Interaction of thermocapillary and natural convection flows during solidification: normal and reduced gravity conditions

Surface tension and buoyancy are two important convection mechanisms in the growth of crystal and alloy from the melt. In the present work, the interaction of thermocapillary and natural convection along with the phase change process has been studied numerically under both normal and reduced gravity. Steady-state solutions of momentum, mass continuity, energy equations and a Darcy law type of mushy zone treatment have been solved for both the augmenting and counteracting convection modes. In general, as Marangoni number increases, the phase interface is of stronger curvature due to enhanced convection, and the temperature as well as velocity gradients along the free surface also increase. Under normal gravity and for counteracting cases, the multiple-cell convection pattern exists with a wide variation of Marangoni number and Prandtl number; for augmenting cases, convection field evolves with the change of Marangoni and Prandtl numbers, exhibiting thin-layer, multiple-cell, or single-cell patterns. Under microgravity, convection is dominated by the Marangoni effect. For the range of Marangoni numbers and aspect ratios examined, convection is always of a single-cell pattern while the thickness of mushy zone changes noticeably with the direction of Marangoni convection.