Effect of the buoyancy parameter on czochralski bulk flow in garnet growth

Abstract

Czochralski bulk flow was simulated with the physical constants of gadolinium gallium garnet (GGG) growth, except for the buoyancy parameter which was assigned eight different values ranging from zero, through the GGG value, to a maximum 25% higher. At low buoyancy the convective eddy is encapsulated between the crucible surfaces and the tip vortex of the rotating crystal. At large buoyancy it penetrates to the free surface; it then dominates the meridional flow, but there are three weak vortices of opposite rotation. At these higher buoyancies, the strength of the convective eddy is approximately proportional to the square root of the buoyancy parameter. Once a certain threshold is passed, the location at which the dividing streamline between the convective and centrifugal eddies intercepts the top surface is not very sensitive to the buoyancy parameter. Below that threshold, however, the sensitivity is quite accentuated, and encapsulation of the convective eddy becomes imminent. © 1979.