Large-scale transfer of molten metal components in thin capillaries

The results of direct numerical simulation of the concentration-induced convection have been presented in this paper. A binary melt of the liquid metals filling a vertical thin capillary with a non-uniform temperature distribution on the boundaries has been considered. It is assumed that the absolute nonwetting condition takes place on the sidewalls of a channel. This effect gives rise to a free surface on the vertical boundaries where the thermocapillary force occurs due to the external longitudinal temperature gradient, which provides the motion of the liquid elements at a long distance compared with an axial size of the capillary. The adsorption-desorption processes occurring along the surface, thermocapillary force, convective motion in a volume, and diffusion are all characterized by essentially different characteristic time. These mechanisms generate both the large-scale process of circulation with a motion of admixture on the surface at the hot top of the capillary with the following transfer down along the boundary due to the thermocapillary force, and the final return into the volume as a consequence of desorption at the bottom of the capillary. The numerical calculations have been performed using the PGU-Tesla supercomputer of the Research Academic Center "Parallel and Distributed Calculations" at Perm State National Research University. The finite difference method has been applied. The numerical code has been written with the use of Fortran-90 programming language. The calculation results show that the lifting speed of the motion back into the volume is less than that on the surface. Therefore, the admixture at the stage of saturation can be accumulated near the bottom of the capillary. The steady-state flow is stationary and it is determined as in the volume as on the surface predominantly by the Marangoni number. Intensity of the motion and adsorption-desorption processes on the free boundary effect essentially on the formation of both the surface and volume concentration fields and the speed of redistribution of components in the volume. Thus, one of the possible mechanisms of longitudinal division of the liquid binary mixtures into components in thin channels has been demonstrated. This modeling can explain the results of some experiments on division of heterogeneous binary metal melts.

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