Other
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002iaf..confe.535b&link_type=abstract
IAF abstracts, 34th COSPAR Scientific Assembly, The Second World Space Congress, held 10-19 October, 2002 in Houston, TX, USA.,
Other
Scientific paper
natural convection suppression and reaching pure diffusion mass transfer in a liquid phase. However, the last results of theoretical studies show that diffusive character of mass transfer can be provided only at residual accelerations level of order of 10-7 - 10-8 go. Such quasi-static accelerations level cannot be provided on spacecrafts in the near future. At the same time, there are numerous convincing proofs of harmful influence of residual accelerations on composition homogeneity of the materials processed in space. This fact does not depend on the type of the spacecraft, since the similar results were obtained both on manned (Mir, Space Shuttle) and on automatic spacecrafts (Foton, EURECA). The transversal homogeneity of composition is influenced, in main, by two factors: curvature of the solidification front and variation of the thickness of the concentration boundary layer. It is possible to influence both these factors by controlling flow in the melt. Therefore, it is necessary to apply an active method of mass transfer control in the liquid phase to provide homogeneity of the properties of the material processed in space. example, application of magnetic fields or vibrations. In the presentation these methods are briefly discussed. Also the new method is offered, namely the control of the accelerations level at g> gmin, where gmin is the lowest-possible level of accelerations for the given spacecraft. One of possible ways of this method realization is the control of the level accelerations acting on the melt by rotation of the spacecraft around the axis with the furnace, specially located relative to the rotation axis. considered. A two-dimensional axisymmetrical theoretical model has been developed. The model allows to investigate numerically an influence of various parameters on growth process, including the influence of gravity level on homogeneity of the growing crystal composition. The model is based on commonly used Navier-Stokes equation set. Five components (Cd, Hg, Te, CdTe and HgTe) are considered in liquid phase. Thermodynamics of the solution is calculated by Brebrick model. A specific feature of our model is using non-equilibrium thermodynamic conditions at the interface. Otherwise, if the conditions of local thermodynamic equilibrium are used at the solid/liquid interface, the problem is mathematically over-determined. To verify the model a number of experiments have been conducted which confirmed reliability of the theoretical results. the high gravity (up to 10 g) were considered. The level of gravity influences the flow intensity in the liquid phase. The basic effect of the gravity level increase consists of changing the radial velocity along the crystallization interface. It leads to modification of the solution zone shape and the form of the growing interface. The homogeneity of the crystal composition depending on the level of axial overload is studied.
Barmin I. V.
Senchenkov Alexander S.
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