LOCAL HEAT TRANSFER MEASUREMENTS USING LIQUID CRYSTALS

Heated coating and transient liquid crystal techniques and their applications are discussed. In the heated coating method a thin vacuum-deposited gold film on the surface is electrically heated and a liquid crystal coating is used to determine the position of an isotherm on the surface. Since the heat flux is uniform, the isotherm corresponds to a particular heat transfer coefficient. By adjusting the level of the heat flux, the position of the isotherm on the surface is changed, and the heat transfer coefficients can be mapped over the entire surface. In the transient technique, liquid crystal is deposited on the surface, and a sudden change of temperature is introduced. A video recorder is used to record the time and the locations of the isotherms as they move to different locations with time.