Determining the thermal properties of materials with complex structures is still a major engineering challenge today. The well-known heat pulse experiment can be used to determine the thermal diffusivity by measuring the temperature history as a thermal response for a fast excitation. However, the evaluation of the measurements can be challenging, especially when dealing with non-homogeneous samples. The thermal behavior of such heterogeneous materials may exhibit a response including two-time scales. Therefore, the Fourier equation is not necessarily applicable. The simplest possible alternatives are the 2-temperature models the Guyer–Krumhansl and Jeffreys heat equations. In the present paper, we focus on the interpretation of the Jeffreys heat equation; studying its analytical solution, we present a fitting method for determining the unknown parameters. We also discuss its relation with the other two heat equations, and we offer an interpretation of how to characterize the transient response of heterogeneous materials.

中文翻译：

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关于热脉冲实验中观察到的动态热导率和扩散率

确定具有复杂结构的材料的热性能仍然是当今的一项重大工程挑战。众所周知的热脉冲实验可用于通过测量作为快速激发的热响应的温度历史来确定热扩散率。然而，测量的评估可能具有挑战性，特别是在处理非均质样品时。这种异质材料的热行为可以表现出包括两倍尺度的响应。因此，傅立叶方程不一定适用。最简单的替代方案是 2 温度模型 Guyer–Krumhansl 和 Jeffreys 热方程。在本文中，我们重点关注杰弗里斯热方程的解释；通过研究其解析解，我们提出了一种确定未知参数的拟合方法。我们还讨论了它与其他两个热方程的关系，并提供了如何表征异质材料瞬态响应的解释。