Computer-assisted liquid crystal thermography in a rotating system: Application to Czochralski crystal growth

Liquid crystal thermography (LCT) is an emerging technique for non-invasive temperature and flow field visualization and measurement. The primary objective of this research is to develop high resolution LCT which can provide isotherms that are usually not visible in a photograph or video frames. This is achieved by quantifying video images using an image processing software that can operate in either the RGB (red, green, blue) field or the HSI (hue, saturation, intensity) field of color. The reconstruction of the visualized temperature field is then used for the calculation of axial and transverse temperature gradients, and temporal change of local temperature and heat flux.; Steady state and transient calibration experiments are performed in a cavity heated at the top (pure conduction). A digital imaging software is developed to extract quantitative temporal and spatial information on the temperature field from the video movie files. The technique allows the measurement of unsteady heat flux for the first time. Even though the error was ∼15.5%, the feasibility of the technique has been demonstrated in explaining certain factors contributing to instabilities in a rotational system. It has also been demonstrated that LCT can be used for the measurement of thermal conductivity and diffusivity in a fluid.; The computer-assisted LCT technique is then applied to analyze the temperature and flow field in a rotating system with particular application to Czochralski growth of single Silicon crystals for electronic devices. The presence of a hydraulic jump in natural convection flows has been captured for the first time. The internal waves that formed as a result, have also been observed. The technique has also allowed us to examine the effects of thermocapillary flow and resolve the Marangoni layer in a large aspect ratio (∼1.4) system. Viscous effects are seen to affect the strength of Marangoni convection.; The influence of Ekman suction in a rotational flow has been observed to strengthen with increase in rotational rate. Counter rotation of cylinder has been shown to produce a more stable temperature and flux field than co-rotation of cylinders. Important conclusions are made on complex features of Czochralski crystal growth and it is demonstrated that the LCT technique can be successfully used to study complex flow in different geometries.