ABSTRACT

Buoyancy driven chimney convection in low Prandtl number melts within a mushy layer during alloy solidification is reviewed under external constraint of rotation, where the rotation axis is inclined at an angle γ to the direction of the solidification velocity. The chimneys within the mushy layer produce undesirable freckles in the final form of the crystal, which are imperfections that reduce the quality of the crystal.  Methods of control aiming at eliminating or reducing significantly the convective flows in the chimneys also serve to eliminate or reduce significantly the existence and presence of the chimneys in the mushy layer which can result in producing higher quality crystals.  Asymptotic and scaling examinations of the governing system for the nonaxisymmetric chimney convection have resulted in discoveries of ranges in γ, Prandtl number, Coriolis parameter and centrifugal parameter where chimney convection can be reduced significantly, or otherwise. These results also confirm experimental observation in low Prandtl number melt that Coriolis effect can have stabilizing or destabilizing influence depending on the rotation sense of the solidification system.