COMPARISON BETWEEN ORDER OF MAGNITUDE AND NUMERICAL ESTIMATES OF THE SOLUTE BOUNDARY-LAYER IN AN IDEALIZED HORIZONTAL BRIDGMAN CONFIGURATION

The scaling procedure proposed recently [Garandet et al., J. Crystal Growth 106 (1990) 437] to estimate the solute boundary layer size-delta in a typical horizontal Bridgman experiment is checked by means of two-dimensional numerical simulations. The results are very good both in the monophase and in the eutectic configurations, as our analysis predicts the exact scaling law, the prefactor error being a mere 25%. A balance between diffusion and convection at the edge of the boundary layer thus gives a fair estimate of delta, but an adequate velocity profile is required as an input in the procedure. A detailed discussion of the validity of our assumptions is also presented.