Measurement of Dynamically Changing Thermal Diffusivity by the Forced Rayleigh Scattering Method (Measurement of Gelation Process)

A measuring method of the thermal diffusivity with high temporal and spatial resolutions has been studied. The forced Rayleigh scattering method is an optical technique to measure the thermal diffusivity of solids and liquids. Based on its characteristics, this method has the applicability to become a ‘‘thermal diffusivity real-time monitoring system.’’ The maximum repetition rate of thermal diffusivity measurement is determined by the attenuation of an excited temperature distribution by laser heating, and a mathematical model of threedimensional heat conduction is constructed. The temporal resolution of continuous measurements was improved to about 1 s, and the sol-gel transition of a gellan gum aqueous solution was studied to check the validity of the dynamic measurement of thermal diffusivity. Through the gelation process, the dynamical change of the thermal diffusivity was measured, and the gelation point of the solution was identified from a series of thermal diffusivity data. The results indicate the capability of the forced Rayleigh scattering method to be a real-time thermal diffusivity measurement technique for monitoring the rapidly changing process of a material.