A Method of Measuring Thermal Diffusivity by Heating of Step Function Change

Abstract

A transient method for quickly measuring the thermal diffusivity of a small solid disk (15mm diameter, 210 mm thickness) has been developed. The disk is placed in vacuum, and heated from the front by thermal radiation whose intensity is varied in a step function. The resulting change in temperature on the rear face is measured by thermocouple and recorded by osillograph, based on which data the thermal diffusivity is calculated. Since each measurement requires only a few seconds, the present method is for less stringent regarding stability of ambient tempenature as compared to steady methods, while saving time without sacrificing accuracy. The measured values in temperatures ranging 25°700°C on lead, copper and nickel of high purity were within ±5% of values from previously reported measurements. Values for thermal diffusivity of UO2-pellets were also determined in temperatures ranging 25°800°C. The error was not more than ±5%. The method has been tested experimentally in the temperature range between 25° and 800°C, but analysis suggests that more accurate measurements of thermal diffusivity can be made by this technique at higher temperatures.