Estimation of molecular and thermodiffusion coefficients for non-ideal molten metal alloys and its implication in solidification process

In this paper an expression is proposed for the estimation of thermodiffusion factor in liquid metal alloys. The expression can be readily used given that it requires properties that could be easily obtained from the physical properties of the mixture constituents, such as viscosity and molar volume. The predictive power of the proposed expression, as well as other pertinent models is examined against the experimental data. The estimated thermodiffusion factor is then used to study thermo-solutal convection in an enclosure filled with molten Sn-Bi alloy by solving the transport equations numerically. Two simulations were carried out in a vertical rectangular cell encapsulated by a quartz container: top heating and bottom heating. The sidewalls in both cases were exposed to the external natural convection and surface radiation to the ambient. Numerical results show that in the top heating case, the distribution of temperature and concentration are linear, but species segregation occurs due to the thermodiffusion effect. In the bottom heating case, boundary-driven convective flow develops with a large Rayleigh number (Ra) where an increase in the Ra number negates the thermodiffusion effect due to the development of strong mixing.