Thermal Diffusivity Measurement by Ring Shape Heating and the Effect of Heat Spread on Flash Method

Abstract

Thermal diffusivity of the sample is measured by the flash method under 1-dimensional thermal conduction. But in the case of measurement of the thin sample by ring laser irradiation or in the case of measurement of the sample larger than the laser diameter, 2-dimensional heat flux is generated, and 1-dimensional thermal conduction approximation is not appropriate. In this paper, thermal diffusivity analysis was carried out in consideration of heat radiation. Accordingly, cylindrical coordinate thermal conduction equation is analyzed in Laplace space and the method for thermal diffusivity analysis of the sample is investigated under 2-dimensional heat flux condition. It is necessary to analyze the thermal diffusivity and Biot number as with normal 1-dimensional analysis. 2 methods were investigated. One is the Direct method which treats these variables independent and the other is the Cooling time constant method which analyses under the condition that the theoretical cooling time constant and the measured cooling time constant are equal. It was confirmed that both methods were able to analyze the thermal diffusivity.