What is it about?
It is demonstrated with measurements using a lock-in infrared thermography technique that a substitution of the circular spot heating source that prescribes the heat flux, by one with a linear shape that prescribes temperature gradient, gives the correct values of the planar thermal diffusivity along any spatial direction on the surface of an anisotropic sample.
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Why is it important?
Heat conduction in anisotropic samples has been extensively analyzed in classical textbooks on heat conduction. However, it is a delicate subject, which leads to some misconceptions. For example, several photothermal methods with optical excitation exist for measurements of the in-plane thermal diffusivity but much care must be taken to directly determine the correct components of the thermal diffusivity tensor in directions other than the principal ones. Some configurations, such as popular laser spot-heating, provide the inverse of the resistivity to diffusion, which does not coincide with diffusivity outside principal directions. It is shown that laser-line excitation provides the values of diffusivity in any direction straightforwardly.
Perspectives
This work is a product of a scientific collaboration between researchers of the photothermal techniques laboratories from the Applied Physics Department at the Engineering School of the Basque Country University, Spain, and from the Centre of Applied Science and Advanced Technology at the National Polytechnic Institute, Mexico. It is a very exciting work in the field of thermal characterization of materials by optical methods because it can contribute to clarifying some misconceptions that often appear when trying anisotropic samples. On the other hand, the scientific community would certainly be interested in the proposed non-destructive laser-line active thermography technique that can extract the information reliably and relatively fast. The methodology can be further developed to optimize direct thermal diffusivity measurements of anisotropic materials in any direction.
Dr Ernesto Marin
Instituto Politecnico Nacional
Read the Original
This page is a summary of: Measuring the in-plane thermal diffusivity of anisotropic solids by lock-in infrared thermography: Laser-spot vs laser-line heating, Journal of Applied Physics, April 2024, American Institute of Physics,
DOI: 10.1063/5.0198882.
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