“Resonance” phenomena in thermal diffusion processes in two-layer structures

Abstract

The dependence on chopper frequency of the effective thermal diffusivity and effective thermal conductivity in photoacoustic experiments is discussed. The theoretical model of a two-layer structure at rear-surface illumination in the high frequency limit is considered. It is shown that the effective thermal diffusivity presents "resonance" while the effective thermal conductivity sharply changes its magnitude and sign. Such "resonant" behavior strongly depends on the surface thermal conductivities associated with the interface thermal contacts.

Thermal properties of composite two-layer systems with a fractal inclusion structure

“…Regarding experimental approaches, the photoacoustic (PA) technique in combination with the thermal relaxation method (TRM) have proven to be reliable and useful non-destructive techniques to measure thermal properties of different kinds of materials [7,13,14,15]. About the first, there has been an ongoing effort to extend the photoacoustic technique for the characterization of multilayered systems, with the purpose to determine their effective thermal diffusivity from the knowledge of the thermal properties of the layers themselves [16,17,18,19,20]. In particular, for two-layer systems, there are some aspects to be taken into account such as the thermal thickness of the layers and their effusivity, that becomes important at the interface in relation to its thermal resistance [21,22,23].…”

“…About the first, there has been an ongoing effort to extend the photoacoustic technique for the characterization of multilayered systems, with the purpose to determine their effective thermal diffusivity from the knowledge of the thermal properties of the layers themselves [16,17,18,19,20]. In particular, for two-layer systems, there are some aspects to be taken into account such as the thermal thickness of the layers and their effusivity, that becomes important at the interface in relation to its thermal resistance [21,22,23].…”

Desarrollo y caracterización de estructuras termoeléctricas con pellets constituidos por nuevos materiales y geometrías no estándar

“…En los modelos 2 y 3, la determinación de la máxima eficiencia fue calculada para una R L óptima; calculada según R L = ) T Z (1 HC + R [5]. Sin embargo la Z se calcula de diferente manera: En el M2, Z se calcula a partir de las propiedades de la integral promedio, y en el M3 a partir de T HC , obteniendo T HC = (T H + T C ) / 2.…”

“…Un análisis cuidadoso del modelo que explica los efectos electrotérmicos y sus interpretaciones físicas nos indica la existencia de un efecto "Barrierless Electrothermal Effect" [5]. Éste aparece cuando la conductividad térmica superficial η es finita.…”