The question of thermal waves in heterogeneous and biological materials

In the 1990s, there were two experimental studies that sparked a renewed interest in thermal wave behavior at the macroscale level. Both reported thermal relaxation times of 10 s or higher. However, no further experimental evidence of this behavior has been reported. Due to the extreme significance of these findings, the objectives of this study were to try to reproduce these earlier studies and offer an explanation for the outcome. These two previous studies, one using heterogeneous materials and one using bologna, were repeated following the experimental protocol provided in the studies as closely and as practically as possible. In both cases, the temperature response to a specified boundary condition was recorded. The results from the first set of experiments suggested that the thermal relaxation times presented in the previous study were actually the thermal lag expected from applying Fourier's law, taking into account the uncertainty of the temperature sensor. In the second set of experiments, unlike the distinct jumps in temperature found previously, no indication of wave behavior was found. Here, the explanation for the previous results was more difficult to ascertain. Possible explanations include problems with either the experimental protocol or the temperature sensors used.