Appropriate Laplace Variables for Thermal Diffusivity Analysis using Laplace Space Analysis in the Flash Method

Abstract

For the thermal diffusivity analysis in Laplace space, it is necessary to set the Laplace variable. When using the theoretical formula obtained under the same conditions as the measurement data, there are no restrictions for Laplace variables setting, but if they are different, the Laplace variables are restricted. In this paper, the finiteness and the time origin deviation of the measurement data are taken up as different conditions from the theoretical formula and the appropriate region of the Laplace variable was confirmed. The appropriate region of the Laplace variable was confirmed by the product of the Laplace variable p and the measurement time t_m (p×t_m). The finiteness of the measurement data determines the lower limit of the Laplace variable appropriate region, and the time origin deviation determines the upper limit of the Laplace variable appropriate region. It is necessary to set the Laplace variable in the range between the upper and lower limits. It was found that the longer the measurement time, the wider the region of the appropriate Laplace variable, and the larger the deviation of the time origin, the narrower the appropriate Laplace variable region. It was also found that the proper region of the Laplace variable for thermal diffusivity is wider than for the Biot number.