Abstract

The results of control possibility investigations for crucibleless AHP crystal grows method are considered. Numerical studies have been carried out basing on a specially designed global heat exchange model.The control methods based on radiation flux variation and circular gap in the lateral thermal insulation against the melt surface have been found to change substantially the temperature fields and thermal fluxes at crystallization front due to the variations of radiation fluxes to the environment/ The effect of the diaphragm height location and of diaphragm and surrounding constructions thermal-physical properties on the crystallization front shape have been considered.

Abstract

The influence of radiation exchange in a crystal-melt system for different (from the point of view of optical properties) material classes and crystal growing methods (at constant crystal-melt system thickness and at a constant melt thickness) is considered. The general approach is based on using of modified numerical one-dimensional crystallization model at radiation-conductive heat exchange. The radiation heat transfer in a crystal-melt system provides conditions for faster front movement. In this case, most favorable conditions with large temperature gradients are created in system with transparent crystal and opaque melt. At simultaneous crystal and melt “transparency” the temperature gradients in melt may decrease and cause stability loss of the directed crystallization.

Abstract

Combined experimental and numerical tools are used to analyze the effect of convective and radiative heat transport, faceting phenomena, and the optical thickness of the Bi4Ge3O12 (BGO) crystal on the measurement and calculation of melt/crystal interface kinetics during the axial heat flux close to the phase interface growth of BGO single crystals. Results show that, in the general case, accurate determination of growth kinetic relations requires the application of models which account for all of the above phenomena (radiative and convective heat transport, faceting phenomena, etc.). Failure to take these into account may result not only in quantitative errors, but also even in qualitatively wrong determination of interfacial kinetic mechanisms.

Abstract

A comprehensive efficiency analysis of the energy consumption is carried out for two types of aluminum electrolyzers using graphitized bottom blocks available from the Ukrainian Graphite JSC. The use of bottom blocks high in graphite (50 and 70%) leads to economic consumption of electric power, increased output, and extended service life of the electrolyzers.

S. V. Bykova, V. D. Golyshev, M. A. Gonik, V. B. Tsvetovsky, V. I. Deshko, A. Ya. Karvatskii, A. V. Lenkin

J. of Heat Transfer Engineering. — 2006. — Vol. 27, Number 2/March. — P. 43—57.

Abstract

Combined experimental and numerical tools are developed and used to define more exactly the growth kinetic relations for (211) crystallographic orientation of Bi4Ge3O12 (BGO) crystal growth—namely, the dependence of crystal growth rate V on supercooling, ∆T of the melt/crystal interface. A new apparatus for in situ measurements of the time dependence of the supercooling, ∆T(t), was used, and a new, two-dimensional numerical model was applied to analyze the effect of temperature boundary conditions and faceting phenomena on the character of the observed V(∆T) dependence. The measurements of the ∆T(t) dependence show that there is a large enough undercooling and a novel effect of the appearance of the local maximum on ∆T(t) dependence at the finish of crystallization. Results on V(∆T) dependence show that, for the variant of the crystal growth technique used (melt cooling during axial heating process method [AHP]), the type of the V(∆T) dependence does not depend on boundary conditions. The new investigations illustrate the superlinear behavior for V(∆T) dependence for (211) BGO crystallographic orientation and show that previous data on sublinear behavior of V(∆T) dependence for this crystallographic orientation of BGO have not been justified.

A.V.Kolesnikov, V.I.Deshko, Yu.V.Lokhmanets, A.Ya.Karvatskii, I.K.Kirichenko

E.N. Panov, A. Ya. Karvatskii, S. V. Leleka

Abstract

Increase of energy cost is highly significant for energy-intensive industrial branches, in particular, for competitiveness of aluminium producers. Therefore, the development and construction of electrolysis cells with decreased specific power consumption and increased lifetime of cathode assembly are of vital importance. Nowadays numerous projects are under intensive development devoted to the electrolysis cells of this type with consideration of preliminary MHD estimations, power and mechanical properties supported with subsequent engineering projects. However, rather frequently the anticipated results do not match actual consequences. One of the major reasons is a set of uncertainties at every stage of development. This is relevant both for methods of modeling of electrolysis cell state, and for influence of changes in technological schedule and properties of involved raw materials on technological process, and for changes of properties of raw materials depending on supplier and manufacturing process, external factors and so on. This report discusses only some of the challenges we met at solution of actual problems, however, we believe, that the discussed scope of the challenges prevents the achievement of reliable approaches and requires for conductance of supplemental investigations. It should be noted, that the development of «successful» design of electrolysis cell results in significantly higher cost savings than the investments into the conductance of such supplemental investigations.