Flash method of measuring the thermal diffusivity. A review
Libor Vozár, Wolfgang Hohenauer
It is more than forty years since Parker et al (1961 J. Appl. Phys. 32 1679 – 1684), working for the US Navy Radiological Defense Laboratory, released their original paper introducing the flash technique. Since then this photothermal experimental method has been extended worldwide and it has become the most popular method for the measurement of the thermal diffusivity of solids. The simplicity and the efficiency of the measurement, the accuracy and the reliability of results,tlsb> and possibilities of application under a wide range of experimental conditions and materials are the main advantages of the flash method. The fact that the flash method has received standard status in many countries acknowledges its universality.
We present an up-to-date summary of the theory and application of the flash method. We discuss the ideal adiabatic model and non-ideal models that account for the influence of the main disturbing phenomena — heat losses from the sample, finite heat pulse durations, and nonuniform heating effects. The paper focuses on the survey of data-reduction methods — algorithms for calculation of thermal diffusivity from the experimental data. It provides also references to several original papers with descriptions of the experimental apparatus. Attention is given to applications of the flash method for the measurement of advanced materials — semitransparent media, materials with significant dependence of their thermophysical properties on temperature, anisotropic materials, layered structures, thin films, and composites. The paper contains a short note about various experimental methods having their origin in the flash method.