[S0022-1481(00)04003-2]
Solidification of water from a crystal seed in a simulated Czochralski growth system is investigated for various rotation rates of the crystal and crucible. Under the influence of a differentially heating condition imposed by the crystal seed and the surrounding melt, a complex flow and thermal field is visualized. Three convection-driving currents, temperature gradient, surface tension gradient, and centrifugal forces due to rotation, along with the density inversion of water are responsible for the resulting flow and thermal field.
Liquid Crystal Thermography is employed to capture the images of the temperature field and the transport phenomena in the melt. The liquid crystals have a bandwidth of 10°C; starting with red at ∼1.2°C, green at ∼2.1°C, blue at ∼3.6°C and clearing at 10°C. These crystals are employed in 0.005 percent by volume to visualize the solidification process.
Experiments are conducted for a range of Grashof numbers of 400,000. Interesting temperature fields are seen in the shape of simple Benard roll type structures to a formation of complex oscillatory finger like patterns with many different size vertices. A quantitative estimate of the temperature field is obtained via a suitable calibration of the liquid crystals in a pure conduction state.
The first set of images captures the temperature field present with no rotation present in the melt. The next set of images is under crucible rotation rates of 1.87 and 4.09 rpm. Crystal rotation effects at 3.60 and 9.70 rpm can be seen in the next set of images. In the last set of images, counter-rotation effects of the crystal and crucible can be seen for (1.70, 3.40) and (3.40, 1.70) rpm.
