterize the particles and their distribution. Comparison between ground and microgravity experiment results is presented. The particle pushing and engulfment of symbiotic growth is discussed based on a particle pushing and engulfment model.
Authors: Yu Qiang Cai, De Cai Li
Abstract: The vapor compression distillation assembly is a phase-change water recovery technology which will reclaim water from urine, whose evaporator is a rotating container involving boiling heat transfer. The production rate of the apparatus depend on the bubble detachment diameter. In the article, based on the force equilibrium of bubble, the bubble detachment diameter formula is obtained, in which, the flow velocity along axis is neglected because it is very slow. The formula is very significant to the design of the apparatus and other relative apparatus.
Authors: M. Meier, O. Hinrichs, H.J. Rath
Authors: Xue Han, Jun Qin, Jun Jun Tao, Ming Hui Feng
Abstract: Water mist technology has been developed and regarded as a promising substitute fire-extinguishing agent in spacecraft. In this paper, a numerical simulation method is introduced to investigate the effect of water mist size, velocity and flow rateon the fire suppressionefficiencyin microgravity. The fire extinguishing efficiency is better for the finer water mist in microgravity due to better heat transfer and more rapid vaporization. The evaporation cooling is the dominant mechanism of fire suppression in microgravity.As for the water mist velocity, the performance of fire suppression is affected slightly in microgravity. The results on the effect of water flow rate show that the flow rate should be higher than a critical value to suppress the fire effectively.
Authors: M. Arivanandhan, G. Rajesh, A. Tanaka, T. Ozawa, Yasunori Okano, Y. Inatomi, Yasuhiro Hayakawa
Abstract: As a preliminary experiment for the growth of InGaSb alloy crystals under microgravity at International Space Station (ISS), bulk crystal was grown under terrestrial condition using the same gradient heating furnace (GHF). Czochralski grown GaSb <111>B single crystal was used as a seed and feed crystals for the growth of InGaSb bulk crystals. During the growth, heat pulses were intentionally introduced periodically to create the growth striations. From the striations, the growth rate of the grown crystal was estimated. The results show that the growth rate was gradually increased from the beginning of the growth and became stable. On the other hand the In composition of the grown crystal decreased along the growth direction. From the In composition, the temperature gradient in the solution was estimated and it was almost the same of that fixed during the growth.
Authors: Georges Salloum-Abou-Jaoude, Henri Nguyen-Thi, Guillaume Reinhart, Ragnvald H. Mathiesen, Gerhard Zimmermann, Daniela Voss
Abstract: In the frame of ESA-MAP (Microgravity Application Promotion) project entitled XRMON (In situ X-Ray MONitoring of advanced metallurgical processes under microgravity and terrestrial conditions), a microgravity (μg) experiment in the XRMON-GF (Gradient Furnace) setup was successfully launched in 2012 on board MASER 12 sounding rocket. During this experiment, in situ and real time observations of the formation of the solidification microstructures in diffusive conditions were carried out for the first time by using X-ray radiography. In addition, two reference experiments with the same control parameters but in ground-based conditions were performed to enable us a direct comparison with the μg experiment and therefore to enlighten the effects of gravity upon microstructure formation. This communication reports on fragmentation phenomenon observed during those experiments. For 1g upward solidification, fragmentations mainly take place in the upper part of the mushy zone. After their detachments, dendrite fragments are carried away by buoyancy force in the bulk liquid where they are gradually remelted. For μg experiment and horizontal solidification, this type of fragmentation is not observed. However, a great number of fragmentations are surprisingly revealed by in situ observation in the deep part of the mushy zone, when the liquid fraction is very small. Moreover, as soon as they are detached, the dendrite fragments move toward the cold part of the mushy zone, even in the case of μg experiment. The observations suggest that sample shrinkage may be at the origin of this fragment motion.
Authors: Charles-André Gandin, Bernard Billia, Gerhard Zimmermann, David J. Browne, M.D. Dupouy, G. Guillemot, Henri Nguyen-Thi, Nathalie Mangelinck-Noël, Guillaume Reinhart, Laszlo Sturz, Shaun McFadden, Jerzy Banaszek, Yves Fautrelle, K. Zaïdat, A. Ciobanas
Abstract: The main objective of the research project of the European Space Agency (ESA) - Microgravity Application Promotion (MAP) programme entitled Columnar-to-Equiaxed Transition in SOLidification Processing (CETSOL) is the investigation of the formation of the transition from columnar to equiaxed macrostructure that takes place in casting. Indeed, grain structures observed in most casting processes of metallic alloys are the result of a competition between the growth of several arrays of dendrites that develop under constrained and unconstrained conditions, leading to the CET. A dramatic effect of buoyancy-driven flow on the transport of equiaxed crystals on earth is acknowledged. This leads to difficulties in conducting precise investigations of the origin of the formation of the equiaxed crystals and their interaction with the development of the columnar grain structure. Consequently, critical benchmark data to test fundamental theories of grain structure formation are required, that would benefit from microgravity investigations. Accordingly, the ESA-MAP CETSOL project has gathered together European groups with complementary skills to carry out experiments and to model the processes, in particular with a view to utilization of the reduced-gravity environment that will be afforded by the International Space Station (ISS) to get benchmark data. The ultimate objective of the research program is to significantly contribute to the improvement of integrated modelling of grain structure in industrially important castings. To reach this goal, the approach is devised to deepen the quantitative understanding of the basic physical principles that, from the microscopic to the macroscopic scales, govern microstructure formation in solidification processing under diffusive conditions and with fluid flow in the melt. Pertinent questions are attacked by well-defined model experiments on technical alloys and/or on model transparent systems, physical modelling at microstructure and mesoscopic scales (e.g. large columnar front or equiaxed crystals) and numerical simulation at all scales, up to the macroscopic scales of casting with integrated numerical models.
Authors: Gerhard Zimmermann, L. Sturz, B. Billia, N. Mangelinck-Noël, D.R. Liu, H. Nguyen Thi, N. Bergeon, C.A. Gandin, D.J. Browne, C. Beckermann, D. Tourret, A. Karma
Abstract: This paper gives an overview of the experiments on-board the International Space Station (ISS) performed so far by the CETSOL team. Al-7 wt% Si alloys with and without grain refiners were solidified in microgravity. Detailed grain structure analysis showed columnar growth in case of non-refined alloy, but the existence of a columnar to equiaxed transition (CET) in refined alloy. One main result is a sharp CET when increasing the solidification velocity and a progressive CET for lowering the temperature gradient. Applying a front tracking model this behavior was confirmed numerically for sharp CET. Using a CAFE model both segregation and grain structures were numerically modeled and show a fair agreement with the experimental findings.
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