Photoacoustic measurement of the thermal properties of two-layer systems

Abstract

Using two different photoacoustic techniques for a two-layer system of variable thickness, we show that the thermal diffusivity and the thermal conductivity are completely determined, based upon the efFective-sample model widely used in heat-transfer problems. A procedure to establish a standard photothermal technique for measuring both the thermal diffusivity and the thermal conductivity is also discussed.

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

“…when both layers are thermally thick or, as a particular case, when their thermal effusivities are equal regardless of their thermal thicknesses [21,22]. For the case of our RCBs, α 1 corresponds to the thermal diffusivity of the pure resin layer with thickness l 1 , α 2 to the composite layer with thickness l 2 , and x = l 2 /l with l = l 1 + l 2 as defined before.…”

“…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]. On the other hand, the TRM has been complimentarily used for the measurement of the heat capacity of small samples [24,25,26].…”

Thermal diffusion of a two-layer system

“…(2) holds, we have only LW phonons and they interact efficiently with electrons and in this case all the quasiparticles system have the same temperature T e = T p = T and the equation for heat flux is similar to Eq. (8).…”

“…They showed that, a high modulation frequencies, the rear-illumination phase angle depends upon a critical frequency above which one of the materials becomes thermally thick. From the analogy between thermal and electrical resistances widely used in heat-transfer problems, 7 Mansanares et al 8 calculated the effective thermal diffusivity of the two layer system as a function of the filling fraction of the composite sample and the ratio of the thermal conductivities of each material. Recently Christofides and Seas 9 made an extension of the theoretical model on photopyroelectric spectroscopy of solids 10 to investigate the optical and thermal properties of a two-layer sample.…”

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

“…Such procedure is considered to be correct since the temperature is measured in the absolute Kelvin scale. Therefore, the "electrical and thermal analogy" [5], [6], generally used for the calculation of the effective thermal parameters, can be inadequate since it is based on the calculations of the temperature difference.…”